Case: as shown in Figure 1, the crystal cold welding defective ratio is about 2%.

Figure 1: Cold welding on above soldering pin

Cause:

there are four blind holes on the second pin pad of crystal . As shown in Figure 2, some solder is absorbed, resulting in less solder on the pad and open welding.

Figure 2: 4 Blind holes on the soldering pad

Countermeasures:

Expand the stencil hole for the crystal 2nd soldering pin, increase the amount of solder and compensate the solder shunted by the blind hole. After the stencil hole was expanded, the crystal cold welding was not found in the production process, and the problem was solved.

Conclusion:

Because HDI hole is a blind hole, tin absorption problem should not occur in theory, but this is not the case. This case is of typical significance. It tells us that even a very small blind hole may cause the problem of less tin. Therefore, the design of punching multiple blind holes on the pad should be resolutely eliminated in the design. If this design is necessary, the blind holes must be electroplated and filled with copper.