Study On Lead-Free Dip Soldering Process Of Thin PCB With Factorial Experiment Design

Selected lead-free dip soldering is a new kind of surface mount technology,which is generated in recent years.It's better for flexible production compare with traditional selected wave soldering.Meanwhile,due to dip soldering machine is easier to operate and equipment maintenance cost is less,it's applied to produce PCB with both SMD and hole mounted electronics by more electronic parts manufacturers gradually.However,due to the new technology application period is short,there are less of experience and guideline on products failure root cause analysis and process modification.Design of Experiment(DOE)is a statistics method,which is used to analysis factor impact on result via less experiment and times.At the same time,the best factor combination and predictive value could be calculated with optimization.The paper would use part 2~k factorial experiment design to analysis two main kinds of failure mode,solder filling insufficient and solder hole in our company.The factors are flux spray amount,pre-heating temperature,soldering temperature,soldering time,soldering speed and height of soldering fixture.The experiment is based on 6 factors with level 2 and the resolution is?.The root cause of parts failure and method of process optimization would be found out after experiment and analysis.The experiment indicates the main factors of soldering filling insufficient and soldering hole are soldering temperature,soldering time and height of soldering fixture.If we want to decrease the failure rate,the three factors must be controlled.And other factors impacts on failure are not significant.The impact of soldering temperature,soldering time and height of soldering fixture to failures are negative effect that means higher soldering temperature,longer soldering time and higher soldering fixture would result in lower failure rate.Besides,the 2 level interaction of factors effect are not significant.Through multiple fitting,we could calculate the linear regression equation of soldering filling insufficient and solder hole with these factors.After calculate the equation,the best factor combination with lowest failure rate are as below:flux spray pulse amount is 20(about 0.5g per solder hole),pre-heating temperature is 200?,the soldering temperature is 310?,soldering time is 3s,soldering speed is 4mm/s,height of soldering fixture is 98mm.Arrange another sets of experiment plan with the best factor combination,the equation is verified correct and the best factor combination is fixed,which is the base of decreasing parts failure rate.Meanwhile,use temperature testing sample and caliper with auxiliary jig to make sure the soldering temperature and fixture height are implemented precisely and the process is stable.