In message <[log in to unmask]> [log in to unmask] writes: > We're having contamination problem which is impacting our > conformal coating process. Here's the story: > > We use "Kapton" style tape to guard the edges of a circuit board > while the board is processed in our wave solder machine. The > board/tape reaches a peak temperature of 220C for three seconds. > The temperature ramp keeps the board above 120C for > approximately three minutes. > > After passing through the wave solder machine, the board is allowed > to cool to room temperature. The tape is then removed. No visible > residue is left on the board. However, when we attempt to conformal > coat the board, the coating is repelled from areas where the tape > was applied. No manner of cleaning (alcohol, water, acetone...) will > remove the contamination and allow the conformal coat to bond to > the board. > > Are you aware of what the source of contamination could be? We > have managed to rule out flux. Boards have been taped and tested > prior to heating and no residue was found. Four different brands of > tape were tested with identically poor results. > > Ceramic edge stiffeners have been tried. The edge stiffeners clamp > mechanically over the edges of the board. Some contamination was > found when edge stiffeners were used, though not as much as with > the tape. > > Boards run without protection show no contamination. > > I would appreciate any insight you could provide into the nature of Most Kapton masking tapes use a silicone based pressure sensitive adhesive, because of its high temperature resistance (good for soldering). I suspect that this silicone is what you are seeing. The residue will vary from tape manufacturer to manufacturer. Try a silicone-free tape. Alternatively, go for a liquid based mask. I do not know why you are getting contamination from a ceramic stiffener though! Peter -- ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: Peter Swanson Oxfordshire, England INTERTRONICS [log in to unmask] http://www.intertronics.co.uk Suppliers of materials and consumables to the electronics & related industries ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: ############################################################## TechNet Mail List 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 web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################