Membrane switch having adhesive label as edge seal

A membrane switch comprised of first and second flexible layers having corresponding patterns of metallization thereon, these layers being separated by an apertured spacer. The first layer is of a larger size than the spacer and the second layer is of a smaller size than the spacer so that when the three are superposed, a border on the first layer and spacer are exposed to meet the second layer. Completing the assembly is a label layer which is of a flexible, non-conductive material having a desired pattern of graphics printed on it and an adhesive coated undersurface. When the label layer is pressed against the exposed surface of the second substrate, it bonds all three of the lower layers together and creates a seal around the perimeter of the switch assembly. With the label layer being of a greater size than the other three layers, it may also be used to affix the composite switch to the appliance on which it would be used.

BACKGROUND OF THE INVENTION 
I. Field of the Invention 
This invention relates generally to membrane or diaphragm switches, and 
more specifically to an improved construction of such switches whereby the 
reliability of the resulting product is increased and the manufacturing 
cost is reduced. 
II. Discussion of the Prior Art 
Diaphragm or membrane switches are now widely used in conjunction with a 
variety of electrical and electronic appliances. Typically, these switches 
comprise a base layer having a pattern of conductive switch contacts 
disposed thereon and overlaying this base layer is a spacer layer which 
has plurality of apertures which are aligned with the conductive elements 
on the base layer when the spacer layer is superimposed on the base layer. 
Atop the spacer layer is a further flexible plastic layer having a pattern 
of conductive switch contacts on the underside thereof, this conductive 
pattern also being aligned with the apertures in the spacer layer. This 
upper layer commonly has graphics on its exposed outer surface to identify 
particular switch positions. The application of finger force to a marked 
area on the graphics layer results in the upper flexible layer being 
deformed through the aperture in the spacer layer so a circuit path is 
completed between the two switch contacts. The memory properties of the 
plastic from which the upper flexible layer is fabricated allow the switch 
contacts to separate once the finger force is removed. 
It has been the existing practice in the fabrication of membrane switches 
to adhesively bond the spacer layer to the lower substrate and then to 
likewise bond the upper metallized layer to the other major surface of the 
spacer member. Then, the graphics may be imprinted on the exposed surface 
of the upper flexible layer or, alternatively, a separate label layer may 
be adhesively bonded to the upper flexible layer. 
The various steps of bonding one layer to the other increases the overall 
manufacturing cost of the membrane switch. I have conceived of a way of 
manufacturing a membrane switch whereby the overall manufacturing cost is 
reduced without an attendant reduction in the reliability or useful life 
of the resulting switch array. 
SUMMARY OF THE INVENTION 
In accordance with my invention, there is provided a lower flexible 
substrate having a pattern of metallization thereon with conductive 
elements being disposed at predetermined coordinate locations. The 
substrate may be rectangular, circular, oval or any other shape. Next, a 
spacer layer is provided, the spacer layer having a pattern of apertures 
which correspond to the same coordinate locations as the metallization on 
the lower flexible substrate. The spacer layer has the same geometric 
shape as the lower substrate, but is of a smaller size in all dimensions 
so that when it is positioned atop the lower substrate layer with the 
apertures aligned with the pattern of metallization, a border or perimeter 
zone of the lower substrate will extend beyond the edges of the spacer 
layer. Next, a further substrate, i.e., the upper substrate, is provided 
and it has a pattern of metallization on the undersurface thereof with the 
pattern corresponding to the same coordinates as the pattern on the lower 
substrate. Thus, when the upper substrate is stacked on top of the spacer 
layer, the conductive elements will be aligned vertically with the pattern 
on the lower substrate, but will be spaced apart from them by the 
thickness dimension of the spacer layer. Again, the upper substrate has 
the same geometric shape as the lower substrate and the spacer layer, but 
is of a smaller dimension so that when positioned atop the spacer layer 
the edges of the spacer layer will extend beyond those of the upper 
substrate around the perimeter of the assembly. 
