Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to a pushbutton switch
assembly for telecommunjcations and other input apparatus, and
part~cularly though not exclusively to a pushbutton dial for a
telephone.
A particular form of pushbutton assembly comprises
a sandwich structure having, starting from the top or outer face,
a bezel having a plurality of apertures therethrough, a plurality
of pushbuttons, a pushbutton in each aperture; a thin flexible
sheet or film~ an assembly of snap action spring switch members
in an insulating holding member; a first printed circuit board
(PCB) on the top surface of which is the contact circuit with
contact positions contacted by contacts on the snap actlon
switch members, a further PC~ spaced from the first PCe, the
further PCB having on its rear surface a printed circuit and
also carrying the various electrical devices of the electrical
- circuit for the assembly; and a metal plate or bracket by which the assembly is mounted~
i PCB's are quite expensive items but have become
standard items for carrying circuits and for mounting of devices.
A PCB is usually formed of glass fibre reinforced resin. Sheets
of the basic~material are manufactured, and then the surface
treated to accept and retain a layer of copper. This layer is
then usually photolithographically etched to produce the desired
circuit pattern. A number of PCB's may be formed 1rom a sheet,
. ,
.
by shearing from the sheet.
The present invention provides for replacing oF
at least the first PCB, carrying the contact circuiit, by a
; porcelain coated steél plate carryiny the contact circuit. A
further feature of the present invention is to use the porcelain
coated steel plate to also replace the further PCB by forming
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the circuit normally on the further PCB on the rear surface of
the porcelain/steel plate and mounting the electrical devices on
the porcelain/steel plate. The porcelain coated steel plate is
cons;derably cheaper to produce than a glass fibre reinforced resin
PCB, the circuits being applied by thick film printing techniques
followed by firing.
As an additional feature, the use of a porcelain
coated steel plate to replace at least one of the PCB's enables the
metal plate or bracket to be dispensed with. The porcelain/steel
plate is rig;d and self supporting, whereas the PCB's are flexible
and are not strong enough to use without the metal plate or bracket.
The invention will be readily understood by the
Following description of certain embodiments, by way of example,
in conjunction with the accompanying drawings, in which:-
Figure 1 is an exploded perspective view of a
pushbutton assembly for a telephone dial, with one PCB replacedi --
Figure 2 is a view on the rear face of the remaining
PCB, with devices mounted;
F;gure 3 is an exploded perspective view of a
pushbutton assembly for a telephone dial with both PCB's replaced;
Figure 4 is an illustrative view on the rear face
of the porcelain coated steel member of the assembly in Figure 3,
with devices mounted;
Figure 5:is an exploded perspective view of the
rear surface of the porcelain coated steel plate, for an
i alternative embodiment, and illùstrating circuit menlbers for
mounting on khe plate;
Figure ~ is an exploded perspectlve view of a further
form of pushbutton assembly for a key strip, as ~or a telephone
set or other apparatus.
.
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As ;llustrated in Figure l~ a pushbutton assembly
comprises a molded plastic bezel lO having a plurality of apertures
ll arranged in columns and rows. At each side of the bezel lO is
a bracket 12, molded integrally with the bezel in the particular
example, but can be separate members attached to the bezel.
Brackets 12 provide the attachment~ or mounting, means for the
pushbutton assembly.
Extending next to the bezel lO and in contact with
its underside is a molded button or key assembly 13. The key
assembly 13 ccmprises a flat sheet 14 witK a plurality of keys or
buttons 15 molded therewith. The keys are separated from the sheet
on three sides3 indicated at 16 but hingedly attached at the fourth
; side - indicated at 17. The keys or buttons 15 extend up through
the bezel, a key or button in each aperture 11.
Beneath the button or key assembly 13 is a thin
flexible membrane 18 followed by a spring contact assembly l9.
In the particular arrangement illustrated ln Figure l, the spring
contact assembly 19 comprises a support and spacer member ~0
having a plurality of apertures 21 therein, arranged 1n columns
and rows corresponding to the apertures 11 in the bezel 10.
Supported on the support and spacér member 20 are a number of
spring contact members 22. In the particular example the spring
contact members 22 are in strips 23 and three such strips 23 are
provitied, corresponding to the three columns of buttons or keys
15. A spring contact member 22 is positioned over each aperture 21
and beneath each button or key 15. To retain the strips in position
they sit in slight recesses 24 in the member 20 and the ends of
the strips flt in s1its cut in a key member 25 at each end.
The spring contact members are conveniently
of the form having
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~, ..
a snap action when the centre portion of a contact member is
depressed by pressure on a button or key 15. ~hen a contact
member snaps down, contacts 27 move into contact with contact
areas of a circuit.
Positioned beneath the support and spacer member
19 is a steel sheet circuit member wh;ch is coated with porcelain,
at least on its upper surface, and indicated at 30. On the
porcelain surface is formed the switch contact circuit 31, as
by thick film techniques, to form a circuit board, the circuit
having a plurality of switch positions, each position having a
plurality of contact areas. In one such technique, a s~lver-
containing frit is thick film printed or deposited on the
porcelain/steel sheet which is then fired to form the conducting
pattern. A particular way of forming the porcelain coated sheet is
by electrodeposition of a frit on the steel sheet, followed by
firing. The conductor pattern is then formed and again fired.
