LTCC device made by electroplating pattern transfer method based on titanium substrate

Abstract

The present invention provides an LTCC device fabricated by a plating pattern transfer method based on a titanium substrate. According to the designed circuit pattern, an anti-plating mask is fabricated on the surface of the titanium substrate; the titanium substrate is electroplated to fabricate a copper circuit pattern; after removing the anti-plating mask, the ceramic slurry is directly cast; the LTCC green ceramic sheet is obtained through baking, drying, and peeling; the fabricated LTCC green ceramic sheets of different layers are processed through lamination, isostatic pressing, and sintering to obtain the LTCC device. The present invention proposes to fabricate the inner electrode electronic interconnect copper circuit of LTCC through a plating method, which can improve the dependence on electronic pastes in the existing LTCC manufacturing technology, solve most of the technical problems caused by the defects of electronic pastes themselves, and effectively improve the reliability and stability of the electronic interconnect circuit of the packaging substrate.

Description

Technical Field

[0001] The present invention relates to the technical field of low-temperature co-fired ceramics, and particularly to an LTCC device made by a plating pattern transfer method based on a titanium substrate. Background Art

[0002] With the higher requirements of the fifth-generation communication technology for data and current density transmission, electronic interconnection circuits are increasingly developing towards miniaturization, high frequency, high integration, and high density. This requires new breakthroughs in the size, design, reliability, and integration method of electronic components.

[0003] Low-temperature co-fired ceramic (LTCC) technology is a multi-layer ceramic technology. It can embed passive components inside multi-layer ceramics, realize the integrated packaging of passive devices in the substrate to assemble circuits, and thus achieve the miniaturization, integration, and three-dimensionalization of passive devices. Through the combination of various passive devices, a functional passive packaging module can be formed in the high-frequency field, which can largely meet the performance requirements of contemporary electronic products. The LTCC packaging substrate has excellent high-frequency characteristics and high reliability, can largely replace discrete components such as resistors and capacitors, meet the design requirements of small size, high performance, and low cost, and shorten the design cycle and cost of the entire module. It has good high-speed transmission performance, microwave performance, and extremely high integration. In addition, it has the advantages of low dielectric loss, low sintering temperature, and low process cost, and has a very broad application prospect.

[0004] Specifically, the LTCC technology is to prepare a slurry of low-temperature sintered ceramic powder by tape casting to make a green tape with precise thickness and density. On the green tape, the required circuit pattern is made by processes such as laser drilling, via filling, and inner electrode printing. Multiple passive components (such as low-capacitance capacitors, resistors, filters, impedance converters, couplers, etc.) are buried in the multi-layer ceramic substrate, and then laminated together. The inner and outer electrodes can use metals such as silver, copper, and gold and are sintered at 900°C. LTCC can make high-density circuits that do not interfere with each other in two-dimensional space, and use its high integration to make a three-dimensional circuit packaging substrate. ICs and active components can be mounted on its surface, which can further miniaturize and densify the circuit, and is particularly suitable for components used in high-frequency communication.

[0005] Since LTCC technology is a multi-layer ceramic technology, electronic circuits are arranged and interconnected on each layer. These electronic circuits, also known as internal electrode circuits, include the interconnect circuit patterns within the layer and the metal vias between layers. Their manufacturing methods are generally divided into three categories: subtractive method, additive method, and semi-additive method. The subtractive method usually requires first attaching a copper layer with a certain thickness on the substrate surface, then transferring the circuit pattern to the copper surface by photochemical method or screen printing method, and etching away the unnecessary copper, leaving the required electronic interconnect pattern. The semi-additive method is to deposit a thin metal layer (about 5 μm or more) on the hole wall and the board surface by electroless plating or magnetron sputtering after drilling, then perform negative pattern transfer, electroplate copper to thicken the pattern, and quickly etch after removing the resist film. The 5-μm copper layer in the non-pattern part is quickly etched away, leaving the pattern part. The additive method is to directly grow the required circuit pattern on the substrate by metal paste or electroless plating. The production of LTCC internal electrode circuit patterns usually adopts the method of printing electronic paste. Holes are drilled and electronic paste is filled in the formed green ceramic sheet according to the circuit design, and then the required electronic interconnect pattern is printed with electronic paste by screen printing.

