CN113103415A

CN113103415A - Manufacturing method of large-size embedded cavity structure LTCC substrate

Info

Publication number: CN113103415A
Application number: CN202110413579.4A
Authority: CN
Inventors: 卢会湘; 赵飞; 唐小平; 严英占; 王康; 李攀峰; 刘秀婷
Original assignee: CETC 54 Research Institute
Current assignee: CETC 54 Research Institute
Priority date: 2021-04-16
Filing date: 2021-04-16
Publication date: 2021-07-13
Anticipated expiration: 2041-04-16
Also published as: CN113103415B

Abstract

The invention discloses a method for manufacturing a large-size LTCC substrate with an embedded cavity structure, and belongs to the technical field of micro-mechanical structure manufacturing. The method comprises the steps of punching, cavity punching, HTCC auxiliary layer manufacturing, blind cavity composite green body manufacturing, cavity top layer composite green body manufacturing, laminating, sintering and the like. The method utilizes the characteristic that the HTCC auxiliary layer is not softened and collapsed in the low-temperature sintering process to provide a certain supporting effect for the top layer of the cavity. By adopting the method, a sacrificial layer material does not need to be added in the cavity, the sintering curve and the lamination parameters do not need to be adjusted, the method is simple to operate, the consumed time is less, the efficiency is high, and particularly good cavity flatness can be obtained for a large-size embedded cavity.

Description

Manufacturing method of large-size embedded cavity structure LTCC substrate

Technical Field

The invention belongs to the technical field of micro-mechanical structure manufacturing, and particularly relates to a manufacturing method of a large-size LTCC substrate with an embedded cavity structure.

Technical Field

Low temperature co-fired ceramic (LTCC) technology is a passive component integrated circuit technology developed in the eighties of the last century. The multilayer LTCC substrate technology can integrate partial passive elements into the substrate, so that the substrate has the advantages of high speed, high frequency, high density, high reliability and the like, is beneficial to miniaturization of a system, improves the reliability of the system while improving the assembly density of a circuit, and is widely applied to the fields of microwave communication, aerospace, military electronics and the like.

In recent years, LTCC technology has been widely used in other fields such as sensors, actuators, and microsystems, in addition to the field of electronics. These applications mainly benefit from the good electrical and mechanical properties of the LTCC substrate, which makes LTCC-based microsystem structures highly reliable and stable. More importantly, the LTCC technology is applied, so that the one-time manufacture of the three-dimensional microsystem structure becomes possible, and a feasible scheme is provided for realizing the more convenient manufacture of the on-chip microsystem. The advantages of high flexibility, low cost, short period, standardized manufacture and the like attract the attention of a plurality of researchers, and become a new hotspot of LTCC technology research in recent years.

In order to realize different functions of a microsystem, a 3D-LTCC (namely, a three-dimensional LTCC) structure mostly comprises a plurality of different structures such as a cavity, a channel, a film layer and the like. These structures, not only can be implemented in microwave circuit applications for chip embedding, but also can be used in microsystem applications for building complex functional structures, such as: a heat dissipation fluid channel structure on the bottom surface of a high-power device, a reaction chamber in a microreactor, a capacitance cavity in a capacitance sensor, a combustion chamber in a micro-fuel device, an LTCC patch antenna and the like.

The large-size embedded cavity is one of LTCC cavities, is a hollow structure cavity completely sealed inside an LTCC substrate, and is mainly characterized in that the top surface of the cavity is suspended, and the flatness of the surface of the finished cavity is required. The cavity structure is schematically shown in FIG. 1, and comprises three main parts, namely a cavity top layer 1-3, a cavity wall layer 1-2 and a cavity bottom layer 1-1. Due to the good mechanical sensitivity and the internal air structure of the top layer structure of the cavity, the large-size embedded cavity structure has wide application in the fields of LTCC three-dimensional structure manufacturing, capacitive film sensors, embedded air cavity patch antennas and the like.

Due to the particularity of the large-size embedded cavity structure LTCC substrate, two technical difficulties in cavity manufacturing are integrated in the structure manufacturing: on one hand, the embedded cavity structure is required to keep the cavity structure not deformed in the manufacturing process; on the other hand, the flatness of the top layer of the cavity is difficult to ensure in manufacturing, and the shape of the cavity and the flatness of the top surface of the cavity are critical to the application of the cavity in various fields.

