Reactions of Sn-3.5Ag-Based Solders Containing Zn and Al Additions on Cu and Ni(P) Substrates

Abstract

In this study we consider the effect of separately adding 0.5 wt.% to 1.5 wt.% Zn or 0.5 wt.% to 2 wt.% Al to the eutectic Sn-3.5Ag lead-free solder alloy to limit intermetallic compound (IMC) growth between a limited volume of solder and the contact metallization. The resultant solder joint microstructure after reflow and high-temperature storage at 150°C for up to 1000 h was investigated. Experimental results confirmed that the addition of 1.0 wt.% to 1.5 wt.% Zn leads to the formation of Cu-Zn on the Cu substrate, followed by massive spalling of the Cu-Zn IMC from the Cu substrate. Growth of the Cu 6 Sn 5 IMC layer is significantly suppressed. The addition of 0.5 wt.% Zn does not result in the formation of a Cu-Zn layer. On Ni substrates, the Zn segregates to the Ni 3 Sn 4 IMC layer and suppresses its growth. The addition of Al to Sn-3.5Ag solder results in the formation of Al-Cu IMC particles in the solder matrix when reflowed on the Cu substrate, while on Ni substrates Al-Ni IMCs spall into the solder matrix. The formation of a continuous barrier layer in the presence of Al and Zn, as reported when using solder baths, is not observed because of the limited solder volumes used, which are more typical of reflow soldering.

Controlling Bulk Cu6Sn5 Nucleation in Sn0.7Cu/Cu Joints with Al Micro-alloying

“…In addition to causing δ-Cu33Al17 to form, Al additions reduced the nucleation undercooling from 46.3 to 3.6 K (see Table 1), similar to past work [1][2][3]. With an undercooling of only ~4K, only a very slightly hypoeutectic alloy would form primary Cu6Sn5 and it is not surprising that primary Cu6Sn5 does not form in Sn-0.7Cu-0.05Al freestanding balls.…”

“…Potential benefits of dilute Al additions include (i) the suppression of nucleation undercooling for βSn in Sn-Ag-Cu [1,2] and Sn-Ag [3] solders, which has been linked to a reduction in primary (pro-eutectoid) Ag3Sn blade formation [4] and may have the potential to grain refine the βSn phase in solder joints [5]; (ii) the suppression of Cu6Sn5 layer growth on Cu substrates [6]; and (iii) the introduction of small, hard Cu-Al intermetallics that could be harnessed as a dispersion in the βSn matrix to improve the performance and reliability of solder joints [5].…”

Grain refinement of electronic solders: The potential of combining solute with nucleant particles

“…This has found that the undercooling can be suppressed significantly by additions including: Zn [1-3, 11, 24-34], Al [2,24,30,[34][35][36], Co [2, 32-34, 37, 38], Mn [2,30,33,39], Pt [40], Ti [33,39,41], and Pd [40]. Of these, Co [38], Pt [40], and Pd [40] have been deduced to suppress undercooling by introducing heterogeneous nucleant particles of αCoSn3, PtSn4, and PdSn4, each of which has been shown to be a relatively good lattice match to βSn and to form a reproducible crystallographic orientation relationship [38,40].…”

Effect of Zn Addition on Interfacial Reactions Between Sn-Bi Solder and Cu Substrate

“…The addition of minor alloying elements for the suppression of interfacial IMC growth has been widely studied [10][11][12][13][14][15][16] . Kotadia et al studied the addition of 0.5-1.5 mass% Zn to SnAgCu solder 17) .…”