Heating substrate for thermal printing head

Abstract

The utility model provides a heating substrate for a thermal printing head. The heating substrate comprises an insulating substrate, the ground coat layer is arranged on the upper surface of the insulating substrate; the electrode layer and the driving IC are arranged on the upper surface of the insulating substrate, and the electrode layer comprises a bonding pad, an electrode wire and a COM wire; the heating resistor body is arranged on the electrode wire and is positioned above the ground coat layer; the thermal expansion coefficient of the second insulation protection layer is 6.8-7.6 ppm / DEG C. The first insulation protection layer is arranged on the portion, not bonded with the driving IC, of the electrode wire, the heating resistor and the COM wire, and the second insulation protection layer is arranged on the driving IC and the portion, located on the periphery of the driving IC, of the first insulation protection layer. And the maximum value of the thickness does not exceed 0.7 mm. According to the technical scheme of the utility model, the problem of product failure caused by water absorption or mismatching of thermal expansion coefficients of conventional epoxy resin packaging glue in a high-temperature processing link can be effectively solved.

Description

Technical Field

[0001] This utility model relates to the field of thermal printhead technology, specifically, it provides a heating substrate for thermal printheads. Background Technology

[0002] The existing thermal printer heating substrate consists of an insulating substrate, a base glaze layer disposed on the surface of the insulating substrate, and electrode wires and heating resistors disposed above the base glaze layer. The electrode wires and heating resistors are covered with a wear-resistant insulating protective layer, while the pads are not covered with an insulating protective layer. The driver IC and the pads on the heating substrate are connected by a BUMP process, and the driver IC is protected by an epoxy resin encapsulant.

[0003] During use, it was found that because epoxy resin encapsulant is hygroscopic, and its coefficient of thermal expansion (20-100 ppm / ℃) is much greater than that of the ceramic heating substrate and the protective layer above the electrode layer (6.8-7.6 ppm / ℃), the epoxy resin encapsulant may crack due to water absorption or cause glass cracks due to the mismatch in coefficients of thermal expansion during subsequent high-temperature pressing or high-temperature reflow, thus leading to product failure. Utility Model Content

[0004] To address the problems existing in the prior art, this utility model provides a heating substrate for thermal printheads with a reasonable structure, simple process, and good weather resistance through embodiments. It can effectively solve the problem of product failure caused by the mismatch between the "water absorption" of epoxy resin encapsulation glue and the coefficient of thermal expansion when the product undergoes subsequent high-temperature treatment.

[0005] The heating substrate for the thermal printhead includes:

[0006] Insulating substrate;

[0007] A base glaze layer disposed on the upper surface of an insulating substrate;

[0008] An electrode layer and a driver IC are disposed on the upper surface of an insulating substrate. The electrode layer includes pads, electrode wires, and COM wires. A portion of the electrode wires is disposed above the base glaze layer, with one end connected to the COM wire and the other end connected to the driver IC.

[0009] A heating resistor disposed on the electrode wire and located above the base glaze layer;

[0010] The first insulating protective layer and the second insulating protective layer with a thermal expansion coefficient of 6.8 to 7.6 ppm / ℃, wherein the first insulating protective layer is disposed on the portion of the electrode wire that is not bonded to the driver IC, above the heating resistor and the COM wire, the second insulating protective layer is disposed above the driver IC and above a portion of the area around the driver IC, and the maximum thickness of the first insulating protective layer does not exceed 0.7 mm.

[0011] In some embodiments, the second insulating protective layer does not cover the pads.

[0012] In some embodiments, the width of the second insulating protective layer covering the first insulating protective layer is not less than 1.5 mm.

[0013] In some embodiments, the maximum thickness of the second insulating protective layer does not exceed 0.5 mm.

[0014] In some embodiments, the thickness of the pads and the COM wires are equal and greater than the thickness of the electrode wires.

[0015] In some embodiments, the porosity of the second insulating protective layer ranges from 1% to 3%.

[0016] In some embodiments, the second insulating protective layer is a protective layer formed after the aluminosilicate slurry has been cured.

[0017] The thermal printhead heating substrate provided by this utility model has a second insulating protective layer above the driver IC, which has a thermal expansion and deformation similar to that of the ceramic substrate and the first insulating protective layer. This ensures that during subsequent high-temperature pressing or high-temperature reflow processes, the second insulating protective layer will not absorb water, thus reducing its bonding strength with the driver IC. This significantly reduces the packaging thickness of the insulating protective layer, facilitating product miniaturization. Furthermore, because its thermal deformation is consistent with that of the ceramic substrate and the first insulating protective layer, it effectively avoids excessive stress and glass cracking caused by mismatched thermal expansion, significantly improving product stability and quality. Attached Figure Description

[0018] Figure 1 This is a structural diagram of the heating substrate for a thermal printhead provided according to an embodiment of the present invention;

[0019] Figure 2 for Figure 1 Cross-sectional view along the AA direction;

[0020] Figure 3 This is a comparative schematic diagram of two embodiments of the present invention.

