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October 2000

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Subject:
From:
Lou Hart <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 4 Oct 2000 18:00:42 -0400
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Jim, there is a repair method in IPC-7721, 5.2.3, I believe, for conductor repair by welding.  However, I have advised against doing such repairs by welding.  The skill and science required are, in my opinion, too high for comfort.   I recommend the other methods that exhibit "High" conformance.  

Some years back, I was testing battery packs, made from AA cells.  They failed a shipping test.  My metallurgist friends examined the welds and found they were exceedingly poor - no metallurgical bond.  Discussions with the pack manufacturer revealed that they had welded the packs with the same weld schedule used for their hitherto sole product - subC packs.  When the weld schedules were adjusted for AA cells, the packs were fine.

Lou Hart
412-858-6184

----------
From:   West, Jim[SMTP:[log in to unmask]]
Sent:   Wednesday, October 04, 2000 4:08 PM
To:     [log in to unmask]
Subject:        [TN] Circuit Board Trace Repair

Hi Everyone!

There is a company that I know that makes a welder that enables you to make
repairs to circuit board traces by using parallel gap bonding.  I had posted
a question about welding a nickel strap to a pad a couple of days ago but I
received no response.  I believe that the repair method falls in the line of
what I want to do, does anyone have any experience in this method of
bonding?  I particularly want to know if IPC has any guidelines to
acceptability to a weld joint versus a solder joint.  Is there anything I
should be cautious about doing this method?  Could this method damage the
pad or substrate?  Below is some info a grabbed off a web-site explaining
this method.

The Parallel Gap Resistance microjoining technique can be used to perform
Resistance Welding, Thermocompression Bonding, Resistance Brazing or Reflow
Soldering. All of these processes use different combinations of Temperature,
Pressure and Time to achieve the final result. The primary applications for
parallel gap microjoining are to bond fine wire and ribbon to:
Hybrid or Microwave circuitry
Thin or thick film substrates
Potentiometers and other miniature components
Semi-rigid substrates
Fine line printed circuit traces
It is also used to weld flat packs to printed circuit boards and parallel
gap reflow solder small parts. The materials which can be bonded with the
parallel gap technique include: copper, gold, gold-plated dumet, gold-plated
Kovar, platinum, silver, nichrome and pyrofuse.
Thanks for your help!!
Jim West

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