Thermal compression process for power IC Attachment and the joint properties

• Main Authors: Chih-Hao Fan, 范志豪
• Other Authors: Jenn-Ming Song
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/34661538905296079697

碩士 === 國立中興大學 === 材料科學與工程學系所 === 103 === An urgent issue in electronic packaging is the die-attachment technique for high power ICs, such as SiC and GaN, which needs to withstand high operation temperature up to 250oC. For this purpose, this study developed a low-temperature soild-state direct bonding process for dissimilar metals. Experimental results show that Cu/Zn can be bonded successfully at 200oC under the loading of 10MPa for 30 minutes. The joints thus formed exhibited a shear strength up to 20MPa. If the thermal compression was performed at 300 oC, the shear strength of bonded Cu/Zn and Cu/Ni/Zn joints exceeded 50MPa, especially for Cu/Zn joint, the strength even reached 70MPa. Microstructural observation results indicate that in the as-bonded state CuZn5/Cu5Zn8 IMCs formed at the interface of Cu/Zn joints, while Ni5Zn21 formed at the interface of Cu/Ni/Zn joints and Cu5Zn8 formed locally between Ni5Zn21 and Cu substrate. With respect to high temperature mechanical properties, due to the softening of Zn, the shear strength of all the joints decreased with a higher testing temperature. During aging at 250 oC, the shear strength of Cu/Zn degraded drastically up to 500hr and after that the joint strength remained almost constant. The strength of Cu/Ni/Zn joints decreased gradually and maintained 30MPa for 500hr. The shear strength of both of the joints tended to be identical subjected to aging for 800hr. The deterioration of the joint strength during aging can be ascribed to the competitive growth between CuZn5 and Cu5Zn8 resulting in collapse and oxidation of CuZn5. The electroplated Ni and Ni5Zn21 thus formed can retard the excessive growth of Cu5Zn8 to some extent. According to interfacial morphology and elemental mapping, Ni-Zn IMCs existed between CuZn5/Cu5Zn8 up to 800hr. In addition, it was also verified that the oxidized Cu and Ni can be reduced by formic acid vapor formic acid vapor treatment. In contrast, formic acid vapor contaminated the surface of Zn and thereby C2H2O4Zn‧2H2O formed. The contamination of Zn surface is harmful for dissimilar metal bonding.