Statistical analysis of the impact of refinishing process on leaded components

Refinishing process such as Hot Solder Dip (HSD) process can be used to prevent tin whisker growth in microelectronics components by replacing the lead-free finishes with conventional tin–lead coatings. In some applications, it is also used to ensure reliable solder joints by replacing contaminated finishes and lead-free alloys with tin–lead to result in a homogeneous solder joint with tin–lead paste. In this paper, the impact of a HSD refinishing process on leaded components was statistically studied by comparing the electrical test data of refinished samples with those not-refinished. The likely damage from the component refinishing was thought to be the degradation of package integrity through thermo-mechanical stressing. This might be detectable as a microscopic leakage current if moisture could be encouraged into any open areas. Ten types of leaded components were selected and samples for each type of the component were allocated into 2 lots, one for refinishing and one used as a control. 150 cycles −65/150 °C thermal cycling followed by 500 h 85%RH/85 °C humidity test was applied to all the samples (both refinished and not-refinished) to amplify any incipient failure points and accelerate moisture ingress into the package. Electrical test was then carried out to measure any small changes in current under zero and reverse bias conditions. In the end, a data reduction process in conjunction with a statistical hypothesis test was used to analyze the electrical test data. The results showed that there was no significant difference between the measured currents of refinished and not-refinished post-aged samples. Therefore it was concluded that the refinishing process did not have a significant impact on the tested components. This conclusion was further strengthened by other experimental test results such as CSAM images.

[1]  S.S. Asfour,et al.  Tin Whisker Electrical Short Circuit Characteristics—Part I , 2008, IEEE Transactions on Electronics Packaging Manufacturing.

[2]  Jun-Mo Yang,et al.  Behavior of tin whisker formation and growth on lead-free solder finish , 2006 .

[3]  S. Asfour,et al.  Tin Whisker Electrical Short Circuit Characteristics—Part II , 2008, IEEE Transactions on Electronics Packaging Manufacturing.

[4]  D. Das,et al.  Assessment of Thermomechanical Damage of Electronic Parts Due to Solder Dipping as a Postmanufacturing Process , 2007, IEEE Transactions on Electronics Packaging Manufacturing.

[5]  S. Rajagopal,et al.  The impact of lead-free legislation exemptions on the electronics industry , 2004, IEEE Transactions on Electronics Packaging Manufacturing.

[6]  Michael Osterman,et al.  Assessment of Solder-Dipping as a Tin Whisker Mitigation Strategy , 2011, IEEE Transactions on Components, Packaging and Manufacturing Technology.

[7]  Herman P. Wijnand,et al.  Mann-Whitney/Wilcoxon's nonparametric cumulative probability distribution , 2000, Comput. Methods Programs Biomed..

[8]  C. Bailey,et al.  Thermal modelling and optimisation of hot solder dip process , 2012, 2012 13th International Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems.

[9]  Anthony J. Rafanelli,et al.  The challenge of lead-free electronics for aerospace electronic systems , 2009, 2009 IEEE Custom Integrated Circuits Conference.

[10]  Dong Nyung Lee,et al.  Spontaneous growth mechanism of tin whiskers , 1998 .

[11]  Sayoon Kang,et al.  Growth of tin whiskers for lead-free plated leadframe packages in high humid environments and during thermal cycling , 2007, Microelectron. Reliab..

[12]  M. Osterman,et al.  Tin whiskering risk factors , 2004, IEEE Transactions on Components and Packaging Technologies.