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by ipc.org (Smail3.1.28.1 #2)
id m0vNh6V-0000S6C; Wed, 13 Nov 96 09:19 CST |
From [log in to unmask] Fri Nov 15 09: |
14:41 1996 |
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Ed,
I would be concerned about my internal layer connection. All the
Z-axis thermal stresses are now borne by the innerlayer connections.
Example: A Plated thru hole is like a rivet. The top and bottom pads
constrain epoxy board material which is expanding at 50+ ppm per degree
faster than the epoxy.
In your design, the rivet has only one side. You should expect the
rivet/ plated barrel to start up pull out. This will cause your
innerlayer connection to be intermittent opens.
The only place you can get away with this is on 2 layer boards.
On Nov 13, 8:04am, [log in to unmask] wrote:
> Subject: ASSY - Padless Plated Thru Holes
>
> To extend clearance and eliminate potential shorts to the bottom
> of a connector, the component side pad must be reduced to zero.
> In other words,a top side padless PTH. The shorts are occuring during
> wave solder.
>
> What reliability down sides can we expect? Im advised that PCB
> fabrication will not be a problem. Im mostly concerned with assembly
> and repair operations.
>
> Parameters: .093", 14 layer board
> Finished hole .033" with solder side pad at .060"
> No external layer traces or connections.
> All connections are internal planes.
>
> Thanks in advance: Ed Cassinelli
> Stratus Computer Inc
> 508-490-6821
>
> [ Attachment (application/rtf): "ASSY" 3107 bytes
> Encoded with "base64" ]
>-- End of excerpt from [log in to unmask]
--
George Franck Jr
Raytheon E-Systems
Product Assurance Engineer
Falls Church Va
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