Ikuo Shohji

Solder joint reliability evaluation of chip scale package using a modified Coffin–Manson equation

Abstract Thermal cycle tests were performed for chip scale package (CSP) solder joints with Sn–37mass%Pb under several thermal cycle conditions. Under the conventional thermal cycle conditions, which heat up to approximately 100 °C, microstructure coarsening occurred and solder joints were fractured. The thermal fatigue lives followed the modified Coffin–Manson equation. The exponential factors m and n, and the activation energy Q in that equation were evaluated as 0.33, −1.9 and 15.5 kJ/mol, respectively. When the maximum temperature is room temperature and the temperature range is very narrow, the solder joint fracture occurred without microstructure coarsening, and the thermal fatigue life does not follow the modified Coffin–Manson equation.

Effect of Interfacial Reaction in Sn-Ag-Cu Solder Alloy with Ni Addition

Sn-Ag-Cu-Ni-Ge solder alloy has been developed to improve the mechanical properties of the Sn-Ag-Cu base solders and prevent oxidation of those solders. In this paper, an interfacial reaction and microstructure between the solder and a Cu electrode were investigated under heat exposure conditions. It was found that intermetallic compounds growth at the interface of the solder and the Cu electrode was greatly affected by amounts of added elements. Adding Ni in the solder can suppress the formation and growth of intermetallic compounds (IMCs) such as Cu-Sn and decreasing the amount of adding Ag in the solder can prevent the formation and growth of Ag3Sn. Moreover, it was found that there was an effect of suppress the growth of the Cu3Sn formed on the interface of Cu and (Cu,Ni)6Sn5 by adding Ni from analysis results of EDX and TEM.

Effect of Strain Rate on Tensile Properties of Miniature Size Specimens of Several Lead-Free Alloys

The effect of strain rate on tensile properties of several lead-free solder was investigated using miniature size specimens. High-temperature lead-free solder which are Sn-Cu and Sn-Sb alloys were prepared. Moreover, low-Ag lead-free solder which are Sn-1Ag-0.7Cu (SAC107, mass%) based alloys were prepared. Sn-3Ag-0.5Cu (SAC305) was also prepared for comparison. Tensile strength is proportion to the logarithm of strain rate in all solder investigated. Although 0.1% proof stress decreases at high strain rate in high-temperature solder, it scarcely changes in low-Ag solder. Elongation somewhat increases with increasing strain rate in high-temperature solder. It increases with increasing strain rate in low-Ag solder although it is lower than that of SAC305. Chisel point fracture mainly occurred except Sn-13Sb. In Sn-13Sb, brittle fracture occurred and thus elongation was lower than those of other solder. Sn-8.5Sb and Sn-1Ag-0.7Cu-1Bi-0.2In show mechanical properties similar to SAC305.

Effect of Se Content in High-Cyanide Silver Plating Solution on {200} Crystal Plane Orientation Ratio of Electrodeposited Silver Layer

Electrodeposited silver layers obtained from high-cyanide silver plating solution are widely applied for connectors and switches of automobiles. However, few groups have discussed the relationship between the crystal structure of silver layers and their properties. In this study, the effect of the concentration of Se, added as a brightener to high-cyanide silver plating solution, was investigated by XRD and EBSD analysis for electrodeposited silver layers with {200} orientation. By optimizing the concentration of Se in the silver plating solution, the {200} orientation ratio of the silver layer was increased to as high as 94%. Since the diffusion of Cu from the Cu substrate used in this study into the silver layer was inhibited, the silver layer with the high {200} orientation ratio exhibited good electrical contact resistance of the surface of 1.3mΩ after a heating test performed at 200°C for 74h. In addition, the silver layer had good bend formability. The results of XRD analysis confirmed that the recrystallization of the electrodeposited silver layer occurred at room temperature within several hours, thus increasing the {200} orientation ratio of the silver layer.

Impact Properties of Sn-0.75Cu Lead-Free Solder Ball Joint

Impact properties of a solder ball joint with a Sn-0.75mass%Cu lead-free solder were investigated under aging conditions at 393 K. Moreover, obtained impact properties were compared with those of the joints with Sn-3.5mass%Ag and Sn-3.5mass%Ag-0.5mass%Cu solders. Ball impact force of a Sn-0.75Cu joint was stable at 4.5~5 N, which is similar to that of a Sn-3.5Ag-0.5Cu joint without aging, upon aging at 393 K for 1000 h. In the Sn-0.75Cu joint without aging, main fracture mode was complex fracture of the solder and an intermetallic compound (IMC) formed in a joint interface. Main fracture mode changed from the complex mode to solder fracture upon aging, and thus the impact toughness improved.

