Truan Sheng Lui

Microstructure, electric flame-off characteristics and tensile properties of silver bonding wires

Abstract Compared with gold wire, silver wire is cheaper and enjoys better electrical conductivity. These days copper wire is becoming more commonly used, but the reliability of its bonding still has problems in some pads. Since Ag wires have similar hardness and bonding properties to Au wires, they can be applied in some pads. In the present study, the annealing effect (at 225–275xa0°C for 30xa0min) on the tensile mechanical properties of silver wires with ϕxa0=xa023xa0μm was investigated. In addition, the microstructural characteristics and the mechanical properties before and after an electric flame-off (EFO) process were also studied. Experimental results indicate that with annealing temperatures of more than 250xa0°C, the silver wires possessed a fully annealed structure, the tensile strength and the hardness decreased, and the elongation was raised significantly. Through recrystallization, the matrix structure transformed from long-thin grains to equiaxed grains. The microstructure of the free air ball (FAB) of the various annealed wires after an EFO process were column-like grains. The column-like grains grew from the heat-affected zone (HAZ) to the Ag ball. Under the thermal effect of EFO, the necks of the Ag balls underwent recrystallization and grain growth was induced, and the annealed Ag wires had a shorter zone of HAZ (220xa0μm). Additionally, the decreased hardness and the low strength of the HAZ resulted in the breakage sites of the EFO wires being in the HAZ near the Ag balls. The bonding strength and the neck-strength of the Ag wires were more than 7gf and possessed excellent bonding properties.

Effect of the direct current on microstructure, tensile property and bonding strength of pure silver wires

Abstract In the microelectronics assembly and packaging industry, the wire bonding has become an important process to connect lead frames and pads. In the past, gold and copper were the main materials of wire bonding. However, the cost of gold wires is getting higher nowadays and yet wire bonding cannot be wholly replaced by copper wire; thus silver wires become a novel bonding material in recent years. The reliability test of wires was a static method; this study leads electrical current into the wires to estimate the structural changing and interface properties of Al pads (positive and negative pad). After leading 90% critical fusing current density (CFCD) into a 23xa0μm silver wire, some grains of silver wire had grown up and formed into equal-diameter grains (EDG). After the current test, the fracture position of bonded wires moved from heat affect zone (HAZ) of electric flame-off (EFO) to the neck of HAZ. Otherwise, the current test would reduce the tensile strength of wire. The bonding strength of the positive pad was lower than that of the negative pad. The intermetallic compound (IMC) of bonding interface was AgAl 2 .

Analysis on the critical strain associated with the onset of portevin-Lecatelier effect of substitutional F.C.C. alloys

Abstract Flow instability of substitutional f.c.c. alloys, which is a common feature of the Portevin-LeChatelier effect, usually develops after a critical strain is reached. With ∈. and T as the tensile strain rate and deformation temperature, respectively, the Arrhenius equation that ∈. ∝ ∈cα exp (−Q/kT) is obeyed in numerous systems. Rationalization of the critical strain exponent, α, based on the conventional Cottrell model is not in agreement with empirical data. A proper modification regards ∈c as related to some critical mobile dislocation density in which the local vacancy enrichment near dislocation core region is considered. Dislocation interception should also play a role in affecting the average dislocation velocity. The rationalization based on the above concepts reveals a correct grain size dependence.

Intermetallic Phase on the Interface of Ag-Au-Pd/Al Structure

Three wires, Au, Cu, and Ag-Au-Pd, were bonded on an Al pad, inducing IMC growth by a 155u2009hr high temperature storage (HTS) so that the electrical resistance was increased and critical fusing current density (CFCD) decreased. Observations of the Ag-Au-Pd wire after HTS (0–1000u2009hr) indicated that IMC between the Ag-Au-Pd wire and Al Pad was divided into three layers: Ag2Al layers above and below the bonding interface and a polycrystal thin layer above the total IMC. A high percentage of Pd and Au existed in this 200u2009nm thin layer, and could suppress Al diffusion into the Ag matrix to inhibit IMC growth. After PCT-1000u2009hr, a noncontinuous structure still remained between the IMC layer and interface, and the main phase of IMC was (Ag, Au, Pd)2Al with a hexagonal structure.

