A highly reliable RF LC filter assembly method

Abstract

The invention relates to the field of radio frequency LC filter manufacturing, and in particular to a high-reliability radio frequency LC filter assembly method, comprising: obtaining a LTCC substrate with a metal frame; spot-coating an adhesive between two adjacent pads for mounting a chip capacitor; using a vacuum suction pen to suck the chip capacitor and place it on the adhesive spot-coating position, and making the chip capacitor contact the two adjacent pads at the same time; pre-fixing an inductor coil on the LTCC substrate after the chip capacitor is bonded; after the pre-fixing is completed, using a glue dispenser to apply solder paste to the pads on the LTCC substrate for mounting the chip capacitor and the inductor coil; and finally performing device welding and assembly in a reflow furnace. The invention solves the problems of difficult manual welding operation, low efficiency, poor consistency, and the like of a radio frequency LC filter with a metal frame shell, and the entire welding process does not require a complex fixed tooling design, can achieve high-reliability product assembly, and is conducive to the mass production of radio frequency LC filters.

Description

Technical Field

[0001] The invention relates to the field of radio frequency LC filter manufacturing, and in particular to a high-reliability radio frequency LC filter assembly method. Background Art

[0002] RF LC filters have a wide relative bandwidth coverage range and can take into account indicators such as small group delay fluctuation, small insertion loss, and high reliability. They are widely used in aviation, aerospace, navigation, communications, remote sensing and telemetry, and other fields. The traditional RF LC filter assembly method is usually to manually solder capacitors, inductors and other components to the printed circuit board, then reflow solder the soldered printed circuit board, and finally assemble the shell. The process of this product is relatively complicated. During the component welding process, the printed circuit board will warp and deform, and the pad will fall off due to repeated thermal shock, resulting in the printed circuit board not fitting tightly with the shell when it is installed in the shell later, affecting the reliability of the product in the later use. In addition, due to the separate structure of the product shell and the printed circuit board, the volume and size of the product are relatively large, which is not conducive to the realization of product miniaturization.

[0003] In recent years, with the continued rapid growth of the electronic industry at home and abroad, the electronic components industry has developed strongly, and the demand for product miniaturization and integration has become increasingly strong. The RF LC filter based on the LTCC cavity structure has come into being. Different from the traditional RF LC filter, which is packaged in a metal cavity after soldering components on the printed circuit board, the RF LC filter based on the LTCC cavity structure uses an LTCC substrate and a metal frame to achieve an integrated structural design, which can greatly reduce the size of the finished product. When designing the RF LC filter based on the LTCC cavity structure, the circuit wires are directly buried in the LTCC substrate, without the need for additional processing to make the printed circuit board, which can effectively reduce the size of the product and avoid the reliability problem of the secondary assembly of the printed circuit board and the shell of the conventional LC filter.

[0004] However, due to issues such as cavity depth and component density of the LTCC cavity structure, assembly and production basically rely on manual welding by skilled technical workers. This requires high welding technology from the operators, and the consistency of the assembled products is poor. It is difficult to guarantee production efficiency and product quality, which is not conducive to mass production. Summary of the invention

[0005] In view of the problems existing in the prior art, the object of the present invention is to provide a highly reliable radio frequency LC filter assembly method to complete the assembly and manufacture of the LC filter based on the LTCC cavity structure.

[0006] The solution provided by the present invention includes:

[0007] S1. Obtaining a LTCC substrate with a metal frame;

[0008] S2. Aim at two adjacent pads on the LTCC substrate for mounting chip capacitors, and use a dispensing machine to apply adhesive at the center of the two adjacent pads;

[0009] S3. Use a vacuum pen to suck up the chip capacitor and place it on the position where the adhesive was applied in step S2, and gently press the chip capacitor to contact two adjacent pads at the same time;

[0010] S4. Pre-fixing the inductor coil on the LTCC substrate after the chip capacitor is bonded;

[0011] S5. After the pre-fixation is completed, solder paste is applied to the pads on the LTCC substrate for mounting chip capacitors and inductor coils using a dispensing machine;

[0012] S6. Put the product obtained in step S5 into a reflow oven for device soldering and assembly.

[0013] Furthermore, the metal frame is welded on the LTCC to obtain the LTCC substrate with the metal frame as described in step S1, wherein the length and width of the metal frame are consistent with the length and width of the LTCC, and metal lines are embedded in the LTCC substrate.

[0014] Furthermore, step S4 of pre-fixing the inductor coil includes:

[0015] S11. aiming at two adjacent pads on the LTCC substrate for mounting the inductor coil;

[0016] S12. Use tweezers to place the inductor coil between the two adjacent pads;

[0017] S13. Apply current and pressure to the inductor coil pins through the chopper to partially melt the metal on the contact surface between the inductor coil pins and the pads, thereby pre-fixing the inductor coil.

[0018] Furthermore, step S1 also includes: cleaning the LTCC substrate with anhydrous ethanol and drying it naturally.

[0019] Furthermore, in step S2, a dispensing needle is used to apply adhesive between two adjacent pads.

