Effect of Aluminum Concentration on the Interfacial Reactions of Sn-3.0Ag-xAl Solders with Copper and ENIG Metallizations

Abstract

Aluminum was added into Sn-3.0Ag (wt.%) solder to investigate the effect of aluminum concentration on the interfacial reaction of Sn-3.0Ag-xAl solders with copper or electroless nickel immersion gold (ENIG) metallizations. Four different Sn-3.0Ag-xAl solders (x = 0 wt.%, 0.1 wt.%, 0.5 wt.%, and 1.0 wt.%) were used for comparison. It was found that the composition, morphology, and thickness of interfacial reaction products were strongly dependent on aluminum concentration. At low aluminum concentration (0.1 wt.%), the typical Cu 6 Sn 5 layer was formed at the interface. When the aluminum concentration was 0.5 wt.%, a continuous CuAl 2 layer spalled off from the interfacial Cu-Sn intermetallic compound (IMC) layer. Only a planar CuAl 2 layer was observed at the interface when the aluminum concentration was increased to 1.0 wt.%. In Sn-Ag-Al/ENIG reactions, Ni 3 Sn 4 was formed and spallation occurred near the interface in the Sn-3.0Ag and Sn-3.0Ag-0.1Al solder joints. When the aluminum concentration was higher than 0.1 wt.%, a thin planar AuAl compound formed at the interface. There was no P-rich phase formation that retarded the spalling phenomenon. The aluminum additive in Sn-Ag solder inhibited the growth of IMCs in the reaction with copper or ENIG metallizations, which was favorable for the reliability of solder joints.

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

“…In a study by Jee et al, 11,12 the Al-Cu IMC appeared at the solder/substrate interface rather than in the solder. In the present study, due to the limited solder volume, Al was quickly depleted while forming the Al-Cu IMC, and Cu 6 Sn 5 forms at the solder/substrate interface.…”

“…Traditionally trace amounts of certain elements, i.e., rare-earth elements, have proven to be effective in suppressing the growth of Cu-Sn IMC layers and consequently improved longterm reliability of the solder joint. 9 Recently, several researchers [9][10][11][12][13][14][15] have demonstrated that the addition of small quantities of Al or Zn can suppress Cu-Sn IMC layer growth.…”

Heterogeneous nucleation of Cu6Sn5 in Sn–Cu–Al solders

“…In Cu-containing solders or during soldering to Cu substrates, Al additions usually cause one or more CuxAly intermetallics to form. Four Cu-Al intermetallics have been reported in solders, θ-CuAl2, η2-CuAl, δ-Cu33Al17 and 1-Cu9Al4, depending on the base solder, Al addition and substrate as summarised in Table 1 [5,6,[8][9][10][11][12][13][14][15][16][17][18]. It can be inferred from Table 1 that, for Sn-Ag-Cu solders solidified without reactive substrates, CuAl2 is observed at Al levels above ~1wt% [12] while CuAl is found at Al levels between 0.1-1wt% [13,18], and that the situation is more complex during soldering to Cu substrates due to substrate dissolution.…”

Soldering Characteristics and Mechanical Properties of Sn-1.0Ag-0.5Cu Solder with Minor Aluminum Addition

“…The addition of aluminum has attracted much interest in recent years. Research on Al addition as nanoparticles or minor alloying element has been reported [ 12 , 13 , 14 , 15 , 16 , 17 , 18 ]. Amagai [ 12 ] observed that the addition of 0.05% Al nanoparticles did not have any significant effect on the interfacial IMC.…”

“…Amagai [ 12 ] observed that the addition of 0.05% Al nanoparticles did not have any significant effect on the interfacial IMC. As for the addition of aluminum as minor alloying element, a few works on the effect of Al on the mechanical properties, microstructure and solder/Cu substrate interfacial reaction have been reported [ 2 , 9 , 11 , 14 , 15 , 16 , 17 , 18 ]. Previous studies have shown that minor addition of Al gives promising results in suppressing undercooling of β-Sn and reduced formation of brittle phase Ag 3 Sn in SAC solder matrix [ 14 ].…”