[0006] The electronic paste for making internal electrode circuit patterns is actually a paste composed of uniform ultra-fine metal particles or metal compounds, co-solvents, binders, solvents, etc., and glass powder and additives are added to achieve the required functions. Moreover, as the conductive material, the metal powder not only affects the conductivity of the sintered film, but also affects the physical and mechanical properties of the sintered film. The metal powder materials used in electronic paste can be one or several of precious metals such as gold, silver, and copper. Performance parameters such as the morphology, particle size, tapped density, and specific surface area of the metal powder will affect the rheology and sintering morphology of the conductive paste, and determine the quality of the electrical properties of the electrode after sintering. The inorganic binder phase of the conductive paste mostly selects glass powder, which can play a role in fixing metal particles during the sintering process.

[0007] Table 1 Physical Properties of Commonly Used Metal Materials

[0008]

[0009] Most of the electronic pastes used to make the internal electrodes of LTCC are conductive silver pastes, which are prepared with ultrafine silver powder as the conductive phase. After drying and sintering, these silver particles can form electronic circuits to achieve electrical connectivity. The current process uses silver powder as the conductive phase because the melting point of silver is higher than the sintering temperature of ceramics (see Table 1), and it will not melt and deform, affecting the reliability of the circuit; and silver has high thermal conductivity and low resistivity, which is very helpful in reducing signal loss and distortion in high-frequency circuits. In terms of these three very critical physical properties, most metals cannot compare with silver. In contrast, metallic copper, which has similar melting point, thermal conductivity and resistivity to silver, is not only much cheaper, but also has a smaller linear expansion coefficient than silver. However, since small-sized copper particles are easily oxidized by oxygen and water in the air, they are not suitable for direct use in the production of electronic pastes.

[0010] In addition, the following problems are unavoidable when using conductive silver paste to make electronic interconnection circuits on LTCC multilayer ceramic packaging substrates: the preparation of conductive paste has very high requirements for metal powder, and there are many restrictions on its morphology, particle size, tap density and specific surface area, and the process threshold is relatively high; the ultrafine metal powder used in the industrial production of conductive paste generally adopts the chemical reduction method, which requires a large amount of strong reducing agents such as formaldehyde, which are highly polluting and difficult to treat waste liquid; a large amount of precious metal silver is required to make internal electrode circuits with conductive silver paste, and the cost is much higher than that of copper interconnection electronic circuits of other packaging substrates; the preparation of the inorganic binder phase of the conductive paste and the use of low-melting glass will produce dust, toxic fumes, and the glass composition contains elements that are very harmful to human health and the environment; the organic support phase of the conductive paste contains a variety of organic solvents and additives, which will evaporate and penetrate into the ceramic and circuit during the printing, drying and sintering process, resulting in the circuit being usually not dense enough and even having pores and collapse, and there are certain problems with the reliability of the electronic interconnection circuit. Summary of the invention

[0011] In view of the shortcomings of the prior art, the present invention provides a LTCC device made based on a titanium substrate electroplating pattern transfer method. The present invention proposes to manufacture the internal electrode electronic interconnection copper circuit of LTCC by electroplating, which can improve the dependence of the existing LTCC manufacturing technology on electronic paste, solve most of the technical problems caused by the defects of the electronic paste itself, and effectively improve the reliability and stability of the electronic interconnection circuit of the packaging substrate.

[0012] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0013] On the one hand, the present invention provides an LTCC green ceramic sheet made by a plating pattern transfer method based on a titanium substrate. The method includes: fabricating an anti-plating mask on the surface of the titanium substrate according to the designed circuit pattern; plating the titanium substrate to fabricate a copper circuit pattern; directly casting a ceramic slurry after removing the anti-plating mask; and baking, drying, and peeling to obtain the LTCC green ceramic sheet.

