High-reliability thermal printing head and manufacturing method thereof

Abstract

The invention relates to the technical field of thermal printing head manufacturing, in particular to a high-reliability thermal printing head and a manufacturing method of the high-reliability thermal printing head. Wear-resistant protective layers are arranged on the surfaces of a heating resistor body and a comb-shaped common electrode and partial surfaces of comb-shaped individual electrodes; the control IC device, the surface of a comb-shaped individual electrode part on the periphery of the control IC device and a bonding pad are packaged by adopting a packaging protection layer, the packaging protection layer adopts a multi-layer packaging protection layer, and the multi-layer packaging protection layer is formed by sequentially overlapping a first electrode protection layer, a water vapor blocking layer, a second electrode protection layer and an outer packaging adhesive layer from inside to outside; the first electrode protection layer and the second electrode protection layer are composite resin protection layers containing a cation trapping agent or a silver ion trapping agent respectively; and interface enhancement processing layers are arranged between the multi-layer packaging protection layer and the electrical component on the insulating substrate and between adjacent layers in the multi-layer packaging protection layer, so that the integrity and long-term effectiveness of the multi-layer protection structure are ensured.

Description

Technical Field

[0001] This invention relates to the field of thermal printhead manufacturing technology, specifically to a highly reliable thermal printhead that is resistant to high humidity, can suppress metal migration, and is suitable for high temperature, high humidity or other harsh environments, as well as its manufacturing method. Background Technology

[0002] Traditional thick-film thermal printhead substrates typically use chemically stable Au as the conductive electrode, but this material is expensive. More and more manufacturers are now using relatively cheaper metals such as Ag and Cu as electrodes. However, Ag and Cu metals have poor electrochemical stability and are prone to metal migration in high humidity or when exposed to moisture, causing short circuits and failures, severely impacting the printhead's lifespan and reliability.

[0003] The patent with publication number CN214137925U discloses a method of coating a dense protective material on the surface of the encapsulating adhesive to block moisture penetration and improve the phenomenon of damage to control IC devices caused by the "popcorn effect". However, it does not address the electromigration of metal electrode terminals such as silver and copper, nor does it consider the catalytic effect of ions that may be released inside the encapsulating material on the migration process.

[0004] The patent with publication number CN116945774A discloses a method that uses two encapsulation layers with different water absorption rates. The first resin layer, which is in contact with the electrode, has a lower hygroscopicity than the second resin layer. This method attempts to suppress silver migration by controlling the distribution of water vapor. However, it does not consider the accelerating effect of ions released from the encapsulation material on metal migration, and it completely ignores the thermomechanical stress failure faced by the multilayer organic encapsulation structure in the specific application scenario of thermal printhead.

[0005] To address the issue of moisture introducing into IC devices, causing free ions to enter the surface of electrical components and resulting in electrochemical corrosion under the influence of potential difference, ultimately leading to open circuits, manufacturers in the current technology also use compounded epoxy resin compositions to enhance the adhesion and density of the encapsulation layer formed by the epoxy resin composition, and add ion trapping agents in the hope of reducing the free ion content and improving the stability of electrical performance. However, this technology is currently unable to meet the needs of thermal printhead products. Summary of the Invention

[0006] This invention addresses the complex technical challenges existing in the aforementioned background technology by providing a multi-layered synergistic protection structure and its manufacturing method. This invention not only solves the ion migration problem but also creatively addresses the thermomechanical stability issue inherent in multi-layered protection structures in the field of thermal printheads. Through its multi-layered synergistic protection structure, this invention achieves the capture of electrode metal ions and internal anions, the barrier against moisture, the effective management of thermomechanical stress, and the fundamental enhancement of interfacial bonding, thereby achieving reliability in high-humidity environments.

[0007] This invention achieves its purpose through the following measures: A highly reliable thermal printhead includes an insulating substrate with a base enamel layer on its surface. The base enamel layer has comb-shaped individual electrodes and a comb-shaped common electrode, forming a comb-shaped electrode pair. A heating resistor is positioned 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 COM electrode. One end of each comb-shaped individual electrode is connected to the heating resistor, and the other end extends to form a pad for connection to a control IC device. A wear-resistant protective layer is provided on the surfaces of the heating resistor, the comb-shaped common electrode, and a portion of the surface of the comb-shaped individual electrodes, and the printhead is encapsulated using an encapsulation protective layer. The control IC device and its peripheral comb-shaped individual electrode surfaces and pads are characterized in that the encapsulation protective layer is a multi-layer encapsulation protective layer, which is composed of a first electrode protective layer, a moisture barrier layer, a second electrode protective layer and an outer encapsulating adhesive layer stacked from the inside out; the first electrode protective layer and the second electrode protective layer are composite resin protective layers containing either a cationic scavenger or a silver ion scavenger, respectively; an interface enhancement treatment layer is provided between the multi-layer encapsulation protective layer and the electrical components on the insulating substrate, as well as between adjacent layers in the multi-layer encapsulation protective layer, and the interface enhancement treatment layer is formed by a synergistic treatment of oxygen plasma treatment and the application of a silane coupling agent.

[0008] To fundamentally solve the thermomechanical stress failure problem caused by severe CTE mismatch, this invention provides an interface enhancement layer between the layers of the multilayer synergistic encapsulation protection structure, and between the innermost layer and the substrate (such as a ceramic substrate, base glaze layer, or electrode surface). The interface enhancement layer is preferably formed through a synergistic treatment of oxygen plasma and the application of a silane coupling agent. Oxygen plasma treatment cleans and activates inorganic or organic surfaces, introducing highly reactive hydroxyl (-OH) functional groups. Subsequently, γ-glycidyl etheroxypropyltrimethoxysilane (KH-560) is coated onto the surface. Bifunctional silane coupling agents, such as methoxysilane, have one end (methoxysilane) that can undergo hydrolysis and condensation with surface hydroxyl groups to form a stable -Si-OM (M is the base element) covalent bond; the other end (epoxy group) can undergo ring-opening addition with the epoxy or amine groups of the organic resin layer during subsequent resin curing to form a covalent chemical bond bridge. This essential chemical bond formed between heterogeneous material interfaces transforms the originally fragile physical adsorption interface into a strong chemical bond interface. Its bonding strength is far higher than that of van der Waals forces, thus fundamentally eliminating interfacial delamination failure during thermal cycling.

