Research on inspection technique of printed circuit board using the probe composed of GMR sensor and planar coil

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The purpose of this study is to contribute to the progress of the high density mounting of electronic equipment by the nature inspection method of the high-density printed wiring based on the compound eddy current testing (ECT) probe by supersensitive magneto-resistance element (GMR). In the features, the testing equipment using eddy-current technology in the printed wiring inspection directly examines electro-conductivity of the printed wiring conductor by eddy currents in comparison with the method by image inspection which is the mainstream.[1]Development of multi-GMR sensor and examination of characteristicsWe developed the multi-GMR sensor for eddy-current probe. There are two type GMR of 50 and 100 mm length which has the sensitivity of 0.2 mV/μT at 1.0 MHz. It is clarified that the sensitivity of the GMR is about 40 dB higher than inductive coil at the same size.[2]Inspection of printed circuit board by eddy-current probe with GMR sensor.The characteristic for the printed circuit board inspection was measured by the production of GMR+ planar coil compound probe which made high frequency exciting coil and SV-GMR to be the detection sensor. For printed circuit testing with 70-100 μm width, the disconnection, 20 % chipping defect, 50 % depth imperfection can be detected from the experimental result.[3]Software for recognizing defectThe signal processing software that extracts the defect portion from two-dimensional detection signal image was developed.[4]Technology exchange with inspection equipment manufacturing company.With the aim of the construction of high-density printed wiring testing system using the eddy current testing probe, the exchange and transfer of technology were tried for GMR element manufacturer, ECT technology manufacturer, and testing equipment manufacturer.