Currently we have a PCA (Printed Circuit Assembly) which is sensitive to
high humidity. Due to the sensitivity of the circuit we believe the failure
mode is possibly related to the presence of contamination on the PCA.
To measure the level of contamination on the PCA and to control the level
of contamination to industrial standards, can anyone recommend the standard
that should be referenced, the level of contamination that is common in
industry and the method of testing.
The PCA is a double sided SMT assembly using no clean solder paste and no
clean solder wire for the few through hole components. For this type of
assembly should I use the Omega Test or the SIR Test or any other test and
what is the acceptable industrial levels.
*Suresh,
You are looking for a magic bullet test - one that will give you a simple
test method, with a universal pass-fail level that will tell you if your
hardware is good or bad. Unfortunately, my friend, the test you are
looking for does not exist. Here is why.
The Omegameter, and other instruments like it, have a relatively benign
extraction method, and the pass-fail level in all the standards is over 25
years old. The test will not tell you if you have good hardware or bad
hardware. Its only valid use is as a process control tool for day to day
production, not product acceptance. Read EMPF report RR0013 "An In-Depth
Look at Ionic Cleanliness Testing". That report will show how bogus this
test can be. I have seen far too many people rely on Omegameter (or
similar) results and still get corrosion and metal migration. You also
indicate that you are using low solids materials (erroneously called
no-cleans). The residues from these materials will cause high Omegameter
results, but are not a problem on your board.
The SIR or electromigration tests might show you if you have a problem with
electrical leakage at high humidity levels, but you already know that.
Also, SIR and electromigration tests are based on test patterns with a set
geometry, such as comb patterns. You can run such tests, but you no longer
have pass-fail numbers that you can use, and you have to use engineering
judgement. In addition, those tests usually do not have the same mix of
metals and solder mask that you have.
The test that I would do in your situation is ion chromatography. It is a
good test to find out what ions are present and in what amount. In the
hands of a skilled analyst, and with knowledge of your materials and
process, the data can indicate if you have a problem, the source of the
problem, and how to fix it. Unfortunately, there are no nationally
"approved" standards for ion chromatography data. Again, you are left with
engineering judgement. You can find some guidelines in J-HDBK-001, section
8.
My old company, CSL, can probably help you in this analysis. They have 10
years of ion chromatography experience in troubleshooting, and they came up
with the guidelines in J-HDBK-001. You can reach them at 765-457-8095 or
[log in to unmask]
If you need more direction, let me know and I will try to help further.
Doug Pauls
Rockwell Collins
Chairman, IPC Diet Mountain Dew Committee 9-45r
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