Stability and properties of PET Films in Electronics Applications in Hygrothermal Environments

Abstract

Polyethylene terephthalate (PET) is an interesting flexible substrate material for many applications in electronics since it is inexpensive and has good mechanical and electrical properties. Due to these good properties there is increasing interest in using PET in applications involving harsh environments. However, PET has relatively poor thermal properties, which may cause reliability concerns in demanding conditions. Above its glass transition temperature, Tg, PET is susceptible to hydrolysis, which may considerably restrict its use. Hydrolysis breaks the molecular structure of PET and makes the material mechanically unreliable. This paper reports the reliability of PET films in an LCD display application and in RFID tags in thermal and humid conditions. Additionally, neat PET films were studied. Several thermal cycling and humidity tests were used. The results clearly showed that above the Tg of PET the combined effect of humidity and high temperature caused PET to become brittle leading to considerable reliability problems. However, in dry thermal cycling conditions and in humid conditions below the Tg of PET, the reliability of PET was found to be excellent even under prolonged exposure.

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“…In plastics film applications pertaining to flexible electronics, stable flexibility at high temperatures is prerequisite for a reliable usage [2,15,16]. As a benchmark, the flexibility of PET films were assessed after storage at elevated temperatures by measuring the force as a function of the constant displacement of the plunger (Figure 2, and S3 of SI).…”

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“…Additionally, above PET's glass transition temperature (70–110 °C) the polymer is vulnerable to water absorption, which also restricts its use, once the hydrolysis phenomena disrupt the PET's molecular structure, making the polymer mechanically unreliable. [ 159 ]…”

Arylenevinylene Oligomer-Based Heterostructures on Flexible AZO Electrodes

“…This is important because, above the glass temperature, T g [45], the combined effect of humidity and high temperature can lead to considerable reliability problems. However, below the T g , even in humid conditions, the reliability of PET was found to be excellent, even under prolonged exposure [46]. On the other hand, vacuum evaporation is not a process involving energetic particles, and therefore, PET covered by AZO is not affected during this deposition process.…”