Good Morning All! I think I've got a case of folks comparing apples to bananas. I'm trying to predict % defects due to inner layer shorts and compare across part numbers. Folks are looking at one part number and saying, "12 layer board with 7% inner layer shorts (of the ones tested) and looking at another part number - 24 layer board has 18% inner layer shorts. You are screwing up more on the big $$$ board - fix it!" Shouldn't inner layer shorts be a linear or geometric relationship? For example, take a 10 layer board, it has 5 signal layers (50-50 signal & plane). Each signal layer will have a certain surface area where traces are packed close enough together that a sliver of metal could cause a short. At electrical test I fail a certain percentage of boards due to shorts - say 10%. Now take a 20 layer board and say it doubles the surface area that could have a short. The failures due to inner layer shorts should be double the 10 layer board or 20%. If the boards were manufactured at the same time the process should, on average, contribute the same number of shorts/area to each. Inner layer short defects come from multiple sources that produces a finely boned fish - metallic contamination, poor IL etching, poor IL imaging/development, missed in IL AOI, equipment, material, method, people - ad nausem. . . And for now I'm ignoring test escapes. The inner layer short generation fluctuates over time but has some average value per area. So I propose a simple equation: Inner Layer Defects = (average # inner layer shorts/surface area) (total critical surface area) Looking at the artwork should get me the critical surface area, the inner layer defects we know from Electrical Test so a graph of defects vs. surface area should get me the shorts/area for the total process, no? Then I can say when the process has changed versus merely a higher tech board being processed. Anybody hit this wall before? Is there a flaw in my logic? Hans PS. If memory serves, I remember Bev mentioning Technetters' lack of gender identification skills at that "Stump the Chumps" session we had a few years ago. And I can relate - every once in a while people see the middle name (Michel) and think "must be a groovy chick". Integrity First - Service Before Self - Excellence in All We Do ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Hans M. Hinners Electronics Engineer Warner Robins - Air Logistics Center (WR-ALC/LUGE) Special Operations Forces System Program Office (SOF - SPO) Gunship Team 226 Cochran Street Robins AFB GA 31098-1622 mailto:[log in to unmask] Com: (478) 926 - 5224 Fax: (478) 926 - 4911 DSN Prefix: 468 --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------