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Screen Mask for Through Hole Printing

IP.com Disclosure Number: IPCOM000102013D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 5 page(s) / 129K

Publishing Venue

IBM

Related People

Takeda, K: AUTHOR [+2]

Abstract

Disclosed is a screen mask to print paste (or polymer thick film) ink onto the inside walls of through holes in printed circuit boards. The screen mask described herein contains doughnut-shaped openings instead of traditional round-shaped openings. The screen mask provides a solution to the problem of controlling air flow through holes during printing, and yields uniform ink coverage of holes of different sizes.

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This is the abbreviated version, containing approximately 52% of the total text.

Screen Mask for Through Hole Printing

       Disclosed is a screen mask to print paste (or polymer
thick film) ink onto the inside walls of through holes in printed
circuit boards.  The screen mask described herein contains
doughnut-shaped openings instead of traditional round-shaped
openings.  The screen mask provides a solution to the problem of
controlling air flow through holes during printing, and yields
uniform ink coverage of holes of different sizes.

      Through hole printing is widely performed in the production of
hybrid ICs and printed circuit boards. Usually, it is done with the
assistance of air flow which passes through the hole.  Fig. 1 shows
the process sequence of typical through hole printing.  Paste ink 1
is placed on the screen mask 2 and the squeegee 3 is actuated (Step
1). The squeegee sweeps across the screen mask and forces the paste
ink through the opening of the screen mask (Step 2). As paste is
printed over a through hole, air flow is simultaneously applied,
pulling the paste into the hole (Step 3).  After the squeegee passes
over the screen pattern, the screen mask is lifted from the substrate
4.  The result is a printed pattern of ink on the substrate and
coating of through holes with ink (Step 4).

      Good print quality in through holes requires fine control of
air flow during printing.  The flow of paste ink into a hole and
coverage of the walls of the hole with ink is partly due to the shear
force generated by air flow onto the paste ink during printing.
Generally, paste ink for screen printing has thixotropic
characteristics.  As shown in Fig. 2, viscosity of paste is high in
low shear rate range.  As the shear force becomes large, the
viscosity decreases.  The th...