Shell structure applied to laser projection and preparation method thereof

Abstract

The invention discloses a shell structure applied to laser projection and a preparation method thereof, and relates to the technical field of laser projection, the shell structure comprises a shell body, the shell body comprises a ceramic base, the thermal expansion coefficient of the ceramic base is 4.5-6.5 ppm / K, and the ceramic base is integrally formed through an HTCC process; the thermal expansion coefficient of the sealing ring is 5.0-6.5 ppm / K, and the sealing ring is in welded connection with the ceramic base through a convex rib to form an airtight packaging structure; the top end, far away from the ceramic base, of the sealing ring is provided with a groove used for mounting a sapphire window. The aluminum nitride ceramic replaces traditional aluminum oxide ceramic, the difference value of the thermal expansion coefficient of the aluminum nitride ceramic and the thermal expansion coefficient of the 4J29 kovar alloy is smaller than 1.5 ppm / K, the welding contact area of the aluminum nitride ceramic and the 4J29 kovar alloy is reduced in cooperation with the convex rib design, and the welding cracking risk is reduced; meanwhile, the HTCC integrated ceramic base replaces a split brazing structure, the oxygen-free copper machining and brazing procedures are omitted, an optical mounting tool is omitted through the groove self-positioning design, and the manufacturing cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of laser projection, and in particular to a shell structure applied to laser projection and a preparation method thereof. Background Art

[0002] In the development of laser projection technology, the performance of the laser chip packaging shell is crucial. Traditional laser projection shell designs are mostly made of alumina ceramic and oxygen-free copper welded structure. This structure has the following defects: On the one hand, the thermal expansion coefficient (CTE) of oxygen-free copper is quite different from that of alumina ceramics, and the difference in welding thermal mismatch is large, resulting in large welding stress, which can easily cause cracking of alumina ceramics and increase the risk of product airtightness reliability.

[0003] On the other hand, if too many chips are packaged in a single housing, the bottom heat dissipation area increases, requiring a correspondingly larger oxygen-free copper baseplate, which further increases welding stress between it and the alumina. Furthermore, traditional structures are complex and expensive to produce, and their heat dissipation performance is limited in both vertical and lateral directions.

[0004] It can be seen that there is an urgent need to design a ceramic shell that can meet the high heat dissipation requirements of laser projection chips, while having low welding stress, high airtightness and low cost. Summary of the Invention

[0005] In a first aspect of the present invention, in order to solve the above technical problems, a housing structure for laser projection is provided, comprising a housing body, wherein the housing body comprises: Ceramic base with a thermal expansion coefficient of 4.5-6.5 ppm / K, and is integrally formed using the HTCC process; The sealing ring has a thermal expansion coefficient of 5.0-6.5 ppm / K. The sealing ring is welded to the ceramic base through ribs to form an airtight packaging structure. The top of the sealing ring away from the ceramic base is provided with a groove for mounting a sapphire window.

[0006] Furthermore, the material of the ceramic base is aluminum nitride; the material of the sealing ring is 4J29 Kovar alloy.

[0007] Furthermore, the ceramic base and the sealing ring are connected by welding using Ag72Cu28 solder.

[0008] Furthermore, rounded corner avoidance structures are provided in the extending directions of the four corners of the groove.

[0009] Furthermore, the vertical cross-section of the convex rib is rectangular, and the height of the convex rib is 0.50±0.02 mm and the width is 0.50±0.02 mm.

[0010] Furthermore, the inner cavity sidewalls and bottom of the ceramic base are provided with a tungsten slurry metallization layer with a thickness greater than 15 μm.

[0011] A second aspect of the present invention provides a method for preparing the shell structure, comprising the following steps: Ceramic base molding: After casting aluminum nitride green ceramic sheets, laser punching, tungsten slurry hole filling, screen printing of metallized patterns, mechanical cavity opening, isostatic pressing and lamination, slitting, high-temperature co-firing at 1600-1800℃, nickel electroplating and grinding wheel cutting into units are carried out in sequence; Sealing ring processing: After stamping 4J29 Kovar alloy plate, decarburization annealing treatment is performed; Welding assembly of the sealing ring and ceramic base: The ceramic base, Ag72Cu28 solder sheet, and sealing ring are sequentially placed into the graphite mold and welded in a nitrogen chain furnace at 780–820°C for 15 ± 5 min. The mold limit misalignment is ≤ 0.10 mm. Surface plating: Power is applied through the blind hole hanger at the upper end of the sealing ring, and nickel layer and gold layer are electroplated in sequence.

