JPH04112049A - Thermal head - Google Patents

Abstract

PURPOSE:To improve yield on manufacture by forming a common conductor connected in common with each terminal of a plurality of driver circuit elements onto a substrate and making the nearest space of the common conductor and a common electrode shorter than those of the common conductor and each discrete electrode. CONSTITUTION:A plurality of driver circuit elements 23 formed at every discrete electrode 31 are arrayed in parallel with a heating resistor row 22 on resistor layers 28, and a common grounding electrode 34 connected in common with each driver circuit element 23 is formed at the distance d6 of the projecting section of the discrete electrode 31. A projecting section 39 facing at a distance d7 smaller than the distance d6 to the common grounding electrode 34 is formed integratelly to the extending section 38 of a common electrode 30. A discharge phenomenon is generated first between the common grounding electrode 34 and the projecting section 39 of the common electrode 30. Accordingly, the flowing of excess currents through a heating resistor 32 and the thermal change of properties by excess Joule heat can be prevented, thus improving yield on the manufacture of a thermal head 21.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to thermal heads, and more particularly to improving the wiring pattern of thermal heads in order to improve the manufacturing yield of thermal heads.

FIG. 11 is a cross-sectional view of a typical thermal nozzle 1.
FIG. 12 is a plan view of the thermal head 1. In the thermal head 1, a glaze layer 3 made of glass or the like is formed on an electrically insulating head substrate 2 made of ceramic or the like. On this glaze layer 3, a resistor layer 4 made of tantalum nitride Ta2N or the like is formed over almost the entire surface of the head substrate 2 by a thin film technique such as sputtering or lithography. A pattern of aluminum or the like is formed on this resistor layer 4 using the thin film technique described above, and a common electrode 5 is formed on the resistor layer 4.
and form a plurality of individual electrodes 6.

The portion of the resistor layer 4 sandwiched between the common electrode 5 and the individual electrodes i6 is configured as a plurality of heat generating resistors 7 that are linearly connected in the left-right direction in FIG.

The common electrode 5 includes an electrode portion 8 extending parallel to the arrangement direction of the heating resistors 7, and an extension portion 9 extending from one end of the electrode portion 8 along the outer periphery of the head substrate 2. Ru.

Further, a common conductor 10 extending in the same direction as the arrangement direction of the heating resistors 7 in the same process as the individual electrodes 6, etc., is provided at a distance d1 from the individual electrodes 6 and the extension portions 9. Open d2 and form! Take. On this common conductor 10, a plurality of drive circuit elements 11 are provided along the arrangement direction of the heat generating resistors 7, which are connected to a predetermined number of individual electrodes and selectively drive the heat generating resistors 7 to generate heat.

The common electrode 5 is supplied with energizing power for the heating resistor 7 by a circuit not shown, and selectively connects one or more of the plurality of individual electrodes 6 to which the drive circuit element 11 is connected to the common conductor. By disconnecting the connection 7 to 10, the heating resistor 7 is energized and an angry printing is performed.

[Problems to be Solved by the Invention] In manufacturing the conventional thermal head 1, the common electrode 5, the individual electrodes 6, and the common conductor 10 are formed as follows. As shown in FIG. 13, a glaze layer 3 and a resistor layer 4 are formed on the head substrate 2, and when the resistor layer 4 is patterned, a third metal layer such as aluminum is coated on the head substrate 2. . . . It is formed into a thin film by talishing or vapor deposition, and a rest layer 12 is patterned by photolithography on this, and a through hole 13 is formed in the area where the heating resistor 7 is to be formed. Thereafter, by performing a predetermined etching process, the metal layer is patterned, and the common type ff15. Individual electrodes 6 and common conductor 10
A heating resistor 7 as described above is formed by forming a pattern.

At this time, in the through hole 13, the metal layer is dissolved and cationized by etching, so that the emitted electrons are accumulated on the surface of the resistor layer 4, as shown in FIG. On the other hand, between the individual electrodes 6 and the common conductor 10, as shown in FIG. There is a capacitance C2, the equivalent circuit of which is shown in FIG.