At present, the manufacturing process commonly used in the industry for manufacturing such cavities is shown in fig. 2. In the manufacturing process, the steps of blanking aging, punching, hole filling, printing, cavity punching and the like of the substrate material are sequentially performed. After each ceramic chip is manufactured, the multiple layers of ceramic chips are sequentially stacked according to the structural sequence by means of the alignment marks among the layers. After lamination is completed, a warm water isostatic pressing lamination step is performed. The purpose of lamination is to tightly integrate the substrates under uniform pressure. For a large-size LTCC substrate with a buried cavity structure, a cavity defect is formed in the large-size LTCC substrate, and if the hollow LTCC multilayer substrate is directly placed in a high-pressure environment, the cavity and even the whole substrate can be damaged. To solve the above problems, the following treatment methods are commonly used: in the lamination stage, the LTCC substrate with "cavity defects" is modified to a flat planar substrate by first filling the cavity with a sacrificial material before sealing the lamination to the cavity. The lamination operation of the cavity cover is then performed. The lamination process is then performed. In the laminating stage, the sacrificial layer plays a role in supporting and protecting the cavity structure, so that the deformation of the cavity structure is avoided. The common sacrificial layer materials include graphite-based materials, ore materials, organic materials and other different systems. In the sintering and ceramic-forming stage of the LTCC substrate, the sacrificial layer material is oxidized into a gaseous state under the high-temperature condition, the substrate structure is discharged through the ceramic micro through holes which are not sintered and compact, the sacrificial layer material is completely discharged, and then the base material is sintered into ceramic, so that the manufacture of the LTCC substrate with the embedded cavity structure is realized.

Although the method of adding the sacrificial layer can realize the manufacture of the LTCC substrate with the embedded cavity structure, the following difficulties exist in the manufacturing implementation:

1) selection and preparation of sacrificial layer materials. The sacrificial layer material has plasticity to fill cavities with different structures. In addition, the sacrificial layer material should be capable of complete oxidation to CO at high temperatures₂Or CO gas is discharged out of the LTCC substrate.

2) Sintering control of LTCC substrates containing sacrificial layer material. If the oxidation discharge of the sacrificial layer material is realized in the sintering of the LTCC substrate, and the smoothness of the top cover of the embedded cavity is ensured, the sintering curve needs to be adjusted. The common method is to first perform thermogravimetric analysis on the sacrificial layer material to obtain its oxidation rate at different temperatures. Then, the sintering curve of the LTCC substrate is adjusted according to the thermogravimetric analysis result. If the oxidation temperature of the sacrificial layer material is lower (lower than the temperature of the softening stage in the sintering of the LTCC substrate), the top layer of the cavity loses support before sintering and softening, and is easy to cause concave-down and even collapse; if the oxidation temperature of the sacrificial layer material is too high (higher than the temperature point at which densification begins in sintering of the LTCC substrate), the sacrificial layer continues to be oxidized and gasified after the base body is sealed, the top layer of the cavity is easy to bulge under the action of gas expansion, and the cavity is broken when the cavity is serious; in addition, if the time for oxidizing the sacrificial layer is not enough, some sacrificial layer materials can remain in the cavity after the LTCC substrate is made into ceramic, and the performance of the substrate is affected.

3) The extra operation of filling the sacrificial layer material is needed in the manufacturing process, and the manufacturing efficiency is reduced.

In patent CN20141012571.1, a method for manufacturing a single film built-in cavity LTCC substrate without the assistance of a sacrificial layer material and with a simple and feasible manufacturing process is disclosed, which can alleviate or even eliminate the "film collapse" caused by lamination through the "shrinkage tension" generated by the sintering shrinkage adaptability after different lamination processes. In particular, the single membrane layer of the buried cavity is subjected to a pressure "less than standard lamination" during manufacture and will exhibit greater shrinkage during sintering than the "cavity wall layer and cavity base (i.e. the common blind cavity in the above example) after being subjected to standard lamination". Shrinkage mismatch between the conventional blind cavity and the single film cap layer will produce shrinkage tension on the single film cap layer, thereby "straightening" the "lower limit" of the single film cap layer during manufacture.

