A heating substrate for a thin film thermal print head

Abstract

The utility model relates to thermal printing head manufacturing technical field, specifically is a kind of can inhibit the small hillock of aluminium electrode wire near heating resistor body produce, and further improve the stability of electrode wire and the adhesion of upper layer insulating protective layer Thin film thermal printing head heating substrate, the upper surface of electrode wire is also provided with high hardness alloy layer of hardness greater than 2000HV, the one end of electrode wire covers heating resistor body, the other end extends to the edge of substrate from heating resistor body, in turn forms individual electrode and bonding electrode located at the edge of substrate, the high hardness alloy layer extends to the above individual electrode along the edge of ceramic substrate, and does not cover bonding electrode, compared with prior art, can inhibit the grain boundary diffusion of aluminium atom and the compression stress generated by absorption aluminium film, and further inhibit the generation of small hillock and improve the coverage and adhesion of electrode wire upper layer insulating protective layer, improve the service life and printing effect of thin film thermal printing head.

Description

Technical fields:

[0001] This utility model relates to the field of thermal printhead manufacturing technology, specifically a heating substrate for a thin-film thermal printhead that can suppress the formation of hillocks on the aluminum electrode wires near the heating resistor, thereby improving the stability of the electrode wires and the adhesion of the upper insulating protective layer. Background technology:

[0002] We know that the main component of the heating substrate for a thin-film thermal printhead is an insulating substrate with an amorphous glaze coating on its surface. A heating resistor layer and a pure aluminum conductor layer covering the heating resistor layer are sequentially formed on the amorphous glaze coating of the insulating substrate. During manufacturing, the pure aluminum conductor layer is formed into pure aluminum electrode wires by photolithography, and the resistor layer is formed into several heating resistors arranged along the main printing direction. Then, using a non-conductive material whose main component is silicon, an insulating thin film protective layer and a conductive hard protective layer are sequentially formed on the heating resistors and at least some of the pure electrode wires by magnetron sputtering.

[0003] However, due to stress changes caused by heating during the production process, the pure aluminum electrode wires experience internal stress release, resulting in hillocks. The presence of these hillocks affects the bonding strength between the upper insulating film protective layer and the aluminum electrode wire layer, as well as the coverage of the insulating protective layer, thus reducing product reliability, lifespan, and printing quality. To address these issues, patent document CN216659329U mentions using an aluminum-neodymium alloy for the first electrode to suppress hillocks near the heating element. However, this existing solution suffers from the high cost of aluminum-neodymium alloys and the excessive hardness of the aluminum-neodymium alloy pads, leading to poor IC bonding. Furthermore, thermal printhead products also suffer from the problem of electrode corrosion due to ion migration effects in high-temperature and humid environments. Summary of the Invention:

[0004] This invention addresses the shortcomings and deficiencies of existing technologies by proposing a heating substrate for thin-film thermal printheads that can suppress the formation of hillocks and corrosion of aluminum electrodes near the heating resistor, thereby improving the stability of the electrode wires and the adhesion of the upper insulating protective layer.

[0005] This utility model achieves its purpose through the following measures:

[0006] A heating substrate for a thin-film thermal printhead includes a ceramic substrate, a substrate glaze layer, a heat storage glaze layer, a heating resistor and electrode wires above the heat storage glaze layer, the electrode wires being aluminum wires, and an insulating protective layer covering the heating resistor and part of the electrode wires. The electrode wires are characterized by having a high-hardness alloy layer with a hardness greater than 2000 HV on their upper surface. One end of the electrode wire covers the heating resistor, and the other end extends from the heating resistor to the edge of the substrate, sequentially forming individual electrodes and bonding electrodes located at the edge of the substrate. The high-hardness alloy layer extends along the edge of the ceramic substrate, covering the individual electrodes but not the bonding electrodes.

[0007] The high-hardness alloy layer of this invention has a thickness of 5nm to 50nm, serving as a high-hardness transition layer on top of the aluminum electrode conductor to suppress grain boundary diffusion of aluminum atoms and absorb the thermal stress generated by the aluminum film.

[0008] The resistivity of the high-hardness alloy layer described in this invention is less than 150 μΩ·cm. It can be a titanium nitride alloy layer or a titanium boride alloy layer. The resistivity of less than 150 μΩ·cm enables the high-hardness alloy layer to have high conductivity, thereby inhibiting electrode migration and corrosion and improving electrode life.

[0009] The thickness of the substrate glaze layer of this invention is set in the range of 5 to 20 μm, covering the surface of the ceramic substrate. The thickness of the heat storage glaze layer is 20 to 60 μm and the width is 0.4 to 1.0 mm. The heat storage glaze layer is set along the long side of the ceramic substrate, and the high hardness alloy layer extends along the edge of the long side of the ceramic substrate to cover the individual electrodes.

