Simple method for flip-chip bonding on a resin substrate

The use of flip-chip bonding on resin substrates (FR-4) in the field of portable equipment has been increasing steadily due to demands for smaller and lighter equipment. The flip-chip bonding methods used for portable equipment require the presence of a solder or a conductive adhesive between the metal ''bump'' on the LSI chip and the electrode pad on the substrate. These materials have been generally considered critical to maintaining the reliability of the electrical contacts. However, the fine control in the manufacturing process required to spread the correct amount of solder or conductive adhesive paste on the minute electrical contacts is extremely difficult. Consequently, control of the soldering or adhesive process proved io be a critical factor influencing the cost of the flip-chip bonding process. We have developed a new manufacturing process for flip-chip bonding that requires neither solder nor conductive adhesive paste. Thermal cycling tests (-40C to +100C 2500 cycles) and high temperature/high humidity rests (+85C 85% RH 3500H) indicate acceptable reliability, and initial process yields reached 99.6% or more. We then used the new flip-chip process to build portable Windows-based equipment for testing purposes and thus confirmed the effectiveness of this new technology. This paper presents the method of our simple flip-chip bonding technique.