[0020] Furthermore, the welded assembled product is immersed in a cleaning agent and then placed in an oven for baking and drying.

[0021] Furthermore, the soaking time is 3 to 5 minutes, the oven temperature is 85° C., and the baking time is 10 minutes. Furthermore, the baked and dried product is packaged with a cover plate by parallel sealing.

[0022] Furthermore, after the cover is packaged, silicone rubber is dotted on the gap between the inductor coil and the LTCC substrate with the metal frame for reinforcement.

[0023] Beneficial effects of the present invention:

[0024] Compared with the existing methods, the assembly method of the present invention solves the problems of low efficiency and poor consistency of manual welding. The welding process does not require complicated fixed tooling design, the skill requirements for assemblers are reduced, the production efficiency and quality of the product can be better guaranteed, and it is conducive to the mass production of RF LC filters. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flow chart of the assembly method of the present invention;

[0026] Figure 2 It is a schematic diagram of the assembly of an embodiment of the present invention;

[0027] Figure 3 The LTCC substrate with a metal frame according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in 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. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] Due to the cavity depth, component density and inductor coil assembly of LC filters based on LTCC cavity structure, chip capacitors and inductor coils are mostly assembled by manual welding, which requires high welding skills of operators, poor consistency of assembled finished products, and difficult to ensure production efficiency and product quality, which is not conducive to mass production. In order to solve such problems, the present invention provides a highly reliable RF LC filter assembly method, which does not require complex fixed tooling and is more efficient and quick.

[0030] A highly reliable RF LC filter assembly method, such as Figure 1 As shown, the following steps are included:

[0031] S1. Obtain a LTCC substrate with a metal frame.

[0032] Specifically, Figure 3 As shown, the metal frame is welded on the LTCC to obtain the LTCC substrate with the metal frame as described in step S1, and the LTCC substrate with the metal frame constitutes a LTCC cavity structure; wherein the length and width of the metal frame are consistent with the length and width of the LTCC, and metal lines are embedded in the LTCC substrate.

[0033] Specifically, after obtaining the LTCC substrate with the metal frame, the LTCC substrate is cleaned with anhydrous ethanol, dried naturally, and then used for subsequent operations.

[0034] S2. First, install the chip capacitor on the LTCC substrate: aim at two adjacent pads on the LTCC substrate for installing the chip capacitor, and apply adhesive between the two adjacent pads.

[0035] Specifically, each chip capacitor requires two adjacent pads to be installed, such as Figure 2 As shown, the present invention mainly uses a dispensing needle to apply adhesive at the center of two adjacent pads, and this dispensing position allows a deviation of 0.5 mm to the left and right and 0.5 mm to the top and bottom.

[0036] Specifically, the diameter of the glue drop of the glue needle is determined by the package size of the installed chip capacitor. If a chip capacitor with an outer size of 0603 is used, the diameter of the glue drop is 0.6-0.8 mm; if a chip capacitor with an outer size of 0805 is used, the diameter of the glue drop is 0.8-1 mm.

[0037] S3. Use a vacuum pen to pick up the chip capacitor and place it on the adhesive dot coating position, and make the chip capacitor contact the two adjacent pads at the same time.

[0038] Specifically, during the mounting process, it is ensured that the chip capacitor is in full contact with the adhesive. Generally, the ends of the chip capacitor should maintain a contact area of ​​no less than 80% with the two pads at the corresponding mounting location.

[0039] S4. Carry out processing according to the technical requirements of the adhesive to ensure that the adhesive used is fully cured and complete the mounting of the chip capacitor on the LTCC substrate; pre-fix the inductor coil on the LTCC substrate after the chip capacitor is bonded.

[0040] Specifically, step S4 of pre-fixing the inductor coil includes:

[0041] S11. aiming at two adjacent pads on the LTCC substrate for mounting the inductor coil;

[0042] S12. Use tweezers to place the inductor coil between the two adjacent pads;

[0043] S13. Use a resistance spot welder to weld the two pins of the inductor coil on the two adjacent pads respectively.

[0044] The pre-fixation of the inductor coil mainly uses the instantaneous current to generate local high heat at the interface between the inductor pin and the pad, so as to melt the metal at the interface between the inductor pin and the pad and then combine them, so that the inductor coil is fixed on the LTCC substrate pad. The inductor coil pin should be pre-tinned to reduce the melting point of the surface material and improve the fixing reliability.

[0045] S5. After completing the pre-fixation, use a dispensing machine to apply an appropriate amount of solder paste to the pads on the LTCC substrate used to install the chip capacitors and inductor coils to ensure that the solder paste can fully cover the parts to be welded.

[0046] S6. The product obtained in step S5 is placed in a reflow oven, and the solder melts and wets and spreads, thereby realizing the soldering assembly of the LC filter. The assembly result is as follows: Figure 2 shown.

[0047] Specifically, the reflow temperature curve should match the selected solder paste, and its peak temperature is generally 40℃ to 60℃ higher than the melting point of the solder paste.

[0048] Specifically, the welded assembled product is immersed in a cleaning agent and then placed in an oven for baking and drying.

