A Reliability Study of a Novel Type of Solder-Less Interconnection

The reliability of a novel type of solder-less electrical interconnection has been investigated. The technique is known as Compressive Displacement (CD). CD is the mechanical bonding of flex to a printed circuit board (PCB) using an adhesive layer under specified temperature, pressure and time process parameters. Unlike the more commonly used anisotropic conductive film (ACF) attach process; CD does not require electrically conductive spheres dispersed in the adhesive. The metal features on the flex and the mating PCB pads are designed to displace the adhesive from between them during processing, resulting in a direct metal-to-metal electrical interconnection between the two and robust mechanical adhesion in the regions other than the metal features. Reliability experiments were performed on specially-designed test assemblies which incorporated a variety of component footprints, including 1206, 0805, 0603, 0402 and 0201 types from the IPC-SM-782 standard. Process parameters and adhesives were varied between test boards in order to evaluate the effect of these parameters on reliabilty. The assemblies were subjected to 3,700 temperature cycles of −45°C to +125°C and a 2,400 hr soak test at 85°C / 85% RH. Continuity tests were performed every 100 cycles / 100 hours. The resulting failure data indicated very few failures for many component footprint types under these conditions and indicated which process parameters had the most influence on life. Analysis of the reliability data also indicated that the CD connections for most component footprints greatly exceed the ten-year service life requirement of the intended application.