Failure analysis and control of gold-plated lead solder joint cracks
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摘要: 宇航元器件镀金引脚钎焊前，需对焊接位置进行去金搪铅锡处理，避免焊接界面生成脆性金锡化合物，防止在使用时受外力作用而发生焊点“金脆”开裂.文中针对某宇航型号所用霍尔元件镀金引脚的焊点经历环境试验后脱落的问题，对相关镀金引脚焊点的形貌、金相与界面结构进行分析. 结果表明，元件引脚焊接位置已进行去金处理，但其焊接位置末端局部去金不彻底，焊点界面局部区域生成脆性金锡化合物，导致焊点前端生成裂纹源；经历宇航级温度循环或外力冲击考核试验时，因裂纹前端存在应力集中，导致裂纹持续扩展并发生焊点开裂脱落失效.确保镀金引线焊接位置去金质量并严控钎焊位置，避免在焊点内局部区域生成脆性金锡化合物，对提升镀金引脚焊点可靠应用具有重要意义.Abstract: After experiencing the mechanical and thermal environment test, one kind of electronic assembled Hall element experienced partial function failure due to the gold-plated pin solder joint cracking. Re-examination results showed that part of the Hall element pin solder joints also suffered partial cracking before environmental assessment tests. Due to the small assembly space of the component, it is difficult to effectively check the solder joint status after electrical installation. Therefore, analysis based on the cause of solder joint failure and targeted improvements are of great significance for improving the reliability of the spacecraft. The failure reasons were analyzed by observation of cracking morphology, metallographic testing and analysis of chemical composition. When the component pin welding position is not completely gold removed, brittle Au-Sn intermetallic compound (IMC) was observer along the cracked welding interface, which led to the generation of cracking source. Due to the stress concentration at the crack front, the crack expansion continued and caused solder joints failure under the effect of temperature alternating or external force. Ensuring the de-gold quality at soldering position and controlling the soldering position are of great significance for improving the reliability of the solder joints at the gold-plated leads.
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图 1 霍尔元件引脚开裂焊点形貌
Figure 1. Morphology of cracked Hall element lead solder joints. (a) No.23 sample; (b) No.160 sample
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图 2 失效焊点引脚开裂面焊接界面金相形貌
Figure 2. Metallographic morphology of the welding interface on the cracked solder joint
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图 3 23号样品开裂焊点金相形貌
Figure 3. Metallographic morphology of No.23 sample cracked solder joint. (a) low-magnification; (b) the front interface; (c) lead surface
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图 4 160号样品开裂焊点金相形貌
Figure 4. Metallographic morphology of No.160 sample cracked solder joint. (a) low-magnification; (b) the front interface; (c) the unsoldered side of the lead
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图 6 23号霍尔元件开裂焊点前端SEM形貌
Figure 6. SEM morphology of No.23 Hall cracked solder joint. (a) low magnification; (b) the front interface; (c) lead surface; (d) end of the crack
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图 7 160号霍尔元件开裂焊点前端SEM形貌
Figure 7. SEM morphology of No.160 Hall cracked solder joint. (a) SEM and element distribution map of solder joint; (b) cracked interface and (d) crack end
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图 8 19号样品未开裂焊点外观与金相形貌.
Figure 8. Appearance and metallographic morphology of No.19 Hall uncracked solder joint. (a) solder joint appearance; metallographic morphology of: (b) low-magnification; (c) the front; (d) solder interface
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图 9 氩离子刻蚀后焊接界面形貌与AES谱图
Figure 9. SEM morphology and AES spectrum of welding interface after argon ion etching. (a) interface SEM after ion etching; (b) AES of P1；(c) AES of P2
表 1 失效焊点引脚表面不同区域EDS分析结果(质量分数，%/原子分数，%)
Table 1 EDS analysis results in areas of the failed lead solder joint interface
分析位置 Ni Sn Pb Au 谱图1 100/100 − − − 谱图2 − 53.4/65.5 − 46.6/34.5 谱图3 − 68.4/78.2 − 31.6/21.8 谱图4 − 68.4/79.0 29.0/19.2 2.6/1.8 
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表 2 23号霍尔元件开裂焊点前端不同区域EDS分析结果(质量分数，%/原子分数，%)
Table 2 EDS analysis results of No.23 Hall cracked solder joint
分析位置 Sn Pb Au Ag 谱图1 97.5/98.5 2.5/1.5 − − 谱图2 11.1/17.9 85.3/78.6 3.6/3.5 − 谱图3 66.5/77.2 21.4/14.3 12.1/8.5 − 谱图4 62.1/73.1 − 37.9/26.9 − 谱图5 53.5/65.6 − 46.5/34.4 − 谱图6 68.3/78.3 3.3/2.2 28.4/19.5 − 谱图7 77.9/84.2 17.4/10.8 0.9/0.6 3.8/4.4
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表 3 160号霍尔元件开裂焊点前端不同区域EDS分析结果(质量分数，%/原子分数，%)
Table 3 EDS analysis results of No.160 Hall cracked solder joint
分析位置 Ni Sn Pb Au 谱图1 100/100 − − − 谱图2 6.8/19.2 3.8/5.3 − 89.4/75.5 谱图3 2.3/5.6 51.9/61.6 − 45.8/32.8 谱图4 29.5/50.1 43.9/36.9 18.8/9.0 7.8/4.0 谱图5 16.0/31.7 49.3/48.5 26.5/14.9 8.2/4.9 谱图6 − 68.2/78.9 30.5/20.2 1.3/0.9
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表 4 19号霍尔元件未开裂焊点前端不同区域EDS分析结果(质量分数，%/原子分数，%)
Table 4 EDS analysis results of No.19 Hall uncracked solder joint
分析位置 Ni Sn Pb Au 谱图1 25.8/43.8 50.0/44.5 21.3/10.3 2.9/1.4 谱图2 − 73.5/83.7 25.0/15.3 1.5/1.0 谱图7 − 64.3/76.9 34.4/22.2 1.3/0.9
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