Note: Descriptions are shown in the official language in which they were submitted.
1080~
This inventio~ relates to a thermal printing
device, particularly but not essentially for facsimile
printing.
Thermal printing devices in the form of ~ -
a number of individual, discrete, heating elements, each of
which is activated as required. The resolution available
is limited by the minimum spacing which can be obtained.
At present resolutions of the order of .02 inches are
available. For high resolution, as for facsimile printing,
resolutions down to .005 inches are desirable. Such high
resolution is desired when printing out drawings, pictures,
small type and other items having fine detail, transmitted
over telecommunications systems. Also, it is desirable to
-; be able to transmit and print a full page width and the speed
of printing should be at a reasonable level. As the paper
used undergoes a colour change by heat it is necessary to
generate sufficient heat, for a sufficient length of time,
to produce the desired colour density of print.
It has been proposed in application serial
no. 239,106 filed November 6, 1975, in the name of the
present assignee, that a continuous bar of electrically
resistive material be used, with patterns of conductors on
each side of the bar connected thereto, with a particular
arrangement of forming the patterns, whereby on selective
energization of patterns, heated areas are produced in the
bar at desired positions.
While the arrangement described in the above-
identified application is effective and provides high resolution
with a satisfactory colour density, it is necessary for the
- 30 conductors to the bar to be very narrow and closely spaced.
~ For example, for a resolution of 200 dots per inch the centre
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to centre distance of ~he contacts is .005" and the conductor
widths are of the order of .003". This can give rise to
difficulties in manufacture. Also, some of the conductors
of the patterns are long and can have a resistance which
can be intrusive in the overall system.
The present invention provides for an
arrangement of the conductors in the conductor patterns
which doubles the centre-to-centre spacing while retaining
a particular resolution. Thus, as an example, while
providing a resolution of 200 dots to the inch, there is a
.005" centre-to-centre spacing of the dots, the conductors
to the bar can have a centre-to-centre spacing of .010". This
is obtained by staggering the conductors on one side of the
bar relative to the conductors on the other side of the bar.
By selective activation of a first conductor on one side it
can be caused to be connected to one or the other of two
conductors on the other side of the bar and positioned on
, . . .
either side of the centre line of the first conductor.
-~ Other details of construction of the device
will also be apparent from the following description of
certain embodiments, by way of example, in conjunction with
the accompanying drawings, in which:-
Figures 1 and 2 are diagrammatic perspectiveviews of a typical cross-section of a device as described in
the above-mentioned application;
Figure 3 is a diagrammatic plan view of a
conductor/bar arrangement in accordance with the present
invention;
Figure 4 is a diagrammatic plan view of
conductor patterns on each side of the bar;
Figure 5 is a cross-section on the line
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V-V of Figure 4;
Figure 6 is a plan view of a section of
conductor patterns and resistor bar, for a facsimile
printer;
- Figure 7 is a diagrammatic plan view of one
form of connector and conductor patterns for the arrangement
of Figure 6;
Figure 8 is a cross-section on the line
VIII-VIII of Figure 7; and
Figure 9 is a cross-section on the line
IX-IX of Figure 7.
Figures 1 and 2 illustrate the proposed concept
in the aforementioned application, Figure 1 being a
diagrammatic view showing the print bar 10, a continuous bar
of electrically resistive material, on a substrate 11, two
conductor patterns 12a and 12b on one side of the bar 10 and
four conductor patterns 13a, 13b, 13c and 13d on the other
side of the bar 10. The two conductor patterns 12a and 12b
each contact the bar 10 at a plurality of spaced apart ,
positions 14a - 14d and 15a - 15d respectively. The conductor
patterns 13a, 13b, 13c and 13d contact the bar 10 at interspersed
spaced apart positions 16a, 16b, 17a, 17b, 18a, 18b, and l9a,
; l9b respectively. By suitably connecting a particular pattern
; 12a or 12b, and a particular pattern 13a, 13b, 13c or 13d, to
an electrical power source, a hot spot can be formed in the
bar 10 at one of the opposed contact positions. It will be
noted that there must be a contact on one side of the bar for
every contact on the other side of the bar. With desired
centre-to-centre spacings of .005", for 200 lines per inch
resolution, the conductor patterns are quite narrow and closely
packed.
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Figure 2 is a typical cross-section through
the conductor patterns for an arrangement as in Figure 1.
The bar 10, for example, is of thick film form, deposited
over the opposed ends of conductors 20, which are of thin
film form. An insulating layer 21 is formed over the conductors
20 leaving gaps 22 on either side of the bar 10. Vias or
interconnect holes 23 are formed at desired positions, and
conductor patterns 25 and 26 formed over the insulating layer,
the conductor patterns having individual conductors 25a
(corresponding to conductor 12a in Figure 1 for example) and
26a and 26b (corresponding to conductors 13d and 13c of Figure
1). The conductors 25a, 26a and 26b contact their respective
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conductors 20 through the vias 23, and can be of thin film
form or screened thick film.
