Conductive adhesive flip-chip bonding for bumped and unbumped die

Conductive adhesive interconnection for flip-chip-on-flex is discussed for both bumped and unbumped die. The flip-chip connections are made by applying heat and pressure to a conductive adhesive film. During the bonding process adhesive is pushed out of the way allowing the conductive particles to connect to the conductive pads and traces. If the proper conditions are applied, a reliable connection is made. The most stable connections were made with a gold-bumped die. However, reliable connections to unbumped die were also demonstrated using gold-coated nickel particles. The samples were prepared by patterning the particles in a grid array and then directing the flow of the adhesive towards the center of the chip rather than outward. This directed flow is accomplished by allowing the chip to deflect under the influence of the adhesive pressure. Results for both kind of die show that once a good initial contact is made, the resistance is stable in accelerated aging environments.