Coating processes – Electrical product produced – Integrated circuit – printed circuit – or circuit board
Reexamination Certificate
2001-01-03
2003-11-04
Talbot, Brian K. (Department: 1762)
Coating processes
Electrical product produced
Integrated circuit, printed circuit, or circuit board
C427S123000, C427S189000, C427S190000, C427S191000, C427S194000
Reexamination Certificate
active
06641860
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to printing of printed circuit boards. More particularly, the present invention relates to offset printing of printed circuit boards.
BACKGROUND OF THE INVENTION
Printed circuit boards have been manufactured by various techniques including chemical etching, polymer thick film deposition, screen printing and sputtering. Each of these methods have certain areas where they can be improved.
Drawbacks associated with chemical etching of printed circuit boards relate to the use of hazardous chemicals and long processing times during the manufacturing process. The disposal of spent chemicals is also of concern.
Polymer thick film is another method for manufacturing printed circuit boards including flexible membrane boards. While this method has been relatively successful, one drawback is that it does not produce as fine a line as chemical etching. Further, the use of a polymer thick film manufacturing method is generally limited to one ink at a time. It is also more labor intensive than various other methods.
The present invention overcomes the drawbacks of the foregoing manufacturing methods by providing a new manufacturing method which more efficiently produces improved printed circuit boards.
SUMMARY AND OBJECTS OF THE INVENTION
The present invention relates to a method of manufacturing printed circuit boards. A preferred method comprises providing a conductive composition and a substrate. The conductive composition may comprise a liquid vehicle and electrically conducive material suspended or dissolved in the liquid vehicle. The method also comprises the step of applying the conductive composition to the substrate through an offset lithography printing technique so that a desired printed circuit pattern is obtained on the substrate.
Preferably, the conductive composition is applied to the substrate under a pressure of at least about 4 psi. More preferably, the application pressure is between about 50 psi and 1000 psi. Even more preferably, the pressure may be between about 50-500 psi.
It is also preferable for the method of manufacturing printed circuit boards to comprise the step of applying conductive composition to a substrate through a cold welding process. As used herein, the concept of “cold welding” the conductive composition to the substrate comprises applying the conductive composition to the substrate under a sufficient pressure so that the conductive material is separated from the liquid vehicle of the conductive composition. At the same time, the conductive material is forced together to form a conductive trace pattern on the surface of the substrate.
In certain embodiments, the substrate may comprise a substantially nonabsorbent material. Such nonabsorbent materials may include, but are not limited to, polyester, Kapton, or the like. When a substantially nonabsorbent substrate is used, a cold weld process takes place where the vehicle (i.e., the liquid portion of the conductive composition) gets squeezed out and the conductive particles (such as nonprecious or precious metals) form together. The liquid vehicle would be supported on the surface of the substantially nonabsorbent substrate and would then evaporate from such surface.
In an environment where the substrate is relatively absorbent, the application of pressure during the cold welding process will force the liquid vehicle to more quickly become absorbed into the substrate itself, while certain amounts of the liquid vehicle would still evaporate. Examples of a nonabsorbent substrate include, but are not limited to, a fibrous substrate that may be made of a paper product or the like, and porous coating such as porous ink, etc. The application of a suitable pressure in this embodiment will also force the conductive particles together to form a continuous conductive trace pattern with suitable conductivity.
In accordance with a preferred aspect of the present invention, the method of manufacturing printed circuit boards comprises initially applying conductive composition to a substrate through a printing process and subsequently subjecting said conductive composition and said substrate to a predetermined pressure after the conductive composition has been applied to the surface of the substrate. The predetermined pressure is preferably at least about 4 psi. More preferably, the predetermined pressure is between about 50 psi-1000 psi. Even more preferably, the predetermined pressure may be between about 50 psi-500 psi.
As used herein, the term “printed circuit board” is intended to cover various types of flexible and nonflexible substrates onto which a conductive trace pattern is applied. In accordance with the preferred method of the present invention, at least a portion of the conductive trace pattern comprises conductive composition printed on the surface of the substrate. It should also be understood that as used herein, the term “printed circuit board” is intended to cover substrates having a printed circuit pattern arranged on the surface thereof either with or without active or inactive circuit components also secured to the substrate. Thus, the term “printed circuit board” is intended to cover what may be considered only a portion of a printed circuit board as conventionally understood. The term “printed circuit board” is also intended to cover complete printed circuit boards that have circuit components thereon as conventionally understood. It should also be understood that as used herein, the term “printed circuit board” is intended to cover various types of substrates having conductive material arranged thereon, such as membrane switches and other types of switch devices.
The method of manufacturing printed circuit boards in accordance with the present invention is intended to cover several embodiments including, but not limited to, applying conductive composition to the surface of a substrate where pressure is applied as the conductive composition itself is applied to the surface of the substrate. The method is also intended to cover an in-line pressure application system where the conductive composition is initially printed on the surface of a substrate and pressure is later applied as part of an in-line manufacturing process. In another embodiment, the method is intended to cover printing conductive composition on the surface of a substrate and applying pressure to the conductive composition and the substrate off-line (i.e., in a separate assembly remote from the printed circuit board manufacturing assembly). Examples of the three foregoing embodiments are shown in the following drawings that form part of this disclosure.
Conductive compositions, such as conductive inks can be printed through various techniques such as offset lithography, letterpress, gravure, flexography, and the like to obtain very fine circuits for printed circuit boards. Simple single layer circuits as well as multilayered circuits can be achieved using the offset or letter press process. The substrates on which the conductive compositions are printed, can be fed into an associated printing press by one or more sheets at a time, or as part of a continuous web where a roller feed mechanism is employed.
Various printing techniques may be employed. For example, the conductive composition may be printed on a substrate through gravure, flexography, lithography, letter press, hot stamping, offset printing, and other methods. Offset printing is one preferred method as it often results in a completed circuit board with very fine conductive lines which have smooth edges. Further offset printing can be used to produce half-tones with controlled dot gain.
Various existing offset ink formulations and other coating compositions that are modified to be conductive, can be used. For example, ultraviolet (UV) cured offset inks and other types of chemistry, depending upon the substrate being printed and the desired properties, can be used. Most any ink or other printable composition, modified to be printed via an offset press, letter press, gravure, flexo and/or coaters' can be used regardl
Kaiserman Terrance Z.
Margolin Keith J.
Lerner David Littenberg Krumholz & Mentlik LLP
T-Ink, L.L.C.
Talbot Brian K.
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