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From:
"Kane, Amol (349)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Kane, Amol (349)
Date:
Thu, 19 Mar 2009 08:30:45 -0400
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Thank you gentlemen for your responses!



Amol







-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /*

Sent: Wednesday, March 18, 2009 5:59 PM

To: [log in to unmask]

Subject: Re: [TN] Underfill Application



 Hi Rick,

This was a good move, because what the underfill did was not only let the solder balls not collapse, but stretched them to some degree. That increase in SJ height is what gave you the increased reliability. I, and others, have been pushing for this technique for years.

BTW, without the underfill, your SJ failures were not stress-initiated, but still creep-fatigue; because of the shorter SJs, the same thermal expansion mismatch caused higher strain levels at those SJs.



Werner















-----Original Message-----

From: Rick Bell <[log in to unmask]>

To: [log in to unmask] <[log in to unmask]>; [log in to unmask] <[log in to unmask]>

Sent: Wed, 18 Mar 2009 5:31 pm

Subject: RE: [TN] Underfill Application



























































Werner,















We placed the adhesive on four corners

and some cleared depopulated areas inside the ball array prior to smt device

placement, and cured it during the reflow process.  Essentially, we didn’t

use it as an underfill, but more as an SMA.  Of your two choices, I guess

that would be “before soldering”.















Our initial temp cycle failures with no

underfill were typical stress-initiated fractures on corner pins.  After

adding the adhesive in this fashion, the parts passed 1k cycles.  We didn’t

evaluate failure mechanisms past that.















rb





















































From:

[log in to unmask] [mailto:[log in to unmask]]



Sent: Wedn

esday, March 18, 2009

4:19 PM



To: [log in to unmask]; Rick Bell



Subject: Re: [TN] Underfill

Application



























Hi Amol,



When you say: "we elected to just do a corner bond approach"--what exactly

do you mean? after or before soldering?







If after soldering, that may have helped the corner SJs, but how did it help all the others?























Werner

























































-----Original

Message-----



From: Rick Bell <[log in to unmask]>



To: [log in to unmask]



Sent: Wed, 18 Mar 2009 4:50 pm



Subject: Re: [TN] Underfill Application









Amol,























I have some admittedly limited experience with underfilling CSP's for increased











reliability.  Some answers to your questions:























1.) Our material selection initially was governed by a host of parameters--











reworkability (see next point), minimum dispense gap, process temperatures, cte











matching, filler content, etc.  In my experience, trying to get a reworkable











version will greatly limit your choices.























2.) We used a Loctite material, I believe it was 3549.  Please be aware that the











term "reworkable" is relative.  We tried using it on polyimide flex substrates,











and found its reworkability was a matter of interpretation.  Your mileage may











vary...























3.) We used an Asymtek dispense jet p

latform with very good results as far as











material deposition.  Our only inspection capability was outsourced CSAM..























4.) Pitfalls-- Our biggest issues were some minor problems with adhesion to the











substrate/device, and incomplete encapsulation of a given solder joint due to











poor capillary fill on our device (this has highly detrimental effects in temp











cycle).  My only advice there is that if you're going to attempt a full











encapsulation, have CSAM inspection available to verify your coverage, or some











very tight process controls once you have a benchmarked process.























In the end, we elected to just do a corner bond approach, rather than trying to











fully encapsulate the BGA array, and we had reasonable success in reliability











improvement.































































































-----Original Message-----











From: TechNet [mailto:[log in to unmask]] On Behalf Of Kane, Amol (349)











Sent: Wednesday, March 18, 2009 2:48 PM











To: [log in to unmask]











Subject: [TN] Underfill Application























Dear Technetters,











We are about the develop a process for underfilling BGAs for a high reliability











application. the underfill will be a rework able underfill. I wanted to poll the











technet on:











1.      Guidance on mater

ial selection











2.      most common materials being used out there and the process equipment











being used to do so.











3.      Common pitfalls and things to lookout for











4.      inspection techniques used to inspect the finished product











5.      a good source for info on underfilling (books, papers etc.,)























Thanks in advance.























Regards,











Amol







































































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WARNING:  Export Control 

This document may contain technical data within the definition of the 

International Traffic in Arms Regulations (ITAR), and subject to the Export 

Control Laws of the U.S. Government.  Transfer of such data by any means to a 

foreign person, whether in the United States or abroad, without proper export 

authorization or other approval from the U.S. Department of State is 

prohibited. 

 

CONFIDENTIALITY NOTICE: 

This e-mail, and any attachments, is for the sole use of the intended 

recipient(s) and may contain information that is confidential and 

protected from disclosure under the law. Any unauthorized review, use, 

disclosure, or distribution is prohibited. If you are not the intended 

recipient, please contact the sender by reply e-mail, and delete/destroy 

all copies of the original message and attachments. 

Thank you.

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