Avoiding PCB soldering defects rests largely on whether or not a thermal profile is correctly developed. These defects can arise from reflow, wave soldering or hand soldering. However, the most prone to defects is reflow soldering for SMT.
The reason is reflow soldering is more complex compared to the other two sources of soldering. Reflow soldering requires a correct thermal profile to be developed and utilized. Most often, the usual industry practice is to develop a thermal profile recipe for a small board, medium board, and large board.
=Then, depending on the assembly job, one of these three profiles is selected for reflow soldering, and assembly is performed using this scheme. This is not the proper way and the result is an unusually higher numbers of solder defects, either open solders, cold solders or a combination of the two.
Here are some tips to follow to help you avoid solder defects in your upcoming PCB assembly projects.
- Keep in mind one size does not fit all when it comes to thermal profiles.
- Ask your PCB assembler what factors they consider when developing your thermal profile.
- If your board has a number of power and ground planes, more higher temperature cycles at different oven zones are required before it is ready for reflow.
- Hybrid board with eutectic and lead-free components demands special attention and different considerations.
- For lead-free assembly, correctly pre-heating reflow oven temperatures are crucial for proper soldering.
- Thermal couples must be accurately used to create a correct thermal profile.
A marginal product results if a perfect thermal profile isn’t dialed in. Even after passing stringent test, a marginal PCB may experience intermittent connections or fail in the field. It then comes back to the EMS provider with solder joint problems that need to be reworked. Also, running a thermal profile tailored for a lead-free PCB and using it on a eutectic board can have devastating effects because an extreme amount of heat is placed on the components, thereby damaging them.