However, in the actual test process, it is found that the method needs to adjust the lamination pressure of the single film layer, the cavity wall layer and the cavity base for many times according to the size of the cavity to obtain the ideal 'shrinkage tension', the difference of the lamination pressure is related to the shape of the cavity, different adjustments need to be carried out according to the product, and the flatness of the single film layer is about 20-30 microns, which has certain limitation in the practical application.

Disclosure of Invention

In view of this, the invention provides a method for manufacturing a large-size LTCC substrate with an embedded cavity structure, which does not require the assistance of a sacrificial layer material, and has a simple and feasible manufacturing process and good flatness of the top surface of the cavity.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

the manufacturing method of the large-size LTCC substrate with the embedded cavity structure comprises the steps that the large-size LTCC substrate with the embedded cavity structure comprises a cavity bottom layer (1-1), a cavity wall layer (1-2) and a cavity top layer (1-3), the size of a cavity is larger than or equal to 10mm by 10mm, and the cavity is completely sealed inside the LTCC substrate; the method specifically comprises the following steps:

(1) finishing the punching of all single-layer LTCC green ceramic chip positioning holes;

(2) punching a cavity area at a corresponding position of the cavity wall layer;

(3) punching a lamination alignment hole by using a first HTCC green ceramic chip;

(4) stacking the first HTCC green ceramic chip, the cavity bottom layer LTCC green ceramic chip and the cavity wall layer LTCC green ceramic chip on the stacking plate in sequence from bottom to top, and laminating according to a blind cavity structure to obtain a blind cavity composite green body;

(5) punching a lamination alignment hole by using a second HTCC green ceramic chip;

(6) laminating the cavity top layer LTCC green ceramic chip and the second HTCC green ceramic chip on the laminated plate according to the sequence from bottom to top, and laminating according to a flat plate structure to obtain a cavity top layer composite green body;

(7) coating a binder on the upper surface of the blind cavity composite green body, performing combined lamination with the cavity top layer composite green body in a cold and low pressure mode, and then baking on a heating table to obtain a laminated green body;

(8) co-firing the laminated green body obtained in the step (7) by using an LTCC co-firing furnace;

(9) and after sintering, removing the HTCC parts on the upper surface and the lower surface of the substrate to obtain the large-size LTCC substrate with the embedded cavity structure.

Further, the total thickness of the first HTCC green ceramic tiles is equal to the total thickness of the second HTCC green ceramic tiles and is greater than 1/2 of the total thickness of the LTCC green ceramic tiles.

Further, the baking temperature in the step (7) is 60-100 ℃, and the time is 0.5-4 hours.

Furthermore, the co-sintering treatment in the step (8) adopts a pressure-assisted sintering mode, and the auxiliary pressure is 5000-20000 Pa.

Further, the HTCC is partially scraped or ground in step (9).

The invention has the beneficial effects that:

1. in the manufacturing of the large-size embedded cavity, a sacrificial layer material is not required to be added into the cavity to support the top layer of the cavity, and the pertinence research on the sacrificial layer material matched with the applied LTCC substrate is not required. Compared with the conventional manufacturing method, the method has the advantages of simple operation, less time consumption, high efficiency and low cost, and particularly can obtain very good chamber flatness.

2. When the LTCC structure is manufactured by adopting the method, the sintering curve and the laminating parameters do not need to be readjusted, and the consistency in manufacturing is ensured.

In a word, the method does not need to be assisted by a sacrificial layer material, the manufacturing process is simple and feasible, and the flatness of the top surface of the cavity is good. The problems that the steps of the existing manufacturing technology of the large-size embedded cavity are complex, the selection and preparation difficulty of the sacrificial layer material is high, the sintering curve or the lamination pressure needs to be continuously corrected and the like can be solved.

Drawings

Fig. 1 is a schematic diagram of a large-sized buried cavity structure according to an embodiment of the present invention.

Fig. 2 is a process flow diagram of a conventional LTCC substrate with a cavity.

FIG. 3 is a process flow diagram of a method of an embodiment of the invention.

