Metallization method for side wall of cavity of low-temperature co-fired ceramic substrate

Abstract

The invention discloses a metallization method for the side wall of a cavity of a low-temperature co-fired ceramic substrate. The metallization method comprises the following steps of: sequentially performing punching treatment on each layer of green ceramic chip according to a preset cavity outline; during lamination, the hole sites on the adjacent green ceramic chips are arranged in a staggered and overlapped manner; the holes are filled with metal slurry in a solid mode, and a blank plate with solid metal points is obtained after drying and leveling treatment; each layer of blank plate is cut according to the cavity contour in sequence; the outline of the cavity is a line connected with each solid metal point on the blank plate; and laminating and pressing the cut blank plates, and co-firing to obtain the ceramic substrate with the metalized cavity side wall. The round holes are designed in the contour lines of the cavities of the green ceramic chips, then the solid metal slurry is filled in the green ceramic chip stage, and the green ceramic chips are laminated and co-fired, so that metal interconnection in all the round holes in the contour area of the substrate is realized, after the cavities are formed, the filled metal slurry is immediately exposed, and metallization of the side walls of the cavities of the substrate is completed.

Description

Technical Field

[0001] The present invention relates to the processing technology of low temperature co-fired ceramic substrates (LTCC) in the field of microelectronics technology, and specifically to a method for metallizing the side walls of cavities of low temperature co-fired ceramic substrates. Background Art

[0002] Low Temperature Co-fired Ceramic (LTCC) technology is an important multi-layer wiring technology in the field of microelectronics packaging, and is widely used in the field of hybrid microelectronics integration. The LTCC substrate is formed by laminating and co-firing multiple green ceramic sheets according to design requirements. Circular vias are punched on each green ceramic sheet according to the circuit design, and then these holes are filled with metal paste to achieve the interconnection of electrical signals between different layers. According to different application requirements, LTCC substrates can be divided into high-strength substrates, high coefficient of thermal expansion substrates, and low dielectric and low loss substrates, which are respectively applicable to fields such as package encapsulation, chip encapsulation, and microwave radio frequency.

[0003] In the field of microwave radio frequency, LTCC substrates are widely used in TR components and high-frequency radio frequency transmission front-end modules. With the expansion of the application scope and the complexity of the application environment, more and more LTCC substrates in high-frequency fields are beginning to require metallization on the side walls of the substrate shape or the inner side walls of cavities to enhance the signal shielding effect.

[0004] Currently, there are mainly two methods for substrate side wall metallization:

[0005] Manual coating method: After the substrate is co-fired to form a mature ceramic, a fine brush is used to dip the metal conductor paste and manually coat the side area of the substrate that needs to be metallized, and then dried and subjected to high-temperature sintering. Due to manual operation, this method has low production efficiency and poor consistency between substrates. In addition, for metallization operations that require a certain depth, especially the metallization of the inner side walls of cavities, due to the narrow space, the operation of brush coating is difficult and almost impossible to achieve.

[0006] Screen printing method in the green ceramic stage: In the green ceramic stage, the side walls of each green ceramic sheet that needs to be metallized are achieved by screen printing (screen printing conductor paste). However, since the green ceramic sheet is relatively thin (usually about 0.1 mm), metal conductor paste will remain on the front and back sides of the green ceramic sheet after printing, increasing the risk of short circuit between the internal network of the substrate and the ground. At the same time, due to the gradual accumulation of excess paste, the corresponding area of the substrate will bulge after sintering, affecting the flatness of the substrate. In addition, the natural fluidity of the conductor paste will cause a large amount of paste to flow onto the porous paper under the green ceramic sheet, resulting in waste, especially when using gold conductor, the cost waste is more significant.

