Large-size double-sided LTCC multi-cavity hermetic packaging process

Abstract

This invention discloses a hermetically sealed assembly process for large-size double-sided LTCC multi-cavity substrates, comprising: setting multiple first welding areas on the front and back sides of the LTCC substrate according to different functional units; setting a first bonding area and a second welding area within the first welding areas; setting a third welding area outside the first welding areas; welding an RF chip onto a molybdenum-copper heat sink to form an RF device; bonding the RF device and a digital chip to the first bonding area; welding a chip capacitor and a chip resistor to the second welding area; welding a chip inductor to the third welding area; bonding the extension legs of a metal frame to a molybdenum-copper pad to form a frame unit; bonding the frame unit to the LTCC substrate and ensuring that the metal frame coincides with the first welding area; welding the bottom of the metal frame to the first welding area; and welding a corresponding metal cover plate to the top of the metal frame. This invention can solve the technical problem of hermetically sealed assembly of multiple cavities on an LTCC substrate.

Description

Technical Field

[0001] This invention relates to a large-size double-sided LTCC multi-cavity hermetic packaging process, belonging to the field of integrated circuit technology. Background Technology

[0002] Currently, hermetic sealing of LTCC substrates typically involves a single cavity, generally using an integrated package with a small size. The typical package structure involves printing conductors on the LTCC substrate surface, soldering a metal frame to the frame soldering area on the LTCC surface, bonding or soldering bare cores and various components to the LTCC substrate surface within the frame, and finally sealing the frame and frame cover plate with parallel seam welding or laser welding to achieve a hermetic seal. This packaging method is only suitable for sealing a single cavity and cannot meet the sealing requirements of multiple cavities. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a large-size double-sided LTCC multi-cavity hermetic sealing process to solve the technical problem of hermetic sealing of multiple cavities on LTCC substrates.

[0004] To achieve the above objectives, the present invention is implemented using the following technical solution: This invention provides a large-size double-sided LTCC multi-cavity hermetic sealing process, including: Multiple first welding areas are provided on the front and back sides of the LTCC substrate according to different functional units; Within the first welding area, a first bonding area and a second welding area are provided according to the corresponding functional units. A third welding area is set outside the first welding area according to the corresponding functional unit; The radio frequency chip is soldered onto the molybdenum copper heat sink to form a radio frequency device, and the radio frequency device and the digital chip are bonded together in the first bonding area. The chip capacitors and chip resistors are soldered to the second soldering area, and the chip inductors are soldered to the third soldering area. The extension legs of the metal frame are bonded to the molybdenum copper pad to form a frame unit. The frame unit is then bonded to the LTCC substrate, ensuring that the metal frame coincides with the first welding area. Weld the bottom of the metal fence to the first welding area, and weld the corresponding metal cover plate of the metal fence to the top of the metal fence.

[0005] Optionally, both the metal frame and the metal cover are made of Kovar alloy 4J29, and the surface of the metal frame is electroplated with nickel with a thickness of 4μm-8μm and gold with a thickness of 1.3μm-3μm; the LTCC substrate is made of low-temperature co-fired green ceramic sheet DuPont 951.

[0006] Optionally, the step of soldering the radio frequency chip onto the molybdenum-copper heat sink includes: Au80Sn20 solder pads with a thickness of 25μm to 30μm were used as the welding material. The radio frequency chip was welded onto the molybdenum copper heat sink in a vacuum eutectic soldering furnace with a solder penetration rate of ≥90% and a solder layer thickness of 5μm to 15μm.

[0007] Optionally, bonding the radio frequency device and the digital chip to the first bonding area includes: H20E conductive silver paste is used to bond the radio frequency devices and digital chips to the first bonding area.

[0008] Optionally, the process of bonding the extension feet of the metal frame to the molybdenum-copper pad includes: The extension legs of the metal frame are bonded to the molybdenum-copper gasket using adhesive patches. The curing temperature is 150℃ and the curing time is 15 minutes. After curing, the distance between the extension legs of the metal frame and the bottom of the molybdenum-copper gasket is 1.11mm-1.14mm.

