Support for connecting wire and LTCC substrate and related hybrid integrated circuit

Abstract

The invention discloses a bracket for connecting a wire and an LTCC (Low Temperature Co-Fired Ceramic) substrate and a related hybrid integrated circuit. The support comprises a bottom plate and a vertical plate, the bottom plate is located at the bottom of the vertical plate, and the bottom plate and the vertical plate form an L-shaped structure; an upper area, a middle area and a lower area are sequentially arranged on the vertical plate from top to bottom, and the middle area is bent or inclined towards the side where the bottom plate is located to form a stress release bend; the bottom plate and the vertical plate are made of conductive materials. The circuit comprises a stress wire, an LTCC substrate and the support, a bottom plate of the support is fixed to the LTCC substrate, the wire is welded to the upper area of a vertical plate of the support, and a welding point and the bottom plate are located on the same side. The bracket adopted by the invention enables the interconnection between the lead and the LTCC substrate to be indirect interconnection, plays a buffering role, can adapt to the interconnection between enameled wires with different thicknesses and numbers and the LTCC substrate, and solves the problem that the direct welding interconnection stress of the lead on the LTCC substrate is large.

Description

Technical Field

[0001] The invention relates to the field of hybrid integrated circuits, and relates to a method for interconnecting a stress conductor with a LTCC substrate. Background Art

[0002] With the development of satellite technology, satellite functions are changing with each passing day, and the number of payloads is increasing significantly. In order to carry more payloads, the size and weight of subsystems and single machines must be greatly reduced. The power supply is an indispensable component of an active single machine, and is generally the largest module in an active single machine. Therefore, miniaturization and lightweighting of the power supply are important factors in the miniaturization of active single machines. Hybrid integration is an important way to miniaturize the power supply. The circuit substrate uses a ceramic substrate, and the commonly used substrate is an alumina ceramic substrate (containing 96% alumina, referred to as 96 ceramic). The assembly adopts a micro-assembly process, including circuit substrates, component reflow soldering, welding of inductors and transformers' own stress wires, gold wire, gold belt, aluminum wire bonding processes, ultrasonic and atomization cleaning processes, and module sealing processes.

[0003] The power supply contains magnetic components, and its assembly is a difficult part in hybrid integrated circuits, involving the interconnection of stress wires such as single enameled wires or multiple enameled wires of different thicknesses with the circuit substrate. During assembly and subsequent screening tests, these wires exert great stress on the substrate pads.

[0004] Existing hybrid integrated circuits, such as thick film power supplies, use alumina ceramic substrates. The film layer of this substrate has strong adhesion, and the stress wires of the inductor and transformer can be directly welded to the ceramic substrate. It can withstand subsequent force and thermal screening tests without film cracking, and is a mature application. The circuit substrate is a single-layer ceramic, and the film forming process is a thick film printing process. Vias cannot be punched on the device pads, so there will be traces on the substrate surface, and the substrate layout density is low.

[0005] Low temperature co-fired ceramic substrate (LTCC) is a multi-layer ceramic substrate commonly used in microwave hybrid integrated circuits. It has the advantages of multi-layer wiring (typically 10 layers) and through-holes at the bottom of the pad, which can achieve compact layout and wiring. It is mainly used for microwave products. The assembly of microwave products is mainly various chips, resistors, capacitors, surface mount inductors and other devices, which generally only involve reflow soldering, chip gold wire, gold ribbon bonding, ultrasonic, atomization cleaning process and module sealing process in the micro-assembly process. Due to the characteristics of the LTCC substrate mixed glass powder and ceramic powder material, the adhesion of the substrate pad film layer is weak. If the stress wire in the power supply is directly welded to the LTCC substrate, the stress generated by welding and the temperature cycle shock and constant acceleration stress in the screening test will cause the substrate pad film layer to crack. Summary of the invention

[0006] In view of the defects or shortcomings of the prior art, the present invention provides a bracket for connecting a wire and a LTCC substrate.

[0007] To this end, the bracket provided by the present invention includes a bottom plate and a vertical plate, wherein the bottom plate is located at the bottom of the vertical plate, and the bottom plate and the vertical plate form an L-shaped structure; the vertical plate is divided into an upper area, a middle area and a lower area from top to bottom, wherein the middle area is bent or inclined toward the side where the bottom plate is located to form a stress release bend; the connection part between the bottom plate and the vertical plate on the bracket, and the bending or tilting part are all transitioned by chamfering; the bottom plate and the vertical plate are made of conductive material.

