Interfacial reaction and mechanical properties between Sn-Ag-Cu alloy and submicron Ni(P) metallization pads

• Main Authors: Chia-Wei Fan, 范家瑋
• Other Authors: Cheng-En Ho
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/92896982361389308716

碩士 === 元智大學 === 化學工程與材料科學學系 === 101 === Recently, thin Ni(P) films (less than 1 μm in thickness) have received significant attention from the electronic industry because they offer greater bondability with Cu wires and less magnetic effect than do thick Ni(P). However, submicron Ni(P) films are approximately one tenth the thickness of those utilized in the past, and they can be completely exhausted during soldering. In Sn-3Ag-0.5Cu-thin ENIG system. The solderability between a Sn-Ag-Cu alloy and a submicron Ni(P) film was examined using a focused ion beam (FIB) and field-emission transmission electron microscope(FE-TEM). After one typical reflow, the Ni(P) film was mostly eliminated from the interface, where Cu6Sn5 with a significant Ni content [(Cu0.6Ni0.4)6Sn5] nucleated. The subsequent diffusion of Sn to the underlying Cu through molten solder channels among the (Cu0.6Ni0.4)6Sn5 grains yielded a second Cu6Sn5 layer at the (Cu0.6Ni0.4)6Sn5/Cu interface. The removal of Ni from the Ni(P) during soldering reaction allowed P to nucleate as nanocrystalline Ni3(Sn,P) between the two Cu6Sn5 layers, which subsequently translated into a chain of amorphous P-Sn-O pores. The propagation of the porous P-Sn-O destroyed the stability of (Cu0.6Ni0.4)6Sn5 and drove the compound layer to separate from the second Cu6Sn5 after the third reflow. These observations suggest that the exhaustion of the Ni(P) induced spallation of the compound layer, thereby degrading the reliability of the joining interface. In Sn-3Ag-0.5Cu- thin ENEPIG system. When Ni(P) = 0.18 μm, the Au/Pd(P)/Ni(P) surface finishes examined were completely exhausted in one reflow, exposing the Cu pad underneath to the solder. The Cu6Sn5 dissolved with various Ni contents, termed (Cu,Ni)6Sn5, was the dominant intermetallic compound (IMC) species at the solder/Cu interface. Additionally, Ni2SnP and Ni3P IMCs might form with the (Cu,Ni)6Sn5 in the thick Ni(P) case, i.e., Ni(P) = 0.9 μm, and the two IMCs were gradually eliminated from the interface after multiple reflows. The HSBS test results indicated that the mechanical strength of the solder joints was also dNi(P)-dependent. The combined results of the interfacial reaction and the mechanical evaluation provided the optimal Ni(P) value for soldering applications.