Measures for PCB Substrate 1
PCB board substrate plays really important role in ensuring the board quality. This article lists 4 common problems caused by PCB substrate, just for your reference.
Dried PCB Substrate
Analysis: Dry is a very troublesome issue, the seriousness one is fully dry, the slight one occurred in the corner. The reason for this may be that the compatibility between the coupling agent and the resin is poor, leading to poor wet out.
Also, it is possible that the film is overcured, thus the resin does not flow well during lamination. If the resin flow is low, it can be a forewarning to substrate dry out, and dry substrates can easily delaminate during solderability testing.
Solution: If the problem occurs due to the finish of the glass cloth, it must be solved by the supplier. If the glue flow is low, it’s better to reduce the gelling time (S/G) of varnish, or improve the gelling time (P/G), plastic content (R/C), etc.
WAC/WAE(White at Corner/ White at Edge)
Analysis: When the resin flow rate is too high or absorb the moisture due to poor storage conditions, it is easy to press large flow. As the film heats up, the resin diffuses from the center to the periphery in an anisortropic manner. As a result, the resin water content is lower. When this part can not be completely avoided, weaved WAC and WAE will appear.
Another possible reason is the rapid heating rate, resulting in a large temperature difference between the inner and outer layers, and the uneven resin flow in each block.
Thus, WAC and WAE are easily formed when pressing. In addition, the resin contains many tiny bubbles and microvoids. When the resin flow rate is low, the bubble is still on the board edge and can not escape smoothly out of the plate. Under such circumstance, WAC and WAE also tend to be formed. It also shows a white corner and white edge.
Solution: If the resin flow is high, adjust the resin by increasing the gelling time (S/G) of varnish or decreasing the gel time (P/G) of the resin. If the WAC or WAE is caused by the low resin flow, you can solve it by adjusting the treating specification or pressure parts.