Steve: How can a no-clean flux be water-washable? If you leave residue on there, any moisture encountered in service would attack it, dissolving and spreading ionic contaminants, and causing corrosion, shorts, lifting of coating. And if it's something that you must clean anyway, why not use something more active, with a wider process window? Or what am I missing? -Joe -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory Sent: Wednesday, January 21, 2009 11:04 AM To: [log in to unmask] Subject: Re: [TN] Strange Mask Appearance Hi Bill! Yes, I would like your photos, thank-you very much. To respond to Tan Geok Ang, the flux we used for the rework is Amtech 4300, a solvent-based (ethanol), water washable no-clean. I know the picture looks like the area around the screw heads is delaminated, but it is not. The copper is relieved around the holes for the hardware in the inner planes and that may contribute to the appearance that there's delamination. Here's a photo of the same exact place on the same exact board after doing nothing but heating the PCB up to 125 C. as I described in my earlier post. http://stevezeva.homestead.com/files/Mask_Discoloration_After_Heating.jp g And the "before" photo: http://stevezeva.homestead.com/files/Mask_Discoloration.jpg Pretty dramatic change huh? Steve -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of [log in to unmask] Sent: Tuesday, January 20, 2009 1:59 PM To: [log in to unmask] Subject: Re: [TN] Strange Mask Appearance Steve- I'm probably the culprit that put that report on TN long ago- and again recently. Liquid solder masks often use fumed silica as filler/thickener to keep it in place. This is often sold under the Cab-O-Sil tradename. Aggressive cleaning agents can dissolve off part of the under or un cured solder mask polymer, exposing the while silica filler. When you heat the undercured mask, it will soften and allow the filler to sink down into the polymer, so the solder mask all looks green again. Re the curing from wave solder, this may not work if you are working with a UV cured mask. That's why it is important to monitor the output of UV lamps, which not all shops do, thinking that UV lamps behave the same as incandescent lamps- which they don't. Yes, the heat gun is a very inexpensive $0.05 test, quick, easy and requires no instrumentation. (Steve- I have some photos of the differences between one, two and three passes under UV lamps to show the difference if you'd like them. If so, pls give me a mailing address.) Bill Kenyon Global Centre Consulting 3336 Birmingham Drive Fort Collins, CO 80526 Tel: 970.207.9586 Cell: 970.980.6373 **************A Good Credit Score is 700 or Above. 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