Tin/Silver Alloy (SnAg) : Applications
Tin/silver alloy is commonly used as solder. SnAg is a lead free alloy which is widely used in consumer electronics because of new legislations.
Tin/silver Alloy solder
The Tin/ silver alloy is a widely used alloy system to replace tin-lead due to its high mechanical strength, thermal fatigue properties, and wettability. Tin/silver alloys were developed to replace the solders containing lead. Typically, tin/silver alloys contain 3-5% silver. SnAg solders are used for interconnect applications which need high temperature and reliability. Solder joints using SnAg alloys can maintain superior high temperature strength than tin/lead solders.
The Tin/Silver alloy is used in electronic assemblies and thick films. In Soldering applications the use of lead is prohibited as in pipe joints for drinking water and soldering of jewelry as the alloy can maintain high brightness levels.
Tin/Silver alloy is gaining more demand as awareness of the environmental effects of lead in industrial products is increasing, and as a result of Europe’s RoHS legislation to remove lead and other hazardous materials from electronics.
What is the soldering process?
Soldering process 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 that the alloy suitable for use 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 need to possess proper electrical characteristics.
Tin/Silver alloy solder in solar industry
SnAg is among the few alloys commonly used in the solar industry. These alloys can be pared down into three types as below:
- SnPb alloys (63Sn37Pb, 62Sn36Pb2Ag)
- SnAg alloys (96Sn4Ag)
- BiSn alloys (58Bi42Sn, 57Bi42Sn1Ag)
After the SnPb alloys which are the most attractive selection, Pb-free alloys are becoming more popular driven by the increasingly attractive green technologies.
SnAg has become the most widely used as a Pb-free solder alloy, particularly in tabbing ribbon designed for cell interconnection. In designs where step soldering is required (although this is uncommon in back end solar module assembly), SnAg can be used as the primary step prior to soldering with Sn63 or similar Lead free solder (though carefully as the second soldering temperature is near the 221 C).
While the Tin/Silver alloy eutectic solder is a needed composition for the soldering of electronic components, for example, power semiconductors, recent studies using the SnAg alloy for stringing of solar modules have shown that the other common alloys used for this application are easier to work with and better designed for meeting the requirements of this particular application of solar assembly. The melting temperature of SnAg is low, and the ideal fluxes for the assembly of modules are not optimized yet for this solder composition.
Yet, Tin/Silver alloy has other benefits, as it is the perfect choice when solder that melts slightly above the melting point of the standard solder alloy is required, and still be lead free.