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It has been a while since the US government banned the use of lead in soldering alloys, since it was toxic and a hazard to the environment and human health. Earlier, solder wires used to consist of a 60-40 ratio of lead and tin, which was a universal combo that got all jobs done satisfactorily.
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Three Guidelines to Use When Choosing a Lead-Free Solder Wire It has been a while since the US government banned the use of lead in soldering alloys, since it was toxic and a hazard to the environment and human health. Earlier, solder wires used to consist of a 60-40 ratio of lead and tin, which was a universal combo that got all jobs done satisfactorily. Today, there are many alloys available which are lead-free, but since they are relatively new, people find it difficult to select which is suitable for the job they are going to perform. Here are three guidelines to use when choosing a lead-free solder wire. Guideline #1: Flux content Tin and lead-based solders had a good wetting property. Wetting property of solder is the property which helps it adequately wet the surface on which it is spread, which enables good cleaning of that surface, thus eliminating all chances of impurities getting stuck in between. When purchasing a lead-free solder, you can check for the flux content that solder carries by weight. Lead-free solders like tin-antimony, tin-silver-copper and tin-copper usually wet slower than tin-lead solders, which makes it important to compensate this shortcoming with flux. A flux content of 2% by weight is a good flux content to choose for satisfactory wetting from a lead-free solder. Guideline #2: Temperature Lead-free solders have higher melting points as compared to the typical tin-lead solders that used to be available a few years ago. Higher melting points of lead-free solders would mean that you would either need to carefully pick the components so that they are not sensitive and likely to warp or get damaged by high temperatures, or you would need to select a lead-free solder alloy which melts at a lower temperature to prevent warpage. Guideline #3: Flux distribution Flux distribution means the density of flux present in the cored lead-free solder wire. A density of 1g/cc is common in lead-free solder wires with a two to three percent flux content by weight. Presence of more flux per cubic centimeter of a cored lead-free solder wire would ensure better wetting than a coil with less amount of flux per cc. Use the guidelines above to ensure that you purchase the right lead-free solder wire for your application.
