Free vibration analysis of printed circuit boards with different types of edge support

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Title: Free vibration analysis of printed circuit boards with different types of edge support
Author: Chen, Beng-ming
Abstract: The high reliability and integrity of avionics required by the Avionics Integrity Program (AVIP ) , initiated by the Department of Defense , has led to intensive research on the design of electronic /avionic equipment . Vibration introduces excessive dynamic loading on printed circuit boards and their surface mounted components , thus , causing premature failure of the equipment . In order to develop highly reliable products , an accurate understanding of the response of a product subject to vibration is required . This study includes two parts . Part one utilizes the finite element method to determine the effect of such variables as the boundary conditions , component layout , stiffener location , point support , lead type , lead height and input force directions on the vibration -induced stresses in the printed circuit board . Part two investigates the effect of board geometry and different types of retainers used to support the printed circuit boards in avionics , on the resonant frequency and the damping of the board /retainer system . For the first part , finite element models were generated using a software . Finite Element Analysis for Printed circuit boards (FEAP ) , developed by Engineering Mechanics Research Corporation . The finite element models included a plastic leaded chip carrier positioned at the geometric centers of the printed circuit boards which were supported by disparate boundary conditions . In some cases , a dual inline package and a stiffener or point support (s ) were included in the finite element models . Forced random vibrations were then simulated using the finite element software . The maximum von Mises stresses within the critical leads of the chip carrier and the first three resonant frequencies of the board systems were computed . The orthogonal array L27 linear type -I relation of the robust design procedure was adopted for the experimental design . The second part of the study was to determine the fundamental resonant frequency and damping of the printed circuit boards supported by different types of retainers . The printed circuit boards were clamped by various clamping devices on two opposite edges while the other two edges were left free of support . The main parameters of the study were the retainer type , length of clamped and free edges , and board thickness . Free vibration tests were conducted using a 3^f factorial experiment with two replications for each case . Computer simulations were also performed to compute the fundamental resonant frequencies of the corresponding cases . Displacements , measured at the geometric center of the boards , versus time were logged for the calculation of resonant frequency and damping value . The Logarithmic Decrement method was employed for the damping computation . Frictional damping at the supports of the board /retainer system was found to dominate the system damping . The measured resonant frequencies were lower than the finite element analysis results . A statistical analysis software , SAS , was utilized to analyze both data sets of the computer simulations and the experiments . Three means , clamping board edges , positioning the stiffener close to and along the free edge or adding point support (s ) at the free edge , were found to increase the resonant frequency . The maximum von Mises stresses were found at the interface between the leads and the solders . The experimental results showed that the retainers did not provide true clamped edge supports , which resulted in larger system damping and lower fundamental resonant frequency . The results are summarized in the form of general design guidelines and comparison is made among various strategies and tools available for PCB design . This study can be extended to find the effect of temperature , exciting frequency , dynamic loading and preloading of the board system on its damping and resonant frequency .
URI: http : / /hdl .handle .net /2346 /11730
Date: 1992-12

Citation

Chen, Beng-ming Free vibration analysis of printed circuit boards with different types of edge support. Doctoral dissertation, Texas Tech University. Available electronically from http : / /hdl .handle .net /2346 /11730 .

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