Insulated Au-Flash PdCu wire processing and wire bond process robustness improvements for TBGA & LQFP packages

Abstract

The insulated Au-Flash PdCu wire (X-PdFLASH) study was first initiated by Freescale, Heraeus and Microbonds with the insulated technology from Microbonds since one year ago. Since then, continuous improvements in the wire processing was conducted by machine hardware modification, process parameter re-optimization to attain a more homogeneous insulation coating layer. This was confirmed by the improved distribution of the Break-Down-Voltage (BDV) measurement as homogeneous insulation coating layer is the most critical aspect of the insulation wire quality and performance. The improvement was further verified on the wire bonding responses with the Freescale TBGA package with significant improvement on the Stitch Pull Strength, MTBA and Floor Life as compared to the original wire condition. Meanwhile under the original wire condition, the 0.8mil X-PdFLASH wire was also bonded on Freescale LQFP package. The inherent LQFP package design causes high-sensitivity to 2nd bond short-tailings due to clamping instability especially on the ground bonds. Many potential optimizing areas were assessed to improve the 2nd bond bondability. Among them were capillary geometry type and design; the wire bonder P-Parts design to improve the clamping and 2nd bond process enhancements which includes Stand-Off-Stitch-Bond(SSB). All of which still does not provide a robust bonding process and minimum stitch value also falls below the specifications. By adopting of the newly improved wire process from 0.7mil wire, the 2nd bond bonding process of 0.8mil X-PdFLASH is still unsatisfactory in terms of stitch pull value and stitch bond shape. Finally, the newly-developed 2nd bond bonding process from K&S, the Pro-Stitch-Plus (PSP) was evaluated together with the improved 0.8mil wire on the LQFP package. Encouraging bonding results were achieved by a stable bonding process, good stitch bond shape and stitch pull values within the specifications. The initial UPH assessment also showed a significant improvement. In summary, the further wire manufacturing process & equipment improvements substantially improve the overall wire coating consistency and thus enable a better HVM wire bond performance. Besides, the joint development work of Heraeus - Freescale - Micorbonds which successfully established an optimized wire bond recipe for LQFP package through a detailed process characterization indicates another great leap in the insulated wire bond application.