| Printed circuit broads(PCB)have lost their original function after wasted.However,the plastic-encapsulated chips on the wasted PCBs are still worth reusing.If the disassembly craft is set improperly,chips will not be disassembled or chips delamination will occur,which have a bad influence on the reusing of chips.In this article,disassembly craft of PCB for avoiding chip delamination is studied.To improve the efficiency of disassembling,disassembling mechanism is redesigned and heating profile is adjusted so that the disassembly cycle is reduced on the premise that components can be disassembled and chip delamination will not happen.This research is a practical guide to develop disassembly equipment for reusing components and set craft parameters.First,to solve the problem that temperature in disassembly heating chamber is hard to reach the target temperature caused by the large amplitude of vibration disassembly mechanism,a new disassembly mechanism in which the disassembly force is impact is designed.Via kinematics analysis,motion equation of PCB is established to estimate whether impact function will carry out,and then the critical rotation speeds of driving axis are got.Next,geometric dimension of new disassembly mechanism is decided by the vibration mechanism.Based on this dimension the impact energy can be got to analyze the components disassembly in different rotation speed of the axis so that the best rotation speed is decided.Furthermore,diameter of driving axis is designed for its strength.After the new disassembly mechanism has been designed completely,disassembly experiments are carried out to test the disassembly result.Second,a transient thermal simulation model is built to get the temperature of chips and solder at each time during PCB heating process,which is proved by experiments.On the basis of this model,the characters of chips heating are got and the fastest heating rate chips is affirmed.Also the exact temperature of solder at each time is got.And the heating efficiency can be improved in the current heating temperature profile.They all lay foundation for optimizing of heating profile.Third,heating temperature profile is optimized for the 6 heating chamber disassembly equipment.To avoid chip delamination,the influence of chips' heating rate under the highest chamber temperature is analyzed first.And then the equations of temperature of chip and solder are set up,which are used for the constraint condition.Next,the shortest disassembly period and corresponding heating temperature profile are got by nonlinear programming method.This heating profile is simulated in the transient thermal model to analyze the situation of solder melting and chip delamination to prove the optimized profile.At last,the optimized disassembly crafts are set on the equipment invited by our lab.Via measuring temperature in the disassembly process,the optimized profile can be used to reflect the heating process.Disassembly experiments are carried out to test the heating profile and disassembly mechanism.And then the chips disassembled in this craft are tested by ultrasonic scanning to analyze the percentage of delamination.And also destructive physical analysis(DPA)is conducted to the chips which are not delaminated to make sure the chips can be reused. |
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