We report test results of bending characteristics of flexible printed circuit board, which contributes to the development of higher density and more sophisticated function of mobile devices and electronic equipment. Our report shows that there is a correlation between mechanical structure and the bending characteristics of flexible printed circuit boards, and that ultra thin structure shows excellent performance in bending applications. We also find that elasticity modulus of adhesive plays a key role in the bending characteristic of flexible printed circuit board. We have utilized the finite element method to evaluate the strain for investigation of the bending fatigue mechanism. We will report on the study of a formula with which we can estimate the flexural fatigue life. We also show the analysis result of generated stress when various constructions of flexible printed circuit boards are bent.
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