Soldering Process

Soldering filler materials are available in many different alloys for differing applications. In electronics assembly, the eutectic alloy of 63% tin and 37% lead (or 60/40, which is almost identical in performance to the eutectic) has been the alloy of choice. Other alloys are used for plumbing, mechanical assembly, and other applications. Some examples of soft-solder types and their applications include tin-lead for general purposes, tin-zinc for joining aluminium, lead-silver for strength at higher than room temperature, cadmium-silver for strength at high temperatures, zinc-aluminium for aluminium and corrosion resistance, and tin-silver and tin-bismuth for electronics.
A eutectic formulation has several advantages for soldering; chief among these is the coincidence of the liquidus and solidus temperatures, i.e. the absence of a plastic phase. This allows for quicker wetting as the solder heats up, and quicker setup as the solder cools. A non-eutectic formulation must remain still as the temperature drops through the liquidus and solidus temperatures. Any differential movement during the plastic phase may result in cracks, giving an unreliable joint. Additionally, a eutectic formulation has the lowest possible melting point, which minimizes heat stress on electronic components during soldering.
Common solder alloys are mixtures of tin and lead, respectively:

• 63/37: melts at 183 °C (361 °F) (eutectic: the only mixture that melts at a point, instead of over a range)
• 60/40: melts between 183–190 °C (361–374 °F)
• 50/50: melts between 185–215 °C (365–419 °F)

For environmental reasons (and the introduction of regulations such as the European RoHS (Restriction of Hazardous Substances Directive)) lead-free solders are becoming more widely used. They are also suggested anywhere young children may come into contact with (since young children are likely to place things into their mouths), or for outdoor use where rain and other precipitation may wash the lead into the groundwater. Unfortunately, most lead-free solders are not eutectic formulations, melting at around 250 °C (482 °F), making it more difficult to create reliable joints with them.
Other common solders include low-temperature formulations (often containing bismuth), which are often used to join previously-soldered assemblies without un-soldering earlier connections, and high-temperature formulations (usually containing silver) which are used for high-temperature operation or for first assembly of items which must not become unsoldered during subsequent operations. Alloying silver with other metals changes the melting point, adhesion and wetting characteristics, and tensile strength. Of all the brazing alloys, brazing has the greatest strength, with silver solders not being substantially stronger than soft solder and having the broadest applications. Specialty alloys are available with properties such as higher strength, better electrical conductivity and higher corrosion resistance.

Flux

Main article: flux (metallurgy)

The purpose of flux is to facilitate the soldering process. The obstacle to a successful solder joint is an impurity at the site of the union, e.g. dirt, oils or oxidation. The impurities can be removed by mechanical cleaning or by chemical means, but the elevated temperatures required to melt the filler metal (the solder) encourages the work piece (and the solder) to re-oxidize. This effect is accelerated as the soldering temperatures increase and can completely prevent the solder from joining to the workpiece. One of the earliest forms of flux was charcoal, which acts as a reducing agent and helps prevent oxidation during the soldering process. Some fluxes go beyond the simple prevention of oxidation and also provide some form of chemical cleaning (corrosion).
For many years, the most common type of flux used in electronics (soft soldering) was rosin-based, using the rosin from selected pine trees. It was ideal in that it was non-corrosive and non-conductive at normal temperatures but became mildly reactive (corrosive) at the elevated soldering temperatures. Plumbing and automotive applications, among others, typically use an acid-based (muriatic acid) flux which provides cleaning of the joint. These fluxes cannot be used in electronics because they are conductive and because they will eventually dissolve the small diameter wires. Many fluxes also act as a wetting agent in the soldering process, reducing the surface tension of the molten solder and causing it to flow and wet the workpieces more easily.
Fluxes for soft solder are currently available in three basic formulations:

1. Water-soluble fluxes (no VOCs required for removal) are higher activity fluxes designed to be removed with water after soldering.
2. No-clean fluxes which are mild enough to not "require" removal due to the non-conductive and non-corrosive residue. Performance of the flux needs to be carefully evaluated; a very mild 'no-clean' flux might be perfectly acceptable for production equipment, but not give adequate performance for a poorly controlled hand-soldering operation. They are so-called "no-clean" because the residue left after the solder operation is non-conductive and won't cause electrical shorts; nevertheless these fluxes leave a white-color residue like dilute bird-droppings. which is plainly visible. Since the presence of foreign matter, detritus, even lint, on circuit boards is a defect for all three classes of electronic circuit boards (ranging from cheap consumer electronics to high-reliability, mission critical applications), these sorts of fluxes must still be cleaned as with all hand solder work, typically brushing with 99% isopropyl alcohol as the solvent and lint-free non-synthetic (eg cotton) wipes.
3. Traditional rosin fluxes are available in non-activated (R), mildly activated (RMA) and activated (RA) formulations. RA and RMA fluxes contain rosin combined with an activating agent, typically an acid, which increases the wettability of metals to which it is applied by removing existing oxides. The residue resulting from the use of RA flux is corrosive and must be cleaned off the piece being soldered. RMA flux is formulated to result in a residue which is not significantly corrosive, with cleaning being preferred but optional.

Processes

There are three forms of soldering, each requiring progressively higher temperatures and producing an increasingly stronger joint strength:

1. Soft soldering, which originally used a tin-lead alloy as the filler metal,
2. silver soldering, which uses an alloy containing silver,
3. brazing which uses a brass alloy for the filler.

