Bondability of electroless metalfinishes for COB-technology
Summary form only given. In recent years, the application of chip on board technology (COB) has become widespread. COB technology offers many advantages compared to conventional packaging techniques, such as the reduced weight and volume of electronic components and high flexibility. For consumer applications and especially for the harsh environmental conditions in automotive applications, a qualified investigation of reliability is necessary. COB technology with wire bonds includes die bonding, wire bonding and encapsulation of bare chips on printed circuit boards (PCBs). In order to obtain a correlation between process conditions and reliability, the bondability and solderability of different electroless metal finishes were investigated. In this paper, the bondability and solderability of palladium metal finishes with an optional gold flash and electroless plated Ni-Au metallizations are shown. The investigation of the bondability was performed in two steps. First, a detailed study was performed to determine the basic factors affecting bondability. This study includes surface investigations such as SEM, Auger spectroscopy and measurement of microhardness and microroughness. As the next step, bond process windows were determined for each type of metallization to obtain information on bondability before and after accelerated ageing tests. The feasibility of different surface investigation methods is shown and the results are compared to results from bond experiments.