[0012] Furthermore, in the ceramic base forming step, the metallized pattern includes an inner cavity core mounting area, an outer bottom mounting area, and a sealing welding area, wherein: The inner cavity core mounting area is used for mounting chips; The outer bottom mounting area is used for external connection; The sealing welding area is used for welding with the sealing ring, and the inner cavity core area and the different functional areas of the outer bottom mounting area are electrically connected through multi-layer ceramic wiring vias.

[0013] Compared with the prior art, the embodiments of the present invention have the following beneficial effects: The present invention replaces traditional alumina ceramics with aluminum nitride ceramics. Since the difference in thermal expansion coefficient between aluminum nitride ceramics and 4J29 Kovar alloy is less than 1.5 ppm / K, the rib design reduces the welding contact area between the two and reduces the risk of weld cracking. Furthermore, the HTCC integrated ceramic base replaces the split brazing structure, eliminating the oxygen-free copper processing and brazing steps. The groove self-positioning design eliminates the need for optical mounting tooling, reducing manufacturing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0015] Figure 1This is a schematic diagram of the overall structure of the housing disclosed in an embodiment of the present invention; Figure 2 This is a front view of the ceramic base disclosed in an embodiment of the present invention; Figure 3 A rear view of the ceramic base disclosed in an embodiment of the present invention; Figure 4 A cross-sectional view of a sealing ring disclosed in an embodiment of the present invention; Figure 5 A top view of a sealing ring disclosed in an embodiment of the present invention; Figure 6 A schematic diagram of the U-shaped Ag72Cu28 solder disclosed in an embodiment of the present invention; Figure 7 This is a cross-sectional view of a finished housing according to an embodiment of the present invention.

[0016] In the picture: 10. Ceramic base; 20. Sealing ring; 21. Raised rib; 22. Groove; 22a. Rounded corner avoidance structure; 23. Blind hole; 24. Ag72Cu28 solder. DETAILED DESCRIPTION

[0017] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0018] The present invention mainly provides a shell structure for laser projection and a preparation method thereof. The purpose is to use a welded structure composed of a high-thermal-conductivity aluminum nitride ceramic base and a 4J29 Kovar alloy sealing ring to ensure the high reliability and high thermal conductivity of the shell, while reducing the existing manufacturing process.

[0019] The following is a detailed description of the housing structure used for laser projection.

[0020] See also Figure 1 A housing structure for laser projection includes a housing body comprising a welded ceramic base 10 and a sealing ring 20. The ceramic base 10 has a thermal expansion coefficient of 4.5-6.5 ppm / K and is integrally formed using the HTCC process. The sealing ring 20 has a thermal expansion coefficient of 5.0-6.5 ppm / K and is welded to the ceramic base 10 via a rib 21, forming an airtight package. A groove 22 for mounting a sapphire window 30 is provided at the top of the sealing ring 20, away from the ceramic base 10.

[0021] The traditional laser projection shell is designed as a welded structure of alumina ceramic and oxygen-free copper. The defect of this structure is that the thermal expansion coefficient of oxygen-free copper is quite different from that of alumina ceramic, that is, the welding thermal mismatch is large, resulting in large welding stress, which can easily cause the alumina ceramic to crack, thereby affecting the airtight reliability of the shell.

[0022] In this embodiment, the ceramic base 10 is made of aluminum nitride ceramic, and the sealing ring 20 is made of 4J29 Kovar alloy. On the one hand, aluminum nitride ceramic has significantly higher thermal conductivity than traditional alumina ceramic, meeting the high heat dissipation requirements of laser chips. On the other hand, the sealing ring 20 is made of 4J29 Kovar alloy, whose thermal expansion coefficient is highly matched with that of the aluminum nitride ceramic and sapphire window. This reduces welding thermal mismatch stress, fundamentally reduces the risk of weld cracking, and ensures the high airtightness requirements of the entire housing structure.

[0023] In this embodiment, the inner cavity sidewalls and bottom of the ceramic base 10 are provided with a tungsten slurry metallization layer with a thickness greater than 15 μm, and the internal via-hole conduction resistance is 30-50 mΩ.

