Array of miniaturized fluxgate sensors for non-destructive testing applications

The physical size of almost any technical component, electronic as mechanic, has been significantly reduced during the last years. Further reduction is intended especially in the microelectronic business. Component test becomes a more and more important working field. Efficient test strategies are necessary to reduce costs even for complex tests. Non-destructive testing is inevitable. Small scale measurements require miniaturized sensors. In the field of non-destructive materials testing cracks, dots and other impurities in ferromagnetic materials can be detected magnetically. High performance sensors with small size can help to overcome detection limits. A first step towards an integrated array of fluxgate sensors is presented: A line of four fluxgates, each smaller than 500µm in width, arranged with 500µm pitch on one sensor chip. This chip will arise further possibilities: non-destructive testing applications in the field of soldering tests or current measurements with high area resolution. The sensors have similar features like the magnetometer with two perpendicular axes used for compass applications [1]. The sensitivity can be adjusted between 5 to 30 mV/µT, the bandwidth between 10 and 400Hz. Using 35Hz for the low pass filter the noise is below 0.1µT. The sensor chip is mounted in chip on board technology on a ceramic substrate with 0.6mm thickness. The whole board has a thickness below 2mm including board, chip, bond wires and encapsulment. Further possibilities for test set-ups can be achieved building two dimensional arrays of stapled boards. The pitch in the second dimension can be as small as 2mm, several boards can be stapled. Using two dimensional arrays a fast high performance test of planar structures is possible. The function is evaluated with the 4 in line array. Measurements of test structures will be presented. In the close future evaluations with longer lines can be made with two chips coupled to an eight in line array. The realization of longer lines require some further work: A new ASIC or a system on board for multiplexing will be necessary. From the sensors side the only challenge is the electrical connection of the chips. [1] H. Grüger, R. Gottfried-Gottfried " Performance and applications of a two axes fluxgate magnetic field sensors fabricated by a CMOS process", Sensors and Actuators A 91 (2001) 61-64