Internal stress and connection resistance correlation study of microbump bonding

Microbump bonding (MBB) method ensures the micro-order direct bonding between the integrated circuit (IC) electrode and circuit substrate electrode. MBB consists of three elements: an IC chip with bumps, a circuit substrate, and a bonding adhesive. The binding force of the applied adhesive achieves electrical connections between the bumps on the IC chip and the electrodes on the substrate. Stress analysis is performed to estimate the contact force that the adhesive imposes to drag together the bumps of the IC and the electrodes of the substrate. The elastic model is adopted herein to determine the stress characteristics of the MBB structure. Two bumps, gold bumps and compliant bumps, are used. As well known, the compliant bumps generally have a low Young's modulus and high coefficient of thermal expansion (CTE). The stresses of the MBB structures with gold bumps or compliant bumps are determined and compared at various environmental temperatures. The stress analysis results are used to identify the appropriate bump for the given MBB structure. Both analytical and experimental results demonstrate the feasibility of using the compliant bumps to achieve a high compressive stress and low as well as stable connection resistance at various environmental temperatures.