Prior to depositing or forming the porcelain coating,
the steel sheet is perforated at various positions, as desired,
for example as indicated, at 32. These per-foratiol~s may be
provided for alignment of the various members, and,'or passage of
studs, screws or rivets, or similar devices for fastening members
together. To prevent a meniscus building up around these
perforations during application of the porcelain to the steel
sheet, the peripheral edges of the perforations are coined to give
a sl;ghtly chamfered edge.
Beneath the porcelain/steel circuit board 30 is
a conventional PCB 35. This is of a normal form, that is being a
sheet of resin impregnated glass fibre with a circuit pattern 36
on the top surface. Only small sections of the circuit pattern
are illustrated for clarity. Contact pads 37 are l'ormed as part
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of the circuit pattern and circuit devices are inserted, from the
undersurface in Figure 1, and wave soldered to thQ contact pads.
Figure 2, which is a view on the undersurface of the PCB 35,
illustrates some of the devices 38 inserted.
Conveniently, in the example illustrated in Figures
1 and 2, small cylindrical protrusions or studs are molded on the
undersurface of the bezel 10, and which pass through holes 40 in
the key assembly 13, the memb~ane 18, the spring contact assembly
support plate 20, perforations 32 in the porcelain/steel circuit
board 30 and holes 40 in the PCB 35. An insulati~g layer is
formed on the rear or undersurface of the porcelain/steel circuit
board 30. This is usually of porcelain as on the front or upper
surface but can be of other material. Another alternative is to
provide an intermediate member such as a flexible membrane similar
to membrane 18. This prevents electrical contac~ between the
PCB 35 and the rear surface of the board 30.
After assembly the protrusions or studs can be
rivetted over~ as by heating or sonic fusion, to provide a
- complete, unitary, assembly for easy handling and assembly into a
20 telephone set or other apparatus. The whole unit is normally
mounted by means oF the brackets 12.
Figures 1 and 2 illustrate what can be considered
as a first stage, eliminating the metal support member normally
provided, the porcelain/steel circuit board 30 providing a rigid
member in its place. Also one conventional form of resin
impregnated glass fibre PCB has been replaced by t:he porcelain/
steel board. This provides two cost reductions; elimination of
the metal support member and a cheaper form oF circuit boarcl.
Figures 3 and 4 illustrate a further stage in which
the second PCB, board 35 in Figures 1 and 2, is eliminated. Figure
3 is similar to Figure 1 insofar as the bezel 10, key assembly
13, membrane 18 and spring contact assembly 19 are concerned.
Thus, in Figure 2 there is the bezel 10 with
apertures 11 and brackets 12. Below the bezel is the button
assembly 13, comprising flat sheet 14, and buttons or keys 15.
Next to the button or key assembly 13 is the membrane 18 and then
the spring contact assembly 19 comprising support and spacer
member 20 and spring contact members 22. Then follows the
porcelain coated steel plate 30.
In this embodiment, as seen in Figure 4, the
porcelain coated steel plate 30 has a circuit pattern 50 on the
undersurface, the plate having porcelain on both surfaces and the
circuit pattern 50 again being formed, ~or example, by thick film
techniques, using a silver frit which is then ~ired. For clarity,
the circuit pattern 50 is shown dotted but is in face composed of
continuous conductors. The various electrical and electronic
components, indicated generally at 51, are attached to the circuit
pattern, for example by heat bonding or soldering~
Figure 5 illustrates a modl~ication of the assembly
of Figures 3 and 4 in which the conventional electrical and
electronic components are replaced by hybrid circuit devices 55 and
56 which are connected to the circuit pattern 50, as by heat
: bonding or soldering. Such an assembly provides a very compact
and economic package which can be used in various telephone sets
and similar devlces. The forming of the circuit 50 pattern is
conveniently by the same method as is used For forming the circuit
31, that is thick Film deposition of a silver containing ~rit
Followed by flring. However other metho~s of forming the circuits
; 31and 50 can be used, For example photolithographic etching.
Interconnection will, o~ course, be required
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between the two circuit boards 30 and 35 in the embodiment of
Figures 1 and 2, and between the two sides of the circuit board
30 in the embod;ments of Figures 3 and 4 and Figure 5.
In the embodiment of Figures 1 and 2, a flexible
tape or strip conductor member can extend between I:he board 30
and board 35 for example being connected at one endl to contact
areas 60 on circuit board 30 at the other end to contact areas
61 on circuit board 35.
In the embodiment of Figures 3 and 4, and Figure 5,
cross-connection or interconnection can be provided by conductor
paths through the porcelain/steel circuit board. I'his can be
obtained by making holes through the steel plate prior to coating,
coating with porcelain and then forming the circuil; patterns.
The porcelain will also coat the interior surfaces of the holes
and the circuit pattern can be caused to extend through the
holes by applying suctionto the board when the circuit is applied.
