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Internal Void Monitoring Using X-Ray

               

The presence of voids in the die attach material and the package body of a device is undesirable. Voids can lead to lower mechanical strength and may allow excessive ingress of moisture and contaminants into the package.  As such, many companies employ various ways of detecting and controlling such voids.  X-ray radiography is a useful technique for internal inspection of a package.  Unfortunately, X-ray inspection is not effective in detecting voids in plastic packages and non-conductive epoxy die attach material.  The ineffectiveness of X-ray inspection for detecting voids in plastic devices is tackled in the archived forum thread below.

   

Posted by Mike_balbuena: Thu May 04, 2006 5:23 am    Post subject: Internal Void Monitoring Using X-ray

 

Does anyone does this in their back-end assembly area? What is the criteria and what equipment are you currently using? I remember generating the criteria for OSEP a while back( 1999) but I forgot already. I would appreciate any help and feedback. I was thinking for incorporating this again on our current process to preliminary monitor delam.

Thanks in Advance.
Mike

Posted by Jefriz: Tue May 09, 2006 7:26 pm    Post subject:

 

Mike,

We use that kind of inspection scheme in my previous company but it does not give much accurate result. You are going to look for 2 kinds of voids, DA region and the mold area. If you are using non-conductive epoxy, chances are you can't see the epoxy and the void using X-ray. Mold compound void is also hard to see using X-ray. I would recommend you use Through scan (T-scan). Then use C-scan for confirmation when you see a void/delamination to determine which layer have the anomaly.

Criteria for X-ray, you can try looking at MIL-STD-883F Method 2012.7. For package delamination (void), use J-STD-020C. This would give you defferent criteria on each area affected.

Added suggestion, if you see suspected delamination/void using T-scan/C-scan, don't just stop there, confirm it with cross section.

Jefriz

Posted by Mike_balbuena: Tue May 09, 2006 11:51 pm    Post subject:

 

Thanks, Jef. Appreciate that input.

Regards,
mike

Posted by newbie PE: Sun Jul 02, 2006 5:06 am    Post subject:

 

i remember my trainor's words when that question was raised while on training, he thinks there's no x-ray capability to detect voids yet, it has something to do with the material composition/ properties versus the capability of what x-ray waves can travel...

we usually use CSAM/ SAT for delam and void monitoring...

Posted by FARel Engr: Mon Jul 03, 2006 12:08 pm    Post subject:

 

Yup - the X-ray image formed by X-ray machines is based on the principle that the different densities of the different features of the package block x-rays at different levels. Denser/thicker features cast a heavier x-ray 'shadow' and appear darker on the image.

Plastic molding compound is not a dense material, and blocks x-rays minimally. This is the reason why plastic package cracks and voids are so difficult, if not impossible, to detect using x-rays - plastic molding compound offers very little x-ray contrast against open spaces.

X-ray, however, would be a good detector of cracks and voids in ceramic packages and eutectic die attach, since ceramic and gold are denser than plastic.

     

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