Coating processes – Electrical product produced
Patent
1985-12-04
1988-05-10
Newsome, John H.
Coating processes
Electrical product produced
427 79, 427 96, 340365C, B05D 512
Patent
active
047434643
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for manufacturing matrix type capacitive keyboards formed of electric circuits providing a plurality of separate controls from key pads forming a keyboard. The invention also relates to keyboards obtained by this process.
Such keyboards comprise a matrix arrangement of conducting studs associated respectively with the keys of the keyboard and disposed in spatial concordance with said keys, each of said studs being formed of two conducting areas insulated electrically from each other and able to be coupled capacitively together by bringing close thereto a conducting armature through actuation of the corresponding key. Such keyboards may be used for controlling apparatus and different machines such as computing machines, typewriters, computers etc..
Generally, the two areas of the same stud are disposed on each side of a foil of insulating material while being generally offset with respect to each other in a direction parallel to the plane of said foil. Thus two matrix arrangements of studs are obtained, namely one on each face of the foil, the areas of one of the arrangements being for example connected together by columns whereas that of the other arrangement are connected together by lines, the foil of insulating material thus allowing crossing of the respective line and column conductors while separating and isolating the lines and the columns.
Thus, in the U.S. Pat. No. 3,921,167, these two matrix arrangements are provided on two different insulating plates, then these two plates are juxtaposed one against the other with their conducting arrangements orientated towards each other but with interpositioning of an insert foil. It will however be understood that in this case the capacitive coupling between the two areas of the same stud is hindered by the presence of the insert insulating foil and by the thickness of that one of the two plates situated on the side of the armature controlled by the key.
This is why, in British patent No. 1 582 640, two matrix arrangements are formed on the two faces of the same insulating foil of the type used for forming printed circuits and which have thicknesses greater than 1mm and permittivities of the order of 2.
In order to solve the problems related to the capacitive coupling through such low value capacities in series, it has already been proposed, in the European patent application No. 83 400 433.5, to form such an insulating foil of material from the group formed of the mono-,di- and tri-fluoroolefins of the ethylene family, having permittivities which may be higher than 10 under a high electric field. These insulating foils may have smaller thicknesses for example of the order of 50 microns.
However in practice, in order to ensure a suitable capacitive coupling because of the low powers available, it is necessary to use insulating foils of very small thicknesses of the order of 10 to 20 microns which have no inherent strength, which leads to serious disadvantages during manufacture and handling. The present invention proposes overcoming these drawbacks and provides a process for manufacturing such capacitive keyboards which allows the problems to be avoided which are related to the use of such foils of very small thicknesses.
Another object of the invention is to provide such a process which allows the thickness of the insulating material to be further reduced and, consequently, the performances due to the capacitive coupling to be increased.
A further object of the invention is to allow such keyboards to be manufactured in very large quantities and at a low cost price.
The invention provides a process for manufacturing capacitive keyboards of the type comprising, on each side of an insulating material of small thickness, two matrix arrangements, one in lines, the other in columns, of areas associated two by two so as to form capacitive studs capable of being subjected to the influence of a key allowing a metal armature to be brought close thereto, characterized by the succession of steps consisting in applying a first m
REFERENCES:
patent: 3951250 (1976-04-01), Pointon
patent: 4391845 (1985-07-01), Denley
Duchalet Daniel
Larguier Jean L.
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