Characterization of the Solder Paste Release From Small Stencil Apertures in the Stencil Printing Process

[+] Author and Article Information
Srinivasa Aravamudhan, Daryl Santos

Watson School of Engineering,  State University of New York, Binghamton, NY

Gerald Pham-Van-Diep, Frank Andres

 Speedline Technologies, Franklin, MA

J. Electron. Packag 127(3), 340-352 (Dec 10, 2004) (13 pages) doi:10.1115/1.1938208 History: Received February 09, 2004; Revised December 10, 2004

Stencil printing is a critical first step in surface mount assembly. However, its robustness can be called into question because of the fact that about 50% or more of the defects found in the assembly of printed circuit boards (PCBs) are attributed to stencil printing 1. Manufacturing techniques for the assembly of certain flip chips, chip scale packages, 0201s, and fine pitch ball grid arrays are testing the limits of current stencil printing capabilities. This paper focuses on understanding the release of solder paste from the stencil, based on experimental and modeling approaches. The primary goal of the study is to characterize the performance of various aperture sizes and geometries based on release efficiencies and to compare them to predictions. The resulting model validation helps us better understand the print process for small features and offers options for increasing print yields. The study is divided into two phases. The first phase examines the release performance of various solder pastes from a variety of aperture sizes and geometries. The focus of this study is a comparison of square versus circular apertures when the nominal volume of paste to be deposited is kept constant. The second phase consists of developing a model that predicts paste-release efficiencies from small apertures and validating the model with experimental results.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 7

Standard deviation plot for 8 mil circle and 7.09 mil square

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Figure 8

Solder paste release for a large aperture

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Figure 9

Solder paste release for a small aperture

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Figure 10

Comparison of paste release between Type III paste (left) and Type V paste (right) for an aperture volume of 251mil3 (aperture dimension circle 8.00 mil, area ratio of 0.42; and square 7.09 mil, area ratio of 0.38)

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Figure 11

Release of the solder paste from the stencil: A - apertures are completely filled and the stencil is about to release from the substrate; B - stencil releases from the substrate; C - shearing of the paste due to the shear force and the phenomenon of “necking” can be observed; and D - conical shaped deposit of solder paste

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Figure 12

Step-by-step release of solder paste from the stencil

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Figure 13

Forces acting on the solder paste during release

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Figure 14

Stress acting on an elemental volume

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Figure 15

Predicted paste release shape

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Figure 16

Model validation with experimental results for Type III paste

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Figure 17

Model validation with experimental results for Type V paste

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Figure 18

Comparison of experimental results and release prediction models

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Figure 1

Stencil printing process

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Figure 2

Experimental setup

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Figure 3

(a)Main effects plot for a deposited volume, (b) effect of stencil thickness on volume deposited, and (c) effect of paste particle size on volume deposited

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Figure 4

Experimental results in terms of measured stencil aperture volume for Type III paste

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Figure 5

Experimental results in terms of measured stencil aperture volume for Type V paste

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Figure 6

(a)Standard deviation plot for 15 mil circle and 13.29 mil square and (b) standard deviation plot for 10 mil circle and 8.86 mil square



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