5/2/2024 0 Comments Leaded solder reflow profileAfter tin/lead components have been reflow-soldered, use selective soldering with a laser to place and solder all lead-free BGAs. Do not place lead-free BGAs with other tin/lead components. Use the standard tin/lead reflow profile with peak reflow of 210˚ to 220˚C for all components except lead-free BGAs. What kind of reflow profile should be used? There are two options: If the tin/lead profile with maximum peak temperature of 220˚C is used because all components are tin/lead, BGA balls will reflow partially, or not at all, creating a serious solder joint reliability issue. The real problem arises when using lead-free BGAs on a primarily tin/lead board. There is no issue when using leaded components with lead-free surface finishes. It is not economical for component suppliers to supply both tin/lead and lead-free versions of the same component. Let’s look at backward compatibility, in which some components are only available with lead-free surface finishes. Backward- compatibility issues in which some lead-free components must be used on a primarily tin/lead board can compound the problem further. ![]() The same is true for smaller, temperature sensitive components requiring lower peak temperatures for shorter durations. Temperature for longer durations, a tighter process control is required to achieve good soldering results in lead-free assemblies. As discussed in my February column, to accommodate constraints imposed by large components with high thermal mass requiring higher peak
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