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1、1,2020/10/8,SMT defects and countermeasure SMT缺陷及防范措施,2,2020/10/8,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
2、件,3,2020/10/8,Major contributor to defects缺陷的主要分布,Source: MPMs A users guide to more Precise SMT printing,4,2020/10/8,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,5,2020/10/8, Chip components standing on a te
3、rminal end (tombstoning). 片式元件末端翘起（墓碑）,Tombstoning/ 立碑,6,2020/10/8,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
4、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.,Tombstoning/ 立碑,7,2020/10/8,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
5、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/ 清洗钢网 b) Replace the recycled paste with fresh one./更换新锡膏 c) Printing machine parameter adjustment./校正丝印机参数 2. Poor solderability of component or pad./元件或焊盘可焊性太低 Roo
6、t cause: a) Old date component or PCB. /陈旧元件或PCB板 b) Contamination on component or PCB. /元件或焊盘受污染 Action: Purge the material for further disposition. /清除来料 3. Insufficient flux volume: increase flux spray rate (wave solder). 助焊剂量不足: 增加助焊剂喷射量 (波峰焊接) 4. Preheat excess: lower preheat temperature proper
7、ly (wave solder). 预热过度: 适当降低预热温度 (波峰焊) 5. Chip wave or solder wave height is low : proper height (wave solder). 波峰高度过低: 调整到适当高度 (波峰焊),33,2020/10/8,Insufficient Solder/少锡,Insufficient solder 焊锡不足,34,2020/10/8,Insufficient Solder/少锡,Countermeasure /对策 1. Stencil aperture clogging cause incomplete sold
8、er printing): Automatic or manual clean the stencil. 钢网孔堵塞导致锡膏不完全印刷: 自动或者手工清洗钢网 2. No enough solder paste volume (Paste height under LCL) : Visual inspection and Cpk control. 锡膏量不足(锡膏高度在LCL以下): 目检和Cpk控制 3. Solder paste print misalignment: Fine tune printing machine 锡膏印刷偏位:校正丝印机使之最优,4. Poor solderabi
9、lity of component or PCB pad: 元件或PCB焊盘可焊性差 a) Optimize reflow profile.优化回流曲线 b) Exchange the poor solderability component. 更换掉低可焊性元件 5. Excess glue or glue misalignment: Fine tune screen print (wave solder). 点胶过多或点胶偏位:优化丝印参数 6. Less flux : Increase the flux spray on board before it pass wave solderi
10、ng (wave solder).助焊剂不足: 增加助焊剂的喷射量,35,2020/10/8, Solder fillet extends on to the top of the component body. 焊锡接触元件体,Excess Solder/多锡,36,2020/10/8,Excess Solder/多锡,Countermeasure /对策 1. Excess solder paste: 锡膏量过多 a). Solder paste height out of UCL: Adjust printing machine to control the paste height.
11、锡膏高度超出UCL: 校正丝印机控制锡膏高度 b). Nonstandard of stencil aperture opening: standardize the stencil aperture opening for different type components. 钢网开孔不标准:为不同类型的元件设置相应钢网的开孔标准 2. Wave soldering/ 波峰焊接 a) Low conveyer ramp, long wave soldering time: Adjust conveyor ramp angle to 57 degree and soldering time t
12、o 35 second. 传送带角度过小, 波峰焊接时间变长: 校正传送带角度到57度, 焊接时间35秒 b) High preheat temperature to dry off the flux: According to flux spec to control the preheat temperature, normally the PCB surface preheat temperature should be under 100oC. 高预热温度造成助焊剂过度挥发: 按照助焊剂的规格控制预热温度, 通常, PCB表面温度 一般低于100oC,37,2020/10/8,Wron
13、g Orientation/Polarity 反向, 极性反,Correct polarity/正确的极性,Wrong polarity/ 极性反,This mark is anode of tantalum capacitor on PCB.,This mark is anode of tantalum capacitor.,Correct polarity/正确的极性,Wrong polarity/ 极性反,This mark is cathode direction.,This mark is cathode direction.,Wrong Polarity:/极性反,38,2020/
14、10/8,Wrong Orientation/Polarity 反向, 极性反,Correct direction/ 正确的方向,Wrong Orientation /反向,This mark is ICs direction.,This mark is ICs direction on PCB.,Wrong Orientation/ 反向: The IC is populated in inverse direction on the PCB./ IC被反方向组装在线路板上,39,2020/10/8,Countermeasure/ 对策 1. Wrong placement machine
15、program : Check and correct the machine program. 贴片机程序错误: 检查和更正机器程序 2. Manual placement in reverse direction: 手工放置元件错误 a) Avoid manual placement components 避免手工放置元件 b) Need special inspection for the manual placement prior to reflow (document control). 炉前需要特别检查那些手工放置的元件 (文件控制) 3. Disordered orientat
16、ion in the tray/reel of the incoming material: 卷装或盘装来料元件的不规则放置 a) Inspect before loading it to SMT. 上料前检查来料 b) Feedback to vendor to take corrective actions. 反馈给供应商采取改善行动,Wrong Orientation/Polarity 反向, 极性反,40,2020/10/8,a. Long lead / short lead 脚长/脚短 b. Missing component 元件丢失 c. Expose copper 露铜 d. Surface scratched 外观划伤 Countermeasure /对策 Take corrective action and preventive action after investiga
