Hi Steve!

I haven't seen that before, but it looks just like what happens if I set a cold glass of water on a varnished table.  For most of these finishes, the water will penetrate the polymer matrix and cause the "blush" effect.  Thorough drying by baking will normally reverse it.

I suspect your water soluable mask did the same thing to your solder mask.

Wayne

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, January 20, 2009 8:43 AM
To: [log in to unmask]
Subject: [TN] Strange Mask Appearance

Mornin' All!

We recently built several boards and discovered that we had to remove two DIP IC's on the boards, re-program the parts, and then put them back into the board.

We used our Air-Vac PCBRM-12 to do the job which made the task a simple one. But after coming out of our inline DI wash, I noticed some discoloration at the area where we did the rework:

http://stevezeva.homestead.com/files/Mask_Discoloration.jpg

At first I thought it was white residue and tried to use a brush with a little saponifier and scrub the area. No luck. Tried alcohol, no luck either.

After looking closely at it, I could see that it wasn't really residue, but that the mask was discolored. If you look at the picture at the area around the screw and nut, you'll see some of same type of discoloration which was the outline of the liquid water soluble mask we applied prior to wave solder.

I remember something that somebody posted on the Technet a long time ago about using a heat gun on areas like that, and it might clear up. I have a Hakko board pre-heater, so I put one of the assemblies on the pre-heater and brought the board up to about 125 C. then let it cool down. Removed the board and flipped it over, and like magic everything cleared up!

I'm glad that it worked, but what was it that might have caused it? Mask that wasn't fully cured? If that was the case, why wouldn't wave solder finish the cure? Or baking? We wash and bake all our bare PCB's prior to building as SOP.


Steve

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------

This e-mail and any files transmitted with it may be proprietary and are intended solely for the use of the individual or entity to whom they are addressed. If you have received this e-mail in error please notify the sender.
Please note that any views or opinions presented in this e-mail are solely those of the author and do not necessarily represent those of ITT Corporation. The recipient should check this e-mail and any attachments for the presence of viruses. ITT accepts no liability for any damage caused by any virus transmitted by this e-mail.

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------