[0014] Further, the process of fabricating the anti-plating mask is as follows:

[0015] Using a titanium substrate with a smooth and flat surface as the support substrate, fabricate an anti-plating mask on the surface of the titanium substrate by screen printing or laser engraving according to the circuit pattern designed on the design drawing.

[0016] Further, the surface grain size of the titanium substrate should be ASTM grade 7 or smaller, and the surface roughness Ra < 0.6 μm;

[0017] During the fabrication of the circuit pattern, the surface of the titanium substrate needs to be kept clean and smooth;

[0018] The material of the anti-plating mask is photoresist, a mixture of titanium dioxide and photoresist, or solder mask ink;

[0019] The process of fabricating the anti-plating mask is as follows: After fabricating the anti-plating mask on the surface of the titanium substrate by screen printing or laser engraving, fix it by means of photocuring or thermal curing.

[0020] Further, the process of electroplating is as follows:

[0021] Using the prepared titanium substrate with an anti-plating mask attached as the cathode and a copper ion solution as the electroplating solution, electroplate to obtain a copper circuit pattern with a thickness meeting the design requirements.

[0022] Further, the electroplating solution is an acidic copper sulfate electroplating copper bath system, which contains copper sulfate, sulfuric acid, chloride ions, and a very small amount of electroplating copper additives;

[0023] During the electroplating process, precisely adjust the thickness of copper in the copper circuit pattern by controlling the current density and electroplating time.

[0024] Further, the preparation process of the LTCC green ceramic sheet is as follows: Remove the fabricated anti-plating mask to obtain grooves, and inject a low-temperature co-fired ceramic slurry into the grooves through a casting machine to cast a film, and then bake and dry to obtain it.

[0025] Further, the thickness of the film in the LTCC green ceramic sheet is controlled according to the slurry viscosity and casting speed, and is kept consistent with the thickness of the copper circuit;

[0026] The anti-plating mask needs to be peeled off, and the peeling is carried out by stamping, laser cutting, or etching methods.

[0027] Further, after the LTCC green ceramic sheet is modified by grinding, trimming, or cutting, a scraper is used to gently slide along the edge of the titanium substrate to quickly peel off the green ceramic sheet containing the copper circuit, obtaining...

[0028] On the other hand, the present invention provides an LTCC device made by a plating pattern transfer method based on a titanium substrate. The LTCC green ceramic sheets described in any one of claims 1 to 7 with different patterns are made into an LTCC device through the processes of laminating, isostatic pressing, and sintering.

[0029] On the one hand, the present invention provides an LTCC device made by a plating pattern transfer method based on a titanium substrate. The specific preparation process of the method is as follows:

[0030] 1) Anti-plating mask production: Using a titanium substrate with a smooth and flat surface as the support substrate, an anti-plating mask is made on the surface of the titanium substrate by methods such as screen printing or laser engraving according to the circuit pattern designed in the design drawing.

[0031] The surface grain size of the used titanium substrate should be ASTM grade 7 or smaller, and the surface roughness Ra < 0.6 μm. When making the circuit pattern, it is necessary to keep the surface of the titanium substrate clean to avoid open circuits or short circuits in the made circuit, and to facilitate the separation of the subsequent process from the finished product. The titanium substrate can be reused when ensuring a smooth surface; the titanium substrate should have a certain thickness to ensure its mechanical strength and reduce the occurrence of problems with the reliability of the circuit caused by the deformation of the titanium substrate.

[0032] The anti-plating mask can be made of a photoresist (i.e., a photolithographic resist), a mixture of titanium dioxide and a photoresist, or a solder mask ink, etc. The mask pattern can be fixed on the surface of the bright titanium substrate through a photocuring or thermal curing method. At the same time, it is necessary to ensure that the mask can be completely removed after electroplating; the anti-plating mask should be insoluble in water but should be conducive to removal in subsequent processes.

[0033] 2) Electroplating circuit: Using the titanium substrate with the anti-plating mask attached prepared in step 1) as the cathode and a copper ion solution as the electroplating solution, electroplating is carried out to obtain a copper circuit pattern with a thickness meeting the design requirements.

