Simulation of the packaging process of embedded components in printed circuit boards

Katerina Macurova

Research output: ThesisDoctoral Thesis

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Abstract

The aim of the thesis is to investigate the critical steps during the embedding process, which is used in the manufacturing of highly integrated printed circuit boards (PCBs). This technology enables reduction of space (and cost) and an increase of board performance by introducing functional components (e.g. silicon dies) inside the PCB. The critical process steps during die embedding are (i) the die attachment, (ii) the die assembly, and (iii) the lamination process. A second objective is to evaluate the package reliability during temperature cycling and provide design rules to increase the lifetime of PCB systems. Concerning the die attachment the focus is set on the description of the adhesive bond line thickness development underneath a silicon die as a function of the attachment force and holding time. The solution is obtained with an analytical squeeze flow approach as well as a numerical simulation using computational fluid dynamics. The die assembly and the lamination process are analyzed in terms of stresses and package warpage, which occur due to the mismatch of coefficients of thermal expansions during adhesive and epoxy resin polymerization at elevated temperatures. Special attention is given to the derivation of a volumetric shrinkage of the polymers during their phase transformation, which results in a major loading mechanism of the structure. The stress-strain state of the assembled structure is investigated both analytically using (i) classical laminate theory and (ii) the interfacial model, and numerically by a finite element analysis, respectively. The complex laminated package containing prepregs (a glass woven structure pre-impregnated with the epoxy resin) is numerically analyzed using finite element analysis (FEA). A special focus is set on orthotropic properties of the prepregs, which are analytically homogenized based on the lamination theory of plain woven composites. The warpage results of the assembled and the laminated packages are validated experimentally by an X-ray diffraction method (Rocking-Curve-Technique) showing a good agreement between the calculated and measured curvature radius values. Finally, reliability of a functional PCB board containing copper vias and traces is numerically analyzed under thermal cycling loading. Based on these results, a model is proposed to identify critical vias within the package. The lifetime of the package associated with the failure of the critical via is estimated using analytical approaches for low-cycle fatigue. As a result of this investigation, a numerical and analytical toolset for simulation of the stress-strain situation during the packaging production process steps has been developed. The influence of material and geometrical parameters on the package reliability has been studied. Finally, design rules for the overall embedding process have been derived, which consequently provide the possibility to improve the reliability of future PCB systems.
Translated title of the contributionNummerische Simulation des Herstellprozesses von Leiterplatten mit eingebetteten Bauteilen
Original languageEnglish
QualificationDr.mont.
Supervisors/Advisors
  • Antretter, Thomas, Assessor A (internal)
  • Pinter, Gerald Gerhard, Assessor B (internal)
Publication statusPublished - 2015

Bibliographical note

embargoed until null

Keywords

  • Printed circuit boards
  • embedding process
  • process flow simulation
  • die attachment process
  • die assembly process
  • lamination process
  • PCB reliability
  • warpage
  • residual stress
  • design rules
  • FEA

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