[0009] The first electrode protective layer of this invention is preferably a composite resin protective layer containing a cation scavenger, which is directly coated on the surface of silver and copper electrodes and IC pads. Its core function is to capture and fix metal ions immediately upon generation, preventing them from entering subsequent migration paths. The cation scavenger can be one or more of the following: organic ion scavengers such as aminosilanes, cation exchange resins, and metal-organic frameworks (MOFs), rare earth modified scavengers, zirconium and titanium multivalent metal acid salts, and hydrated oxides of antimony. The matrix is ​​epoxy resin or organosilicon. One type of resin is preferred, with a thickness of 1-50 μm; further, the cation-scavenging composite resin protective layer is preferably an epoxy resin containing a -SH-functionalized UiO-66 type metal-organic framework compound, wherein the amount of the UiO-66 type metal-organic framework compound added to the epoxy resin matrix is ​​preferably 3-7 wt%, and the particle size is preferably 50-300 nm to ensure good dispersibility and sufficient active sites; the specific surface area is preferably ≥650 m² / g, the pore volume is preferably ≥0.35 cm³ / g, and the ion exchange capacity is preferably >1.5 meq / g to provide efficient ion scavenging ability.

[0010] The core function of the water vapor barrier layer described in this invention is to maximally block the penetration of water vapor rather than liquid water, creating a dry working environment for the internal ion scavenger, thereby preventing it from prematurely failing due to water saturation. It also fundamentally cuts off the moisture conditions required for electrochemical migration. The layer can be an organic hydrophobic layer such as polyvinylidene fluoride or organosilicon, an inorganic superhydrophobic film, or a superhydrophobic composite coating. The preferred thickness is 0.01~10 μm, preferably a nano-dichlorodiphenyl ether modified with hexamethyldisilazane (HMDS). The silica epoxy resin coating has nano-silica with a purity of >99.5%, a particle size of 10~50nm, a specific surface area of ​​150~300m² / g, a silanization coverage of >70% after modification, and a content in the resin ranging from 0.1~10wt%. Through the labyrinth effect of the nanofiller and the low surface energy of the surface, it achieves excellent water vapor barrier performance. The water vapor transmission rate (WVTR) measured at 38℃ and 90%RH is 0.1~1g / m² / day, which is 1~2 orders of magnitude lower than that of traditional polymer hydrophobic layers.

[0011] The second electrode protective layer of this invention is preferably a composite resin protective layer containing anion scavengers, located outside the moisture barrier layer. Its core function is to capture and neutralize corrosive anions (such as halide ions) released from the external environment (such as halogens and sulfides in the air) or from the outermost encapsulating adhesive during curing or aging. It works in conjunction with the first electrode protective layer to form a bidirectional ion-capturing mechanism, preventing corrosion or migration caused by the electrochemical reactions of anions and cations. The anion scavenger can be anion exchange resin, triethylamine, metal-organic frameworks (MOFs), or other organic compounds, or hydrated basic compounds. One or more inorganic ion scavengers, such as magnesium aluminum carbonate, aluminosilicate, and bismuth hydrate oxide, are used. The matrix resin can be either epoxy resin or silicone resin, and its thickness is preferably 1-20 μm. Magnesium aluminum hydrotalcite with a layered ion exchange structure, which has been surface-treated with a silane coupling agent (preferably KH-560), is preferred as an anion scavenger for exchanging and fixing anions such as Cl⁻ and SO₄²⁻ that have invaded the environment. The magnesium aluminum hydrotalcite preferably has a purity of >99.5%, a particle size of 100-300 nm, a specific surface area of ​​50-150 m² / g, an ion exchange capacity of >1.5 meq / g, a silane coverage of >70% after treatment, and is preferably added to the epoxy resin matrix at a rate of 5-10 wt%.

[0012] The encapsulation layer of the present invention is a low thermal expansion and high thermal conductivity composite encapsulation layer, which provides final environmental barrier and mechanical protection, and provides a way for IC chip heat dissipation. The CTE of the encapsulation layer is preferably 15~20 ppm / °C, its thermal conductivity is preferably >3W / m·K, and its thickness is preferably 0.3~1mm. The encapsulation layer is composed of an epoxy resin matrix with a high glass transition temperature (Tg) and a high volume fraction of mixed ceramic filler. The filler preferably contains 60-70 wt% spherical alumina with a multi-size distribution and 5-10 wt% lamellar hexagonal boron nitride; the spherical alumina preferably has a purity >99.5%, and is preferably a mixture of large particles (10-20 μm) and small particles (0.5-2 μm) in a 4:1 weight ratio to increase the packing density, thereby reducing CTE and improving thermal conductivity; the lamellar hexagonal boron nitride preferably has a purity >99% and a diameter of 5-10 μm; the ceramic filler preferably undergoes surface treatment with a silane coupling agent (preferably KH-560) to enhance the interfacial bonding between the filler and the resin matrix.

[0013] This invention also proposes a method for manufacturing the aforementioned high-reliability thermal printhead, comprising the following steps: forming an amorphous glass base glaze layer on the surface of an insulating substrate by screen printing and sintering at a high temperature of 900~1300℃; printing and sintering electrode paste on the base glaze layer and a portion of the insulating substrate to form a metallized substrate; forming comb-shaped individual electrodes and comb-shaped common electrodes on the metallized substrate by photolithography; forming a heating resistor on the comb-shaped electrode pair formed by the comb-shaped individual electrodes and the comb-shaped common electrodes by printing or drawing and sintering at 600~900℃; setting a wear-resistant protective layer 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 electrodes by printing and sintering at 500~900℃; and bonding a pressure-bonded or flip-chip bonded layer at one end of the comb-shaped individual electrodes. The method involves soldering IC devices; characterized in that, in the control IC device and some comb-shaped individual electrode areas, a first electrode protective layer, a moisture barrier layer, a second electrode protective layer, and an encapsulation layer are sequentially stacked by printing and spraying; before each protective layer is applied, the surface of the previous layer or the substrate surface is subjected to interface enhancement treatment, namely, plasma treatment and coating with KH-560 silane coupling agent and curing; after the first and second protective layers are arranged, ultraviolet (UV) light curing and / or thermal curing processes are used; the UV curing conditions can be wavelength 300~500nm, light intensity 100~500mW / cm², and time 10~60 seconds; the thermal curing can be carried out in a programmable temperature-controlled oven, and after curing for 1~4 hours, the oven is cooled to ensure that each protective layer is completely cured and to minimize internal stress.

