Wire bonding process optimization for overhang stacked die

• Main Authors: Chao-YungWang, 王朝永
• Other Authors: Jung-Hua Chou
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/30114140299774717326

碩士 === 國立成功大學 === 工程科學系專班 === 101 === The portable devices created under the trend of lightness, thinness and smallness have triggered a massive wave of buying. This trend has also leaded to the popularity of flash memory. Since these portable devices need larger and larger memory storage space, for example, the enhanced pixel count for digital cameras, manufacturers keep developing flash memories with larger capacities to meet the requirements of the consumer need. However, the internal space of the small form factor portable device is restricted and unable to accommodate more memory components to expand the memory capacity. Therefore, manufacturers have to find a way to expand the memory capacity of the flash memory in a single package, and this relies on the advances of the semiconductor manufacturing technology and capability. This study takes the die thickness of 1.2 mils as the test object to develop a nine-layer overhang-stacked package for microSD card, the smallest flash memory in size. Without changing the equipment and materials currently used, this study focuses on the investigation of the required equipment and software by applying Taguchi method to optimize the wire bonding yield and quality. Reverse bonding is applied, and ball shear test and wire pull test are used to measure the bonding conditions on bonding pads, gold balls and gold wires. At 90% confidence level, the significant control factors are found and the relatively optimal process parameters are obtained. S/N ratios for ball shear and wire pull after optimization improves by 6.94 dB and 1.25 dB respectively. Moreover, the finite element analysis software ANSYS is used to simulate the stress and deformation during wire bonding on the overhanged chips so as to verify satisfied mechanical strength of the optimization results obtained by the Taguchi method.