The alloy of the filler metal for each type of soldering can be adjusted to modify the melting temperature of the filler. Soldering differs from gluing significantly in that the filler metals alloy with the workpiece at the junction to form a gas- and liquid-tight bond.
Soft soldering is characterized by having a melting point of the filler metal below approximately 400 °C (752 °F), whereas silver soldering and brazing use higher temperatures, typically requiring a flame or carbon arc torch to achieve the melting of the filler. Soft solder filler metals are typically alloys (often containing lead) that have liquidus temperatures below 350°C.
In this soldering process, heat is applied to the parts to be joined, causing the solder to melt and to bond to the workpieces in an alloying process called wetting. In stranded wire, the solder is drawn up into the wire by capillary action in a process called 'wicking'. Capillary action also takes place when the workpieces are very close together or touching. The joint strength is dependent on the filler metal used. Soldering produces electrically-conductive, water- and gas-tight joints.
Each type of solder offers advantages and disadvantages. Soft solder is so called because of the the soft lead that is its primary ingredient.Soft soldering uses the lowest temperatures but does not make a strong join and is unsuitable for mechanical load-bearing applications. It is also unsuitable for high-temperature applications as it softens and melts. Silver soldering, as used by jewelers, machinists and in some plumbing applications, requires the use of a torch or other high-temperature source, and is much stronger than soft soldering. Brazing provides the strongest joint but also requires the hottest temperatures to melt the filler metal, requiring a torch or other high temperature source and darkened goggles to protect the eyes from the bright light produced by the white-hot work. It is often used to repair cast-iron objects, wrought-iron furniture, etc.
Soldering operations can be performed with hand tools, one joint at a time, or en masse on a production line. Hand soldering is typically performed with a soldering iron, soldering gun, or a torch, or occasionally a hot-air pencil. Sheetmetal work was traditionally done with "soldering coppers" directly heated by a flame, with sufficient stored heat in the mass of the soldering copper to complete a joint; torches or electrically-heated soldering irons are more convenient. All soldered joints require the same elements of cleaning of the metal parts to be joined, fitting up the joint, heating the parts, applying flux, applying the filler, removing heat and holding the assembly still until the filler metal has completely solidified. Depending on the nature of flux material used, cleaning of the joints may be required after they have cooled.
Each alloy has characteristics that work best for certain applications, notably strength and conductivity, and each type of solder and alloy has different melting temperatures. The term silver solder likewise denotes the type of solder that is used. Some soft solders are "silver bearing" alloys used to solder silver-plated items. Lead based solders should not be used on precious metals because the lead dissolves the metal and disfigures it.

Soldering and brazing

The distinction between soldering and brazing is based on the melting temperature of the filler alloy. A temperature of 450 °C is usually used as a practical delineating point between soldering and brazing . Soft soldering can be done with a heated iron whereas the other methods require a higher temperature torch or furnace to melt the filler metal.
Different equipment is usually required since a soldering iron cannot achieve high enough temperatures for hard soldering or brazing. Brazing filler metal is stronger than silver solder, which is stronger than lead-based soft solder. Brazing solders are formulated primarily for strength, silver solder is used by jewelers to protect the precious metal and by machinists and refrigeration technicians for its strength but lower melting temperature than brazing, and the primary benefit of soft solder is the low temperature used (to prevent heat damage to electronic components and insulation).
Since the joint is produced using a metal with a lower melting temperature than the workpiece, the joint will weaken as the ambient temperature approaches the melting point of the filler metal. For that reason, the higher temperature processes produce joints which are effective at higher temperatures. Brazed connections can be as strong or nearly as strong as the parts they connect, even at elevated temperatures.

Silver soldering

"Hard soldering" or "silver soldering" is used to join precious and semi-precious metals such as gold, silver, brass, and copper. The solder is usually referred to as esay, medium, or hard. This refers to its melting temperature, not the strength of the joint. Extra-easy solder contains 56% silver and has a melting point of 1,145 °F (618 °C). Extra-hard solder has 80% silver and melts at 1,370 °F (740 °C). If multiple joints are needed, then the jeweler will start with hard or extra-hard solder and switch to lower temperature solders for later joints.
Silver solder is absorbed by the surrounding metal, resulting in a joint that is actually stronger than the metal being joined. The metal being joined must be perfectly flush, as silver solder cannot normally be used as a filler and any gaps will remain.
Another difference between brazing and soldering is how the solder is applied. In brazing, one generally uses rods that are touched to the joint while being heated. With silver soldering, small pieces of solder wire are placed onto the metal prior to heating. A flux, often made of borax and water, is used to keep the metal and solder clean and to prevent the solder from moving before it melts.
When silver solder melts, it tends to flow towards the area of greatest heat. Jewelers can somewhat control the direction the solder moves by leading it with a torch; it will even run straight up along a seam.

Induction soldering

Induction soldering uses induction heating by high-frequency AC current in a surrounding copper coil. This induces currents in the part being soldered, heat then being generated by resistive heating. The copper rings can be made to fit the part needed to be soldered for precision in the work piece. Induction soldering is a process in which a filler metal (solder) is placed between the facing surfaces of (to be joined) metals. The filler metal in this process is melted at a fairly low temperature. Fluxes are commonly used in induction soldering. This is a process which is particularly suitable for soldering continuously. The process is usually done with coils that wrap around a cylinder/pipe that needs to be soldered.
Some metals are easier to solder than others. Copper, silver, and gold are easy. Iron, mild steel and nickel are found to be more difficult. Because of their thin, strong oxide films, stainless steel and aluminium are even more difficult. Titanium, magnesium, cast irons, some high-carbon steels, ceramics, and graphite can be soldered but it involves a process similar to joining carbides. They are first plated with a suitable metallic element that induces interfacial bonding.

