Mr. Kasprzak,
As one of the authors of J-STD-001, Appendix D, and the author of IPC-TP1043
and 1044, I will attempt to answer your questions. First, I would not try to
apply too much from the Phase 3 Water Soluble Flux testing (TP-1044) to the
J-STD-001 document. There is a variety of reasons. Give me a call if you
want more details.
<< - Why do the boards have copper traces ? Why aren't they tin-lead ready
for
soldering ?
In all phases of the IPC Cleaning and Cleanliness test program, we used B-36
boards with bare copper traces. WE had endless discussions on whether the
boards should be bare copper (cleaner, no HASL process) or should be tin-lead
coated. Since we wanted to look at the fluxes themselves, rather than
interactions between fabrication residues and the fluxes, we chose bare
copper. No test program is perfect. If you had the B-36 boards tin-lead
plated and you had a failure in ionics or SIR testing, was the fault due to
the flux or due to the HASL process? We did a case study (#2) where a
customer did use tin-lead coated B-36 boards. He had all kinds of trouble
with failures, even on the control boards which never saw the candidate
process. The boards had been HASLed with a brominated HASL flux and
improperly cleaned. So beware of tin-lead coated test boards. Anyone
interested in this case study, let me know.
I have had this discussion many times. Bare copper boards allow you to study
the candidate process with a board that is relatively easy to keep very
clean, without the clouding effects of fabrication. Tin-lead boards with
solder mask are more representative of process, but introduce other variables
into the evaluation, and the question becomes "How do we evaluate the
results?"
For those interested, the revision of Appendix D in the proposed J-STD-001B
will have you testing the candidate process with boards from your
fabricators. No precleaning.
>> - Is there a simpler way to get these boards clean in preparation for
soldering ? >>
Sure. There's more than one way to skin an armadillo. Admittedly, the Phase
3 test program was a little paranoid in it's approach to outside
contaminants. As manager of that program, I will admit to being the source.
For all practical purposes, if you have an Omegameter, Ionograph, etc. A
10-15 minute run is sufficient if your incoming boards are fairly clean. I
know that ECD uses an isopropanol/water wash on their B-24 and B-36 test
boards, and we do a similar wash on the boards we get from our fabricator.
We have also done ion chromatography analysis on both our incoming boards
from the fabricator and after the isopropanol/water wash. The wash is
sufficient. You might also want to do a dip in pure isopropanol to displace
any residual water so that the copper is not water tarnished. A mild bake
(nitrogen preferably) following this is good for baking out residual
moisture.
If you have questions on how to process an IPC-B-24 and B-36 boards, I
suggest you get "The Laymans Guide to MIL-STD-2000 and MT-0002" which I have
made available to the IPC for distribution. Has many helpful pointers. For
the uninitiated, there is no practical difference between MT-0002 and
J-STd-001A.
Hope this was helpful. If not, call me and I can go into greater depth.
Doug Pauls
Contamination Studies Laboratories
(317) 457-8095
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