[0008] In a further solution, the bottom plate and the vertical plate are an integrated structure.

[0009] An optional solution is that the thickness of the bracket is 0.1mm-0.2mm, the overall height of the bracket is 4-6mm, the height of the lower area of ​​the vertical plate is 1.5-2.5mm, and the upper area of ​​the vertical plate is offset by 0.4-0.6mm relative to the lower area of ​​the vertical plate toward the side where the bottom plate is located.

[0010] Optionally, the support material is Kovar or silver-plated copper.

[0011] An optional solution is that both the bottom plate and the vertical plate are quadrilateral structures.

[0012] The present invention also provides a hybrid integrated circuit that uses the above bracket to achieve connection, the hybrid integrated circuit includes a stress conductor, an LTCC substrate and the above bracket; the bottom plate of the bracket is fixed on the LTCC substrate, the conductor is welded to the upper area of ​​the bracket riser, and the welding point is located on the same side as the bottom plate. In particular, the hybrid integrated circuit is a thick film power supply.

[0013] Furthermore, the present invention provides a welding method for the hybrid integrated circuit, the method comprising:

[0014] (1) Bracket pretreatment: Perform the first tinning treatment on the surface of the bracket bottom plate and the connecting corners between the bottom plate and the vertical plate;

[0015] (2) Fixing the bracket: fix the bracket base plate on the LTCC substrate by reflow soldering; then use insulating glue to wrap the pad, base plate, the connection between the base plate and the vertical plate, and the lower area of ​​the vertical plate;

[0016] (3) Pretreatment of stress wire: depainting and second tinning of the stress wire end;

[0017] (4) Welding of the wire to the bracket: The welding position of the upper area of ​​the bracket is subjected to a third tinning treatment, and then the wire is lap-welded to the welding position after the third tinning treatment; the soldering iron temperature during lap welding is 280 to 330°C, and the welding time is 2 to 3 seconds.

[0018] Optionally, the printing thickness of the solder paste for reflow soldering is 0.15 mm. The insulating glue in the above step (2) is Nanda 705 glue.

[0019] The transition bracket device used in the present invention enables indirect interconnection between the wire and the LTCC substrate. The bracket is a thin sheet structure, which is reflow soldered to the LTCC substrate, and has less stress than that of multi-strand enameled wires soldered to the LTCC substrate by a manual electric soldering iron. Less lead-tin solder is required for welding the thin sheet bracket, and under the impact of temperature cycle, the less lead-tin solder brings less mechanical stress to the LTCC substrate pad. At the same time, the bracket plays a buffering role, reducing the mechanical stress of constant acceleration in the screening test link. The use of a bracket device for transition interconnection can adapt to the interconnection of enameled wires of different thicknesses and strands with the LTCC substrate, solving the problem of high interconnection stress when the wires are directly soldered on the LTCC substrate.

[0020] The present invention is suitable for applications where LTCC substrate is used for circuit design and stress wire welding is required. Typical applications are hybrid integrated circuits such as thick film power supplies. The present invention can realize welding of stress wires in a small welding area. The bracket used not only realizes the electrical connection between the stress wire and the LTCC substrate, but also reduces the direct welding stress between the wire and the LTCC substrate, as well as the temperature cycle shock and constant acceleration stress in the subsequent screening test link.

[0021] In addition, the present invention makes it possible to design a power supply using an LTCC substrate, and can promote the LTCC substrate used in the microwave field to the power supply field, expanding the application selection of power modules for different types of ceramic substrates. Compared with traditional alumina substrates, LTCC substrates have the advantages of multi-layer wiring and solid vias at the bottom of the pad, making the layout wiring density higher and the layout design more compact. The use of LTCC substrates can realize the miniaturization of power modules to a greater extent, and can also take advantage of its multi-layer wiring to realize the key routing in two ground planes, thereby improving the anti-interference ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the structure and dimensions of the bracket in Example 1, where the dimensions are in mm and the transition angles are in degrees.

[0023] Figure 2 Schematic diagram of the connection principle between the stress conductor and the LTCC substrate.