Electronic components (PCBs)

A tube of multicore electronics solder used for manual soldering

An improperly soldered 'cold' joint

Broken solder joints on a circuit board

Currently, mass-production printed circuit boards (PCBs) are mostly wave soldered or reflow soldered, though hand soldering of production electronics is also still standard practice for many tasks. In wave soldering, parts are temporarily adhered to the PCB with small dabs of adhesive, then the assembly is passed over flowing solder in a bulk container. Reflow soldering is a process in which a solder paste (a mixture of prealloyed solder powder and a flux-vehicle that has a peanut butter-like consistency^[4]) is used to stick the components to their attachment pads, after which the assembly is heated by an infrared lamp; a hot air pencil; or, more commonly, by passing it through a carefully controlled oven. Since different components can be best assembled by different techniques, it is common to use two or more processes for a given PCB. For example, surface mounted parts may be reflow soldered first, with a wave soldering process for the through-hole mounted components coming next, and bulkier parts hand-soldered last.
For hand soldering of electronic components, the heat source tool should be selected to provide adequate heat for the size of joint to be completed. A 100 watt soldering iron may provide too much heat for printed circuit boards, while a 25 watt iron will not provide enough heat for large electrical connectors, joining copper roof flashing, or large stained-glass lead came. Using a tool with too high a temperature can damage sensitive components, but protracted heating by a tool that is too cool or under powered can also cause extensive heat damage.
Hand-soldering techniques require a great deal of skill to use on the finest pitch chip packages. In particular ball grid array (BGA) devices are notoriously difficult if not impossible to rework by hand.
For attachment of electronic components to a PCB, proper selection and use of flux helps prevent oxidation during soldering, which is essential for good wetting and heat transfer. The soldering iron tip must be clean and pre-tinned with solder to ensure rapid heat transfer. Components which dissipate large amounts of heat during operation are sometimes elevated above the PCB to avoid PCB overheating. After inserting a through-hole mounted component, the excess lead is cut off, leaving a length of about the radius of the pad. Plastic or metal mounting clips or holders may be used with large devices to aid heat dissipation and reduce joint stresses.
A heat sink may be used on the leads of heat sensitive components to reduce heat transfer to the component. This is especially applicable to germanium parts. (Note the heat sink will mean the use of more heat to complete the joint.) If all metal surfaces are not properly fluxed and brought above the melting temperature of the solder in use, the result will be an unreliable "cold solder joint".
To simplify soldering, beginners are usually advised to apply the soldering iron and the solder separately to the joint, rather than the solder being applied direct to the iron. When sufficient solder is applied, the solder wire is removed. When the surfaces are adequately heated, the solder will flow around the joint. The iron is then removed from the joint.
Since non-eutectic solder alloys have a small plastic range, the joint must not be moved until the solder has cooled down through both the liquidus and solidus temperatures. Visually, a good solder joint will appear smooth and shiny, with the outline of the soldered wire clearly visible. A matte gray surface is a good indicator of a joint that was moved during soldering. Too little solder will result in a dry and unreliable joint; too much solder (the 'solder blob' very familiar to beginners) is not necessarily unsound, but tends to mean poor wetting. With some fluxes, flux residue remaining on the joint may need to be removed, using water, alcohol or other solvents compatible with the process. Excess solder and unconsumed flux and residue is sometimes wiped from the soldering iron tip between joints. The tip of the iron is kept wetted with solder ("tinned") when hot to minimize oxidation and corrosion of the tip itself.
Environmental legislation in many countries, and the whole of the European Community area (see RoHS), has led to a change in formulation of both solders and fluxes. Water soluble non-rosin based fluxes have been increasingly used since the 1980s so that soldered boards can be cleaned with water or water based cleaners. This eliminates hazardous solvents from the production environment, and effluent.

Hot-bar reflow

Hot-bar reflow is a selective soldering process where two pre-fluxed, solder coated parts are heated with heating element (called a thermode) to a sufficient temperature to melt the solder.
Pressure is applied through the whole process (usually 15 s) to ensure that components stay in place during cooling. The heating element is heated and cooled for each connection. Up to 4000 W can be used in the heating element allowing fast soldering, good results with connections requiring high energy.

] Laser

Laser soldering is a technique where a ~30-50 W laser is used to melt and solder an electrical connection joint. Diode laser systems based on semiconductor junctions are used for this purpose.
Wavelengths are typically 808 nm through 980 nm. The beam is delivered via an optical fiber to the workpiece, with fiber diameters 800 um and smaller. Since the beam out of the end of the fiber diverges rapidly, lenses are used to create a suitable spot size on the workpiece at a suitable working distance. A wire feeder is used to supply solder.
Both lead-tin and silver-tin material can be soldered. Process recipes will differ depending on the alloy composition. For soldering 44-pin chip carriers to a board using soldering preforms, power levels were on the order of 10 Watts and solder times approximately 1 second. Low power levels can lead to incomplete wetting and the formation of voids, both of which can weaken the joint.

