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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