Effect of Moisture on Thermal Properties of Halogen-Free and Halogenated Printed-Circuit-Board Laminates

Lili Ma, Bhanu Sood, Member, IEEE, and Michael Pecht, Fellow, IEEE


Moisture plays an important role in the integrity and reliability of printed circuit boards (PCBs). The presence of moisture in a PCB alters its thermal performance and thermomechanical properties, thereby affecting overall performance. Due to the shift in market trends toward halogen-free products, halogen-free PCB materials have recently gained popularity. There are many studies on the behaviour of halogenated PCBs exposed to moisture, but there are less data available on the use of halogen-free flame retardants in PCBs. Therefore, it is necessary to understand the moisture behaviour of halogen-free PCB materials and the effect of moisture on material thermal properties when compared with halogenated PCBs materials. In the past, the Center for Advanced Life Cycle Engineering has conducted thermal-property measurements on halogen-free PCB materials. Measurements were conducted per industry-adopted test methods, including preconditioning of test samples. Some measurement results did not match manufacturer's datasheets. This paper examines the dependence of out-of-plane coefficient of thermal expansion, glass-transition temperature, time to delamination, and decomposition temperature on the moisture content in halogenated and halogen-free PCB materials. Four types of PCB materials from two manufacturers, including two halogen-free and two halogenated, were tested in this paper. Furthermore, this paper investigates the suitability of IPC-TM-650 preconditioning steps for thermal-property measurements.

Index Terms - Coefficient of thermal expansion (CTE), glass transition temperature, halogen-free, laminate, moisture.

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