The upper and lower substrate segments may comprise the same sheet of 
flexible plastic material with their respective patterns of metallization 
symmetrically disposed on the same surface on opposite sides of a 
fold-line such that when folded with the spacer layer sandwiched 
therebetween, their conductive segments will be aligned with the spacer 
apertures. 
Once the various members are superimposed one above the other with the 
proper registration maintained, a label layer which is also formed from a 
flexible material and which has a pressure sensitive adhesive coated on 
the undersurface thereof is pressed onto the exposed upper surface of the 
upper substrate. The dimensions of the label layer are at least as large 
as those of the lower substrate and, hence, the borders of the lower 
substrate, the spacer layer and the upper substrate are all individually 
adhesively bonded to the label layer. Because of the staggered 
relationship of the various parts, no noticeable irregularity or ripple 
appears on the exposed surface of the label layer. 
By using the technique of the present invention, it is unnecessary to use 
pressure sensitive adhesive to bond the spacer to the lower substrate and 
the upper substrate to the spacer. This appreciably reduces the 
manufacturing cost of the switch array. Further, because the upper label 
layer is adhesively bonded to the edges of all of the other layers within 
the diaphragm switch, a perimeter seal is established precluding moisture 
or dust particles from entering into the switch array and possibly 
compromising the integrity of the switch contacts. 
OBJECTS 
It is accordingly the principal object of the present invention to provide 
a new and improved diaphragm-type electrical switch array. 
Another object of the invention is to provide an improved diaphragm-type 
switch array which can be produced at a lower relative cost than known 
prior art arrangements. 
A still further object of the invention is to provide a diaphragm switch 
array in which the individual parts are held together by an adhesive 
coating applied to only one layer in the assembly. 
A still further object is to provide a diaphragm-type switch array in which 
the spacer layer and the upper substrate are of the same shape but of a 
lesser area than the layers immediately below whereby when an upper label 
layer of the same or greater area than the lower substrate is adhesively 
bonded to the assembly, the several parts are each bonded to the label 
layer about their respective perimeters. 
These and other objects and advantages of the invention will become 
apparent to those skilled in the art from the following detailed 
description of a preferred embodiment, when considered in conjunction with 
the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, the internal construction of the diaphragm switch of 
the present invention is illustrated. Numeral 10 refers to the lower or 
base substrate and this may comprise a thin sheet of a flexible plastic 
material. Sheet materials of plastics sold under the trademarks Mylar, 
Kapton or Tradlon have been found to be entirely suitable. Formed on the 
upper surface 12 of the substrate 10 is a pattern of conductive elements 
as at 14, 16, these elements being disposed at predetermined spaced apart 
locations, preferably in the form of a rectangular grid. The conductive 
elements may be formed from a silver/graphite paste when a silk-screening 
process is the method employed for applying the conductive elements 14 and 
16 to the substrate 10. Alternatively, the conductive pattern may be 
formed from copper or other conductive materials using any of the various 
well-known printed circuit techniques. With reference to FIG. 2, it can be 
seen that the lower substrate 10 may be generally rectangular in shape, 
but limitation to this shape is not essential as will become apparent as 
the description of the preferred embodiment progresses. 
Disposed immediately above the lower substrate layer 10 is a spacer member 
18 having a pattern of apertures, as at 20, formed through the thickness 
dimension thereof, the center-to-center spacing of the apertures being 
consistent with the center-to-center spacing of the conductive elements 
14, 16, etc. on the upper surface 12 of the lower substrate 10. The spacer 
member has the same general shape in its plan view as the lower substrate 
10, but is of a smaller area such that a peripheral portion or border zone 
22 on the lower substrate extends outwardly from the side edges of the 
spacer member 18 when that member is positioned on the lower substrate 
with the apertures 20 aligned with the metallization elements 14 and 16. 
The spacer layer 18 may also be fabricated from a sheet of suitable 
plastic material such as those trademarked Mylar, Kapton or Tradlon. 
