A long-term reliability of adhesive flip chip joints using very thin chips

Anisotropic conductive adhesives were used to attach daisy chained test chips on FR-4 test board. The area of the test chips was 5 mm/spl times/5 mm and the pitch was 250 /spl mu/m. Half of the test chips were thinned to the thickness of 50 /spl mu/m. Both test chip types had exactly the same test layout with peripherally situated gold bumps. Contact resistance measurements were performed using four-point and daisy chain methods. The reliability of the joints was studied by subjecting the specimens to temperature cycling and humidity tests. In addition, some of the test samples were subjected to a reflow treatment. Finally, the structure of the joints was studied with scanning electron microscopy. After 1000 cycles of the temperature cycling test both chip types showed good results. The average contact resistance of the joints had decreased, but a couple of open circuits had formed. Humidity tests caused some increase in contact resistance value. Reflow treatment did not cause significant degradation in joints.