[0007] In summary, the existing methods for metallizing the sidewalls of substrates have problems such as low production efficiency, poor consistency, high operation difficulty, affected substrate flatness, and paste waste, making it difficult to meet the growing demand for sidewall metallization of LTCC substrates in the high-frequency field. Therefore, it is of great practical significance to develop a new, efficient method that can accurately metallize the sidewalls of cavities. Summary of the Invention

[0008] In view of this, the present invention provides a method for metallizing the sidewalls of cavities in a low-temperature co-fired ceramic substrate to solve the problems raised in the above background technology. By punching holes along the cavity contour line of the green ceramic sheet, then solidly filling the holes with metal paste, and subsequently using laser cutting to cut the green ceramic sheet and the solidified metal points in the round holes along the cavity contour, after lamination and co-firing, interconnection at the edge of the cavity contour is achieved, and the purpose of metallizing the sidewalls of the cavity is achieved.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] In a first aspect, the present invention discloses a method for metallizing the sidewalls of cavities in a low-temperature co-fired ceramic substrate, comprising the following steps:

[0011] S1. Punch each layer of green ceramic sheet in sequence according to a preset cavity contour; during lamination, the hole positions on adjacent green ceramic sheets are arranged in a staggered and overlapping manner;

[0012] S2. Use metal paste to solidly fill the holes, and after drying and leveling, obtain a blank plate with solid metal points;

[0013] S3. Cut each layer of blank plate in sequence according to the cavity contour, and the cutting energy is 50% - 95%; the cavity contour is a line connecting each solid metal point on the blank plate;

[0014] S4. Stack and press the cut blank plates and then co-fire them to obtain a ceramic substrate with metallized sidewalls of the cavity.

[0015] As a further scheme of the present invention: in step S1, before the punching process, set the hole diameter as r and the center distance between adjacent holes as L, then 2r < L < 3r.

[0016] As a further scheme of the present invention: in step S1, the specific staggered and overlapping of the hole positions on adjacent green ceramic sheets is as follows:

[0017] According to the lamination order, divide the green ceramic sheets into odd-layer green ceramic sheets and even-layer green ceramic sheets, and the center of the hole on the even-layer green ceramic sheet is located at the midpoint of the line connecting the centers of two adjacent holes on the adjacent odd-layer green ceramic sheet.

[0018] As a further scheme of the present invention: the thickness of the green ceramic sheet is 0.08 - 0.12 mm; and / or:

[0019] The metal paste is gold paste, silver paste or palladium-silver paste.

[0020] As a further solution of the present invention: in step S2, the drying temperature is 50-60°C, and the drying time is 30-40 min.

[0021] As a further solution of the present invention: in step S2, the leveling treatment is specifically: using a leveling machine to press the paste higher than the hole surface into the hole.

[0022] As a further solution of the present invention: according to the method for metallizing the side wall of the cavity of the low-temperature co-fired ceramic substrate described in claim 1, characterized in that in step S2, the solid filling is specifically:

[0023] Make a screen plate according to the punching position, cover the screen plate on the green ceramic sheet, inject metal sauce into the hole, the distance between the screen plate and the green ceramic sheet is 0 mm, the movement speed of the hole filling squeegee is 10-15 mm / s, and the solidification pressure of the round hole (i.e., the slurry injection pressure) is 110-120 N.

[0024] As a further solution of the present invention: in step S4, the pressing is specifically: isostatic pressing the laminated blank plates with an aluminum foil bag, the pressing temperature is 60-70°C; the pressure is 2500-3500 psi, and the pressing time is 25-30 min.

[0025] As a further solution of the present invention: in step S4, the co-firing temperature is 845-850°C, and the time is 20-25 min.

[0026] In the second aspect, the present invention discloses a ceramic substrate with metallized side walls of the cavity prepared by the method for metallizing the side walls of the cavity of the low-temperature co-fired ceramic substrate as described above.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] In the present invention, by punching holes in a staggered manner along the cavity contour of multiple green ceramic sheets and combining the control of the number of stacked green ceramic sheets, the interconnection of the metallized side walls of the cavity and the precise control of the overall depth are realized, which can well ensure the consistency between the side wall metallized substrates and meet the gradient requirements of the local shielding area in the millimeter wave band.

[0029] Based on the constraint relationship (2r < L < 3r) between the radius r of the round hole and the spacing L, it is ensured that the metallized area has sufficient coverage along the cavity contour line, avoiding the fracture of the structure after punching the green ceramic sheet.

