As you surmised, the condition you described is most likely moisture related. The prebake requirement is entirely dependent on the part construction and adhesive type. Typically something like 250F for 30 min. is used. Some combinations do better with a 275F bake for 2-4 hours. If the dielectric is Upilex in a multi-layer part it can take a very long time (24 hrs) to bake out the moisture due to the low transmission rate of the film. Typical Values Kapton HN Upilex S Water Absorption 2.8% 1.2% wt. % Water Vapor Permeability 54 1.7 g / sq. m / mil Other possible causes: Insufficient adhesive thickness. Improper surface cleaning prior to coverfilm lamination. Improper lamination cycle. Relaminated parts. (Looks ok, but has no real bond strength.) Undercured adhesive. Local "hot spots" on the part during IR. Solder temperatures exceeding those recommended for the adhesive. The more you can tell us about the parts the closer we can come to being specific for you. Andy Magee - Applications Engineer Rogers - Circuit Materials Unit Phone: (602) 917-5237 Fax: (602) 917-5256 E-Mail: [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: PRE-BAKE FOR FLEXIBLE CIRCUITS Author: BOB (BOB HOENE) {NAME:BOB HOENE|EMS:INTERNET|MBX:[log in to unmask] at MCIMAIL Date: 9/11/95 11:01 AM WOULD ANYONE CARE TO ADVISE THE GUIDELINES FOR FLEXIBLE PRINTED WIRING PERTAINING TO PRE-BAKE BEFORE ASSEMBLY. DURING THIS LAST AND LONG HOT SUMMER, WE SEEM TO HAVE EXPERIENCED UNFAVORABLE STORAGE CONDITIONS AND OUR FLEX CIRCUITS ARE "BLISTERING", THAT IS, THE COVERLAY IS LETTING GO OF THE BASE MATERIAL DURING PROCESSING. WE BELIEVE THIS TO BE A MOISTURE RELATED PROBLEM. WE WAVE SOLDER AND IR REFLOW CIRCUITS IN OUR PROCESS. YOUR ADVICE AS TO BAKE TEMPERATURE, DURATION, AND SUGGESTED WORKING TIME ALLOWABLE BETWEEN BAKE AND ASSEMBLY WOULD BE APPRECIATED.