Tin/lead (Sn/Pb) solder alloys: application
Tin/lead is the main solder alloy used for soldering in the manufacturing process of Solar PV modules.
What is the soldering process?
Soldering is using the fusible metal alloy to create a permanent bond between different metal pieces. The solder must be melted first in order to adhere to and connect the pieces together after cooling down. This requires the alloy suitable as solder should have a lower melting point than the two pieces being joined. The solder should be also resistant to both corrosive and oxidative effects which can degrade the joint over time. Also, the solder used in electrical conductive connections needs to possess proper electrical characteristics.
Soldering in solar industry
Soldering is widely used in the Solar PV Industry. It is mainly used in stringing, bussing and ribbon tab installation in solar cells.
For solar module manufacturers, a few solder alloys have become common, market wide, and those can be pared down into three categories. Below are the typical Tabbing Ribbon Solders commonly used :
- Bi/Sn alloys (58Bi42Sn, 57Bi42Sn1Ag)
- Sn/Pb alloys (63Sn37Pb, 62Sn36Pb2Ag)
- Sn/Ag alloys (96Sn4Ag)
The reliability and wetting attributes of Sn / Pb alloys have long made them a smart selection. Yet, in the emerging green technologies, Pb-free material selections are preferred.
Different types of solder
The Soft solder normally has a melting point in the range of 90 to 450 °C and is usually used in electronics and sheet metal work. Alloys that have melting point between 180 and 190 °C are the most commonly used alloys. Soldering which is performed using alloys that have a melting point above 450 °C is named hard soldering, also silver soldering, or brazing.
For different electrical and electronics work, the solder wire is available in a wide range of thicknesses for manual soldering using a soldering iron or gun, and with cores that contain flux. Also solder material can be available as a paste, more suitable for automatic mass-production, or in small tabs which can be wrapped around a joint and melted with a flame, if no equipment is available for emergency field repairs. The common Alloys of lead and tin were mainly used in the past and are still available and widely used nowadays; they are very convenient for manual soldering applications. Lead free solders have been rapidly increasing and are having a high demand because of regulatory requirements in addition to their health and environmental benefits of avoiding any lead based electronic components. They are gaining more ground today in the different consumer electronics.
Tin/lead (Sn/Pb) solder alloys
The tin/lead mixture allows for a solder with a lower melt point than the two metals being bonded.
In Welding, the same base metal can be used, for joining the two parts together. Yet, copper, and other metals have a high melting temperature, so to overcome the difficulty in getting a high temperature for welding the material, the mixture of tin/lead is what enables two dissimilar metals, for example brass and copper, to be joined together.
By using a low melting temperature for the solder, fragile parts such as resistors, and capacitors can be joined electrically, into a circuit.
Tin/lead (Sn-Pb) solders- which is also named soft solders-are available commercially with tin concentrations between the range of 5% and 70% by weight. It is eutectic meaning that the alloy’s melting point is lower than that of the pieces being soldered. As tin concentration increases, the solder’s shear and tensile strengths increase as well. 60/40 Sn-Pb is one of the alloys which are commonly used for electrical soldering. It melts at 188 °C (370 °F) and 63/37 Sn-Pb is another alloy used mainly in electrical or electronic work. This alloy of these metals has the lowest melting point (183 °C or 361 °F) of all the different tin/lead alloys; and the melting point is a single point — not a range.