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September 2000

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Subject:
From:
"Ingemar Hernefjord (EMW)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 22 Sep 2000 12:53:48 +0200
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text/plain
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Ave Dave,
I have been involved in epoxy bleeding up and then, especially then, don't like the issue, half magic half science. We have used 84LMI, H31 and similar silver epoxies from the glue family and we found that under certain circumstances you may get bleeding that disturbs wire bonding. Normally, bleeding is natural to occur some 10-200 microns on outside of the pad, in general acceptable, but when Murphy is nearby, bleeding can be a trouble at much more distance from the pad. We use 125 micron Aluminium wire, in which case possible bleeding will not be much of a trouble, wedge 125 micron U/S will sweep away most contaminations. As you say, the surface properties will have great influence on bleeding, a preparation glass will make epoxy bleed much more than a rough metallised pad, that' for sure. We realize that wetting is something happening in the nanometer uppermost region of the pad and also that the time to maximum wetting is also an important factor (like the wet phase's vi!
scosity), but specify the ENIG in this viewpoint we have still not done. Only (reasonable) way we have found is a thorough coop with the supplier of boards, make tests on coupons and boards, feed the result back to the supplier and tell him that batch xx so and so was good, and hopefully the supplier will freeze his line data for that very product.

So, if anyone has succeded to specify what Dave asks for my ears will be teacups...eyes too....

Ingemar Hernefjord
Ericsson Microwave Systems


-----Original Message-----
From: Dave Gardiner [mailto:[log in to unmask]]
Sent: den 21 september 2000 04:09
To: [log in to unmask]
Subject: [TN] Silver Epoxy Bleed on imersion Ni Au PCBs


We are manufacturing immersion nickel gold boards for an automotive
sensor OEM using aluminum wire bonding and snap cure silver epoxy
adhesive. We have tried to develop surface roughness standards to
predict surfaces that will not allow excessive bleed. Does anyone have
similar trouble that can exchange experiences?

Dave Gardiner
Circuit~Tech Inc.
275 Steelcase Rd. E.
Markham, Ontario
L3R1G3
905-474-9227 ext. 233

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