[0009] Optionally, the welding of the chip capacitor and chip resistor in the second welding area, the welding of the chip inductor in the third welding area, and the welding of the bottom of the metal fence in the first welding area are all done using 63Sn37Pb solder paste or 62Sn36Pb2Ag solder paste as the welding material, and are completed by infrared reflow soldering once, with a solder penetration rate of ≥75% and a solder layer thickness of 1μm to 5μm.

[0010] Optionally, welding the corresponding metal cover plate of the metal fence to the top of the metal fence includes: Laser sealing welding is used to weld the corresponding metal cover plates of the metal fence to the top of the metal fence.

[0011] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: This invention provides a large-size double-sided LTCC multi-cavity hermetic assembly process. By dividing the welding area and bonding area, the chip capacitor, chip resistor, chip inductor and metal fence are welded together in one step using low-temperature solder, improving assembly efficiency. The sealed cavity composed of multiple metal fences and metal cover plates integrated on the front and back of the LTCC substrate effectively reduces the isolation of microwave circuits, thereby improving the microwave performance of the product. Attached Figure Description

[0012] Figure 1 This is a flowchart of the large-size double-sided LTCC multi-cavity hermetic assembly process provided in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the region division on the reverse side of the LTCC substrate provided in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the radio frequency device provided in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the fence unit provided in Embodiment 1 of the present invention; Figure 5 This is a schematic diagram of the welding area on the reverse side of the LTCC substrate provided in Embodiment 1 of the present invention; Figure 6 This is a schematic diagram of a large-size double-sided LTCC multi-cavity hermetic sealing structure provided in Embodiment 1 of the present invention. Detailed Implementation

[0013] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0014] Example 1

[0015] like Figure 1 As shown, this embodiment of the invention provides a large-size double-sided LTCC multi-cavity hermetic sealing process, including the following steps: 1. Multiple first welding areas are provided on the front and back sides of the LTCC substrate according to different functional units; 2. Within the first welding area, a first bonding area and a second welding area are set according to the corresponding functional units; 3. A third welding area is set outside the first welding area according to the corresponding functional unit; like Figure 2 As shown, taking the reverse side of an LTCC substrate as an example, the first welding area, the second welding area, the third welding area, and the first bonding area are shown in the figure.

[0016] 4. Solder the RF chip onto the molybdenum-copper heat sink to form an RF device, and bond the RF device and the digital chip to the first bonding area; like Figure 3 As shown, soldering the RF chip onto the molybdenum-copper heatsink includes: Au80Sn20 solder pads with a thickness of 25μm to 30μm were used as the welding material. The radio frequency chip was welded onto the molybdenum copper heat sink in a vacuum eutectic soldering furnace with a solder penetration rate of ≥90% and a solder layer thickness of 5μm to 15μm.

[0017] The process parameters of the vacuum eutectic welding furnace are shown in Table 1: Table 1

[0018] Bonding the radio frequency device and the digital chip to the first bonding area includes: H20E conductive silver paste is used to bond the radio frequency devices and digital chips to the first bonding area.

[0019] 5. Solder the chip capacitors and chip resistors in the second soldering area, and solder the chip inductors in the third soldering area. 6. Attach the extension legs of the metal frame to the molybdenum copper pad to form a frame unit, attach the frame unit to the LTCC substrate and ensure that the metal frame coincides with the first welding area; like Figure 4 As shown, attaching the extension legs of the metal frame to the molybdenum-copper pad includes: The extension legs of the metal frame are bonded to the molybdenum-copper gasket using adhesive patches. The curing temperature is 150℃ and the curing time is 15 minutes. After curing, the distance between the extension legs of the metal frame and the bottom of the molybdenum-copper gasket is 1.11mm-1.14mm.

[0020] 7. Weld the bottom of the metal fence to the first welding area, and weld the corresponding metal cover plate of the metal fence to the top of the metal fence.