Tensile and Fatigue Properties of Miniature Size Specimens of Sn-5Sb Lead-Free Solder

Tensile and low cycle fatigue properties of Sn-5Sb (mass%) solder were investigated with miniature size tensile specimens. The effect of temperature and strain rate on tensile properties and the effect of temperature on low cycle fatigue properties were examined. Tensile strength increases with increasing strain rate regardless of temperature investigated. For elongation, the effect of temperature on it is negligible although it slightly increases with increasing strain rate. The low cycle fatigue life of Sn-5Sb obeys by the Manson-Coffin’s equation. The effect of temperature on the fatigue life is negligible in the temperature range from 25 oC to 150 oC. In the low cycle fatigue test with a high total strain range of 4%, cracking at phase boundary mainly occurs regardless of temperature investigated. In the case of a low total strain range of 0.4%, ductile fracture mainly occurs, and cracking at phase boundary with generation of grooves also occurs at high temperature.

Cu/Cu direct bonding by metal salt generation bonding technique with organic acid and persistence of reformed layer

In this study, the effect of the metal salt generation bonding technique on the strength of a direct-bonded copper–copper interface was investigated. Copper surfaces were modified by boiling in several types of organic acids, and direct bonding was performed at a bonding temperature of 423–673 K under a load of 588 N (for a bonding time of 0.9 ks). As a result of the surface modification, bonded joints were obtained at bonding temperatures of 150 K (after treatment with formic acid) and 100 K (after citric acid treatment) lower than that required for the unmodified surfaces. In addition, the duration of the modification effects was investigated by exposing the modified surface to an air atmosphere furnace kept at 323 K. The bonding strength of the citric acid-modified surface remained unchanged even after 168 h, whereas that of the surface modified with formic acid decreased within 6 h.

Effect of fiber direction and temperature on mechanical properties of short fiber-reinforced PPS

Effects of fiber direction and temperature on mechanical properties of glass short fiber-reinforced poly phenylene sulfide have been investigated. Tensile properties degraded with increasing the angle between the tensile direction and the fiber direction; θ, except elastic modulus. Tensile strength and elastic modulus decreased and elongation increased with the increase of temperature. The tensile properties greatly varied at the temperature over Tg. The pull-out and peeling of fibers were observed in the case of θ = 0° and θ = 90°, respectively. The S-N diagram in the specimen with θ = 90° is approximated by two straight lines. At high stress amplitude, the fibers were peeled off with the breakdown of the matrix. At low stress amplitude, the fibers are peeled off due to interfacial fracture.

Effect of filler content on tensile properties of underfill material for flip chip bonding

The effects of the filler content and temperature on tensile properties of underfill were investigated using underfill materials which are composed of bisphenol F-type epoxy resin and spheroidal SiO2 filler. Youngs modulus of underfill increased and fracture strain decreased with increasing the SiO2 filler content. The effects of the SiO2 filler content on Youngs modulus and fracture strain were relatively large. However, the effect on tensile strength was negligible. Tensile strength was strongly affected by the strength of matrix resin itself. When the temperature was above Tg, Youngs modulus decreased and fracture strain increased remarkably. Fracture mainly occurred in matrix resin below Tg and in the interface between matrix resin and filler above Tg.

Effect of Interfacial Reaction on Joint Strength of Semiconductor Metallization and Sn-3Ag-0.5Cu Solder Ball

Semiconductor packages that use metallization and lead-free solders are increasingly being used in electronic products. In this study, interface reactions and joint-strength reliability were investigated for Sn-3W%Ag-0.5W%Cu solder ball joints joined to Cr/Cu and Cr/Ni-40W% metallization layers that were heat treated at 260°C. The strength of the joint with the Cr/Cu metallization layer decreased as the duration of the heat treatment increased. Sn and Cr interface reactive layers were generated after the loss of Cu in the Cr/Cu metallization layer, but the connection was maintained. By contrast, the connection of the joint to the Cr/Ni-40W metallization layer was relatively stable under the heat treatment conditions investigated.