Characterization and Simulation of the Deformation and Failure Behavior of Printed Circuit Boards (PCB)

Peter Fuchs

Research output: ThesisDoctoral Thesis

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Abstract

In this thesis a systematic approach for the lifetime assessment of printed circuit boards (PCB) under drop impact was shown. While current procedures are based on a standardized board level drop test (BLDT), where PCBs are repeatedly dropped under defined conditions till failure is detected, it was tried to develop alternative methods applying finite element simulations. Doing so, it was aimed for the reduction of necessary complementary experiments, which are time consuming and expensive. However, in order to simulate a drop test, the experiments boundary conditions and the behavior of the modeled materials had to be known. Thus, the BLDT and the PCB materials were analyzed in detail. Based on the gained results a simulation model of the test was set up. The simulation outcome was compared with the experimental results of a BLDT, in order to verify the model. To a large extend, a good correlation could be observed, but with respect to some important parameters, it appeared, that the boundary conditions of the BLDT were too complex to properly map them in the simulation. Thus, and due to other drawbacks of the BLDT, an alternative testing method, a board level cyclic bend test (BLCBT) was developed in a consecutive step. The BLCBT and BLDT test were compared on the basis of six test PCBs and a very good correlation, proving the experiments correlation, could be shown. The main advantages of the BLCBT were that it was faster to perform, less sensitive to operator influences, better adaptable and easier to model in a finite element simulation. Thus, the simulation of the BLCBT was realized without further problems. In order to use the model for a lifetime assessment, simulated loading parameters had to be correlated to times-to-failure. As all analyzed boards were state of the art multilayer PCB, the material behavior of the individual layers had to be characterized in order to be able to analyze the local conditions. The anisotropic material behavior of the insulating (glass fiber woven fabric reinforced epoxy) and conducting (copper structure/epoxy composites) PCB layers was determined by a combination of both, an experimental characterization and a micromechanics approach. As not only the deformation behavior, but also the damage behavior was of interest, also fracture mechanics approaches were evaluated and applied. An in plane and out of plane cohesive zone model, applicable to describe failure initiation and propagation, was determined for the insulating layers. Using the generated material data, a simulation model of the BLCBT was used to determine local loading parameters, which were supposed to correlate with the PCB lifetime. Dependent on the failure mode, either a fracture mechanics parameter, a strain based or stress based parameter was used. In order to be able to perform a PCB lifetime assessment, BLCBT results and the local loading parameter simulations were correlated. So called ‘characteristic failure curves’, describing the correlation were generated performing BLCBT at different set-ups (amplitudes). Thus, the prediction of the expected lifetime of unknown PCB types, with respect of the regarded failure type, was enabled. For the lifetime assessment only a local loading parameter had to be simulated and evaluated using the characteristic failure curve. A sample lifetime assessment was done for three PCBs and an excellent accuracy of prediction could be found. The shown methodology represents a powerful design and optimization tool for PCBs and as only the analysis of one PCB type is necessary for the generation of a characteristic failure curve, the procedure is fast and easy to perform. Based on the developed procedure future work will also take into account different load cases, failure locations and failure modes of interest.
Translated title of the contributionCharakterisierung und Simulation des Deformations- und Schädigungsverhaltens von Leiterplatten
Original languageEnglish
QualificationDr.mont.
Supervisors/Advisors
  • Pinter, Gerald, Assessor A (internal)
  • Major, Zoltan, Assessor B (external)
Publication statusPublished - 2012

Bibliographical note

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Keywords

  • Printed Circuit Board
  • Reliabilty
  • Fracture Mechanics
  • Cohesive Zone Model

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