George,

Seems a bit exotic, but as odd as it may seem, we've completed may projects
using this machining into the edge method. When first asked to reduce overly
thick boards along the edge contacts we considered compression, or reducing
the metal thickness, but both proved impractical.

Steps we followed to reduce the edge by machining:
1. We precisely mount the circuit board in a milling machine. A carbide saw
is mounted in the chuck of the miller. This saw is roughly 2" diameter and
.005" to .010" thick.

2. We mill into the edge of the board centering the cut. The depth required
will likely be up to 0.50" or more.

3. We select a thin section of laminate that will be inserted into the cut.
Thickness of this laminate may be .003" to .007" depending. This piece of
laminate will extend out beyond the edge and will be trimmed as the final
step.

4. We protect both sides of the board with tape to prevent epoxy
contamination.

5. We coat both sides of the replacement laminate with high strength epoxy.
Then insert the laminate into the board, apply tool bars to both sides held
with clamps, and insert the whole package into an oven top cure the epoxy.

6. After cure, we remove the clamps and check. Final step is to trim off any
excess laminate and restore the bevel if needed.

Using this technique we can typically reduce edge thickness along a contact
area by .002" to .007" depending on the job.

Jeff Ferry
CEO
Circuit Technology Center, Inc.
www.circuittechctr.com
[log in to unmask]
978-374-5000

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-----Original Message-----
From: George Becker [mailto:[log in to unmask]]
Sent: Friday, November 09, 2001 8:41 AM
To: [log in to unmask]
Subject: [TN] Thick PCBs


Occasionally I have been asked if there is some type of mechanical repair
process for PCBs with edge contacts that exceed the thickness measured at
the contacts.  I have heard that there is a process to machine out an edge
'kerf,' squeeze the PCB down to size and epoxy it to required thickness.
Does anyone perform this type of repair?  Where can I find out info. on
this?
Is there any method that has been tried and was successful which uses
pressure (like from a press) to squeeze edge metallization down? (This
pressure method would appear to be less intrusive than the machining method
above since the board is not cut.)

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