These capacitances C1 and C2 are connected in parallel as shown in FIG. 13, and once the coupling capacitance C0CO=C1+C
2-11) is assumed as shown in Fig. 15. Here, when charge QO is accumulated on the resistor layer 14 in the through hole 13, a potential difference vO V O= Q O,, " 2 CO,= (2) occurs, the distance between the individual electrode 6 and the common conductor 10 is 1Qffl d1
An electric field E = VO/dl (3) is generated between the two. These equivalent circuits are shown in FIGS. 14 and 15. The resistance value R in these equivalent circuit diagrams is the resistance value of the heating resistor 7.

Generally, the distance ldl between the plurality of individual electrodes 6 and the common conductor 10 is not constant due to manufacturing errors, and the capacitances CI, C2 and coupling capacitance CO also vary. At this time, if the electric field E is lower than the critical electric field EO uniquely determined by the materials of the photoresist layer 12, the glaze layer 3, and the head substrate 2, the individual electrodes 6 and the common conductor 10 are connected as shown in FIG. If a potential difference VO exists between 1 and 1 and the electric field E exceeds the critical electric field EO, then the photoresist layer 12. Dielectric breakdown occurs in the resin layer 3 and the henode substrate 2, and current flows through the heating resistor 7 as shown in FIG. Discharge phenomena such as dielectric breakdown occur in each individual type 8i! 6 and the common conductor 10, but is known to occur at a small number of points starting from a portion with relatively weak insulation strength.

Therefore, the individual electrodes 6a and the common conductor 1 shown in FIG.
0, if dielectric breakdown occurs between the remaining individual electrodes 6
The charges accumulated in the heat generating resistor 7 flow in a concentrated manner to the individual electrode 6 corresponding to the location where dielectric breakdown has occurred, causing an excessive current to flow through the heat generating resistor 7.

In such a case, the heating resistor 7 undergoes a combination of electrical, thermal, and oxidative alterations due to the excessive amount of current and excessive Joule heat, and the thermal head 1 becomes unusable. In order to solve these problems, conventional methods have been to change the individual electrodes 6 and the etching solution used, or to adjust the etching pattern, or to reduce the efficiency of the manufacturing process. In addition, if the adjustment of the error conditions as described in 2 is insufficient, the heating resistor 7 will be damaged as described above, and the yield will be significantly reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal head that can solve the above-mentioned technical problems, improve manufacturing yield, improve reliability, and simplify the manufacturing process.

[Means for Solving the Problems] The present invention provides a common electrode commonly connected to one side of a heating element line formed by arranging a plurality of heating elements on a substrate;
A thermal head comprising a plurality of individual electrodes connected to two sides of the heating element line, and a drive circuit element connected to selectively switch the plurality of individual electrodes, the plurality of drive circuit elements A common conductor commonly connected to each terminal of is formed on the substrate, and the closest distance between the common conductor and the common electrode is shorter than the closest distance between the common conductor and each individual electrode. To thermal I).

[For fv] A heating element line consisting of a plurality of heating elements is formed on the substrate of the thermal heating element of the present invention. A common electrode is commonly connected to one side of the heating element line.

Supply driving power to each heating element. A plurality of individual electrodes are connected to the side opposite to the common electrode of the heating element line, and the individual electrodes are connected to a drive circuit element to perform an operation of selectively switching the individual electrodes corresponding to the heating elements driven to generate heat. It will be done.

A common conductor commonly connected to each terminal of each drive circuit element is formed on the substrate, and a drive current that flows into the drive circuit element from the individual electrodes and is output flows into this common conductor. Here, the closest distance between the common conductor and the common electrode is selected to be shorter than the closest distance between the common conductor and each individual electrode. Therefore, when manufacturing the thermal head, the individual electrodes and the
Even if static electricity is accumulated in the heating element between the electrodes, the discharge phenomenon such as dielectric breakdown between the common electrode and individual electrodes and the connecting conductor will occur at the closest distance between them or at the shortest common distance. Occurs between the conductor and the common electrode.

The static electricity previously accumulated in each heating element flows into the common conductor via the common electrode, thereby preventing the heating elements from being deteriorated due to overcurrent and overheating caused by this overcurrent. Therefore, manufacturing yield can be improved and reliability of the thermal head can be improved.

