Short synopsis of how wedge voids are born: During drilling, small amounts of vibration of the bit against copper planes in an ML can do some damage to the resin around the holes created. This damage or fracturing is then invaded by the solvent/sensitizer solution of the permanganate desmear process. The permanganate bath then preferentially etches this already loosened resin, forming the "wedge" in severe cases. It can be big or very small, depending on the amount of fracturing to that resin area. Acid attack to the oxide can begin as early as the acidic neutralizer in the permanganate process, but the microetch on the electroless or DM line is a more likely candidate. Often the electroless copper will fully cover the wedge area and "seal" it from further attack during acid copper plating. Pink ring is known to be an indicator that there may be a wedge void. Meaning that, if you have a wedge void, you most certainly have pink ring, but you may have pink ring without the wedge void. But remember, it all starts way back in the beginning, even before drill, if the lamination process is not optimized (heat rise, pressure, temp., cool down, etc.) or if the prepreg is aged and does not fully penetrate the oxide structure during lamination. Optimizing a drilling operation helps to minimize any damage done by a drill bit. See Glenn's paper - it can be done. Small holes and closely spaced holes are usually the most affected. I always preached that, unless you laminate and drill correctly (at least with the best possible process), nothing you do later on will "fix" the problem - it can only get worse. Then the oxide post-treatments came along and either hid the pink ring so you didn't see this "process indicator", or actually provided more/better adhesion of prepreg to the oxide. Note that you won't see pink ring from the surface unless the oxide layer is facing outward! Patty ---------- From: Miscantor To: TechNet Subject: Re: Re[2]: Mechanism of Wedge Void Formation Date: Thursday, July 17, 1997 6:49PM Patty - good reading material - unfortunately haven't read till u mentioned. would like to dispute Lenny's views - have seen too many cross sections to know otherwise. Whenever pinkring occurrs - look at those cross sections carefully - u will notice some sort of copper folding after plating - means had to be minor space - most llikely filled with air - then solution - whether plain shifting or whatever - the wall has either a gough in it - or minute fracture in the oxide layer. Reduced oxide is nice - but is the oxide layer reduced chemically or is it being chemically etched back - be careful when ur chemical supplier says " we have reduced oxide".Can SERA determine breakdown product is left in? When does the reducer have to be changed? And when we speak about multi-layers - 4 - 6 - 8 - 10 - what happens on 16 layer boards - 20 layers? Saw some occurances happen this year on some pretty thick boards - hydrolization of the reducer - ain't a pretty sight when a 20 layer board seperates. Final conclusion as to how and why? Will know in a month or so .... will try to remember to pass info on. Little pressed for time these days .... once i get freed up will try to forward this info through the net. Yes - reduced oxide does help out when using DM - to an extent - but drilling is still where it starts - from there - your guess is as good as mine as to where the acid attack occurrs. best regards Richard Fudalewski Atotech Canada Ltd *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To subscribe/unsubscribe send a message <to: [log in to unmask]> * * with <subject: subscribe/unsubscribe> and no text in the body. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * *************************************************************************** *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To subscribe/unsubscribe send a message <to: [log in to unmask]> * * with <subject: subscribe/unsubscribe> and no text in the body. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************