Lead-free Sn-Ag and Sn-Ag-Bi solder powders prepared by mechanical alloying

Abstract

A mechanical alloying (MA) process was used to produce lead-free solder pastes of Sn-3.5Ag and the Sn-3.5Ag-4Bi system. Because of the high energy induced by repeated fracturing and welding, the grinding media played an important role during the MA process. A ceramic container was used to provide stronger impact force, which could induce phase transformation better than a Teflon container. In addition, it was found that 1-cm balls could fracture Bi particles and promote their dissolution into the Sn matrix. On the contrary, the milling process tended to achieve homogeneous mixing when using 3-mm balls. The MA powders, after milling with 3-mm balls, showed a small endothermic peak from the differential scanning calorimetry (DSC) profile at around 138°C, which was the eutectic temperature of Sn-Bi. The melting points of the MA powders in the ceramic container were measured to be 221°C and 203°C, respectively, for Sn-3.5Ag and Sn-3.5Ag-4Bi from the DSC curves. The reduced melting point ensured the complete melting during reflow with a peak temperature of 240°C. The formation of Ag 3 Sn was also observed from the x-ray diffraction peaks, indicating successful alloying by MA. The solder pastes could, thus, be produced by adding flux into the MA powders. The wetting property of the solder joint was also evaluated. The as-prepared solder pastes on electroless Ni-P/Cu/Si showed good metallurgical bonding with a contact angle less than 20°.

Effect of Cu concentration on morphology of Sn-Ag-Cu solders by mechanical alloying

“…The characteristics of the MA process have been studied in the literature. [25][26][27][28] It is a solid-state process technique to produce particles with submicron homogeneity by repeated welding, fracturing, and rewelding powder particles in a high-energy ball mill. 31 It overcomes the disadvantage of forming new alloys by using a starting mixture of low-and high-melting temperature elements.…”

“…Recently, Lai and Duh showed SnAg and SnAgBi solder materials by the MA technique, 28 in which good wettability and good alloying performance were revealed.…”

Pulse Electrodeposition of Lead-Free Tin-Based Composites for Microelectronic Packaging

“…In the present state, the advanced solders that have been developed so far are mostly Sn coupled with other elements like Cu, Ag, Zn, Bi, Sb, Ni. [8][9][10][11][12][13][14] Among all the binary eutectic Pb-free alloys, Sn-Ag, Sn-Zn, and Sn-Cu are considered to be the potential candidates to replace Sn-Pb. For ternary alloys, the most commonly used system is Sn-AgCu which is proved the most effective due to its lower melting temperature and superior mechanical properties compared to the other combinations.…”

“…[18,20] Various processing routes like melting and casting, powder metallurgy, high-energy ball milling/mechanical alloying, physical vapor deposition, sol-gel, plasma sprayed deposition, chemical methods, and electroplating have been employed to produce solder materials. [9][10][26][27][28][29][30][31] Powder metallurgy and mixing methods have been often used to fabricate the lead-free solders reinforced with nanoparticles: Cu, SiC, ZrO 2, Al 2 O 3 , SnO 2 , Y 2 O 3, TiB 2 , carbon nanotube (CNT), rare earth. [9, 21-22, 25, 32-36] There is also a limit on the amount of nanoreinforcement addition in the solder matrix; otherwise, it will deteriorate the solderability and strength.…”

Effect of Antimony Additions on Corrosion and Mechanical Properties of Sn-Bi Eutectic Lead-Free Solder Alloy

“…In fact, this alloy, which has the eutectic temperature of 139˚C, has a higher ultimate tensile stress and shear strength than Sn-Pb eutectic [2,3]. Bismuth has also been used as the alloying element in ternary Sn-Zn-Bi [4] Sn-Ag-Bi [5,6] and Sn-BiCu [7] systems to provide suitable substitutes for Sn-Pb solder alloys.…”