As stated, the present invention enables
the centre-to-centre distances of the conductors connecting
to the bar to be doubled, thus enabling the width of the
conductors to be increased substantially, while still providing
the same resolution as in the arrangement of Figure 1. This
is obtained by staggering one set of connections to the bar
relative to the other set of connections. This is illustrated
diagrammatically in Figure 3. For clarity, apart from the
resistance bar, still identified as item 10, and the support
or substrate 11, all other items have different references,
relative to Figures 1 and 2.
Thus, as seen in Figure 3, conductors 30 are
connected to one side of the bar 10 and conductors 31 are
connected to the other side of the bar. The conductors 31
are staggered relative to conductors 30, the centre lines of
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` 30 conductors 31 being midway between the centre lines of conductors
30. Depending upon the power connections, a conductor 31 can
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be connected to one or the other of two conductors 30. Thus, ~ -
in Figure 3, if conductor 30a is connected to a power source
and also conductor 31a, then a hot spot will be formed at 32a,
`~ while if conductors 30a and 31b are connected to a power source
a hot spot will be formed at 32b. The position of hot
spots are indicated generally at 32.
Figure 4, in association with Figure 5,
illustrates in slightly more detail one form of conductor
arrangement. On substrate 11 a plurality of transverse
conductors 35 are formed on one side of the bar 10, the
conductor 35 extending parallel to the bar. There is no
physical limitation on the width and spacing of the conductors
35, except that the ultimate size of the finished device, in
a direction normal to the axis of the bar 10, will depend upon
the width and spacing and also the lengths of the connections
from the conductors to the bar will be affected, as will be
appreciated later with respect to Figure 6. However, with
these details in mind, it is possible to make the widths and
spacing of the conductors 35 such that manufacturing problems
; 20 will be minimal and a very high level of good quality
manufacture attained. This is important as, after forming of
` the conductors 35, as by thick film, for example fritless gold,
process, the conductors 35 are covered by an insulating glaze
layer 36. Thereafter repair is at least, extremely difficult.
Other ways of forming the conductors 35 can be used, such as
etching back of thick or thin film materials. Various metalliz-
ations are available, apart from gold, for example palladium -
silver thick film.
; At the same time as the conductors 35 are
formed on the one side of the bar 10, a plurality of primary
connector portions 37 are formed on the substr~te, the prim~ry
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connector portions extending normal to the bar 10 and stopping
short of the first conductor 35. These primary connector
portions 37 can be formed of the same material as the conductors
35 in the one process step. Also formed at the same time, and
conveniently of the same material, are conductor and connector
patterns on the other side of the bar 10. These patterns are
in two forms. Thus a plurality of connectors 38 are formed,
extending normal to the axis of the bar 10, the connectors 38
positioned midway between the connector portions 37. Alternate
i 10 connectors 38 are formed unitarily with conductors 39, the
connectors 38, conductors 39 and terminal pads 40 formed at the
same time. An insulating glaze layer 41 is then applied over
the conductors 39 and part of each connector 38. Layer 41 is
usually applied at the same time as layer 36 over conductors 35.
The bar 10 is not actually formed until at
least after the connector portions 37 and 38 are formed. It is
normally formed by a thisk film process and may be of more than
one layer.
In the layer 36, vias 42 are formed in a
20 predetermined pattern. The vias 42 can be formed by laser
machinery or by suitable screening in the thick film process
for applying the glaze layer. Secondary connector portions 43
are then formed on the glaze layer 36. At one end, the end closest
to the bar 10, each secondary connnector overlaps the end of a
primary connector portion 37 and is electrically connected
thereto. At its other end, each secondary connector portion
overlaps a particular conductor 35 and is electrically connected
thereto through the related vias 42.
Also formed at the same time as the secondary
30 connector portions 43, and of the same material, on the other
side of the bar 10, Are additional conductors 44. These
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conductors 44 overlap the alternate connectors 38 not unitary
with the conductors 39. These alternate connectors 38 are formed
shorter than the other connectors 38, as seen in Figure 4, and
extend only a short way under the glaze layer 41. The
conductors 44 have terminal pads 45.
Terminal pads, not shown in Figure 4, are
provided at one end of each conductor 35. For convenience,
and to permit large pads, these may be formed at alternate
ends, as will be seen in Figure 6. The particular relative
widths of conductors and connectors, in Figure 4, is
illustrative only and can be varied. Thus, for example, some
or all of the secondary connector portions 43 can be made wider
than the primary connector portions 37. It is also conceivable
that the primary and secondary connector portions 37 and 43
could be formed at one time, the bar 10 being formed after
forming the connectors. This would particularly be the case
if thin film resistive elements are used.
