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January 2012

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Subject:
From:
Phil Bavaro <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 4 Jan 2012 08:48:32 -0800
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I would have to have more information before I would allow this to be
considered a defect that requires rework.  For example, are you using a
2 dimensional top down look to measure the void size?  Have you cross
sectioned any of the BGAs to determine what the void shape is?  

I personally find that many people make an error when trying to
calculate the voiding percentages. 

I would expect to find that process parameter is out of control, perhaps
either something relative to the paste or the reflow profile which has
been approved.

These days when someone mentions xray, there can be a lot of variance in
what that data actually means, given that some lucky operations have
been given the expensive CT models, or have the 3D systems in place.
With a standard 2D with tilt models, it is not as easy to investigate
voiding.

If this is just on one PWA, is there something special about this
particular board, such as microvias within the pads...?  Just some
things to think about.


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Lum Wee Mei
Sent: Tuesday, January 03, 2012 5:17 PM
To: [log in to unmask]
Subject: [TN] Solder voids in BGA balls

Dear TechNet Buddies,

My colleague was performing BGA x-ray inspection to 20pcs of the PCBA,
each of them has a BGA on the board. She observed that all the BGA
solder balls have high number of multiple solder voids of various sizes
within each of them. The estimated summation of the solder voids from
each ball ranges from 20 - 25%. As the voids are within the acceptable
value of 25%, process manager wanted QC to consider the workmanship as
process indicator.

My colleague approached me for advice and being a QC, I decided to
consider them as reject base on :

(a)    When consulted, Process Manager is not able to determine whether
such extensive solder voids will have any impact on the PCBA
reliability.

(b)   Though the solder voids size/summation are within the 25%, this
value are observed on every BGA's solder balls, across all the 20 BGAs.

(c)    The PCBAs are Class 3 and to be used on mission critical
application.

Before QC decision to reject them was communicated, the process engineer
recall 5 of the PCBA to perform another round of reflow.

Questions :

1.       Should the above solder voids workmanship be considered as
"process indicator" or "reject"?

2.       Is there disposition for workmanship that is classified as
"process indicator" such as rework or replacement? For me, it should
not.

3.       Since the process engineer recall 5 of them to perform another
round of reflow, does it not mean he also concur that the workmanship is
not acceptable?

I am a self-learned QC, so any sharing on this matter will be greatly
appreciated.

Thanks and regards,
~wee mei~


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