Research On The Heating Uniformity Of Waste Printed Circuit Boards Disassembling For Components Reuse

Waste Printed Circuit Board(PCB) is a common part of Waste Electrical and Electronic Equipment(WEEE). And waste plastic chip is one of the most important components on PCB, which possesses highly valuable of reuse. In the heating process of waste PCB disassembling, nonuniform heating of PCB would easily cause partial high temperature, which will lead to delamination damage of plastic chips, and is not conducive to reuse. Therefore, the thermal impact analysis of waste plastic chip delamination and the analysis and optimization of PCB disassembling heating uniformity are studied, which is of great significance to the high value reuse of waste plastic chip.Firstly a method of waste plastic chip thermodynamic simulation is proposed. With this method, the influence rules ofdifferent disassembling temperature on chip warping deformation, maximum stress distribution of internal structure and interface stress distribution are analyzed, as well as the possible delamination areas of old chip are determined.Interface shear strength test of plastic chip is done, and the influence rulesof disassembling temperature on the interface strength of old and new chip is contrastively analyzed, and then the thermal impactrelationship of waste plastic chipdelamination is obtained, which provide theoretical foundation for the analysis and optimization of PCB heating uniformity.According to the analysisresults of waste PCB disassemblingheating uniformity, the key factors influencing heating uniformityof waste PCB arepointed out. Based on the impinging jet model, the convective heat transfer coefficient between hot air and PCB is calculated, and the heat transfer model of PCB surface is built. With this heat transfer model, the influence rules of outflow height, air distribution plate structure parameters on the PCB heat transfer are both analyzed. And the fan rotation speed’s effect on PCB heating uniformity is analyzed with the method of flow field simulation. Finally, the influence extents of the outflow height, air distribution plate structure parameters, fan rotation speed on the PCB heating uniformity are obtained, which provides decision support for the optimization design of heating zones’ structure.Based on the analysis results of PCB heating impact characteristics, the optimization design of air distribution plate structural parameters is proposed. A method of simplifying the air distribution plate to porous medium impedance model is proposed. With this method the mathematical relationship between the hot air physical property parameters, such as pressure and velocity on both sides of air distribution plate, and the porous medium impedance is established. Based on the porous medium model, the optimization design of air distribution plate impedance is done, and the optimized surface impedance distribution is obtained. Then the geometry topology adjustment scheme is proposed according to the results of optimized impedance characteristics, and the optimized surface impedance is transformed to the specific geometry of air distribution plate. Finally the optimization design of heating zones’ structure for PCB heating uniformity is realized.Wind velocity detection test of air distribution plate outlet and PCB disassembling temperature detection test are done with the developed PCB disassembly apparatus and auxiliary measuring instrument. The results show that, the wind velocity nonuniformity of air distribution plate outlet reduced from 31.8% to 8.3% after optimization. In the heating process of PCB, the maximum temperature difference of PCB reduced from 50℃ to 20℃, which verified the rationality of air distribution plate structure optimization method and the feasibility of optimization results. It can provide technical support to the waste PCB heating disassembling for components reuse.