Pipe soldering

soldered copper pipes

Solder

Copper pipe, or 'tube', is commonly joined by soldering. When applied in a plumbing trade context, soldering is more often referred to as sweating and a tubing connection so made is referred to as a sweated joint.
Copper conducts heat away much faster than a soldering iron or gun can provide, so a propane torch is most commonly used to deliver the necessary BTUs per minute; for large tubing sizes and fittings a MAPP†-fueled, acetylene-fueled, or propylene-fueled torch is used with atmospheric air as the oxidizer; MAPP†/oxygen or acetylene/oxygen are rarely used because the flame temperature is much higher than the melting point of copper. Too much heat destroys the temper of hard-tempered copper tubing, and can burn the flux out of a joint before the solder is added, resulting in a faulty joint. For larger tubing sizes, a torch fitted with various sizes of interchangeable swirl tips is employed to deliver the needed BTUs/minute.
Most experienced plumbers seldom use propane fuel. In the hands of a skilled tradesman, the hotter flame of acetylene, MAPP, or propylene allows more joints to be completed per hour.
†True MAPP gas has not been produced or sold in North American since 2008 when the last plant producing the fuel closed. The yellow canisters available in hardware stores, while labeled MAPP, are MAPP substitutes that burns at a somewhat cooler temperature.
Solder fittings, which are short sections of smooth pipe designed to slide over the outside of the mating tube, are usually used for copper joints. There are two types of fittings: end feed fittings which contain no solder, and solder ring fittings, in which there is a ring of solder in a small circular recess inside the fitting.
As with all solder joints, all parts to be joined must be clean and oxide free. Internal and external wire brushes are available for the common pipe and fitting sizes; emery cloth and wire-wool are frequently used as well, although metal wool products are discouraged, as they can contain oil, which would contaminate the joint.
Because of the size of the parts involved, and the high activity and contaminating tendency of the flame, plumbing fluxes are typically much more chemically active, and more acidic, than electronic fluxes. Because plumbing joints may be done at any angle, even upside down, plumbing fluxes are generally formulated as pastes which stay in place better than liquids. Flux should be applied to all surfaces of the joint, inside and out. Flux residues should be removed after the joint is complete or they can, eventually, erode through the copper substrates and cause failure of the joint.
Many plumbing solder formulations are available, with different characteristics such as higher or lower melting temperature, depending on the specific requirements of the job. Building codes currently almost universally require the use of lead-free solder for potable water piping, though traditional tin-lead solder is still available. Studies have shown that lead-soldered plumbing pipes can result in elevated levels of lead in drinking water.
Since copper pipe quickly conducts heat away from a joint, great care must be taken to ensure that the joint is properly heated through to obtain a good bond. After the joint is properly cleaned, fluxed and fitted, the torch flame is applied to the thickest part of the joint, typically the fitting with the pipe inside it, with the solder applied at the gap between the tube and the fitting. When all the parts are heated through, the solder will melt and flow into the joint by capillary action. The torch may need to be moved around the joint to ensure all areas are wetted out. However, the installer must take care to not overheat the areas being soldered. If the tube begins to discolor it means that the tube has been over-heated and is beginning to oxidize, stopping the flow of the solder and causing the soldered joint not to seal properly. Before oxidation the molten solder will follow the heat of the torch around the joint. When the joint is properly wetted out, the solder and then the heat are removed, and while the joint is still very hot, it is usually wiped with a dry rag. This removes excess solder as well as flux residue before it cools down and hardens. With a solder ring joint, the joint is heated until a ring of molten solder is visible around the edge of the fitting and allowed to cool.
Solder connections are usually considered the most difficult of the three methods of connecting copper tubing, but soldering copper is a very simple process, provided some basic conditions are provided:

• The tubing and fittings must be cleaned to bare metal with no tarnish
• Any pressure which is formed by heating of the tubing must have an outlet

Copper is only one material that is joined in this manner. Brass fittings are often used for valves or as a connection fitting between copper and other metals. Brass piping is soldered in this manner in the making of brass and some woodwind (saxophone and flute) musical instruments

Mechanical and aluminium soldering

A number of solder materials, primarily zinc alloys, are used for soldering aluminium metal and alloys and to some lesser extent steel and zinc. This mechanical soldering is similar to a low temperature brazing operation, in that the mechanical characteristics of the joint are reasonably good and it can be used for structural repairs of those materials.
The American welding society defines brazing as using filler metals with melting points over 450 °C (842 °F) — or, by the traditional definition in the United States, above 800 °F (427 °C). Aluminium soldering alloys generally have melting temperatures around 730 °F (388 °C). This soldering / brazing operation can use a propane torch heat source
These materials are often advertised as "aluminium welding", but the process does not involve melting the base metal, and therefore is not properly a weld.
United States Military Standard or MIL-SPEC specification MIL-R-4208 defines one standard for these zinc-based brazing/soldering alloys A number of products meet this specification. or very similar performance standards
Resistance soldering is soldering in which the heat required to flow the solder is created by passing an electric current through the solder. When current is conducted through a resistive material a certain level of heat is generated. By regulating the amount of current conducted and the level of resistance encountered, the amount of heat produced can be predetermined and controlled.
Electrical resistance (usually described as a material's opposition to the flow of an electric current) is used to convert electric energy into thermal energy as an electric current (I) conducted through a material with resistance (R) releases power (P) equal to: P = I² R, where P is the power measured in watts, I is the current measured in amperes and R is the resistance measured in ohms.

Resistance soldering

Resistance soldering is unlike using a conduction iron, where heat is produced within an element and then passed through a thermally conductive tip into the joint area. A cold soldering iron requires time to reach working temperature and must be kept hot between solder joints. Thermal transfer may be inhibited if the tip is not kept properly wetted during use. With resistance soldering an intense heat can be rapidly developed directly within the joint area and in a tightly controlled manner. This allows a faster ramp up to the required solder melt temperature and minimizes thermal travel away from the solder joint, which helps to minimize the potential for thermal damage to materials or components in the surrounding area. Heat is only produced while each joint is being made, making resistance soldering more energy efficient. Resistance soldering equipment, unlike conduction irons, can be used for difficult soldering and brazing applications where significantly higher temperatures may be required. This makes resistance comparable to flame soldering in some situations. When the required temperature can be achieved by either flame or resistance methods the resistance heat is more localized because of direct contact, whereas the flame will spread thus heating a potentially larger area.

Stained glass soldering

Historically, stained glass soldering tips were copper, heated by being placed in a charcoal-burning brazier. Multiple tips were used; when one tip cooled down from use, it was placed back in the brazier of charcoal and the next tip was used.
More recently, electrically heated soldering irons are used. These are heated by a coil or ceramic heating element inside the tip of the iron. Different power ratings are available, and temperature can be controlled electronically. These characteristics allow longer beads to be run without interrupting the work to change tips. Soldering irons designed for electronic use are often effective though they are sometimes underpowered for the heavy copper and lead came used in stained glass work. Oleic acid is the classic flux material that has been used to improve solderability.
Tiffany type stainglass steel is made by gluing copper foil around the edges of the pieces of glass and then soldering them together. This method makes it possible to create three dimensional stained glass pieces.

Solderability

Main article: Solderability

The Solderability of a substrate is a measure of the ease with which a soldered joint can be made to that material.

Desoldering and resoldering

Main article: Desoldering

Used solder contains some of the dissolved base metals and is unsuitable for reuse in making new joints. Once the solder's capacity for the base metal has been achieved it will no longer properly bond with the base metal, usually resulting in a brittle cold solder joint with a crystalline appearance.
It is good practice to remove solder from a joint prior to resoldering—desoldering braids or vacuum desoldering equipment (solder suckers) can be used. Desoldering wicks contain plenty of flux that will lift the contamination from the copper trace and any device leads that are present. This will leave a bright, shiny, clean junction to be resoldered.
The lower melting point of solder means it can be melted away from the base metal, leaving it mostly intact, though the outer layer will be "tinned" with solder. Flux will remain which can easily be removed by abrasive or chemical processes. This tinned layer will allow solder to flow into a new joint, resulting in a new joint, as well as making the new solder flow very quickly and easily.

