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July 2005

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Subject:
From:
"Ingemar Hernefjord (KC/EMW)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Ingemar Hernefjord (KC/EMW)
Date:
Mon, 4 Jul 2005 09:03:28 +0200
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text/plain
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text/plain (80 lines)
The below was Creswick's First Law.
Creswick's Second Law is this: don't trespass the First Law.

I dare ask very humbly: Mr Creswick, could globtop be a solution?
Sorry for being prudent...he-he

Ingemar

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Creswick, Steven
Sent: den 1 juli 2005 13:27
To: [log in to unmask]
Subject: Re: [TN] Is wire bonding reflowable?


Ioan,

If this is correct and there is NO encapsulation, no cover, or anything to protect the device and wires from the ravages of human fingers and the nasties of corrosive fluxes, you are certainly treading on very thin ice with respect to a reliable manufacturing process.

As others have indicated to one degree or another, bare chips and wire bonds are not meant to be exposed to the environment.

Please remember that even spittle [aka - spit] readily corrodes the aluminum bond pads on most devices.  Just imagine what a droplet of flux that happened to spatter during reflow would do to the short term and long term reliability of the bond pad/wire interface.

If you need to make a few prototypes this way, do it on a 'best effort' basis.

If you plan to go into production with this approach - be aware of that sledge hammer which will certainly come down across your head at any moment.  This is certainly not a reliable method of creating a module.

Now then, if it were to be encapsulated [aka - chip on board], then you stand a chance provided the CTEs of the PWB and encapsulant materials are in reasonable agreement, etc.  Even then, however, problems can arrise with reflow profile A being different than B, etc. etc.

Summary - as has been said by someone else.  Protos - okay [just leave yourself a disclaimer], Production - have a REALLY big disclaimer.

Steve Creswick - Gentex Corp


-----Original Message-----
From: Tempea, Ioan [mailto:[log in to unmask]]
Sent: Thursday, June 30, 2005 10:49 AM
To: [log in to unmask]
Subject: [TN] Is wire bonding reflowable?


Hi Technetters,

a customer of ours is wondering if a module they are ordering will be OK to solder in regular (SnPb for now) reflow. The module has an exposed die, no encapsulation, wire bonded to gold pads on an FR4 substrate. For me, since regular ICs can be reflowed with no issue, this module should not present any hickup.

My exposure to wire bonding is zero, so I take this issue with you. Can this question be answered as is, or would you need more details?

Thanks,
Ioan

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