Hello,
I’ve got a question about manufacturing boards with a high-enough Comparative Tracking Index (CTI) and solder mask applied. I think I’ve got an understanding on the subject, but since I basically lack both the experience and material/chemical knowledge, I would like to ask people here. Thank you for your help.
Let’s assume I have a PCB with solder mask (in order to get an understanding of how manufacturing for CTI works, please don’t ask if the solder mask is required). 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?
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). Is my understanding correct on these?
Thanks for helping me getting a grip on the subject.