Bluetooth specification

 BLUETOOTH HISTORY

Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances (using short-wavelength radio transmissions in the ISM band from 2400–2480 MHz) from fixed and mobile devices, creating personal area networks (PANs) with high levels of security. Created by telecoms vendor Ericsson in 1994, it was originally conceived as a wireless alternative to RS-232 data cables. It can connect several devices, overcoming problems of synchronization.
Bluetooth is managed by the Bluetooth Special Interest Group, which has more than 15,000 member companies in the areas of telecommunication, computing, networking, and consumer electronics. The SIG oversees the development of the specification, manages the qualification program, and protects the trademarks. To be marketed as a Bluetooth device, it must be qualified to standards defined by the SIG. A network of patents is required to implement the technology and are only licensed to those qualifying devices; thus the protocol, whilst open, may be regarded as proprietary.

Implementation

Bluetooth uses a radio technology called frequency-hopping spread spectrum, which chops up the data being sent and transmits chunks of it on up to 79 bands (1 MHz each; centered from 2402 to 2480 MHz) in the range 2,400–2,483.5 MHz (allowing for guard bands). This range is in the globally unlicensed Industrial, Scientific and Medical (ISM) 2.4 GHz short-range radio frequency band. It usually performs 800 hops per second, with AFH enabled.
Originally Gaussian frequency-shift keying (GFSK) modulation was the only modulation scheme available; subsequently, since the introduction of Bluetooth 2.0+EDR, π/4-DQPSK and 8DPSK modulation may also be used between compatible devices. Devices functioning with GFSK are said to be operating in basic rate (BR) mode where an instantaneous data rate of 1 Mbit/s is possible. The term Enhanced Data Rate (EDR) is used to describe π/4-DPSK and 8DPSK schemes, each giving 2 and 3 Mbit/s respectively. The combination of these (BR and EDR) modes in Bluetooth radio technology is classified as a "BR/EDR radio".
Bluetooth is a packet-based protocol with a master-slave structure. One master may communicate with up to 7 slaves in a piconet; all devices share the master's clock. Packet exchange is based on the basic clock, defined by the master, which ticks at 312.5 µs intervals. Two clock ticks make up a slot of 625 µs; two slots make up a slot pair of 1250 µs. In the simple case of single-slot packets the master transmits in even slots and receives in odd slots; the slave, conversely, receives in even slots and transmits in odd slots. Packets may be 1, 3 or 5 slots long but in all cases the master transmit will begin in even slots and the slave transmit in odd slots.
Bluetooth provides a secure way to connect and exchange information between devices such as faxes, mobile phones, telephones, laptops, personal computers, printers, Global Positioning System (GPS) receivers, digital cameras, and video game consoles.

Communication and connection

A master Bluetooth device can communicate with a maximum of seven devices in a piconet (an ad-hoc computer network using Bluetooth technology), though not all devices support this limit. The devices can switch roles, by agreement, and the slave can become the master (for example, a headset initiating a connection to a phone will necessarily begin as master, as initiator of the connection; but may subsequently prefer to be slave).
The Bluetooth Core Specification provides for the connection of two or more piconets to form a scatternet, in which certain devices simultaneously play the master role in one piconet and the slave role in another.
At any given time, data can be transferred between the master and one other device (except for the little-used broadcast mode). The master chooses which slave device to address; typically, it switches rapidly from one device to another in a round-robin fashion. Since it is the master that chooses which slave to address, whereas a slave is (in theory) supposed to listen in each receive slot, being a master is a lighter burden than being a slave. Being a master of seven slaves is possible; being a slave of more than one master is difficult. The specification is vague as to required behaviour in scatternets.
Many USB Bluetooth adapters or "dongles" are available, some of which also include an IrDA adapter. Older (pre-2003) Bluetooth dongles, however, have limited capabilities, offering only the Bluetooth Enumerator and a less-powerful Bluetooth Radio incarnation. Such devices can link computers with Bluetooth with a distance of 100 meters, but they do not offer as many services as modern adapters do.

Uses

Bluetooth is a standard wire-replacement communications protocol primarily designed for low power consumption, with a short range (power-class-dependent, but effective ranges vary in practice; see table below) based on low-cost transceiver microchips in each device. Because the devices use a radio (broadcast) communications system, they do not have to be in visual line of sight of each other, however a quasi optical wireless path must be viable.

Class	Maximum permitted power		Range (m)
	(mW)	(dBm)
Class 1	100	20	~100
Class 2	2.5	4	~10
Class 3	1	0	~5

The effective range varies due to propagation conditions, material coverage, production sample variations, antenna configurations and battery conditions. In most cases the effective range of class 2 devices is extended if they connect to a class 1 transceiver, compared to a pure class 2 network. This is accomplished by the higher sensitivity and transmission power of Class 1 devices.

Version	Data rate	Maximum application throughput
Version 1.2	1 Mbit/s	0.7 Mbit/s
Version 2.0 + EDR	3 Mbit/s	2.1 Mbit/s
Version 3.0 + HS	See Version 3.0+HS.
Version 4.0	See Version 4.0LE.

While the Bluetooth Core Specification does mandate minimums for range, the range of the technology is application specific and is not limited. Manufacturers may tune their implementations to the range needed to support individual use cases.

Bluetooth profiles

Main article: Bluetooth profile

To use Bluetooth wireless technology, a device has to be able to interpret certain Bluetooth profiles, which are definitions of possible applications and specify general behaviors that Bluetooth enabled devices use to communicate with other Bluetooth devices. These profiles include settings to parametrize and to control the communication from start. Adherence to profiles saves the time for transmitting the parameters anew before the bi-directional link becomes effective. There are a wide range of Bluetooth profiles that describe many different types of applications or use cases for devices

 List of applications

Add caption

A typical Bluetooth mobile phone headset.

