Issue link: https://iconnect007.uberflip.com/i/1494346
74 DESIGN007 MAGAZINE I MARCH 2023 lizing the CAD data, the probes can be preset to comply with an unlimited number of circuit patterns, enabling the uncompromised testing of individual or panel format circuit boards. Finally, the flying probe test is safe. To prevent the probe contactors from coming into con- tact with any other components or people, the probes are protected by a guard, minimizing the risk of damage or injury caused by faulty circuit boards. Flying probe testing is one of the most effi- cient and cost-effective methods of testing PCBs. It is accurate, fast, flexible, and safe, making it the ideal solution for many types of testing requirements. A leading circuit board fabricator in the Silicon Valley recommends: • Designated probe contact surfaces must be free of dielectric coatings, resist material, or solder mask • e preferred surface area provided for probe contact is 0.50 mm (~0.020") • Minimum probe contact area should not be less than 0.15 mm (~0.006") • When probing via holes, the preferred land diameter is 0.25 mm (~0.010") but, depending on the test system employed, they may range between 0.20 mm and 0.50 mm (~0.008" and 0.020") diameter e system shown in Figure 1 is equipped with eight probe heads (4X on the topside and 4X on the bottom) and can simultaneously probe both surfaces of the bare circuit board or panel, enabling micro-pad probe targets as small as 0.30 μm. e test system can provide probing speeds up to 180 touches per second and accuracy in the range of ±10 μm, and repeatability of ±5 μm. Circuit board manufacturers note that the manufacturing process of printed circuit boards is complex, and the process is cumber- some. Any defects not detected during the post etching phase of the manufacturing process, if not corrected, will seriously affect the quality of the final product. In order to effectively con- trol the progression of quality defects in the production process, and prevent the imperfec- tions from occurring on future runs, prompt corrective action is warranted. e following identifies defects that may occur during the circuit board fabrication pro- cess: • Electroplating short circuit: When the copper conductors are closely spaced and equal in both height and width, copper bridging between circuit paths can occur. e cause of bridging is likely due to dry film resist breakdown during the plating process. • Copper bridge short circuit: A very thin wire-like copper connection between two conductors forming a short circuit. e cause may be attributed to foreign particles that remain trapped between the resist film and copper surface. Figure 1: Two-sided, high-speed flying probe test system. (Source: SPEA Automated Test Equipment)