The shape of the metal-free slice in the hole caused by such reasons is mainly manifested by the obvious copper in the copper plate of the defect, and the inner layer of copper is plated and thickened at the defect.
For deep-hole electroplating products, the aspect ratio tends to be large. In this case, the exchange rate of the syrup in the pores is significantly reduced, resulting in the copper layer in the center of the hole being often not dense enough during the PTH process.
In this case, if the inner hole of the plate has the design shown in FIG. 5 below, in the process of PTH rear plate, the inner layer copper A is not dense enough because of the excessive aspect ratio of the copper layer, which is not dense. After the board is energized, the potential is higher than B, because the B is electrically connected to the C phase through the inner layer of copper, so although A is closer to the orifice than C, the potential is still higher, and the ability to absorb copper ions is less than C. In the deep hole plating process, the solution exchange rate in the hole is slower, and the copper ion in the hole is relatively less.
Based on the above two points, in the process of plate electricity, when A is relatively less than the original copper ions, the ability to absorb copper ions due to potential causes decreases again, which directly leads to insufficient thickness of the electroplated copper layer, and A is in the subsequent process (outside Layer pattern and pattern plating) Pre-treatment causes open holes in the holes due to loss of copper, resulting in no metal defects in the holes.