[Embodiment] FIG. 1 is an enlarged plan view of a thermal head 21 according to an embodiment of the present invention, FIG. 2 is a plan view of the thermal head 21, and FIG. FIG. 4 is an enlarged plan view of the shown portion, and FIG. 4 is a sectional view taken along section line IV-IV in FIG. 3. The thermal head 21 is equipped with a plurality of drive circuit elements 23 that drive a heat generating resistor array 22 as a heat generating element line to generate heat, and is made of aluminum oxide A120z.
The present invention includes a head substrate 24 made of ceramic such as, for example, and an external wiring board 25 connected to the head substrate 24 and having circuit wiring formed on a support made of a flexible synthetic resin material or glass epoxy resin material.

On the head/board substrate 24, a glue layer 26 and a thick film electrode layer 27 formed by screen printing silver paste are formed. A resistor layer 28 is formed on this layer to a thickness of several hundred layers using a thin film technique such as sputtering vapor deposition of Ta2N or the like. Furthermore, on top of that, a metal conductor layer such as aluminum is formed by sputtering or vapor deposition.
, 24 is patterned as shown in the second figure, and a common electrode 30 is formed. Further, a plurality of band-shaped individual electrodes 31 are formed, and the heating resistor row 22 consisting of a plurality of heating resistors 32 as heating elements is obtained.

On the resistor layer 28, a plurality of drive circuit elements 23, which are provided for each of the plurality of individual electrodes 31 using the same process and the same material as the individual electrodes 31, are arranged in parallel with the heating resistor row 22. A common grounding conductor [! 34 or individual electrode 31 and distance d
It is formed by leaving 6 blanks. For example, a common ground electrode connecting terminal 35 is integrally formed on this common ground electrode 34 for each drive circuit element 23. Further, a plurality of external connection terminals 36 are provided for each drive circuit element 23 to supply signals, drive power, etc. for individually driving the corresponding heat generating resistor 32 to generate heat.

the common ground electrode connection terminal 35 and the external connection terminal 36;
Alternatively, the common electrode connection terminals 37 formed in the extending portions 38 parallel to the individual mold i31 at both ends of the head substrate 24 in the longitudinal direction of the common electrode 30 are connected to the external wiring substrate 25.
The head board 24 is connected to the head board 24 over the entire length in the left-right direction in FIG.

Further, a protrusion 39 is integrally formed on the extended portion 38 of the common electrode 30 and faces the common ground electrode 34 with a distance d7 smaller than the distance d6.

Covering the common electrode 30 and the vicinity of the individual electrodes 31,
The wear-resistant layer 40 is formed, for example, by sputtering Vika thin film technology. Further, the vicinity of the drive circuit element 23 is coated,
A protective layer 41 made of an electrically insulating material such as epoxy resin is formed.

5 [ ] (1) to (4) are plan views explaining the manufacturing process of the thermal head/soto 21, and FIGS. Line At-A1~A4-A
FIG. The manufacturing process of the thermal head 21 of the above embodiment will be explained with reference to FIGS. 5 and 6. On the head substrate 24, there are shown in FIG.
) and as shown in FIG. 6(1), the glaze layer 2
6 is formed over the entire surface, and the resistor layer 28 is also formed over the entire surface by thin film technology, and then patterned as shown in FIG. 5(1). Subsequently, as shown in FIG. 5(2) and FIG. 6(2), a metal layer 42 of, for example, aluminum is formed on the head substrate 24 on which the resistor layer 28 has been patterned using a thin film technique such as sputtering. Form it over the entire surface.

After 2, as shown in FIG. 5(2), the common electrode 30 and the individual electrodes 31 shown in the first diagram are patterned. Further, in the metal layer 42, a through hole 43 is formed in a region where the heating resistor 32 is to be formed, and the heating resistor 32 defined by the common electrode 30 and the individual electrodes 31 is configured as described above.

Here, when forming the common ground electrode 34 in the same process as the individual electrodes 31, at the stage when the metal layer 42 is formed on the resistor layer 28, the photoresist layer 44 is formed on the metal layer 42, and the heating resistor A pattern for forming a through hole 45 in a region corresponding to the body 32 is exposed and developed to form the through hole 45. Thereafter, by performing a predetermined wet etching, the metal layer 42 exposed in the through hole 45 is dissolved and ionized, and the through hole 43 is formed. In this way, the heating resistor 32 is constructed as described above.