Figure 6 illustrates one section of a device,
with an arrangement of conductors and connectors to provide a
- 20 wide, easy to manufacture contact area between conductors and
connectors. A pattern of conductors 50 is formed on substrate
11 extending parallel to each other and to the bar 10. These
conductors 50 correspond to the conductors 35 of Figure 4.
Over the conductors 50 is formed an insulating glaze layer,
the periphery of which is indicated by the chain-dotted line
51. A trough or channel 52 is formed in the glaze layer, which
leaves exposed a short length of each conductor 50. On the glaze
layer is formed a pattern of connectors 53 which extend at one
end to the bar 10 via short conductive connectors 53a - which
; 30 correspond to the connector portions 37 of Figure 4. Each
connector 53 extends to a unique conductor 50. The shorter
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connectors, that is the left-hand part of the section in
Figure 6 except for the first connec'cor are of narrower
configuration and follow a cranked or bent path to provide room
for the channel 52. The connections having longer paths are
straight and also wider. This enables the resistance of the
longer connector paths to be kept to a desirable low value.
Then a further short transverse conductive extension to each
connector is formed, overlying a related conductor and making
electrical contact with the conductor in the channel 52. These
transverse extensions are indicated at 54. A short transverse
extension 54 is also formed for the first, or most left-hand,
connector.
There is an advantage in this construction
that the more closely spaced connectors 53 are on top of the
glaze layer and can be repaired quite easily. The connectors
can be of thin film structure.
The conductors 50 terminate at alternate ends
in terminal pads 56 which can be formed at the same time as
the conductors or at a separate stage in the manufacture.
By forming the pads 56 at alternate ends, large pads can be
provided. However, the pads 56 can all be at the same end and
it is possible to provide two columns of pads, the connectors
alternating, with alternate conductors extending between the
pads of the innermost column.
A second pattern of conductors and connectors
is formed on the substrate on the remote side of the bar
relative to the conductors 50. As seen in Figure 6, a plurality
of connectors 57 extend from the bar 10, the centres of the
connectors 57 midway between the centres of the connectors 53.
Alternate connectors 57 extend to a transverse conductor 58
- and are connected to the bar 10 by connectors 57a. The
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remaining connectors are then connected to a short conductor
59. This is shown diagrammatically in Figure 6 by the line
60.
Figures 7, 8 and 9 illustrate one way of
connecting the connectors 57 alternately to transverse
conductors 58 and 60. On the substrate 11 is formed the bar
10. The bar 10 overlies the inner ends of the connectors 57.
Alternate connectors continue to, and can be integral, and
formed at the same time, with the transverse conductor 58.
The other connectors finish short of the transverse conductor
58, as indicated by dotted lines 65. A dielectric glaze 66
is then formed over the transverse conductor 58, the glaze
extending to the line 67. The transverse conductor 60 is
formed and at the same time conductors designated 57a in Figures
8 and 9, are formed on the connectors 57. The thin film
gold layer extends substantially from the bar 10, over thick
film gold connectors 57, over the glaze and into contact with
conductor 60, as seen in Figure 7. For the connectors connected
.
to the conductor 58, the thin film layer 57a extends substant-
ially from the bar 10, along part of each connector 57 and then
up and over the glaze 66 for a short distance, as seen in
Figure 8. Conductors 57a can be formed separately from conductor
60, if desired.
The glaze layer 66 assists in ensuring that
there is lifting of the ends of the connectors 57. The thin
film gold layers 57a provide connection between the connectors
; 57 and the transverse conductor 60 and also improve the physical
structure of the connectors 57. Thick film layers, as used
for the connectors 57, can often have pin holes therein, and
the thin film closes such pinholes and improves the conductivity
of the connectors 57.
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The section illustrated in Figure 6 has forty
connectors 57, and forty connectors 53. By selective connection
of terminal pads 56 and 61 this provides eighty possible hot
spots in the bar lO for that section. For a 200 line per inch
resolution, hot spots must be formed at .OOS" centres. However,
with the constructional arrangement described above, and
illustrated in Figures 3, 4 and 5, and Figure 6, centre-to-centre
distances for the connectors are .010". This enables wider
conductors and wider gaps to be used, for at least a large part
of each section, with increased processing efficiency and
higher yield. The number of connectors is halved, forty
instead of eighty for a section as described.
A protective layer can be applied over the
connectors 53 and 57.
The various layers for the bar 10, conductors
35, 39 and 44, and connectors 37, 38 and 43, in Figures 4
and 5, conductors 50, 58 and 59 and interconnection 60 and
connectors 53 and 57 of Figure 6, are formed by well known ~: .
conventional processes, and can be of thin film, thick film
20 or other form as desired.
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