A Novel Method for Co-Rich Amorphous Alloy Wire Electrical Interconnection by Using PI Film as Solder Mask

Co-rich amorphous alloy wire is an excellent material for magnetic sensor due to its extremely high giant magnetoresistance effect (GMI) performance. While, it shows poor wettability with solder, thus hard to control the welding area, which leads to large contact resistance variance when soldering with substrate or package due to the interconnection area can't be accurately controlled. To improve the wettability between amorphous alloy wire and solder and achieve small contact resistance variance, a novel electrical interconnection method is proposed. First, a photosensitive polyimide film (PSPI) is patterned by spin coating, exposure and developing to form vias at the two ends of the amorphous alloy wire. Next, a thin Cu/Ni composite layer with thickness 200nm/300nm were deposited sequentially on the surface of amorphous alloy wire. Then, solder paste is stencil printed into these vias and reflow to compete the electrical interconnection between the amorphous alloy wire and the substrate or package. Thick PSPI film is employed as solder mask due to its excellent properties, such as high temperature stability, thick film formation and easy to be patterned. The test results showed that there is one order magnitude reduction in standard deviation of the electrical resistance comparing to the results obtained by conventional welding process.