Susan Here's my opinions: 1) REAL ESTATE. When holes only go halfway or part way through a board, the hole and associated pads don't take up space on all layers. This gives more routing room to designers to run traces, where a normal through via would not allow. 2) & 3) Blind and buried via's "typically" get filled with resin during the lamination step(s). I can't imagine a case where you prevent the holes from becoming filled. 4) I wouldn't say they are required to be capped with plating and or soldermask. As part of the natural process after lamination, boards see an e'less deposition (direct platers, no offense) and electroplate of coppers. This tends to "cap" the blind via's. I have seen cases of "thermal via's" actually being depth drilled after lamination to remove some of the resin. During thermal cycling, the resin will soften and "move" and can cause the plating on the surface to break away or lift. I would offer some pictures of the above conditions, but I'm not very skilled in ASCII art, as are some of our fellow `netters. Please feel free to call me to discuss or perhaps I could FAX you something! Regards, Tom Bresnan Product Eng'g Mgr MULTEK 16 Hammond Irvine, CA 92718 714.951.3388 714.951.8794 FAX [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: Unidentified subject! Author: [log in to unmask] at internet_gateway Date: 2/18/96 12:09 PM ding Blind Vias in multilayer printed boards. 1) Why would someone want to use them? 2) If used are they always filled? 3) When does the filling operation take place? 4) Are they required to be capped by plating or solder mask? I am looking at a lot of multilayers with blind vias and need some help in understanding the manuf process. Thanks, Susan Mansilla Robisan Laboratory