[0034] The electroplating copper plating solution for making the circuit pattern should use an electroplating solution system that does not react with the anti-plating mask. The obtained copper layer should be bright and dense to ensure the reliability of the circuit. The plating solution can be reused when maintained well.

[0035] The electroplating solution is generally an acidic copper sulfate electroplating copper plating solution system, which contains copper sulfate, sulfuric acid, chloride ions, and a very small amount of electroplating copper additives. The plating solution can be used for a long time with simple maintenance.

[0036] During the electroplating process, the thickness of copper in the copper circuit pattern is precisely adjusted by controlling the current density and electroplating time;

[0037] As the conditions for electroplating treatment, the currently known conditions can be applied. For example, the cathode current density is 0.05 - 5 A / dm 2 , preferably 0.5 - 3 A / dm 2 . The anode can use known substances. Soluble anodes such as copper plates can be used, or insoluble anodes can also be used. In addition, the electroplating temperature is 15 - 35 °C, preferably 22 - 28 °C. Electroplating techniques mentioned in the prior art can also be referred to, such as CN201010293494.9, CN2000811809.4, CN2002128625.6, CN2002140504.2, etc.;

[0038] 3) Demasking and casting: Remove the anti - electroplating mask obtained in step 2) to obtain grooves, and cast the low - temperature co - fired ceramic slurry into a film in the above - mentioned grooves through a casting machine, then bake and dry to volatilize the organic solvent in the slurry, forming a green ceramic sheet with a certain strength and toughness;

[0039] During this step, the slurry is closely combined with the copper circuit without bubbles. The thickness of the film can be controlled according to the viscosity of the slurry and the casting speed, and is kept consistent with the thickness of the copper circuit;

[0040] The low - temperature co - fired ceramic slurry used for casting can be formulated according to a commercial formula, but it is necessary to ensure that the green ceramic sheet formed after drying has a certain strength and toughness to avoid cracks or direct cracking due to uneven stress during drying and peeling;

[0041] When the cast film is dried, with the volatilization of the organic solvent, shrinkage in size and volume will occur. The bonding force between the green ceramic sheet and the smooth surface of the titanium substrate is small. Under the condition that the green ceramic sheet has a certain strength and toughness, it can be completely peeled from the titanium substrate together with the copper circuit;

[0042] In the present invention, the method for removing the anti - electroplating mask can be a conventional method to ensure the complete peeling of the anti - electroplating mask. Methods such as stamping, laser cutting, etching, etc. can be used, or methods involved in the prior art solutions CN201210262373.7, CN201210501786.6, CN201610307546.0, etc. can be referred to.

[0043] 4) Peeling: Use a scraper to gently slide along the edge of the titanium substrate for the green ceramic sheet obtained in step 3) to quickly peel off the green ceramic sheet containing the copper circuit;

[0044] Before peeling the green ceramic sheet from the surface of the titanium substrate, the green ceramic sheet needs to be modified. The modification methods can include but are not limited to grinding, trimming, cutting, etc. The purpose is to make the interface of the interlayer copper electronic interconnection circuit coplanar with the interface of the green ceramic sheet, which is conducive to ensuring good contact between the circuits of different layers during subsequent alignment and laminating, and ensuring the reliability of the circuit.

[0045] 5) Repeat steps 1) to 4) to fabricate LTCC green ceramic sheets of different layers, which have the same or different internal electrode circuits.

[0046] 6) Laminating: Use a laminating device to align and laminate the processed LTCC green ceramic sheets in the order given by the design, by means of laser or positioning pin alignment through punching positioning holes or image recognition positioning methods to form a three-dimensional interconnected circuit structure; during this process, ensure good contact between the internal electrode circuits of each layer; pour conductive paste into the positioning holes to form a stacked film sheet with electrical connection between each layer.

[0047] 7) Isostatic pressing: Use an isostatic press to press the processed LTCC green ceramic sheets to a tight state to control the shrinkage rate during its sintering process.

