Ryan - it has to do with density of the deposit. If you perform a porosity
test on DIG, the results mimic that of 30 microinches of gold rather than
the 2-4 microinches that is actually there. I have been testing in real time
DIG and using a wetting balance have a data set over 900 days of storage -
non protected office environment. If I compare my ENIG longterm test to DIG,
the DIG solders better at 899 days, wets faster and produces a higher
wetting force. The underlying Cu (oxide) I guess is easier to solder to than
a partially passivated nickel layer.
After 900 days it does not look very nice - rather brown in color but boy
does it solder.
Regards
Gerard O'Brien
Photocircuits.
-----Original Message-----
From: Ryan Grant [mailto:[log in to unmask]]
Sent: Wednesday, October 12, 2005 10:34 AM
To: [log in to unmask]
Subject: [TN] Direct Immersion Gold
Hi Techies,
Can anyone explain what direct immersion gold is?
My supplier gave me samples of several different board finishes, of
which two groups were direct immersion gold from two different
suppliers. The gold over copper was 5uin and 7uin, which I was
surprised the copper hadn't already diffused into the gold. I told him
I had no interest in direct immersion gold...but, since he gave me the
samples, I might as well test them with the samples that I am interested
in (immersion silver). First, I baked the boards at 125C for 48 hours
to kill the solderability. Then they were reflowed twice to kill
solderability, and checked for wetting. Again, I expected the copper to
completely diffuse through the gold, and/or the solderability to be
dead. To my surprise, the gold was still there and solderability was
still good; whereas immersion tin and OSP showed evidence of dewetting.
(ENIG and immersion silver still had good wetting too).
So can anyone explain why the copper and gold didn't diffuse into each
other?
Thanks,
Ryan
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