Stability and properties of PET Films under Harsh Environments

摘要

Polyethylene terephthalate (PET) is an interesting flexible substrate material for many applications in electronics. It has a low price and good mechanical and electrical properties. Due to these good properties there is an increasing interest to use this material also in applications which are used under harsh environments. For instance PET flexible printed circuit boards have been widely used to attach LCD displays in industrial electronics. Although PET has good mechanical and electrical properties, it has relatively poor thermal properties, which may cause reliability concerns under demanding conditions, especially, if these environments consist of both high temperature and humidity. Above its T_g, PET is vulnerable to hydrolysis which may restrict its use considerably. Hydrolysis breaks the molecular structure of PET and makes the material mechanically unreliable. In this paper the reliability of PET films in an LCD display application and in RFID tags was studied under humid conditions. Additionally, neat PET films were studied. Several humidity tests were used. The results clearly showed that above the glass transition temperature of PET the combined effect of humidity and high temperature caused embrittlement of PET and considerable reliability problems. However, below the glass transition temperature the reliability of PET was found to be excellent even under prolonged exposure to high humidity.