Metal substrate low-cavity welding jig and welding method

Abstract

The invention relates to the technical field of circuit board preparation, in particular to a metal substrate low-cavity welding jig and a welding method.The metal substrate low-cavity welding jig comprises a lining plate used for bearing a stacked body, the stacked body comprises a metal plate and a printed circuit board welded and fixed to the metal plate, a height limiting stud is installed on the lining plate, the height of the height limiting stud is adjustable, and the height limiting stud is fixed to the lining plate. The pressing plate and the height limiting stud are oppositely arranged, and in a locking state, the lower surface of the pressing plate makes contact with the top end face of the height limiting stud so as to limit a pressing gap; the high-temperature-resistant silica gel plate is located between the pressing plate and the printed circuit board and is in plane overlapping contact with the pressing plate, and the pressing units are arranged in four directions of the lining plate and are used for clamping overlapping bodies of different specifications. The formation of holes is avoided, and the voidage is greatly reduced to an acceptable level.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of circuit board preparation, and more particularly to a metal substrate low-cavity soldering jig and soldering method. BACKGROUND

[0002] In modern high-power electronic devices (such as radio frequency power amplifiers, power modules, LED lighting) and high-performance microwave circuits, thermal management and signal integrity are two core elements that determine product performance, reliability and service life. In order to effectively dissipate the heat generated by high-power devices, the commonly used solution is to firmly attach the metal-based (such as copper-based or aluminum-based) printed circuit board (PCB) to the aluminum alloy, copper, etc. high thermal conductivity metal heat sink through large area tin soldering. This structure can significantly reduce the thermal resistance and improve the heat dissipation efficiency. Similarly, in microwave radio frequency circuits, in order to achieve precise impedance matching, provide excellent radio frequency grounding, and reduce signal crosstalk and loss, the microwave printed circuit board is also usually soldered to the metal cavity or back plate.

[0003] The common requirement of the above two application scenarios is that the solder layer between the printed circuit board and the metal plate must have extremely low cavity rate. Soldering cavity is the bubble remaining in the solder layer, which can sharply reduce the effective heat conduction and conduction area, form local hot spots, increase thermal resistance, and reduce heat dissipation efficiency; at the same time, in the microwave circuit, the cavity will destroy the consistency of the ground plane and affect the signal quality.

[0004] Research shows that the main cause of soldering cavity is that the flux used to remove oxides and enhance wettability will decompose and volatilize at high temperature during the soldering process, generating a large amount of gas. In the two large area, flat and airtight plate materials, these gases are difficult to escape and are eventually wrapped by the solidified solder, forming a cavity.

[0005] In order to solve this technical problem, the existing technology mainly develops along two paths:

[0006] CN103934534B, a vacuum soldering method for thick film substrate and power shell, uses vacuum soldering instead of reflow soldering, and uses solder sheet tin instead of solder paste, which helps to remove bubbles caused by delayed flux discharge, reduces the interface cavity rate, and does not need to clean the flux after vacuum soldering. The fatal defect of this method is that it is highly dependent on the equipment, and must use expensive special equipment such as vacuum reflow soldering furnace, vacuum vapor soldering machine or vacuum brazing furnace. The procurement cost of these equipment is high, and the operation and maintenance cost is also high. For most small and medium-sized enterprises, research and development projects or cost-sensitive products, it is difficult to bear.

[0007] There is, for example, a metal substrate circuit board welding tool and its use method disclosed in the publication CN107971602A, which sets a spring screw to achieve the close combination of the printed board and the substrate by automatically adjusting the pressure, designs a hollow slot on the middle part of the backing plate, and uses the spring at the bottom of the pressing plate to apply downward pressure to the middle part of the circuit board to constrain the deformation of the printed board. However, the existing fixtures are mostly designed for specific size products, and the structure is complex, and the adjustment of different specifications of products is tedious, which is not good in general applicability and is low in operation efficiency. Moreover, whether it is fastened by a screw or pressed by a spring column, the force is concentrated on a few discrete points. This "point contact" type of hard pressure application results in extremely uneven pressure distribution on the entire welding surface, and the high pressure points may damage the components or cause excessive loss of solder, while the low pressure area cannot effectively discharge bubbles, and the void problem still exists. SUMMARY

[0008] Therefore, the purpose of the present application is to provide a metal substrate low-void welding fixture and welding method, which effectively suppresses the surface tension, metal oxide and gas accumulation generated during the melting and flowing of the solder, avoids the formation of voids, and greatly reduces the void rate to an acceptable level.