[0030] The filled solid paste is completely within the circular hole area of the green ceramic sheet and will not overflow to the upper and lower surfaces of the green ceramic sheet; through the application of the leveling process, the excess paste directly above the circular hole can be vertically pressed into the circular hole. Therefore, the sidewall metallized substrate has good flatness. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the punching positions of the odd-numbered green ceramic sheets and the even-numbered green ceramic sheets in the embodiment;

[0032] Figure 2 It is a schematic diagram of the cavity contour after laser cutting of the odd-numbered green ceramic sheets in the embodiment;

[0033] Figure 3 It is a schematic side sectional view of the sintered sidewall metallized substrate in the embodiment;

[0034] In the figure, 1 - substrate, 2 - circular holes in the odd-numbered green ceramic sheets, 3 - circular holes in the even-numbered green ceramic sheets, 4 - cavity contour, 5 - solid paste in the circular holes, 6 - cavity. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] For the convenience of understanding the present invention, the present invention will be described more comprehensively below in conjunction with specific drawings and embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0037] In this embodiment, the LTCC substrate is designed with 10 layers. The substrate has a regular cuboid shape with dimensions of 3.3 mm * 2.7 mm * 0.8 mm. The cavity contour has dimensions of 1.35 mm × 1.35 mm, and the cavity depth is 0.8 mm. The design requires metallization of the cavity sidewalls.

[0038] Step 1, punching: Punch holes at the edges of the cavities of the green ceramic sheets that require sidewall metallization

[0039] The sintering thickness of each green ceramic sheet is about 0.1 mm. Therefore, the upper 8 layers of the 10 layers of green ceramic sheets of the substrate are selected for sidewall metallization, which can meet the requirement of 0.8 mm depth of sidewall metallization of the cavity. The 8 green ceramic sheets of 168 mm × 168 mm that need sidewall metallization are divided into two parts according to the stacking order: odd-layer green ceramic sheets (the 1st, 3rd, 5th, and 7th layers) and even-layer green ceramic sheets (the 2nd, 4th, 6th, and 8th layers). The green ceramic sheets are placed horizontally layer by layer on the vacuum adsorption table of the laser punching machine. After turning on the vacuum adsorption, the green ceramic sheets are punched with laser energy along the cavity contour. After punching, round holes penetrating the thickness direction of the green ceramic sheets are formed at the laser-cut positions of the green ceramic sheets. The radius of all round holes is 0.1 mm for subsequent solid filling of metal paste. The centers of all round holes are located on the cavity contour line so that the metal area can be exposed to the maximum extent at the cavity edge after cutting. The distribution positions of the round holes on the cavity contour line are different for odd and even layers to ensure that the paste in all subsequent round holes can be interconnected.

[0040] For odd-layer green ceramic sheets, 1 round hole is distributed at each corner of the cavity. The cavity size is 1.35 mm × 1.35 mm, so 5 round holes are equally distributed on each contour side. There are a total of 24 round holes on each layer of green ceramic sheet. The distance between the centers of adjacent round holes is 0.23 mm to ensure that there is still 0.03 mm of green ceramic sheet connected between adjacent round holes after the green ceramic sheet is punched, thus maintaining a certain strength.

[0041] For even-layer green ceramic sheets, 6 round holes are equally distributed on each contour side, with a total of 24 round holes. And the center of each round hole is at the center point on the contour line of the centers of two round holes in the odd layer. In this way, it can be ensured that two non-connected round holes on the contour line of the same layer of green ceramic sheet are connected through the round holes of the upper and lower layers of green ceramic sheets, realizing the connection of all round holes at the cavity contour edge of all green ceramic sheets, as Figure 1 shown.