[0010] The upper surface of the insulating protective layer of this utility model is also provided with a conductive wear-resistant protective layer. The target material is mainly composed of carbon and silicon carbide composite. A DC or AC magnetron sputtering device is used, and a mixed gas of argon is introduced as the working gas to form a protective layer with a thickness of several thousand nm on the insulating film protective layer. This is the prior art and will not be described in detail.

[0011] The beneficial effects of this invention are that by forming a thin, high-hardness alloy layer on the upper region of the pure aluminum conductor, the conductivity of the aluminum electrode conductor is preserved, and the high-hardness alloy layer on the upper layer of the aluminum electrode conductor strengthens the grain boundaries of aluminum atoms, forming a transition layer with higher hardness on the upper layer of the pure aluminum conductor. This can suppress the diffusion of aluminum atoms at the grain boundaries and absorb the compressive stress generated by the aluminum film, thereby suppressing the formation of hillocks and improving the coverage and adhesion of the upper insulating protective layer of the electrode conductor, thus improving the service life and printing effect of the thin-film thermal printhead. Attached image description:

[0012] Appendix Figure 1This is a cross-sectional view of the substrate for the thin-film thermal printhead of this utility model.

[0013] Reference numerals: 10: Insulating substrate; 20: Heat storage base glaze layer; 30: Substrate base glaze layer; 40: Heating resistor; 50a: Individual electrode near the heating resistor; 50b: Individual electrode near the bonding electrode; 50c: Bonding electrode; 60: High hardness alloy layer; 70: Insulating protective layer; 80: Conductive protective layer. Detailed Implementation

[0014] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0015] Example 1:

[0016] This example proposes a heating substrate for a thin-film thermal printhead, wherein the insulating substrate (10) is made of aluminum oxide and is sintered at 1600℃. A base glaze glass paste is printed on all areas of the insulating substrate (10) and sintered at 1200-1300℃ to form a substrate base glaze (30). After sintering, the thickness of the substrate base glaze layer is set in the range of 5-20μm.

[0017] A heat-storing base glaze layer (20) is formed by printing and sintering on a portion of the surface of the long side of the insulating substrate on which the base glaze is formed. The sintering temperature is about 600℃~850℃. The thickness of the heat-storing base glaze layer (20) is 20~60μm and the width is 0.4~1.0mm.

[0018] By controlling the process conditions, a tantalum-silicon dioxide composite target is sputtered using a sputtering method to form a heating resistor layer on the heat storage base glaze layer (20) and the substrate base glaze layer (30). The thickness of the heating resistor layer is 20-500nm. The heating resistor layer is patterned by photolithography and etching to form a heating resistor (40).

[0019] On the surfaces of the heat storage base glaze layer (20), the substrate base glaze layer (30), and the heating resistor (40), a pure aluminum wire electrode layer with a thickness of 0.5 to 1 μm is formed by magnetron sputtering using a metal aluminum target. Then, a titanium nitride alloy layer is formed on the pure aluminum wire electrode layer. The pure aluminum wire electrode layer and the aluminum-tantalum alloy layer are then patterned using photolithography and etching. After the patterning is completed, individual electrodes (including 50a near the heating resistor and 50b near the bonding electrode) and bonding electrodes (50c) are formed on the wire electrode layer. The lead wire (50a) of the heating resistor is connected to both ends of the heating resistor (40) to form a heating resistor unit. The bonding electrode (50c) is used to connect external logic control signals. Then, using magnetron sputtering, an insulating protective layer (70) is formed on the surface of the heat storage base glaze layer (20), the substrate base glaze layer (30), the heating resistor (40) and the titanium nitride alloy layer (60), with a thickness of 3 to 8 μm.

[0020] Using carbon-silicon carbide composite material as the target material, a conductive protective layer (80) is formed on the insulating protective layer (70) by DC magnetron sputtering. The thickness of the conductive protective layer (80) is 3-8 μm.

[0021] This example demonstrates how forming a thin titanium nitride alloy layer on top of a pure aluminum conductor preserves the conductivity of the aluminum electrode conductor while reinforcing the grain boundaries of aluminum atoms. This creates a high-hardness transition layer on top of the pure aluminum conductor, which inhibits grain boundary diffusion of aluminum atoms and absorbs compressive stress generated by the aluminum film. This, in turn, suppresses hillock formation and improves the coverage and adhesion of the insulating protective layer on top of the electrode conductor, thereby enhancing the lifespan and printing quality of the thin-film thermal printhead.