[0009] To achieve the above purpose, the present application provides the following technical solutions:

[0010] A metal substrate low-void welding fixture, comprising:

[0011] a backing plate for carrying a stack, the stack comprising a metal plate and a printed circuit board welded and fixed thereto,

[0012] a height-limiting stud mounted on the backing plate, the height-limiting stud being adjustable in height, and the top end face being located in the same plane;

[0013] a pressing plate arranged opposite to the height-limiting stud, and the lower surface of the pressing plate being in contact with the top end face of the height-limiting stud in the locked state to define a pressing gap;

[0014] a high-temperature-resistant silica gel plate located between the pressing plate and the printed circuit board, and the planes being in contact in a stack;

[0015] a pressing unit arranged in four directions of the backing plate for clamping different specifications of the stack.

[0016] The present application is further provided as follows: the uncompressed thickness of the high-temperature-resistant silica gel plate is T, the preset compression amount is T0, the thickness of the printed circuit board is T1, and the thickness of the metal plate is T2;

[0017] In the locked state, the geometric relationship is satisfied: H=(T-T0)+T1+T2,

[0018] H is the distance between the pressing plate and the lining plate defined by the height limiting stud, and makes the high-temperature-resistant silica gel plate in the compressed thickness state.

[0019] The application is further provided that the pressing unit comprises a plurality of clamping units arranged around the periphery, each clamping unit comprising two support seats arranged at intervals in front and back, and a sliding rod arranged between the front support seat and the rear support seat;

[0020] A clamping plate is slidably connected to the sliding rod, and a first spring is sleeved on the sliding rod, one end of the first spring being connected to the back of the clamping plate and the other end being connected to the rear support seat, for providing elastic thrust to the clamping plate;

[0021] An active opening is formed on the pressing plate corresponding to the position of the clamping plate, so that the clamping plate can move forward and backward in the active opening along the direction of the sliding rod, realizing clamping of different specifications of stacked bodies.

[0022] The application is further provided that a connecting hole is arranged on the rear support seat, and a guide rod is penetrated through the connecting hole, one end of the guide rod being fixedly connected to the lining plate;

[0023] A second spring is sleeved on the guide rod, both ends of the second spring being connected to the lining plate and the pressing plate respectively, for providing elastic action when the pressing plate is pressed down,

[0024] A positioning nut is movably connected to the end of the guide rod, and the top end surface of the positioning nut abuts against the top end surface of the rear support seat, so as to lock the position of the pressing plate after being pressed down.

[0025] The application is further provided that a plurality of screw rods and locking nuts are arranged between the lining plate and the pressing plate, for locking after the pressing plate is pressed down to a predetermined position, the screw rods and the locking nuts being arranged along the length direction of the lining plate and the pressing plate.

[0026] A welding method of a metal substrate low-cavity welding jig, characterized in that the method comprises the following steps:

[0027] S1, determining a preset pressure value P; calculating the compression amount T0 required to generate the preset pressure P by the formula T0=(P*T) / E, and taking T0 as a constant for subsequent calculation;

[0028] Wherein, T is the original uncompressed thickness of the high-temperature-resistant silica gel plate, and E is the elastic modulus of the silica gel plate material.

[0029] S2, calculating the height H of the height limiting stud as (T-T0)+T1+T2 according to the thickness T1 of the printed circuit board, the thickness T2 of the metal plate and the thickness T of the high-temperature-resistant silica gel plate, and adjusting the height H of the height limiting stud so that the top end surfaces are located on the same plane;

[0030] S3, cutting the high-temperature-resistant silica gel plate to match the size of the printed circuit board;

[0031] S4, laying a solder sheet on the metal plate and placing the printed circuit board, aligning the printed circuit board, solder sheet and metal plate according to the design requirements to form a stack;

[0032] S5, placing the stack on the backing plate and covering the high-temperature-resistant silica gel plate and the pressing plate;

[0033] S6, clamping the stack by the pressing unit and pressing the pressing plate to contact the top end surface of the height-limiting stud to achieve a locked state;

[0034] S7, heating and welding using a reflow oven or a flat plate heating table;

[0035] S8, after the heating and welding is completed, naturally cooling the stack to below 80℃, releasing the locked state of the pressing unit, and removing the pressing plate and the welded product.