[0024] Figure 3 The figure is a comparison of the temperature rise of the bracket base plate welding in the embodiment and the comparative example. DETAILED DESCRIPTION

[0025] Unless otherwise specified, the scientific and technical terms used herein are understood according to the knowledge of ordinary technicians in the relevant fields.

[0026] The material of the bracket of the present invention is a conductive material, for example, copper (such as oxygen-free copper), kovar and other metals can be selected. Considering the structural characteristics, processing characteristics, assembly process and other factors of the bracket, oxygen-free copper is a suitable choice for the bracket.

[0027] In the specific scheme, the width of the bracket is determined according to the thickness and number of enameled wires to be welded. In principle, the thicker the wire or the larger the number of strands, the above dimensions need to be appropriately enlarged to meet the mechanical requirements during connection. The thickness of the bracket depends on the material, processing technology and mechanical requirements. According to the materials and related processing technology available in the current existing technology, the thickness of the bracket can be selected as 0.1-0.2mm. Under this size, the processing performance of the bracket is good, and the stress release bend is easy to make; the single-chip fundamental frequency is low during operation; and the mechanical stress is small. The height of the bracket depends on the assembly requirements, stress release bend processing and stress release effect. For example, the height of the bracket is 4-6mm, the height of the lower area is 1.5-2.5mm, and the upper area of ​​the vertical plate is offset by 0.4-0.6mm relative to the lower area of ​​the vertical plate to the side where the bottom plate is located, to ensure that the stress release bend is easy to make. At the same time, the stress release effect is better at this height, which can meet the assembly of the stress conductor and have a good stress release effect.

[0028] The following are specific embodiments provided by the inventor to further illustrate the solutions of the present invention.

[0029] Embodiment 1:

[0030] The support structure and dimensions for connecting the wire and the LTCC substrate provided in this embodiment refer to Figure 1 As shown, the main structure of the bracket is an L-shaped structure consisting of a vertical plate and a bottom plate, wherein the middle area of ​​the vertical plate is inclined toward the side where the bottom plate is located to form a stress release bend, and the bracket is made of oxygen-free copper with a silver-plated surface; the overall height of the bracket is 5mm, the thickness is 0.1mm, the width is 2.1mm, the bottom plate size is 2.1mm*2.1mm, the height of the stress release bend from the bottom surface (or the height of the area under the vertical plate) is 2mm, and the vertical plate in the upper area is offset by 0.5mm to the side where the bottom plate is located relative to the vertical plate in the lower area; in this embodiment, the transition between the bottom plate and the vertical plate on the bracket and the various curved structural parts is chamfered, and each chamfer is R0.3.

[0031] The bracket of the present invention can realize low-stress interconnection between the stress wire and the LTCC substrate circuit, and can reduce the direct welding stress between the wire and the LTCC substrate as well as the temperature cycle shock and constant acceleration stress in the subsequent screening test link. Figure 2 As shown, when the bracket of the present invention is used to connect the stress wire 2 to the LTCC substrate 1, the bottom of the bracket 3 is fixed on the LTCC substrate such as welding, the stress wire is connected to the inner side of the bracket, and the connection point between the bracket and the wire is located in the upper area of ​​the vertical plate.

[0032] The specific welding process includes the following steps:

[0033] (1) Use a soldering iron and solder wire to tin the surface of the bottom plate of the L-shaped bracket and the corner where the bottom plate and the vertical plate are connected (specifically, a soldering iron and solder wire can be used for tinning) to increase the wettability of the bracket;

[0034] (2) Fix the bracket bottom plate on the LTCC substrate by reflow soldering; then use insulating glue to wrap the pad, bottom plate and the lower area of ​​the vertical plate; specifically, use a leak plate to print 0.15mm thick solder paste on the LTCC substrate, and mount the bracket on the LTCC substrate to ensure that the L-shaped bracket device does not deviate from the pad or tilt; then perform hot air reflow soldering on the LTCC substrate and the bracket, and place it on an anti-static tray for natural cooling after completion; after cooling, the bottom pad of the bracket, the bottom plate, the corner connecting the bottom plate and the vertical plate, and the surface of the lower area of ​​the vertical plate are coated with Nanda 705 for wrapping, and the coating height on the bracket does not exceed 2mm, that is, it stops at the stress release bend, and after completion, it is placed at room temperature for 24 hours to cure;

