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86 SMT007 MAGAZINE I MAY 2020 Developing a reflow profile for electronic assemblies is like trying to figure out the time and temperature (bake profile) to bake turkey, chicken, and shrimp for the same length of time at the same temperature in the same oven with- out undercooking the turkey or overcooking the shrimp. The difference, however, is that using a bad reflow profile for electronic products is much more consequential than an undercooked turkey or overcooked shrimp and some disap- pointed guests you invited for dinner. The basic idea of developing a good pro- file is to make sure all solder joints reach the minimum temperature to achieve good solder joints but don't exceed maximum temperature to prevent damage to components or to solder joints. This is not an easy task, especially when you have a board with components of different sizes and thermal masses: BGAs, sockets, fine- pitch, BTCs, and 0402/0201, similar to the pre- vious example. Developing a Reflow Profile The good news is that we have the tools, tech- nologies, and processes to deal with the profil- ing challenge. What I plan to do in this and a few follow-up columns is to provide specific guidelines and rules for developing a unique profile for each product without any damage and warpage to components and boards and with minimum possible profile-related defects. More specifically, I will try to: a. Provide an overview of various types of thermal profiles, purpose, key require- ments, and challenges in developing thermal profiles. b. Explain the importance of different soldering zones—such as preheat, soak, reflow, and cooling—and their impact on solder quality. c. Discuss the details of how and where to attach thermocouples to achieve the desired soldering temperatures in various soldering zones. SMT Solver Feature Column by Ray Prasad, RAY PRASAD CONSULTANCY GROUP

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