[0024] The traditional sealing ring is a flat plate structure, while in this embodiment, the sealing ring 20 is provided with a rib 21 on the contact surface with the ceramic base 10, and a groove 22 is provided on the top away from the ceramic base 10. Figure 4-5 As shown: The dimensions of the groove 22 precisely match the sapphire window, enabling self-positioning and placement of the sapphire window without the need for additional fixtures. Furthermore, rounded corner avoidance structures 22a are provided at the four corners of the groove 22, and the base requires a clean corner. In this embodiment, the radius of the rounded corner avoidance structures 22a is 0.3mm to facilitate the placement of the window.

[0025] The vertical cross section of the rib 21 is rectangular, and the height and width of the rib 21 are 0.50±0.02mm and 0.50±0.02mm, respectively. Figure 7 The purpose of the rib 21 design is to, on the one hand, reduce the welding stress by significantly reducing the welding contact area between the aluminum nitride ceramic and the Kovar alloy; on the other hand, the aluminum nitride ceramic and the Kovar alloy are welded together through the rib 21 to form a double rounded structure inside and outside, ensuring airtight reliability.

[0026] A circular blind hole 23 is provided on the left and right sides of the top center line of the sealing ring 20, and the hole depth is preferably 0.20 mm, so that the metal clamping ring can realize the electrical connection between the isolated pad and the sealing ring 20 during the subsequent electroplating and rack plating, thereby realizing the electroplating and rack plating process of the entire shell.

[0027] In this embodiment, the ceramic base 10 and the sealing ring 20 are welded together by Ag72Cu28 solder 24. Figure 6As shown, eutectic Ag72Cu28 solder is used as the brazing solder, and its shape is a U-shaped structure, and the thickness is preferably 0.07 mm.

[0028] The following is a detailed description of the process for preparing the shell structure used for laser projection.

[0029] The method for preparing the shell body for laser projection in this embodiment mainly includes the following four steps: Step 1: Ceramic base forming: After casting aluminum nitride green ceramic sheets, laser punching, tungsten slurry hole filling, screen printing of metallized patterns, mechanical cavity opening, isostatic pressing and lamination, slitting, high-temperature co-firing at 1600-1800℃, nickel electroplating and grinding wheel cutting into units are carried out in sequence.

[0030] Step 2: Sealing ring processing: After stamping the 4J29 Kovar alloy plate, decarburization annealing is performed.

[0031] Step 3: Welding and assembling the sealing ring and the ceramic base: Place the ceramic base, Ag72Cu28 solder sheet, and sealing ring into the graphite mold in sequence, and weld them in a nitrogen chain furnace at 780–820°C for 15±5 min. The mold limit misalignment should be ≤0.10 mm.

[0032] Step 4: Surface plating: Power is applied through the blind hole hanger at the upper end of the sealing ring, and nickel and gold layers are electroplated in sequence. The coating thickness requirements are that the nickel layer thickness is ≥6 μm and the gold layer thickness is ≥0.60 μm.

[0033] Specifically, in the ceramic base forming step, the metallized pattern includes an inner cavity core mounting area, an outer bottom mounting area and a sealing welding area, wherein: the inner cavity core mounting area is used for chip mounting; the outer bottom mounting area is used for external connection; the sealing welding area is used for welding with the sealing ring, and the different functional areas of the inner cavity core mounting area and the outer bottom mounting area are electrically connected through multi-layer ceramic wiring vias.

[0034] like Figure 2-3 As shown, metallized areas A and B are inner pads; metallized areas C and D are outer pads. The connection relationships are A and C conductive, and B and D conductive. X, Y, Z, and X1 are all grounded. X1 is the mounting mark, and Y metallized area has a 0.05mm margin around it to facilitate cracking after full-plate ceramic electroplating. Furthermore, through the design of the aperture and trace width inside the multilayer ceramic, the inner and outer pads are conductive, with an on-resistance between 30-50mΩ and the ability to withstand 3A current. The insulation resistance between non-conductive pads is ≥1x10 10 Ω (100VDC), the metal filling metal for the internal wiring of the ceramic and the surface metal are all made of metal tungsten slurry. After the ceramic base is co-fired, the entire base is pre-plated with electroplated nickel with a thickness of 2-5μm. The entire ceramic after nickel plating is split by grinding wheel and divided into ceramic base units.

