Steve, That extra layer of solder mask will result in much more volume of solder paste deposited, and even more where the silk is close to the pads. Not a good situation. We have seen this on 1oz copper boards that have white solder mask supposedly for the same reason. We had to instruct our pcb suppliers that this practice is not acceptable, and in some cases had to remove silk from areas near pads for fine pitch, QFN, LGA, CSP, etc. Steve Steven E Herring Director of Engineering Pennatronics Corp -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory Sent: Tuesday, February 19, 2019 12:14 PM To: [log in to unmask] Subject: [TN] Double masking... Hi All, Seeing that there is a recent solder mask thread, I have a question about double masking. We have an assembly that we're building that has a 15.7-mil pitch QFP and 0201's on the assembly, so when I ordered my stencil I spec'd .004 thick foil and 8-mil wide apertures for the QFP (since there's no solder mask web between the pads) and 13-mil squares for the 0201 pads. The 0201's did great but I had a ton of bridging on the QFP! That really surprised me. I started looking at the PCB a little closer and noticed that there was a double layer of solder mask on the board. Here's a couple of photos: https://photos.google.com/share/AF1QipNeiheoq_Go0K7zsQY_iF6vfJk_YNws-6UlCC6i3z7p5LHn-HSQ31rVj-Cl-EJ-xg?key=bUJEdkRsQzlaOUkzcWdLaXI3dEI2TV91V2lhbHlR I inquired the board shop why there was two layers of mask on the board and was told that because of the 2-oz. copper weight being called out on the outer layers, it required two layers to get complete coverage and not have it thin out on feature edges. Lines are at 8-mils and space is 6-mils. That doesn't seem too extreme to me. Is that really true? I've built boards before that had way more than 2-oz. copper that didn't require double layers of the mask to ensure good coverage, but those weren't boards that had 15-7-mil pitch devices and 0201's on them either. -- Steve Gregory Kimco Design and Manufacturing Process Engineer (208) 322-0500 Ext. -3133 -- This email and any attachments are only for use by the intended recipient(s) and may contain legally privileged, confidential, proprietary or otherwise private information. Any unauthorized use, reproduction, dissemination, distribution or other disclosure of the contents of this e-mail or its attachments is strictly prohibited. If you have received this email in error, please notify the sender immediately and delete the original.