• Wireless control of and communication between a mobile phone and a handsfree headset. This was one of the earliest applications to become popular.
• Wireless control of and communication between a mobile phone and a Bluetooth compatible car stereo system
• Wireless Bluetooth headset and Intercom.
• Wireless networking between PCs in a confined space and where little bandwidth is required.
• Wireless communication with PC input and output devices, the most common being the mouse, keyboard and printer.
• Transfer of files, contact details, calendar appointments, and reminders between devices with OBEX.
• Replacement of previous wired RS-232 serial communications in test equipment, GPS receivers, medical equipment, bar code scanners, and traffic control devices.
• For controls where infrared was often used.
• For low bandwidth applications where higher USB bandwidth is not required and cable-free connection desired.
• Sending small advertisements from Bluetooth-enabled advertising hoardings to other, discoverable, Bluetooth devices.
• Wireless bridge between two Industrial Ethernet (e.g., PROFINET) networks.
• Three seventh-generation game consoles, Nintendo's Wiiand Sony's PlayStation 3 and PSP Go, use Bluetooth for their respective wireless controllers.
• Dial-up internet access on personal computers or PDAs using a data-capable mobile phone as a wireless modem.
• Short range transmission of health sensor data from medical devices to mobile phone, set-top box or dedicated telehealth devices.
• Allowing a DECT phone to ring and answer calls on behalf of a nearby cell phone
• Real-time location systems (RTLS), are used to track and identify the location of objects in real-time using “Nodes” or “tags” attached to, or embedded in the objects tracked, and “Readers” that receive and process the wireless signals from these tags to determine their locations
• Personal security application on mobile phones for prevention of theft or loss of items. The protected item has a Bluetooth marker (e.g. a tag) that is in constant communication with the phone. If the connection is broken (the marker is out of range of the phone) then an alarm is raised. This can also be used as a man overboard alarm. A product using this technology has been available since 2009.

Bluetooth vs. Wi-Fi (IEEE 802.11)

Bluetooth and Wi-Fi (the brand name for products using IEEE 802.11 standards) have some similar applications: setting up networks, printing, or transferring files. Wi-Fi is intended as a replacement for cabling for general local area network access in work areas. This category of applications is sometimes called wireless local area networks (WLAN). Bluetooth was intended for portable equipment and its applications. The category of applications is outlined as the wireless personal area network (WPAN). Bluetooth is a replacement for cabling in a variety of personally carried applications in any setting and can also support fixed location applications such as smart energy functionality in the home (thermostats, etc.).
Wi-Fi is a wireless version of a common wired Ethernet network, and requires configuration to set up shared resources, transmit files, and to set up audio links (for example, headsets and hands-free devices). Wi-Fi uses the same radio frequencies as Bluetooth, but with higher power, resulting in higher bit rates and better range from the base station. The nearest equivalents in Bluetooth are the DUN profile, which allows devices to act as modem interfaces, and the PAN profile, which allows for ad-hoc networking.

Devices

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A Bluetooth USB dongle with a 100 m range. The MacBook Pro, shown, also has a built in Bluetooth adaptor.

Bluetooth exists in many products, such as the iPod Touch, Lego Mindstorms NXT, PlayStation 3, PSP Go, telephones, the Nintendo Wii, and some high definition headsets, modems, and watches. The technology is useful when transferring information between two or more devices that are near each other in low-bandwidth situations. Bluetooth is commonly used to transfer sound data with telephones (i.e., with a Bluetooth headset) or byte data with hand-held computers (transferring files).

Bluetooth protocols simplify the discovery and setup of services between devices. Bluetooth devices can advertise all of the services they provide. This makes using services easier because more of the security, network address and permission configuration can be automated than with many other network types.

Android4.0 Platform

ANDROID 4.0 VERSION(DUALPROCESSOR)

 Simple, beautiful, beyond smart

Android 4.0 builds on the things people love most about Android — easy multitasking, rich notifications, customizable home screens, resizable widgets, and deep interactivity — and adds powerful new ways of communicating and sharing.

Refined, evolved UI

Focused on bringing the power of Android to the surface, Android 4.0 makes common actions more visible and lets users navigate with simple, intuitive gestures. Refined animations and feedback throughout the system make interactions engaging and interesting. An entirely new typeface optimized for high-resolution screens improves readability and brings a polished, modern feel to the user interface.
Virtual buttons in the System Bar let users navigate instantly to Back, Home, and Recent Apps. The System Bar and virtual buttons are present across all apps, but can be dimmed by applications for full-screen viewing. Users can access each application's contextual options in the Action Bar, displayed at the top (and sometimes also at the bottom) of the screen.
Multitasking is a key strength of Android and it's made even easier and more visual on Android 4.0. The Recent Apps button lets users jump instantly from one task to another using the list in the System Bar. The list pops up to show thumbnail images of apps used recently — tapping a thumbnail switches to the app.

The Recent Apps list makes multitasking simple.

Jump to the camera or see notifications without unlocking.

For incoming calls, you can respond instantly by text.

Rich and interactive notifications let users keep in constant touch with incoming messages, play music tracks, see real-time updates from apps, and much more. On smaller-screen devices, notifications appear at the top of the screen, while on larger-screen devices they appear in the System Bar.

The All Apps launcher (left) and resizable widgets (right) give you apps and rich content from the home screen.

Home screen folders and favorites tray

New home screen folders offer a new way for users to group their apps and shortcuts logically, just by dragging one onto another. Also, in All Apps launcher, users can now simply drag an app to get information about it or immediately uninstall it, or disable a pre-installed app.
On smaller-screen devices, the home screen now includes a customizable favorites tray visible from all home screens. Users can drag apps, shortcuts, folders, and other priority items in or out of the favorites tray for instant access from any home screen.

