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Subject:
From:
Bob Willis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Bob Willis <[log in to unmask]>
Date:
Fri, 5 Jun 2009 07:54:18 +0100
Content-Type:
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text/plain (689 lines)
Bev I am very sorry but I did not send my old text as I agreed after my
trip, I just could not find it as it dated back to May 2001. I never sorted
out the images for the flip chip and uBGA from my libarary for the
posters/wall charts.

The draft text is below which I actually found on line at SMTNet Forum with
three comments see link:

http://www.smtnet.com//forums/index.cfm?fuseaction=view_thread&CFApp=1&Threa
d_ID=1600&#Message6706 




Here is a draft visual inspection guide for underfill, please pass this on
to the relevant people for any comments or suggestions. I am currently
working on the pictures to go with the reference guide.

Flip Chip/uBGA Underfill Visual Standards

The aim of this document is to produce some draft text and then select
photographs to make up a draft visual standard for inspection. There is also
a need to produce some reference material for C Scan images.

The following images provide a guide to the inspection requirement after the
underfilling operation. They may also be applied after curing of the
underfill.

CLASSIFICATION OF QUALITY STANDARDS

During the assessment the following classifications, which are pictorially
illustrated, should apply:

SATISFACTORY

This is a satisfactory condition which should be achieved and used as the
standard for manufacture.

ACCEPTABLE

This condition represents the maximum acceptable departure from the
"Satisfactory" condition. Examples within this limit of deviation will not
require reworking. Individual clarification accompanies each example
illustration. Consideration should be given to modification to the process
materials or conditions.

UNACCEPTABLE

This applies to an unacceptable condition which should not be reworked
without the cause of the fault being established. Rework may be possible
after assessment of the fault and corrective action taken on the process.
Flip Chip/uBGA Underfill Visual Standards

Satisfactory
The underfill should be visible at the edge of the device and extend
completely around the perimeter.

Satisfactory
The underfill should be visible on all four sides, there may be evidence of
more material on one or two sides to aid complete filling of device base.

Satisfactory
The underfill if by design should be visible on the side of the device and
reach a minimum height of 25% of the thickness of the package.

Satisfactory
The base of the device should be completely filled with no evidence of voids
in the underfill or solder joints being visible around the perimeter of the
device.

Satisfactory
Curing of the underfill material should be compared with the reference
colour standards. Evidence of colour change illustrates a correctly cured
sample.

Acceptable
Flow out of underfill from the device is acceptable provided that it does
not completely cover any solder joints. Flow out on to test points, through
holes is unacceptable and needs to be reworked and the process modified.


Acceptable
Small bubbles in the surface of the underfill fillet is acceptable provided
that no solder joint is visible.

Acceptable
Evidence of a needle dispense pattern around the device is acceptable, the
width of the pattern should be kept to a minimum.

Acceptable
The underfill if by design should be visible on the side of the device and
reach a height of no less than 20% of the thickness of the package in the
centre of any side.

Acceptable
Underfill fillets which are not visible on the side of the device are not
rejectable, however modifications to the dispense process should be made

Unacceptable
There is no evidence of underfill on the top side of the device

Unacceptable
Curing of the underfill should be compared with the reference colour
standards. No evidence of colour change is unacceptable.

Unacceptable
The underfill is not visible along the complete side of any device

Unacceptable
Solder joints are visible without underfill on the side of the device

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

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

Unacceptable
There should be no evidence of damage to the board or device caused by
contact with the dispensing needle or height sensor.

When using CSAM to asses the underfilling/curing process the following
criteria may apply:

Satisfactory
Underfill is complete and there is no evidence of voiding between the device
and the board.

Acceptable
Underfill is complete and there is evidence of small voids of less than 50%
of the solder bump diameter. There is no evidence of voids around solder
joints.

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

Unacceptable
Underfill is incomplete and there is evidence of voids around or between the
solder joints

Unacceptable
Underfill is complete but there is evidence of voids which are larger than
50% of the solder bump

Unacceptable
Underfill filler shows evidence of separation or uneven flow and will
expansion matching and affect the long-term reliability.


Draft Produced by Bob Willis
28/5/2001 Issue 4.


Bob Willis
2 Fourth Ave, Chelmsford, Essex, CM1 4HA England
Tel: (44) 1245 351502
Fax: (44) 1245 496123
Mobile: 07860 775858
www.ASKbobwillis.com
www.SolderingStandards.com 

PCB Design for Manufacture & Assembly Workshop 15th October
www.ASKbobwillis.com 
PCB Inspection & Quality Control Workshop 3rd November
www.ASKbobwillis.com/faworkshops.pdf
Book Bob's "Step by Step Failure Analysis Workshop" 4th November
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: 04 June 2009 21:45
To: [log in to unmask]
Subject: Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal

Bob,
This is weird. You are the second TechNetter to ask for the draft document,
which I posted on TechNet this morning at 11:07 AM EDST.  Here it is again.
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

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of bob wettermann
Sent: Thursday, June 04, 2009 4:42 PM
To: [log in to unmask]
Subject: Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal

Dear Richard:
 
Pls send the proposal on to us. We perform underfill rework and this issue
presents itslf fairly frequently.
 
Thanks
 
Bob Wettermann
[log in to unmask]

Bob Wettermann
PH 847-767-5745

--- On Thu, 6/4/09, Stadem, Richard D. <[log in to unmask]> wrote:


From: Stadem, Richard D. <[log in to unmask]>
Subject: Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal
To: [log in to unmask]
Date: Thursday, June 4, 2009, 1:10 PM


I reviewed the proposed items for the standard and I think it looks
great. I have sent it to several other people directly involved in BGA,
CSP, and flipchip underfill at various companies in Minnesota for their
review and will pass on their comments as well.
Thank you for doing all of this work.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Thursday, June 04, 2009 11:43 AM
To: [log in to unmask]
Subject: Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal

The doc we are discussing is only for CSPs and BGAs. I did not want to
try and tackle too much, especially something that: 
a) I don't know about
b) Has been around a lot longer and might already have a set of
pass/fail criteria

Bev
RIM

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Thursday, June 04, 2009 12:40 PM
To: [log in to unmask]
Subject: Re: [TN] Underfill Workmanship Pass/fail Criteria Proposal

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
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
[log in to unmask]


To
[log in to unmask]
cc

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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