[0014] The first electrode protective layer of this invention is a composite resin containing a cation scavenger. The preparation method is as follows: Add 5 parts by weight of 100-300 nm UiO-66-(SH)2 powder to 100 parts by weight of low-viscosity bisphenol A epoxy resin. The powder has a specific surface area ≥650 m² / g, pore volume ≥0.35 cm³ / g, and ion exchange capacity >1.5 meq / g. Mix the resin at 1500 rpm for 20 minutes using a planetary centrifugal mixer to prepare a uniformly dispersed cation scavenging resin. The resin viscosity is controlled at 10-20 mPa•s (50℃) by adding propylene glycol diglycidyl ether for inkjet printing.

[0015] The method for preparing the water vapor barrier layer of this invention is as follows: 1 wt% of hexamethyldisilazane (HMDS) hydrophobically modified nano-silica is added to an epoxy resin solution. The silica particles before treatment have a particle size of 10-50 nm, a purity >99.5%, a specific surface area of ​​150-300 m² / g, and a silanization coverage >70%. The solution is ultrasonically treated for 30 minutes to ensure sufficient dispersion of the nanoparticles, thus forming a water vapor barrier coating. The resin viscosity is controlled at 10-20 mPa•s (50°C) by adding propylene glycol diglycidyl ether. The water vapor barrier coating is then sprayed onto the surface of the first electrode protective layer at 20-25°C, a speed of 5-10 cm / s, and a frequency of 1-10 kHz using inkjet printing, forming a coating with a thickness controlled to 1-10 μm. The coating is then dried in an oven at 80°C for 30 minutes to form a dense water vapor barrier layer.

[0016] The second electrode protective layer of this invention is a composite resin containing anion scavenging agent. The preparation method is as follows: 7 parts by weight of magnesium aluminum hydrotalcite powder treated with KH-560 are added to 100 parts by weight of epoxy resin. Before treatment, the magnesium aluminum hydrotalcite powder has an average particle size of 0.2 μm, a purity of >99.5%, a particle size of 100~300 nm, a specific surface area of ​​50~150 m² / g, and an ion exchange capacity of >1.5 meq / g. The mixture is prepared by mixing at 1500 rpm for 20 minutes using a planetary centrifugal mixer to form anion scavenging resin. The resin viscosity is controlled at 10~20 mPa•s (50℃) by adding propylene glycol diglycidyl ether.

[0017] The encapsulation layer fabrication method of this invention is as follows: 65 parts by weight of spherical alumina (where 15μm and 1μm particles are mixed in a weight ratio of 4:1) and 7 parts by weight of flake-shaped hexagonal boron nitride (diameter 5~15μm) are added to 27.5 parts by weight of high-Tg epoxy resin, along with 0.5 parts by weight of KH-560 coupling agent. All components are thoroughly mixed and degassed in a vacuum kneader to prepare the final encapsulating adhesive. The CTE of this encapsulating adhesive is approximately 17ppm / ℃, and its thermal conductivity is approximately 3.5W / m·K. Using a printing method, the encapsulating adhesive is printed in the control IC device area, covering the cation scavenger resin layer, moisture barrier layer, anion scavenger resin layer, IC, and part of the electrode and glass protective layer; the thickness is 0.5mm.

[0018] The manufacturing method of this invention further includes plasma treatment of the previous layer surface or substrate surface before applying each protective layer, coating with KH-560 silane coupling agent and curing it to improve interfacial bonding. The substrate with the IC is placed in a plasma cleaner, oxygen is introduced, and it is treated at a vacuum of 50 Pa and a power of 100 W for 60 seconds to clean and activate the surface, forming hydroxyl groups. 1 wt% of KH-560 silane coupling agent is added to an ethanol / water (95:5 v / v) solution and mixed thoroughly; this mixture is then applied by spraying between the IC device and some individual comb-shaped electrodes on the plasma-treated substrate, and cured in an oven at 110 °C for 15 minutes to form a monomolecular covalent bond layer.

[0019] Compared with traditional encapsulation layers, the thermal printhead provided by this invention adds a first electrode protective layer, a hydrophobic layer, and a second electrode protective layer, which has the following advantages: By introducing a low CTE and high thermal conductivity encapsulation layer and interfacial chemical bonding technology, the bonding force between the protective layers and between the protective layer and the substrate is significantly enhanced. This effectively prevents delamination under the influence of thermal stress and moisture penetration, and solves the problem of thermal stress failure in the multi-layer encapsulation structure of the thermal printhead during the working cycle. This makes the multi-layer protection a stable and reliable whole, and also provides an efficient heat dissipation channel for the IC chip, which helps to reduce the operating temperature, reduce thermal stress, and further improve the stability and lifespan of the device.

[0020] The multi-layered structure of this invention is not a simple superposition of functions. The moisture barrier layer greatly delays moisture intrusion, creating a dry working environment for the ion capture agent, preventing it from rapidly saturating and thus extending the effective lifespan of the ion capture. The cation capture agent contained in the first electrode protective layer effectively absorbs metal ions released from the electrode, while the anion capture agent contained in the second electrode protective layer blocks the intrusion of external anions such as halide ions. The combination of the two achieves precise interception of ions from different sources and with different properties, significantly reducing the concentration of internal metal ions and external anions. The synergistic effect of the multiple layers is far superior to that of single or mixed ion capture systems, thereby inhibiting metal migration.

