Interfacial reactions of lead-free solders with electroless palladium on the nickel substrate

• Main Authors: Li, Poyi, 李柏毅
• Other Authors: Wang, Chaohong
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/22944125394377238894

碩士 === 國立中正大學 === 化學工程研究所 === 100 === With the miniaturization of electronic products, the plating finishing techniques can not conform to the requirement. Therefore, electroless plating finishing techniques play an important in electronic industry. Among finishing techniques, ENEPIG has many advantages and begin using widely. In this study, we used the Ni plate as substrate and then electroless Pd and immersion Au on the substrate. Therefore, the influence of Cu substrate can be neglected. Besides, Pd foils were also studied in this research. The solid-solid reaction couple and liquid-solid reaction couple were made by electroless plating and electroplating. The results indicated that PdSn4 had much Ni amount than Pd because of Ni diffusion from Ni substrate, and the PdSn4 became more thicker. However, Sn/Au/Pd(1µm)/Ni reaction couple would observe PdSn4 had much Pd content than Ni after 10 s of reflow time. The reflow time and the thickness of Pd layer had a significant effect on microstructure. Interface of Sn/Au/Pd(1µm)/Ni could produce PdSn4 layer in short period of time. However, PdSn4 layer could not maintain with increasing reflow times. On the other hand, the intermetallic growth kinetics of solid/solid reaction was studied. The results showed electroless Pd on Ni could influence thickness of Ni3Sn4. Our research also studied in electro-Ni/Au/Sn/Au/Pd/Ni and electro- Cu/Au/Sn/Au/Pd/Ni. A needle shape PdSn4 compound grew on electroplate Ni side in electro-Ni/Au/Sn/Au/Pd/Ni reaction couple. This indicated that needle shape PdSn4 compound will be affected by the opposite Sn/Au/Pd/Ni interfacial reaction. PdSn4 had a large amount of Au content on Ni plate side in electro-Cu/Au/Sn/Au/Pd/Ni reaction couple. The phenomenon might be related to (Cu,Ni)6Sn5. (Cu,Ni)6Sn5 acted as barrier layer to prevent Ni diffusion into PdSn4. In addition, we also studied in Sn-3Ag-0.5Cu/Au/Pd/Ni. The results indicated that Ni content of PdSn4 decreased and Cu6Sn5 compound grew on PdSn4/Ni interface. Besides, Ni3Sn4 will appear on the interface with increasing time. The results show that (Cu,Ni)6Sn5 acted as barrier layer to prevent Ni diffusion into PdSn4 and Ni3Sn4 will apear on the interface with increasing time. The Zn concentration effect was studied in Sn-Zn/Pd solid/solid reaction and Sn-Zn/Pd liquid/solid reaction. In solid/solid reaction, adding small amount of Zn could inhibit formation of PdSn4 on interface. In liquid/solid reaction, Pd2Zn9 was formed as the Zn is about 1.5wt%. However, PdSn4 was found when below 2wt%Zn. Sn-Zn solder reacted with Ag substrate or Ni substrate that was also discussed in this study. The Zn contentment difference would alter the species of reaction phase in Sn-Zn/Ag couple and Sn-Zn/Ag/Cu couple. Ag-Zn phase was formed as the Zn concentration is higher. However, Ag-Sn phase was formed as the Zn concentration is lower. IMC was changed between Ag3Sn and Cu with reaction increasing time. IMC was changed from Ag5Zn8 to Cu5Zn8, and then transfered into CuZn. Finally, IMC will be transfered into CuZn and Cu6Sn5 mixed-layer phase. Ni5Zn21 has two different contrasts in BEI image. Therefore, We etched interface by FIB that can observe four different microstructure in liquid/solid couple. The results showed that interface had two different microstructure in solid/solid couple. Besides, the microstructure will changed with reaction time increase in liquid/solid couple.