How Eo X-ray Machines Work For Electronics?

The X-ray machines are extensively used to determine the quality of electronic components. Their rays enter and produce images of the interior of a device clearly showing its state. This type of inspection is especially used on a printed circuit board (PCB) to check on its quality without doing any damage to the board.

The wider part of the electronics industry prefers the smaller, densely populated printed circuit board assemblies (PCBAs). Not necessarily because they have to be smaller, however new designs come with hidden solder connections such as the ball grid array (BGA), (QFN) quad flat no leads, and land grid arrays (LGAs).

These kinds of devices come with cost and performance benefits and therefore the trend is expected to continue. A recognized key process in surface mount is automated optical inspection (AOI) but what about devices whose solder connections cannot be optically seen? This is where x-ray machines come in handy.

Among the most notable trends that are affecting inspection include:

  • Component size: Most circuit boards are becoming smaller and more miniaturized with dense boards and PCB components are already a route.
  • Surface mount technology (SMT): this technology has made packages and leads smaller making PCBs denser with more parts hidden between layers.
  • Component placement: Electronic components are becoming smaller and further layered to maximize functionality and save on space.

How x-ray electronics add value to the manufacturing process

Incorporating x-ray inspection in the production quality control process eliminates the risks of making assemblies that are uneconomical and impossible to repair because of the hidden connections in these devices. It can be time-consuming to rework a misplaced device and can as well cause problems in the assembly and the surrounding components.

You may also surpass the maximum required solder reflow cycles when trying to rework a misplaced device which may bring additional expenses in diagnostics and retesting. Therefore, x-ray machines should be used as the first inspection process to ascertain that the oven profile is excellent for leadless devices.

X-ray inspection as well reduces end-of-line manual inspection especially for devices that AOI cannot fully cover or where BGA inspection methods may have been used. X-ray electronics also go a long way in resolving quality issues in a non-destructive way. Upgrading x-ray machines to full 3D capacity helps an inspector go through an assembly to find faults like broken barrels or tracks in a PCB and leadless components.

Having a capable x-ray inspection system is today deemed a must-have for contemporary electronics manufacturing plants.  Your organization however has to decide if it needs to buy one for itself or have an (EMS) electronics manufacturing services partner to invest on your behalf.

How an x-ray electronics machine works

Three basic components make up an x-ray inspection machine which includes:

  • The x-ray tube: This tube is responsible for generating x-ray photons.
  • The platform: This is the operation platform where samples are moved in different directions enabling them to be inspected from various magnitudes and angles.
  • The detector:  The detector which is on the other side of the sample catches and assembles x-ray photons transforming them into an image.

X-ray machines work by using x-ray photons which are moved through a sample then collected on the opposite side. X-ray photons move through samples differently depending on physical properties like density, atomic weight, and thickness.  Typically, the heavier the sample the more x-ray photons it absorbs.

Generally, heavier samples are easier to image than lighter samples whose images become more transparent. Because of the unique behavior of different samples, various amounts of photons are gathered on the other side which creates the image. Components of a PCB usually consist of heavier elements which makes it easier for an x-ray machine to image.

What to consider before choosing x-ray electronics equipment

There are several x-ray equipment vendors out there, so you need a must-have list in mind before you start looking for one.  Ensure that the x-ray equipment you want is large enough to fit with the things you intend to inspect. Here are three areas to consider before choosing an x-ray machine:

1.   Image quality

When looking to purchase a camera, people usually go for one with the higher megapixels for better-quality pictures. This however is more complicated when choosing x-ray systems because it is not as simple as choosing one with higher pixels. X-ray systems tend to have very intelligent software and a tone of physics involved.

Image quality is affected by several things such as power, spot size, voltage, the closeness of the x-ray source, the field of view, and the detector resolution. For instance, an x-ray system with a voltage of 160kV has a better x-ray penetration capacity than one with a 130kV capacity. However, the bigger voltage may negatively affect the image contrast and consequently the quality.

To make a decision, a practical solution would be to take sample assemblies to try out the x-ray system since image quality is mostly a subjective opinion. The good news is there are x-ray systems specifically made for PCB assemblies and the quality of their images is anywhere between very good and excellent.

2.   How many dimensions does it have?

Currently, there are three dimensions for x-ray systems.

  • A 2D system that gives a straight top-down view.
  • A 2.5D system that is enabled for top-down and angled or tilted views.
  • A 3D system that has a three-dimensional rebuild of the assembly. It may also use other techniques such as aluminography, topography, or the computed tomography (CT) which is the full 3D effect.
  • It is expected that the more you get to see the slower the x-ray inspection becomes because it may take hours for complex CT scans to be done.

3.   Ease of use

Some x-ray systems have a degree of automated inspection and program sequences of inspection with criteria for pass/fail. This makes operation and repeatable inspection very easy and can be enabled for an inline process if need be. However, doing ad hoc inspections and setting it up will require some skill.

Whilst contemporary x-ray systems are easy to use, the inspector has to know what all the settings do and be able to interpret the results with reasonable knowledge of a PCB assembly.

Adam Hansen