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Research Papers

Modeling of Resin Flow in Reinforced Dielectric Prepregs

[+] Author and Article Information
Pavel Simacek, Suresh G. Advani

Department of Mechanical Engineering, and Center for Composite Materials,  University of Delaware, Newark, DE 19711

Kossi Zonvide, Leonard W. Barrett

 W. L. Gore and Associates, Elkton, MD 21921

J. Electron. Packag 130(2), 021001 (Apr 15, 2008) (8 pages) doi:10.1115/1.2837510 History: Received May 10, 2006; Revised September 05, 2007; Published April 15, 2008

Manufacturing of printed circuit boards or chip-packaging substrates involves the use of resin-filled reinforcement materials, known as prepregs, to bond together laminates with patterned copper layers and serve as dielectric material. In the circuit board or substrate lamination process, the prepreg sheet is placed on top of the conductive copper patterns and pressure is applied to squeeze the resin out of the prepreg to flow and fill the gaps between the baseboard and the copper as well as drilled holes and vias. The primary processing requirement is for resin to fill all the gaps within reasonable time and pressure limits, before the resin cures to a hardened thermoset material. As the resin flow path may be nontrivial, it is desirable to model resin flow and filling of the gap as a function of applied pressure and lamination press closing rate so that one can successfully manufacture a variety of circuit board designs with different material systems. In this work, we model the flow during the filling of the gaps and justify noteworthy simplifications to provide a solution in closed form. This allows us to relate the material and process parameters such as prepreg thickness and applied pressure to the circuit board design. It also permits prediction of the transient development of gap filling. We illustrate the factors that influence the flow and fill process and discuss their importance. Finally, we analyze the process with typical material and processing parameters and compare it with laboratory scale and industrial experiments.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Manufacturing PCB using resin saturated membrane

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Figure 2

Test circuit board pressed by 200psi pressure with two different prepreg thicknesses (1.5mil and 3.4mil). The copper pattern includes variety of element sizes and spacings. Resin-filled areas appear darker. Note that there are many unfilled regions with thinner prepregs but even the thicker prepregs fail to yield complete fill for the selected processing conditions.

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Figure 3

(a) Realistic outboard layout and (b) simplified layout used for analysis and experimental evaluation

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Figure 4

Resin path to infiltrate gaps

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Figure 5

Dimensions and geometry of unit cell for flow modeling

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Figure 6

Filled region and the assumed pressure and flow field

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Figure 7

Transient behavior of resin viscosity

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Figure 8

Prepreg deformation (negative linear strain) dependent on applied load: experimental data and curve fit

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Figure 9

Depth of penetration after 3600s dependent on copper content and applied pressure. The cell width or trace pitch is 50mm. Dotted line shows the depth of 18μm corresponding to the thickness of copper layers.

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Figure 10

Depth of penetration as a function of copper content and time. Cell width is 50mm; processing pressure 500kPa. The dotted line shows the required depth (18μm).

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Figure 11

Dependence of depth of penetration (at 3600s) on initial porosity of the prepreg. Copper cell width (trace pitch) is 50mm; applied load is 500kPa. The dotted line shows the copper depth (18μm).

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Figure 12

Dependence of the depth of penetration (at 1800s) on the width of copper cell. Load is 500kPa.

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Figure 13

Gap fill (in percent) dependent on the predicted depth of penetration for three different prepregs (1.5mil, 2.2mil, and 3.4mil thick). Actual depth of gap is only 35μm, but the material parameters are at best approximated.

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