Experienced same problem and found that the Kapton tape adhesive in deed was repelling the coating - solved problem with 3M 218 masking tape. http://products.3m.com/us/electronics_mfg/products/electronics_ehp.jhtml?pow url=VBZVSB2DTFbe54FL4R3WNKgeGST1T4S9TCgvPNTCW5KRV1gl I'm sure there must be others that would perform as well. Rich Buccieri Operations Manager Techdyne, Inc - Round Rock, Texas Phone: (512) 310-9139 Fax: (512) 310-9138 E-mail: [log in to unmask] -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of [log in to unmask] Sent: Tuesday, July 23, 2002 5:43 AM To: [log in to unmask] Subject: [TN] Conformal Coating repelled by masking Hi, Folks, I have a theory about one phenomenon out of two that I have just witnessed, but seek your sage thoughts on the matter. Our fabrication shop was spray coating an FR4 / HASL-finished board with Humiseal 1B31, which was masked with some very expensive Kapton tape. The tape is meant to be a no-static, no-residue type. We noticed that, under the UV inspection lamp in the spray booth, the coating appears to recede from the edge of the Kapton tape - at least there is a "line" 1 or 2 mm wide at the edge of the masking, that indicates (to me) a different thickness of coating in that zone compared with the rest of the board. We tried over-spraying the affected areas again once the initial coat had set a bit, but the line reappeared. It only happens where there is Kapton tape. At the same time, the coating on the solder side of the board is a nice shiny finish, while the component side has quite large areas that have a more matte, slightly "rough" appearance. I doubt there is a connection between the two phenomena, but you never know. My theory about coating recession from the tape is that there is a static charge on the Kapton tape, in spite of the "no-static" presumption, and that the coating particles in the spray are likewise charged from their passage through the spray gun. The two like charges are then repelling one another. I noticed that neither board nor spray gun are grounded, and think that they should be (comments, anyone?). My secondary theory is that the coating is reacting with the tape adhesive at the edge of the tape, creating a line of contamination that the coating doesn't stick to properly. Kapton tape is a commonly used masking material, though, and I haven't heard of this problem occurring with it before. I haven't come up with an explanation for the matte areas of coating on the component side of the board. The board had just come from the customary cleaning and drying that I give all boards just prior to coating. Can you come up with possible explanations and cures for what is happening here? MTIA Peter ---------------------------------------------------------------------------- ----- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------- ----- --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------