Jim,

I have done a considerable amount of gap welding over the years to a variety
of substrate materials.  Gap welding to traces on FR-4 can be quite tricky
especially for a nickel strap.  If the trace is less than 3X  the area of
the strap the risk of inconsistency exists. Less than 2X in area and the
risk of a lifted or damaged trace is very real. Less than 1.3X in area...
say goodbye to the trace.

If the strap and trace are pretinned and you use gap welding to reflow (can
be fluxless) a good result becomes quite easy.  The key in all cases is to
do a good job of maintaining the weld tips. Cleaning and dressing every 4-8
welds for nickel or every 25-50 welds for reflow would be typical.  If you
need more info contact me off line.

Good Luck,
Bruce
> ----------
> From:         West, Jim[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.;West, Jim
> 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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