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82 The PCB Magazine • April 2016 Summary The following conclusions are based on data from 1,000-hour test data and +25,000-hour test data (T3, T4, and T5) and are summarized in Table 13. Some materials that were base lined with a high dielectric strength did not main- tain (hold) their advantage over other materi- als. Laminate E with the lowest initial dielectric strength was more capable of maintaining its performance over time and at higher temper- atures than some of other laminates. Thermal aging tests showed not all materials are viable for rigorous applications where thermal excur- sions, high temperatures, high power, or high voltages are involved. Both laminate A and laminate B had delamination as time increased at temperature. Laminates C and D tended to warp as time increased with temperature. Lami- nates D, B, and E performed better in thermal aging tests especially at higher temperatures while laminate E and D performed the best in PTH reliability tests. Some of the more commonly used materials types, such as Laminate A, are at high risk for failure over long periods of time at high tem- peratures, over many thermal cycles, or in high power and high voltage applications. Families of materials less commonly used are more ap- propriate for these applications and include B, C, D, and E laminate systems. The application demands for long-term reliability must be con- sidered in PWB materials selection. PCB Acknowledgments DfR Solutions provided guidance on test methodology, background information, and also performed the testing and analytical ser- vices for the Phase 1, 500-hour pre-screen test. References 1. Underwriters Laboratories Inc., Standard for Safety, UL 746 A, Polymeric Materials—Short Term Property Evaluations. 2. Underwriters Laboratories Inc., Standard for Safety, UL 746 B, Polymeric Materials—Long Term Property Evaluations. 3. IEEE Standard for the Preparation of Test Procedures for the Thermal Evaluation of Solid Electrical Insulating Materials, IEEE STD 98– 2002. 4. ASTM D149, Test Method for Dielectric Breakdown Voltage and Dielectric Strength of Solid Electrical Insulating Materials at Commer- cial Power Frequencies. 5. ASTM D 5374-93, Standard Test Methods for Forced-Convection Laboratory Ovens for Evaluation of Electrical Insulation. 6. ASTM D 5423-93, Standard Specification for Forced-Convection Laboratory Ovens for Evaluation of Electrical Insulation. 7. IEEE Recommended Practice for the Prep- aration of Test Procedures for Thermal Evalua- tion of Insulation Systems for Electrical Equip- ment, IEEE STD 99–2007. 8. IEEE Guide for the Statistical Analysis of Thermal Life Test Data, ANSI/IEE STD 101–1987. This paper was originally presented at IPC Apex Expo 2015 and published in the proceedings. Eva McDermott is materials engineer at Amphenol Printed Circuit Board Technology. Bob McGrath is manager of applications engineering at Amphenol Printed Circuit Board Technology. Christine Harrington is director of operations at Amphenol Printed Circuit Board Technology. long-term thermal reliability of pCb materials