Research On Effects Of Diode Laser On Mechanical Properties Of Soldered Joints Of SOP And CR

LY-FCDL-WS90 diode laser soldering system was used to study the wettability, the effects of output currents, heating time and duty ratios on solder paste by use of pure copper as base metal and Sn-Pb solder paste and Sn-Ag-Cu lead-free solder paste. The fracture micrograph of joints was also analyzed under the different conditions by means of SEM. The results indicate that there was an optimal laser output current corresponding to the best wettability and spreadability of the diode laser soldering system. Microstructure of soldered joint and interface between soldering seam and substrate were obviously influenced on different heating time and the duty ratios affect the wettability of solders slightly under low frequency.SOP (Small Outline Package) devices were sorldered by diode-laser soldering system and IR reflow soldering method respectively, and the tensile strengths of soldered joints were detected by means of Micro-joints Tester (STR-1000), and the effects of lasrer soldering speed on mechanical properties of SOP micro-joints were studied and the characteristics of fracture microstructures of micro-joints were also analyzed by use of SEM. The results indicate that laser soldering speed affects the tensile strength of soldered joints and mechanical properties of Sn-Pb soldered joints were more sensitive to laser soldering speed than those of Sn-Ag-Cu, and there was an optimal laser soldering speed to the best smechanical property. There were some micropores and low toughness cavities at the comparative low speed, which was called micropore aggregation fracture. With the increase of speed of laser soldering, the form of fracture turned into cavity and cleavage fratures.The effects of duty ratios of laser beam on mechanical properties of soldered joints of chip resistance were studied and the sheare strengths of soldered joints were detected by use of the Micro-joints Tester. The results show that the sheare strength of soldered joint was best with pulse laser heating at low frequency, when the duty ratios was 0.1, which was 50% higher than those of with continute laser heating. The microstructures of fractures by SEM and the EDX results show that a part of the form of fracture appeared as toughness cavity and the other as short and uncontinuous laminated arris when the duty ratio was 0.1, in which the fracture topography was accompanied with cacity and cleavage frature. Most of area of the form of fracture was slick and there were some holes when the duty ratio was 0.5. The form of fracture was brittle fracture.The temperature field that affected the wetting and spreading behavior of solder under the unsteady lase heating was simulated and studied with the help of ANSYS software.The simulation results suggest that, with the increase of heating time, the width of isotherm was getting wider and wider and the spread area was getting larger and larger. When the time was about 0.9s, the temperature in the temperature enhanced quickly and the temperature almost keept the same when the heating time was about 1.5s. The change of temperature field was sensitive to the laser output power, which a little change of the output power would lead to the temperature largely increase in the temperature field.