[0036] The application further provides that in step S4, the thickness of the solder sheet is 0.05-0.10mm; the edge of the solder sheet is inwardly retracted by 1.5-3mm compared to the corresponding welding area of the printed circuit board, and the solder sheet is brushed or dipped with flux.

[0037] The application further provides that in step S4, a high-temperature adhesive tape is used to assist in sticking and fixing the printed circuit board, solder sheet and metal plate as a whole.

[0038] The application further provides that in step S7, the temperature curve of the heating and welding is set as follows: the peak temperature is set to be 25-35℃ higher than the liquidus temperature of the solder sheet; the time for the solder to be above the liquidus temperature is controlled to be 30-60s, and the time window for maintaining the peak temperature is 10-15s.

[0039] Compared with the prior art, the application has the following beneficial effects:

[0040] By using the precise height-limiting stud combined with the adjustable pressing gap H, the pre-compression amount of the high-temperature-resistant silica gel plate can be accurately controlled, so that a constant and uniform pressure is applied during the welding process. This pressure effectively suppresses the surface tension, metal oxides and gas aggregation generated during the melting and flowing of the solder, avoids the formation of voids, greatly reduces the void rate to an acceptable level, and significantly improves the reliability and conductivity of the welded joint.

[0041] By effectively controlling the welding cavity, not only the quality of the single welding point is improved, but also the functionality and long-term reliability of the entire PCB assembly are indirectly improved. This is particularly crucial for high-density and high-performance electronic products (such as automotive electronics, communication equipment, etc.). BRIEF DESCRIPTION OF DRAWINGS

[0042] Fig. 1 is a schematic diagram of the three-dimensional structure of the present application;

[0043] Fig. 2 is a schematic diagram of the internal three-dimensional structure of the present application.

[0044] back support seat 52, clamping plate 53, sliding rod 54, first spring 55, guide rod 6, positioning nut 61, second spring 62, screw rod 7, locking nut 71. DETAILED DESCRIPTION

[0045] Reference Figs. 1-2 The metal substrate low-cavity welding jig and welding method of the present application are further described in the embodiments.

[0046] The jig specifically includes: a backing plate 1, a height-limiting stud 2, a pressing plate 3, a high-temperature-resistant silica gel plate 4, and a pressing unit.

[0047] The backing plate 1 serves as a base for stably bearing the stacked body to be welded. The stacked body is composed of a metal plate and a printed circuit board welded thereto. The high-temperature-resistant silica gel plate 4 is pressed on the top surface of the printed circuit board. The material of the backing plate 1 can be selected from high-strength, high-temperature-resistant, and moderately heat-conductive materials such as ceramics, high-strength aluminum alloy, or stainless steel. The surface of the backing plate 1 is designed to have structures facilitating the installation of the height-limiting studs 2 and the positioning and pressing unit.

[0048] The height-limiting studs 2 are installed on the backing plate 1. Their number and layout are determined according to the size of the backing plate 1 and the size of the stacked body. They are usually distributed around the stacked body. The height of the height-limiting studs 2 is adjustable, which is the key to achieving precise gap control. This means that the studs themselves have precise threads and can be raised or lowered by rotation. The top end surfaces of all the height-limiting studs 2 must be located on the same plane to ensure that the pressing plate 3 is uniformly stressed in the locked state.

[0049] The pressing plate 3 is arranged opposite to the height-limiting studs 2 and placed on the stacked body. In the locked state, the lower surface of the pressing plate 3 is in contact with the top end surfaces of the height-limiting studs 2, thereby defining the total gap between the pressing plate 3 and the backing plate 1. This gap is the pressing gap between the pressing plate 3 and the backing plate 1 for accommodating the stacked body, the silica gel plate, and limiting the compression thereof. The pressing plate 3 needs to have sufficient rigidity to withstand clamping forces and pressures in all directions. Its material can be selected from similar or higher strength materials than the backing plate 1.