[0048] 8) Sintering: Sinter the laminated LTCC green ceramic sheets in a sintering furnace in the temperature range of 850 °C to 950 °C according to the process-given procedure to complete the densification and hardening of the ceramic.

[0049] 9) Finished product: Use a dicing machine to cut the sintered LTCC product to the required size; complete the tests on the size, appearance, and electrical properties of the product.

[0050] The multi-layer low-temperature co-fired ceramic includes ceramic layers, and copper circuits are arranged in each of the ceramic layers. Each of the copper circuits is used as a conductive material to achieve electrical interconnection. Further, the ceramic is made of the LTCC device described in the present invention. The ceramic layer is the LTCC device or a single-layer or multi-layer LTCC green ceramic sheet.

[0051] Further, the distance between adjacent copper circuits is less than 45 μm, preferably less than 25 μm, and can be as low as 1 - 2 μm at the lowest.

[0052] Further, the thickness of each copper circuit is 2 - 50 μm, preferably 5 - 25 μm.

[0053] Further, the resistivity of each copper circuit is less than 10 μΩ·cm, preferably less than 2 μΩ·cm.

[0054] Further, the material of each ceramic layer can be selected from amorphous glass, glass-ceramic (glass ceramics), glass / ceramic composite materials, preferably glass / ceramic composite materials, such as borosilicate glass / aluminum oxide composite materials.

[0055] Furthermore, each of the ceramic layers and the copper circuits provided therein should be well-bonded and not separated or warped in a high-temperature working environment above 100°C.

[0056] The electronic interconnection circuits play a role in electrically connecting various components embedded and mounted in the LTCC multi-layer ceramic packaging substrate. After sintering the ceramic substrate, a circuit that does not interfere with each other and has a high density in three-dimensional space can be obtained. These circuits with the characteristics of miniaturization and high density are particularly suitable for components used in high-frequency communication. The performance of the LTCC packaging substrate is closely related to the quality of its electronic interconnection circuits.

[0057] The present invention proposes to fabricate the inner electrode electronic interconnection copper circuits of LTCC by electroplating, which can improve the dependence on electronic pastes in the existing LTCC manufacturing technology, solve most of the technical problems caused by the defects of the electronic pastes themselves, and effectively improve the reliability and stability of the electronic interconnection circuits of the packaging substrate. Compared with the micro-imprinting forming technology and the conventional screen printing conductive paste technology in the prior art, the present invention forms copper circuits by first reverse-designing an anti-electroplating mask and then selecting electroplating. After removing the anti-electroplating mask, a green ceramic sheet is tape-cast, which is not mentioned in the prior art.

[0058] Beneficial effects

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] The present invention provides an LTCC device fabricated by a plating pattern transfer method based on a titanium substrate. The prepared LTCC device can solve the problem defects of traditional conductive silver paste circuits. By innovatively applying copper to the circuits of LTCC green ceramic sheets in the form of copper electroplating, limitations in aspects such as the morphology, particle size, tapped density, and specific surface area of metal powders in the conductive paste can be avoided; problems such as pollution and health damage during the industrial production of conductive paste can be avoided; the use of precious metals can be avoided; and the influence of the organic support phase on the reliability of the electronic ear connection circuits during drying or sintering can be avoided, etc.

[0061] Compared with the electronic interconnection circuits fabricated by traditional conductive silver paste, the fabrication of electronic circuits by electroplating copper only needs to be carried out in a copper-containing electroplating solution, avoiding the use of high-specification silver microparticles and various organic additives, and the electroplating solution can be reused for a long time. For the electronic interconnection circuits fabricated by conductive silver paste, such as Figure 2As shown in (a) and (b), electrical interconnection is mainly achieved through ultrafine metal particles uniformly dispersed in the electronic paste. However, the organic solvents and additives in the conductive silver paste may escape from the interconnection lines during drying, forming, and sintering, resulting in phenomena such as loose lines and voids in the vias, and low line reliability. The additive manufacturing method described in the present invention uses electroplating to fabricate the lines. By adjusting the composition of the plating solution and electroplating parameters, dense and flat pure metal lines can be obtained. The specific effects can be seen in Figure 2 (c) and (d), which have excellent performance in aspects such as signal transmission and heat dissipation, and relatively high reliability of the electronic interconnection lines.

