The effect of temperature ramp rate on flip-chip joint quality and reliability using anisotropically conductive adhesive on FR-4 substrate

In this work, the effect of temperature ramp rate on flip-chip anisotropically conductive adhesive joint quality and reliability has been studied. The experiments were performed on bumped and unbumped die. They were assembled onto bare ITO-glass and FR-4 substrates. The reason for using the transparent glass substrate is that the particle deformation and settlement can be visualised without destroying the assembled module. The temperature ramp rates studied ranged between 8.1 and 65.7°C/s. The experiments show that the best joint quality is obtained when a slow temperature ramp rate is applied to unbumped dies. A good joint is achieved when many particles have been entrapped on the die pad and when there is a significant degree of particle deformation. A large degree of deformation of particles results in a large contact area for the electrical conduction path. When a high temperature ramp rate is applied, there is a risk that the adhesive is already cured before full compression is reached. This will prevent the particles in the adhesive from contacting the bonding surface. When assembling bumped die, the temperature ramp rate does not seem to have a significant influence on the result. The joint quality evaluation has been performed using Scanning Electron Microscopy (SEM) and Optical Microscopy (OM). Furthermore, temperature cycling between -40 to +125 °C, 1000 cycles, has been performed to characterise the joint reliability under the optimum temperature ramp rate conditions. The electrical resistance has been measured continuously. A theoretical simulation of the influence of the temperature ramp rate on the adhesive joint quality has been performed using the same test module conditions as for the experimental work. The results coincide with the experimental results, particularly in the range of low bonding pressure values