[0050] The high-temperature-resistant silica gel plate 4 is placed between the pressing plate 3 and the printed circuit board, and is in contact with the PCB in a plane. The role of the silica gel plate is crucial:

[0051] The silica gel plate has good elasticity and compressibility, can absorb some uneven stress during the PCB and welding process, and uniformly transmit the pressure applied by the pressing plate 3 to the PCB, so as to avoid damage to the PCB caused by excessive local stress; when pressed, the silica gel plate can produce a certain lateral extrusion on the edge of the PCB, which helps to form a preliminary seal on the periphery, reduces the overflow of solder during the welding process, and provides a certain support for the PCB to prevent it from warping during the heating process.

[0052] With the precise gap set by the height-limiting stud 2, the silica gel plate is compressed, and the compression amount is a key parameter affecting the welding cavity. In the locked state, in order to make the high-temperature-resistant silica gel plate 4 be in a compressed state and achieve low-cavity welding, the following geometric relationships need to be met:

[0053] H=(T-T0)+T1+T2.

[0054] Where H represents the total vertical distance between the lower surface of the pressing plate 3 and the upper surface of the backing plate 1 finally defined by the height-limiting stud 2. This distance determines the stacking height of the entire stack and the compression degree of the silica gel plate; T represents the original uncompressed thickness of the high-temperature-resistant silica gel plate 4. This is the optical thickness of the silica gel plate when no external pressure is applied; T0 represents the preset compression amount. This is the deformation amount intentionally caused by the silica gel plate to achieve the target pressure; T0 is calculated according to the material properties (elastic modulus E) and the target pressure P through the formula T0=(P*T) / E;

[0055] T1 represents the thickness of the printed circuit board, which is the physical size of the PCB itself; T2 represents the thickness of the metal plate, which is the physical size of the metal substrate itself. By accurately setting H, the silica gel plate is forced to be compressed by T0 during the entire stacking process. This controlled compression can ensure that the solder forms a good wetting surface with the PCB and the metal plate, and provides a certain pulling force during the cooling process due to the elastic recovery of the silica gel plate, effectively inhibiting the formation of cavities.

[0056] The pressing unit is arranged in four directions of the backing plate 1, which is used to clamp different specifications of the stack. This ensures that the stack does not move during the welding process, especially during the heating and cooling cycle, the material may deform due to thermal expansion and contraction, and the pressing unit provides a stable external force to firmly fix the stack on the backing plate 1.

[0057] The detailed structure and working principle of the pressing unit: the pressing unit includes a plurality of clamping units arranged around, so as to realize stable clamping in all directions.

[0058] Each clamping unit is composed of two support seats arranged in front and back. The function of these support seats is to provide installation reference and guide for the components that dominate the clamping action.

[0059] The slide rod 54 is located between the front and back support seats 52, and the clamping plate 53 is slidingly connected on the slide rod 54. The slide rod 54 provides the clamping plate 53 with a trajectory for front and back movement, ensuring the accuracy of the movement direction of the clamping plate 53.

[0060] The first spring 55 is sleeved on the slide rod 54, one end of which is connected with the back of the clamping plate 53, and the other end is connected with the back support seat 52. The spring here plays the role of elastic thrust. When the size of the PCB board or metal plate changes, the compression or elongation of the first spring 55 can automatically adjust the position of the clamping plate 53, realizing self-adaptive clamping of different specifications of the stacked body.

[0061] The movable opening is provided on the pressing plate 3 corresponding to the position of the clamping plate 53. It allows the clamping plate 53 to move forward and backward along the direction of the slide rod 54 after being pressed down and locked by the pressing plate 3. This structure allows the clamping plate 53 to exert adaptive clamping force without affecting the overall pressing and locking of the pressing plate 3, and the movement of the clamping plate 53 can be adjusted according to the actual size of the stacked body to provide optimal clamping contact.

