Coating apparatus – Solid member or material acting on coating after application – Diverse members
Reexamination Certificate
1999-04-30
2001-07-31
Edwards, Laura (Department: 1734)
Coating apparatus
Solid member or material acting on coating after application
Diverse members
C015S256500, C101S123000
Reexamination Certificate
active
06267818
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to blades for spreading and depositing media onto substrates, and, more particularly, pertains to an applicator assembly which includes a reversible squeegee blade for transferring and depositing various kinds of spreadable, viscous media onto a substrate.
In the surface mount technology field and in hybrid microelectronics fields, manual, semiautomatic or automatic screen and stencil printing equipment is used for printing solder paste, adhesives, epoxies (both conductive and adhesive), flux, inks (conductive, resistive, and dielectric), and other spreadable, viscous print media comprising generally paste-like substances, onto printed circuit boards, metal and ceramic substrates, and other types of substrates used in electrical and electronic assemblies.
The circuit board, or other substrate, is supported on the stencil or screen printer, and then one of the above-mentioned materials is transferred through a mask, masking surface or workpiece, such as an open-apertured template, screen or stencil for deposition onto the substrate. The apertures of the masking surface correspond to and are aligned with the areas to be printed on the circuit board, but the masking surface apertures are generally smaller than the areas or lands of the circuit boards. In addition, the above-listed materials can be forced through a cross-sectional screen mesh permeated with an emulsion so that the circuit or pattern to be printed is etched out of the emulsion. The above-described materials are used for the purpose of holding surface-mounted electronic components to the surfaces of the circuit boards and metal and ceramic substrates prior to soldering. Some of the epoxies currently being used are electrically conductive and do not require soldering, but they are deposited onto the various substrates by the above-described process.
The typical screen or stencil printer includes a tooling plate upon which the circuit board is positioned and aligned, a squeegee assembly or squeegee head assembly, and a metal or polyurethane blade referred to in the industry as a squeegee blade. A squeegee blade holder is mounted to the squeegee assembly and both the squeegee blade holder and the squeegee assembly are positioned above, and extend transverse to, the circuit board or other substrate which is horizontally positioned on the tooling plate.
In operation, the squeegee blade is driven down under pressure until it comes into contact with, or is positioned immediately above, the top surface of the screen or stencil.
With the squeegee blade forced down under pressure, the drive assembly drags the squeegee blade across the stencil. For manual screen and stencil printers, the operator manually moves the squeegee assembly in a linear direction above the screen or stencil and the circuit board. As the squeegee blade travels above the stencil, the solder paste—or other material previously described—is dragged and pushed along the top surface of the stencil by the squeegee blade. The squeegee blade pathway is in a linear direction relative to the masking surface and the circuit board, and the squeegee blade can travel in a linear reciprocable path relative to the masking surface and circuit board.
The squeegee blade always travels parallel to the masking surface and not at an angle with respect thereto. The simultaneous downward pressure and forward travel of the squeegee blade against the solder paste forces the paste through the stencil or screen and deposits the solder paste onto the circuit board. The combined downward pressure and longitudinal movement of the blade forces the solder paste through the stencil or screen apertures and in the process wipes clean the surface of the screen or stencil. The bead of solder paste is not dragged across the top surface of the screen or stencil; in fact, the bead of solder paste rolls across the top surface of the screen or stencil like a steamroller traveling over the road surface. The rolling action of the solder paste, caused by simultaneous downward pressure and forward movement of the squeegee blade, causes the paste to be pushed and transferred through the screen or stencil apertures for deposition onto the circuit board. Once the solder paste is transferred through the apertures or interstices of the template, screen or stencil, and deposited on the circuit board, electrical components, such as capacitators and resistors, are mounted onto the wet paste deposited on the circuit board to complete the electrical circuitry of the board. The circuit board then goes through a heating/curing process whereupon the solder paste is transformed into what the industry refers to as pads and lines for creating the electrical circuitry on the circuit board.
DESCRIPTION OF THE PRIOR ART
The majority of squeegee blades currently in use comprise a blade assembly which includes two flat, elongated aluminum or steel plates between which a flat or bent piece of steel (the actual squeegee blade) is sandwiched, leaving a portion of the blade exposed for transferring material onto the substrate. The plates are fastened together for holding the blade in position, and then the entire assembly is inserted into the blade holder. The angle between the squeegee blade and the screen or stencil superposed on the circuit board can be fixed or variable depending upon the type of blade holder to which the assembly is mounted. The above-mentioned angle is referred to in the industry as the “angle of attack”, and U.S. Pat. No. 6,660,632 (incorporated herein by reference) discloses a number of different blade holders which permit the adjustment and variability of the angle of attach of the squeegee blade. In addition, some screen and stencil printers include a feature that allows the selective adjustment of the entire squeegee head assembly for varying the blade's angle of attack. This feature is usually not a standard feature on printers but comes as an option and is a separate mechanism from the squeegee assembly.
Among the structures superposed on the circuit boards and metal and ceramic substrates are metal mask stencils, wire mesh and silk-screens, and, as a relatively new development, open aperture plastic mask stencils. Hard metal squeegee blades should not be used for transferring material, such as solder paste or epoxies, through the plastic mask stencils for deposition onto the substrate because the metal squeegee blades will scratch and damage the plastic mask stencils while traveling thereover. In addition, during any given screen printing process, both metal and plastic blades may need to be used but, as disclosed in U.S. Pat. No. 5,660,632, it is not necessarily a quick and easy procedure to move the squeegee head assembly free of the tooling plate of the screen/stencil printer so that one type of squeegee blade can be removed from the squeegee blade holder for replacement by another type of squeegee blade. Moreover, both plastic and metal mask stencils may be used in successive printing operations, and this will require constant changing of squeegee blades in order to mount the appropriate blade for use with the plastic or metal mask stencil.
SUMMARY OF THE INVENTION
The present invention comprehends an applicator assembly including an improved squeegee wiper or blade structure having a metal blade portion and a polymer (plastic) blade portion, and the blade structure being reversible on a squeegee blade holder so that either the plastic blade portion or the metal blade portion can be exposed for a printing operation.
The blade structure includes a first elongated, generally rigid blade portion and a second elongated, flexible blade portion joined to the first blade portion to form a unitary structure. Both blade portions are coequal in length and are joined together along one of their respective longitudinal edges. In order to permit selective adjustment of the blade structure within certain kinds of blade holders, a pair of half circle-shaped retaining rods, between which a lengthwise end of either blade portion is positio
Atwell George C.
Edwards Laura
JNJ Industries Inc.
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