Issue link: https://iconnect007.uberflip.com/i/921680
26 SMT007 MAGAZINE I JANUARY 2018 tion without resorting to potentially destructive re-work or micro sectioning, which adds cost and, of course, leads to a scrapped assembly. Micro-sectioning also requires a bit of anedu - cated guess as to where the problem might be. How often have your heard someone say, "It fails test, it doesn't work, and I can't see where the problem is, so it must be the BGA"? Enhancing X-ray to provide laminography, or indeed, full 3D capability that enables the inspector to walk through an assembly, helps find faults such as broken tracks or barrels in a PCB, for example, as well as any issues with leadless components. Away from PCBAs, X-ray can provide non- destructive inspection of other manufac- tured components such as cable assemblies or machined parts where there is a need to see interior detail. It can also provide a degree of measurement capability. So, a capable X-ray inspection facility is now considered a must-have for modern electronics assembly lines. But now that you have decided you need one yourself, or that your electronics manufacturing services (EMS) partner should be investing on your behalf, how do you go about choosing the right system? Key Considerations There are a lot of vendors and systems out there, so as with all capital equipment evalu- ations it is best to start looking with a must- have list already in mind. We will assume that price (and payback) will be part of the equa- tion, and of course, the system must be large enough to accommodate the items that you want to inspect. The following are four more areas to consider: 1. Image quality If you were looking to buy a camera, then one with a higher pixel count, say, 24MP, is better quality than one with 16MP, right? If you know a bit about photography, you will know this is a great over-simplification (if not just plain nonsense), and if anything, X-ray can seem even more complicated. There are physics and very clever software involved. Things that can affect image qual- ity include the power, voltage, spot size, detec- tor resolution, proximity of the X-ray source to the item and the field of view. Take voltage, for example. A 160kV system will have greater X-ray penetration capability than say a 130kV system, but the higher voltage can adversely affect the image contrast and hence, quality. How do you decide? The most practical solu- tion is to take some typical sample assemblies and try the X-ray system out. Image quality can be a subjective opinion. The great news is that you will probably find that systems aimed at PCB assemblies provide image quality that ranges from very good to excellent. This can perhaps be more to do with how the inspection is set up than the technical capability of its components. 2. How many 'Ds'? The D, of course, stands for dimensions. There are three kinds of systems: • 2D, which provides a straight top-down view • 2.5D, which allows top down and tilted or angled views • 3D, which is a three-dimensional re-construction of the assembly. This might use such techniques as tomography, laminography or (for the full 3D effect) computed tomography, or CT Figure 1: X-ray allows inspection without resorting to potentially destructive re-work or micro-sectioning.