[0021] Meanwhile, the multi-layer protective structure allows for the selection of different types of cationic / anionic scavenging resins, adjusting thickness, viscosity, and curing processes according to actual needs. The formation of the multi-layer protective layer can utilize mature screen printing, inkjet printing, and spraying processes, ensuring compatibility with existing thermal printhead manufacturing processes. This guarantees the integrity and long-term effectiveness of the multi-layer protective structure. Attached Figure Description Appendix Figure 1 This is a cross-sectional schematic diagram of the heating substrate for the thermal printhead finally formed in Example 1.

[0022] Appendix Figure 2 This is a planar schematic diagram of a multilayer insulating encapsulation protective layer for the heating substrate of the thermal printhead finally formed in Example 1.

[0023] Reference numerals: 1-Insulating substrate, 2-Base glaze layer, 3b-Comb-shaped individual electrodes, 3a-Comb-shaped common electrode, 4-Heating resistor, 5-Wear-resistant protective layer, 6-Control IC device, 7a-First electrode protective layer, 7b-Moisture barrier layer, 7c-Second electrode protective layer, 7d-Outer encapsulation adhesive layer. Detailed Implementation To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0024] To address the shortcomings and problems of existing technologies, this invention, in the process of improving these issues, discovered a significant difference in CTE between the ceramic substrate of the thermal printhead (CTE approximately 6.5-7.7 ppm / ℃) and traditional polymer encapsulation materials (CTE often exceeding 60 ppm / ℃). During the rapid, repeated heating-cooling cycles of the printhead, this mismatch generates enormous stress at the interface of the heterogeneous materials, easily leading to microcracks or even delamination of the protective layer. Once structural integrity is compromised, it provides a rapid entry channel for moisture and corrosive ions, rendering any single protective measure ineffective and ultimately causing electromigration.

[0025] Existing technologies, which only consider water blocking or ion capture in isolation, or form an entire encapsulation body by incorporating ion-capturing epoxy resin compositions, have proven through testing to still fail to meet the requirements of thermal printing products. How to construct a stable multi-layered protective structure that can effectively suppress ion migration and withstand long-term thermal cycling stress while maintaining structural integrity, thereby improving product reliability and lifespan, remains a key technical challenge that urgently needs to be solved in this field.

[0026] Example 1 This embodiment provides a highly reliable thermal printhead, including an insulating substrate 1, with a base glaze layer 2 disposed on a portion or the entire surface of the insulating substrate 1; comb-shaped individual electrodes 3b and comb-shaped common electrodes 3a are disposed on the surface of the base glaze layer 2, forming a comb-shaped electrode pair; a heating resistor 4 is disposed in the middle of the comb-shaped electrode pair along the main printing direction; one end of the comb-shaped common electrode 3a is connected to the heating resistor 4, and the other end is connected to a COM electrode; 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 device 6; a wear-resistant protective layer 5 is provided on the surface of the heating resistor 4 and the comb-shaped common electrode 3a, and on a portion of the surface of the comb-shaped individual electrode 3b; a control IC device 6 or wires connected to the control IC device 6 are disposed on the comb-shaped individual electrode 3b of the control IC section; a multilayer insulating encapsulation protective layer 7 is disposed on the comb-shaped individual electrode 3b and the control IC device 6 of the control IC section; the multilayer insulating protective layer 7 includes a first electrode protection layer 7a, a moisture barrier layer 7b, a second electrode protection layer 7c, and an encapsulating adhesive layer 7d.

[0027] This embodiment also provides a method for manufacturing a highly reliable thermal printhead, the method comprising the following steps: Step 1: An amorphous glass base glaze layer 2 is formed on the surface of the insulating substrate 1 by screen printing and sintering at a high temperature of 900~1300℃; electrode paste is printed and sintered on the base glaze layer 2 and part of the insulating substrate 1, and comb-shaped common electrode 3a and comb-shaped individual electrode 3b are formed by photolithography; heating resistor 4 is formed on the comb-shaped electrode pair formed by the comb-shaped common electrode 3a and comb-shaped individual electrode 3b by printing or spraying and sintering at 600~900℃; wear-resistant protective layer 5 is set on the surface of the heating resistor 4 and the comb-shaped common electrode 3a and part of the surface of the comb-shaped individual electrode 3b by printing and sintering at 400~900℃.

