Thomas, Yes, this ttype of phenomenon has been observed previously by anyone who has done temperature/humidity/bias (THB) test on bare and assembled PCBs. Look at Figures 6.62 (a) through (d), page 223, chapter 6 in 'Failure Modes and Mechanisms in Electronic Packages', published by Chapman & Hall ( available at http://www.wkap.nl, Kluwer Academic Press). Via to via, plane to via and line to line migration growth shown are from real product failures. Pages 222- 233 discuss the migration failur in more details. Without looking at picture of your specific failure(s), it is difficult to discuss your root cause. In general if you have - 1) moisture, 2) ionic contamination and 3) voltage, there is high probability of migration to occur. The mechanism goes something like this- at anode: meta l> metal(+) + ne(-) and H2O > 1/2 O2 + 2H(+) + 2e(-) at cathode: metal(+) + ne(-) > metal and H2O + 2e(-) > H2 + 2OH(-) Metal ions at cathode start accumulating and grow like a dendrite towards anode causing an electrical short. Thomi wrote: > Dear Technetters, has anyone come across a root cause for electric > shorts between neighboring copper lines of different potential within > a layer laminated with RCC (resin coated copper)? We have carefully > ground away layers 1+2 from one side, and layer 4 from the other, to > find a (ca.) 1 micrometer diameter filament connecting two neighboring > lines in layer 3. Cross sectioning this further, we could analyse this > filament by using SEM/EDX and found copper. The surrounding resin > shows peaks of Bromium (probably from flame retardants) and Aluminum > (??Al2O3 filler material??). The electric short was not detected > during bare board testing, but occured within one week of functional > testing of the full assembly in an environmental chamber operating at > 120°C (I wouldn't believe it!). Is there a certain resin condition > under which copper migration is enhanced within the RCC-resin (however > close to the interface with the core to which the RCC is laminated)? > There is a recommendation to ensure driving/baking out humidity from > the multilayer, which makes me somewhat suspicious, but I don't know > enough about the constituents (resin, hardener, flame retardant, maybe > filler material) to try and explain what happens > electrochemically. Best regards, Thomas Ahrens, Memellandstr. 8, > D-24598 Boostedt > Tel. ++(49) (0) 4393 97769 e-mail [log in to unmask] > Bitte beachten - please note: > - Mails groesser als 2 MB werden nicht angenommen > - messages larger than 2 MB will not be downloaded -- ____________________________________ Regards, Pratap Singh Tel./Fax: 512-255-6820, e-mail: [log in to unmask] or [log in to unmask]