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 for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################