PCB007 Magazine

PCB-Jan2017

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32 The PCB Magazine • January 2017 Although in some cases it also can be reworked, customer/industry requirements may disallow the rework. Again, in this case the board would be scrapped. Figures 4−6 are examples of wit- ness mark damage. Combating excessive witness marks can be a challenge. With fixture testers, there are mul- tiple variables that can contribute to damaging marks. A malfunctioning fixture is the most sig- nificant contributor. In these cases, a test probe can stick or become jammed which will not allow it to travel freely when compressed. The probe locks in place and drives a damaging sig- nature into the targeted landing pad. Second, the actual pressure used by the machine itself can contribute to the excessive marks. There- fore, it is imperative that proper set-up proce- dures be used when fixture testing. The time it takes to properly set up the fixture test greatly outweighs the cost and time lost scrapping an expensive board—not to mention the unhappy customer who now has a delayed delivery. Flying probes, although not known to con- tribute extensively to board damage, do have their caveat as well. Improper setup or adjust- ments with these machines can also cause dam- age. The main attributes are velocity and com- pression. Most significant is the Z-axis velocity. When the Z-axis travels to the board surface, its speed is important as it will travel at full veloc- ity until the board surface is detected. If this ve- locity is too high the inertia of the movement may be too significant for the tensile strength of the surface finish and may damage the surface upon impact. Further, once contact is made the variable of compression also may contribute. This is the further distance the probe will move towards the landing pad once contact has been initiated. Proper adjustments to these param- eters are crucial to provide the desired results without leaving damaging witness marks. As illustrated here, even mechanical and chemical processes pose challenges to ET. It's not just the cut and dried check for opens and shorts. Care and different diagnostic measures must be used to successfully validate the prod- uct without leaving an "ET was here" type of damaging mark on the board. HAPPY NEW YEAR! PCB Todd Kolmodin is the vice presi- dent of quality for Gardien Services USA, and an expert in electrical test and reliability issues. To read past columns, or to contact Kolmodin, click here. PLATING AND SURFACE FINISH: THE CHALLENGES TO ELECTRICAL TEST Figure 6: Witness mark 3. Researchers from Korea's Electronics and Tele- communications Research Institute (ETRI) have de- veloped a high-performance processor for auton- omous vehicles called Aldebaran. Increased focus by the automotive and IT industries on enhancing autonomous vehicle technology has increased the market for dedicated core processors customized for autonomous vehicles. Aldebaran uses all-Korean technology and it consists of four superscalar processors and an ob- ject recognition vision engine integrated to meet all functional safety requirements as specified by ISO 26262, an international standard concerning the functional safety of electrical/electronic systems in production automobiles developed by the Interna - tional Organization of Standardization (ISO). ETRI Develops High Performance, Autonomous Vehicle Processor

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