Resizable widgets

Home screens in Android 4.0 are designed to be content-rich and customizable. Users can do much more than add shortcuts — they can embed live application content directly through interactive widgets. Widgets let users check email, flip through a calendar, play music, check social streams, and more — right from the home screen, without having to launch apps. Widgets are resizable, so users can expand them to show more content or shrink them to save space.

New lock screen actions

The lock screens now let users do more without unlocking. From the slide lock screen, users can jump directly to the camera for a picture or pull down the notifications window to check for messages. When listening to music, users can even manage music tracks and see album art.

Quick responses for incoming calls

When an incoming call arrives, users can now quickly respond by text message, without needing to pick up the call or unlock the device. On the incoming call screen, users simply slide a control to see a list of text responses and then tap to send and end the call. Users can add their own responses and manage the list from the Settings app.

Swipe to dismiss notifications, tasks, and browser tabs

Android 4.0 makes managing notifications, recent apps, and browser tabs even easier. Users can now dismiss individual notifications, apps from the Recent Apps list, and browser tabs with a simple swipe of a finger.

A spell-checker lets you find errors and fix them faster.

A powerful voice input engine lets you dictate continously.

Improved text input and spell-checking

The soft keyboard in Android 4.0 makes text input even faster and more accurate. Error correction and word suggestion are improved through a new set of default dictionaries and more accurate heuristics for handling cases such as double-typed characters, skipped letters, and omitted spaces. Word suggestion is also improved and the suggestion strip is simplified to show only three words at a time.
To fix misspelled words more easily, Android 4.0 adds a spell-checker that locates and underlines errors and suggests replacement words. With one tap, users can choose from multiple spelling suggestions, delete a word, or add it to the dictionary. Users can even tap to see replacement suggestions for words that are spelled correctly. For specialized features or additional languages, users can now download and install third-party dictionaries, spell-checkers, and other text services.

Powerful voice input engine

Android 4.0 introduces a powerful new voice input engine that offers a continuous "open microphone" experience and streaming voice recognition. The new voice input engine lets users dictate the text they want, for as long as they want, using the language they want. Users can speak continously for a prolonged time, even pausing for intervals if needed, and dictate punctuation to create correct sentences. As the voice input engine enters text, it underlines possible dictation errors in gray. After dictating, users can tap the underlined words to quickly replace them from a list of suggestions.

Data usage controls let you monitor total usage by network type and application and then set limits if needed.

Control over network data

Mobile devices can make extensive use of network data for streaming content, synchronizing data, downloading apps, and more. To meet the needs of users with tiered or metered data plans, Android 4.0 adds new controls for managing network data usage.
In the Settings app, colorful charts show the total data usage on each network type (mobile or Wi-Fi), as well as amount of data used by each running application. Based on their data plans, users can optionally set warning levels or hard limits on data usage or disable mobile data altogether. Users can also manage the background data used by individual applications as needed.

Designed for accessibility

A variety of new features greatly enhance the accessibility of Android 4.0 for blind or visually impaired users. Most important is a new explore-by-touch mode that lets users navigate without having to see the screen. Touching the screen once triggers audible feedback that identifies the UI component below; a second touch in the same component activates it with a full touch event. The new mode is especially important to support users on new devices that use virtual buttons in the System Bar, rather than dedicated hardware buttons or trackballs. Also, standard apps are updated to offer an improved accessibility experience. The Browser supports a script-based screen reader for reading favorite web content and navigating sites. For improved readability, users can also increase the default font size used across the system.
The accessibility experience begins at first setup — a simple touch gesture during setup (clockwise square from upper left) activates all accessibility features and loads a setup tutorial. Once accessibility features are active, everything visible on the screen can be spoken aloud by the standard screen reader.

Communication and sharing

Contacts and profiles are integrated across apps and social networks, for a consistent, personal experience everywhere — from incoming calls to emails.

Designed for the way people live, Android 4.0 integrates rich social communication and sharing touchpoints across the system, making it easy to talk, email, text, and share.

People and profiles

Throughout the system, a user’s social groups, profiles, and contacts are linked together and integrated for easy accessibility. At the center is a new People app that offers richer profile information, including a large profile picture, phone numbers, addresses and accounts, status updates, events, stream items, and a new button for connecting on integrated social networks.
The user's own contact information is stored in a new "Me" profile, allowing easier sharing with apps and people. All of the user's integrated contacts are displayed in an easy to manage list, including controls over which contacts are shown from any integrated account or social network. Wherever the user navigates across the system, tapping a profile photo displays Quick Contacts, with large profile pictures, shortcuts to phone numbers, text messaging, and more.

Unified calendar, visual voicemail

To help organize appointments and events, an updated Calendar app brings together personal, work, school, and social agendas. With user permission, other applications can contribute events to the calendar and manage reminders, for an integrated view across multiple calendar providers. The app is redesigned to let users manage events more easily. Calendars are color-coded and users can swipe left or right to change dates and pinch to zoom in or out agendas.
In the phone app, a new visual voicemail features integrates incoming messages, voice transcriptions, and audio files from one or more providers. Third-party applications can integrate with the Phone app to add their own voice messages, transcriptions, and more to the visual voicemail inbox.

Capture the picture you want, edit, and share instantly.

Rich and versatile camera capabilities

The Camera app includes many new features that let users capture special moments with great photos and videos. After capturing images, they can edit and share them easily with friemds.
When taking pictures, continuous focus, zero shutter lag exposure, and decreased shot-to-shot speed help capture clear, precise images. Stabilized image zoom lets users compose photos and video in the way they want, including while video is recording. For new flexibility and convenience while shooting video, users can now take snapshots at full video resolution just by tapping the screen as video continues to record.
To make it easier to take great pictures of people, built-in face detection locates faces in the frame and automatically sets focus. For more control, users can tap to focus anywhere in the preview image.
For capturing larger scenes, the Camera introduces a single-motion panorama mode. In this mode, the user starts an exposure and then slowly turns the Camera to encompass as wide a perspective as needed. The Camera assembles the full range of continuous imagery into a single panoramic photo.
After taking a picture or video, users can quickly share it by email, text message, bluetooth, social networks, and more, just by tapping the thumbnail in the camera controls.

