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Subject: FAB:Questions about pink-ring
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There are some things that I can't understand about the black oxide, pink
ring and the use of DMAB
Pink ring is the result of the attack of BO by acids in the electroless
copper line. DMAB prevents this attack.
The black oxide treated with DMAB can resist a lot of time in a 10% HCl
solution but only a mom in a sulphuric/hidrogen peroxide solution. Then, why
we don't have pink-ring using DMAB?
The peel-off for the black oxide treated is lower than the non treated.
During the drilling , I think it would be easier to delaminate. Again ,why
we don't have pink-ring using DMAB?
I would like to understand how DMAB works, because sometimes it doesn't do.
Is there another systems to protect de black oxide?
I would like also to find some papers, articles, etc. about this process.
Thanks and excuse my bad english.
Toni.
======== Fwd by: Tony King / N ========
I can state that DMAB does reduce the defect known as pink ring, I have used
it for about 3 years with almost complete elimination of the defect.
Control must be placed at the oxide process to insure adequate reduction,
the reduced surface should withstand 5 minutes in a 5% sulfuric acid
solution. This can easily be tested in production by placing a copper clad
strip of material on each rack with the product, and then dip the test strip
in a sulfuric solution afterwards for 5 minutes, a coating should still
exist. The reduced oxide does reduce the adhesion, testing on light black
oxide that yielded 7-8 lbs/in before reduction yielded 4.5-5.5 lbs/in after
reduction. The real key to the process is the oxide coating itself, the
thickness and color. Oxide is a combination of CuI and CuII, the percentage
of each in the coating defines the color of the oxide and the chemical
characteristics. I have seen that light black oxide (25-30 mg/sqcm) has the
best performance with the DMAB reduction process. If oxide thickness exceeds
40-50 mg/sqcm the DMAB is not able to reduce the entire thickness of oxide
and pink ring results. Some oxide solutions are more self-limiting in
thickness than others, there can also be a problem with the self limited
oxide coating, because even though thickness does not increase, the
percentage of CuI/CuII does change. Extended dwells in a self limiting oxide
bath also result in pink ring. The best way to control the quality of the
oxide deposit is by monitoring the time required to initiate the DMAB
reaction. The oxide coated product should initiate (begin to violently
outgas) in the DMAB within 15-30 seconds after contact, if initiation is
delayed beyond a minute the oxide should be reviewed (most people would
expect the DMAB concentration to be bad however this is usually not the
case). Standard oxide dwell time should be 3-5 min. at 160-170 F. If
initiation is delayed on the 5 minute oxide coating, try reducing the time
in oxide (within your operating window) to 4 min.
Tony King
Elexsys International Inc.
Nashua, N.H.
603-886-0066
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