At this time, electrons emitted when the metal material constituting the metal layer 42 is ionized are accumulated on the resistor layer 28 in the through hole 45, as described in the section of the prior art. This lick common electric Ff! 3o, a capacitance C1 as described in the prior art section is formed between the individual electrodes 31 and the common ground electrode 34 via a photoresist layer 44;
In addition, the resistor layer 28, the glaze layer 26, and the head substrate 2
4, a capacitance C2 is constructed. Further, as shown in FIG. 1, the common ground electrode 34 and the protrusion 3 of the common electrode 3°
9, an electrostatic capacitance c3 is provided via the photoresist layer 44, the resistor layer 28, the grid layer 26, and the head substrate 24, with a distance d7 smaller than the distance d6 from the individual mold &31. configured.

FIG. 7(1) shows an equivalent circuit between the coupling capacitance CO shown in the first equation of these capacitances C1 and C2 and the capacitance c3. There is a residual charge on the resistor layer 28 described above between these capacitances C1 and C2. 0, a potential difference o shown in the second equation occurs, and the individual electrode 31 and the common ground electrode 3
Electric field E1 between distance 1idG and 4 E 1 = VO'd6 −
(4> occurs.

i-When the residual charge Q, O is relatively large and the electric field E1 increases, a discharge phenomenon first occurs between the common ground electrode 34 and the protrusion 39 of the common electrode 30. At this time, the residual charge QO in each through hole 43 is transmitted through the common electrode 30 and the protrusion 39 as shown in FIG. 7(2).
into the common ground electrode 34. Therefore, heating resistor 3
In the portion of the resistor layer 28 constituting the resistor layer 2, current only flows due to the movement of the charge remaining in each through hole 45, and an excessive current flows through the heating resistor 32, causing electrical deterioration, and It is possible to prevent thermal deterioration and oxidative deterioration due to excessive Joule heat generated by electric current.

As a result, the manufacturing yield of the thermal head 21 is significantly improved.

According to experiments conducted by the inventor of the present invention, the failure rate of the heating resistor 32 due to the excessive current in the thermal head 21 was about 10 to 20% in the conventional case, but in this embodiment, the heating resistor was destroyed. It has been confirmed that this will prevent the occurrence of defective products.

Furthermore, since the heating resistor 32 is not altered or damaged, the reliability of the thermal conductor 21 can be significantly improved.

On the other hand, in the thermal head 21 as described above, when used for actual thermal printing, the common electrode 3o and the common ground electrode 34 are
A constant driving potential difference, for example 12V or 24V, is applied between the protrusion 39 and the common ground electrode 34, and a leakage current may occur between the protrusion 39 and the common ground electrode 34 under high humidity conditions. In order to prevent such a situation, it is necessary to cover the space between the protrusion 39 and the common ground and the pole 34 to make it moisture resistant. In the embodiment described above, the protective layer 41 made of a synthetic resin material that covers the drive circuit element 23 also covers the vicinity of the protrusion 39. Thereby, there is no need to perform a special moisture-proofing process near the protrusion 39, and the manufacturing process of the thermal head 21 having such characteristics is simplified.

FIG. 8 is an enlarged plan view of a thermal head 21a according to another embodiment of the present invention. This example is similar to the previous example;
Corresponding parts are given the same reference numerals. What is noteworthy about this embodiment is that the portion of the common ground electrode 34 facing the extended portion 38 is placed in a common type [, 30] at a position corresponding to directly below the wear-resistant layer 40, and the individual electrode 31 and the extended portion 38 to form a band-shaped connecting portion 46. The free end of the connection part 46 and the common electrode 30 are separated by a distance d8, and the connection part 46 and the extension part 38 are separated by a distance d9.

Further, the distance d between the connecting portion 46 and the individual electrode 31 at the closest position is
The configuration is such that lo is separated. At this time, distance d6. d8
．． d9. For dlo, d8<d6
...(5) d9>d6 ・
...(6)d10>d6...
Set as in (7).

With this configuration, the discharge phenomenon due to dielectric breakdown described above can be prevented from occurring between the roadside portion of the connection portion 46 and the common electrode 3.
This occurs at a distance d8 from 0. Therefore, this embodiment can also achieve the same effects as those described in the previous embodiments. Further, in this embodiment, the end portion of the connecting portion 46 where a discharge phenomenon occurs and the common electrode 3o are formed in a region covered with the wear-resistant layer 40 described above.

This makes it possible to simplify the manufacturing process described in the above embodiments.

