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August 2001

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Subject:
From:
"Caldon W. Driscoll" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 21 Aug 2001 08:36:07 -0400
Content-Type:
text/plain
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text/plain (77 lines)
I asume these are FR4 boards.
What you are trying to do is get the best contrast between fiducial and the
Board surface. A nice shiny (White as the vision system sees it) fiducial is
best. Some HASL fiducials have a small dimple in the center that can cause
the P&P machine to reject it.
Use the vision system to teach a new fiducial from the boards that are
failing. There are various lighting techniques to help in the vision system
recognition.
Make sure the fiducial is symmetrical.
Try teaching a pad or another fiducial on the board to see if you can get
repeatability.
Some times you can "hit" the fiducial with a soldering iron (no wick) to
reflow for solder consistency.
You can also try burnishing (Clean with a pencil eraser -preferably the
white rubber kind) the fiducial.

I would try reteaching the fiducial or try a different (component) fiducial.

Remember what you see is not what the vision system sees. What you think may
be good may fail.

Cal
ACI


°-----Original Message-----
°From: TechNet [mailto:[log in to unmask]]On Behalf Of Mark Hargreaves
°Sent: Tuesday, August 21, 2001 7:57 AM
°To: [log in to unmask]
°Subject: [TN] P&P can't locate fiducials
°
°
°Hi All,
°We've made boards for a customer for a few years.  They've  been very
°satisfied with HASL finish.  Last month they started rejecting
°approx 40% of
°boards received (3 lots) because their P&P camera couldn't locate the
°fiducials.  The coating looks typical to us (thickness & smoothness).
°Customer can't see any difference between good & bad boards until
°they're on
°the P&P machine.  They say they haven't changed equipment, processes or
°operators.  We say the same.  No HASL hassles from other customers in this
°time period.  We tried reworking by wicking solder from the fiducials.
°Customer rejected approx. 20% for the same reason.  They also say that
°boards from another vendor are working fine.
°Any comments/ ideas?
°
°
°Mark
°
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