SMT defect countermeasure_RevisedSMT缺陷及防范措施

2013/7/11
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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．
SMT defects and countermeasure SMT缺陷及防范措施
2013/7/11
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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．


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 it) : 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:
2. Component termination oxidization: Solderability 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致吹偏了元件.
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Tombstoning/ 立碑
Countermeasure/对策 3. Component terminal oxidization or contamination : Solderability test if necessary and RTV the defect material.
Insufficient soak time: Reflow profile optimization.
保温区时间太短:优化回流曲线参数. 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.
分析可能的原因
Countermeasure for the defects
基于以上原因采取的对策
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Tombstoning/ 立碑
• Chip components standing on a terminal end (tombstoning). 片式元件末端翘起（墓碑）
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2013/7/11
2Baidu Nhomakorabea
Major contributor to defects 缺陷的主要分布
Reflow solder and Cleaning 15.2% Incoming Component 5.7% Component Placement 15%
Solder Paste Screening 63.8%
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: 波峰焊接之前加大助焊剂的喷射量
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.
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Solder bridge/ 桥联
• A solder connection 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.
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Tombstoning/ 立碑
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.
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Solder bridge/ 桥联
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.
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Component damaged (Nicks, cracks, or stress fractures)/ 元件损坏
Nicks, cracks, or stress fractures. 缺口，裂纹，压痕

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Component damaged (Nicks, cracks, or stress fractures)/ 元件损坏
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.
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Component lead lifted 元件引脚翘高

Countermeasure/对策
1. Component lead bent before placement : Sort the defective 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．
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 stencil aperture opening : Study and improve the aperture./不标准的钢网开孔: 研究并改善开孔.
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Source: MPM’s A user’s guide to more Precise SMT printing
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Learning Objectives 学习目的
Know the common defect
了解常见缺陷类型
Analysize the possible cause
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Solder ball 锡珠

Countermeasure/对策
1. Stencil Aperture do not focus to pad: improve 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 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).
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Solder ball 锡珠
Solder balls are spheres of solder that remain after the soldering process. Solder balls violate minimum electrical clearance. 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.
Icicle printing 丝印拉尖
Bridging 桥联
Paste collapse 锡膏塌陷
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Misalignment 印刷偏位
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Solder bridge/ 桥联
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) High 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
Reflow stage Peak temp. Soak stage Cool down <4oC/s Preheat stage

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Misalignment 偏位
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Misalignment 偏位

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.