Hi Bev - one other telltale sign in the cross-section is the "comet tails"
swirling off the void pockets which is part of the issue that Stewart
detailed.
Dave
Bev Christian <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
06/11/2010 10:40 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Bev Christian <[log in to unmask]>
To
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Subject
Re: [TN] Weird formation of voids
Stewart,
I lieu of a Dave Hillman Friday quiz, consider this it. And you WIN!
Using an SEM and then carefully examining those pictures and the shape and
placement of the "voids" we were able to determine that it is exactly as
you describe. We are now in the process of hitting our grinding paper
supplier "up the side of the head" for a crappy lot of product.
Bev
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stewart McCracken
Sent: Friday, June 11, 2010 11:36 AM
To: [log in to unmask]
Subject: Re: [TN] Weird formation of voids
Importance: High
Hi All,
Looks as though sample preparation condition is less than ideal. Sample is
a little rounded and it appears that the voids might in fact be embedded
debris from the polishing equipment(?) I'm sure Vladimir would agree - get
it in the SEM to be sure! Need some better imaging and if possible EDS -
these will go a very long way to confirming what's going on. Lumps of
silicon carbide can really make a mess of a x-section. If you don't have
access to a SEM, you could etch the structure and look for abnormal
/unusual structures surrounding these features. Etching would also help to
refine the soft edges on a x-section (provide a more natural edge) and let
you see if you have shrinkage or gas voids (look at shape) filled with
grinding debris.
Contaminated mats on a polishing station could explain the pattern of
occurrence and the feature. As always though, more info about condition
would make diagnosis easier!
Kind regards,
Stewart
Stewart McCracken
MCS Ltd.
Centre House
Midlothian Innovation Centre
Roslin
Midlothian
EH25 9RE
m. +44(0)7711 541735
t. +44(0)131 440 9090
f. +44(0)131 440 9085
e. [log in to unmask]
w. www.themcsgroup.co.uk
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of stephen gregory
Sent: 11 June 2010 16:21
To: [log in to unmask]
Subject: Re: [TN] Weird formation of voids
Hi Bev!
Got your picture today, and have it posted now:
http://stevezeva.homestead.com/Bevs_Ball.jpg
Almost looks like little pieces of dross. I wonder if something is going
on with the solder paste? Or leaded reflow profile with a lead-free BGA?
Steve
--- On Wed, 6/9/10, Bev Christian <[log in to unmask]> wrote:
From: Bev Christian <[log in to unmask]>
Subject: [TN] Weird formation of voids
To: [log in to unmask]
Date: Wednesday, June 9, 2010, 9:51 AM
TechNetters,
I am sending a picture to Steve to post. I have labs in three locations.
One of them has seen weird voids in cross-sections of BGAs while the other
two locations have not. For the lab that has seen them, the
cross-sections were prepared by different people on different days for
different products, using the same equipment. The voids are not in all
balls cross-sectioned but may be only in one of two of the balls in a row
of multiple solder joints examined.
Have you seen anything like this? Do you know the root cause?
Vlad,
You know what is going on, so please don't respond.
Bev
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