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The effect of joint strength of PbSn and AuSn solders on temperature cycling tests in laser packages has been studies experimentally and numerically. It was found that the joint strength increased as temperature cycle number increased and then decreased after 300 cycles. The break surface of PbSn and AuSn solders showed that there increased the brittle manner in the solder joints after 300 temperature cycles. This joint strength decreased may be due to the brittle fractures associated with crack initiation in solder joints. A finite-element method (FEM) simulation of joint strength was in good agreement with the experimental measurements. Introduction: Optoelectronic dies, such as laser diodes, are often bonded to submounts. The submounts are then bounded to substrates, as shown in Fig.1 of a dual-in-line package (DIP). A laser module of DIP structure consisted of a 1.3 pm laser diode, the Invar housing materials, a thermoelectric cooler, and a single-mode fiber. The purpose of the submounts is used to spread heat laterally from the active area of the laser, reduce the temperature rise at hotspots, and match the coefficient of thermal expansion (CTE). In this work, we study the joint strength and intermetallic compound (IMC) growth of PbSn and AuSn solders of submount and substrate under temperature cycling tests. Experiment: In a DIP construction, the fiber-to-Invar tube, laser-to-submount, and the submountto-Invar plate assemblies were solder joints, where the Invar tube-to-u channel and the U channelto-Invar plate assemblies were weld joints. Both lead-tin (T, = 183"C), and gold-tin (T, = 283°C) were employed to form the solder joints in laser-to-submount, and the submount-to-Invar plate assemblies, respectively. To simplify the study of the solder joints in laser assembly, the laser-tosubmount, and the submount-to-Invar plate were substituted by the gold plated AlN submount-toInvar plate. The dimension of Invar plate and AlN were 10 x 5 x 1.5 and 6 x 2 x 0.2 mm3, respectively. The IMC thickness in solder joints was measured by the cross-section microstructure through SEM. To examine the joint solderability, the joint strength of the soldered samples was measured with a push test fixture of in-house design. Measurement: Fig. 2 shows the measured IMC thickness as a finction of the cycle number with PbSn and AuSn solders. The IMC thickness increased as the cycle number increased. However, the IMC thickness became stable after 300 cycles. Fig. 3 shows the measured joint strength as a function of the cycle number with PbSn and AuSn solders. The joint strength increased as the cycle number increased. Then the joint strength decreased after 300 cycles. The break surface of PbSn and AuSn solders showed that there increased the brittle manner in the solder joints after 300 temperature cycles. This joint strength decreased may be due to the brittle fractures associated with crack initiation in solder joints. Figs. 3 and 4 indicates that there is a correlation between the IMC growth and joint strength of PbSn and AuSn s...