[0049] Specifically, the soaking time is 3 to 5 minutes, the oven temperature is 85° C., and the baking time is 10 minutes.

[0050] Specifically, the silicone rubber is dotted on the gap between the inductor coil and the LTCC frame for reinforcement.

[0051] Specifically, the baked and dried product is packaged with a cover plate by means of parallel sealing.

[0052] The present invention optimizes the assembly process of the radio frequency LC filter by drawing on the hybrid integrated circuit wire bonding method. Wire bonding, also known as wire welding, is to connect the electrode pad of the bare chip with the input / output lead of the electronic package shell or the metal wiring pad on the substrate with a metal filament. The connection process is generally achieved by heating, pressurizing, ultrasonic and other energies with the help of a bonding tool (chopper). The process implementation process has clear requirements on the material and wire diameter of the bonding wire (gold wire and silicon aluminum wire, etc., with a diameter of ≤50 microns). Because the inductor coil is mostly wound with copper wire with a diameter greater than 0.1 mm, the hybrid circuit wire bonding process cannot achieve a reliable connection between the inductor coil pin and the substrate, and cannot be directly applied to the welding assembly process of the LC filter of the present invention.

[0053] Therefore, the present invention draws on the wire bonding process of the hybrid integrated circuit manufacturing process, uses tweezers to place the inductor coil pins on the corresponding pads, and applies the chopper current and pressure to the inductor coil pins to partially melt the metal on the contact surface between the pins and the LTCC substrate pads, thereby pre-fixing the inductor coil and ensuring the positioning of the subsequent LC filter assembly process. The melting of the solder in the subsequent reflow soldering process will fully wrap the inductor coil and the LTCC substrate pads, ensuring the reliable interconnection between the inductor coil and the LTCC substrate.

[0054] The present invention draws on the wire bonding method, realizes the pre-fixation of the inductor coil by resistance spot welding (current and pressure), realizes the fixation of the capacitor by glue dispensing, and subsequently realizes the assembly of a radio frequency LC filter with a highly reliable LTCC cavity structure by solder paste dispensing and reflow soldering.

[0055] In the present invention, unless otherwise clearly stipulated and limited, the terms such as "installation", "setting", "connection", "fixation" and "rotation" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, ordinary technicians in this field can understand the specific meanings of the above terms in the present invention according to the specific circumstances.

[0056] Although 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 the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A high-reliability radio frequency LC filter assembly method, characterized in that: Assembling an LC filter based on a LTCC cavity structure includes the following steps: S1. Obtaining a LTCC substrate with a metal frame; S2. Aim at two adjacent pads on the LTCC substrate for mounting chip capacitors, and use a dispensing machine to apply adhesive at the center of the two adjacent pads; Use a dispensing needle to apply adhesive in the center of two adjacent pads. If a chip capacitor with an outer size of 0603 is used, the diameter of the glue drop is 0.6~0.8mm; if a chip capacitor with an outer size of 0805 is used, the diameter of the glue drop is 0.8~1mm; S3. Use a vacuum pen to suck up the chip capacitor and place it on the position where the adhesive was applied in step S2, and gently press the chip capacitor to contact two adjacent pads at the same time; S4. Pre-fixing the inductor coil on the LTCC substrate after the chip capacitor is bonded, including: S11. aiming at two adjacent pads on the LTCC substrate for mounting the inductor coil; S12. Use tweezers to place the inductor coil between the two adjacent pads; S13. Applying current and pressure to the inductor coil pins by a chopper to partially melt the metal on the contact surface between the inductor coil pins and the pads, thereby pre-fixing the inductor coils; S5. After the pre-fixation is completed, solder paste is applied to the pads on the LTCC substrate for mounting chip capacitors and inductor coils using a dispensing machine; S6. Put the product obtained in step S5 into a reflow furnace for soldering and assembly.

2. A high-reliability radio frequency LC filter assembly method according to claim 1, characterized in that: The metal frame is welded on the LTCC to obtain the LTCC substrate with the metal frame as described in step S1, wherein the length and width of the metal frame are consistent with the length and width of the LTCC, and metal lines are embedded in the LTCC substrate.

3. A high-reliability radio frequency LC filter assembly method according to claim 1, characterized in that: Step S1 also includes: cleaning the LTCC substrate with anhydrous ethanol and drying it naturally.

4. A high-reliability RF LC filter assembly method according to claim 1, characterized in that: The welded and assembled products are soaked in a cleaning agent and then placed in an oven for baking and drying.

5. A high-reliability RF LC filter assembly method according to claim 4, characterized in that: The soaking time is 3~5min, the oven temperature is 85℃, and the baking time is 10min.

6. A high-reliability RF LC filter assembly method according to claim 4, characterized in that: The baked and dried product is packaged with a cover plate by parallel sealing.

7. A high-reliability RF LC filter assembly method according to claim 6, characterized in that: After the cover is packaged, silicone rubber is dotted on the gap between the inductor coil and the LTCC substrate with a metal frame for reinforcement.

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