[0062] The rear support seat 52 is provided with a connecting hole, and a guide rod 6 penetrates through the connecting hole, one end of the guide rod 6 being fixedly connected with the backing plate 1. The function of the guide rod 6 is to provide accurate guide for the up and down movement of the overall pressing plate 3, ensuring that the pressing plate 3 remains horizontal during the stress process.

[0063] The second spring 62 is sleeved on the guide rod 6, and the two ends of the second spring 62 are connected with the backing plate 1 and the pressing plate 3 respectively. The second spring 62 mainly provides elastic action when the pressing plate 3 is pressed down, playing a role of buffer or auxiliary positioning, which helps to preliminarily position the pressing plate 3 before locking.

[0064] The end of the guide rod 6 is movably connected with a positioning nut 61. When the pressing plate 3 is pressed down to a predetermined position (i.e. in contact with the height limiting stud 2), the positioning nut 61 is in contact with the top end surface of the rear support seat 52, thereby locking the position of the pressing plate 3 after the pressing plate 3 is pressed down. This is an auxiliary locking method, which cooperates with the fastening screw to ensure the stability of the position of the pressing plate 3.

[0065] There are also several threaded rods 7 and locking nuts 71 between the backing plate 1 and the pressing plate 3. These components are arranged along the length direction of the backing plate 1 and the pressing plate 3, and pass through the corresponding hole positions on the backing plate 1 and the pressing plate 3. After the pressing plate 3 is pressed to the predetermined position (contacting the height-limiting stud 2, which sets the value of H), the pressing plate 3 can be fixed by the locking nuts 71, so as to lock the position. This is the most direct and main locking mode, which ensures that the interval of (T-T0)+T1+T2 is accurately fixed.

[0066] The present application provides a low-cavity welding method suitable for the jig, which significantly reduces the welding cavity by accurately controlling the pressure and temperature curve.

[0067] Step one, preset pressure determination and compression amount calculation:

[0068] Determine the preset pressure value P: according to the specific welding process requirements, PCB size, metal plate type and the characteristics of the solder alloy, determine a preset welding pressure value P. This pressure value is the key to ensure that the solder is fully filled and reduce the cavity. The pressure P usually refers to the force applied per unit area (for example, N / mm² or Pa).

[0069] Calculate the required compression amount T0: combined with the material properties of the high-temperature-resistant silica gel plate 4, calculate the required compression amount T0 for generating the preset pressure P by the following formula: T0=(P*T) / E, wherein P is the preset pressure value (for example, PdPa, or PdN / mm²).

[0070] T is the original uncompressed thickness of the high-temperature-resistant silica gel plate 4 (for example, mm); E is the elastic modulus of the high-temperature-resistant silica gel plate 4 material (for example, GPa or N / mm²), and the value of the elastic modulus E needs to be based on the technical specifications provided by the specific silica gel material supplier.

[0071] T0 is the calculated thickness of the silica gel plate that needs to be compressed (the unit is the same as T, for example, mm). The value of T0 should be less than the original thickness T of the silica gel plate, to ensure that the elastic limit of the material is not exceeded in actual compression. The calculated T0 will be used as a constant in the subsequent steps.

[0072] Step two, setting the height H of the height-limiting stud 2:

[0073] Calculate H according to specific parameters: according to the actual measured thickness T1 of the printed circuit board, the thickness T2 of the metal plate (21), and the original thickness T of the high-temperature-resistant silica gel plate 4 (13), and substitute the constant T0 calculated in step S1, calculate the required height H of the height-limiting stud 2: H=(T-T0)+T1+T2

[0074] Adjusting the height-limiting stud 2: according to the calculated height H, the top end face of the height-limiting stud 2 is accurately adjusted to the same horizontal plane by rotating the adjusting nut of the height-limiting stud 2.

[0075] Step three, cutting of the high-temperature-resistant silicone rubber plate 4:

[0076] The high-temperature-resistant silicone rubber plate 4 is cut into a shape matching the size of the soldering area of the printed circuit board. It is ensured that the silicone rubber plate completely covers the soldering surface of the PCB, but does not overflow to the non-soldering area of the metal plate, so as to avoid affecting the subsequent process steps or cleaning.