Thus, for example, if a silver-containing frit is applied on one
surface by thick film deposition, a suction is applied at the
other surface to draw the frit through the hole. The same can be
done when the circuit material is applied to the ot:her side, to
ensure good interconnections. The holes are coinecl prior to
coating the steel plate with porcelain.
The circuit board 30, both in Figures 1 and 2,
and in Figures 3 and 4~and Figure 5~ can be connected to any
further components in the apparatus by a further f'lexible conductor
member, as illustrated at 62 in Figure 5.
In addition to the conventional form of pushbutton
switch assembly as lllustrated in F~gures 1 to 5, l;he invention is
applicable to other ~orms of pushbutton assembly and one example
of such altternative forms is illusrated in Figure fi.
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In Figure 6 sim~lar members or items are provided
as in the embodiments of Figures 1 and 2, or 3 and 4, or Figure
5, but the shapes are different. There is an elongate bezel 10
with apertures 11. Beneath the be~el is an elongate molded
button assembly 13 with buttons or keys 15, one for each aperture
11. The basic form of the button assembly is as in Figures 1 or 3.
Beneath the button assembly 13 is thin flexible membrane 18 and
then spring assembly 19 comprising a strip of contact members 22
on a support and spacer member 20. Then there is an elongate
circuit board 30.
In the embodiment of Figure 6, it is assumed that
the circuit board 30 is as in Figures 3 and 5, that is porcelain
coated steel with one circuit - 31 - on the top surface and the
other circuit - circuit pattern 50 of Figure 4 - on the under-
surface and the electronic components connected to the circuit
on the undersurface. Hybrid devices, as in Figure 6, can be used.
Alternatively, the Pmbodiment of Figure 6 can bb modified to be
generally as that of Figures 1 and 2, that is with the circuit
board 30 of porcelain/steel and carrying the circuit 31, but with
a separate circuit board carrying the second circuit and the
associated electronic components.
The pushbutton, or key, assembly of Figure 6 is,
.
for example, assembled in a sandwich structure and screws passed
through the holes 65 in the various members~ These can also serve
as mounting and/or attachment screws for the complete assembly.
~lternatively other mountiny means can be provided, or protrusions
molded 4n the undersurface of the bezel 10 passing through suitable
holes in the various members, used to assemble the members, as
in Figures 1 and 2, or 3 and 4.
The pushbutton, or ~ey, assembly need not be
s
restricted to a telephone set style as in Figures 1 to 5, or in
a strip form as in Figure 6,can be much larger wi~h many rows and
columns, or other configurations. A very simple, economic and
strong assembly is provided. Assemblies in accordance with the
present invent;on can be used for telephones, and other
telecommunications apparatus, keyboard terminals, calculators and
other input apparatus.
6S
SUPpLEMENTARY DISCLOSURE
Figure 7 is a cross-section throu!~h another form
o~ pushbutton dial;
Figure 8 is a plan view of a contact member as
used 1n the pushbu-tton dlal of Figure 7;
Figure 9 is a plan vie~ of one face of a porcelain
or steel circuit member~ illustrat1ng the circult associated with
the contact member of Figure 8.
The form of pushbutton assembly, or dial7
illustrated in Fiyures 7, 8 and 9 has the spring contact assembly 19
of Figures 1 to 6 replaced by a ~lexible electr~cally insulating
contact member having a plural;ty of domed areas formed therein. A
suitable material is *Mylar. The assembly comprise$ a circuit member
70, which ;s of porcelain coated steel similar to the circuit member 30
of Figures 1 and 2~ in Figures 3, 4, and 5~ and also in Figure 6, an
electrically insulating sheet 71, the flexible contact member 72 and a
molded button or key member 73. The flexible contact member has thP
domed areas 74 arranged in columns and rows and t~le concave surfaces
of the domed areas are metallized, at 75, the metallized areas
connected to circuit conduc~ors 76.
; 20 The concave surfaces of the domed areas face towards
the circuit member. On the surface of the circuil; member is a
conductor pattern 77. The conductor pattern defines a plurality of
contact areas, indicated at 78, a contact area aligned with each
domed area 74. The contact areas are interconnected by conductors
79 which extend to an edge of the circuit member, at 80. The
conductors 80 provide ~or connection to other electrical and
electronlc components. Conductors 81 are also proYided to connect
to the conductors 76 o~ the contact member. Electrical connection
between conductors 76 and conductors 81 can be made by stapling the
assemb1y together, metal staples passing through conductqrs 76 and 81.
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Conductors 81 can also connect to electrical and electronic
components? for example mounted on the back surface of the circuit
member 72.
The pushbutton or key member 73 has a plurality
of cantilevered pushbuttons 85 arranged in columns and rows, the
buttons extending from the front or top s1de of the member 73.
The buttons 85 are molded integrally as parts of the member 73
but are separated on three sides and connected by a thin portion
86 which acts as a hinge. Projections 87 extend from the back of
each button 85 and are in contact with the domed areas 74.
Pressure on a button 85 pushes down a domed area, which moves into
contact with a contact area on the circuit member, with a snap
actionO Pins 88 extending from the back of the member 73 pass
through alignment holes 89 in the contact member and circuit member.
~i3j~
