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June 2009

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Subject:
From:
Victor Hernandez <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Mon, 8 Jun 2009 07:17:24 -0500
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text/plain
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What is the adhesion property of the underfill?   How can you
calculate/measure the suspected strength?   The same inquiry is true for
BGA 4 corner glue.

Victor,

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Collins
Sent: Monday, June 08, 2009 6:17 AM
To: [log in to unmask]
Subject: Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal

'morning Bev

OK, here is a question for you.

You've commented recently that you have an underfill requirement where
the design means you can't use acoustic microscopy to inspect the part.
Therefore, how can you expect a contract manufacturer to assemble that
product to your specification?  You've handed them an impossible task...
And the way this is worded it sounds like an inline inspection step.
How many manufacturers have this type of capability?  It may be a
reasonable requirement for very high rel equipment, but volume
production???  For a smaller manufacturer who doesn't have a C-SAM
machine on site this will either involve spending $$ on equipment and
training, or they will have to contract it out ($$ and lead-time).

Could the section on voids have some wording allowing a qualified
process to be used without verification of voiding on each part?
Similar to the BGA section in A-610?

--------------------
From IPC-A-610 D:
A BGA criterion defined herein assumes an inspection process is
established to determine compliance for both X-Ray and normal visual
inspection processes. To a limited extent, this may involve visual
assessment, but more commonly requires evaluation of X-Ray images to
allow assessment of characteristics that cannot be accomplished by
normal visual means. Process development and control is essential for
continued success of assembly methods and implementation of materials.
Nonconformance to the requirements of Table 8-12 is a defect when visual
inspection or X-Ray inspection is performed to verify product
acceptance. Process validation can be used in lieu of X-ray/visual
inspection provided objective evidence of compliance is available.
---------------------

regards,
 - Graham

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Friday, June 05, 2009 3:04 PM
To: [log in to unmask]
Subject: Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal

Joe,
Perhaps you have not been following the thread.  Voids are included.
So, here is the WHOLE THING plus with Bob's contribution added in.
I'm getting requests to add in flip chip underfill, no flow underfill
and corner bond adhesives.  Groan.  :) 

So there isn't anything already for flips chips? I've never used one, so
I don't know.  Anyone want to write a section of two?  :)
Bev

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 95% 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

*	Underfill interfering with proper placement of heatsink

*	There should be no evidence of underfill flowing out through
holes under the device.

*	After curing there should be no visual evidence of cracks
between the device surface, underfill or board.

*	There should be no evidence of damage to the board or device
caused by contact with the dispensing needle or height sensor.
*	Underfill filler shows evidence of separation

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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