Adhesive bonding strength for printed and hybrid electronics

Electrically conductive adhesives offer a low-temperature alternative for soldering process in electronics assembly. Adhesive bonding technology is especially advisable when integrating components on printed structures on soft substrates with low heat-tolerance. This study investigates mechanical durability of surface mounted chip resistors bonded on a flexible substrate with an isotropic conductive adhesive. The test specimen are manufactured in fully automated roll-to-roll processes by rotary screen printing a conductive circuitry, and subsequently dispensing silver epoxy, pick-and-placing components and heat-curing the adhesive. The adhesive bonding strength is studied with an automated test setup pulling a component off from the substrate. This destructive test method is used to evaluate the mechanical strength when varying adhesive volume at the interconnection areas with different component sizes. The results prove that the adhesive bonding strength for printed and hybrid electronics can be improved by increasing the adhesive volume in bonds when using a silver epoxy. At the same time, spreading of adhesive dots during assembly process limits the applicable adhesive volume to avoid short circuits and to maintain the electrical functionality. The study provides guidelines to optimize dispensing routines to achieve stable electro-mechanical interconnections.