[0028] Step 2: At one end of the comb-shaped individual electrode 3b, solder the IC controller 6 by pressure bonding or wire bonding. Step 3: Complete the interface enhancement treatment layer: Step 3a: Place the substrate with IC in a plasma cleaner, introduce oxygen, and treat it for 60 seconds at a vacuum of 50Pa and a power of 100W to clean and activate the surface and form hydroxyl groups; Step 3b: Add 1 wt% KH-560 silane coupling agent to an ethanol / water (95:5 v / v) solution and mix thoroughly; apply the mixture by spraying between the plasma-treated substrate IC device 6 and some comb-shaped individual electrodes 3b, and cure in an oven at 110°C for 15 minutes to form a monomolecular covalent bond layer. Step 4a: Add 5 parts by weight of 100-300 nm UiO-66-(SH)2 powder to 100 parts by weight of low-viscosity bisphenol A epoxy resin. The powder has a specific surface area ≥650 m² / g, pore volume ≥0.35 cm³ / g, and ion exchange capacity ≥4 meq / g. Mix at 1500 rpm for 20 minutes using a planetary centrifuge to prepare a uniformly dispersed cation-capturing resin. By adding propylene glycol diglycidyl ether, the resin viscosity is controlled at 10-20 mPa•s (50℃) for inkjet printing. Step 4b: At an environment of 20~25℃, the above-mentioned cationic scavenger composite resin is uniformly filled between IC device 6 and some comb-shaped individual electrodes 3b by inkjet printing at a speed of 5~10cm / s and a frequency of 1~10kHz. It is then irradiated with an LED ultraviolet light source with a wavelength of 365nm and a light intensity of 300mW / cm² for 30 seconds to rapidly crosslink and cure it. It is then baked at 120℃ for 30 minutes to cure it, with the thickness controlled at 10~50μm, forming the first electrode protective layer 7a. Step 5: Repeat steps 3a and 3b to perform plasma activation and KH-560 coupling agent treatment on the surface of the cured first electrode protective layer 7a; Step 6a: Add 1 wt% of hexamethyldisilazane (HMDS) hydrophobically modified nano-silica to the epoxy resin solution. The silica particle size is 10~50 nm, purity >99.5%, silanization coverage >70%, and specific surface area 150~300 m² / g. Ultrasonic treatment for 30 minutes is performed to ensure that the nanoparticles are fully dispersed, thus preparing a water vapor barrier coating. The resin viscosity is controlled at 10~20 mPa•s (50℃) by adding propylene glycol diglycidyl ether. Step 6b: At an environment of 20~25℃, water vapor barrier coating is sprayed onto the surface of the first electrode protective layer 7a by inkjet printing at a speed of 5~10cm / s and a frequency of 1~10kHz to form a coating with a thickness controlled at 1~10μm. Then, it is dried in an oven at 80℃ for 30 minutes to form a dense water vapor barrier layer 7b. The water vapor transmission rate (WVTR) of this coating measured at 38℃ and 90%RH is less than 0.5g / m² / day. Step 7: Repeat steps 3a and 3b to perform plasma activation and KH-560 coupling agent treatment on the surface of the cured water vapor barrier layer 7b. Step 8a: Add 7 parts by weight of magnesium aluminum hydrotalcite powder treated with KH-560 to 100 parts by weight of epoxy resin. Before treatment, the magnesium aluminum hydrotalcite powder has an average particle size of 0.2 μm, a purity of >99.5%, a particle size of 100~300 nm, a specific surface area of ​​50~150 m² / g, and an ion exchange capacity of >1.5 meq / g. Mix at 1500 rpm for 20 minutes using a planetary centrifugal mixer to prepare an anion capturing resin. By adding propylene glycol diglycidyl ether, the resin viscosity is controlled at 10~20 mPa•s (50℃). Step 8b: Using the same inkjet printing and curing parameters as in Step 4b, anion capture resin is coated onto the water vapor barrier layer 7b to form a second electrode protective layer 7c with a thickness of 15μm. Step 9a: To 27.5 parts by weight of high-Tg epoxy resin, add 65 parts by weight of spherical alumina (where 15μm and 1μm particles are mixed in a weight ratio of 4:1), 7 parts by weight of flake-shaped hexagonal boron nitride (5~15μm in diameter), and 0.5 parts by weight of KH-560 coupling agent. Thoroughly mix and degas all components in a vacuum kneader to prepare the final encapsulating adhesive. The CTE of the outer encapsulating layer formed by this encapsulating adhesive is approximately 17 ppm / ℃, and the thermal conductivity is approximately 3.5 W / m·K. Step 9b: Using a printing method, encapsulating adhesive is printed in the control IC device 6 area to cover the cationic scavenger resin layer, water vapor barrier layer, anionic scavenger resin layer, IC and part of the electrode, with a thickness of 0.5mm, forming an outer encapsulating adhesive layer 7d; Step 10: Increase the temperature from room temperature to 125°C at a rate of 2°C / min and hold for 60 minutes, then increase the temperature to 165°C at a rate of 1°C / min and hold for 90 minutes. Finally, cool the furnace to room temperature to ensure that each protective layer is fully cured and the stress is fully released, thus forming a multi-layer insulating encapsulation protective layer 7.

[0029] Example 2 This embodiment provides an alternative solution using ALD atomic layer deposition to replace superhydrophobic coatings. Steps 1-5 are the same as in Embodiment 1.

[0030] Step 6: Place the substrate in a plasma-enhanced atomic layer deposition (PEALD) apparatus and perform photolithography and lift-off processes at 100°C using trimethylaluminum (TMA) and oxygen plasma as precursors, with alternating pulses to deposit a 30nm thick Al2O3 film on the surface of the first electrode protective layer 7a, forming a dense water vapor barrier layer 7b. The WVTR of this layer can be less than 10-4 g / m² / day.

[0031] Steps 7-10 are the same as in Example 1, except that the interface enhancement treatment in step 7 is performed on the surface of the Al2O3 film.

[0032] Example 3 This embodiment provides a scheme using α-zirconium phosphate powder as a cation scavenging agent. Except for step 4a, the remaining steps are the same as in Example 1.

[0033] Step 4a: Add 6 parts by mass of layered α-zirconium phosphate powder treated with KH-560 coupling agent to 100 parts by mass of epoxy resin. The initial average particle size of the α-zirconium phosphate powder is 300 nm, the specific surface area is 100~150 m² / g, the anionic group loading is ≥4.0 meq / g, and the silane coverage after treatment is >75%. Mix at 1500 rpm for 20 minutes using a planetary centrifugal mixer to prepare a cation capture resin. By adding propylene glycol diglycidyl ether, the resin viscosity is controlled at 10~20 mPa•s (50℃).

[0034] Example 4 This embodiment provides a scheme using functionalized mesoporous silica as a cation scavenger. Except for step 4a, the remaining steps are the same as in Example 1.

[0035] Step 4a: Add 6 parts by mass of thiol-functionalized mesoporous silica (SBA-15-SH) powder to 100 parts by mass of epoxy resin. The average particle size is 400 nm, the specific surface area is 700~1200 m² / g, the pore size is 6~15 nm, the pore volume is ≥0.8 cm³ / g, and the anionic group loading is 1.5~4.5 meq / g. Mix at 1500 rpm for 30 minutes using a planetary centrifuge to prepare a cation-capturing resin. The resin viscosity is controlled at 10~20 mPa•s (50℃) by adding propylene glycol diglycidyl ether.

[0036] Example 5 This embodiment provides a scheme using layered titanate nanofibers as a cation scavenger. Except for step 4a, the remaining steps are the same as in Example 1.

