Internal stress and connection resistance correlation study of microbump bonding

Microbump bonding (MBB) method ensures the micro-order direct bonding betwe en the integrated circuit (IC) electrode and circuit substrate electrode. M BB 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 forc e that the adhesive imposes to drag together the bumps of the IC and the el ectrodes 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 ha ve a low Young's modulus and high coefficient of thermal expansion (CTE). T he stresses of the MBB structures with gold bumps or compliant bumps are de termined and compared at various environmental temperatures. The stress ana lysis results are used to identify the appropriate bump for the given MBB s tructure. Both analytical and experimental results demonstrate the feasibil ity of using the compliant bumps to achieve a high compressive stress and l ow as well as stable connection resistance at various environmental tempera tures.