[0035] (3) Depaint the stress conductor, and then tin the depainted part; in the specific scheme, the tinning length is consistent with the depainting length; if the stress conductor is a multi-strand enameled wire, the multi-strand lead wires after depainting should be twisted together first, dipped in flux, and then tinned;

[0036] (4) Perform a third tinning treatment on the welding position of the upper area of ​​the bracket, and then lap-weld the wire to the welding position after the third tinning treatment. The soldering iron temperature during lap welding is 280-330°C, and the welding time is 2-3)s. In the specific scheme, a soldering iron and solder wire can be used to tin the welding position of the L-shaped bracket device, and the inner side of the bracket is tinned, and a tin-absorbing rope is used to remove excess solder at the tinning position. The stress wire is lap-welded, and the lap-welding length is (1-1.5) times the width of the bracket device, and is welded to the inner side of the L-shaped bracket device. When tinning and welding, wrap the bottom pad of the bracket with alcohol non-woven fabric or cotton balls, and the solder must not flow to the bend of the bracket device. When welding, use a brush to apply an appropriate amount of flux to the bracket device at the tap welding position.

[0037] After the stress wire is welded, the flux near the welding part and the substrate is cleaned immediately with bromopropane. Under a (10-45) times microscope, the welding point is qualified, the bracket device is not deformed, the enameled wire coating is not damaged, and there is no flux residue in the welding point.

[0038] A thick film power module for a satellite designed based on the bracket of the present invention has completed temperature cycling and constant acceleration tests in accordance with Condition B in Method 1010.1 and Condition A in Method 2001.1 of GJB548B-2005 "Test Methods and Procedures for Microelectronic Devices". The LTCC substrate pad has no cracks, meeting the requirements for satellite-borne applications.

[0039] Comparative Example 1:

[0040] The structure of the bracket of this comparative example is different from that of the above-mentioned embodiment. Specifically, it is an L-shaped bracket composed of a vertical plate and a bottom plate, and there is no stress release bend in the middle area of ​​the vertical plate. The overall height, thickness and bottom plate size of the bracket of this comparative example are the same as the corresponding sizes of the bracket of Example 1.

[0041] Comparative Example 2:

[0042] The structure of the bracket of this comparative example is different from that of the above-mentioned embodiment. Specifically, it is an inverted T-shaped bracket composed of a vertical plate and a bottom plate, and there is no stress release bend in the middle area of ​​the vertical plate. The overall height, thickness and bottom plate size of the bracket of this comparative example are the same as the corresponding sizes of the bracket of Example 1.

[0043] The brackets of Example 1 and Comparative Examples 1-2 were welded using the welding process described in Example 1. The welding time of the wire and the bracket in step (4) was about 3 seconds. During the process, the temperature of the bottom of each bracket was measured. The temperature rise of the bottom of each bracket was as follows: Figure 3 As shown, the temperature of the bracket of comparative example 2 (line C) has reached the melting point of lead-tin solder, 183°C, and the bracket of comparative example 2 heats up the fastest; the bracket of comparative example 1 (line A) and the bracket of embodiment 1 (line B) are lower than the lead-tin soldering temperature, and the bracket of embodiment 1 has a slower temperature rise because the solder point at the bottom of the bracket is far away from the heat source.

[0044] Considering that during the assembly process, the bracket is first reflow-soldered onto the LTCC substrate, and then the stress wire is manually soldered to the upper end of the bracket by an electric soldering iron, the bracket metal is a good conductor of heat, and the bottom pad may remelt during the soldering process, affecting the soldering quality of the bracket on the LTCC substrate. Therefore, the bottom of the designed bracket should heat up slowly and be lower than the lead-tin soldering temperature. Therefore, the bracket of the present invention can better meet the technical requirements than the bracket of Comparative Examples 1-2.

[0045] Embodiment 2:

[0046] The difference between the bracket of this embodiment and that of embodiment 1 is that the bracket is made of Kovar and has a thickness of 0.2 mm.

[0047] Comparative Example 3:

[0048] The difference between this comparative example and comparative example 1 is that the bracket is made of Kovar and has a thickness of 0.2 mm.

[0049] Comparative Example 4:

[0050] The difference between this comparative example and comparative example 2 is that the bracket is made of Kovar and has a thickness of 0.2 mm.

