Ed,

Are you using a handheld device (eddy current?) or a benchtop unit (x-ray
fluorescence).  I have very limited experience with a handheld unit, but we
used to have a CMI x-ray fluorescence benchtop unit for measuring metal
thicknesses.  Most of our errors used to be due to what (copper, no copper)
was in the layers underneath the area that we were measuring.  We had to be
fairly specific where a measurement was taking place.  We also would see
errors due to metal density fluctuations.

Are you sure that the copper isn't smearing during the cross-sectioning
process?  Is it nickel gold plated?  Do you etch the copper after
polishing?  The differences that you are seeing seem to be large for
smearing, but I thought I would ask.

As an aside, one of the responses mentioned room-temperature annealing of
copper.  At a past employer, this was mentioned quite a few times as well.
Does copper really anneal at room temperature?  I was always taught that
annealing was an elevated temperature operation (deformed, stressed grains
are consumed and regrown).  As a rule of thumb, recrystallization occurs at
0.3 to 0.5 times the melting point of the material (on the order of 325 -
525 C for copper).

There was a process called "Recovery" in my textbooks which occurs from
room temperature to ~300 C for copper.  It involves the annihilation of
dislocations, reducing the internal stresses.  Is this what's causing the
shift in electrical properties?  I didn't mean to veer from the original
question, but this room temperature annealing thing has been bothering me
for some time.  Can anyone explain the phenomenon?

I haven't been much help to Ed, but maybe I can learn something.

Dave Anderson
Medtronic, Inc.

Reply
separator------------------------------------------------------------------

Hi all,

Just a question. I have been having problems getting my CMI unit to read =
copper thickness consistently. It has typically been reading low. For =
instance, the meter will show .0005 to .0006 of copper on a standard =
.042 thru hole but a section of the same hole shows .0012.  The meter =
reads fine to the provided standard.  Has anyone else experienced this =
problem. I should note that the meter was just calibrated a few weeks =
ago so calibration should not be an issue.

Ed Cosper

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