[0042] Step 2: Solidify the round holes: Solidly fill the round holes in the cavity contour area with metal paste

[0043] According to the different positions of the round holes at the edges of the cavities of the green ceramic chips in the odd and even layers, two stainless-steel round-hole solidification stencils with dimensions of 360 mm × 360 mm and a thickness of 50 μm are made respectively. The two stencils correspond one by one to the sizes and positions of the round holes in the green ceramic chips of the odd and even layers, and the hole diameter is 0.1 mm, so as to press the slurry to be solidified in the round holes into the round holes of the green ceramic chips from the opening. First, place the green ceramic chips of the odd layer on the vacuum adsorption table of the semi-automatic printing machine in sequence, use the corresponding round-hole solidification stencil, put the solidification gold slurry on it, and set the round-hole solidification parameters: the screen spacing is 0 mm, the round-hole solidification speed is 10 mm / s, and the round-hole solidification pressure is 110 N. After starting the round-hole solidification machine, use the downward pressure of the printing squeegee on the slurry to press the slurry above the circular opening in the stainless-steel stencil into the green ceramic chip. As the squeegee moves from the front to the back of the stencil in one cycle, all the round holes are filled with metal solidification slurry. After all the green ceramic chips of the odd layer are completed with round-hole solidification, replace the round-hole solidification stencil for the even layer, place the green ceramic chips of the even layer on the vacuum adsorption table of the round-hole solidification machine in sequence, and still use the same round-hole solidification parameters to carry out gold slurry solid filling on them in sequence. Put all the green ceramic chips after round-hole solidification into the oven, set the drying temperature to 50 °C and the drying time to 30 min.

[0044] Step 3, leveling: Use a leveling machine to press the slurry higher than the surface of the green ceramic chip into the round hole after drying.

[0045] Cover both the front and back sides of all the green ceramic chips after round-hole solidification and drying with clean A4 paper, place them horizontally layer by layer on the lower workbench surface of the leveling machine in sequence, set the leveling machine parameters: pressure 5T, time 30 s, start the leveling machine, and the upper workbench surface drops to press the slurry part higher than the surface of the green ceramic chip into the round hole.

[0046] Step 4, cutting the cavity: Use a laser cutting machine to perform laser cutting on each layer of green ceramic chip along the cavity contour.

[0047] Place the 8 flattened green ceramic wafers layer by layer on the vacuum adsorption table of the laser cutting machine. The other 2 green ceramic wafers have no cavity design and do not need to be cut, and are reserved. Set the cutting parameters: the laser energy is 90%. Start the equipment to cut along the cavity contour line. After cutting, each green ceramic wafer is separated into two parts along the cutting line: the substrate part + the cavity part. The cavity part of the green ceramic wafer detaches from the substrate area, and the substrate cavity is formed. During this process, all the solid cylindrical slurries located at the edge of the cavity contour are also divided into two along the contour line, and the cut surfaces of the solid slurries remaining in the substrate area are exposed. In the even-numbered green ceramic wafers, each contour edge has 6 rectangular slurry cut surfaces with a size of 0.12 mm × 0.2 mm (0.12 mm is the thickness of the green ceramic wafer). In the odd-numbered green ceramic wafers, in addition to 5 rectangular slurry cut surfaces with a size of 0.120 mm × 0.2 mm on each contour edge, there are 2 rectangular slurry cut surfaces with a size of 0.12 mm × 0.1 mm at the endpoints. The slurry cut surfaces in all 8 layers of green ceramic wafers constitute the metallization of the substrate cavity contour, as Figure 2 shown.

[0048] Step 5: Laminating and co-firing: Layer the green ceramic wafers, isostatically press and co-fire them

[0049] Stack the 8 green ceramic wafers after cavity cutting in sequence according to the established order. After stacking, any two adjacent metal slurry semi-cylinders at the cavity edge of the odd-numbered layers overlap with the metal slurry semi-cylinders at the cavity edge of the even-numbered green ceramic wafers in the vertical direction, and the overlapping length in the horizontal direction is 0.09 mm, so that all the metal slurry semi-cylinders at the cavity edge are connected to achieve the microwave signal shielding effect. Subsequently, stack the 8 green ceramic wafers with the 2 uncut green ceramic wafers, and after overall plastic packaging, put them into an isostatic press (temperature 70°C; pressure 2500 psi, time 25 min) to adhere all the green ceramic wafers together. Take out the pressed whole-board green ceramic wafers and put them into a co-firing furnace for sintering. The sintering peak temperature is 845°C, and the peak temperature time is 20 min. After co-firing, the metal slurry in the holes at the edge of the substrate cavity combines with the substrate ceramic body to form a dense and firm whole. At the same time, the surface of the substrate in the cavity edge area is flat and does not affect the subsequent assembly, thus realizing the metallization of the cavity side wall. The side wall structure schematic diagram is as Figure 3 shown.

