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Wed, 8 May 2019 17:03:41 +0000
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Fellow TechNetters:

   What are some Pros & Cons of using a HASL covered PTH for grounding high current hardware?

Victor,

-----Original Message-----
From: TechNet <[log in to unmask]> On Behalf Of Whittaker, Dewey (EHCOE)
Sent: Monday, May 2, 2011 2:06 PM
To: [log in to unmask]
Subject: Re: [TN] Mounting holes with plated barrels

Phil,
I do not allow them for aerospace applications. Your memory is correct and there are some other issues, but most of those are design specific.
If the non-plated mounting holes are needed for thermal, chassis ground or other pathway issues extend the plane area on layer 1 and N sufficiently to allow mounting hardware contact to the plane and still allow vias in the planes to establish interconnect scenarios out of the crush zone.
Dewey

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Bavaro
Sent: Monday, May 02, 2011 10:19 AM
To: [log in to unmask]
Subject: [TN] Mounting holes with plated barrels

I was reviewing a new design and found the mounting holes have plated barrels.

In my past, I have always steered Design away from plating the barrels of PWB holes used for mounting holes (and torque).

Far back in my memory, I remember experiments I had run which revealed that the HASL solder on the mounting hole annular ring allowed solder creep making the fasteners come loose over time.  I also seem to remember something about not wanting to put a barrel in compression.
This is a double sided board mounted to a copper plate and the entire assembly is tin lead plated and then fused.  On a multilayer board, the argument is easily made to not compress the internal layers.

I am looking for something in the standards which might provide some direction against this type of design.

The only stated reason from the mechanical designer was increased thermal dissipation, for which my argument is that the fastener provides much more capacity for transfer than does the barrel wall.

Am I being too conservative?

Phil



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