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April 2007

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Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Tue, 17 Apr 2007 07:18:50 -0500
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However, I would caution anyone who wishes to try this: qualify it on your product first. I have no idea if it could cause problems in certain applications. 

-----Original Message-----
From: Stadem, Richard D. 
Sent: Tuesday, April 17, 2007 7:14 AM
To: [log in to unmask]; [log in to unmask]
Subject: RE: [TN] Tacking corners of BGAs

Just a small amount capturing the corner on two sides. We had a requirement that none be touching the solderball itself. 

-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Tuesday, April 17, 2007 7:08 AM
To: [log in to unmask]; Stadem, Richard D.
Subject: RE: [TN] Tacking corners of BGAs

Can you share the Chip bonder application requirement for 4 corner BGA solder bump bonding?   ie: coverage - amount - height - etc.

Victor,

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Tuesday, April 17, 2007 6:57 AM
To: [log in to unmask]
Subject: Re: [TN] Tacking corners of BGAs

I have used Chipbonder for many years to epoxy the four corners of BGAs. The reason I was doing this was to prevent any movement of the BGA during a second reflow. I did not want to go with full underfill as we wanted to be able to rework the BGAs in case of field failures. 
This method was first "tried out" on some scrap production boards, and it worked well using a solder paste designed to go through the reflow oven twice before wash (Kester R562). So my next step was to qualify the process, and I used two sets of assemblies, one set used the old method (no chipbonder) for benchmarking purposes. Qualification included running the assemblies through thermal cycling and microsectioning.
Imagine the surprise when the BGAs with the four corners bonded with a small bead of Chipbonder averaged 1610 cycles to failure compared to 967 for the ones without. The small amount of time required to bond the four corners was less than 30 seconds per BGA, manually.
Adding a little chipbonder in the four corners not only allowed us to gain our objective, but we greatly increased the reliability of the BGAs. 

 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David Tremmel
Sent: Monday, April 16, 2007 4:56 PM
To: [log in to unmask]
Subject: [TN] Tacking corners of BGAs

Dear Technetters,

 

We have a quality issue where some of our boards are returning because the BGAs need to be protected against mechanical stress.  We were considering using Loctite´s Chipbonder 348 on the corner of the BGAs in question (we would not to use an underfill).

 

Does anyone have any experience with Chipbonder 348 in this kind of application?

 

Would anyone care to suggest a heat-cured adhesive for tacking down corners of BGAs?

 

 

Thank you in advance,

 

David

[log in to unmask]


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