A high reliability thermal printhead
Patent Information
- Application Number
- CN202521616203.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-31
- Publication Date
- 2026-10-09
- Estimated Expiration
- 2035-07-31
AI Technical Summary
[0004]本实用新型针对现有热敏打印头工作时因热应力和湿应力差异造成的界面开裂、分层及失效问题，提供一种能够有效缓解热、湿应力并提高可靠性的高可靠性的热敏打印头
[0012]本实用新型有益效果在于，通过设置过渡层，利用过渡层的热膨胀系数介于耐磨保护层和封装胶的热膨胀系数之间，使该层作为热膨胀系数梯度层，缓和界面间膨胀系数较大的差异，从而降低了因温度变化产生的热应力；同时，过渡层对氧有高亲和力，在沉积过程中能与耐磨保护层(主要成分SiO2)表面的氧原子形成牢固的金属-氧化物化学键(如A-O-Si)，确保了耐磨保护层和过渡层的界面附着力。疏水层阻止外部环境中的液态水或水蒸气渗透至关键的封装界面，从而从根源上抑制了湿应力以及由湿气引发的材料性能退化和界面附着力下降。二者协同作用，同时降低热应力与湿应力，抑制了湿热耦合效应对界面的破坏，显著提高热敏打印头在高温高湿等严苛工作环境下的长期可靠性和使用寿命，降低因环境因素导致的失效率。
Smart Images
Figure CN224828171U_ABST
Abstract
Description
Technical fields:
[0001] This utility model relates to the field of thermal printhead manufacturing technology, specifically a high-reliability thermal printhead with high temperature resistance and low migration. Background technology:
[0002] To ensure operational stability and durability, thermal printheads typically have a glass protective layer over the heating resistor and electrodes. For external circuit connections, organic encapsulation materials are often used to encapsulate certain areas. However, the coefficient of thermal expansion (CTE) of the glass protective layer is generally low, while that of the organic encapsulant is very high. When the printhead operates or the ambient temperature changes, this significant mismatch in CTEs generates substantial thermal stress at the interface. Under repeated temperature cycling, this thermal stress leads to interface fatigue, microcrack initiation and propagation, ultimately causing interface delamination or encapsulation cracking. Furthermore, moisture penetration in high-humidity environments generates superimposed wet stress, causing interface cracking, delamination, and even failure, thus affecting the overall reliability and lifespan of the printhead.
[0003] Current technological approaches are limited, primarily addressing this issue by improving material formulations, such as modifying the glass formulation or adding fillers to the encapsulating adhesive to slightly reduce the difference in thermal expansion coefficients. While these measures reduce thermal stress to some extent, their effectiveness is limited. Under high-temperature and high-humidity conditions, the presence of moisture stress can still damage the interface, causing delamination or cracking. Therefore, material modification alone is insufficient to simultaneously meet the requirements of both high-temperature and high-humidity environments. The problem of effectively suppressing the effects of thermal and moisture stress between the glass protective layer and the encapsulation layer, thus preventing interfacial failure, remains unresolved. Summary of the Invention:
[0004] This invention addresses the problems of interface cracking, delamination, and failure caused by the difference between thermal and wet stress during the operation of existing thermal printheads, and provides a highly reliable thermal printhead that can effectively alleviate thermal and wet stress and improve reliability.
[0005] This utility model achieves its purpose through the following measures:
[0006] A highly reliable thermal printhead includes an insulating substrate with a base glaze layer. Individual electrodes, a common electrode, a heating resistor, and a control IC are disposed on the base glaze layer. A wear-resistant protective layer is provided on the surfaces of the heating resistor, the common electrode, and some of the individual electrodes. An encapsulating adhesive layer is provided on the control IC, with the edge of the encapsulating adhesive layer covering the wear-resistant protective layer. The key feature is that a composite interface structure is provided between the encapsulating adhesive and the wear-resistant protective layer. The planar projection of the composite interface structure completely covers the overlapping area of the wear-resistant protective layer and the encapsulating adhesive layer, and extends 20-100 micrometers outward into the non-overlapping area. The composite interface structure includes a transition layer and a hydrophobic layer located between the wear-resistant protective layer and the encapsulating adhesive layer, wherein the transition layer is located below the hydrophobic layer.
