Until a couple of years ago, on .5mm pitch, the smallest solder mask
     web allowed was always spec'd at .005", since any narrower then that
     and flaking was almost guaranteed. I have just addressed this issue
     with two of our board vendors, who were resistant, since I wanted wide
     pads AND solder mask on our .5mm pitch parts....but they were able to
     obtain compliance when I relaxed my spec to..."....minimum solder mask
     web of .004" with adhesion of web (i.e., no flaking). Also, solder
     mask can be allowed to go up to the pad, but NOT encroach onto the
     pad".

     Most suppliers can hold this process, and the "newer" solder masks are
     capable of good adhesion if processed properly.

     Hope this helps
     Jeff Hempton, Sr. SMD Mfg. Engineer
     United Technology Electronic Controls
     e-mail:   [log in to unmask]


______________________________ Forward Header __________________________________
Subject: Re: [TN] Fab: Mask dams between fine pitch smt pads
Author:  Mike Bailey <[log in to unmask]> at Internet
Date:    10/13/1999 6:41 AM


.0035 - .004 is within the capabilities of most shops, even on .5mm pitch
devices.  Occasionally, this is an issue when small via holes in high aspect
ratio boards must remain open after developing. It requires a slightly
overdeveloped condition to clear all mask residue from the holes.  Otherwise
it is consistently achievable.

-----Original Message-----
From: Ed Cosper [mailto:[log in to unmask]]
Sent: Wednesday, October 13, 1999 5:16 AM
To: [log in to unmask]
Subject: [TN] Fab: Mask dams between fine pitch smt pads


Hi all,

Just a quick industry capability questions. Are board manufactures still
having trouble holding mask dams between fine pitch (19mil) SMT pads. As
recent as a year or so ago I was under the impression that board shops would
ask the remove these small dams when they got them on the Gerber data. Is
this still common. I am interested in what most people think is feasible
regarding mask dams that are 4 mils wide and smaller. All responses are
appreciated.

Ed Cosper
ABC

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