[0062] Compared with the traditional method of screen printing, electroplating is used to fabricate the lines. The high current efficiency of electroplating copper enables high utilization of copper, and the copper plating solution used has stable properties and can be reused, without the problem of having to be used up at once (traditional LTCC manufacturing technology usually fabricates electronic interconnection lines by screen printing. A separate screen stencil needs to be made for each circuit pattern, and the silver paste on the screen must be used up at once, otherwise it will solidify and be scrapped).

[0063] Compared with the traditional screen printing method, controlling the thickness of the electronic circuit by applying pressure to the stencil is essentially a physical coating, which is greatly affected by the rheology of the conductive silver paste and difficult to control the accuracy. While the additive manufacturing method described in the present invention relies on electrochemical reactions to electrochemically reduce copper ions in the plating solution to metallic copper, and the line thickness can be precisely adjusted by controlling the current density and electroplating time.

[0064] From fabricating the anti-electroplating mask to electroplating the copper lines, and then removing the anti-electroplating mask and casting the film, the entire process closely cooperates with the designed circuit pattern, which can ensure the reliability of the copper lines and solve the problems of the conductive silver paste. The stacking process can be used to achieve series and parallel designs of multiple-layer components, improving the design specifications of the product. The LTCC devices obtained by the method of the present invention have better quality and are easier to fabricate fine lines.

[0065] The method for fabricating LTCC devices provided by the present invention can be applied to the manufacture of large quantities of LTCC multi-layer ceramic packaging substrates, as well as the process adjustment of test samples. In addition, independent LTCC passive devices and integrated functional devices can also be fabricated using the technical concept described in the present invention. And there are no special requirements for the production manufacturers and product series of related materials and equipment. Description of the Drawings

[0066] Figure 1 Simulation diagram of the manufacturing technology of the LTCC internal electrode electronic interconnection circuit described in the present invention. In the figure, A fabricates the mask pattern; B electroplates the circuit pattern; C removes the mask pattern; D casts the ceramic paste; E peels off the green ceramic sheet; 1 mask; 2 titanium substrate; 3 copper line; 4 ceramic paste; 5 green ceramic sheet

[0067] Figure 2 Microscopic morphology diagrams of conductive silver paste and electroplated copper circuits. (a) SEM cross-sectional view of a silver paste circuit sintered at 800 °C; (b) SEM cross-sectional view of a silver paste circuit sintered at 900 °C; (c) SEM cross-sectional view of the product made in step 2) of the method of the present invention; (d) SEM diagram of the electroplated copper circuit made by the method of the present invention, photoresist Detailed implementation manners

[0068] The following is a further detailed description of the present invention in conjunction with the specific implementation manners, but this should not be construed as limiting the scope of the subject matter of the present invention to the following examples only.

[0069] For the process equipment or devices not specifically specified in the following examples, conventional equipment or devices in the art are used; all reagents can be commercially purchased.

[0070] Example 1

[0071] An LTCC device made by an electroplating pattern transfer method based on a titanium substrate is prepared as follows:

[0072] 1) Select a titanium substrate with a surface grain size of ASTM grade 7 or smaller and a surface roughness Ra < 0.6 μm, clean the surface to keep it clean, and draw a photosensitive resist or solder mask ink on the surface of the titanium substrate according to the circuit pattern designed in the design drawing by means of screen printing or laser engraving. Through processes such as photocuring or thermal curing, exposure, development, and etching, an anti-electroplating mask attached to the surface of the titanium substrate is made;

[0073] The thickness of the photosensitive resist or solder mask ink is controlled according to the designed parameters; the temperature for thermal curing is controlled at 100 - 120 °C and baked for 0.5 - 2 min; for photocuring, an infrared lamp is used for irradiation and baking for 0.5 - 5 min; processes such as exposure, development, and etching are processed according to the conventional operation methods; the main purpose of the etching process is to finely remove the excess parts;

