Gil

Transmission x-ray inspection is the technique most people are familiar with. Since materials will absorb or transmit x-rays as a function of their atomic number and thickness, the transmission x-ray image provides a two dimensional represenation of a three dimensional structure analagous to the two dimensional shadow image cast on a wall of a three dimensional,translucent structure. As such, we need to know something about the anatomy of the three dimensional structure in order to interpret the two dimensional shadow image. Both for shadow and x-ray images.

Laminography is a coined term for a technique well known in medical imaging called tomography. Tomography attempts to image isolate a two dimensional plane in the structure being inspected by moving the x-ray source and imaging plane in a prescribed manor so as to cause all other planes to be defocussed. It can be an effective method of determing the position of a solder void or positively determining a non-contact situation. Unfortunately the image sharpness of tomographic images tend to be poor due to the image motion and the nature of the x-ray imaging phosphor design. In addition, advances in understanding the meaning of the variations in size and shape of ball bond images is improving the detection of non-contact and other process related problems by transmission x-ray at significant cost savings.

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