Research on Reliability of Potting Adhesive in Ceramic Substrate

Wire bonding was the most widely used electronic packaging technology at present. In the actual application process, the components had the characteristics of high-density assembly. Accordingly, the wire bonding characterized by small pads, fine spacing and multiple layers. In this paper, 800 bonding points were set in the range of 13.9 mm × 13.9 mm. The diameter of the bonding wire was 18 μm and the center distance was 52 μm. Four layers of bonding surface arranged and the wire bonding process was soldering process with gold ball. In order to prevent failure of wire bonding, potting adhesive technology added behind the wire bonding process. The process could fix the gold wires and played the role of insulation protection. Through modeling and simulation, the potting adhesive could transfer the stress concentration point of the ceramic substrate from the inside to the outside. The highest value reached at 150 °C, when the stress was 33.24 MPa. Viewed from the outside, the potting adhesive was intact after the implementation, but it cracked after several temperature cycling tests. Interestingly, the gold wire protected by the potting adhesive remained intact, but the ceramic substrate cracked. Through mechanical analysis, this related to the internal stress of potting adhesive. The internal stress related to coefficient of thermal expansion and elastic modulus. The bending strength of ceramic substrate decreased with the increase of times of temperature cycling. When the internal stress reached 55.93 MPa, the ceramic substrate cracked. Finally, experimental verification gave two solutions. One was to reduce the application temperature and the other was to replace the potting adhesive. In the ceramic packaging, wire bonding and potting adhesive technology were compatible, which had guiding significance for the subsequent high-density packaging.