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June 2009

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Subject:
From:
"David D. Hillman" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Thu, 4 Jun 2009 11:40:10 -0500
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Hi Graham - in the words of Sir Doug, "it depends"! Under most situations, 
that thin of underfill will have no influence on the solder joint 
integrity. However, a specific component construction may not be happy 
with any underfill on its top causing issues. The simple way to avoid the 
question is to not allow underfill on the top of the BGA or CSP. I can't 
speak for a flip chip as I don't have any underfill experience in that 
realm.

Dave



Graham Collins <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
06/04/2009 11:20 AM
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TechNet E-Mail Forum <[log in to unmask]>; Please respond to
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Subject
Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal






Absolutely.  If material interferes with installing heatsinks, it's
unacceptable.  But that would be true also of other methods like corner
bonding.

My question: would a thin film of underfill material, say a thou or two,
on a small section (say 15% of the top area) of a BGA have any impact to
reliability?  I am not talking about having big globs of the stuff on
top (although I still wonder how that would influence reliability).

In terms of impacting reliability, I think a more important criteria
would be that the underfill be even volume on each side (so the part
would be underfilled reasonably symmetrically).  Same size fillets on
opposing sides.

regards,
 - Graham

-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]] 
Sent: Thursday, June 04, 2009 1:12 PM
To: [log in to unmask]; Collins, Graham (FN) @ ESI
Subject: RE: [TN] Underfill Workmanship Pass/fail Criteria Proposal

Too much material over the top of the component many add uncalculated
thickness when installing a heat sinks.

Vic,

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Collins
Sent: Thursday, June 04, 2009 11:01 AM
To: [log in to unmask]
Subject: Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal

How?  And to what extent??  Would a tiny bit of underfill on one corner
hurt the reliability?  Are you talking about big lumps of underfill, or
a thin skin? 

The underfill we use is pretty thin, runs everywhere if allowed to, and
will form a thin coating on top if it gets there. 

regards,
 - Graham

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Thursday, June 04, 2009 12:41 PM
To: [log in to unmask]
Subject: Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal

Yes, having some on top of the component hurts the reliability.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Collins
Sent: Thursday, June 04, 2009 10:27 AM
To: [log in to unmask]
Subject: Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal

Hi Bev
Why would material on the component top be considered a defect?  Process
indicator I can see, but does it impact reliability?

regards,
 - Graham

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Thursday, June 04, 2009 12:07 PM
To: [log in to unmask]
Subject: [TN] Underfill Workmanship Pass/fail Criteria Proposal

TechNetters,
OK after speaking to a couple of industry friends, this is what we have
come up with. I will leave it to them to speak up and identify
themselves, if they wish.  I have written this up in IPC-A-610 format
and have tried to cover all situations for Class 2 and 3 products in
particular. 

If we can nail this, I would like to present this to the IPC as the
first IPC draft doc essentially hammered out by out TechNet community.

Comments readily accepted!
Bev
RIM


Workmanship Standards for BGA and CSP Underfills

Target - Class 1,2,3
*                Component requiring underfill completely underfilled with 
a good
fillet all the way around, the fillet just approaching the maximum
component body height, completely cured, no encroachment onto other
components and no voiding whatsoever

Acceptable - Class 3
*                At least 50% fillet height up the side of the component 
body

*                Small pin holes and voids are permissible provided they 
do not
exceed 5% of fillet surface area and have a maximum diameter of 0.5 mm
(0.020 inches).

Acceptable - Class 1,2
*                Component requiring underfill underfilled such that all 
balls
are covered, but no evidence of an exterior fillet, no encroachment onto
other components and no voiding whatsoever

*                Component requiring underfill underfilled such that all 
balls
are covered, with or without an exterior fillet, no encroachment onto
other components and only small voids, not touching any solder joints

*                Component requiring underfill underfilled such that all 
balls
are covered, with or without an exterior fillet, no encroachment onto
other components and even large voiding, but not touching any solder
joints

*                A void or voids less than or equal to 50% around the 
perimeter
of one or more solder joints

Defect - Class 1,2,3
*                Underfill completely missing from components where it is
required

*                Underfill not completely covering all the peripheral 
solder
joints

*                Voiding such that a void traverses the distance between 
two or
more solder joints under the array device requiring underfill

*                A void or voids more than 50% around the perimeter of one 
or
more solder joints

*                Material extending on to the top of the BGA or CSP

*                Uncured material

Special Conditions - Class 1,2
*                Encroachment onto other components, but meeting all other
criteria above for target or acceptable conditions will be dealt with as
a pass/fail on a case-by-case basis

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