PCB变形的建模与仿真----

印刷电路板在回焊过程中变形的建模与仿真摘要在SMT中，回焊是非常重要的工站。在回焊过程中受到热冲击已成为印刷电路板(简称为PCB)组件生产过程中产生缺陷的主要原因之一。PCB组件组成材料不同，热膨胀系数等热性能参数相差较大，容易产生翘曲变形等缺陷，造成元器件和PCB之间的电气和物理连接失败，导致整个PCB组件失效。而由于传统的,经反复试验、反复调整来改进回焊工艺的方法既费时又耗费大量实验经费，不能适应当前电子产品更新速度快、竞争日益激烈的需求，在这一背景下，焊接工艺的建模与仿真、预测与控制研究引起了广泛的关注。模拟仿真可以识别在回焊过程中的温度变化以及确定其对生产质量的影响;对回焊温度曲线的设定使设计者根据PCB热分布重新排布组件从而使产品设计达到最优化。本文利用有限元法对PCB组件在回焊过程中的受热进行分析，建立瞬态温度场和应力场模型。用ANSYS软件对PCB组件在回焊过程中由于受热产生的热机械反应进行了模拟和建模，得出了温度场以及应力场的分布。由于PCB组件组成材料的热物理性能不同，以及经过不同的温区加热，模拟了不同时刻整个PCB组件的温度场分布。建立了一个贴装了3个PLCC的4层PCB板物理简化模型，模拟了在三种约束条件下，该组件在回焊过程中受热冲击时，产生的热应力及热变形。选取PCB上3个点，得到了在三种约束下面位移和离面位移的位移量，即在底面对角两点约束下面位移和离面位移的位移量最大;底面4顶点约束下面位移和离面位移的位移量其次;底面两对边约束下面位移和离面位移的位移量最小。通过仿真可对回焊温度曲线进行优化，使得PCB组件得到比较均匀的温度场分布，并调整对PCB的约束，使得变形最小化。关键词:回焊;热应力;建模;温度场;仿真;,1ModellingandsimulatingforPCBDeformedinrefolwsolderingAbstractofthesisReflowsolderingisveryimportanttechnicsinSMT.ThermalimpacttoPCBAduringreflowsolderingisconsideredoneofthemaindriversformanufacturingdefects.ThematerialsmakingupaPCBAisvarious,andthethermalpropertyofthematerialsisalsodifferent,thismaycausesomedefectsforexamplewargpage.ExcessivewarpageinthePCBmayresultingapsformingbetweenthemoduleleadsandthemoltensolderonthesolderpads,thenthefailureofelectronicallyandphysicalconnectionleadtoPCBA'sdefect.Thetraditionalapproachofexperimentallyanalysingproductiondefectswouldbecostlyandvirtuallyimpossible,andcan'treachthedemandoftheproducerforthefastrenovationandtheacutecompetition.Analternativetothisapproachistoderivecomputationalandnumericalmodelsthatencapsulaterepresentationsofthekeyprocessphysics,sothateffectanalysisofthepertinentprocessvariablesmaybeexamined.TheapplicationofthemodellingandsimulationtoasamplePCBAhasbeencarriedouttoexplorehowunduevariationsinthereflowtemperaturecanbeminimizedbyanumberofdifferentstrategies.IthasbeenshownthatsimplemovementsofcomponentscanhavequitebeneficialeffectsontheoverallprocessthermalhistoryofthePCB.ThepaperusefiniteelementanalysismethodanalysisthethermalimpactofPCBAduringthereflowsoldering,andbuildingthetemperatureandstressdistributionmodel.ThepapermodelandsimulatethethermalwarpageofPCBAduringreflowsoldering,getthetemperatureandstressdistributionofPCBA.ThispapersimulatethetemperaturedistributionofPCBAundertheconditionofthematerialmakingupPCBAisdifferent,andPCBAwillgothroughdifferentovensection,buildingasimplephysicalmodelofa4-layerPCBwith3PLCCstosimulatethethermalstressandwarpageofPCBAunderthreeconstrainedconditions,whenthePCBAgothroughtheovensections.ComparedthesurfacedisplacementandtheZaxisdisplacementofthreepointsonthePCBunderthethreeconstrainedconditiontogettheresultoffollowing.Thethermalwarpagehappenedundertheconstrainedconditionsofthetwopointsonthecrosswereconstrainedislargethanthathappenedundertheconstrainedconditionsofthefourpointswereconstrained.theconstrainedconditionsofthetwosideswereSimulationwarpageisconstrained.Optimizeandthetemperatureminimizedbyadjusting,thetemperaturefigureisattainablethroughthedistributionofPCBAismoreuniform,alsotheconstrainedcondition.KEYWORD:refolwsoldering;thermalstress;modelingtemperaturefield;Simulation;2目录摘要..................................................................................................................................................1Abstract..............................................................................................................................................1目录.............................................................................................................................................2第一章绪论....................................................................................................................................31.课题背景意义.................................................................................................................32.国内外研究概况............................................................................................................33.研究思路及方法............................................................................................................4第二章PCB组件概述.................................................................................................................52.1PCB简介........................................................................................................................52.1.1PCB的分类.........................................................................................................52.1.2PCB的材料组成.................................................................................................62.1.3PCB的制造流程.................................................................................................72.2PCB组件........................................................................................................................82.3小结................................................................................................................................8第三章PCB理论分析与建模.......................................................................................................123.1温度场数学模型的建立.....................