Sujet: Soldermask requirements for high-CTI boards

Soldermask requirements for high-CTI boards

This is not really a question that is specific to Beta Layout services, but a question that concerns general high-voltage PCB manufacturing. I'm asking here because a PCB manufacturer like Beta Layout is probably among the most qualified to answer this question.

Let's assume I have a PCB with solder mask. Let's also say that the PCB's FR4 laminate is made of high-CTI material. The question: If the solder mask is only normal/low CTI, will it reduce the CTI-rating of the finished board?

Of course, the presence of a solder mask is not required to get high-CTI. But my question explicitly relates to the case when there is solder mask on a high-CTI board.

My understanding is that CTI (although it also depends on the material thickness) is primarily a surface material property. That is, a low-CTI coating applied to a high-CTI base will not have the same high-CTI performance as the base material itself. Also, given a high-CTI coating, due to the dependence on material thickness, to get the high-CTI rating for the whole product, the coating either 1) needs to have a high enough thickness, or 2) the base material will also need to be high-CTI. That is, it is possible to have a high-CTI product if only the solder mask is high-CTI (depending on the mask's properties), but it is never enough to make only the base laminate high-CTI but not the solder mask (assuming that there is a solder mask at all). Am I correct on these points?

Thank you for helping me understand how CTI requirements work.
18/11/2018 02:11:23
Soldermask requirements for high-CTI boards