How To Design PCBA Assembly Reliability
Assembly reliability, also known as process reliability, usually refers to the ability of the PCBA to not be damaged by normal operations during assembly and soldering. If it is not designed properly, it is easy to damage the soldered joints or components.
Stress sensitive devices such as BGAs, chip capacitors, and crystal oscillators are easy to be destroyed by mechanical or thermal stress. Therefore, they should be placed in areas where the PCB is not easily deformed, or be reinforced, or take appropriate measures to avoid being destroyed.
(1) Stress-sensitive components should be placed as far away as possible from where bending occurs during PCB assembly. In order to eliminate the bending deformation when the daughter board is assembled, the connector connecting the daughter board and the mother board should be placed on the edge of the daughter board as far as possible, and the distance from the screw should not exceed 10mm.
As another example, in order to avoid stress fracture of BGA solder joints, BGA layout should be avoided in places where PCB is prone to bending. The bad design of BGA can easily cause cracks in the solder joints when the board is held in one hand.
(2) Reinforce the four corners of the large BGA.
When the PCB is bent, the solder joints at the four corners of the BGA are subjected to the most stress, and cracks or fractures are most likely to occur. Therefore, it is very effective to strengthen the four corners of the BGA to prevent cracking of the solder joints at the corners. Special glue should be used for reinforcement, and patch glue can also be used for reinforcement. This requires leaving space for component layout and indicating the reinforcement requirements and methods on the process documents.
The above two suggestions are mainly considered from the aspect of design. On the other hand, the assembly process should be improved to reduce the generation of stress, such as avoiding holding the board with one hand and using support tools for mounting screws. Therefore, The design of assembly reliability should not be limited to the improvement of the layout of components, but more importantly, it should start from reducing the stress of assembly-using appropriate methods and tools, strengthen the training of personnel, and standardize the operation actions. Only in this way we can solve the problem of solder joint failure in the assembly stage.