[0077] Step four, assembly of the stack:

[0078] The solder sheet is accurately laid on the soldering area of the metal plate;

[0079] The thickness of the solder sheet is preferably in the range of 0.05mm-0.10mm. Too thin may result in insufficient solder, and too thick may result in solder overflow or reduced solder strength.

[0080] The edge of the solder sheet needs to be inwardly retracted by 1.5mm-3mm compared to the corresponding soldering area of the printed circuit board. This is done to avoid direct contact of the solder with the peripheral area of the PCB pad during reflow, or excessive diffusion at high temperature, reducing the possibility of false welding.

[0081] The solder sheet is brushed or dipped with flux, which removes the oxide layer on the metal surface, reduces the surface tension, promotes solder wetting, and thus improves the reliability of the soldering.

[0082] The cut printed circuit board is placed above the laid solder sheet.

[0083] The printed circuit board, solder sheet and metal plate are accurately aligned to ensure correct alignment of the three in the soldering area. To prevent the PCB from shifting during subsequent loading, high-temperature adhesive tape can be used to assist in sticking and fixing the printed circuit board, solder sheet and metal plate as a whole.

[0084] Step five, loading and covering of the stack:

[0085] The assembled stack is placed on the backing plate 1; the cut high-temperature-resistant silicone rubber plate 4 is covered on the PCB of the stack. Then, the pressing plate 3 is covered on the high-temperature-resistant silicone rubber plate 4.

[0086] Step six, assembly and locking of the jig:

[0087] The pressing unit is started, and the stack is clamped and fixed all around by the clamping plate 53. The clamping plate 53 will automatically adhere to the edge of the PCB under the action of the first spring 55, providing stable clamping force.

[0088] The pressing plate 3 is pressed down to make its lower surface uniformly contact with the top end surface of all the height-limiting studs 2 to reach the set height H, and the locking state is completed. At this time, the pressing plate 3 is firmly locked in the predetermined position by the screw rod 7 and the locking nut 71.

[0089] Step seven, heating and welding: the whole set of fixtures is sent into a reflow furnace or placed on a flat heating table for heating and welding together with the stacked body;

[0090] The setting of the welding temperature curve is very important, and the following principles need to be followed:

[0091] The peak temperature is set to be 25-35℃ higher than the liquidus temperature of the solder alloy used. For example, if the TL of the solder is 217℃ (SAC305), the peak temperature can be set to be between 242℃ and 252℃;

[0092] The time (TAL) during which the solder is controlled to be above the liquidus temperature is 30-60s. A time that is too short may cause the solder not to melt completely and form defects, and a time that is too long may cause the PCB or metal plate to be excessively oxidized or the components to be damaged.

[0093] During the entire TAL time period, the time window during which the temperature is maintained near the peak temperature is controlled to be 10-15s. This ensures that the solder is sufficiently melted and has fluidity while avoiding excessive temperature exposure time and reducing the possibility of void formation.

[0094] Step eight, cooling and product removal:

[0095] After the heating and welding is completed, the entire stacked body is naturally cooled in the fixture. Preferably, it is cooled to below 80℃. Too fast cooling may cause stress to occur at the welding interface, affecting the strength.

[0096] After the temperature is cooled to a safe range, the locking state of the pressing unit is released, usually by loosening the positioning nut 61 and the sliding clamp plate 53 and loosening the locking nut 71.

[0097] The pressing plate 3 and the silica gel plate are removed, and then the product with completed welding is carefully taken out.

[0098] The above only describes the preferred embodiments of the present application and is not used to limit the present application. Those skilled in the art can make usual changes and replacements within the technical scheme of the present application, which should be included in the protection scope of the present application.

Claims

1. A low-void welding fixture for metal substrates, characterized in that, include: A liner plate is used to support a stack, the stack comprising a metal plate and a printed circuit board welded to it. A height-limiting stud is installed on the liner plate. The height of the height-limiting stud is adjustable, and the top end faces are located on the same plane. A pressure plate is disposed opposite to the height limiting stud. In the locked state, the lower surface of the pressure plate contacts the top end face of the height limiting stud to limit the clamping gap. A high-temperature resistant silicone sheet is located between the pressure plate and the printed circuit board, with planar overlapping contact. The clamping unit is located in four directions of the liner and is used to clamp stacked bodies of different specifications.

