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United States Patent usi
Robinson et al.
 METHOD OF MANUFACTURING KEYSWITCH ASSEMBLIES
 Inventors: Max S. Robinson, Richland, Wash.;
Thomas J. Studebaker, Boulder,
 Assignee: Mohawk Data Sciences Corporation, Herkimer, N.Y.
 Filed: Mar. 15, 1976
 Appl. No.: 666,732
Related U.S. Application Data
 Division of Ser. No. 505,389, Sept. 12, 1974, Pat. No. 4,018,999.
 U.S. CI. 29/622; 29/628;
156/230; 178/17 C; 179/90 K; 264/272; 200/5
A; 200/159 B
 IntCI.2 H01H 11/00
 Field of Search 29/622, 628; 264/89,
264/90, 88, 272; 156/87, 228, 230, 232, 285, 286, 311, 382; 200/1 R, 5 R, 5 A, 11 R, 11 G, 11 H, 11 I, 11 K, 160, 159 B, 166 BH; 178/17 C; 340/365 A; 179/90 K
 References Cited
UNITED STATES PATENTS
3,722,086 3/1973 Wikkerink et al 29/622
[in 4,033,030  July 5, 1977
3,725,907 4/1973 Boulanger 200/159 B UX
3,808,384 4/1974 Boulanger 200/5 A
3,860,771 1/1975 Lynn et al 200/5 A
3,898,421 8/1975 Suzumura 200/159 B
Primary Examiner—Victor A. DiPalma
Attorney, Agent, or Firm—Robert R. Hubbard
A keyswitch assembly including a circuit board having a plurality of circuits, each circuit terminating with a pair of first and second contacts, and a curved, resilient contact plate associated with each pair of contacts having at least a portion of its periphery in communication with one of the pair of contacts, the plate being selectively deflectable so that it communicates with the other contact to close the respective circuit. The contact plates are fixed in position by a retaining element comprising a film formed by a layer of thermoplastic material bonded to a flexible sheet of insulative material, the thermoplastic material being bonded to the resilient plates and circuit board thereby maintaining the former in correct position relative to the latter. The method of manufacturing the assembly includes precisely locating the plates over the pairs of contacts, placing the retaining element over the circuit board an applying pressure to the assembly at an elevated temperature for a predetermined time.
13 Claims, 9 Drawing Figures
METHOD OF MANUFACTURING KEYSWITCH
This is a division of application Ser. No. 505,389 filed 9/21/74, now U.S. Pat. No. 4,018,999. 5
BACKGROUND OF THE INVENTION
This invention relates generally to contact switch assemblies and methods for their manufacture, and more particularly to a contact switch assembly for use 10 in a keyboard having one or more keys.
Presently available contact switch assemblies for use in keyboards generally include a printed circuit board having a plurality of circuits, each of which terminates with first and second contacts located proximately to 15 each other. These printed circuit boards may have the circuit conductors provided only on the top or front surface of the board or, alternatively, on both the top and bottom surfaces in which case the circuit conductors are printed on the bottom or back board surface 20 with the contacts extending through the board to the front surface through a plated hole or equivalent opening in the board. A resilient contact plate, such as a snap-acting dome, cooperates with each pair of contacts to perform the switching function in a known 25 manner. The invention described below can be utilized with either type of printed circuit board and is not limited to use with the particular type illustrated in the drawings.
One of the difficulties involved in the above de- 30 scribed contact switch assemblies has been the manner in which the snap-acting domes are fixed in position on the printed circuit board. Each dome must be precisely located and fixed in position so that at least a portion of its periphery electrically communicates with one of a 35 pair of contacts so that, upon deflection, an inner portion of the dome will move into communication with the other contact thereby closing that particular circuit. A technique in current use for fixedly locating the domes comprises providing a thin sheet of polyester 40 material or the like having a pattern of openings punched in it which precisely corresponds to the desired pattern of the domes on the circuit board. This type of sheet which may be called a "dome cage," an example of which is shown in FIGS. 4-6 of U.S. Pat. 45 No. 3,749,859 granted to Webb et al. on July 31, 1973, has a pressure-sensitive adhesive layer on each of its surfaces so that subsequent to the punching operation, the cage is adhesively connected to the printed circuit board. The domes are then subsequently loaded into 50 the individual locations defined by the openings in the cage and are thereby correctly positioned relative to the contact pairs. A cover sheet is then provided over the outwardly facing adhesive surface of the dome cage thereby completing the assembly which comprises the 55 circuit board, the cage and the domes, whereupon the covered assembly may be heated and pressed to insure good adhesion between the cage and the printed circuit board. A precise second punching operation may be used subsequent to positioning the cover sheet to form 60 mounting apertures and/or switch holes.
These dome cages, however, are not entirely satisfactory. The cost of th« cage material, adhesives, and the labor involved in providing the adhesive on the cage material is relatively expensive. THe quality of the 65 adhesive and cage material has been found to vary. Due to this inconsistency in quality of the adhesive and cage material, the punching process not infrequently causes
the dome cage to crack or its surfaces to become contaminated with particles of adhesive and dome cage material. Relatively expensive and time-consuming cleaning and inspection steps are necessary in order to insure that these extraneous particles are kept to a minimum. Further, the openings formed in the dome cage must be precisely located with exact tolerances to assure proper electrical contact. This requires extensive, costly tooling equipment. If the temperatures occurring during the final heating step are too high, adhesive might flow into the dome area often resulting in malfunctioning. Additionally, if temperatures were too low, the final punching step frequently caused the circuit board to crack. Thus, a precisely controlled oven is required which adds yet further expense and additional time to the manufacturing process.
SUMMARY OF THE INVENTION
Accordingly, one object of this invention is to provide a new and improved contact switch assembly for keyboards.
Another object of the invention is the provision of a new and improved contact switch assembly which utilizes snap-acting domes.
Still another object of the present invention is to provide inexpensive apparatus for locating and maintaining the snap-acting domes in position.
A still further object of this invention is the provision of apparatus for retaining snap-acting domes in accurate position over the contacts formed on a printed circuit board.
Another still further object of the instant invention is the provision of a new and improved method of manufacturing contact switch assemblies for keyboards.
Still another further object of the instant invention is to provide a new and improved method for manufacturing contact switch assemblies for keyboards which is relatively inexpensive and less time-consuming than methods prevously employed.
Briefly, in accordance with a preferred embodiment of this invention, these and other objects are attained by first locating the snap-acting domes over respective pairs of contacts by one of various techniques, such as by vacuum. A retaining element comprising a film formed of a layer of thermoplastic material bonded to a flexible insulative materia! is positioned over the domes and circuit board after which the assembly is placed within a press. Pressure is applied at an elevated temperature for a predetermined time bonding the thermoplastic material to the domes and to the circuit board. A cover sheet may be provided over the back face of the circuit board with a foam layer interposed therebetween.
DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many of the attendant advantages thereof will be understood by reference to the following detailed description when considered in connection with the accompanying drawings in which:
FIG. 1 is an exploded perspective view of the contact switch assembly in accordance with the present invention;
FIG. 2 is a detail side view in section of the retaining element for the contact switch assembly;
FIG. 3 is a side view in section of a portion of a printed circuit keyboard incorporating the present invention;