[0007] The transition layer of this invention is made of any one of titanium, nickel, or aluminum, or an alloy of titanium, nickel, or aluminum. The coefficient of thermal expansion of the transition layer is between that of the wear-resistant protective layer and the encapsulating adhesive, and the difference between the coefficient of thermal expansion of the transition layer and the coefficient of thermal expansion of the wear-resistant protective layer is less than or equal to 10 × 10⁻⁶. -6 At / ℃, the coefficient of thermal expansion of the wear-resistant protective layer is 4~6×10. -6 / ℃, the coefficient of thermal expansion of the encapsulating adhesive is 20~60×10 -6 / ℃.
[0008] The transition layer of this invention can be formed by high-temperature sintering, coating and other processes, and has a thickness of 1 to 20 micrometers. The planar projection of the transition layer completely covers the overlapping area of the wear-resistant protective layer and the encapsulating adhesive, and extends 20 to 100 micrometers outward from the non-overlapping area, that is, extends 20 to 100 micrometers away from the control IC.
[0009] The transition layer of this invention has a hydrophobic layer on its surface; the hydrophobic layer is a hydrophobic coating with a contact angle greater than 100°, and can be an organosilicon coating, a fluorinated coating, or a polyvinylidene fluoride coating; the thickness of the hydrophobic layer is 1 to 30 micrometers; the hydrophobic layer completely covers the transition layer on its planar projection and extends outward by 10 to 20 micrometers; the hydrophobic coating can be deposited on the transition layer by spraying, dipping, printing, or physical vapor deposition processes.
[0010] In this invention, a surface treatment layer or a chemical coupling agent layer is provided between the transition layer and the hydrophobic layer, and between the hydrophobic layer and the organic encapsulating adhesive layer, respectively, to enhance the bonding force between the two.
[0011] The insulating substrate of this invention has a base glaze layer on a portion or the entire surface. A comb-shaped individual electrode and a comb-shaped common electrode are disposed on the surface of the base glaze layer, forming a comb-shaped electrode pair. A heating resistor is disposed in the middle of the comb-shaped electrode pair along the main printing direction. One end of the comb-shaped common electrode is connected to the heating resistor, and the other end is connected to a power supply. One end of the comb-shaped individual electrode is connected to the heating resistor, and the other end is connected to a control IC. A wear-resistant protective layer is provided on the surface of the heating resistor and the comb-shaped common electrode, and on a portion of the surface of the comb-shaped individual electrode. The above configuration is a common feature of thermal printhead products.
[0012] The beneficial effects of this invention lie in the fact that by setting a transition layer, utilizing the fact that the coefficient of thermal expansion of the transition layer is between that of the wear-resistant protective layer and the encapsulating adhesive, this layer acts as a gradient layer of thermal expansion coefficient, mitigating the large difference in expansion coefficients between the interfaces, thereby reducing thermal stress caused by temperature changes. Simultaneously, the transition layer has a high affinity for oxygen, and during the deposition process, it can form strong metal-oxide chemical bonds (such as AO-Si) with oxygen atoms on the surface of the wear-resistant protective layer (mainly composed of SiO2), ensuring the interfacial adhesion between the wear-resistant protective layer and the transition layer. The hydrophobic layer prevents liquid water or water vapor from the external environment from penetrating to the critical encapsulation interface, thereby fundamentally suppressing wet stress and the degradation of material properties and decreased interfacial adhesion caused by moisture. The synergistic effect of these two layers simultaneously reduces thermal and wet stress, suppressing the damaging effects of the thermo-hydro-humidity coupling effect on the interface, significantly improving the long-term reliability and service life of the thermal printhead in harsh working environments such as high temperature and high humidity, and reducing the failure rate caused by environmental factors. Attached image description:
[0013] Figure 1 This is a plan view of the present invention.
[0014] Figure 2 This is a cross-sectional schematic diagram of the present invention.
[0015] Reference numerals: 1. Insulating substrate; 2. Base glaze layer; 3. Conductor electrode; 3a. Comb-shaped common electrode; 3b. Comb-shaped individual electrode; 4. Heating resistor; 5. Wear-resistant protective layer; 6a. Transition layer; 6b. Hydrophobic layer; 7. Control IC; 8. Encapsulating adhesive layer. Detailed implementation method:
[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments.
