SMT007 Magazine

SMT-July2016

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102 SMT Magazine • July 2016 by Hsiang-Chuan Chen, Ya-Ching Chuang, Jen-Yio Shiu, and Chang-Meng Wang, SHENMAO TECHNOLOGY INC. and Watson Tseng, SHENMAO AMERICA INC. Abstract Laser soldering method becomes attrac- tive in the packaging and assembly of surface- mounted devices and microelectronics. The method transfers laser energy for reflow process with a non-contact procedure and determines the soldering location precisely. It is critical to consider formulated solder paste due to the amount of heat absorbed by flux and alloys when applying the method to reliable joints. A new solder paste of alloy composition of Sn- 3.0Ag-0.5Cu in a dispensing way is developed for the automatic laser soldering processes. This paper presents the results of soldering BGA spheres on circuit boards with minimal voiding and no splash or solder balling issues. Cross- sectional studies showed the reduction of inter- metallic formation in well-formed solder joints. In addition, the joints have high shear strength due to lower thermal stress during the process. This new solder paste was proved to be suitable for repair of electronic components and man- ufacturing electronic parts that cannot be sol- dered in a conventional reflow oven. Introduction With the miniaturization of modern elec- tronics with selective soldering and the uses of heat-sensitive electronic components, conven- tional reflow soldering process can no longer satisfy the requirements in advanced packag- ing. In recent decades, several alternative reflow soldering processes, such as infrared radiation reflow, vapor phase reflow, and laser soldering, were proposed [1] . The inferior uniformity of tem- perature is mostly concerned as the use of infra- red radiation reflow though the running cost is inexpensive. The characteristics of vapor phase reflow soldering is absolutely opposite to infra- red radiation reflow. Compared with various soldering processes, laser soldering technology has distinct advantages over both former ones, in which the entire assembly is passed through an oven that can lead to problems concerning A New Dispensing Solder Paste for Laser Soldering Technology ARTICLE

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