Incremental printing of symbolic information – Thermal marking apparatus or processes – Specific resistance recording element type
Reexamination Certificate
2000-05-01
2001-10-16
Hilten, John S. (Department: 2854)
Incremental printing of symbolic information
Thermal marking apparatus or processes
Specific resistance recording element type
C347S200000, C347S202000
Reexamination Certificate
active
06304280
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a thermal printhead which is designed to perform printing on a recording medium thermosensitively or by thermal transfer. It also relates to a method of making such a thermal printhead.
BACKGROUND ART
FIG. 7
is a schematic plan view of a prior art thin-film thermal printhead. The thermal printhead
51
includes an elongated rectangular substrate
52
having longitudinal sides
52
a
and
52
b.
The substrate
52
has a surface formed with a linear resistor layer
53
extending longitudinally adjacent one longitudinal side
52
a.
A band-like region between the resistor layer
53
and the longitudinal side
52
a
of the substrate
52
is provided with a common wiring pattern
54
. The common wiring pattern
54
has opposite ends extending to the other longitudinal side
52
b
of the substrate
52
. One of the opposite ends of the common wiring pattern
54
is connected to a common terminal
55
.
FIG. 8
is an enlarged plan view showing a principal portion of the thermal printhead
51
. The common wiring pattern
54
includes a plurality of comb-tooth electrodes
54
a
extending therefrom. Individual electrodes
56
have respective one end extending between two adjacent comb-tooth electrodes
54
a.
The other end of each individual electrode
56
extends adjacent to a drive IC
57
mounted on the substrate
52
and is connected, via a non-illustrated wire-bonding pad, to an output terminal of the drive IC
57
.
As indicated by the chain lines in
FIG. 8
, the resistor layer
53
is laid over the comb-tooth electrodes
54
a
and the individual electrodes
56
alternate therewith, thereby defining a heating element
53
a
between each two adjacent comb-tooth electrodes
54
a.
Thus, when power is applied to any individual electrode
56
, current passes through a portion of the resistor layer
53
defined between two comb-tooth electrodes
54
a
sandwiching this individual electrode
56
, consequently working as a heating element
53
a.
FIG. 9
is an enlarged sectional view showing a principal portion of the thermal printhead
51
. The substrate
52
formed of an insulating material such as alumina ceramic material is provided, on a surface thereof, with a glaze layer
61
extending longitudinally at a portion adjacent to the longitudinal side
52
a.
The glaze layer
61
is formed with a resistor layer
53
in the form of a thin film for covering the glaze layer. Conductor layers
62
a,
62
b
are formed on the resistor layer
53
in such a manner as to expose the resistor layer
53
at a portion at the top of the glaze layer
61
. The exposed portion of the resistor layer
53
serves as heating elements
53
a.
The conductor layer
62
b
extending rightward in
FIG. 9
serves as the individual electrodes
56
, whereas the conductor layer
62
a
extending leftward in
FIG. 9
serves as comb-tooth electrodes
54
a.
Further, an anti-oxidation film
63
and a protective film
64
are formed to cover the heating elements
53
a
and the conductor layers
62
a,
62
b
while exposing the wire-bonding pad of each individual electrode
56
.
An aggregate board divisible into a plurality of substrates
52
may be used for forming the glaze layer
61
, the resistor layer
53
, the conductor layers
62
a,
62
b
and the anti-oxidation film
63
A. A protective film
64
is further formed on the aggregate board thus formed with the anti-oxidation film
63
. Specifically, the protective film
64
may be formed in the following manner for example. First, a resist layer
65
is formed to cover the region, including the wire-bonding pads, which is not to be covered with the protective film
64
. Then, a Ta
2
O
5
film for example may be formed by chemical vapor deposition or spattering. Subsequently, the resist layer
65
is etched away. The aggregate board thus formed with the protective film
64
is then divided into a plurality of individual substrates
52
to each of which drive ICs
57
are mounted. The drive ICs
57
and the individual electrodes
56
are connected by wire-bonding for example to provide a thermal printhead
51
.
However, according to the method described above, the thermal printhead
51
is prepared by dividing the aggregate board after forming the protective film
64
. Accordingly, the divisional surface
66
, namely the side surface of the substrate
52
along the longitudinal side
52
a
at longitudinal edge of each layer
61
,
53
,
62
a,
63
, are not formed with the protective film
64
. Thus, the divisional surface
66
is exposed. Generally, the division of the aggregate board is performed, for example, by providing a nick along a scribing line and then applying stress therealong. This results in irregularities at the divisional surface
66
, which is, therefore, in poor condition. In this way, the divisional surface
66
of the thermal printhead
51
is not only in a poor condition but also is exposed. Accordingly, during handling of the thermal printhead
51
such as incorporation into a casing, the edge of the substrate
52
along the longitudinal side
52
a
or the edges of the layers
61
,
53
,
62
a,
63
may chip or break if the side surface of the substrate
52
along the longitudinal side
52
a
comes into contact with the casing or any other object.
Further, since the protective film
64
is formed by first forming the resist layer
65
and then removing the resist layer
65
after the growth of the protective film, an edge
64
a
of the protective film
64
results in a step which is equivalent in height to the thickness to the protective layer
64
. When the thermal printhead
51
having such a step at the edge
64
a
of the protective film
64
is incorporated in an image forming apparatus, an edge of a recording paper
67
transferred in contact with the heating elements
53
a
may get caught at the step. In such a case, the image forming apparatus recognizes a paper jam because the recording paper
67
does not reach the heating elements
53
a,
thus resulting in stoppage of the apparatus.
Another method of making a thermal printhead is also proposed wherein a plurality of substrates
71
are laminated in such a manner as to expose a film-forming portion of each substrate
71
which is subsequently formed with a protective film by spattering (See e.g. JP-A-5-92596), as shown in FIG.
10
. At the time of forming a glaze layer on the substrate
71
, a plurality of projections
72
each made of the same material as the glaze layer are formed in a row on the surface of the substrate. These projections
72
are provided to prevent the laminated substrates
71
from rubbing against each other to avoid damaging of the individual electrodes or other elements due to such rubbing.
However, such a method makes it necessary to provide a mounting space on the surface of the substrate
71
for mounting the plurality of projections, which may bar increasing the density of the wiring pattern. Moreover, depending on the location of the projections
72
, the edge of the recording paper may get caught at the projections
72
during the recording operation of the thermal printhead.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to prevent a thermal printhead from partially breaking due to the bad surface condition and to minimize the likelihood that a recording paper gets caught in during the recording.
In accordance with a first aspect of the present invention, there is provided a thermal printhead comprising: a multiplicity of heating elements formed in a row on an obverse surface of an elongated substrate at a portion which is offset widthwise toward one longitudinal side of the substrate, and a protective film formed on the obverse surface of the substrate at the widthwise offset portion for covering the heating elements, wherein the protective film is formed to extend on the obverse surface of the substrate continuously from the widthwise offset portion onto one longitudinal side surface of the substrate, and wherein a longitudinal edge of the protective film directed toward the other longitud
Hayashi Hiroaki
Yamade Takumi
Yokoyama Eiji
Bednarek Michael D.
Hilten John S.
Rohm & Co., Ltd.
Shaw Pittman LLP
Williams Kevin D.
LandOfFree
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