Interfacial reaction studies on lead (Pb)-free solder alloys

Abstract

Recently, the research and development activities for replacing Pb-containing solders with Pb-free solders have been intensified due to both competitive market pressures and environmental issues. As a result of these activities, a few promising candidate solder alloys have been identified, mainly, Sn-based alloys. A key issue affecting the integrity and reliability of solder joints is the interfacial reactions between a molten solder and surface finishes in the solder joint structures. In this paper, a fundamental study of the interfacial reactions between several Pb-free candidate solders and surface finishes commonly used in printed-circuit cards is reported. The Pb-free solders investigated include Sn-3.5 Ag, Sn-3.8 Ag-0.7 Cu, and Sn-3.5 Ag-3.0 Bi. The surface finishes investigated include Cu, Au/Ni(P), Au/Pd/Ni(P), and Au/Ni (electroplated). The reaction kinetics of the dissolution of surface finishes and intermetallic compound growth have been measured as a function of reflow temperature and time. The intermetallic compounds formed during reflow reactions have been identified by SEM with energy dispersive x-ray spectroscopy.Index Terms-Dissolution, electroless Ni(P), interfacial reactions, intermetallics, morphology, Pb-free solders, Sn-3.5Ag, Sn-3.5Ag-3Bi, Sn-3.8Ag-0.7Cu.

Stability of Flip-Chip Interconnects Assembled with Al/Ni(V)/Cu-UBM and Eutectic Pb-Sn Solder During Exposure to High-Temperature Storage

“…This effect is called the Cu concentration effect. 9,10 Furthermore, the reactions between Ni, Cu, and Sn are influenced by the presence of Au in the system. [11][12][13][14][15][16][17] Zhang et al 17 reported that, independent of solder alloy, the presence of Au during high-temperature storage changes the UBM/solder interface reaction product from a binary Cu 6 Sn 5 phase to a ternary CuSnAu or quaternary CuSnNiAu phase.…”

Nanoindentation: a suitable tool to determine local mechanical properties in microelectronic packages and materials?

“…Whenever possible alternative measurement techniques, such as micro Vickers indentation, are used to validate the mechanical properties resulting from nanoindentation. In addition literature data of nanoindentation and other micro-mechanical experiments (e.g., [4,5]) are carefully examined and compared. Moreover, it is investigated if and how nanoindentation can be used to quantify the growth of IMCs in the bulk as well as at the interface.…”

‘Effects of Minor Alloying Additions on the Properties and Reliability of Pb‐Free Solders and Joints’

“…The interfacial reactions between Sn-rich solders (Sn-3.5Ag, Sn-3.8Ag-0.7Cu, Sn-3.5Ag-3.0Bi) and several surface finishes commonly used in printed circuit boards were investigated in terms of their dissolution kinetics and interfacial IMC growth [55]. Table 5.10 summarizes the dissolution and IMC growth rates at 250 C up to 20 min reflow.…”

“…A Ni-Sn-P layer forms between Ni 3 Sn 4 and crystalline Ni 3 P, causing Ni-Sn IMC spalling to occur from the Ni-Sn-P surface [68]. The IMC spalling becomes less severe from a Ni(P) layer when Sn-rich solders contain a small amount of Cu, possibly by altering the structure or composition of Ni-Sn IMCs [55,57,69].…”