SMTA International Conference Proceedings

New X-Ray Technologies for Enhanced Void Investigation

Authors: Ragnar Vaga and Keith Bryant
Company: YXLON International
Date Published: 9/22/2019   Conference: SMTA International

Abstract: X-ray machines are not measuring devices, their full name is x-ray microscope, so measurement and metrology have traditionally not been key functions. However, in recent years accurate void measurement has become a critical part of the inspection process with finite limits being set and products passing or failing based on the x-ray measurement results.

The first thing we must state is x-ray systems do NOT measure voids, they simply measure differences in greyscale within an image, attributing areas below a certain (normally pre-set) level as being voids. X-ray images are in greyscale and the lower the materials atomic number the lighter the shade of grey, so Tungsten is very dark, and aluminium is very light.

Therefore, the more accurately the system is able to image these differences the more accurate the resulting voiding measurement. High end systems now boast 65,000 levels of greyscale, very stable x-ray sources, high pixel count digital Flat Panel Detectors, software to control image consistency and enhancement filters. All of these parts help to produce more accurate measurements, as does the improved and more sensitive void measurement software itself, with some systems able to do these calculations automatically, as part of an automated routine, even processing multi voiding area calculations automatically.

This paper will look at these improvements and also feature on the relatively new computer tomography technique which allows very accurate measurements of voiding at joint interfaces, the key area for joint strength and thermal transfer. Known as Partial or Included CT or 2.5D this technology has 2 main advantages, x-ray looks through the whole sample so determining the exact position of a void in 3 dimensions can be tough, even with good angled views. Also when measuring voiding traditionally you are unsure of the exact position of the void within the structure, There is a saying “voids in the middle of a ball are OK, voids at the ball interfaces are failures waiting to happen!’, so being able to measure voiding exactly on the plane which you want to investigate is key to achieving accurate results.

Also traditional CT (3D) with cone beam systems only works on a small sample size so is basically a destructive technique, unlike 2.5D where an area of interest can be selected on a complete assembly.

After lead-free arrived voids became even bigger talking points, now with even smaller component sizes and increased requirements for thermal transfer this will become a prominent decision factor for the future. Without accurate measurements you cannot make a good decision, so you either accept bad products or fail good ones.

Key Words: 

x-ray, void, Image chain, PCB inspection, CT methods

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