Airtight multi-layer stacked LTCC (Low Temperature Co-Fired Ceramic) packaging structure and manufacturing method

Abstract

The invention discloses an airtight multi-layer stacked LTCC (Low Temperature Co-Fired Ceramic) packaging structure and a manufacturing method, and belongs to the field of microwave radio frequency high-density assembly. The multi-layer stacked LTCC ceramic substrate comprises LTCC ceramic substrates, metal partition plates and BGA balls, wherein one metal partition plate and a plurality of BGA balls are clamped between every two ceramic substrates, so that multi-layer stacking is realized; a cavity for placing a chip is reserved on the ceramic substrate, and input and output bonding pads on the surface of the LTCC substrate are communicated up and down through BGA balls. The microwave radio frequency module is compact in structure, high in welding strength, capable of achieving air tightness, high in reliability and capable of improving the integration density and reliability of the microwave radio frequency module.

Description

Technical Field

[0001] The invention belongs to the field of microwave radio frequency high-density assembly, in particular to an airtight multi-layer stacked LTCC packaging structure and a manufacturing method. Background Art

[0002] LTCC (low temperature co-fired ceramic) technology is a circuit and passive component integration technology developed in the 1980s. LTCC substrate technology can integrate some passive components into the substrate, making it have the advantages of high speed, high frequency, high density, high reliability, etc., which is conducive to the miniaturization of the system, improves the assembly density of the circuit, and helps to improve the reliability of the system. It is widely used in microwave communications, aerospace and military electronics.

[0003] In recent years, with the development of technology, the integration density of microwave RF modules / microsystems has become higher and higher, gradually shifting from the original conventional planar integration to multi-substrate stacking integration, especially the development of tile-type phased-control transceiver component technology, which requires the integration of signal links through multi-layer stacking. It has the advantages of high integration, small size, flexible use, and strong reconfigurability.

[0004] At present, the main connection methods for realizing vertical stacking interconnection between multi-layer circuit substrates are ball interconnection and button interconnection. Ball grid array welding is to use solder balls to vertically interconnect the upper and lower sides of the substrate. Its advantage is that it eliminates the coplanarity difference and warpage problems caused by thousands of leads of fine pitch devices. The disadvantage is that due to the effective contact area of ​​BGA interconnection, the welding strength is low (there are generally chips in the substrate, and it is difficult to choose bottom filling for reinforcement), and the airtightness cannot be guaranteed. The elastic connector of the button is used as a connecting device to realize solderless connection and has good microwave and DC connection performance. Some scholars in the United States, Japan and China have achieved some results in the low-frequency band of microwaves, but the application in the high-frequency band of microwaves needs to be further improved. In addition, the vertical interconnection of the button also requires other supporting structures to realize the physical connection between the two layers of the substrate. At the same time, the thickness of the button connection is large and it is difficult to achieve airtightness. Summary of the invention

[0005] In view of the problems that it is difficult to ensure airtightness, low welding strength, poor reliability, etc. in the conventional LTCC substrate multi-layer stacking structure, the present invention proposes an airtight multi-layer stacking LTCC packaging structure and a manufacturing method.

[0006] The technical solution adopted by the present invention is:

[0007] A hermetic multi-layer stacked LTCC packaging structure comprises an LTCC ceramic substrate, a metal partition and a BGA ball; the number of the LTCC ceramic substrates is n, n≥2, the number of the metal partitions is n-1, the n LTCC ceramic substrates and the n-1 metal partitions are stacked together, and a metal partition is sandwiched between every two LTCC ceramic substrates; each layer of the LTCC ceramic substrate is provided with a cavity for placing a device on at least one side of the surface provided with the metal partition, two adjacent LTCC ceramic substrates are provided with input and output pads and welding metals that are oppositely positioned on opposite surfaces, and there is a blank area between the input and output pads and the welding metal, each layer of the LTCC ceramic substrate is provided with a substrate circuit for connecting the input and output pads, the welding metal and the connection position in the cavity, the metal partition is left blank at the position corresponding to the input and output pad, the input and output pads that are oppositely positioned on the adjacent two LTCC ceramic substrates are connected through the BGA ball, the BGA ball is located in the blank area of ​​the metal partition, the metal partition is welded to the welding metal and serves as the power ground of the substrate circuit.

