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October 2005

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Subject:
From:
Anil Kher <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Fri, 14 Oct 2005 10:28:33 +0530
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Dear Gerard

This is interesting. I wonder what was the reason for incorporating Nickel
under layer then. Did it automatically derive from the spec for gold tabs ?
The reason for nickel in gold tabs was lower contact resistance. The direct
Gold shows what little copper oxide migrates on top is easily fluxed during
soldering.

Please correct me if I am wrong.

Anil Kher
micro interconnexion pvt. ltd
D3-12A, Corlim Industrial Estate
Corlim, Ilhas , Goa , India 403110
tel: 91-832-2284209/337. fax 2284209/2285271
e mail: [log in to unmask]
Leaders in Gold plated PCBs - selective/ cob
an ISO 9001-2000 Company


-----Original Message-----
From: Gerard O'Brien [mailto:[log in to unmask]]
Sent: Thursday, October 13, 2005 5:26 PM
Subject: Re: Direct Immersion Gold

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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