Reliability Evaluation of Eutectic SnAg and 95.5Sn-3.5Ag-1Zn Solder Joint in Electronic Package
| Autor: | Wei, Y.Y., 魏郁穎 |
|---|---|
| Rok vydání: | 1997 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 85 As-fabricated solders of eutectic SnAg and ternary Sn-3.5wt%Ag1wt%Zn alloys are coupled with metallized substrates inclduing PtAg/Al2O3 and Cu/Al2O3 to simulate the solder joint in microelectronics. Characteristics of as-fabricated solders including melting point, microstructure, coefficient of thermal expansion,and wetting behaviors are investigated. The growth mechanism of intermetallics and the mechanical properties of solder joints after thermal aging (150℃ and 200℃) and cycling (－50℃~100℃) are evaluated. In this study, as 1206 passive device/solder/metallization/Al2O3 SMT (surface mount technology) assembly is employed, and a Cu stud is connected on the ceramic substrate assembly to measure mechanical properties and the fracture morphology by pull-off test. With the specially designed pattern, the contact resistance of solder joint is obtained. In addition, microstructure evolution of the interfacial morphology, elemental and phase distribution are probed with the aid of SEM, EPMA and X-ray diffractometer. With Zn introduction into the binary eutectic SnAg solder, the melting pointed is reduced. Another merit is that more uniform dispersion of fine precipitate is derived in the ternary alloy as compared to the binary one. However, the Sn-Ag solder exhibits better wettability than the Sn-3.5Ag-1Zn solder. There are two intermetallics (Cu3Sn and Cu6Sn5) formed at the eutectic SnAg solder/Cu metallized layer interface, while only Cu6Sn5 is observed in the Sn-3.5Ag-1Zn/Cu system. However, in the PtAg metallized substrate, only Ag3Sn is presented regardless of which solders are employed. Cu6Sn5 and Ag3Sn in the Sn-3.5Ag-1Zn system possess about 2-5 at% Zn due to higher solubility of Zn in both Cu and Ag. The adhesion strength decreases as the time increases for al systems in two thermal tests. The solder joint with eutctis SnAg alloy exhibits higher fracture load than that with Sn-3.5Ag-1Zn alloy. From the fracture surface analysis, as the aging time increases, the fracture takes place from the solder/conductor interface toward the inside of IMC (intermetallic compound). Cracks occur at the conductor edge in the solder fillet after thermal cyclign test. The majority of creaks propagate through the IMC/bulk interface with a few exist within IMC and bulk solder adjacent to IMC layer. It is argued that the increase of contact resistance is predominated by the presence of cracks rather than the growth of IMC. In commercial eutectic SnAg solder paste used in FR-4 substrate systems only a thin Cu6Sn5 IMC layer is found at the Cu-Sn interface. However, no Cu-Ni intermetallic is ever detected. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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