Lead-free Wave Soldering

Lead-free wave soldering can be achieved reliably and is being done in a large scale in Asia now forsome time. Lead-free wave can be more demanding to implement as a lead-free process, when compared to SMT and hand soldering operations. A solid understanding of the various principles of wave soldering will go a long way in reducing its implementation time but also insure reliable through-hole joints with a limited loss of production output. With traditional leaded wave soldering the use of 63/37 solder with its relatively low surface tension, tinned or tin-lead coated components and the use of well developed fluxes, wave soldering had become quite unchallenging. This is no longer the case; with lead-free solders the need to revisit the basic principles of soldering is required. The wave soldering equipment will have to be lead-free compatible. Due to the higher tin content of leadfree alloys such as tin-silver-copper, the leaching of iron can be an issue, which may require the solder pot, impeller and ducts to be replaced with materials, which prevent dissolution. This can be a capital expenditure ranging from a cost of $15,000 to $25,000 or more depending on pot size and features. In transitioning to lead-free wave soldering, alloy selection will be the primary choice that will impactsolder joint quality, reliability and production yields. Most assemblers are choosing tin-silver-copper alloys (SAC) for leaded solder replacement. On a global basis Sn96.5 Ag3.0 Cu0.5 has been the favored solder recipe. This alloy also known as SAC305 has melting range of 217-220 °C; the traditional alloy 63/37 has a melting point of 183°C. These alloys have higher melting temperatures but also have higher surface tensions.