FIG. 9 shows a thermal head 2 according to still another embodiment of the present invention.
It is an enlarged plan view of 1b. This embodiment is similar to the first embodiment described above, and corresponding parts are given the same reference numerals.

The noteworthy point of this embodiment is that the first
In the illustrated configuration, the free end portion of each individual electrode 31 is formed into a trapezoidal end portion 47 having a tapered trapezoidal shape. That is, the angles θ of the respective corners 48 of the trapezoidal end portion 47 are all obtuse angles, for example.

Even in such an embodiment, the same effects as those described in the previous embodiment can be achieved.

Furthermore, in this embodiment, in the shape of the individual electrode 31 shown in the first diagram of the first embodiment, the end portion thereof is chamfered. Electrode 3l and common ground type Ff! 3
4, the occurrence of undesirable discharge phenomena is prevented.

FIG. 10 is a modification of the embodiment shown in FIG.

The free end portion of each individual electrode 31 is formed into an arcuate end portion 49 having a circular arc shape. Even in the thermal head 21c having such a configuration, it is possible to achieve the same effects as those described in each of the above embodiments.

[Effects of the Invention] As described above, according to the present invention, the closest distance between the common conductor and the common electrode through which the drive current that flows into the drive circuit element from the individual electrodes and is outputted is the distance between the common conductor and each individual electrode. It is selected to be shorter than the closest distance to the electrode. Therefore, even if static electricity is accumulated in the heating element between the individual electrodes and the common electrode during the manufacture of the thermal head, discharge phenomena such as dielectric breakdown between the common electrode and the individual electrodes and the connecting conductor will not occur. It occurs between the common conductor and the common electrode with the shortest distance between them.

Therefore, the static electricity accumulated in each heating element flows into the common conductor via the common electrode, causing overheating (overheating) due to overcurrent (force on the heating element) and overcurrent (1). Therefore, it is possible to improve the production by a small amount, and it is possible to improve the reliability of thermal insulation.

[Brief explanation of the drawing]

Figure 1 is an enlarged plan view of the thermal head 21 of an embodiment of the present invention, Figure 2 is a plan view of the thermal head 21, and Figure 3 is a plan view of the thermal head 21 of an embodiment of the present invention.
The figure is a detailed enlarged plan view of the thermal head 21, FIG. 4 is a sectional view taken from the cutting plane line Vl-Vl in FIG. 1, and FIG. 5 is a plan view explaining the manufacturing process of the thermal head 21. , FIG. 6 is a sectional view explaining the manufacturing process of the thermal head 21, FIG. 7 is an equivalent circuit diagram of the thermal head 21, and FIG. 8 is a plan view of a thermal head 21a according to another embodiment of the present invention.
FIG. 9 is a plan view of a thermal head 21b of still another embodiment, and FIG. 10 is a plan view of a thermal head 21b of still another embodiment.
1C is a plan view of 1C, FIG. 11 is a cross-sectional view of a typical conventional example of thermal conductor 1, FIG. 12 is an enlarged plan view of thermal conductor 1, and FIG. The sectional views and FIGS. 14 to 16 are equivalent circuit diagrams illustrating the problems of the conventional example. 21.21a, 21b, 21cm thermal, ・I de,
22... Heating resistor array, 23... Drive circuit element, 24
13. Head substrate, 26...Glaze layer, 28...Resistor layer, 30...Common electrode, 31...Individual electrode, 3
2... Heat generating resistor, 34... Common ground electrode, 39...
・Protrusion, 40... Wear-resistant layer, 41... Protective layer, 47
... Trapezoidal end, 49... Arc-shaped end Agent Patent attorney Number of strokes Keiichi part m5 Figure 6 Sekibori diagram Figure ffi Figure 10 Figure Figure 12 Figure Figure 15 Figure Figure 16

Claims (1)

[Claims] A common electrode commonly connected to one side of a heating element line formed by arranging a plurality of heating elements on a substrate, and a plurality of individual electrodes connected to the other side of the heating element line, respectively. In a thermal head comprising an electrode and a drive circuit element connected to selectively switch a plurality of individual electrodes, a common conductor commonly connected to each terminal of the plurality of drive circuit elements is connected on a substrate. A thermal head characterized in that the distance between the common conductor and the common electrode is shorter than the distance between the common conductor and each individual electrode.