A Photo Gallery widget on the home screen.

Redesigned Gallery app with photo editor

The Gallery app now makes it easier to manage, show, and share photos and videos. For managing collections, a redesigned album layout shows many more albums and offers larger thumbnails. There are many ways to sort albums, including by time, location, people, and tags. To help pictures look their best, the Gallery now includes a powerful photo editor. Users can crop and rotate pictures, set levels, remove red eyes, add effects, and much more. After retouching, users can select one or multiple pictures or videos to share instantly over email, text messaging, bluetooth, social networks, or other apps.
An improved Picture Gallery widget lets users look at pictures directly on their home screen. The widget can display pictures from a selected album, shuffle pictures from all albums, or show a single image. After adding the widget to the home screen, users can flick through the photo stacks to locate the image they want, then tap to load it in Gallery.

Live Effects let you change backgrounds and use Silly Faces during video.

Live Effects for transforming video

Live Effects is a collection of graphical transformations that add interest and fun to videos captured in the Camera app. For example, users can change the background behind them to any stock or custom image, for just the right setting when shooting videeo. Also available for video is Silly Faces, a set of morphing effects that use state-of-the-art face recognition and GPU filters to transform facial features. For example, you can use effects such as small eyes, big mouth, big nose, face squeeze, and more. Outside of the Camera app, Live Effects is available during video chat in the Google Talk app.

Snapping a screenshot.

Sharing with screenshots

Users can now share what's on their screens more easily by taking screenshots. Hardware buttons let them snap a screenshot and store it locally. Afterward, they can view, edit, and share the screen shot in Gallery or a similar app.

Cloud-connected experience

The Browser tabs menu (left) lets you quickly switch browser tabs. The options menu (right) gives you new ways to manage your browsing experience.

Benchmark comparisons of Android Browser.

Android has always been cloud-connected, letting users browse the web and sync photos, apps, games, email, and contacts — wherever they are and across all of their devices. Android 4.0 adds new browsing and email capabilities to let users take even more with them and keep communication organized.

Powerful web browsing

The Android Browser offers an experience that’s as rich and convenient as a desktop browser. It lets users instantly sync and manage Google Chrome bookmarks from all of their accounts, jump to their favorite content faster, and even save it for reading later in case there's no network available.
To get the most out of web content, users can now request full desktop versions of web sites, rather than their mobile versions. Users can set their preference for web sites separately for each browser tab. For longer content, users can save a copy for offline reading. To find and open saved pages, users can browse a visual list that’s included with browser bookmarks and history. For better readability and accessibility, users can increase the browser’s zoom levels and override the system default text sizes.
Across all types of content, the Android Browser offers dramatically improved page rendering performance through updated versions of the WebKit core and the V8 Crankshaft compilation engine for JavaScript. In benchmarks run on a Nexus S device, the Android 4.0 browser showed an improvement of nearly 220% over the Android 2.3 browser in the V8 Benchmark Suite and more than 35% in the SunSpider 9.1 JavaScript Benchmark. When run on a Galaxy Nexus device, the Android 4.0 browser showed improvement of nearly 550% in the V8 benchmark and nearly 70% in the SunSpider benchmark.

Improved email

In Android 4.0, email is easier to send, read, and manage. For composing email, improved auto-completion of recipients helps with finding and adding frequent contacts more quickly. For easier input of frequent text, users can now create quick responses and store them in the app, then enter them from a convenient menu when composing. When replying to a message, users can now toggle the message to Reply All and Forward without changing screens.
For easier browsing across accounts and labels, the app adds an integrated menu of accounts and recent labels. To help users locate and organize IMAP and Exchange email, the Email app now supports nested mail subfolders, each with synchronization rules. Users can also search across folders on the server, for faster results.
For enterprises, the Email app supports EAS v14. It supports EAS certificate authentication, provides ABQ strings for device type and mode, and allows automatic sync to be disabled while roaming. Administrators can also limit attachment size or disable attachments.
For keeping track of incoming email more easily, a resizable Email widget lets users flick through recent email right from the home screen, then jump into the Email app to compose or reply.

Android Beam lets users share what they are using with a single tap.

Innovation

Android is continously driving innovation forward, pushing the boundaries of communication and sharing with new capabilities and interactions.

Android Beam for NFC-based sharing

Android Beam is an innovative, convenient feature for sharing across two NFC-enabled devices, It lets people instantly exchange favorite apps, contacts, music, videos — almost anything. It’s incredibly simple and convenient to use — there’s no menu to open, application to launch, or pairing needed. Just touch one Android-powered phone to another, then tap to send.
For sharing apps, Android Beam pushes a link to the app's details page in Google Play. On the other device, the Google Play client app launches and loads the details page, for easy downloading of the app. Individual apps can build on Android Beam to add other types of interactions, such as passing game scores, initiating a multiplayer game or chat, and more.

Face recognition lets you unlock your phone with your face.

Face Unlock

Android 4.0 introduces a completely new approach to securing a device, making each person's device even more personal — Face Unlock is a new screen-lock option that lets users unlock their devices with their faces. It takes advantage of the device front-facing camera and state-of-the-art facial recognition technology to register a face during setup and then to recognize it again when unlocking the device. Users just hold their devices in front of their faces to unlock, or use a backup PIN or pattern.

Wi-Fi Direct and Bluetooth HDP

Support for Wi-Fi Direct lets users connect directly to nearby peer devices over Wi-Fi, for more reliable, higher-speed communication. No internet connection or tethering is needed. Through third-party apps, users can connect to compatible devices to take advantage of new features such as instant sharing of files, photos, or other media; streaming video or audio from another device; or connecting to compatible printers or other devices.

Android 4.0 also introduces built-in support for connecting to Bluetooth Health Device Profile (HDP) devices. With support from third-party apps, users can connect to wireless medical devices and sensors in hospitals, fitness centers, homes, and elsewhere.