[0008] Furthermore, the metal partition is an alloy material with a thermal expansion coefficient of 5-11 ppm / °C, and the surface is processed by nickel plating and gold plating.

[0009] Furthermore, the thickness of the metal partition is 0.1-0.15 mm smaller than the diameter of the BGA ball.

[0010] Furthermore, the input and output pads of the LTCC ceramic substrate include microwave signal port pads and power signal port pads, the blank area of ​​the metal partition corresponding to the microwave signal port pads is circular, the size of the blank area meets the microwave transmission impedance matching requirements, and the blank area corresponding to the power signal port pad is circular, square or a combination of shapes.

[0011] Furthermore, a chip, a resistor and a capacitor are mounted in the cavity of the LTCC ceramic substrate, and the chip, the resistor and the capacitor are connected to the connection position in the cavity by gold wire bonding or flip-chip method.

[0012] The method for manufacturing the above-mentioned airtight multi-layer stacked LTCC packaging structure comprises the following steps:

[0013] 1) According to the requirements of the design drawings, the production of LTCC ceramic substrates is completed according to the process of cutting, aging, punching, filling, graphic printing, cavity punching, lamination and sintering;

[0014] 2) Select Kovar or molybdenum-copper alloy material to make a metal partition, groove the metal partition at the position corresponding to the input and output pads of the upper and lower LTCC ceramic substrates to form a blank area, and then perform nickel plating and gold plating processes on the surface of the metal partition;

[0015] 3) Mount the required devices inside the cavity of the LTCC ceramic substrate and connect them by gold wire bonding or flip chip;

[0016] 4) Solder the metal partition and the BGA ball to the corresponding welding surface of one LTCC ceramic substrate to complete the first welding; then, print the solder paste on the corresponding welding surface of another LTCC ceramic substrate, and then turn it upside down on the metal partition welded last time, perform reflow, complete the second welding, and realize the preparation of a sandwich structure;

[0017] 5) Repeat step 4) to prepare all sandwich structures and obtain a multi-layer stacked LTCC packaging structure, wherein solders with different melting points are selected for each welding to increase the welding temperature gradient.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1) In the multi-substrate stacking structure of the present invention, a metal partition is used for transition. The welding area between the metal partition and the LTCC substrate is much larger than that of the conventional BGA ball. Therefore, the welding strength is high and the reliability is high. More importantly, the airtightness after the two substrates are stacked can be guaranteed, which is beneficial to protecting the long-term reliability of the embedded chip.

[0020] 2) In the present invention, the input and output pads of multiple substrates are interconnected using BGA balls, and the size and thickness of the metal partition opening cavity are limited, which can ensure the performance of microwave signals and the reliability of interconnection. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the cross-sectional structure of the airtight multi-layer stacked LTCC packaging structure in an embodiment of the present invention.

[0022] Figure 2 Schematic diagram of the structure of the bottom surface of the upper substrate in an embodiment of the present invention.

[0023] Figure 3 Schematic diagram of the structure of the top surface of the lower substrate in an embodiment of the present invention.

[0024] Figure 4 Schematic diagram of the structure of the metal partition in an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0026] A hermetic multi-layer stacked LTCC packaging structure comprises an LTCC ceramic substrate, a metal partition and a BGA ball; the LTCC ceramic substrate and the metal partition are stacked and placed together, and a metal partition is sandwiched between every two LTCC ceramic substrates; each layer of the LTCC ceramic substrate is provided with a cavity for placing a device on at least one side of the surface provided with the metal partition, two adjacent LTCC ceramic substrates are provided with oppositely positioned input and output pads and a large area of ​​welding metal on the opposite surface, and there is a blank area between the input and output pads and the welding metal, each layer of the LTCC ceramic substrate is provided with a substrate circuit for connecting the input and output pads, the welding metal and the connection position in the cavity, the metal partition is left blank at the position corresponding to the input and output pad, the oppositely positioned input and output pads on the adjacent two LTCC ceramic substrates are connected through the BGA ball, the BGA ball is located in the blank area of ​​the metal partition, the metal partition is welded to the welding metal and serves as the power ground of the substrate circuit.

