Hello Hans, I have actually had the same problem before. I was using permanganate desmear chemistry as a hole cleanup. Before the desmear process I had no evidence of negative etchback, but after up to 1.5 mils. The root cause was a short from the electric heater grounding through the rack. After it was repaired the problem went away. Joe Dickson Dir of Engineering Tyco Santa Clara > > >>> "Hinners, Hans - LYPME" <[log in to unmask]> 04/20/99 01:15PM >>> > Hi All, > > I have a mystery on my hands and I hope somebody out in cyberland can help. > > We have a 10 layer board made out of 1 oz. FR-4 material. Tg = 140 degrees C > which is intermittently showing negative copper etchback during the > electroless process (using Atotech chemistry) but, only on a few layers. > > For instance, layers 2,4, and 6 have negative etchback but layers 1,3,5,7-10 > are fine. This etchback feature is not apparent in the (plasma) desmear > coupon, the process in-between being drilled and electroless copper plating. > The only distinguishing feature of these layers is that they are all thermal > layers (which are mostly solid copper). I'm at a loss to explain how the > layers being solid relates to their etch characteristics but it's the only > thing that jumps out as being unique. To make it even more confusing > another thermal layer came out okay, layer 9. > > We have also seen this on a 17 layer board where a thermal layer has > negative etchback but everything else is okay. > > E-mail me directly and I will send you two jpegs of my cross-sections (only > 200k!) so you can see what I am talking about. > > Anybody seen this before? Suggestions? Comments? Questions? > > Thanks a bunch! > > Hans > > Air Force Material Command - We keep them flying! > ~~~~~~~~ > Hans M. Hinners WR-ALC/LYPME Bldg. 640 > Materials Engineer 380 Second Street, > Suite 104 > Manufacturing Eng. Sec. Robins AFB GA 31098-1638 > 912-926-1970 (Voice) 468 - 1970 (DSN) 912-926-7974 (Fax) > [log in to unmask] > > ################################################################ > TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c > ################################################################ > To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: > To subscribe: SUBSCRIBE TechNet <your full name> > To unsubscribe: SIGNOFF TechNet > ################################################################ > Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section fo r additional information. > For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 > ################################################################ > > ################################################################ > TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c > ################################################################ > To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: > To subscribe: SUBSCRIBE TechNet <your full name> > To unsubscribe: SIGNOFF TechNet > ################################################################ > Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. > For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 > ################################################################ > > ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################