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July 2008

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Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Mon, 21 Jul 2008 14:34:32 -0500
Content-Type:
text/plain
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text/plain (214 lines)
Look at another populated board, because the "via" may be inside the
component.
If the location of the solder balls is in different locations from
assembly to assembly, it is a solder ball, not a via.
If you have minor solder balls that do not violate the minimum
electrical clearance (typically .006") and the board will be conformally
coated, and is not intended for space, these are not an issue. Unless
there are a lot of them, of course.
If you get two or more close to each other that could possibly shift and
violate the minimum electrical clearance between two non-common
conductors, and you need to meet J-STD-001 Class 3, rework it.
For corrective action, I would slightly reduce the apertures (10%
reduction) for the component leads (for this part only), and I do a 50%
reduction in the belly pad aperture, centering the paste deposit. This
gets all of the printed solder paste up on the metal pads. These solder
balls are from solder paste misregistration issues or if too much solder
is being printed such that small amounts (paste fines) are not entirely
on the pads. However, I think your solder balls in this particular case
are caused by the excess paste on the component leads; it appears as if
you have just the right amount of solder on the belly pads.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Sewell
Sent: Monday, July 21, 2008 2:15 PM
To: [log in to unmask]
Subject: Re: [TN] Solder balls

I was replying to Vladimir's suggestion that you might be looking at
PTHs - just a quick way to check without having to get an unpopulated
board or look at the gerber.  


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard
Sent: Monday, July 21, 2008 1:56 PM
To: [log in to unmask]
Subject: Re: [TN] Solder balls

The solder balls are near the arrows.  Faint grey round objects.
This device does have a heat slug, and there are plated thru holes under
it for heat transfer.

And yes, our X-ray does allow oblique viewing.  What are you suggesting
we look for?  

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Sewell
Sent: July 21, 2008 12:53 PM
To: [log in to unmask]
Subject: Re: [TN] Solder balls

Genny,

Does your new X-Ray allow for oblique viewing?  Your solderballs will
stay round - vias will appear as columns.  If not you can always prop up
the board on one side but magnification/focus will change and the image
won't be as "pretty".

Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Igoshev, Vladimir
Sent: Monday, July 21, 2008 1:21 PM
To: [log in to unmask]
Subject: Re: [TN] Solder balls

Hi Genny,

Here is a dummy question: Why are you talking about QFN and solder
balls? I guess what you see are kind of PTH for heat transfer, but not
solder balls.

Vladimir

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Monday, July 21, 2008 1:54 PM
To: [log in to unmask]
Subject: Re: [TN] Solder balls

Hi Genny!

Sorry it's taken me a bit to get your picture posted, but I just got
back from 2-weeks vacation and a week in Colorado going to a
IPC-771/7721 instructor certification class, so I've been catching up on
things this morning. But here is your picture:

http://stevezeva.homestead.com/files/solderballs-QFN.jpg

Myself, I wouldn't worry about them tiny solderballs. They probably
aren't going anywhere, and besides if they did, they're so small what
problem could it cause?

Steve

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard
Sent: Monday, July 21, 2008 10:52 AM
To: [log in to unmask]
Subject: [TN] Solder balls

Have you ever gotten a much better analytical tool available to you, and
have it cause major panic due to what you can see now that you never saw
before?
We got a major fancy dancy brand new X-Ray.
Now we see things like the attached picture.  Steve, could I trouble you
to post it for me?  
 <<solderballs-QFN.jpg>>
Our old X-Ray would have never seen this.
Would you fail these solder balls?

It is a QFN, 0.5mm pitch, 0.3mm pad width with a heat slug.
I think trying to replace this device by hand would cause more trouble
than we see right now.

Genny 

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