The Effects of Temperature and Aging on Young's Moduli of Polymeric Based Flexible Substrates

摘要

Polymeric based flexible substrates are widely used as bendable printed circuit boards in automotive and other electronic systems for easy interconnection and processing. Their flexibility however brings issues such as high dynamic stresses and dynamic fatigue associated with structural instability. Stress analysis and fatigue prediction requires fundamental understanding of thermal mechanical properties of these materials. This paper specifically studies the effects of temperature and aging on Young's moduli of the flexible substrates and their components. The performance of the bulk substrate depends to the large extent on the selection of the core layer material which is the primary load-bearing structure in the flexible substrate. The tested core layers include polyethylene naphthalate (PEN), polyester (Mylar, PET) and polyimide (PI). Two types of copper traces and two types of traces deposited on different polymer films are studied under various temperature conditions. These samples include 1.4 mil electronic deposited (ED) copper, 1.4 mil rolled and annealed copper, 1.4 mil ED with 2 mil PET and 1 mil A523 epoxy coating, and 1.4 mil vapor deposited and plated copper with 2 mil PI. Substrates with different compositions and manufacturing processes are experimentally studied on Dynamic Mechanics Analyzer under various temperatures from -40℃ to 125℃. The corresponding components for each type of substrates are tested to identify key contributing factors in the material systems. Thermal aging effects on the Young's moduli are analyzed accordingly. The volume fraction model for evaluating moduli of composite materials is shown to have good correlation with the experimental results. The comprehensive test results on these flexible substrates and their components not only provide a complete data set for design and analysis, but also provide some bases for failure analysis and reliability assessments.