[0074] 2) Using the titanium substrate with the anti-electroplating mask prepared in step 1) as the cathode and a copper ion solution as the electroplating solution, electroplate to obtain a copper circuit pattern (i.e., the inner electrode circuit pattern) with a thickness meeting the design requirements;

[0075] The electroplating solution is generally an acidic copper sulfate electroplating copper bath system, which contains copper sulfate, sulfuric acid, chloride ions, and a very small amount of electroplating copper additives;

[0076] As the conditions for electroplating treatment, the currently known conditions can be applied, for example, the cathode current density is 0.05 - 5 A / dm 2 , preferably 0.5 - 3 A / dm 2; The anode can use well-known substances, such as soluble anodes like copper plates or insoluble anodes. In addition, the electroplating temperature is 15 - 35°C, preferably 22 - 28°C; reference can also be made to the electroplating techniques mentioned in the prior art X, such as CN201010293494.9, CN2000811809.4, CN2002128625.6, CN2002140504.2, etc.;

[0077] Based on Faraday's law of electrolysis, the thickness of the electroplated copper circuit is proportional to the current density and time. That is, when electroplating for 1 minute at a current density of 1 A / dm 2 , the electroplated copper thickness is 0.2206 μm. Therefore, according to the requirements of different LTCC devices, the thickness of the copper interconnect circuit can be controlled by adjusting the electroplating current density and time. For example, when planning to electroplate a copper circuit with a thickness of 5 μm, at a current density of 2 A / dm 2 , at least 12 minutes of electroplating is required, and at a current density of 5 A / dm 2 , only 5 minutes is needed.

[0078] 3) Remove the electroplating resist mask prepared in step 2) so that there are grooves between the copper circuits. Inject the low-temperature co-fired ceramic slurry into the grooves through a casting machine to cast an LTCC ceramic film, and bake and dry it to form an LTCC green ceramic sheet; the thickness of the sheet can be controlled according to the slurry viscosity and casting speed and kept consistent with the copper circuit thickness; the low-temperature co-fired ceramic slurry used for casting can be formulated using existing formulas;

[0079] The cured electroplating resist mask can be broken and peeled off in an alkaline environment under certain conditions. For example, the photosensitive dry film with an alkali-soluble polymer and vinyl unsaturated groups in patent CN201811278277.5 can be removed by spraying or immersing it in a 3% - 5% mass fraction sodium hydroxide solution for 1 - 3 minutes, and the remaining mask fragments and sodium hydroxide on the titanium plate can be rinsed with deionized water.

[0080] 4) Modify the green ceramic sheet obtained in step 3) by methods such as but not limited to grinding, polishing, and cutting. Gently slide a scraper along the edge of the titanium substrate to quickly peel off the green ceramic sheet containing the copper circuit;

[0081] 5) Repeat steps 1) to 4) to fabricate inner electrode circuits of different layers;

[0082] 6) Use a laminating device to stack the processed LTCC green ceramic sheets in the order given by the design, and align them by methods such as laser or positioning pins through punching positioning holes to form a three-dimensional interconnected circuit structure; conductive paste is poured into the positioning holes to form stacked sheets with typical connections between layers;

[0083] 7) Use an isostatic press to press the processed LTCC green ceramic sheets into a tight state to control the shrinkage rate during its sintering process:

[0084] 8) Sinter the laminated LTCC green ceramic sheets in a sintering furnace in the temperature range of 850 °C to 950 °C according to the procedure given by the process to complete the densification and hardening of the ceramics;

[0085] 9) Use a dicing machine to cut the sintered LTCC product to the required size; complete the tests of the product's size, appearance, and electrical properties.

[0086] The electrical conductivity of the electroplated copper circuit of the LTCC product prepared by the method described in this patent is close to that of pure copper, and the resistivity measured by the four-probe test is 1.8 μΩ·cm; the adhesion test of the copper circuit and the ceramic material is carried out by the cross-cut test. The test result shows that the edge of the copper coating scratch is smooth, and the actual peeled area within the conductive layer lattice is less than 5%; after the LTCC device is sintered and subjected to thermal shock (treated 6 times in a lead-free soldering furnace at 288 °C), no obvious cracking occurs in the ceramic sheet matrix, the copper circuit and the matrix do not separate or warp, and the surface conductive layer still has good welding adhesion.

