Humidity effects on the fatigue of fiber reinforced polymers in micro/nano functional systems
Micro and nano functional systems like MEMS and smart systems are exposed to complex and very challenging service conditions (e.g., within airframe structures or in automotive applications under the hood or within battery cells). Therefore, long-term reliability and structural integrity of the chassis and the printed wiring boards is of rising concern. These parts are often made of fiber reinforced polymers (FRP). Recently, a new methodology for accelerated fatigue testing of FRP has been presented. It allows predictions of the structural fatigue lifetime of FRP for arbitrary temperatures and loading ratios based on three simple tests: visco-elastic DMA, constant strain rate tests, and high cycle fatigue tests at a limited number of temperatures and strain rates. However, this methodology considers dry samples only, which does not suffice for describing the behavior of micro/nano systems as mentioned before. The paper reports the approach to the expansion of this testing methodology to the effects of humidity. Choosing PCB material as typical example for FRP in micro/nano systems, the time / temperature shift functions have been determined for wet and dry samples. Subsequently, constant strain rate and high cycle fatigue tests have been performed. They show a substantial loss in strength and fatigue lifetime for FRP structures that were exposed humid environment. Determining the quantities measuring this reduction in structural reliability paves the way to the expansion of the fatigue testing methodology towards accounting for the humidity effect as well.
Accelerated fatigue testing methodology for reliability assessments of fiber reinforced composite polymer materials in micro/nano systems
The paper addresses the determination of the effects of time and temperature on strength and lifetime of structural polymer composites. For some time, this topic has already concerned the aerospace industry during their fatigue tests of light structures made of fiber reinforced polymer (FRP) under various loading modes. More recently, the issue has also become of great relevance to applications in microelectronics and micro/nano system technologies. Following the More-than-Moore development strategy, substrates and new innovative structural parts of those systems are exposed to complex and very challenging service conditions (e.g., implantable bio-medical, aeronautic, or automotive applications). In this paper, a new approach to accelerated testing highlighted in open literature has been assessed with respect to its potential for determining the fatigue behavior of composite materials used in microelectronics and micro/nano system technologies.
Combined effects of humidity and thermal stress on the dielectric properties of epoxy-silica composites
Abstract We report on the effects of hydrothermal ageing on the dielectric properties of epoxy-silica composites used for microelectronic packaging. The study was carried out for samples with various degrees of curing. Epoxy compounds were subjected to moisture exposure (standard JEDEC procedures) and consecutive thermal stress (240°C). Changes in the dielectric constant and in the loss factor were measured in the 100 Hz–100 kHz frequency range. It is found that water absorption increases with curing. After ageing the dielectric constant is decreased and the loss factor increased. Cured materials have a higher resistance against hydrothermal ageing.