FIG. 4 is a schematic representation of a blind cavity composite green body structure in an embodiment of the present invention.

FIG. 5 is a schematic representation of a cavity top composite green body structure in an embodiment of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

A manufacturing method of a large-size LTCC substrate with a buried cavity structure comprises the following steps:

(2) punching a cavity at a corresponding position of the cavity wall layer;

(3) punching a lamination alignment hole by adopting an HTCC (high temperature co-fired ceramic) green ceramic chip with a certain thickness;

(4) laminating the laminated plate according to the sequence of the HTCC, the bottom layer of the cavity and the cavity layer from bottom to top, and laminating according to the blind cavity structure to obtain a blind cavity composite green body;

(5) punching a laminated alignment hole by using an HTCC green ceramic chip with a certain thickness;

(6) laminating the laminated plate from bottom to top according to the sequence of the top layer of the cavity and the HTCC, and laminating according to a flat plate structure to obtain a composite green body of the top layer of the cavity;

(7) coating a binder on the upper surface of the blind cavity composite green compact obtained in the step (4) and the cavity top layer composite green compact obtained in the step (6) in a cold and low pressure mode for combined lamination, and then baking on a heating table to obtain a laminated green compact;

(8) co-firing the laminated green body processed in the step (7) by using an LTCC co-firing furnace;

(9) and after sintering, removing the HTCC on the upper surface and the lower surface of the substrate to obtain the large-size LTCC substrate with the embedded cavity structure.

In the step (3) to the step (6), the embedded cavity structure is divided into 2 parts, and each part is laminated by using 2 materials, so that the HTCC-LTCC composite structure is obtained.

Wherein the thickness of the HTCC used in the step (3) and the step (5) is the same and is greater than 1/2 of the total thickness of the LTCC.

Wherein, the baking condition in the step (7) is 60-100 ℃ and 0.5-4 hours.

Wherein, the co-sintering process in the step (8) adopts a pressure-assisted sintering mode, and the auxiliary pressure is as follows: 5000-20000 Pa.

In the step (9), the HTCC may be removed by scraping, polishing, or the like.

The following is a more specific example:

as shown in figure 1, the large-size LTCC substrate with the embedded cavity structure consists of a cavity bottom layer 1-1, a cavity wall layer 1-2 and a cavity top layer 1-3 from bottom to top. The material used for the LTCC substrate in the examples was 8 inch DuPont 951 PT. The cavity bottom layer of the large-size embedded cavity LTCC substrate manufactured in the example has a 5-layer structure, the cavity wall layer has a 3-layer structure, and the cavity top layer has a 2-layer structure; the sizes of the cavities in the 3-layer cavity wall layer structure are 12mm multiplied by 12 mm.

Figure 3 shows the process flow of the present method. The specific process comprises the following steps:

(1) blanking and aging

According to the structural layer number of the large-size embedded cavity designed in the example, 10 DuPont 951PT green ceramic tiles (single layer thickness is 0.114 mm) are blanked, and the tiles are aged correspondingly.

(2) Punching and filling holes

And manufacturing a punching file according to the internal electrical connection property of the LTCC substrate, and punching an internal interlayer interconnection through hole, a lamination alignment hole and the like by using a mechanical punching machine. Thereafter, the through-hole is filled with a metal paste by a printer.

(3) Line printing

And printing a line pattern on each layer of green ceramic sheet by adopting a screen printing mode through a printer according to the metallization structure on each layer.

(4) Cavity manufacturing method

Firstly, making a punching file according to the designed size and the position of the cavity, and then respectively processing corresponding cavities on the 3 layers of cavity wall layers by utilizing ultraviolet laser equipment in a secondary alignment mode.

(5) As an auxiliary layer

6 HTCC green ceramic chips (single layer thickness about 0.23 mm) are taken, and then lamination alignment holes are machined by a punching machine.

