The new IPC-A-610C (6.5.2) and J-STD-001C (9.2.4.1)  both support acceptance
including Class 3.  This criteria is also consistent in the defunct
MIL-STD-2000A (4.21.1).
For what it's worth there was some concern that copper could support or
contribute to metal migration under adverse conditions and there are
textbook references that support that viewpoint.
Mel Parrish
ACI/EMPF
One International Plaza, Suite 600
Philadelphia, PA 19113
[log in to unmask]
www.empf.org
610 362 1200 x238
610 362 1290 Fax



-----Original Message-----
From:   TechNet [mailto:[log in to unmask]] On Behalf Of Howieson, Rick
Sent:   Wednesday, April 05, 2000 2:11 PM
To:     [log in to unmask]
Subject:        Re: [TN] Exposed copper around the periphery of anular pads..

Vertical areas do not need to be covered. The vertical edges do not get
plated (Tin/Lead) due to the photo resist and when fused the tin/lead
typically will not wet down the edges.
Rick
GTC

>-----Original Message-----
>From:  Stephen R. Gregory [SMTP:[log in to unmask]]
>Sent:  Wednesday, April 05, 2000 9:56 AM
>To:    [log in to unmask]
>Subject:       [TN] Exposed copper around the periphery of anular pads..
>
>Hi ya'll!
>
>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....
>
>Thanks!
>
>-Steve Gregory-
>
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