[0027] Among them, the surface of the metal partition adopts nickel plating and gold plating process, and the alloy material with a thermal expansion coefficient of 5-11ppm / ℃ is preferred, such as Kovar, molybdenum copper, etc. The thickness of the metal partition is 0.1-0.15mm smaller than the diameter of the BGA ball. The metal partition is grooved corresponding to the input and output positions on the surface of the LTCC substrate to form a blank area, and the blank area at the microwave signal port is circular, and the size design is related to the microwave signal frequency, which meets the microwave transmission impedance matching requirements. The blank area at the power signal port can be circular, square or a combination of shapes.

[0028] The packaging structure is suitable for LTCC multi-substrate stacking structure to form a high-density integrated microwave radio frequency module / microsystem.

[0029] Here is a more specific example:

[0030] A hermetic multi-layer stacked LTCC packaging structure, such as Figure 1-4 As shown, it includes a LTCC ceramic substrate 101, a LTCC ceramic substrate 102, a metal partition 2 and a BGA ball 3. The LTCC ceramic substrate 101 and the LTCC ceramic substrate 102 are stacked together, a metal partition 2 and a plurality of BGA balls 3 are sandwiched between the LTCC ceramic substrate 101 and the LTCC ceramic substrate 102, a cavity 5 for placing a chip 4 is reserved on the LTCC ceramic substrates 101 and 102, input and output pads 6 and a large area of ​​welding metal 7 are provided on the surface of the LTCC ceramic substrate, and the input and output pads 6 between the two LTCC ceramic substrates are connected up and down through the BGA balls 3.

[0031] This example is a K-band vertical interconnection structure based on LTCC ceramics. The LTCC substrate uses Ferro A6M ceramics, the LTCC ceramic substrate 101 is 21 layers thick, the LTCC ceramic substrate 102 is 19 layers thick, the BGA ball 3 is a tin-lead ball with a diameter of 0.3 mm, and the metal partition 2 is a Kovar material with a thickness of 0.2 mm, and the surface is plated with Ni and Au.

[0032] Further, considering the application frequency band and according to the impedance matching requirements, the blank area 8 of the metal partition 2 at the RF signal is circular with a diameter of φ0.8mm, and the blank area 9 at other power ports is square with sizes of 0.8mm*0.8mm and 0.8mm*1.5mm. The size of the blank area can avoid short circuit with the BGA ball.

[0033] The manufacturing method of the airtight multi-layer stacked LTCC packaging structure is as follows:

[0034] 1) According to the conventional process and the requirements of the design drawings, the production of LTCC ceramic substrates is completed according to the process of cutting, aging, punching, filling, graphic printing, cavity punching, lamination, sintering, etc.;

[0035] 2) Using a 0.2 mm thick kovar material to make a metal partition, slotting the metal partition to form a blank area, and then plating Ni and Au on the surface of the metal partition;

[0036] 3) Mount the chip 4, resistors and capacitors and other components into the cavity 5 of the LTCC ceramic substrate, and then perform wire bonding to complete the assembly of a single substrate;

[0037] 4) Solder the metal partition 2 and the BGA ball 3 to the LTCC ceramic substrate 101 to complete the first welding; then, print the solder paste on the welding surface of the LTCC ceramic substrate 102, and then turn it upside down on the metal partition 2 to reflow and complete the second welding; the first welding and the second welding must use solders with different melting points to increase the welding temperature gradient;

[0038] At this point, a multi-layer stacked LTCC packaging structure is obtained.

[0039] In the above structure, two LTCC substrates are stacked and welded via a large-area metal partition, which can improve the bonding strength of the substrate welding, ensure the airtightness of the embedded chip cavity, and improve the reliability of the entire circuit module.