[0037] Step 4a: Add 7 parts by mass of layered titanate nanofibers treated with KH-560 coupling agent to 100 parts by mass of epoxy resin. The initial diameter of the layered titanate nanofibers is 20~100nm, the length is 1~20µm, the aspect ratio is >50, the ion exchange capacity is >4.0meq / g, the specific surface area is >200m² / g, and the silane coverage after treatment is >75%. Mix at 1500rpm for 30 minutes using a planetary centrifuge to prepare a cation capturing resin. The resin viscosity is controlled at 10~20mPa•s (50℃) by adding propylene glycol diglycidyl ether.

[0038] Example 6 This embodiment provides a scheme using aminosilane as a cation scavenging agent. Except for step 4, the remaining steps are the same as in Example 1.

[0039] Step 4a: Add 3 wt% of 3-aminopropyltriethoxysilane (APTES) and 0.1 wt% of nano-SiO2 dispersion with a particle size of 30 nm to the epoxy resin substrate. The equivalent ion exchange capacity (IEC) provided by the amine functional group is about 1~2 meq / g. Mix at 1500 rpm for 30 minutes using a planetary centrifuge to prepare a cation capturing resin. By adding propylene glycol diglycidyl ether, the resin viscosity is controlled at 10~20 mPa•s (50℃).

[0040] Example 7 This embodiment provides a scheme using a cationic MOF as an anion scavenger. Except for step 8a, the remaining steps are the same as in Example 1.

[0041] Step 8a: Add 8 parts by weight of cationic MOF MIL-101(Cr)-Cl powder to 100 parts by weight of epoxy resin. The particle size is 200~800nm, specific surface area ≥2500m² / g, pore size 2.9~3.4nm, pore window size about 1.6nm, pore volume ≥1.4cm³ / g, and ion exchange capacity >1.5meq / g. Mix at 1500rpm for 20 minutes using a planetary centrifuge to prepare an anion capturing resin. The resin viscosity is controlled at 10~20mPa•s (50℃) by adding propylene glycol diglycidyl ether.

[0042] Example 8 This embodiment provides a scheme using layered rare earth hydroxides as anion scavengers. Except for step 8a, the remaining steps are the same as in Example 1.

[0043] Step 8a: Add 8 parts by weight of layered yttrium oxychloride (LYH-Cl) powder treated with KH-560 coupling agent to 100 parts by weight of epoxy resin. The initial particle size of the layered yttrium oxychloride (LYH-Cl) powder is 100~500nm, the ion exchange capacity is ≥2.5meq / g, the specific surface area is 50~200m² / g, and the silane coverage after silane coupling agent treatment is >75%. Mix at 1500rpm for 20 minutes using a planetary centrifugal mixer to prepare an anion capturing resin. By adding propylene glycol diglycidyl ether, the resin viscosity is controlled at 10~20mPa•s (50℃).

[0044] Example 9 This embodiment provides a scheme using bismuth oxide hydrate powder as an anion scavenger. Except for step 8a, the remaining steps are the same as in Example 1.

[0045] Step 8a: Add 5 parts by mass of bismuth oxide hydrate powder (β-Bi2O3・H2O) treated with KH-560 coupling agent to 100 parts by mass of epoxy resin. The initial particle size of the bismuth oxide hydrate powder is 100~500nm, the particle size distribution index (PDI) is ≤0.3, the specific surface area is 20~100m² / g, the anion exchange capacity is ≥1.5meq / g, and the silane coverage after silane coupling agent treatment is >75%. Mix at 1500rpm for 20 minutes using a planetary centrifugal mixer to prepare an anion capturing resin, and adjust the viscosity to 10~20mPa•s (50℃) using propylene glycol diglycidyl ether.

[0046] Example 10 This embodiment demonstrates a scheme using a conventional polymeric anion exchange resin as an anion scavenger. Except for step 8, all other steps are the same as in Example 1.

[0047] Step 8a: Add 5 parts by mass of strongly basic quaternary ammonium salt styrene-based anion exchange resin micro powder to 100 parts by mass of epoxy resin. The micro powder has a particle size of <20 μm, an ion exchange capacity of ≥1.5 meq / g, a crosslinking degree of 6~10%, and a thermal stability of ≥180°C. Mix the powder at 1500 rpm for 20 minutes using a planetary centrifugal mixer to prepare anion capturing resin. Adjust the viscosity to 10~20 mPa•s (50°C) using propylene glycol diglycidyl ether.

[0048] Example 11 This embodiment provides a structure in which the positions of the anion trapping layer and the cation trapping layer are interchanged. The manufacturing method of this embodiment is basically the same as that of Embodiment 1, but the order of steps is adjusted as follows: Steps 1-3: Same as in Example 1.

[0049] Step 4 (New): Forming an anion trapping layer. Using the resin formulation of Step 8a in Example 1 and the application and curing process of Step 8b, an anion trapping layer is formed on the substrate after interface enhancement treatment.

[0050] Step 5 (New): Perform interface enhancement treatment on the surface of the anion trapping layer.

[0051] Step 6: Apply a water vapor barrier layer, as in Step 6 of Example 1.

[0052] Step 7: Perform interface enhancement treatment on the surface of the water vapor barrier layer.

[0053] Step 8 (New): Set the cation trapping layer. Using the resin formulation of Step 4a in Example 1 and the application and curing process of Step 4b, a cation trapping layer is formed on the moisture barrier layer.

[0054] Steps 9-10: Apply the encapsulation layer and perform final curing, as in Example 1. The final structure of this example, from the inside out, consists of: an anion trapping layer, a moisture barrier layer, a cation trapping layer, and a low thermal expansion, high thermal conductivity encapsulation layer.

