The fiber alignment shifts of fiber-solder-ferrule (FSF) joints in butterfly laser module packaging under temperature cycle testing are studied experimentally and numerically. Using a novel image capture camera system as a monitor probe and the Sn-based solders as bonding materials, we have achieved the minimum fiber eccentric offsets of 8 and 20mm in FSF joints with the PbSn and AuSn solders, respectively. The measured results showed that the fiber alignment shifts of FSF joints with the hard AuSn solder exhibited shifts two times less than that with the soft PbSn solder. The experimental measurements of fiber alignment shifts were in good agreement with the numerical calculations of the finite-element method (FEM) analysis. The major fiber shift formation mechanisms of FSF joints in temperature cycling may come from the localized plastic solder yielding introduced by the local thermal stress variation, the redistribution of the residual stresses, and the stress relaxation of the creep deformation within the solder.
The thermally induced fiber alignment shifts of fiber- solder-ferrule (FSF) joints in laser module packaging under temperature cycling tests have been studied numerically by a elastic-plastic finite-element method (FEM). The FSF joints were assembled using both the Pb(37)/Sn(63) and Au(80)/Sn(20) solders. Comparison between the calculated results shows that the Au/Sn solder in the FSF joint exhibits three times less fiber than Pb/Sn solder. This is due to the higher Young's modulus, yield strength, and melting temperature of AuSn hard solder than PbSn soft solder. This suggests that the hard solder of Au/Sn is more suitable for use in FSF assembly than soft solder Pb/Sn for laser module packaging to reduce thermally induced fiber alignment shift. Numerical calculations show that the major cause of fiber shift in FSF joints may come from the plastic solder yielding introduced by the thermal stress variation and the redistribution of the residual stresses during temperature cycling.
The effect of PbSn solder joint strength on temperature tests in laser diode packaging has been studied experimentally and numerically. It was found that the solder joint strength increased as temperature cycle number increased. A finite-element method (FEM) analysis is performed on the calculation of joint strength of PbSn solder in temperature cycling tests for laser diode packaging. Numerical calculations were in good agreement with the experimental measurements that the solder joint strength increased as the temperature cycle increased. This is may be due to the redistribution of the residual stresses within the solder during the temperature cycling tests, and hence reducing the residual stresses and increasing the solder joint strength as the temperature cycle number increased. The result suggests that the FEM is an effective method for predicting the solder joint strength in laser diode packages.
A finite -element method (FEM) analysis is performed on the calculation of residual stresses during spot -welding for Au- coated Invar materials. Numerical results show that the high residual tensile stresses of the phosphorus rich segregation layer generated by rapid solidification shrinkage is the possible cause for crack formation. This indicates that the FEM calculations may provide one of the effective methods for predicting the crack formation in laser -welded Au- coated materials Keywords: Crack, thermal stress, laser packaging, finite -element method 1. INTRODUCTION To enhance the solderability for chip and wire bonding, optoelectronic materials of Invar' or Kovar2 of very low coefficient of thermal expansion (CTE) are often coated with a Au thin film. There have been well documented in the area of thin film coating that an inadequate thickness of Au coating on optoelectronic materials in laser welding process can cause undesirable reactions such as crack defects in the welded joints34. Prior to Au plating on optoelectronic material, a Ni underlayer coating is often applied to improve adhesion. The Ni underlayer can be formed by P -free electroplating or P- containing electroless plating, denoted hereafter as Ni and Ni(P), respectively. However, the chemical reducing agent NaH2P02 is required in the electroless Ni(P) plating process, which introduces additional phosphorus (P) element in the Ni(P) underlayer. Recently comprehensive measurements of laser -welded Au -, Ni -, Ni(P), and Au/Ni- coated Invar have shown that the existence of the P element content in the Ni(P) underlayer instead of the Au element in the Au plating layer play a major role in determining the crack formation in laser welded Au- coated optoelectronic materials8. The purpose of this work is to study the solidification crack formation mechanism in laser -welded Au- coated optoelectronic materials due to P- containing underlayer by using finite- element method (FEM). This work has led to important result that the FEM provides an effective method for predicting the crack formation in laser -welded Au- coated optoelectronic materials. 2. LASER WELDING SYSTEM AND PACKAGE CONSTRUCTION 2.1 Laser Welding System: Fig. 1 (a) shows the experimental setup of the laser welding system. The system consisted of a pulsed Nd: YAG laser and a dual -beam fiber optic beam delivery. Two laser beams delivered from the Nd:YAG laser to the workpiece were accurately adjusted with the same energy and with the incident angles of (45° ± 1 0)9. The laser energy required to create the welds was delivered simultaneously through two fibers placed 180° apart. The simultaneous and equal energy delivery is designed to reduce the post -weld -shift (PWS) in the two components because the solidification- shrinkage of both welds can compensate each other, resulting in minimized displacement shifts9. 2.2 Package Construction: A top view of dual -in -line package (DIP) indicating the pigtail fiber to the laser chip is also shown in Fig. 1 (a). The DIP construction consisted of a 1.3 j.tm laser, the Invar housing materials, a thermoelectric cooler, W.H. Cheng (correspondence): E -mail: email@example.com; Telephone: (886) 7 -525 -2000 ext. 4450; Fax: (886) 7 -525 -4499 Part of the SPIE Conference on Optoelectronic Materials and Devices Taipei, Taiwan July 1998 SPIE Vol. 3419 0277 -786X/98/$10.00 93 Finite-element analysis of thermal stresses in laser packaging Maw-Tyan Sheen#, Cheng-Huang Chen*, Jao-Hwa Kuang', and Wood-Hi Cheng* #Mh•c1 Engineering Department and *Jjj ofElectro—Optical Engineering, National Sun Yatsen University, Kaohsiung, Taiwan 804 Huang-Lon Chang, Szu-Chun Wang, Chungyung Wang, Chy-Ming Wang, and Jy-Wang Liaw Chunghwa Telecom Laboratories, 12, Lane 55 1, Min-Tsu Rd, Sec. 3, Yang-Mei, Taoyuan, Taiwan 326 ABSTRACT A finite-element method (FEM) analysis is performed on the calculation of residual stresses during spot-welding for Au- coated Invar materials. Numerical results show that the high residual tensile stresses of the phosphorus rich segregation layer generated by rapid solidification shrinkage is the possible cause for crack formation. This indicates that the FEM calculations may provide one of the effective methods for predicting the crack formation in laser-welded Au-coated materials