Investigations on the Interfacial Reaction, Shear and Electrical Properties of Sn-Ag-Cu Solder Joints with Sn-Zn-Bi Paste Addition

Autor: Po-Cheng Shih, 施伯錚
Rok vydání: 2006
Druh dokumentu: 學位論文 ; thesis
Popis: 95
Among proposed lead-free solders, Sn-Ag-Cu ternary alloy has been regarded as the most potential candidate to replace the conventional Sn-Pb alloy. However, the eutectic melting point of Sn-Ag-Cu solder is notably higher (roughly 34oC) than that of Sn-Pb alloy, denoting that the soldering temperature is expected to surge which may cause reliability concerns during soldering process. Therefore, Sn-Zn-Bi solder paste of lower melting point (188-199oC) was introduced as a medium to joint Sn-Ag-Cu solder ball with Au /Ni /Cu metallized BGA (Ball Grid Array) substrates and the soldering temperature was successfully dropped to 210oC, close to manufacturing temperature of Sn-Pb alloys. This study targeted the effect of the addition of Sn-Zn-Bi paste in Sn-Ag-Cu joint systems on interfacial reaction between Sn-Ag-Cu /Sn-Zn-Bi solder and Au /Ni /Cu metallization, shear and electrical properties of Sn-Ag-Cu /Sn-Zn-Bi joints under multiple reflows and thermal aging tests. Besides, the Sn-Ag-Cu joints without Sn-Zn-Bi addition were compared as a control system. Interfacial compounds formed in Sn-Ag-Cu joints were (Cu, Ni)6Sn5 and (Ni, Cu)3Sn4 while Ag3Sn and Au-Sn compounds were identified in the bulk solder. After ten reflow cycles, (Cu, Ni)6Sn5 and (Ni, Cu)3Sn4 compounds coarsened significantly, but the latter grew morphologically loose. Ag3Sn compounds became intensive in Sn-rich bulk solder but Au-Sn compounds seemed not to grow with reflow cycles. After aging for 1000 hrs, as similar to multi-reflowed joints, (Cu, Ni)6Sn5, (Ni, Cu)3Sn4 and Ag3Sn compounds coarsened notably, but Au-Sn compounds did not. Furthermore the morphology of (Ni, Cu)3Sn4 compounds was compact after aging for 1000 hrs. The Sn-Ag-Cu /Sn-Zn-Bi joints soldered at 210oC formed Ag-Au-Cu-Zn, Ni-Sn-Cu-Zn, Ag3Sn, Ag5Zn8 and Ag-Zn-Sn compounds. The spallation behavior of Ag-Au-Cu-Zn compounds during various soldering time at 210oC was examined and discussed. Interfacial Ag-Au-Cu-Zn compounds shrunk, even disappeared with increasing reflow cycles whereas Ni-Sn-Cu-Zn and Ag3Sn compounds grew notably. Moreover Ni-Sn-Cu-Zn compounds were morphologically compact. Ag-Sn phases of ternary Ag-Zn-Sn compounds became rich with reflow cycles but Ag-Zn phases did the reverse way. Bi was not involved in compound formation but dissolved in Sn-rich phase or separated in the bulk solder. In 240oC-soldered Sn-Ag-Cu/Sn-Zn-Bi joints, the formation of compounds was similar to 210oC-soldered joints. Nevertheless, the morphology of the Ni-Sn-Cu-Zn compounds was loose after 10 reflow cycles. After aging for 1000 hrs at 150oC, the joints reflowed at 210oC or 240oC gave rise to compact Ni-Sn-Cu-Zn compounds while the Ag-Au-Cu-Zn compounds hardly coarsened. Moreover Bi was not involved in compound formation. XRD analysis was carried out to examine the crystalline phases of two quaternary Ag-Au-Cu-Zn and Ni-Sn-Cu-Zn compounds. Based on the results of shear test, Sn-Ag-Cu joints fractured in the solder bulk after 1, 10 reflows and aging for 1000 hrs, whereas Sn-Ag-Cu /Sn-Zn-Bi joints exhibited various fractured regions upon various tests. The detailed results were respectively investigated and discussed, including the effect of microstructural evolution of the joints on fractured regions and on strength variation under tests. The electrical resistance of the joint (R1) consisted of three sub-proportions：the solder bulk (Rsolder bulk, upper solder highly beyond the mask), interfacial solder /IMCs (Rsolder/IMC), and the substrate (Rsubstrate). The Rsolder/IMC raised but Rsolder bulk and Rsubstratre did not change with respect to reflow cycle or aging time. In addition, Rsubstratre is a major proportion of R1. R1, Rsolder bulk and Rsolder/IMC of Sn-Ag-Cu /Sn-Zn-Bi joints were respectively higher than those of Sn-Ag-Cu joints. Electrical resistance contributions of (Ni, Cu)3Sn4 and Ni-Sn-Cu-Zn compounds to R1 of Sn-Ag-Cu and Sn-Ag-Cu /Sn-Zn-Bi joints under various tests were also calculated and discussed.
Databáze: Networked Digital Library of Theses & Dissertations
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