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首页> 外文期刊>Components, Packaging and Manufacturing Technology, IEEE Transactions on >Laser Ultrasonic Inspection of Solder Bumps in Flip-Chip Packages Using Virtual Chip Package as Reference
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Laser Ultrasonic Inspection of Solder Bumps in Flip-Chip Packages Using Virtual Chip Package as Reference

机译：使用虚拟芯片封装作为参考的倒装芯片封装中焊点的激光超声检查

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摘要

In flip-chip (FC) packages, the solder bumps are sandwiched between the silicon die and the substrate, making them no longer visible for usual visual inspection. An inspection system capable of evaluating the quality of the hidden solder bumps in FC packages has been developed. The system pulses a laser on the top surface of a chip package to generate ultrasonic waves in the package to excite structural vibrations which can then be measured using an interferometer. Since defective solder bumps cause changes in the transient vibration response of a test sample, quality of the test sample can be assessed by correlating its vibration responses to that of a known-good reference sample. The limitation to this method is the necessity to use a known-good reference chip package, which typically involves expensive testing using alternate methods. In this paper, the development of a method without the need of known-good reference samples is presented. This method, called hybrid reference method, uses a statistical approach to find the most similar packages and then average their time domain vibration signals to generate virtual time domain signals. These virtual signals are what we call hybrid reference signals and they are correlated back with the vibration signals from the sample under inspection to obtain a quality signature. Finally, defective and nondefective chip packages are separated by estimating a beta distribution that fits the quality signature histogram of the inspected packages, and then determining a critical threshold for an acceptable quality signature. This method was applied on two types of FC packages with no available pre-established known-good reference chip package. The results of this quality assessment were validated by comparison with electrical test and X-ray technique results.
机译：在倒装芯片（FC）封装中，焊料凸点被夹在硅芯片和基板之间，因此对于常规的目视检查来说，它们不再可见。已经开发了一种能够评估FC封装中隐藏的焊料凸点质量的检查系统。该系统在芯片封装的顶面上脉冲激光，以在封装中产生超声波，以激发结构振动，然后可以使用干涉仪进行测量。由于有缺陷的焊料凸块会导致测试样品的瞬态振动响应发生变化，因此可以通过将其振动响应与已知质量的参考样品的振动响应相关联来评估测试样品的质量。该方法的局限性是必须使用已知质量良好的参考芯片封装，这通常涉及使用替代方法进行的昂贵测试。在本文中，提出了一种无需已知良好参考样品的方法的开发。该方法称为混合参考方法，它使用统计方法来查找最相似的程序包，然后将其时域振动信号取平均值，以生成虚拟时域信号。这些虚拟信号称为混合参考信号，它们与受检样品的振动信号相互关联以获得质量特征。最后，通过估算适合所检查的包装的质量特征直方图的beta分布，分离出有缺陷和无缺陷的芯片封装，然后确定可接受的质量特征的临界阈值。此方法应用于两种类型的FC封装，没有可用的预先建立的已知良好参考芯片封装。通过与电气测试和X射线技术结果进行比较，验证了此质量评估的结果。

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