Effect of annealing on the microstructure and bonding interface properties of Ag–2Pd alloy wire

Abstract This study investigated the mechanical and electrical properties of Ag–2Pd wire after thermal annealing. The thermal stability of the tested wire was examined by separately imposing static annealing atxa0275xa0°C,xa0325xa0°C and 375xa0°C in a vacuum environment. It was found that annealing the Ag–2Pd wire at 275xa0°C promoted the formation of a fully annealed structure with equiaxed grains. Annealing Ag–2Pd wire had a shorter heat affect zone (HAZ) length than those of conventional wire, and offered outstanding mechanical properties. A long-term electrical test found Ag 3 (Pd)Al and Ag 2 (Pd)Al compounds between the Ag–Pd ball and Al pad.xa0These results confirmed the high-reliability properties of annealed Ag–2Pd wires for the wire bonding process.

Microstructure, electric flame-off (EFO) characteristics and tensile properties of silver–lanthanum alloy wire

Abstract Silver has potential for application in the electronic packaging industry because of its great electrical and thermal properties and lower price compared to that of gold. Silver oxidizes easily, so doping lanthanum to form Ag–La alloy improves its anti-oxidation capacity. In this study, the microstructure, tensile properties, electronic flame-off (EFO) characteristics, and fusing current of Ag–La alloy wire (φxa0=xa020xa0μm) are studied. Samples annealed at three temperatures (325xa0°C, 375xa0°C, and 425xa0°C) are analyzed. According to the experimental results, after annealing at 425xa0°C, Ag–La alloy wire recrystallized, giving it a tensile strength similar to that of pure silver wire and a uniform structure. Doping lanthanum reduced the diameter of free air balls (FABs) in the EFO process. The fusing current of Ag–La wire was about 0.45xa0A, and the grains of Ag–La wire grew to the size of the wire diameter when a 0.4xa0A current (90% fusing current) was applied for a long time. Ag–La alloy wire can be used in the electronic packaging industry.

A study on electromigration-inducing intergranular fracture of fine silver alloy wires

In this study, Pd-coated Cu, Ag (purityu2009=u20094 N), and Ag alloy (Ag-8Au-3Pd) wires were employed to measure the tensile properties during current stressing using the so-called dynamic current tensile (DCT) test. Both the tensile strength and elongation of the wires decreased dramatically in the DCT test, particularly of the Ag-based wires, and the fracture morphology of the Cu-based and Ag-based wires was ductile fracture and intergranular fracture, respectively. Compared to the Cu-based wires, electromigration occurred more easily in the Ag-based wires, and it always generated voids and cracks at the grain boundaries; therefore, the fracture morphology of the Ag-based wires was intergranular fracture owing to the weakened grain boundary. Further, the results indicated that the Ag-based wires could not carry a higher current density than the Cu-based wires, primarily because their extremely low strength and elongation in current stressing might cause serious reliability problems.

A modification on the portevin-le chatelier effect of substitutional FCC alloys

Proposition dune modification de leffet Portevin-Le Chatelier et application aux alliages Cu-5%Sn et Al-Mg-Si.

Recrystallization of Ag and Ag-La Alloy Wire in Wire Bonding Process

Sliver wire was the novel material to replaced gold wire in wire bonding process, and rare earth element was often added to improve the properties of silver wires. The annealing effect (at 225°C~275°C for 30min) on the tensile mechanical properties of silver wires with φ=20μm was investigated. In addition, the microstructural characteristics and the mechanical properties before and after an electric flame-off (EFO) process were also studied. Free-air ball (FAB) of 85μm diameter from 20μm diameter pure silver wire was too huge for bonding process, otherwise the silver wire was added 0.05 wt.% lanthanum to form Ag-La alloy wire to reduce the diameter of FAB. FAB of Ag-La alloy wire with a 55μm diameter, and can avoid short-circuited. In addition, microstructures, tensile properties and the micro-hardness of Ag-La alloy wires indicated that the best annealing temperature was 425 °C.