The Process for Resin Plugging Hole and Its Defect

- Oct 23, 2017-

Sometimes we make resin plugging holes in the PCB production process, that's because generally we need to make vias between pads and pads, and make circuits through the vias in the back of PCB board.But if BGA too thick offen cause via can't walk out, you can directly drill from the PAD to make via and walk the line through other layers, then fill the via with resin and plate copper flatly to be a PAD, this process is known as VIP process (via in pad). If just make via on PAD and no resin plug hole, it is likely to cause leakage tin which lead to short circuit on the pcb back and empty welding of the front.

At present generally the resin plug hole production process is that, after the inner core board hole metallization, use special resin ink filling the hole,after curing using dedicated ceramics high cutting brush roller or abrasive belt grinding flating, then remove excessive resin and do subsequent graphics. 

If plugging didn't seal good, when there are bubbles in the hole,becuase bubbles are easily moisture absorption, the board could explode when do hot air levelling through tin stove; but if bubbles in the hole in the process of plugging hole, bubble will be extrusion when baking resin, which cause highlights in one side and concave in the other side, at that point can find out the defective boards.

The main defects of resin plug hole are: concave, void, crack. Concave can be solved by controlling the plug hole plumpness, crack is generally associated with resin its composition and curing parameters. While for the void, when it locates the hole neck, the concave lead by void break after grinding will seriously influence the reliability of the plug hole.

According to the void echanismand and a large number of experimental results, for the common plug hole method, it is difficult to fundamentally solve the problem of plug hole void. Using the vacuum plug hole method and do vacuum deaeration for the recycled resin, can greatly reduce bubbles in the resin, and have very big improvement for the bubbles. On the other hand, the production efficiency of vacuum plug hole and resin utilization are lower, which leads to higher production cost. For common blind /buried PCB, because in plug hole position there is no weld or fold hole, the existence of the plug hole bubble has little influence for the quality, so using ordinary plug hole method can satisfy the quality requirement. Therefore, suitable plug hole method can be selected according to the product structure.