[0055] Comparative Example 1 This comparative example provides a thermal printhead without a multilayer insulating encapsulation protective layer, including an insulating substrate 1. A base glaze layer 2 is disposed on a portion or the entire surface of the insulating substrate 1. Comb-shaped individual electrodes 3b and a comb-shaped common electrode 3a are disposed on the surface of the base glaze layer 2, forming a comb-shaped electrode pair. A heating resistor 4 is disposed in the middle of the comb-shaped electrode pair along the main printing direction. One end of the comb-shaped common electrode 3a is connected to the heating resistor 4, and the other end is connected to a COM electrode. 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 device 6. A wear-resistant protective layer 5 is provided on the surfaces of the heating resistor 4 and the comb-shaped common electrode 3a, and on a portion of the surface of the comb-shaped individual electrodes 3b. A control IC device 6 or wires connected to the control IC device 6 are disposed on the comb-shaped individual electrodes 3b of the control IC section. An encapsulating adhesive layer 7d is disposed on the comb-shaped individual electrodes 3b and the control IC device 6 of the control IC section. The manufacturing method of the thermal printhead in this comparative example includes the following steps: Step 1: An amorphous glass base glaze layer 2 is formed on the surface of the insulating substrate 1 by screen printing and sintering at a high temperature of 900~1300℃; electrode paste is printed and sintered on the base glaze layer 2 and part of the insulating substrate 1, and comb-shaped common electrode 3a and comb-shaped individual electrode 3b are formed by photolithography; heating resistor 4 is formed on the comb-shaped electrode pair formed by the comb-shaped common electrode 3a and comb-shaped individual electrode 3b by printing or spraying and sintering at 600~900℃; wear-resistant protective layer 5 is set on the surface of the heating resistor 4 and the comb-shaped common electrode 3a, and part of the surface of the comb-shaped individual electrode 3b by printing and sintering at 400~900℃. Step 2: At one end of the comb-shaped individual electrode 3b, solder the IC controller 6 by pressure bonding or wire bonding. Step 3: Using a printing method, print unfilled epoxy encapsulant in area 6 of the control IC device. The thickness is 0.3~1mm. Use an oven at 100~170℃ to cure for 1~4 hours to form an encapsulant layer.

[0056] Comparative Example 2 The manufacturing method is the same as that of Comparative Example 1, steps 1-2. In step 3, steps 9 and 10 of Example 1 are used, and an outer encapsulation adhesive layer with low thermal expansion and high thermal conductivity is set for 7d.

[0057] Comparative Example 3 The manufacturing method is the same as steps 1 to 5 of Example 1.

[0058] Steps 6-9 follow the steps 7-10 in Example 1.

[0059] Comparative Example 4 The manufacturing method sequentially follows steps 1-2, 4, 6, and 8-10 of Example 1. The plasma and silane coupling agent interface enhancement treatments described in Example 1 are not performed between layers or between layers and the substrate.

[0060] Comparative Example 5 All the functional fillers (UiO-66-(SH)2, HMDS-SiO2, and magnesium aluminum hydrotalcite) used in steps 4a, 6a, and 8a of Example 1 were mixed into a single epoxy resin matrix at the same total solids content ratio as in Example 1 to form a single-function encapsulation layer. Then, the encapsulation and curing were carried out in the same manner as in Comparative Example 1.

[0061] In accelerated aging tests, all examples and comparative samples were tested for 20,000 hours at 85°C and 85% relative humidity with a voltage of 10.5V applied. Examples 1-11 showed no failure after 2000 hours, Comparative Example 1 failed after 500 hours, Comparative Example 2 failed after 750 hours, Comparative Example 3 failed after 1000 hours, and Comparative Examples 4 and 5 failed after 1500 hours.

[0062] In the high-temperature cooking test, all examples and comparative samples were placed at 121°C, 100%RH, and 2 atm for 24 hours. After the test, the delamination and cracking between the layers of the encapsulation area were examined using an ultrasonic scanning microscope. Among them, the encapsulation areas of the products in Examples 1-11 showed no delamination or cracking, while Comparative Examples 1-5 all showed varying degrees of cracking.

[0063] In the high-temperature cooking test, Comparative Examples 1-5 all exhibited varying degrees of interlayer delamination or cracking at the product packaging area, demonstrating the necessity of interface treatment. In the aging test, Comparative Examples 3 and 5 showed longer lifespans than Comparative Example 1, but significantly shorter than the Example 1, illustrating the necessity of multi-layer synergy.

[0064] Therefore, the multi-layer protective design of the high-reliability thermal printhead provided by this invention effectively improves the stability and durability of the electrode material through technical measures such as cation capture, anion capture, and water vapor barrier layers, solving the ion migration problem; through interface treatment, it solves the structural stability problem, improves the adaptability of the thermal printhead to the working environment, extends the product life, and significantly improves long-term reliability.

Claims

1. A high-reliability thermal printhead, comprising an insulating substrate, the surface of which is provided with a base glaze layer; the surface of the base glaze layer is provided with comb-shaped individual electrodes and a comb-shaped common electrode, the comb-shaped individual electrodes and the comb-shaped common electrode forming a comb-shaped electrode pair, a heating resistor being 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 COM electrode; one end of the comb-shaped individual electrode is connected to the heating resistor, and the other end extends to form a pad for connection to a control IC device; a wear-resistant protective layer is provided on the surface of the heating resistor and the comb-shaped common electrode, as well as a portion of the surface of the comb-shaped individual electrodes, and an encapsulation protective layer is used to encapsulate the control IC device and the peripheral surface of the comb-shaped individual electrodes and the pad, characterized in that, The encapsulation protective layer is a multi-layer encapsulation protective layer, which is composed of a first electrode protective layer, a moisture barrier layer, a second electrode protective layer and an outer encapsulating adhesive layer stacked from the inside out; the first electrode protective layer and the second electrode protective layer are composite resin protective layers containing cation scavengers or silver ion scavengers, respectively; an interface enhancement treatment layer is provided between the multi-layer encapsulation protective layer and the electrical components on the insulating substrate, as well as between adjacent layers in the multi-layer encapsulation protective layer, and the interface enhancement treatment layer is formed by the synergistic treatment of oxygen plasma treatment and the application of silane coupling agent.

2. The high-reliability thermal printhead according to claim 1, characterized in that: The first electrode protective layer is a composite resin protective layer containing a cation scavenger, with a thickness of 1~50μm, used to capture electrode metal cations; the water vapor barrier layer is a superhydrophobic layer with a contact angle ≥100° and a thickness of 0.01~10μm; the second electrode protective layer is a composite resin protective layer containing anion scavengers, with a thickness of 1~20μm; the encapsulating adhesive layer is a polymer composite encapsulating adhesive with a thickness of 0.3~1mm.

