Limitations of gluing as a replacement of ultrasonic welding: Attaching Lithium battery contacts to PCBs

Rechargeable shapeable Lithium batteries have been in research and development by Philips in the last years resulting in an option to optimize the size of a System-in-Package. In a previous work, it was shown that gluing can replace ultrasonic welding in low power applications, nevertheless, the glued contacts require of a material to protect them from humidity in order to avoid corrosion. In this work, the reliability of the glued and welded contacts is studied, when protected by a glob top material. The contact resistance of the bonds is measured before and after a high humidity and temperature aging process. If the contacts present a change of resistance of less than 20% after the reliability test, the test is considered a pass. The welded contacts presented a change in resistance of less that 20% and the glued contacts of at least 50%. The welded contacts protected with a high purity UV curable material are the most reliable.