Solid-State Interface Reactions between Silver and 95.5Sn-3.9Ag-0.6Cu and 63Sn-37Pb Solders

Abstract

The microstructure and rate kinetics were investigated for solid-state intermetallic compound (IMC) layer growth in Sn-Ag-Cu/Ag and Sn-Pb/Ag couples. The aging temperatures were 55°C to 205°C and 70°C to 170°C, respectively. The aging times were 1 day to 400 days. The SnAg-Cu/Ag IMC layer included the phases: Ag 3 Sn (dominant), the f phase, and a solid-solution phase, xAg-ySn, (94 to 96 at. pct Ag). Void formation was observed at the solder/IMC (Ag 3 Sn) interface, which was attributed to the Kirkendall effect. The rate kinetics of IMC layer growth were expressed through t n exp(-DH/RT). The values of n and DH for the IMC layer phases were:(1) f + xAg-ySn, n = 0.68 ± 0.23, DH = 59 ± 15 kJ/mol; (2) Ag 3 Sn, n = 0.22 ± 0.05, DH = 28 ± 2 kJ/mol; and (3) total layer, n = 0.34 ± 0.06, DH = 45 ± 3 kJ/mol. The very low DH value for Ag 3 Sn suggested a very fast, fast-diffusion mechanism. The IMC layer of SnPb/Ag couples was predominantly the Ag 3 Sn stoichiometry. The IMC layer growth was accompanied by the development of a Pb-rich phase layer at the solder/IMC interface. There was insignificant void development in these couples. The rate kinetics parameters, n and DH, were 0.44 ± 0.06 and 51 ± 4 kJ/mol, respectively, indicating a traditional fast-diffusion mechanism.

Effect of strongly oxidizing environment on whisker growth form tin coating

“…Also the Kirkendall vacancy zone forms inside the tin layer instead of the underlying copper substrate [9]. There is no exact research yet about the effect of silver underlayers, although experiments of [27] show similar results about the interdiffusion of Ag and Sn, but in this research no evidence was found for the Sn-Ag intermetallics formation (Fig. 5c).…”

Geometric size effect on IMC growth and elements diffusion in Cu/Sn/Cu solder joints

“…These illustrated that the size of the solder joint has a significant impact on the diffusion behavior of metal elements in solder joints. However, the diffusion dynamics equation (x=x0+Dt ) was valid to calculate the thickness of the IMC layer in many research studies about the IMC layer growth, bonding pad depletion and electromigration (Wu et al , 2009; Choi et al ., 2003; Kim et al , 2008; Vianco et al , 2007; Lee et al , 2003; Chang and Chiang, 2004; Jeon et al , 2003). On the macroscopic scale, the concentration of metal elements which diffuse into the solder layer is lower and exhibits little change during aging.…”

Concentration Gradient of Ni in Reduced SnAg Thickness in Ni/SnAg/Cu Microbumps during Solid-State Aging

“…[8][9][10][11][12] Furthermore, the minor species in solder can also affect the growth of interfacial IMCs. [13][14][15][16][17][18][19][20][21] For instance, a small amount of Ni in solder is able to influence the growth of microstructure in the Cu 6 Sn 5 IMCs. [22][23][24][25] It is reported that the addition of Ni atoms will ease the formation of Cu 3 Sn.…”