Duane J Marcroft wrote: > Doug, > I've been recommending clearances of 2mm (0.080") for over 20 years. I > have also used 2mm for PCB's that are required to meet UL 1950. The > creepage and clearance for Tip-GND, Ring to GND, Tip-GSELV and Ring-GSELV > have never been a problem. > With one exception: Some unscrupulous PCB Mfgr's cut there materials > costs on multilayer PCB's by purchasing board material for 6 layer, 10 > layer and 16 layer PCB's. To makeup a 4 or 8 layer board they mix and > match layer material to get the correct thickness. This has cost me and > companies I worked for some tough problems to solve. That is to say if > you are relying on a certain amount clerance or insulation between layers > this maybe a problem. The problem's I experienced were caused by pin > holes in the layers and arcing occured between traces that were on opposite > sides of a layer and opposites sides of the barrier. This problem only > occured when we changed to a new board vendor. > My advice is not count on the clearances between layers. What passed > today might not pass tomorrow. On last comment I'm using 3.5mm (0.140") of > clearance for worldwide designs.
Interesting that 'between layers' of say FR4 with a dielectric constant of little over 4 would be a problem. It should multiply the air clearance by a factor of 4. I've only had a problem once that sounds similar to yours but it was during the early prototype stage and we wrote it off as such. It never surfaced during production. Thanks for the input. ******************************************************* Doug McKean [email protected] ------------------------------------------------------- The comments and opinions stated herein are mine alone, and do not reflect those of my employer. ------------------------------------------------------- *******************************************************