Disposed immediately above the spacer layer 18 is a further (upper) 
substrate layer 24. The upper substrate has a pattern of metallization on 
its undersurface which, too, may be formed using silk-screening, copper 
etching or any other suitable and well-known printed circuit process. The 
center-to-center spacing of the conductive elements 26 corresponds to the 
spacing between elements on the lower substrate 10 so that when the upper 
substrate layer 24 is superimposed over the spacer layer and properly 
registered, the conductive elements 26 will be generally aligned with the 
conductive elements 14 and 16, but will be maintained out of contact with 
one another by the thickness dimension of the spacer member 18. 
The upper substrate member 24 has the same general shape in its plan view 
as the lower substrate and the spacer member. However, the area of the 
upper substrate 24 is less than that of the spacer member such that when 
properly registered, a border zone 28 of substrate 18 extends beyond the 
edges of the upper substrate 24. 
Completing the assembly is an upper cover or label layer 30 which may 
typically have alphanumerics or other graphics printed thereon at spaced 
apart locations corresponding to the locations of the metallization 
elements 26, the apertures 20 and the elements 14, 16 on the several 
layers. The label layer 30 is also preferably formed from a suitable 
flexible plastic material having a memory property and on the undersurface 
thereof is a coating 31 of a suitable pressure-sensitive adhesive. The 
layer 30 is generally of the same size as the lower substrate 10 such that 
when it is pressed firmly into contact with the members 24, 18 and 10, the 
exposed borders 22, 28 and the surface 24 will all adhere to the label 
layer 30, thereby holding all of the parts together and forming a seal 
about the entire perimeter. 
With reference to FIG. 2, during manufacture, it has been found convenient 
to form registration holes 32 and 34 through the layers 10, 18 and 24. 
Then, by stacking these parts onto a manufacturing jig having spaced-apart 
pins extending upward from it, the parts are held in proper registration. 
Once so registered, it has also been found helpful to ultrasonically bond 
or otherwise tack or join the layers 24, 18 and 10, one to the other, as 
at 36, 38, 40 and 42 to hold the various parts in their proper 
registration during handling prior to the application of the adhesively 
coated label layer 30 as the final step in the manufacturing process. 
Furthermore, it has been found expedient from a cost standpoint to use a 
common sheet of flexible plastic material for both the lower substrate 10 
and the upper substrate 24. To do so, the pattern of metallization is 
formed symmetrically on opposite sides of a fold-line such that when the 
common substrate is folded along that line with the spacer layer 18 
inserted between the folded "halves" the metallized elements on the lower 
half will be vertically aligned with those on the upper half. The common 
sheet is also cut so that the portion which will become the upper 
substrate section will be of lesser size than either the lower portion or 
the spacer to be used, the two segments being joined only by a narrow 
strip 43 which permits conductors to extend between the two "halves". To 
ensure that the fold zone does not spread apart and overcome the adhesive 
force of the label layer to thereby destroy the seal, it has been found 
helpful to also ultrasonically bond the substrates 10 and 24 together in 
the zone of the strips 43 proximate their point of folding as at 42. 
Numeral 44 refers to the portion of the substrate 10 having conductors 
thereon which is brought out to be connected to the external circuitry 
with which the switch array is to be used. 
Because the members 18 and 24 are gradually successively stepped inwardly 
from the outermost edge perimeter of the assembly, no noticeable or 
unsightly step is observable on the exposed outer surface of the label 
layer 30. 
Where the diaphragm switch array of the present invention is to be used on 
an appliance having a generally flat surface, it has been found expedient 
to extend the borders of the label layers outward beyond the edges of the 
lower substrate 10 and, in this fashion, the switch assembly may be 
adhesively bonded to the flat surface of the appliance. 
There has been shown and described a preferred embodiment of the invention 
and the best mode contemplated by me for carrying out the invention. Those 
skilled in the art, upon reading the present specification may conceive of 
variations which do not depart in spirit from the true scope of the 
invention. Accordingly, it is intended that the scope of the invention be 
determined from the accompanying claims.