[0021] Numbers in the diagram

[0022] Insulating substrate 1, base glaze layer 2, electrode wire 3-1, solder pad 3-2a, COM wire 3-2b, heating resistor 4, first insulating protective layer 5, driver IC 6, second insulating protective layer 7. Detailed Implementation

[0023] The present invention will now be further described based on preferred embodiments and with reference to the accompanying drawings.

[0024] Furthermore, for ease of understanding, various components on the drawings have been enlarged or reduced, but this is not intended to limit the scope of protection of this utility model.

[0025] In the description of the embodiments of this utility model, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this utility model is in use, are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this utility model. Furthermore, in the description of this utility model, the terms "first," "second," etc., are used to distinguish different units, but these are not limited by the manufacturing order, nor should they be construed as indicating or implying relative importance. Their names may differ in the detailed description and claims of this utility model.

[0026] The terminology used in this specification is for illustrative purposes and is not intended to limit the scope of the invention. It should also be noted that, unless otherwise explicitly stated and limited, the terms "set," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, a direct connection, or an indirect connection via an intermediate medium; or they can refer to the internal communication between two components. Those skilled in the art will understand the specific meaning of these terms in this invention.

[0027] As analyzed in the background section, in existing thermal printhead substrates, insulation protection for the driver IC components is generally achieved by applying an epoxy resin encapsulating layer on top of them. During actual use, the applicant discovered that the epoxy resin encapsulating layer cracked, or cracks appeared in the glass insulating protective layer above the electrode wires, during subsequent high-temperature bonding or high-temperature reflow processes on the aforementioned thermal printhead substrates using the epoxy resin encapsulating layer.

[0028] Analysis revealed that the above problems were caused by the following: epoxy resin has a certain degree of water absorption, and during high-temperature pressing or high-temperature reflow, the epoxy resin encapsulant will crack due to water absorption. In addition, since its coefficient of thermal expansion ranges from 20 to 100 ppm / ℃, which is much greater than that of ceramic insulating substrates and glass insulating protective layers (6.8 to 7.6 ppm / ℃), increasing the thickness or contact area to improve the bonding strength of the epoxy resin encapsulant will cause glass cracks due to the mismatch in their coefficients of thermal expansion, thus leading to product failure.

[0029] To address the aforementioned problems, this utility model provides a novel heating substrate for thermal printheads. Figure 1 This is a schematic diagram of the structure of the heating substrate in some embodiments. Figure 2 for Figure 1 AA section view in the image.

[0030] refer to Figure 1 , Figure 2 The thermal printhead heating substrate includes an insulating substrate 1, a base glaze layer 2, an electrode layer, a driver IC 6, a heating resistor 4, a first insulating protective layer 5, and a second insulating protective layer 7.

[0031] The substrate has a base glaze layer 2 on its upper surface; a driver IC 6 and an electrode layer on its upper surface, the electrode layer including pads 3-2a, electrode wires 3-1 and COM wires 3-2b, wherein a portion of the electrode wires 3-1 is disposed above the base glaze layer 2, one end of which is connected to the COM wires 3-2b and the other end is connected to the driver IC 6; a heating resistor 4 is disposed on the electrode wires 3-1 and above the base glaze layer 2; a first insulating protective layer 5 is disposed above the portion of the electrode wires 3-1 that is not bonded to the driver IC 6, above the heating resistor 4 and the COM wires 3-2b; a second insulating protective layer 7 is disposed above the driver IC 6 and above a portion of the area surrounding the driver IC 6, the maximum thickness of which does not exceed 0.7 mm and the coefficient of thermal expansion is in the range of 6.8 to 7.6 ppm / ℃.

[0032] like Figure 1 , Figure 2As shown, by placing a second insulating protective layer 7 above the driver IC6, which has a thermal expansion deformation equivalent to that of the insulating substrate 1 and the first insulating protective layer 5, waterproof encapsulation is achieved. This ensures that during subsequent high-temperature pressing or high-temperature reflow processes, the protective layer will not absorb water, thus reducing its bonding strength with the driver IC. Consequently, the encapsulation thickness of the insulating protective layer can be significantly reduced, facilitating product miniaturization. Furthermore, since its thermal deformation is consistent with that of the first insulating protective layer 5, it effectively avoids excessive stress and glass cracking caused by mismatched thermal expansion, significantly improving product stability and quality.

[0033] The preferred embodiment of the heating substrate for the thermal printhead will be described below.

[0034] like Figure 1 and Figure 2 As shown, firstly, a base glaze layer 2 is formed on the upper surface of the insulating substrate 1 by screen printing and sintering. Then, a metal layer is formed on the insulating substrate 1 by screen printing and sintering. Finally, an electrode layer including electrode wires 3-1, pads 3-2a, and COM wires 3-2b is formed by processes such as coating, light leakage, and etching.

[0035] In some embodiments, the thickness of the pads 3-2a and the COM wires 3-2b is equal, ranging from 18.5um to 21.5um, and the thickness of the electrode wires 3-1 ranges from 2 to 4um.