[0050] Although this specification is described according to the embodiments, not each embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0051] Therefore, the above description is only a preferred embodiment of the present application and is not intended to limit the scope of implementation of the present application; that is, all equivalent transformations made according to the scope of the claims of the present application fall within the protection scope of the claims of the present application.

Claims

1. A method for metallizing the cavity sidewall of a low temperature co-fired ceramic substrate, characterized in that: The following steps are involved: S1. Punching holes on each layer of green ceramic sheets in sequence according to a preset cavity profile; when stacking, the holes on adjacent green ceramic sheets are arranged in a staggered and overlapping manner; S2, using metal slurry to solidly fill the hole, and after drying and leveling, a blank plate with solid metal points is obtained; S3, cutting each layer of the blank sheet in turn according to the cavity contour; the cavity contour is a line connecting each solid metal point on the blank sheet; S4, stacking and pressing the cut blank plates and then co-firing them to obtain a ceramic substrate with metallized cavity side walls.

2. The method for metallizing the cavity sidewall of a low temperature co-fired ceramic substrate according to claim 1, characterized in that: In step S1, before punching, the hole diameter is set to r, and the center distance between adjacent holes is set to L, then 2r<L<3r.

3. The method for metallizing the cavity sidewall of a low temperature co-fired ceramic substrate according to claim 1, characterized in that: In step S1, the holes on adjacent green ceramic sheets are staggered and overlapped as follows: The raw porcelain sheets are divided into odd-numbered raw porcelain sheets and even-numbered raw porcelain sheets according to the stacking order. The center of the hole in the even-numbered raw porcelain sheet is located at the midpoint of the line connecting the centers of two adjacent holes on the adjacent odd-numbered raw porcelain sheets.

4. The method for metallizing the cavity sidewall of a low temperature co-fired ceramic substrate according to claim 1, characterized in that: The thickness of the raw ceramic sheet is 0.08-0.12 mm; and / or: The metal paste is gold paste, silver paste or palladium silver paste.

5. The method for metallizing the cavity sidewall of a low temperature co-fired ceramic substrate according to claim 1, characterized in that: In step S2, the drying temperature is 50-60°C and the drying time is 30-40 minutes.

6. The method for metallizing the cavity sidewall of a low temperature co-fired ceramic substrate according to claim 1, characterized in that: In step S2, the leveling process is specifically as follows: using a leveling machine to press the slurry above the hole surface into the hole.

7. The method for metallizing the cavity sidewall of a low temperature co-fired ceramic substrate according to claim 1, characterized in that: The method for metallizing the cavity sidewall of a low-temperature co-fired ceramic substrate according to claim 1, characterized in that in step S2, the solid filling is specifically: Make a screen according to the punching position, cover the screen on the raw porcelain sheet, inject metal slurry into the hole, the distance between the screen and the raw porcelain sheet is 0mm, the movement speed of the hole filling scraper is 10-15mm / s, and the circular hole solidification pressure is 110-120N.

8. The method for metallizing the cavity sidewall of a low temperature co-fired ceramic substrate according to claim 1, characterized in that: In step S4, the pressing is specifically as follows: isostatic pressing the laminated blank sheet material using an aluminum foil bag, the pressing temperature is 60-70° C., the pressure is 2500-3500 psi, and the pressing time is 25-30 min.

9. The method for metallizing the cavity sidewall of a low temperature co-fired ceramic substrate according to claim 1, characterized in that: In step S4, the co-firing temperature is 845-850° C. and the time is 20-25 min.

10. A ceramic substrate with metallized cavity sidewalls made by the method for metallizing cavity sidewalls of a low-temperature co-fired ceramic substrate according to any one of claims 1 to 9.

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