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Long Term Thermal Reliability of Printed Circuit Board Materials
Long Term Thermal Reliability of Printed Circuit Board Materials
This paper describes the purpose, methodology, and results to date of thermal endurance testing performed at the company.
Materials Tech

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Authored By:
Eva McDermott, Ph.D., Bob McGrath, and Christine Harrington
Amphenol Printed Circuit Board Technology
Nashua, NH 03062 USA

Summary
This paper describes the purpose, methodology, and results to date of thermal endurance testing performed at the company. The intent of this thermal aging testing is to establish long term reliability data for printed wiring board (PWB) materials for use in applications that require 20+ years (100,000+ hours) of operational life under different thermal conditions.

Underwriters Laboratory (UL) testing only addresses unclad laminate (resin and glass) and not a fabricated PWB that undergoes many processing steps, includes copper and plated through holes, and has a complex mechanical structure. UL testing is based on a 5000 hour expected operation life of the electronic product. Therefore, there is a need to determine the dielectric breakdown / degradation of the composite printed circuit board material and mechanical structure over time and temperature for mission critical applications.

Thermal aging testing consisted of three phases. Phase I - A 500 hour pre-screen at four fixed temperatures following IEEE98 A.1 and UL746B 20A1 (completed). Phase II - Short term aging for 1000 hours at four revised, fixed temperatures. Plated through hole reliability testing using IST and HATS was also completed. Phase III - Long term aging for 25,000 hours at five, revised fixed temperatures. This paper will discuss results of this testing to date.

Conclusions
The following conclusions are based on data from 1000 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 maintain (hold) their advantage over other materials. Laminate E with the lowest initial dielectric strength was more capable of maintaining its performance over time and at higher temperatures than some of other laminates.

Thermal aging tests showed not all materials are viable for rigorous applications where thermal excursions, 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. Laminates 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.

Initially Published in the IPC Proceedings

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