[0036] Among them, pad 3-2a is used to transmit communication signals, COM wire 3-2b is used to connect power supply, and electrode wire 3-1 is comb-shaped and disposed between pad 3-2a and COM wire 3-2b. A portion of it extends from one side of the base glaze layer 2 to the other side of the base glaze layer 2 (in this utility model, the area covered by the electrode wire 3-1 above the base glaze layer 2 is called the central area), and is connected to COM wire 3-2b through one end; the other end is connected to driver IC6, wherein driver IC6 is connected to the substrate through BUMP process.

[0037] Furthermore, in the central area of ​​the electrode wire 3-1 (i.e., the part of the electrode wire 3-1 located above the base glaze layer 2), a resistive paste is drawn or printed, and then sintered to form a heating resistor 4. Then, except for the pads 3-2a and the part of the electrode wire 3-1 that is bonded to the driver IC 6, glass paste is printed on the other parts of the electrode wire 3-1 and above the heating resistor 4 and the COM wire 3-2b, and then sintered to form a first insulating protective layer 5 of wear-resistant glass material.

[0038] Finally, a regularly shaped, smooth aluminosilicate slurry is applied above the driver IC6 and a portion of the first insulating protective layer 5 around the driver IC6 using a casting or printing process. This slurry is then cured by heating or infrared radiation to form the second insulating protective layer 7. This second insulating protective layer 7, after molding, has a maximum height of no more than 0.7 mm, achieving a firm bond with the driver IC6. It also possesses excellent waterproof and corrosion-resistant properties, preventing detachment due to water absorption and expansion. Furthermore, its coefficient of thermal expansion is between 6.8 and 7.6 ppm / ℃, matching the first insulating protective layer 5, resulting in good thermal stability. Therefore, it effectively prevents cracking caused by mismatched thermal expansion during subsequent high-temperature pressing or high-temperature reflow.

[0039] It should be noted that, without departing from the technical concept of this application, other ceramic materials with the same or similar thermal expansion coefficient range can also be selected to make slurry, and the above-mentioned second insulating protective layer 7 can be obtained by heating or infrared radiation.

[0040] In some embodiments, the waterproof performance of the second insulating protective layer 7 can be further improved by reducing its porosity. For example, preferably, the porosity of the second insulating protective layer 7 is in the range of 1%-3%.

[0041] In some embodiments, such as Figure 2 As shown, the second insulating protective layer 7 does not contact the pad 3-2a, that is, it does not cover the pad 3-2a, so as to avoid affecting signal transmission.

[0042] As mentioned above, since the second insulating protective layer 7 has thermal expansion deformation characteristics that match those of the first insulating protective layer 5, its insulating encapsulation range can be further increased to achieve a better waterproof and insulating protection effect. In some preferred embodiments, the width of the second insulating protective layer 7 covering the first insulating protective layer 5 is not less than 1.5 mm.

[0043] By expanding the coverage area of ​​the second insulating protective layer 7, its bonding with the driver IC 6 and the first insulating protective layer 5 is strengthened. Therefore, its thickness can be further reduced, such as... Figure 3 As shown, in some preferred embodiments, the maximum thickness of the second insulating protective layer 7 can be further reduced to 0.5 mm.

[0044] The specific embodiments of this utility model have been described in detail above. For those skilled in the art, several improvements and modifications can be made to this utility model without departing from the principle of this utility model, and these improvements and modifications also fall within the protection scope of the claims of this utility model.

Claims

1. A heating substrate for a thermal printhead, comprising: Insulating substrate; A base glaze layer disposed on the upper surface of an insulating substrate; An electrode layer and a driver IC are disposed on the upper surface of an insulating substrate. The electrode layer includes pads, electrode wires, and COM wires. A portion of the electrode wires is disposed above the base glaze layer, with one end connected to the COM wire and the other end connected to the driver IC. A heating resistor disposed on the electrode wire and located above the base glaze layer; Its characteristic is that it further includes: The first insulating protective layer and the second insulating protective layer with a thermal expansion coefficient of 6.8 to 7.6 ppm / ℃, wherein the first insulating protective layer is disposed on the portion of the electrode wire that is not bonded to the driver IC, above the heating resistor and the COM wire, the second insulating protective layer is disposed above the driver IC and above a portion of the area around the driver IC, and the maximum thickness of the first insulating protective layer does not exceed 0.7 mm.

2. The heating substrate for a thermal printhead according to claim 1, characterized in that, The second insulating protective layer does not cover the pads.

3. The heating substrate for a thermal printhead according to claim 1, characterized in that, The width of the second insulating protective layer covering the first insulating protective layer is not less than 1.5 mm.

4. The heating substrate for a thermal printhead according to claim 3, characterized in that, The maximum thickness of the second insulating protective layer shall not exceed 0.5 mm.

5. The heating substrate for a thermal printhead according to claim 1, characterized in that, The thickness of the pads and the COM wires is equal and greater than the thickness of the electrode wires.

6. The heating substrate for a thermal printhead according to any one of claims 1 to 5, characterized in that, The porosity of the second insulating protective layer ranges from 1% to 3%.

7. The heating substrate for a thermal printhead according to claim 6, characterized in that, The second insulating protective layer is a protective layer formed after the aluminosilicate slurry is cured.

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