Morphology Change, Size Distribution, and Nano-sized Channels in Cu 6 Sn 5 Intermetallic Compound Formation at the SnPb
- PDF / 451,710 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 40 Downloads / 224 Views
B10.3.1
Morphology change, size distribution, and nano-sized channels in Cu6Sn5 intermetallic compound formation at the SnPb solder and copper interface J. O. Suh, K. N. Tu1, and A. M. Gusak2 1 Department of Materials Science and Engineering, UCLA, Los Angeles, CA 90095-1595 Tel: 1-310-836-4028 Fax: 1-206-7353 E-mail: [email protected] 2 Department of Theoretical physics, Cherkasy State University, Cherkasy, Ukraine ABSTRACT The growth and size distribution of scallop-type Cu6Sn5 intermetallic compound (IMC) at the interface between molten SnPb solder and Cu was investigated, along with a systematic study of morphology change of Cu6Sn5 morphology change as a function of SnPb solder composition. When SnPb solder composition was changed from eutectic (63Sn37Pb) to about 40Sn60Pb, Cu6Sn5 with round scallop-type morphology was found. In other compositions, the Cu6Sn5 scallops showed faceted scallop-type morphology. This morphological change is due to variation of interfacial energy between Cu6Sn5 and solder with a change of solder composition. The growth rate of Cu6Sn5 layer was proportional to cube root of time, and size distribution was in good agreement with the Flux-Driven-Ripening (FDR) theory. The pre-exponent factor k obtained by the measurement was 2.10×10-14 cm3/sec. Based on the k value, the calculated channel width with was about 2 nm, which was in good agreement with experimental observation by transmission electron microscopy. INTRODUCTION To achieve higher interconnect array density, solder bump size in flip chip technology has been continuously reduced. However, the thickness of intermetallic compound (IMC) in the solder joint remains same. The use of lead (Pb) free solder will result in even thicker IMC layer, due to the high concentration of tin. This leads to an increase of IMC volume fraction in solder joint. While IMC layer provides good metallic bonding, excess thickness of IMC layer can cause brittle fracture of solder joints. Spalling of intermetallic compound (IMC) by interfacial reaction between molten solder and under-bump metallization (UBM) is another important reliability issue related to the excessive IMC growth [1]. Spalling is due to a complete consumption of thin film UBM metal during growth of IMC layer. Thus control of the IMC layer growth rate can improve reliability of solder joints. It was found that both ripening and growth of IMC takes place at the solder/metal interface, reported in previous studies by H.K. Kim [2] on the molten solder/metal interfacial reaction. The ripening is a non-conservative ripening, because there is a constant supply of UBM metal
Fig.1. Theoretical normalized curve of particle size distribution by FDR theory, plotted together
B10.3.2
through channels between scallops. The classic theory of the conservative ripening of precipitates by Lifshitz and Slyozov [3] and Wagner [4] (the LSW theory) is not suitable for the case of the IMC ripening in solder joint. In the solder-metal reaction, the IMC scallops are almost in contact with each other, and UBM metal
Data Loading...
