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June 2010

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Subject:
From:
Stewart McCracken <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stewart McCracken <[log in to unmask]>
Date:
Fri, 11 Jun 2010 16:46:16 +0000
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Hi Paul,

We generally use SiC for grinding unless we have lots of alumina or something super-hard to cope with in which case diamond film can be helpful (although expensive and you need to be really careful with edge of your specimens so as not to catch an edge and wreck the film).
From there ever smaller diamond (usually 3micron and 1micron) followed by silica and/or alumina suspension for finishing. 

Like most, we have a range of different "recipes" to get the job done on a wide range of samples. 

BR

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 Paul Edwards
Sent: 11 June 2010 17:35
To: [log in to unmask]
Subject: Re: [TN] Weird formation of voids

Just out of curiosity is every one using SiC instead of diamond for cutting and lapping?

Paul

Paul Edwards
Surface Art Engineering


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Friday, June 11, 2010 8:52 AM
To: [log in to unmask]
Subject: Re: [TN] Weird formation of voids

Steve,
Good observation!  This is one of the things that lead my lab manager to determine that the voids were an artifact of preparation and were not caused by the solder paste and/or manufacturing process.  The re-polished samples look GREAT.
Bev
RIM

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Friday, June 11, 2010 11:47 AM
To: [log in to unmask]
Subject: Re: [TN] Weird formation of voids

Another thing that's weird, is that you see the intermetallic layer even
where the voids are...how does that happen?

Steve

-----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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