I have a customer who has asked what is the required spacing on both innerlayers and outerlayers for 1500 VAC (~2100 VDC). Outerlayers have dryfilm soldermask covering them. I looked up IPC-D-275 and have referenced the data from table 3-1. This customer feels these values are extremely conservative and is curious if other designers are using that criteria rigidly? [log in to unmask]