Reducing the Impact of Stress on PCB Deformation through Mechanism Design
In earlier sections, WorkingBear briefly mentioned the possible solution by changing mechanism design to address the problem of solder cracking. One such approach involves replacing the SMDs (surface mount devices) that are prone to falling off with HTDs (through hole devices). This modification can significantly improve the strength of solder joints.
If you had studied the actual phenomenon of BGA solder cacking under a microscope, you should find that most BGAs start to break from the solder balls at the four corners. This is because the four corners of the BGA have the farthest distance from the force moment of the board bending, so they are also the positions that sustain the maximum stress during the board bending and warping, and of course, are the most likely to cause solder ball fractures.
In the previous article, WorkingBear talked about how to improve the adhesion of PCA to resist the impact of stress. Today, We will move on to another topic: “How to increase the ability of components or circuit boards to resist stress?” Because the maximum impact of stress on solder cracking is board bending, we only need to think about how to enhance the product’s ability to resist the stress impact caused by board bending to solve the problem of solder cracking.
PCB is composed of layers of Copper Clad Laminate (CCL) and Prepreg (PP) stacked together. In modern PCB manufacturing, CCL has become a standard material. Each CCL manufacturer provides customers with product specifications that indicate the peel strength of the CCL. From these specifications, we can see that the peel strength is higher when using 1.0 oz copper foil thickness than when using 0.5 oz. Different models and manufacturers of CCL also have different peel strengths, so selecting the appropriate CCL specifications is necessary to enhance the bonding force between the copper foil and PCB substrate.
Below are recommendations for BGA pad design to enhance the soldering strength from Workingbear.
We had several pages talking about the relationship between solder cracking and bonding force. Workingbear personally doesn’t think that making design a change to the pad of PCB can help much with the ability of BGA soldering to resist stress, as it is like a drop in the bucket! A board’s bending or deformation can easily negate all your efforts in improving pad design and solderability. Workingbear still thinks that strengthening the mechanism design and improving the board’s ability to resist bending and deformation is the best solution to fix BGA solder cracking.
