Laser micro-welding of flex lead with solder paste

There are some problems of low efficiency and poor consistency in manual welding of flex lead. In order to realize automatic soldering,an experimental platform with micro-dispensing solder paste,visual location of soldered joints,laser heating and infrared temperature measurement was designed. Firstly,the emissivity calibration and accuracy measurement of infrared thermometer was performed,the coaxiality compensation between laser energy center and camera vision center was made. The micro-spot welding experiment was carried out on the goldplated pad. Finally,the conductivity of the soldered joints of the 30 μm flex lead was measured. The experimental results show that there are some problems in laser micro-welding with solder paste such as pseudo solder joints,multi-tin beads generation,variability of contact area of soldered joints and flux residue. By optimizing the laser heating power curve and the process,a soldered joint with good conductivity about 0.2 mm in diameter has been obtained. The automatic design of laser and solder paste micro-welding of flex lead is feasible.