Recently WorkingBear got complaint from R&D and ask increase the solder paste volume on the MLCC (Multi-Layer Ceramic Capacitor) component pads to improve the capacitor broken issue. R&D said he had verified that the capacitor’s footprint in the board design is correct and followed manufacturer’s design guidelines. However, looks like there is not enough solder paste to form proper heel fillet on the terminal of capacitor. This insufficient solder paste volume make the solder cracking?
Well, WorkingBear reviewed the picture provided by RD and found this MLCC component shall be damaged by the stress from the board warpage. It better to find out what make the board warpage and break the capacitor and not ask SMT to increase the solder paste volume. Because of the soldering fillet is good and without soldering damage from the broken picture show. The broken start from the MLCC soldering edge and not break the solder. As experience show really don’t think this capacity broken can be improved by solder paste volume incensement.
I strongly think the stress may come from outside of product. Maybe the drop impact make the board warpage or cable insertion wobble the board. Because of this product apply 1.2mm thickness of printed circuit board and one type-A of USB connector is closely to this damage capacitor component. People plug/unplug the USB cable will give a push and twist force. It is easily to twist the circuit board. I finally got the feedback that this capacitor broken came from the tumble test.
By the way, my experience tell me that increase solder paste is nothing help on the MLCC crack improvement. Reviewing this capacitor will find its broken position out of its soldering pad. That means no matter how many solder paste volume be increased the solder always can’t over its heel pad. More solder paste may give more stress under the capacitor because it may lift the capacitor body and give more chance to bend the capacitor.
As experience tell me below solutions may help to solve this kind of MLCC broken issue:
1. Enhance the board strength
Increase board thickness or apply high TG material will enhance the board strength to give more robust to against stress.
2. Apply mechanical structure to support the board
It better to apply the strain gage to measure the stress location and direction then design mechanical structure to support or hold the board to prevent the board from bending during tumble or product impact drop test.
3. Choice the MLCC or capacitor component with longer soldering pads
We usually find the different capacitor supplier provide different size of solder pads. As WorkingBear experience show if the soldering pads from same size of capacitor is longer than others then its anti-stress ability will be better. This shall be longer soldering pads will reduce the air gap size and reduce the stress effect due to the lever effect.