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BGA Xray inspection

Ron Costa

#4341

BGA Xray inspection | 27 April, 2000

Hello all!

I am looking for an xray machine that can show me an open BGA solder joint. Does anybody have any experience with different type machines? I have used Nicolet model NXR 1400i.It's good at showing shorts but it cannot show me an open. Any feedback appreciated

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D Scott

#4342

Re: BGA Xray inspection | 27 April, 2000

Ron,

I too use a Nicolet NXR 1400i. By using the rotation fixture and offsetting the board, a good BGA solder joint will appear elongated. If you rotate the board away from you the wetted joint will appear to lighten and become flat (looking at the bottom of the ball). An open joint would not show this, it would still look round with no signs of wetting to the board. If you do not have the fixture you can still support the board with something and see the same results. I hope this helps

D.Scott

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#4343

Re: BGA Xray inspection | 27 April, 2000

Ron: Good news: Nicolet makes excellent machines. Bad news: I�m unaware of a machine with the capabilities you seek. * X-ray machines lack of resolution needed in relation to the crack geometries encountered within a high density single material. The crack sizes are in the noise limits of the x-ray resolution measurements. * Neither laminographic nor transmissive x-ray can define the area where the solder meets the pads well enough to determine opens. * A best, x-ray can check for insufficient amount of solder, which is not necessarily an open or a crack.

Alternatives are: * More relevant data can be obtained with electrical test methodology (i.e. boundary scan). * Acoustic microscopy is no better than x-ray. * Environmental screening using vibration may cause your opens to hard fail.

Good luck Dave F

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Dean

#4344

Re: BGA Xray inspection | 27 April, 2000

Here are some pointers to use during your X-ray inspection.

Microcracking is virtually impossible to determine with X-ray. However, I suspect you are looking for "hard" opens. Those are much easier to find visually. If using a paste-and-place process...

1. If solder paste is missing from a pad or a ball is missing from the device you will see an obvious diameter difference between the defective interconnect and adjacent ones. Why? the solder balls collapse, spreading outward. This volume will be very consistent from ball to ball. Except in the case of missing solder paste or balls. That location will be smaller in diameter. Good x-ray machines have the ability to measure diameter to help aid the technician. In additon the missing solder often will show up "lighter" vs. normal balls.

Hope this helps. Happy x-raying!

Dean

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Peter Loten

#4345

Re: BGA Xray inspection | 13 November, 2000

I agree with all the previous comments. You need an XRay system with good software capabilities to "clean up" the images, but you also need to interperate the results and training/experience comes into this. Get free trials first on a machine like CR Technology in California or Diagnosys.com in UK. You really do need to run trials before committing to any machine.

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