[0017] Example 1
[0018] This embodiment provides a highly reliable thermal printhead, as shown in the attached image. Figure 1 and Figure 2As shown, the system includes an insulating substrate 1, on which a base glaze layer 2 is formed by printing and sintering on a portion or the entire surface. Comb-shaped individual electrodes 3b and a comb-shaped common electrode 3a are formed on the surface of the base glaze layer 2 through screen printing, sintering, and photolithography. A silver COM electrode 3c, with a thickness of 8–20 micrometers, is formed by screen printing and sintering at specific locations to connect to a power supply. The comb-shaped individual electrodes 3b and the comb-shaped common electrode 3a form a comb-shaped electrode pair. A heating resistor 4 is positioned in the middle of the comb-shaped electrode pair along the main printing direction by screen printing or spraying. One end of the comb-shaped common electrode 3a is connected to the heating resistor, and the other end is connected to the power supply. One end of the comb-shaped individual electrode 3b is connected to the heating resistor 4, and the other end is connected to a control IC 7.
[0019] Screen printing is performed on the surfaces of the heating resistor 4 and the comb-shaped common electrode 3a, and on parts of the comb-shaped individual electrodes 3b. The thickness of the wear-resistant protective layer 5 after sintering is controlled at 4–15 micrometers, and the coefficient of thermal expansion of the wear-resistant protective layer is approximately 4–6 × 10⁻⁶. -6 / ℃;
[0020] On the surface of the wear-resistant protective layer 5, in the overlapping area between the wear-resistant protective layer 5 and the encapsulating adhesive 8, a transition layer 6a is formed by sputtering. Using 99.99% pure titanium (Ti) as the target material, sputtering is performed under an argon (Ar) atmosphere. The sputtering power is set to 80W, the argon pressure to 0.5Pa, and the deposition time to 30 minutes. This results in a titanium transition layer with a thickness of approximately 5 micrometers on the wear-resistant protective layer. The coefficient of thermal expansion of the titanium layer is approximately 8.6 × 10⁻⁶. -6 / ℃(;The transition layer 6a completely covers the overlapping area of the wear-resistant protective layer 5 and the encapsulating adhesive 8 on the plane projection, and extends 20-100 micrometers into the non-overlapping area;
[0021] Plasma treatment is applied to the surface of the transition layer 6a, and then a polyvinylidene fluoride (PVDF) hydrophobic layer 6b is formed on the surface of the transition layer by spraying or screen printing. The hydrophobic layer 6b completely covers the transition layer 6a on the plane projection and extends outward by 10 to 20 micrometers with a thickness of 10 to 20 micrometers. It is then cured by ultraviolet light irradiation.
[0022] After plasma treatment of the surface of hydrophobic layer 6b, silane coupling agent is applied by spraying, leveling is performed for 5 minutes, and then cured in an oven at 110°C for 15 minutes.
[0023] After conventional assembly of ICs, resistors, etc., on the surface of the above-mentioned product, epoxy resin encapsulation is applied and cured to complete the thermal printhead assembly. The coefficient of thermal expansion of the epoxy resin encapsulation is approximately 20–60 × 10⁻⁶. -6 / ℃;
[0024] Under the conditions of 121℃, 2atm, and 100%RH for 24 hours of steaming, the above products were tested in 5 units. No cracking or delamination of the encapsulation adhesive, glass protective layer, or the interface between the two occurred, and no Ag migration short circuit was observed during the power-on test. For the comparison product without a composite interface structure, 5 units were tested. The interface between the encapsulation adhesive and the glass protective layer cracked, and the product short-circuited during the power-on test.
[0025] Example 2
[0026] The basic steps are the same as in Example 1, the difference being:
[0027] During the formation of the transition layer, a nickel (Ni) target was used for magnetron sputtering to obtain a nickel transition layer 6a with a thickness of 8 micrometers. The coefficient of thermal expansion of this nickel layer is approximately 13.0 × 10⁻⁶. -6 / ℃, also located between the glass protective layer and the encapsulating adhesive.
