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1、2018/9/25,1,SMT defects and countermeasure SMT缺陷及防范措施,2018/9/25,2,Identify SMT defects,Identify the SMT defects according to IPC-A-610 (Rev: D) 根据 IPC-A-610 (Rev: D)确定缺陷This standard is a collection of visual quality acceptability requirements for electronic assemblies. IPC-A-610是关于电子组装外观质量验收条件要求的文件
2、,2018/9/25,3,Major contributor to defects 缺陷的主要分布,Source: MPMs A users guide to more Precise SMT printing,2018/9/25,4,Know the common defect了解常见缺陷类型Analysize the possible cause分析可能的原因Countermeasure for the defects基于以上原因采取的对策,Learning Objectives 学习目的,2018/9/25,5, Chip components standing on a termina
3、l end (tombstoning).片式元件末端翘起（墓碑）,Tombstoning/ 立碑,2018/9/25,6,Countermeasure/ 对策 Mechanism: Surface tension in component terminal is uneven in reflow. 原理:在回流过程中零件两末端的表面张力不均衡.1. Component terminal heat distributed unevenly 零件两末端受热分布不均衡.Insufficient soak time: Reflow profile optimization.保温区时间太短:优化回流曲线
4、参数. 2. PCB Pad design issue (the pads distance is too big): improve PCB pad design. PCB焊盘设计问题(焊盘间距太大):改善PCB焊盘设计.,Tombstoning/ 立碑,2018/9/25,7,Countermeasure/对策3. Component terminal oxidization or contamination : Solderability test if necessary and RTV the defect material.元件末端氧化或者受污染: 根据情况做可焊性实验并且退还缺陷
5、物料. 4. Printing misalignment: adjust printing machine parameters.丝印偏位: 校正丝印机的参数. 5. Placement misalignment: Optimize the P&P machine parameters.贴片偏位: 优化贴片机的参数. 6. Stencil aperture design issue: study and improve the aperture design.钢网开孔的设计问题: 研究并且改善开孔设计.,Tombstoning/ 立碑,2018/9/25,8, A solder connect
6、ion across conductors that was joined. 焊锡在导体间非正常连接. Solder has bridged to adjacent non-common conductor or component. 焊锡桥连到相邻的非导体或元件.,Solder bridge/ 桥联,2018/9/25,9,Countermeasure/对策1. Screen printing issue/丝印问题:a) Paste height out of UCL: Adjust the printer to control the paste height.锡膏高度超出控制上线: 校正
7、丝印机, 控制锡膏高度.b) Paste printing misalignment or bridging: Fine tune printing machine. /锡膏印刷偏位或者桥联: 优化丝印机.c) Icicle printing: Fine tune printing machine or change to lower viscosity paste.丝印拉尖: 优化丝印机或者使用低粘性的锡膏. d) Solder paste collapse: change to higher viscosity paste./锡膏塌陷:使用高粘性的锡膏.e) Nonstandard ste
8、ncil aperture opening : Study and improve the aperture./不标准的钢网开孔: 研究并改善开孔.,Solder bridge/ 桥联,Icicle printing 丝印拉尖,Paste collapse 锡膏塌陷,Bridging 桥联,Misalignment 印刷偏位,2018/9/25,10,Countermeasure/对策2. Pick & Placement/贴片a) Component placing misalignment: Fine tune the P&P machine .元件贴片偏位: 优化贴片机的参数.b) Hi
9、gh pressure for placement: reduce pressure to proper value .贴片压力过大: 减少压力到适当的参数.3. Wave soldering/波峰焊a) Low conveyor ramp: Raise the conveyor ramp per actual status.传送带角度过小: 根据实际情况加大传送带角度b) Less flux on board : Increase the flux spray volume on board before going through wave soldering.板上的助焊剂较少: 波峰焊接
10、之前加大助焊剂的喷射量,Solder bridge/ 桥联,2018/9/25,11,Component damaged (Nicks, cracks, or stress fractures)/ 元件损坏,Nicks, cracks, or stress fractures. 缺口，裂纹，压痕,2018/9/25,12,Countermeasure/对策1. Raw material damaged: purge the batch material./来料损坏: 清除这批来料.2. Damaged during SMT process (Fixture or machine touch i
11、t) : Investigate and take corrective actions for nonstandard operation.在SMT流程中损坏(夹具和设备接触): 调查分析并且对不规范的操作作出矫正行动.3. Fast cooling rate on reflow process : Control the cooling rate to below 4degree per second.在回流过程中冷却速率过快: 控制冷却速度使斜率保持在每秒4度以下.Typical reflow profile/ 回流曲线典例:,Component damaged (Nicks, crac
12、ks, or stress fractures)/ 元件损坏,2018/9/25,13,Misalignment 偏位,2018/9/25,14,Countermeasure/对策1. P&P machine function unstable: Fine tune the P&P machine.贴片机性能不稳定: 优化贴片机性能参数.a) Fine tune X,Y data/ 调整X,Y坐标b) Optimize pick and placement parameters./ 校正吸料和贴片的参数.2. Component termination oxidization: Soldera
13、bility test if necessary. Purge the failed material/ 元件末端氧化: 可焊性实验, 清除不合格的来料.3. Operator touch the component prior to reflow: Standardize the operator handling (document control)/ 在回流炉前目检操作员碰到贴片元件: 标准化操作员操作(文件控制)4. Air flow rate in the reflow oven is so high that the components are moved.回流炉内空气流量太高以
14、致吹偏了元件.,Misalignment 偏位,2018/9/25,15,Component lead lifted 元件引脚翘高,One lead or series of leads on component is out of align-ment and fails to make contact with the land.元件一个或多个引脚变形不能与焊盘正常接触,2018/9/25,16,Component lead lifted 元件引脚翘高,Countermeasure/对策1. Component lead bent before placement : Sort the d
15、efective part and return it to vendor. 贴片前元件引脚变形: 挑选出缺陷元件,退回供应商2. Manual placement the loose part : Inspect the part before pass it to reflow. 手放散料: 回流前目检,2018/9/25,17,Solder ball 锡珠,Solder balls are spheres of solder that remain after the soldering process. Solder balls violate minimum electrical c
16、learance.焊锡球是焊接后形成的呈球状焊锡.Solder fines are typically small balls of the original solder paste metal screen size that have splattered around the connection during the reflow process.焊锡残渣是在回流中形成的小的球状或不规则状焊锡球.,2018/9/25,18,Solder ball 锡珠,Countermeasure/对策1. Stencil Aperture do not focus to pad: improve
17、stencil aperture opening.钢网开孔没有对准焊盘中心: 改善钢网开孔.2. Printing misalignment: Fine tune print machine.丝印偏位: 调整丝印机状态.3. Excess paste : Cpk control. 多锡: Cpk控制.4. Damp PCB : Bake the PCB before loading it to SMT.PCB焊盘受潮: SMT组装流程之前烘烤PCB.6. Stencil polluted: clean the stencil. 钢网脏污: 清洗钢网.7. Profile ramp up is
18、too fast : Optimize reflow profile.回流曲线升温速度过快: 优化回流曲线.8. Paste oxidized: exchange with fresh solder paste. 锡膏氧化: 更换新锡膏.9. Chip wave or solder wave height is too high caused excess solder to top side: adjust the wave soldering height to proper level (wave solder).波峰高度设置的太高致使多余的焊锡到顶面: 校正波峰焊设置到适当的高度 (波峰焊接).,