[0087] It can be understood that the above embodiments are only exemplary embodiments adopted to illustrate the principle of the present invention. However, the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be included within the protection scope of the present invention.

Claims

1. An LTCC green ceramic sheet made by a plating pattern transfer method based on a titanium substrate, characterized in that, The method refers to: Based on the designed circuit pattern, a titanium substrate with a smooth surface is used as the support substrate, and an anti - electroplating mask is fabricated on the surface of the titanium substrate by screen printing or laser engraving according to the circuit pattern designed on the design drawing; Using the prepared titanium substrate with an anti - electroplating mask as the cathode and a copper ion solution as the electroplating solution, electroplating is carried out to obtain a copper circuit pattern with a thickness meeting the design requirements; the prepared anti - electroplating mask is removed to obtain grooves, and the low - temperature co - fired ceramic slurry is injected into the grooves through a casting machine to form a film, and then baked, dried, and peeled to obtain an LTCC green ceramic sheet; The thickness of the film in the LTCC green ceramic sheet is controlled according to the slurry viscosity and casting speed, and is kept consistent with the thickness of the copper circuit.

2. The LTCC green ceramic sheet according to claim 1, wherein The surface grain size of the titanium substrate should be ASTM grade 7 or smaller, and the surface roughness Ra < 0.6μm; When fabricating the circuit pattern, the surface of the titanium substrate needs to be kept clean and smooth; The material of the anti - electroplating mask is a photoresist, a mixture of titanium dioxide and a photoresist, or a solder mask ink; The process of fabricating the anti - electroplating mask is as follows: after fabricating the anti - electroplating mask on the surface of the titanium substrate by screen printing or laser engraving, it is fixed by a photocuring or thermal curing method.

3. The LTCC green ceramic sheet according to claim 1, wherein, The electroplating solution is an acidic copper sulfate electroplating copper bath system, which contains copper sulfate, sulfuric acid, chloride ions, and a very small amount of electroplating copper additives; During the electroplating process, the thickness of copper in the copper circuit pattern is precisely adjusted by controlling the current density and electroplating time.

4. The LTCC green ceramic sheet according to claim 1, wherein, The anti - electroplating mask needs to be peeled off, and the peeling is carried out by stamping, laser cutting, or etching; after the LTCC green ceramic sheet is modified by grinding, trimming, or cutting, a scraper is gently slid along the edge of the titanium substrate to quickly peel off the green ceramic sheet containing the copper circuit to obtain.

5. An LTCC device made by a plating pattern transfer method based on a titanium substrate, characterized in that, The LTCC devices are fabricated by laminating, isostatic pressing, and sintering the LTCC green ceramic sheets described in any one of claims 1 - 4 with different patterns.

6. The LTCC device according to claim 5, characterized in that, The specific process of the fabrication method of the LTCC device is as follows: Laminating: Using a laminating device, the processed LTCC green ceramic sheets are aligned and laminated in the order given by the design, by methods such as aligning with a laser or positioning pin through punching positioning holes or image recognition positioning, to form a three - dimensional interconnected circuit structure; Isostatic pressing: Using an isostatic press to press the processed LTCC green ceramic sheets into a tight state to control the shrinkage rate during its sintering process; Sintering: The laminated LTCC green ceramic sheets are sintered in a sintering furnace in the temperature range of 850°C to 950°C according to the process - given procedure to complete the densification and hardening of the ceramic; using a dicing machine to cut the sintered LTCC product to the required size to obtain.

7. Multilayer low-temperature co-fired ceramics, characterized in that, It includes ceramic layers, and copper circuits are arranged in each of the ceramic layers, and each of the copper circuits is used as a conductive material to achieve electrical interconnection; the ceramic layer is the LTCC device described in any one of 5 - 6.

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