Long-Term Thermal Reliability of PCB Materials

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Abstract

This paper describes the purpose, methodology, and results to date of thermal endurance testing performed at Amphenol Printed Circuit Board Technology in Nashua, NH. The intent of this thermal aging testing is to establish longterm reliability data for 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 PCB material and mechanical structure over time and temperature for mission critical applications.

Thermal aging testing consisted of three phases.

• Phase I: 500-hour pre-screen at four fixed temperatures following IEEE98 A.1 and UL746B 20A (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.

Introduction

The objective of this testing is to establish the electrical strength-temperature Arrhenius curve (temperature life curve) for materials used in PWB for applications that exceed the typical 5,000 hour end of life test defined in UL Standard UL746B. The test methodology presented in this report generates data representing 25,000 hours of operational life.

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Editor's Note: This article originally appeared in the April 2016 issue of The PCB Magazine.