Micro Eddy-Current Technology (.MU.-ECT) and Applications

Eddy-current testing (ECT) technique is a well-known methodology of nondestructive evaluation technique that is usually applied to inspect the material flaws without changing or altering testing materials. Generally, ECT technique is used as crack detection in piping systems of nuclear power plants and as an imperfect welding spot detection on aircrafts. The advantage of ECT technique is to highly sense material conductivity which depends on many variables such as material thickness, crack, aging and etc.. The planar exiting coil and the advanced magnetic sensor instead of the conventional inductive ECT probe enable us to invent the probe structure and its applications. The proposed ECT probe consists of a planar meander coil as exciter and spin-valve type giant magnetoresistive (SV-GMR) sensor. The utilization of SV-GMR as a magnetic sensor of ECT probe provides the feasibility of high-spatial resolution, high-sensitivity to low magnetic fields, and high operating frequency range. Due to the SV-GMR advantages, the inspection of micro defect and the detection of micro conductors can be performed by the proposed ECT probe. We call this system“μ-ECT ”. The advanced SV-GMR sensor improves the on-site ECT system in the previous metal inspection industry and also invents a new application in a different industrial field. We proposed the ECT system to the inspection system to electronic products, the PCB inspection system and the recognition of solder bead for ball-grid array package. Defects on high-density PCB are examined by ECT technique. The inspection evaluates not only imperfections of the PCB conductor but also PCB conductor dimensions and alignment. We discuss the ECT system and the experimental results.