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April 2000

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Subject:
From:
Alain Savard <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 5 Apr 2000 12:21:10 -0400
Content-Type:
text/plain
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text/plain (69 lines)
This is use to be common when boards were reflowed instead of HASLed. It is
usually observable on the sections, but unaided eye examination is rare. You
should get some magnification to insure that the top pad is TOTALLY covered,
If it is just the peripheral edge, I would deem it acceptable. My opinion is
based on IPC-6012, which states in section 3.2.6, that "Coverage of platings
and metallic coatings does not apply to vertical conductor edges".

I could be wrong, but this seems to apply to class 3 product. This kind of
discrepancy should be brought to the attention of  the committee of these 2
standards.

Just my three Canadian cents (2 cents US),

Alain Savard, B.Sc.
Chemical Process Analyst
CAE Electronics Ltd.
e-mail: [log in to unmask]


-----Original Message-----
From: Stephen R. Gregory [mailto:[log in to unmask]]
Subject: [TN] Exposed copper around the periphery of anular pads..

I got called back to incoming this morning to look at a PTH board that shows
exposed copper, but it's only at the side edges around the periphery of the
anular pads...it's like this over the whole board. The top surfaces have
tin/lead plating, but not the side edges.

                            Top surface of pad is plated
                                               |
                                ________V_________
__________________|__________________|__<-----Exposed copper on sides

                                            PCB

Is this a defect? Looked in the IPC-A-600F on page 85, (3.3.10 Solder
coating
thickness) and there's a conflicting statement I think. It says; Acceptable
-
Class 1,2,3, "Solder coating thickness is uniform. Vertical (conductor and
land) areas may not be covered. No exposed copper is evident."

On one hand it says that the vertical surface may not be covered, but on the
other hand it says you can't have exposed copper. If the vertical surface
doesn't have to be covered, then you're gonna have exposed copper. So which
is it?

Also there's a statement at the bottom of the page that visual observations
are made on cross sections only. I can see this with my own two
eyeballs...don't need a cross section to see it.

This board is for a hi-rel product by the way....

-Steve Gregory-

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