3. The high-reliability thermal printhead according to claim 1, characterized in that, The cation scavenger is one or more of the following: aminosilanes, cation exchange resins, metal-organic frameworks (MOFs), rare earth modified complexes, zirconium, titanium multivalent metal acid salts, and antimony hydrated oxide inorganic ion scavengers; the composite resin matrix is ​​epoxy resin or silicone resin.

4. The high-reliability thermal printhead according to claim 1, characterized in that: The water vapor barrier layer is an organic hydrophobic layer of polyvinylidene fluoride or organosilicon, or an inorganic superhydrophobic film, or a superhydrophobic composite coating, with a thickness of 0.01~10μm.

5. The high-reliability thermal printhead according to claim 1, characterized in that: The anion capture agent is one or a mixture of quaternary ammonium salt anion exchange resin, triethylamine, metal-organic framework (MOF) organic ion exchanger, hydrated basic magnesium aluminum carbonate, aluminosilicate, and bismuth hydrated oxide inorganic ion exchanger, and the composite resin matrix is ​​epoxy resin or silicone resin.

6. The high-reliability thermal printhead according to claim 1, characterized in that: The outer encapsulation layer is a low thermal expansion and high thermal conductivity encapsulation layer with CTE < 20 ppm / ℃ and thermal conductivity > 3 W / m·K. It is composed of an epoxy resin matrix and a high volume fraction of mixed ceramic filler. The mixed filler contains 60-70 wt% of spherical alumina with a multi-size distribution and 5-10 wt% of lamellar hexagonal boron nitride. The spherical alumina is mixed with large particles of 10-20 μm and small particles of 0.5-2 μm at a weight ratio of 4:1, and the lamellar hexagonal boron nitride has a diameter of 5-15 μm.

7. A method for manufacturing a high-reliability thermal printhead as described in any one of claims 1-6, characterized in that, Includes the following steps: An amorphous glass base glaze layer is formed on the surface of an insulating substrate by screen printing and sintering at a high temperature of 900~1300℃. Electrode paste is printed and sintered on the base glaze layer and part of the insulating substrate to form a metallized substrate. Comb-shaped individual electrodes and comb-shaped common electrodes are formed on the metallized substrate by photolithography. Heating resistors are formed on the comb-shaped electrode pairs formed by the comb-shaped individual electrodes and the comb-shaped common electrodes by printing or drawing and sintering at 600~900℃. Wear-resistant protective layers are formed on the surfaces of the heating resistors and the comb-shaped common electrodes, and on part of the surface of the comb-shaped individual electrodes by printing and sintering at 400~900℃. At one end of the comb-shaped individual electrodes, a bonding layer is formed by pressure bonding or wire bonding. IC device; characterized in that, in the control IC device and some comb-shaped individual electrode areas, a first electrode protective layer, a moisture barrier layer, a second electrode protective layer and an encapsulation layer are sequentially stacked by printing and spraying; before each protective layer is applied, the surface of the previous layer or the substrate surface is subjected to interface enhancement treatment, that is, plasma treatment and coating with KH-560 silane coupling agent and curing; after the first protective layer and the second protective layer are arranged, ultraviolet (UV) light curing and / or thermal curing processes are adopted; the UV curing conditions can be wavelength 300~500nm, light intensity 100~500mW / cm², time 10~60 seconds; the thermal curing can be carried out in a programmable temperature controlled oven, and the oven is cooled after curing for 1~4 hours.

8. The method for manufacturing a high-reliability thermal printhead according to claim 7, characterized in that, The first electrode protective layer is a composite resin containing a cation scavenger. The preparation method is as follows: 5 parts by weight of 100~300nm UiO-66-(SH)2 powder with a specific surface area ≥650m² / g and a pore volume ≥0.35cm³ / g are added to 100 parts by weight of low-viscosity bisphenol A epoxy resin. The mixture is then mixed at 1500rpm for 20 minutes using a planetary centrifugal mixer to prepare a uniformly dispersed cation scavenger resin. By adding propylene glycol diglycidyl ether, the resin viscosity is controlled at 10~20mPa•s for inkjet printing.

9. The method for manufacturing a high-reliability thermal printhead according to claim 7, characterized in that, The method for preparing the water vapor barrier layer ink is as follows: 1 wt% of hexamethyldisilazane (HMDS) hydrophobically modified nano-silica is added to an epoxy resin solution. The silica particle size is 10-50 nm, purity >99.5%, specific surface area 150-300 m² / g, and silanization coverage >70%. The solution is ultrasonically treated for 30 minutes to ensure sufficient dispersion of the nanoparticles, thus preparing a water vapor barrier coating. The resin viscosity is controlled at 10-20 mPa•s by adding propylene glycol diglycidyl ether. The water vapor barrier coating is sprayed onto the surface of the first electrode protective layer at a speed of 5-10 cm / s and a frequency of 1-10 kHz under an environment of 20-25°C, forming a coating with a thickness controlled at 1-10 μm. The coating is then dried in an oven at 80°C for 30 minutes to form a dense water vapor barrier layer.

10. The method for manufacturing a high-reliability thermal printhead according to claim 8, characterized in that, The second electrode protective layer is a composite resin containing anion scavengers. The preparation method is as follows: 7 parts by mass of magnesium aluminum hydrotalcite powder that has been surface-treated with KH-560 are added to 100 parts by mass of epoxy resin. Before treatment, the magnesium aluminum hydrotalcite powder has an average particle size of 0.2 μm, a purity of >99.5%, a particle size of 100~300 nm, and a specific surface area of ​​50~150 m² / g. The mixture is prepared by mixing at 1500 rpm for 20 minutes using a planetary centrifugal mixer to form a cation scavenging resin. The resin viscosity is controlled at 10~20 mPa•s by adding propylene glycol diglycidyl ether.

Images