[0051] Furthermore, Ansys Workbench simulation software was used to perform simulation comparison on the brackets of the above embodiment and the comparative example under 5000g constant acceleration stress conditions. The results are shown in Table 1. The welding surface stress in the table is the welding surface stress between the bottom of the bracket and the substrate.

[0052] Table 1 Simulation results

[0053] sample Welding surface stress Mpa Comparative Example 1 Welding surface stress 28.9Mpa Example 1 Welding surface stress 16.1Mpa Comparative Example 2 Welding surface stress 31.6Mpa Comparative Example 3 Welding surface stress 25.2Mpa Example 2 Welding surface stress 19.4Mpa Comparative Example 4 Welding surface stress 35.4Mpa

[0054] From the results in Table 1 above, it can be seen that the L-shaped bracket with stress release bend of the present invention has the smallest stress on the pad under constant acceleration compared with the inverted T-shaped bracket and the L-shaped bracket without stress release bend; the stress of the Kovar bracket is slightly larger than that of the pure copper bracket under constant acceleration.

[0055] The hardness of the kovable material is relatively high. Based on the existing processing technology, it is difficult to process a thin sheet bracket with a thickness of 0.1mm. The actual thickness that can be processed is 0.2mm.

Claims

1. A bracket for connecting a wire and a LTCC substrate, characterized in that: The bracket includes a bottom plate and a vertical plate, wherein the bottom plate is located at the bottom of the vertical plate, and the bottom plate and the vertical plate form an L-shaped structure; the vertical plate is provided with an upper region, a middle region and a lower region from the top to the bottom, wherein the middle region is bent or inclined toward the side where the bottom plate is located to form a stress release bend; The connection part between the bottom plate and the vertical plate on the bracket, as well as the bending or tilting part, are all transitioned by chamfering; The bottom plate and the vertical plate are made of conductive material.

2. The bracket for connecting a wire and a LTCC substrate according to claim 1, characterized in that: The bottom plate and the vertical plate are an integrated structure.

3. The bracket for connecting a wire and a LTCC substrate according to claim 1, characterized in that: The thickness of the bracket is 0.1mm-0.2mm, the overall height of the bracket is 4-6mm, the height of the lower area of ​​the vertical plate is 1.5-2.5mm, and the upper area of ​​the vertical plate is offset by 0.4-0.6mm relative to the lower area of ​​the vertical plate toward the side where the bottom plate is located.

4. The bracket for connecting a wire and a LTCC substrate according to claim 1, characterized in that: The bracket is made of copper or silver-plated copper.

5. The bracket for connecting a wire and a LTCC substrate according to claim 1, characterized in that: The bottom plate and the vertical plates are both quadrilateral structures.

6. A hybrid integrated circuit connected by the bracket of claim 1, characterized in that: It comprises a stress conductor, a LTCC substrate and the bracket according to claim 1; The bottom plate of the bracket is fixed on the LTCC substrate, the wire is welded to the upper area of ​​the vertical plate of the bracket, and the welding point is located on the same side as the bottom plate.

7. The hybrid integrated circuit according to claim 6, characterized in that: The hybrid integrated circuit is a thick film power supply.

8. The welding method of the hybrid integrated circuit according to claim 6, characterized in that the method include: (1) Bracket pretreatment: Perform the first tinning treatment on the surface of the bracket bottom plate and the connecting corners between the bottom plate and the vertical plate; (2) Fixing the bracket: fix the bracket base plate on the LTCC substrate by reflow soldering; then use insulating glue to wrap the pad, base plate, the connection between the base plate and the vertical plate, and the lower area of ​​the vertical plate; (3) Pretreatment of stress wire: depainting and second tinning of the stress wire end; (4) Welding of the wire to the bracket: The welding position of the upper area of ​​the bracket is subjected to a third tinning treatment, and then the wire is lap-welded to the welding position after the third tinning treatment; the soldering iron temperature during lap welding is 280 to 330°C, and the welding time is 2 to 3 seconds.

9. The welding method according to claim 8, characterized in that: The solder paste printing thickness of the reflow soldering is 0.15 mm.

10. The welding method according to claim 8, characterized in that: The insulating glue in step (2) is Nanda 705 glue.

Images