SMT设备原理与应用-3-表面组装工艺

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1、SMT设备原理与应用表面组装工艺SurfaceMountAssemblyProcesses内容•焊膏涂敷•印刷工艺•拾取和贴放•再流焊接•再流焊接气体对焊接的影响•特殊焊接•焊点检查•清洗•在线监测•再流焊接故障分析焊膏涂敷solderpastedeposition•焊膏处理及存储（Pastehandlingandstorage）–建议保存于电冰箱refrigerator或冷冻器freezer里，盒口向下以免助焊剂分离；–正式使用并暴露在空气前，先将焊膏的温度升至室温，以免水汽凝结；–解冻时间，参看图4.1。焊膏涂敷solderpas

2、tedeposition•常见的焊膏涂敷工艺：–印刷•丝网印刷screenprinting•模板印刷stencilprinting模板印刷stencilprinting•相比丝网印刷，可以更加准确控制焊膏涂敷量•工艺简图如图所示：•其制约是必须要平坦的表面•要想印刷质量好，印膏的颗粒尺寸不大于其窗孔尺寸的1/7滴涂法dispensing气动滚轮滴涂器时间-压力气动滴涂器时间-压力收缩阀气动滴涂器俄歇阿基米德螺旋型滴涂器针移法pin-transferring滚轮涂布Rollercoating印刷工艺考虑的因素Printerlevelco

3、nsideration•模板材料模板成形技术•参见上表•最常见：化学蚀刻–工艺：Theprocessincludes(1)cleaningmetal,(2)applyingphotoresist,(3)imagingphototool,(4)developing,(5)etching,and(6)removingphotoresist•沙漏曲线问题细间距用的窗口设计模板厚度和阶梯模板刮刀Squeegee•刮刀的材料：•聚氨酯橡胶polyurethanerubber•金属metal印刷及检测工艺Printingandinspection

4、process•印刷前加焊膏的量取决于使用的焊膏类型，一般来说，在刮刀前形成的焊膏直径应为0.25～0.75英寸•Theprintercanbesetinoff-contact（非接触）modeoron-contactmode.–Foroff-contactmode：•themaximumsnap-off（印刷间隙）shouldnotbegreaterthan10×stencilthickness.Thecommonlyusedsnap-offvaluerangesfrom30to50mil.•couldreducesmear（污斑）

5、forapoorlyregisteredsystem（校准系统）.•Aclam-shell（openingmechanismisacceptable.印刷及检测工艺Printingandinspectionprocess•Theprintercanbesetinoff-contact（非接触）modeoron-contactmode.–Foron-contactmode：•providesamoreaccurateprint.•requiresapureverticalmotionopeningmechanism.•Ingeneral

6、,aslowsnap-outspeed,suchas0.04in./sec,ismoredesirableinordertoachievegoodprintquality刮刀速度•Acommonlyusedsqueegeespeedrangesfrom0.75to4in./sec.•thefinerthepitch,theslowerthesqueegeespeeddesired.•attooslowasqueegeespeed,thepastewillnotrollandhencewillnotflowevenlyintoopeni

7、ngs.•Whenthesqueegeespeedistoohigh,thepastewillslideandskiptheapertures.Asaresult,insufficiencyandshadowingwilloccur.•Currentlytheindustryisgraduallyshiftingtowardafastersqueegeespeed,duetothedemandforahigherthroughput.刮刀的压力•Fortheoff-contactmode,thesqueegeepressurecomm

8、onlyusedis1–1.5lb/inchsqueegeeblade.•Fortheon-contactmode,asqueegeepressureof0.75lb/inchsqueegeebladeispreferr