[0028] Under the conditions of 121℃, 2atm, and 100%RH for 24 hours of steaming and boiling, five units of the above products were tested. No cracking or delamination occurred in the encapsulation adhesive, glass protective layer, or the interface between the two. No Ag migration short circuit was found during the power-on test.
[0029] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the scope of protection of the present utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the scope of protection of the present utility model.
Claims
1. A high-reliability thermal printhead, comprising an insulating substrate, a base glaze layer on the insulating substrate, individual electrodes, a common electrode, a heating resistor, and a control IC disposed on the base glaze layer, wherein the heating resistor, the common electrode, and some of the individual electrodes are provided with a wear-resistant protective layer, and the control IC is provided with an encapsulating adhesive layer, the edges of which are covered by the wear-resistant protective layer, characterized in that... A composite interface structure is provided between the encapsulating adhesive and the wear-resistant protective layer. The planar projection of the composite interface structure completely covers the overlapping area of the wear-resistant protective layer and the encapsulating adhesive layer, and extends 20 to 100 micrometers outward into the non-overlapping area. The composite interface structure includes a transition layer and a hydrophobic layer located between the wear-resistant protective layer and the encapsulating adhesive layer, wherein the transition layer is located below the hydrophobic layer.
2. The high-reliability thermal printhead according to claim 1, characterized in that, The transition layer is a functional layer whose coefficient of thermal expansion is between that of the wear-resistant protective layer and that of the encapsulating adhesive.
3. A high-reliability thermal printhead according to claim 2, characterized in that, The transition layer is made of any one of titanium, nickel, or aluminum, or an alloy of titanium, nickel, or aluminum. The coefficient of thermal expansion of the transition layer is between that of the wear-resistant protective layer and the encapsulating adhesive, and the difference between the coefficient of thermal expansion of the transition layer and the coefficient of thermal expansion of the wear-resistant protective layer is less than or equal to 10 × 10⁻⁶. -6 At / ℃, the coefficient of thermal expansion of the wear-resistant protective layer is 4~6×10. -6 / ℃, the coefficient of thermal expansion of the encapsulating adhesive is 20~60×10 -6 / ℃.
4. A high-reliability thermal printhead according to claim 3, characterized in that, The thickness of the transition layer is 1 to 20 micrometers; the planar projection of the transition layer completely covers the overlapping area of the wear-resistant protective layer and the encapsulating adhesive, and extends 20 to 100 micrometers outward from the non-overlapping area, that is, extends 20 to 100 micrometers away from the control IC.
5. A high-reliability thermal printhead according to claim 3, characterized in that, The surface of the transition layer is provided with a hydrophobic layer; the hydrophobic layer is a hydrophobic coating with a contact angle greater than 100°.
6. A high-reliability thermal printhead according to claim 5, characterized in that, The transition layer is an organosilicon coating, a fluorinated coating, or a polyvinylidene fluoride coating.
7. A high-reliability thermal printhead according to claim 5, characterized in that, The hydrophobic layer has a thickness of 1 to 30 micrometers; the hydrophobic layer completely covers the transition layer on its planar projection and extends outward by 10 to 20 micrometers.
8. A high-reliability thermal printhead according to claim 1, characterized in that, Between the transition layer and the hydrophobic layer, and between the hydrophobic layer and the organic encapsulating adhesive layer, a surface treatment layer or a chemical coupling agent layer is respectively provided to enhance the bonding force between the two.
9. A high-reliability thermal printhead according to claim 1, characterized in that, A base glaze layer is disposed on a portion or the entire surface of the insulating substrate. Comb-shaped individual electrodes and a comb-shaped common electrode are disposed on the surface of the base glaze layer, forming a comb-shaped electrode pair. A heating resistor is disposed in the middle of the comb-shaped electrode pair along the main printing direction. One end of the comb-shaped common electrode is connected to the heating resistor, and the other end is connected to a power supply. One end of each comb-shaped individual electrode is connected to the heating resistor, and the other end is connected to a control IC. A wear-resistant protective layer is provided on the surfaces of the heating resistor and the comb-shaped common electrode, and on a portion of the surface of the comb-shaped individual electrodes.