Why don’t the electronic components on the first side of the double-sided PCB fall off due to re-melting of the solder during the second time reflow process in the SMT oven? How much does the melting temperature of the lead-free SAC305 solder alloy increase during the second time reflow process? Perhaps it’s because the components on the first side are more well-behaved and don’t cause trouble! This is just a joke, of course.
BGA solder joint cracking has always been a nightmare for electronic assembly (industry) manufacturer, and there are many reasons that are beyond the control of assembly manufacturer, but the final result is often required to be borne by assembly manufacturer.
There are many reasons for BGA solder joint failure, but the main reason comes from PCB deformation, resulting in solder joints to be break under bending stress. PCB deformation usually comes from two reasons:
A question from a netizen, “In the past, many mobile phone PCB assemblies would use Underfill depositing under the BGA package to enhance the mechanical strength of the solder joints. However, it has been found that most mobile phone assemblies no longer use underfill today. Is Underfill still necessary for the BGA on PCB? What is the relationship between using or not using Underfill and product quality? How should it be defined?”
Questions from a newcomer about electronic manufacturing assembly process: Since there are already solder balls locate on the BGA substrate, why is it necessary to apply solder paste on the PCB pads during SMT reflow? Is it necessary to apply solder paste during BGA repair? And how should we apply solder paste to the corresponding pads on the BGA when there are other electronic components around the BGA?
Before the development of Surface Mount Technology (SMT), almost all printed circuit board assemblies (PCBAs) had to go through the process of wave soldering to achieve the purpose of soldering electronic components to the board.
The process of “wave soldering” gets its name from using a large pool of molten tin during the soldering process. This pool of tin is heated to a temperature where the solid tin bar can melt and form a solution. This molten solution can be thought of as a “lake”. When the lake is still, it is called a “laminar wave”. When the lake is agitated, it becomes a “turbulent wave”. The PCB is like a boat sailing on the surface of the lake, allowing the molten tin solution to adhere to the electronic components and the PCB. After the soldered parts pass through the molten tin, it rapidly cools and solder the electronic component to the PCB.