[0021] like Figure 5 As shown, the chip capacitors and chip resistors are welded to the second welding area, the chip inductors are welded to the third welding area, and the bottom of the metal fence is welded to the first welding area. All of them use 63Sn37Pb solder paste or 62Sn36Pb2Ag solder paste as the welding material. The welding is completed by infrared reflow soldering once, with a solder penetration rate of ≥75% and a solder layer thickness of 1μm~5μm.

[0022] The reference temperature settings for infrared reflow soldering are shown in Table 2: Table 2

[0023] Welding the corresponding metal cover plates to the top of the metal fence includes: Laser welding is used to weld the corresponding metal cover plates to the top of the metal fence. The baking conditions for laser sealing are: Baking temperature: 80℃, baking vacuum degree: ≤10Pa, baking time: 24h.

[0024] The welding parameters for laser sealing are shown in Table 3: Table 3

[0025] Specifically, both the metal frame and the metal cover are made of Kovar alloy 4J29, and the surface of the metal frame is electroplated with nickel with a thickness of 4μm-8μm and gold with a thickness of 1.3μm-3μm; the LTCC substrate is made of low-temperature co-fired green ceramic sheet DuPont 951.

[0026] In summary, the embodiments of the present invention provide a large-size double-sided LTCC multi-cavity hermetic packaging structure as follows: Figure 6 As shown.

[0027] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A large-size double-sided LTCC multi-cavity hermetic sealing process, characterized in that, include: Multiple first welding areas are provided on the front and back sides of the LTCC substrate according to different functional units; Within the first welding area, a first bonding area and a second welding area are provided according to the corresponding functional units. A third welding area is set outside the first welding area according to the corresponding functional unit; Using Au80Sn20 solder sheets with a thickness of 25μm to 30μm as the welding material, the RF chip is soldered onto the molybdenum-copper heat sink through a vacuum eutectic bonding furnace, with a solder penetration rate of ≥90% and a solder layer thickness of 5μm to 15μm; the RF device and the digital chip are bonded to the first bonding area; The chip capacitors and chip resistors are soldered to the second soldering area, and the chip inductors are soldered to the third soldering area. The extension legs of the metal frame are bonded to the molybdenum copper pad to form a frame unit. The frame unit is then bonded to the LTCC substrate, ensuring that the metal frame coincides with the first welding area. Weld the bottom of the metal fence to the first welding area, and weld the corresponding metal cover plate of the metal fence to the top of the metal fence; Specifically, the welding of the chip capacitor and chip resistor in the second welding area, the welding of the chip inductor in the third welding area, and the welding of the bottom of the metal fence in the first welding area all use 63Sn37Pb solder paste or 62Sn36Pb2Ag solder paste as welding materials, and are completed by infrared reflow soldering once, with a solder penetration rate of ≥75% and a solder layer thickness of 1μm~5μm.

2. The large-size double-sided LTCC multi-cavity hermetic sealing process according to claim 1, characterized in that, Both the metal frame and the metal cover are made of Kovar alloy 4J29, and the surface of the metal frame is electroplated with nickel with a thickness of 4μm-8μm and gold with a thickness of 1.3μm-3μm; the LTCC substrate is made of low-temperature co-fired green ceramic sheet DuPont 951.

3. The large-size double-sided LTCC multi-cavity hermetic sealing process according to claim 1, characterized in that, The process of bonding the radio frequency device and the digital chip to the first bonding area includes: H20E conductive silver paste is used to bond the radio frequency devices and digital chips to the first bonding area.

4. The large-size double-sided LTCC multi-cavity hermetic sealing process according to claim 1, characterized in that, The process of bonding the extension legs of the metal frame to the molybdenum-copper gasket includes: The extension legs of the metal frame are bonded to the molybdenum-copper gasket using adhesive patches. The curing temperature is 150℃ and the curing time is 15 minutes. After curing, the distance between the extension legs of the metal frame and the bottom of the molybdenum-copper gasket is 1.11mm-1.14mm.

5. The large-size double-sided LTCC multi-cavity hermetic sealing process according to claim 1, characterized in that, The step of welding the corresponding metal cover plate of the metal fence to the top of the metal fence includes: Laser sealing welding is used to weld the corresponding metal cover plates of the metal fence to the top of the metal fence.

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