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Research Papers

Modeling of Thermoplastic Materials for the Process-Simulation of Press-Fit Interconnections on Moulded Interconnected Devices

[+] Author and Article Information
Thomas Fellner, Elena Zukowski, Jürgen Wilde

Department of Microsystems Engineering (IMTEK), Laboratory for Assembly and Packaging,  University of Freiburg, Georges-Koehler-Allee 103, 79110 Freiburg, Germany

H. Kück, H. Richter, M. Schober, P. Buckmüller

 Hahn-Schickard-Institute for Microassembly Technology HSG-IMAT, Allmandring 9B, 70569 Stuttgart, Germany

J. Electron. Packag 134(3), 031002 (Jul 18, 2012) (10 pages) doi:10.1115/1.4006927 History: Received April 21, 2011; Revised March 04, 2012; Published July 18, 2012; Online July 18, 2012

This investigation is aimed at the modeling of both the fabrication process and the reliability of press-fit interconnections on moulded interconnect devices (MID). These are multifunctional three-dimensional substrates, produced by thermoplastic injection moulding for large-series applications. The assembly process and subsequently the durability of press-fit interconnections has been modeled and proved with a finite element software. Especially, a simulation tool for process optimizations was created and applied. In order to obtain realistic results, a creep model for the investigated base material, a liquid-crystal polymer (LCP), was generated and verified by experiments. Required friction coefficients between metal pin and base material were determined by adapting simulations and experiments. Retention forces of pins pressed into substrate holes during as well after the assembly process, and after temperature loads were predicted by simulations. Additionally, the decreasing extraction forces over time due to creep in the thermoplastic base material have been predicted for different storage temperatures as well with finite element analyses. Following, the numerical results of the process and reliability modeling were verified by experiments. It is concluded that the behavior of the mechanical contact of the pin-substrate system, can be suitably described time- and temperature-dependent.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Press-in operation of a C-profile shaped pin into the substrate

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Figure 2

Side view and cross section of a press-fit pin with a C-profile. Gap opening angle: 35 deg.

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Figure 3

MID test substrate (LCP) with cross-sectional view of the metallized hole (via). Metallization: 20 μm electroplated Cu.

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Figure 4

Testing machine (top); the press-in (unfilled symbols) and pull-out forces (filled symbols) of the initial tests after 24 h storage for different hole diameters (bottom)

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Figure 5

Pull-out forces after 24 h storage for different hole diameters with their corresponding cross sections. Pin diameter: 1 mm.

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Figure 6

LDS test substrate with press-fit pins: Overview (a) and X-ray photographs with standard (b) and Cu electroplated hole metallization (c)

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Figure 7

Reliability test program for MID press-fit interconnects

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Figure 8

Metallographic cross-section of the SBS press-fit pin

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Figure 9

Mesh of 3D finite element model of the press-fit pin

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Figure 10

Cross-sectional view of the press-fit pin inserted into the conical hole (3D FE-model)

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Figure 11

Clamped specimen during a creep experiment (left) and its schematic sketch (right)

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Figure 12

Measured stress–strain curves (a) and the results of creep data modeling compared to the simulation (b), (c), and (d). Material: Vectra E840i-LDS (Ticona).

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Figure 13

Retention forces obtained by experiments and numerical calculations versus displacement

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Figure 14

Press-fit pins with 35 deg gap opening angle (above) and no gap (below)

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Figure 15

Insertion and retention force versus displacement for different hole diameters D, numerically obtained by FE-simulation

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Figure 16

Cross-section of the pin contact area with initial 10 deg (left) and 35 deg (right) gap after insertion into the hole. FE-simulation: pin diameter 1000 μm, hole diameter 910 μm.

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Figure 17

Elastic deformation in the pin for different hole diameters

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Figure 18

Plastic deformation in the pin for different hole diameters

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Figure 19

Elastic deformation in the LCP-substrate for different hole diameters

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Figure 20

Plastic deformation in the LCP-substrate for different hole diameters

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Figure 21

Average von Mises stress levels in the substrate for different hole diameters

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Figure 22

The computed pin retention force for different hole diameters after 24 h storage according to the measurements

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Figure 23

Computed and measured pin retention forces in LCP substrates for different hole diameters, at room temperature and after a storage time of 24 h

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Figure 24

Computed pin retention forces for 25 °C and 125 °C over time and for different gap opening angles

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Figure 25

Computed and measured pin retention forces over time, stored at room temperature. Equal hole diameters (910 μm) were used in the simulation and in the measurement.

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