Mechanical Properties and Microstructure of Tin-Silver-Bismuth Lead-Free Solder

Abstract

This paper presents the mechanical properties and microstructure of Sn-Ag-Bi Pb-free solder. We evaluated the effects of Bi content on the mechanical properties of Sn-Ag-Bi solder such as tensile strength, elongation and deformation behavior at cross-head speeds of 0.1 mm/min and 500 mm/min. The experimental results show that at low cross-head speeds, the addition of Bi to Sn-Ag solder initially increases the tensile strength and decreases elongation due to solid-solution hardening of Sn-phase. As the Bi content is increased to 10 mass% and more, however, elongation increases to a maximum at Sn-Ag-Bi solder containing 57 mass%Bi. Deformation of Sn-Ag solder is governed by slip within the Sn phase, and for high-Bi solders (about 57 mass%Bi) deformation occurs due to slip at Sn-Bi grain boundaries. Intermediate-Bi solders, on the other hand, do not slip in either the Sn phase or at Sn-Bi grain boundaries. At high cross-head speeds, the elongation of both intermediate-Bi solders and high-Bi solders was low and almost constant, indicating slip at Sn-Bi grain boundaries becomes difficult. The impact resistance of these solders was investigated through charpy impact tests, and it is found that Bi has a marked effect on impact resistance. The impact absorption energy of Sn-Ag solder decreases rapidly with the addition of Bi.

Interfacial microstructure and shear behavior of Sn–Ag–Cu solder balls joined with Sn–Zn–Bi paste

“…The studies on mechanical properties of Sn-Ag series joints are plentiful [1,2,4,7,8,[12][13][14][15][20][21][22][23][24][25]. Packages of Sn-Ag-Cu with introduction of Sn-Zn-Bi are rarely investigated.…”

Electrical resistance of Sn–Ag–Cu ball grid array packages with Sn–Zn–Bi addition jointed at 240 °C

“…The addition of Bi to Sn-Zn near-eutectic solder can improve the soldering properties by lowering melting temperature 3 , 1 0 and strengthening the joint. 7,10,[14][15][16][17] Sn-Ag-Cu packages with the introduction of Sn-ZnBi are rarely investigated. In our previous study, 18 Sn-Ag-Cu/Sn-Zn-Bi packages show higher shear strength than Sn-Ag-Cu joints under thermal aging.…”

Impact Behavior of Thermomechanically Fatigued Sn-Based Solder Joints

“…To overcome this deficiency, several impact studies on solder materials have been carried out using bulk alloy samples. 3,4 Some of these studies were concerned with the ductile-brittle transition exhibited by tin as it has a body-centered tetragonal structure in the temperature regions of concern. 3 Results of these studies indicate that the temperature range over which such a transition occurs is too low to be of importance in consumer electronics.…”

“…The rapid increase in the number of miniaturized consumer electronics which can be easily dropped by the user has resulted in significant interest in the impact response of such interconnects. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Impact reliability tests carried out by dropping the device, either once or a specific number of times, from a chosen height provide a simple means of quantitative joint system evaluation. 16 However, such studies do not provide sufficient information to select solder materials and/or joint geometries for improving the impact reliability of solder interconnects.…”