[0040] In summary, the present invention has a compact structure, high welding strength, can achieve airtightness, has high reliability, and can improve the integration density and reliability of the microwave radio frequency module.

[0041] The layout structures and parameters given in the above embodiments are provided to those skilled in the art to implement or use the present invention, and the present invention is not limited to the above disclosed values. Without departing from the idea of ​​the invention, those skilled in the art can make various modifications or adjustments to the above embodiments. Therefore, the protection scope of the present invention is not limited by the above embodiments, but should be the maximum scope of the innovative features mentioned in the claims.

Claims

1. An airtight multi-layer stacked LTCC packaging structure, comprising an LTCC ceramic substrate, a metal separator and a BGA ball; characterized in that: The number of LTCC ceramic substrates is n, n≥2, the number of metal partitions is n-1, n LTCC ceramic substrates and n-1 metal partitions are stacked together, and a metal partition is sandwiched between every two LTCC ceramic substrates; each layer of LTCC ceramic substrates is provided with a cavity for placing devices on at least one side of the surface provided with the metal partition, two adjacent LTCC ceramic substrates are provided with input and output pads and welding metals that are oppositely positioned on opposite surfaces, and there is a blank area between the input and output pads and the welding metal, each layer of LTCC ceramic substrates is provided with a substrate circuit for connecting the input and output pads, the welding metal and the connection position in the cavity, the metal partition is left blank at the position corresponding to the input and output pad, the input and output pads that are oppositely positioned on the adjacent two LTCC ceramic substrates are connected through BGA balls, the BGA balls are located in the blank area of ​​the metal partition, the metal partition is welded to the welding metal, and serves as the power ground of the substrate circuit.

2. The hermetic multi-layer stacked LTCC packaging structure according to claim 1, characterized in that: The metal partition is an alloy material with a thermal expansion coefficient of 5-11 ppm / °C, and the surface is processed by nickel plating and gold plating.

3. The hermetic multi-layer stacked LTCC packaging structure according to claim 1, characterized in that: The thickness of the metal partition is 0.1-0.15 mm smaller than the diameter of the BGA ball.

4. The hermetic multi-layer stacked LTCC packaging structure according to claim 1, characterized in that: The input and output pads of the LTCC ceramic substrate include microwave signal port pads and power signal port pads. The blank area of ​​the metal partition corresponding to the microwave signal port pad is circular, and the size of the blank area meets the microwave transmission impedance matching requirements. The blank area corresponding to the power signal port pad is circular, square or a combination of shapes.

5. The hermetic multi-layer stacked LTCC packaging structure according to claim 1, characterized in that: Chips, resistors and capacitors are mounted in the cavity of the LTCC ceramic substrate, and the chips, resistors and capacitors are connected to the connection points in the cavity through gold wire bonding or flip-chip method.

6. The method for manufacturing a hermetic multi-layer stacked LTCC packaging structure according to claim 1, characterized in that: The following steps are involved: 1) According to the requirements of the design drawings, the production of LTCC ceramic substrates is completed according to the process of cutting, aging, punching, filling, graphic printing, cavity punching, lamination and sintering; 2) Select Kovar or molybdenum-copper alloy material to make a metal partition, groove the metal partition at the position corresponding to the input and output pads of the upper and lower LTCC ceramic substrates to form a blank area, and then perform nickel plating and gold plating processes on the surface of the metal partition; 3) Mount the required devices inside the cavity of the LTCC ceramic substrate and connect them by gold wire bonding or flip chip; 4) Solder the metal partition and the BGA ball to the corresponding welding surface of one LTCC ceramic substrate to complete the first welding; then, print the solder paste on the corresponding welding surface of another LTCC ceramic substrate, and then turn it upside down on the metal partition welded last time, perform reflow, complete the second welding, and realize the preparation of a sandwich structure; 5) Repeat step 4) to prepare all sandwich structures and obtain a multi-layer stacked LTCC packaging structure, wherein solders with different melting points are selected for each welding to increase the welding temperature gradient.

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