Results of experiments on PTH parts.

Use of low-temperature solders (LTS) is growing in popularity. LTS are predominantly composed of tin and bismuth, with a small quantity of a “special blend” of other elements to suit a given manufacturer’s performance specifications. The opportunity, as the name suggests, is to create solder joints at far lower temperatures than those required for tin/silver/copper (SAC) alloys, and which are even lower than that needed for the (historic?) tin/lead eutectic solder. These LTS have a melting temperature of ~138°C. The benefits of using LTS mean no Pb is present in the joint, and lower processing temperatures can be used. Using lower temperatures means reduced energy consumption during manufacture, lower manufacturing costs and reduced greenhouse emissions. In addition, it offers the opportunity to use different, thinner and possibly cheaper PCB substrates and components compared with those used today. This obviates the “overengineering” required of today’s boards and components to mitigate warpage, which due to LTS are operating close to the glass transition temperature of the board material. It also makes it possible to rework SAC area array package joints with low-temperature alloys.

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