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January 2003

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Subject:
From:
Bev Christian <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 27 Jan 2003 14:27:52 -0500
Content-Type:
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Jason,
That must have been SOME CRACK!  Just imagine two saw toothed pieces of metal meshed - the amount of metal parallel to the direction of the mated surfaces is virtually identical to that of a solid piece of metal.  So I still contend that except in VERY unusual circumstances, x-ray will not work.
Bev Christian
Research in Motion

-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: January 27, 2003 9:06 AM
To: TechNet E-Mail Forum.; Bev Christian
Subject: Re: [TN] BGA micro cracks



Bev,

One X-ray system/technology that WILL see these cracks is the Agilent 5DX.
Due to it's scintillator technology, it will see cracks in BGA's. I have
used it for this before. One can "slice" through the joint at micron level
and see voided areas where the crack is. As far as the fancy scope, I'm not
sure, but think you may be referring to an Ersascope or something like the
new Metcal system.

Jason Gregory
SMT Production Supervisor
LaBarge Inc.
(918)459-2367
(918)459-2221 fax
[log in to unmask]




Bev Christian <[log in to unmask]>@ipc.org> on 01/27/2003 07:52:12 AM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
       to Bev Christian <[log in to unmask]>

Sent by:    TechNet <[log in to unmask]>


To:    [log in to unmask]
cc:

Subject:    Re: [TN] BGA micro cracks



David,
Let me  try and use an analogy to explain why you cannot use x-rays to find
micro-cracks  or intermittent full cracks (opens), as Werner has aptly
called them.   Imagine being at the base of the Rockies on the east side
and looking  west.  You can't see to the other side obviously because the
mountains are  in the way.  If you go up the east face of the first
mountain in front of  you, 4900 feet of the 5000 height, you still can't
see west.  Just  consider, for the purposes of cracks, that x-rays need a
visual line of  site.  Don't have that?  Then x-rays aren't going to help
you.   Period.  The mass of stuff in front of the x-rays is almost the same
with or without the crack, even if the beam is parallel to the
micro-crack.

What  MIGHT help you is use one of those fancy microscopes/boroscopes that
let you  peek under array devices and use one of those calibrated
torque-limited screw  drivers that Celestica (Bruce Houghton and co.)
talked about in a committee  meeting at the last APEX.  Now that might
work, unless you are talking  about one open in the middle surrounded by
solid joints.

regards,
Bev  Christian
Research in Motion
-----Original Message-----
From: David Harman  [mailto:[log in to unmask]]
Sent: January 24, 2003 8:45  PM
To: [log in to unmask]
Subject: [TN] BGA micro  cracks







Here is my issue.



We have a CM that x-rays 100% of  the BGAs on our product and notes no
abnormalities. We might have some micro  cracking at the ball joints.
(This was discovered because the product electrical properties are
intermittent when we press the BGA down.).  In addition to having our CM
x-ray the  board we had an outside company perform this inspection with the
same  results.  If it is not micro  cracking we are un-clear what else can
be causing this abnormality.



Any suggestions on how and what we  can do to capture this abnormality in
production?

What type of screening can be done  after production? (We have performed a
static thermal testing (-0 to 125  degrees) with no failures after testing.

What other type of testing or  inspection can be performed to evaluate ball
joints on  BGAs?



Thanks  David.


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