[0022] Example 2:

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] This example proposes a heating substrate for a thin-film thermal printhead, wherein the insulating substrate (10) is made of aluminum nitride and is sintered at 1600℃. The base glaze glass paste is printed on all areas of the insulating substrate (10) and sintered at 1200~1300℃ to form a substrate base glaze (30). After sintering, the thickness of the substrate base glaze layer is set in the range of 5~20μm.

[0025] A heat-storing base glaze layer (20) is formed by printing and sintering on a portion of the surface of the long side of the insulating substrate on which the base glaze is formed. The sintering temperature is about 600℃~850℃. The thickness of the heat-storing base glaze layer (20) is 20~60μm and the width is 0.4~1.0mm.

[0026] A tantalum-silicon carbide composite target is sputtered to form a heating resistor layer on the heat storage base glaze layer (20) and the substrate base glaze layer (30). The thickness of the heating resistor layer is 20-500 nm. The heating resistor layer is patterned using photolithography to form a heating resistor (40). On the surface of the heat storage base glaze layer (20), the substrate base glaze layer (30), and the heating resistor (40), a pure aluminum wire electrode layer with a thickness of 0.5-1 μm is formed using a metal aluminum target and magnetron sputtering. Then, a pure aluminum wire electrode layer is formed on the pure aluminum target. A titanium boride alloy layer is formed on top of the wire electrode layer; then, a photolithography process is used to pattern the pure aluminum wire electrode layer and the titanium boride layer. After the patterning process is completed, individual electrodes (including 50a near the heating resistor and 50b near the bonding electrode) and bonding electrode (50c) are formed on the wire electrode layer. The lead wire (50a) of the heating resistor is connected to both ends of the heating resistor (40) to form a heating resistor unit. The bonding electrode (50c) is used to connect external logic control signals.

[0027] Then, using magnetron sputtering, an insulating protective layer (70) is formed on the surface of the heat storage base glaze layer (20), the substrate base glaze layer (30), the heating resistor (40) and the titanium boride alloy layer (60), with a thickness of 3 to 8 μm.

[0028] Using a carbon-silicon carbide composite material as the target, a conductive protective layer (80) is formed on the insulating protective layer (70) by DC magnetron sputtering. The thickness of the conductive protective layer (80) is 3 to 8 μm.

[0029] This example demonstrates how forming a thin titanium boride alloy layer on top of a pure aluminum conductor preserves the conductivity of the aluminum electrode conductor while reinforcing the grain boundaries of aluminum atoms. This creates a high-hardness transition layer on top of the pure aluminum conductor, which inhibits grain boundary diffusion of aluminum atoms and absorbs compressive stress generated by the aluminum film. This, in turn, suppresses hillock formation and improves the coverage and adhesion of the insulating protective layer on top of the electrode conductor, thereby enhancing the lifespan and printing quality of the thin-film thermal printhead.

Claims

1. A heating substrate for a thin-film thermal printhead, comprising a ceramic substrate, a substrate glaze layer on the ceramic substrate, a heat storage glaze layer on the substrate glaze layer, a heating resistor and electrode wires above the heat storage glaze layer, wherein the electrode wires are aluminum wires, and an insulating protective layer covering the heating resistor and part of the electrode wires, characterized in that... The upper surface of the electrode wire is also provided with a high-hardness alloy layer with a hardness greater than 2000HV. One end of the electrode wire covers the heating resistor, and the other end extends from the heating resistor to the edge of the substrate, forming individual electrodes and bonding electrodes located at the edge of the substrate in sequence. The high-hardness alloy layer extends along the edge of the ceramic substrate to cover the individual electrodes, but does not cover the bonding electrodes.

2. The heating substrate for a thin-film thermal printhead according to claim 1, characterized in that, The resistivity of the high-hardness alloy layer is less than 150 μΩ·cm.

3. The heating substrate for a thin-film thermal printhead according to claim 1, characterized in that, The thickness of the high-hardness alloy layer is between 5 nm and 50 nm.

4. The heating substrate for a thin-film thermal printhead according to claim 1, characterized in that, The heat-storing base glaze layer is disposed along the long side of the ceramic substrate, and the high-hardness alloy layer extends along the edge of the long side of the ceramic substrate to cover the individual electrodes.

5. The heating substrate for a thin-film thermal printhead according to claim 1, characterized in that, The thickness of the substrate glaze layer is set in the range of 5 to 20 μm, covering the surface of the ceramic substrate. The thickness of the heat storage glaze layer is 20 to 60 μm, and the width is 0.4 to 1.0 mm.

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