Solder used for soldering in electronics is the lifeline of any PCB or rather PCA (Printed Circuit Assembly). In electronic PCB Manufacturing, assembly and rework, the metals to be joined are the leads of the electronic components (thru-hole or SMD) with the copper tracks on the PCB. The alloy used to join these two metals is solder which is basically tin-lead (Sn-Pb) or Lead-Free - tin-silver-copper (Sn-Ag-Cu). Tin-lead solder is called leaded solder because of the lead present in it while the tin-silver-copper solder is called lead-free solder because no lead is present in it. The solder is melted using either a wave soldering machine or a reflow oven or a normal soldering iron and this molten solder is then used to solder the electronic components on to the PCB. A PCB or Printed Circuit Board after assembly of electronic components is called PCA or Printed Circuit Assembly.

Quality of solder and the soldering technique decides the life and performance of any electronic equipment, appliance or gadget. There are expensive as well as low-cost, eutectic lead-free solder alloy with high reliability and shiny joints.

Solder is the lifeline of any PCB. The quality of solder used during soldering and PCB assembly decides the life and performance of any electronic machine, equipment, appliance or gadget.

Different alloys of solder are available but real solder has to be eutectic which means it has to melts exactly at the temperature of 183 Degree Celsius. An alloy of tin and lead in the ration 63/37 is eutectic and hence 63/37 tin-lead solder is called eutectic solder. Solders that are non-eutectic will not change from solid to liquid at 183 Degree Celsius. They may remain semi-solid at this temperature. The nearest alloy to eutectic solder is tin-lead in the ration 60/40. The favorite solder for electronic manufacturers have been 63/37 for years. It is still widely used across the world.

Lead is harmful to the environment and human beings. Because of this reason, the European Union took the initiative to ban lead from electronics (WEEE and RoHS). It has been decided to get rid of lead from solder and electronic components. This has given rise to another form of solder called lead-free solder. This solder is called-free because there is no lead in it. Lead-free solder alloys melt around 250 °C (482 °F), depending on their composition. Most common lead-free alloy is tin / silver / copper in the ratio Sn96.5/Ag3.0/Cu0.5 (SAC). Lead-Free solder is also called "No-Lead" Solder.

Solder is available in various forms:

1. Wire: These are called solder wire and are available in various combinations of alloy and in various diameters ranging from 0.2 to 1.5mm. Solder wire is basically used in hand soldering.

2. Solder Bar: Solder bars are in the form of bar is sizes of .5 to 1 kg. Solder bar is used in wave soldering.

3. Solder Preforms: As the name suggests, these are solder in predefined shapes and sizes depending on the soldering requirement. They can be circular, triangular, rectangular or square or in any other shape.

4. Solder Paste: These are solder in paste form. Solder paste is used in Reflow Soldering and Hot Air Soldering.

5. Solder Balls: These are solder in the form of tiny balls in sizes ranging from 18 to 30 MIL. Solder balls are used in BGA of Ball Grid Array soldering. Most of the tiny gadgets have BGA.