What is x-ray CT and do I need it for my PCB or Semiconductor application?

If 2D x-ray inspection for PCB and semiconductor applications can be seen like taking an x-ray of a broken arm or leg in a hospital (although providing large magnification) then CT, or Computerised Tomography, can be seen like taking a CAT, or CT, scan of the body in a hospital. In a CT scan, a whole series of 2D x-ray images are taken at every angle all around an object and this is repeated along the object’s length. These images are then taken into a PC and computationally re-constructed so as to provide the ability to look at a complete x-ray image of any slice through the object. The accuracy of the reconstruction is dependent on maintaining the positional accuracy of the sample throughout taking the x-ray images. That is why the person in the hospital has to remain as still as possible when undergoing a CAT scan. Unfortunately, the magnification and resolution that are needed for PCB/Semiconductor CT examinations technically means that the final results of such a CT investigation is much more limited compared to what would be perceived as being the case based on a hospital examination. For example it is typically limited to samples of around 10mm x 10mm and requires a stand-alone system to provide the positional accuracy to enable the best CT re-constructions possible.

As it is, this process for PCB and semiconductor applications still requires that many x-ray images are taken for each sample and then the computing time and power needed to re-construct the final slices is also very high. This is why a CT scan will typically take many tens of minutes, if not hours, to complete. If more resolution is needed and the sample is larger then this will increase the time to produce the CT image substantially.

So to consider if a CT system is appropriate for your needs the following questions might be asked:

Does the substantial cost of a CT system, suitable for electronics applications, actually provide much more information on the sample for your needs than can be obtained, simply and quickly, from a single 2D image in a 2D x-ray system?

What is the maximum size of the object that can be inspected?

Must I destroy my sample to make it into an object of sufficiently small size to fit within the CT system?

How long will it take to produce a CT image for an object of that size and at what resolution?

If I sacrifice resolution to speed up the time of CT acquisition then will it provide sufficient information for my needs?