Ultra-thin pick-up coil for surface flux detection

In surface magnetic field measurements an absolute flat active sensor part is essential to decrease the distance between an induction coil and the sam ple surface. To fulfill this requirement a new bonding technique is present ed which allows to perform contact pads not towering above the active senso r surface. The method is based on drilling of funnel-shaped holes in a Al2O 3-ceramic substrate using a CO2-laser. After plating the substrate's surfac e with a solderable metalization, the funnel mouth is used to integrate the whole interconnection volume within the substrate thickness. The contact w ires are guided through the holes perpendicular to the opposite substrate s urface. Finally, the CO2-laser is used to perform the soldering process and for shaping and separating the respective single sensor units from the cer amic substrate. The combination of all these production steps in a flexible numerically controlled laser micromachining process is an advantage partic ularly for small-lot fabrication and the rapid production of low cost proto types. (C) 2001 Elsevier Science B.V. All rights reserved.