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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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