The reflow profile must meet the specific requirements of solder paste and the critical value of heat treatment for PCB assembly. Achieving an accurate profile curve is critical, so an accurate data recording system and a properly tested circuit board must be used. Lead-free solder paste will not change the basic principle of reflow soldering. However, they do significantly reduce the size of the heat treatment window, thus making reflow a more critical step on the assembly line, affecting the yield of qualified products.
It should also be noted that most solder defects originate from the solder deposition stage, either due to improper printer parameters, or due to template damage or improper design, or insufficient amount of solder paste. A few years ago, a legendary study conducted by Hewlett-Packard showed that up to 60% of soldering defects in the PCB assembly process are caused by this reason. The subsequent experience of the author and user is consistent with this number.
The initial design of the circuit board, especially the geometry of the pad and the parameters of the solder mask, also have a profound impact on the quality of soldering. Good design for manufacturability is the basis for achieving low welding defects. Finally, the quality of welding materials is also the most important. In addition to high-quality (qualified) solder paste, there are also parts and boards with good solderability. Controlling procurement and storage of parts and PCBs is essential
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