Wire bonding characteristics of 0.7mil Au-Pd-plated Cu wires

• Main Authors: Pei-FuChung, 鍾沛孚
• Other Authors: Jung-Hua Chou
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/75255799222694720740

碩士 === 國立成功大學 === 工程科學系碩博士班 === 101 === In semiconductor packaging industry, the wire bonding technology has been developed for a long time. Since the equipment and technology are more mature than the others, wire bonding technology is still the mainstream for packaging technology. For the material used in the process, copper wires have numerous advantages over gold wires. Copper wires can save the cost up to 30~50% compared with gold wires, and the high electrical conductivity, good thermal conductivity, high stability of wire and slower growth speed in intermetallic compound (IMC) are all the advantages making copper wires more favorable. The formation of the IMC can strengthen the bond, but the IMC layer has higher electric resistance. During the growth of the IMC, Kirkendall voids[31] will appear at the interface between the IMC layer and the wire, and the voids will enlarge to form cracks through heat treatment, thus leading to the deterioration of electrical contacts and the reduction of reliability of bondability. The materials used in this experiment are the 0.7mil Au-Pd-plated copper wires which are not yet on the market and the existing Pd-plated copper wires. The experimental results show that Au-Pd-plated copper wire has a better breaking load and better elongation than these of the Pd-plated copper wire. The micro-hardness test shows that Au-Pd-plated copper wire is softer than the Pd-plated copper wire. With the same forming gas flow rate, Au-Pd-plated copper wire has better FAB (Free Air Ball) formation roundness than the Pd-plated copper wire. This experiment also examines the coverage of the coating on the copper ball after the EFO (Electrical Flame-Off). By choosing seven different spots on Pd-plated copper wire for element analysis, it is observed that the surfaces are all covered with a layer of palladium, and there is no exposed Cu. Gold and palladium are also found on the surface of the Au-Pd-plated copper wire. The growth of IMCs (Intermetallic Compounds) test shows that the growth rate on Au-Pd-plated copper wire is the same as the Pd-plated copper wire. During the wire bonding process, the Pd-plated copper wire is found unstable in the formation of second bond stitch and on the joint with the finger. Moreover, the tails are cut-off too fast causing alarm of the equipment with short tail defect. However, the experiment result shows that with an extra layer of gold coated on the palladium layer, voids on the plating layer can be reduced and the work efficiency can be improved.