(6) Manufacture of blind cavity composite green body

Sequentially overlapping 3 layers of HTCC (high temperature ceramic) raw porcelain, 5 layers of cavity bottom layers and 3 layers of cavity layers on the lamination plate from bottom to top according to the product structure sequence, laminating according to a blind cavity structure (the pressure is 3000 psi; the temperature is 70 ℃) to obtain a blind cavity composite green body, as shown in figure 4, wherein 4-1 is an HTCC auxiliary layer, 4-2 is a cavity bottom layer, and 4-3 is a cavity layer;

(7) manufacture of cavity top composite green body

Sequentially overlapping 3 layers of HTCC (high temperature ceramic) raw porcelain and 2 layers of cavity top layers on the laminated plate from bottom to top according to the product structure sequence, laminating according to the flat plate structure (pressure 3000 psi; temperature 70 ℃) to obtain a cavity top layer composite green compact, as shown in figure 5, wherein 5-1 is an HTCC auxiliary layer, and 5-2 is a cavity top layer;

(8) cavity combination body

Coating a certain adhesive on the upper surface of the blind cavity composite green body, aligning and laminating the blind cavity composite green body and the cavity top layer composite green body according to the product structure sequence by using a lamination plate, then placing a metal flat plate, carrying out small-pressure lamination (100 psi, room temperature) in an axial pressing mode, taking out the laminated green body after lamination, and baking the laminated green body on a heating table at 80 ℃ for 2 hours.

(9) Hot cutting

Cutting the 8-inch composite green body into small units by using a hot cutting machine;

(10) pressure assisted sintering

Placing the small composite green body on a burning bearing plate, measuring the size of a product by using a caliper, calculating the plane area, and placing a corresponding weight on the top surface of the composite green body for pressure-assisted sintering (according to a conventional sintering curve) according to the configuration requirement of the pressure of 10000-12000 Pa.

(11) Removing the auxiliary layer

And after sintering, lightly scraping the HTCCs on the upper surface and the lower surface of the laminated substrate by using a blade to obtain a large-size embedded LTCC substrate structure sample.

In a word, the method comprises the steps of punching, cavity punching, HTCC auxiliary layer manufacturing, blind cavity composite green body manufacturing, cavity top layer composite green body manufacturing, laminating, sintering and the like. According to the method, the characteristics that the HTCC auxiliary layer is not softened and collapsed in the low-temperature sintering process are utilized, a certain supporting effect is given to the top layer of the cavity, and further the smoothness of the upper surface and the lower surface of the large-size embedded cavity is guaranteed, wherein the HTCC with the same thickness is added on the upper surface and the lower surface of the LTCC substrate to play a balancing role, and the smoothness of the whole LTCC substrate is guaranteed.

By adopting the method, a sacrificial layer material does not need to be added in the cavity, the sintering curve and the lamination parameters do not need to be adjusted, the method is simple to operate, the consumed time is less, the efficiency is high, and particularly good cavity flatness can be obtained for a large-size embedded cavity.

It should be noted that the coefficients and parameters given in the above embodiments are provided for persons skilled in the art to realize or use the invention, and the invention is not limited to the values disclosed in the foregoing, and those skilled in the art can make modifications or adjustments to the above embodiments without departing from the inventive idea, therefore, the scope of protection of the invention is not limited by the above embodiments, but should be in the broadest scope of the inventive features set forth in the claims.

Claims

1. The manufacturing method of the large-size LTCC substrate with the embedded cavity structure comprises the steps that the large-size LTCC substrate with the embedded cavity structure comprises a cavity bottom layer (1-1), a cavity wall layer (1-2) and a cavity top layer (1-3), the size of a cavity is larger than or equal to 10mm by 10mm, and the cavity is completely sealed inside the LTCC substrate; the method is characterized by comprising the following steps:

2. The method of claim 1, wherein the total thickness of the first HTCC green ceramic sheets is equal to the total thickness of the second HTCC green ceramic sheets and is greater than 1/2 of the total thickness of the LTCC green ceramic sheets.

3. The method for manufacturing a large-sized LTCC substrate with an embedded cavity structure as claimed in claim 1, wherein the baking temperature in step (7) is 60-100 ℃ for 0.5-4 hours.

4. The method as claimed in claim 1, wherein the co-firing treatment in step (8) is performed by pressure-assisted firing at an assisted pressure of 5000-20000 Pa.

5. The method for manufacturing a large-sized LTCC substrate with a buried cavity structure in it according to claim 1, wherein the HTCC removing part in the step (9) is scraped or polished.