2. The low-void welding fixture for metal substrates according to claim 1, characterized in that: The uncompressed thickness of the high-temperature resistant silicone sheet is T, the preset compression amount is T0, the thickness of the printed circuit board is T1, and the thickness of the metal plate is T2. Under the locked state, the geometric relationship is satisfied: H=(T-T0)+T1+T2, H is the distance between the pressure plate and the liner plate defined by the height limiting stud, and it keeps the high-temperature resistant silicone sheet in a state of compressed thickness.

3. The low-void welding fixture for metal substrates according to claim 2, characterized in that: The clamping unit includes multiple clamping units arranged around the perimeter. Each clamping unit includes two support seats arranged at intervals from front to back, and a sliding rod is provided between the front support seat and the rear support seat. A clamping plate is slidably connected to the slide rod, and a first spring is sleeved on the slide rod. One end of the first spring is connected to the back of the clamping plate, and the other end is connected to the rear support seat, which is used to provide elastic thrust to the clamping plate. An open opening is provided on the pressure plate corresponding to the position of the clamping plate, so that the clamping plate can move back and forth along the direction of the slide rod within the open opening to clamp stacked objects of different specifications.

4. The low-void welding fixture for metal substrates according to claim 2, characterized in that: The rear support is provided with a connection hole, through which a guide rod passes, and one end of the guide rod is fixedly connected to the liner plate; A second spring is fitted onto the guide rod, with its two ends connected to the liner and the pressure plate, respectively, to provide elasticity when the pressure plate is pressed down. A positioning nut is movably connected to the end of the guide rod. The positioning nut abuts against the top surface of the rear support seat to lock the position after the pressure plate is pressed down.

5. The low-void welding fixture for metal substrates according to claim 2, characterized in that: There are also several screws and locking nuts between the liner and the pressure plate, which are used to lock the pressure plate after it is pressed down to a predetermined position. These screws and locking nuts are arranged along the length of the liner and the pressure plate.

6. A welding method using the low-void welding fixture for metal substrates according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Determine the preset pressure value P, calculate the compression amount T0 required to generate the preset pressure P using the formula T0=(P*T) / E, and use T0 as a constant for subsequent calculations; Where T is the original uncompressed thickness of the high-temperature resistant silicone sheet, and E is the elastic modulus of the silicone sheet material; S2. Calculate the height limit stud height H=(T-T0)+T1+T2 based on the printed circuit board thickness T1, metal plate thickness T2 and high temperature resistant silicone plate thickness T, and adjust the height limit stud to height H so that its top end face is on the same plane. S3. Cut the high-temperature resistant silicone sheet to match its dimensions with the printed circuit board; S4. Solder sheets are laid on the metal plate, and the printed circuit board is placed on it. The printed circuit board, solder sheets and metal plate are aligned according to the design requirements to form a stack. S5. Place the stacked body on the liner and cover it with the high-temperature resistant silicone plate and the pressure plate; S6. The stacked body is clamped by the clamping unit, and the pressure plate is pressed down until it contacts the top end face of the height limiting stud to achieve a locking state; S7. Use a reflow oven or flat heating table for heating and welding; S8. After the heating and welding are completed, allow the stacked body to cool naturally to below 80°C, release the locking state of the clamping unit, and remove the pressure plate and the welded product.

7. The welding method according to claim 6, characterized in that, In step S4, the thickness of the solder sheet is 0.05mm-0.10mm; the planar dimensions of the solder sheet are 1.5mm-3mm smaller at the edges than the corresponding soldering area of ​​the printed circuit board, and flux is brushed or dipped onto the solder sheet.

8. The welding method according to claim 6, characterized in that, In step S4, high-temperature tape is used to help adhere and fix the printed circuit board, solder sheet, and metal plate together.

9. The welding method according to claim 6, characterized in that, In step S7, the temperature curve for heating and welding is set as follows: the peak temperature is set to be 25°C-35°C higher than the liquidus temperature of the solder sheet; the time for the solder to remain above the liquidus temperature is controlled to be 30s-60s, of which the time window for maintaining it near the peak temperature is 10s-15s.

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