Gold- and Palladium-Induced Embrittlement Phenomenon in Microbumps with Au/Pd(P)/Ni(P) Metallization Pads

2015

Materials Letters

Abstract:Microstructure development in solder joints between Sn-3.5Ag and Ni-based substrates has been widely reported. However, in the present study we illustrate a new phenomenon: that during soldering of Sn-3.5Ag to Ni or ENIG (electroless nickel, immersion gold), the bulk solder solidifies to contain a metastable eutectic consisting of βSn+Ag3Sn+NiSn4 instead of the βSn+Ag3Sn+Ni3Sn4, expected of equilibrium solidification. It is shown that metastable NiSn4 coarsens and then decomposes into Ni3Sn4 and βSn during ageing at 150 and 200˚C and that coarsened NiSn4 deteriorate impact shear properties.

Section: Ag/enig Joints At 150°csupporting

confidence: 54%

Metastable eutectic in Pb-free joints between Sn–3.5Ag and Ni-based substrates

2015

Materials Letters

“…Further analysis revealed large amounts of (Ni,X)Sn 4 particles on the fracture surfaces suggesting that NiSn 4 was involved in crack nucleation and/or propagation. NiSn 4 or (Ni,X)Sn 4 particles seem to act similar to the widely reported embrittlement of solder joints by isomorphous AuSn 4 /PdSn 4 phases [32][33][34][35].…”

Section: Resultssupporting

confidence: 64%

The influence of alloying elements on metastable NiSn4 in Sn-Ag solders on Ni-containing metallizations

2015 IEEE 17th Electronics Packaging and Technology Conference (EPTC)

2015

Sn-Ag based solders are a popular Pb-free alternative in consumer electronics and have a relatively long history with a large body of dedicated research. Past research has primarily focused on the formation of interfacial intermetallic (IMC) layers and the growth of Sn, and little attention has been paid to Ni-containing IMCs that form in the bulk solder when SnAg alloys are soldered to Ni-containing metallizations. The present study illustrates a new phenomenon: formation of metastable NiSn 4 as a primary and a eutectic phase in solder joints between Sn-Ag solders and Ni-containing surface finishes. The metastable NiSn 4 was demonstrated to transform into Sn and equilibrium Ni 3 Sn 4 IMC phase during ageing at 150°C. Impact shear tests suggested a significant drop in solder joint mechanical response when larger than 2μm NiSn 4 crystals were present in the solder bulk. Further exploration of the influence of alloying elements on metastable NiSn 4 in solder joints yielded three scenarios: (i) Au, Pt, Pd and Co promoted NiSn 4 formation and increased its volume fraction by substituting for Ni atoms in NiSn 4 ; (ii) Bi, In, Fe and Pb additions appeared to have little or no discernible effect on NiSn 4 and (iii) Cu was found to promote equilibrium Ni 3 Sn 4 phase formation that replaces metastable NiSn 4 at Cu levels above 0.3wt%.

“…Ni 3 Sn 4 interfacial IMC layer was not detected to dissolve any Bi or In in amounts above the detection limit of the SEM-EDX technique (Table 3). As reported previously [11], NiSn 4 has a similar effect to the widely reported embrittlement of solder joints by isomorphous AuSn 4 /PdSn 4 phases [15][16][17][18]. The shear impact test results in [11] demonstrated that the presence in solder joints of NiSn 4 crystals larger than 2µm leads to their embrittlement.…”

supporting

confidence: 79%

Effect of Bi and In on Microstructure Formation in Sn-3Ag-3Bi-3In/Cu and /Ni Solder Joints

2016

KEM

Sn-3Ag-3Bi-3In solder has been investigated to improve the understanding of microstructure formation in this solder during solidification and soldering to Cu and Ni substrates. The as-solidified microstructures of Sn-3Ag-3Bi-3In samples were found to consist of a significant fraction of βSn dendrites with a complex eutectic between the dendrites. In total five phases were observed to form during solidification: βSn, Ag3Sn, Bi, ζAg and a “Sn-In-Bi” ternary compound. Soldering of Sn-3Ag-3Bi-3In to substrates changed the phase equilibria in the system and caused the formation of additional phases: Cu6Sn5 during soldering to Cu and Ni3Sn4 and metastable NiSn4 during soldering to Ni. It is shown that metastable NiSn4 forms as a primary phase in a complex 5-component Sn-3Ag-3Bi-3In-Ni system. In and Bi were detected in solid solution in the βSn matrix in amounts of ~1.5-2at% and ~1.2at% respectively. Bi also existed as fine particles of two distinct types. (i): sub-micron (<500nm) coral-like particles and (ii) facetted particles measuring up to 7-8 μm.