In situ scanning electron microscopy study of eutectic SnPb and pure Sn wetting on Au/Cu/Cr multilayered thin films
- PDF / 297,899 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 50 Downloads / 185 Views
MATERIALS RESEARCH
Welcome
Comments
Help
In situ scanning electron microscopy study of eutectic SnPb and pure Sn wetting on AuyyCuyyCr multilayered thin films D. W. Zheng, Weijia Wen, and K. N. Tu Department of Materials Science and Engineering, UCLA, Los Angeles, California 90095-1595
P. A. Totta IBM East Fishkill Facility, Hopewell Junction, New York 12533 (Received 5 May 1998; accepted 20 August 1998)
˚ ˚ Wetting behavior of eutectic SnPb and pure Sn on Au(500 A)yCu(1 mm)yCr(800 A) layered thin films were monitored in situ in a ramping temperature profile using a scanning electron microscope (SEM) with a vacuum of 1025 –1026 Torr. We found that the wetting behavior of these two solders in SEM was dramatically different from their behavior in RMA soldering flux; a smaller wetting angle and rough wetting front morphology were observed. Very surprisingly, no dewetting could be observed inside the SEM chamber, yet dewetting happened to the same sample when it was removed from the SEM and immersed in RMA soldering flux. We estimate the interfacial energy between liquid Sn and solid Cr and assume the reduction of surface and interfacial energies caused by possible oxidation of Cr and liquid Sn surface in the SEM in order to explain the above-mentioned wetting and dewetting behaviors.
I. INTRODUCTION
Reactive wetting is a fundamental liquid-solid interaction problem that has drawn much attention in recent years.1– 5 It provides a basic understanding of the soldering processes used in electronic packaging technology for the semiconductor manufacturing industry. As opposed to the rapid advancement pace of silicon chip technology, the fundamental understanding of reactive wetting on thin films is relatively slow and far from complete. For example, even in the most common soldering reaction between eutectic SnPb and AuyCuyCr6,7 layered or phased-in thin films, there still exist a lot of puzzles. Two illustrative questions could be given. (a) When eutectic SnPb wets AuyCuyCr layered thin films above 200 ±C in the flux, why does a precursor called “sideband” form ahead of the macroscopic contact line of the solder? (b) Why does the dewetting of eutectic SnPb on AuyCuyCr blanket thin film have a size dependence?8 Remarkably, when the solder size is small, the dewetting starts from the center of the cap.8 This “center dewetting” is unique for the eutectic SnPb solder. Among all other Sn bearing solders we have tested, namely, eutectic SnBi, eutectic SnAg, eutectic SnIn, eutectic SnSb, eutectic SnZn, and pure Sn, dewetting begins from the edge. In order to conduct a more detailed study of the above-mentioned problems, we have carried out an in situ scanning electron microscopy (SEM) study of the wetting processes of eutectic SnPb and pure ˚ ˚ thin films. We Sn on Au(500 A)yCu(1 mm)yCr(800 A) observed a phenomenon of solder wetting in vacuum of 1025 to 1026 Torr, which is quite different from that in J. Mater. Res., Vol. 14, No. 3, Mar 1999
http://journals.cambridge.org
Downloaded: 15 Mar 2015
flux. No dewetting could
Data Loading...