[0035] This embodiment uses the high thermal conductivity aluminum nitride material to quickly transfer heat from the center of the cavity to the edge, solving the pain point of overheating in the edge area of ​​the laser chip.

[0036] Specifically, during the sealing ring processing step, the light window can use a self-positioning method to sequentially place the Au80Sn20 solder and the light window directly into the groove at the top of the sealing ring to complete the airtight seal.

[0037] In order to verify the airtight reliability of this embodiment, an airtight reliability evaluation experiment was performed on the finished shell structure.

[0038] Experimental Conditions: Five gold-plated housings were selected and sealed with Au80Sn20 "U"-shaped solder and the sapphire window described above in a chain atmosphere furnace. The soldering temperature was 300°C ± 10°C in a hydrogen atmosphere, and the solder was held above the eutectic point for 10 minutes. This produced a dummy sample of the laser projection package module. After simulating laser chip packaging process conditions and device-level reliability testing, the housing was tested for airtightness, completing the dummy sample qualification test (all qualification tests were stacked).

[0039] Table 1 Test conditions for identifying fake product closures

[0040] The experimental results are shown in Table 2 below:

[0041] The shell structure for laser projection provided in this embodiment achieves multiple improvements in heat dissipation efficiency, reliability, electrical performance, and cost through the application of aluminum nitride ceramic and 4J29 Kovar alloy materials, the combination of HTCC co-firing process, and the optimization of the sealing ring structure and the side wall of the ceramic base cavity. This provides key support for the popularization of laser projection technology from professional fields to the consumer market.

[0042] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A housing structure for laser projection, characterized in that: The invention comprises a housing body, wherein the housing body comprises: A ceramic base (10) having a thermal expansion coefficient of 4.5-6.5 ppm / K and formed in one piece by a HTCC process; A sealing ring (20) has a thermal expansion coefficient of 5.0-6.5 ppm / K, and the sealing ring (20) is welded to the ceramic base (10) via a convex rib (21) to form an airtight packaging structure; a groove (22) for mounting a sapphire window is provided at the top of the sealing ring (20) away from the ceramic base (10).

2. The housing structure for laser projection according to claim 1, characterized in that: The material of the ceramic base (10) is aluminum nitride; the material of the sealing ring (20) is 4J29 Kovar alloy.

3. The housing structure for laser projection according to claim 1, wherein: The ceramic base (10) and the sealing ring (20) are connected by welding using a U-shaped Ag72Cu28 solder (24).

4. The housing structure for laser projection according to claim 1, characterized in that: Rounded corner avoidance structures (22a) are provided in the extending directions of the four corners of the groove (22).

5. The housing structure for laser projection according to claim 1, characterized in that: The vertical cross-section of the convex rib (21) is rectangular, and the width and height of the convex rib (21) are both 0.50±0.02 mm.

6. The housing structure for laser projection according to claim 1, characterized in that: The inner cavity sidewall and bottom of the ceramic base (10) are provided with a tungsten slurry metallization layer with a thickness greater than 15 μm.

7. A method for preparing the shell structure according to any one of claims 1 to 6, characterized in that: The following steps are involved: Ceramic base molding: After casting aluminum nitride green ceramic sheets, laser punching, tungsten slurry hole filling, screen printing of metallized patterns, mechanical cavity opening, isostatic pressing and lamination, slitting, high-temperature co-firing at 1600-1800℃, nickel electroplating and grinding wheel cutting into units are carried out in sequence; Sealing ring processing: After stamping 4J29 Kovar alloy plate, decarburization annealing treatment is performed; Welding assembly of the sealing ring and ceramic base: The ceramic base, Ag72Cu28 solder sheet, and sealing ring are sequentially placed into the graphite mold and welded in a nitrogen chain furnace at 780–820°C for 15 ± 5 min. The mold limit misalignment is ≤ 0.10 mm. Surface plating: Power is applied through the blind hole hanger at the upper end of the sealing ring, and nickel layer and gold layer are electroplated in sequence.

8. The preparation method according to claim 7, characterized in that In the ceramic base forming step, the metallized pattern includes an inner cavity core mounting area, an outer bottom mounting area and a sealing welding area, wherein: The inner cavity core mounting area is used for mounting chips; The outer bottom mounting area is used for external connection; The sealing welding area is used for welding with the sealing ring, and the inner cavity core area and the different functional areas of the outer bottom mounting area are electrically connected through multi-layer ceramic wiring vias.

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