In the contemporary era of the increasing development of electronic products, in order to pursue the smallest possible size and intensive assembly of plug-ins, double-sided PCBs have become quite popular, and more and more, designers in order to design smaller, more compact and low-cost products. In the lead-free reflow soldering process, double-sided reflow soldering has been gradually used.
Double-sided lead-free reflow soldering process analysis:
In fact, most of the existing double-sided PCB boards still solder the component side by reflow, and then solder the pin side by wave soldering. Such a situation is the current double-sided reflow soldering, and there are still some problems in the process that have not been solved. The bottom component of the large board is easy to fall off during the second reflow process, or part of the bottom solder joint melts to cause reliability problems of the solder joint.
So, how should we achieve double-sided reflow soldering? The first is to use glue to stick the components on it. When it is turned over and enters the second reflow soldering, the components will be fixed on it and will not fall off. This method is simple and practical, but it requires additional equipment and operations. Steps to complete, naturally increases the cost. The second is to use solder alloys with different melting points. Use a higher melting point alloy for the first side and a lower melting point alloy for the second side. The problem with this method is that the choice of low melting point alloy may be affected by the final product. Due to the limitation of working temperature, alloys with high melting point will inevitably increase the temperature of reflow soldering, which will cause damage to components and PCB itself.
For most components, the surface tension of the molten tin at the joint is sufficient to grip the bottom part and form a high-reliability solder joint. The standard of 30g/in2 is usually used in design. The third method is to blow cold air at the lower part of the furnace, so that the temperature of the solder point at the bottom of the PCB can be kept below the melting point in the second reflow soldering. Due to the temperature difference between the upper and lower surfaces, internal stress is generated, and effective means and processes are required to eliminate stress and improve reliability.
Post time: Jul-13-2023