Process control in electronic production:

Huber Group puts more emphasis on 3D X-ray inspection for highest quality standards / X-ray to control even the most complicated assemblies while simultaneously saving time

Short time-to-market and high quality are part of Huber Group’s company philosophy. Speed and high quality standards accompanied by smaller and more complex components play a considerable role in the field of electronic production. In order to meet the high demands for quality assurance of printed circuit boards, such as the multilayer printed circuit board (PCB) for the „blue PiraT“ data logger by Telemotive AG , Huber Group relies increasingly on its fully automatic, in-line X-ray inspection system , the „XStation MXTM“ by Teradyne. This X-ray system provides the automotive supplier with a quality control system, which also identifies alleged sources of error in a very short test in assemblies with a high component density, dual-sided assembly and BGAs (Ball Grid Arrays), as well as many fine pitch and THT components with covered or shielded solder joints.

When manufacturing electronic control units or assembling circuit boards, Huber group guarantees fast and precise quality control even for the most demanding of projects. Therefore the Group recently accepted the order to assemble the multilayer PCBs for the blue PiraT“ automotive data logger for Telemotive AG. This so-called ocean main board has a multilayer circuit board, with 10 layers, a high-grade density of a total of 851 parts, and 162 varieties on a board only 168x168mm in size, as well as a total of 3,950 solder joints and several Ball Grid Arrays (1×256-pole and 1×272-pole). Such complex assemblies put enormous demands on quality assurance and process controls in electronic production.

If, as in this case, BGAs are also present, then conventional optical test procedures, so-called AOIs (Automatic Optical Inspection), are no longer adequate. The BGA-soldering process can only be 100% guaranteed by using the AXI-method (X-ray inspection) whereby the balls are described with up to 30 parameters, and their average, minimum and maximum and variance are tested. Even the current approach to solder joints on the surface is not suitable for a double-sided board such as the ocean board to completely uncover sources of error. It is necessary to inspect the board on both sides for double-sided assembled boards and vertical solder joints that overlap one another. When using the AOI system, a board would have to be tested separately on both sides. In comparison the X-ray procedure shows 9 images instead of only one, which can be mathematically shifted (pixel shift), so that only one side can be seen on the X-ray image. The system, according to the operating principle of digital tomosynthesis, provides a complex and very exact quality analysis of manufactured solder joints to guarantee the long-term quality of the hardware. Thus the 3 D X-ray inspection system facilitates more than just considerable time saving.

As the boards are X-rayed in various positions, the user obtains several cuts per solder joint, which allow for a coherent image of the quality.  Overlapped solder joints can therefore be assessed via software on the top and bottom sides of the board in mathematically separate images. Overlapping components and their possible solder joint defects can then be clearly attributed to the top or bottom side of the component. The system has an X-ray detector with a resolution of almost 5 megapixels, facilitating a pixel size of   25 µm. Even the smallest deviations in the fine pitch region or in the R-packs can be identified. Every solder joint model has its own parameter and rules, which guarantee the quality required. Using this procedure Huber Group is in a position to identify not only solder defects such as open, lacking or cold solder joints, but also undesired solder bridges or even missing, voltage reversed or displaced components and short circuits, as the source of error will be identified quickly and precisely. The X-ray procedure has a pseudo error rate of less than 300ppm, which is below even that of the high end AOI systems. The image processing and evaluation is undertaken online by a high-performance computer, which automatically conveys corresponding X-ray images to a rework station, should it detect the slightest of abnormalities or defects. Multiple use tests are also feasible for assemblies up to 18″ x 18″ in size.

Using the same X-ray inspection system, Huber Group is also in a position to investigate less complex assemblies, by conducting an even more time-saving 2 D inspection. In this way Huber Group can accommodate standards of the highest quality at all times while considering the economic viewpoint.

Additional information:

The manufacturing of ECU’s and PCB assembly is performed in two assembly lines at the headquarters in Mühlhausen, Germany and also at an own electronic manufacturing facility in the United Arab Emirates. At the moment approx. 100,000 control units in SMT (Surface Mount) technology per year are manufactured. Having printing capacities of 200 million components a year, Huber group is also prepared for large-scale orders. At its headquarters Huber Group runs ten Pick & Place machines, five soldering facilities, several silk printing machines, in-circuit and function testers and one 3D X-Ray station. For Run-In or Burn-In processes climate chambers are available. Endurance tests as well as shock testing are performed with an in-house vibration testing equipment with integrated climate chamber.