Hi, Fabrice
Yes, Alan's method is a good one. The issue here is the X-ray "blooming" makes it difficult to know just where you are in terms of being able to measure a round white image, such as a void. One must understand that the X-ray measures the image you see on the screen. The software is actually an image processor. If the voltage or current level is set a little high, the void, which is white, blooms slightly and appears larger than it actually is, and this image is "measured" by the machine software and as such the voids are exaggerated. By using a ball bearing of a known diameter, you can "calibrate" the power and current levels on the X-ray until the image measured matches the known diameter of the ball bearing, eliminating the bloom factor, and then measure the voids, possibly with some minor focusing.
The newer X-rays, particularly the Dage and the Phoenix models, use some algorithms that will automatically focus on a dark object and perform an autocalibration adjustment. Then they continue on to perform the automatic measuring, and they are remarkably accurate, down into the micron range.
I use a similar method when using older X-rays, but what I use is a small scrap board with a BGA attached that has voids of a known size. The BGA on this board is already microsectioned, and I measure the 1/2 spheres with voids of a known diameter which were verified under a precision scope with reticule. This only works from a 2D standpoint, however. Alan's ball bearing is going to provide a standard from any angle.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of fabrice pires
Sent: Wednesday, September 10, 2008 7:40 AM
To: [log in to unmask]
Subject: Re: [TN] precise void size measurement
Alan,
I guess these ball bearings helped you to test image quality of tested equipment and calibrate the Xray equipment to define size of BGA balls and other things.
But do you thing metal balls can be used as precise calibration for measurement of voids inside BGA balls?
I mean voids are lack of material and balls are presence of material (metal).
In other way, does the equipment setups for correct observation of ball bearings is really the same for the voids observation and size measurement?
Thanks in advance for your input.
Fabrice
Alan Kreplick a écrit :
> Fabrice,
>
> When I was evaluating X-Ray equipment, I brought precision ball
> bearings (I think they were .050").
>
> Each machine had some sort of measurement tool, but no matter the
> machine or changing focus, tilting 50-75 degrees, etc., the .050" ball
> bearing was my benchmark.
>
> To stop the ball bearing from rolling around on the table or assembly,
> I glued it to a small piece of conductive composite material
> (left-over wave solder fixture stock).
>
>
> Al Kreplick
> Sr. Manufacturing Engineer
> Circuit Card Assembly
> Air-toAir/Precision Strike/Land Combat Raytheon Integrated Defense
> Systems 978-470-9931office
> 978-245-1702 pager
> 978-470-4307 fax
> [log in to unmask]
>
>
>
> fabrice pires <[log in to unmask]> Sent by: TechNet
> <[log in to unmask]>
> 09/09/2008 11:01 AM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to fabrice
> pires <[log in to unmask]>
>
>
> To
> [log in to unmask]
> cc
>
> Subject
> [TN] precise void size measurement
>
>
>
>
>
>
> Hi Techneters,
>
> I would like your advices on the best way to calibrate XRay pictures
> in aim to measure precisely voids inside BGA balls, after assembly.
> Everyone should agree on the fact slight setup variation on XR
> equipment could change significantly the void size results.
>
> Do you have any trick to improve precision measures whatever the XR
> equipment?
> Does the use of any reference/calibration on boards exists in that aim?
>
> Fabrice
>
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