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April 2011

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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:
Wed, 27 Apr 2011 14:02:38 -0500
Content-Type:
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text/plain (203 lines)
I would refer you to IPC-7095. In there, they show some examples of tilted or shifted solder balls, but they classify them as "disturbed" SJs. In your case, I don't think they are. BGAs are oftentimes not placed perfectly, but usually during reflow they shift into full alignment over the pads due to the surface tension of the molten solder. Sometimes, however, that does not happen, and you end up with angled solder "columns".
Based on your Xrays, I see that full wetting took place on both the BGA pad and the PWB pad. I also see that the SJ is not hourglass shaped, but is still a ball. Based on that, I don't think that these are "defective". There are specifications for BGA ball roundness, etc. but I believe they are intended to be used for the fabrication acceptance criteria for the BGA itself, not for after assembly to the CCA.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Bavaro
Sent: Wednesday, April 27, 2011 1:50 PM
To: [log in to unmask]
Subject: Re: [TN] BGA Ball Tilt

My question is:  do the rest of the BGA balls look like pumpkins and
these corner balls are stretched and leaning towards the middle?  

A 900 pin bga is large enough I can envision some corner movement
potential due to package movement.

I don't know of any specific reject paragraph which would apply to this
condition but when approving up a new reflow process, my preference is
to have the BGA cross sectioned so that I could compare the height of
the balls along the entire side (and across the middle as well).   

Sometimes xray images can be very deceiving and actual cross sections
resolve any doubt.

Phil



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Wednesday, April 27, 2011 11:33 AM
To: [log in to unmask]
Subject: Re: [TN] BGA Ball Tilt

Hi Mark,

I have your pictures up on my web page:

http://stevezeva.homestead.com/corner_1_45_degrees.jpg

http://stevezeva.homestead.com/corner_2_135_degrees.jpg

and in looking at your images, I don't know that I see a real problem
there.
The ball shape may not be perfectly symmetrical, but I see the same sort
of
shape in the other two balls in each image. 

Maybe others can look at these images and say if there's anything to be
too
concerned about...

Steve



-----Original Message-----
From: Woolley, Mark D. (Mark) [mailto:[log in to unmask]] 
Sent: Wednesday, April 27, 2011 12:51 PM
To: Steve Gregory
Subject: RE: [TN] BGA Ball Tilt

Steve,
The X-ray images are taken 60degrees to the beam direction.  The
magnification is geometric not mathematical.  These are same side
corners
(not opposite corners).
Thanks,
mark


mark
Mark Woolley |PTRL Laboratory | Avaya | 1300 West 120th Ave |
Westminster,
CO 80234  USA | Voice (Lab): (303) 538-2166 | email: [log in to unmask]
|

-----Original Message-----
From: Steve Gregory [mailto:[log in to unmask]]
Sent: Wednesday, April 27, 2011 10:03 AM
To: 'TechNet E-Mail Forum'; Woolley, Mark D. (Mark)
Subject: RE: [TN] BGA Ball Tilt

Do you have any pictures Mark?

Steve Gregory

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Woolley, Mark D.
(Mark)
Sent: Wednesday, April 27, 2011 11:56 AM
To: [log in to unmask]
Subject: [TN] BGA Ball Tilt

I am experiencing a BGA condition I have never encountered before.  A
large
>900 pin BGA has corner pins that are not perpendiculat to the PWB
surface.
They are slightly angled toward the center of the BGA.  This is seen on
all
four corners.  Obviously, this condition is not preferred.  Is there a
specification that states the condition of the ball?

Thanks,

mark

 

 

mark

Mark Woolley |PTRL Laboratory | Avaya | 1300 West 120th Ave |
Westminster,
CO 80234  USA |

Voice (Lab): (303) 538-2166 | email: [log in to unmask] |

 


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