Modeling Study on the Solder Joint Reliability of a Leadframe Package under Powered Thermal Cycling

This paper aims to present a thermo-mechanical modeling approach to predict the solder joint reliability of a leadframe-based package under powered thermal cycling (PTC) test from -40oC to 105oC. The study involves modeling the PTC condition as a standard thermal cycling with a modified temperature boundary to account for the temperature increase due to the applied power to the device package mounted on board. The temperature ramp and dwell times were maintained. Based on the finite element analysis (FEA) results and comparison with actual data, modeling a PTC as a modified thermal cycling process provides a good prediction of the solder joint life. The analysis is simpler and would be beneficial for getting quick assessments of new leadframe package designs.

Thermal Shock Behavior of Twill Woven Carbon Fiber Reinforced Polymer Composites

In the current research, the effect of cyclic temperature variation on the mechanical and thermal properties of woven carbon-fiber-reinforced polymer (CFRP) composites was investigated. To this, carbon fiber textiles in twill 2/2 pattern were used as reinforced phase in epoxy, and CFRPs were fabricated by vacuum-assisted resin-infusion molding (VARIM) method. Thermal cycling process was carried out between −40 and +120 °C for 20, 40, 60 and 80 cycles, in order to evaluate the effect of thermal cycling on mechanical and thermal properties of CFRP specimens. In this regard, tensile, bending and short beam shear (SBS) experiments were carried out, to obtain modulus of elasticity, tensile strength, flexural modulus, flexural strength and inter-laminar shear strength (ILSS) at room temperature (RT), and then thermal treated composites were compared. A dynamic mechanical analysis (DMA) test was carried out to obtain thermal properties, and viscoelastic properties, such as storage modulus (E’), loss modulus (E”) and loss factors (tan δ), were evaluated. It was observed that the characteristics of composites were affected by thermal cycling due to post-curing at a high temperature. This process worked to crosslink and improve the composite behavior or degrade it due to the different coefficients of thermal expansion (CTEs) of composite components. The response of composites to the thermal cycling process was determined by the interaction of these phenomena. Based on SEM observations, the delamination, fiber pull-out and bundle breakage were the dominant fracture modes in tensile-tested specimens.

Microstructure and Properties of Ultrasonic Assisted Sn2.5Ag0.7Cu0.1RExNi/Cu Solder Joint S Under Thermal Cycling

Through ultrasonic wave assisted Sn2.5Ag0.7Cu0.1RExNi/Cu(x=0, 0.05, 0.1) soldering test and -40~125℃ thermal shock test, the microstructure and mechanical properties of Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints under thermal cycling were studied by the SEM, EDS andXRD. The results show that the Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints with high quality and high reliability can be obtained by ultrasonic assistance. During the thermal cycling process, the shear strength of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints had a linear relationship with the thickness of interfacial intermetallic compound (IMC). The addition of an appropriate amount of Ni could inhibit the excessive growth of IMC, improve the shear strength of solder joints and improve the reliability of solder joints. Under the condition of 1000 cycles of thermal cycling, the thickness and roughness of IMC of the solder joints with 0.05 wt.% Ni were the smallest, and the shear strength of the solder joints was 19.8 MPa, which was 28.6% higher than that of the solder joints without Ni.The interfacial IMC layer of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints consisted of (Cu,Ni) 6Sn5 and Cu3Sn. In the thermal cycling, the thickness of interfacial IMC of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints was linearly related to the square root of equivalent time. The growth of interfacial IMC of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints had an incubation period, and the growth of IMC was slow within 300 cycles. And after 300 cycles, the IMC grew rapidly, the granular IMC began to merge, the thickness and roughness of IMC increased obviously, the defects such as microcracks and microvoids began to appear, and the shear strength of the solder joints decreased rapidly.The fracture mechanism of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints changed from the ductile-brittle mixed fracture in the solder/IMC transition zone to the brittle fracture in the interfacial IMC.

Influence of Thermal Cycling Temperature on the Recrystallization of Cold Rolled Stainless Steel 316L

Investment casting of an orthopedic implant plate based on stainless steel 316L was considered an economical process. Nevertheless, the mechanical properties of the investment casting product were found to be inferior as compared to the implant plate fabricated with other methods such as forging due to their differences in the microstructure. Investment casting mostly produced coarser grain as compared to those with forging or rolled process. In order to improve their mechanical properties, cold-rolling followed by a repetitive thermal cycling process is proposed. The goal is to generate finer grain size through recrystallization process leading to nucleation of new grain during the thermal cycling process thus increasing their strength. Stainless steel 316L was cold-rolled to 52% reduction in thickness and this process generate stored strain energy in the form of dislocation density in the material. The thermal cycling treatment performed within several cycles after cold rolling enabling gradual disperse of stored strain energy that facilitates the recrystallization process that initiates new grain formation. The short holding time within several cycles limits the grain growth that normally occurs during annealing. It was found that thermal cycling treatment at a temperature of 950 °C for 35 seconds within four cycles led to the formation of finer grain size of 22 µm on average as compared to the initial investment casting average grain size of 290 µm. The hardness also increases to 253 HV0.3 in this condition as compared to 155 HV0.3 of investment casting products. Lower thermal cycling temperature than 950 °C during the test did not result in grain refinement thus indicating that strain energy relieves were not enough to aid the recrystallization process.