Welding furnace and welding method

Abstract

According to the welding furnace and the welding method, the workpiece is positioned through the containing groove, an additional pressing plate is not needed, and damage such as indentation and microcracks is avoided. A gap is formed between the heating plate and the workpiece, heat is transferred through radiation and convection coupling, a local low-temperature area is avoided, and the peak temperature difference is reduced. The contact area of the workpiece on the welding carrier is small, the heat capacity is low, and the thermal response is fast; the adopted suspended structure forms a thermal short circuit effect and is matched with the high-emissivity coating to improve the heating rate; contact thermal resistance is avoided during cooling, heat dissipation is fast, and time is shortened; and the suspended structure avoids carbonization and residue of volatile matter of the soldering flux, is suitable for various atmosphere environments, and meets the high-reliability soldering-flux-free welding requirement. Based on the radiation heat transfer characteristic, the voidage of the process is still kept stable when a workpiece warps and fluctuates, the process window is widened, and the incoming material requirement is reduced. The welding carrier can adapt to various contact type welding furnaces, parts and procedures do not need to be replaced, and replacement can be achieved without stopping production.

Description

Technical Field

[0001] This invention relates to the field of power semiconductor packaging, and in particular to a welding furnace and welding method. Background Technology

[0002] As the mainstream equipment in the industrial welding field, contact heating welding furnaces rapidly transfer heat through direct contact with the workpiece. With the advantages of short heat conduction path, high thermal efficiency and strong energy penetration, they are irreplaceable in deep welding of thick-walled components, dissimilar metals and high melting point materials.

[0003] However, with the widespread adoption of thin-walled precision components, semiconductor power devices, and complex 3D packaging, contact heating, due to its inherent limitations, is no longer sufficient to meet the requirements of high-precision welding processes. Microscopic undulations and oxide films on the workpiece surface result in an effective contact area of ​​less than 50%, leading to uneven heat distribution and significant temperature gradients, easily inducing defects such as warping, cracks, and incomplete soldering. Furthermore, the clamping pressure applied to reduce contact thermal resistance may cause microcracks and indentations in brittle / soft materials, increasing the risk of premature device failure. Moreover, the heating plate has a large heat storage capacity, limiting the heating and cooling rates, resulting in long production cycle times and difficulty in meeting high-efficiency production demands. Simultaneously, contact welding requires strict workpiece flatness; excessive warping leads to increased contact gaps, resulting in increased thermal resistance and weld voids, drastically narrowing the process window. Under long-term high temperature and pressure, the heating plate is prone to wear and tear, requiring frequent maintenance and replacement, increasing costs and posing a risk of contamination. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a welding furnace and welding method to solve the problem of thermomechanical coupling caused by contact heating in the prior art contact welding process.

[0005] To achieve the above and other related objectives, the present invention provides a welding furnace, the welding furnace comprising at least:

[0006] A welding carrier, comprising a frame and at least one heat spreader, wherein the frame has a fixing groove inside, the heat spreader has a fixing member, the fixing member cooperates with the fixing groove to fix the heat spreader inside the frame, the heat spreader has a placement groove for accommodating a workpiece, the placement groove penetrates the heat spreader, and the side wall of the placement groove has a boss for supporting the workpiece.

[0007] A heating plate, wherein the heating plate is provided with a radiation coating.

[0008] Preferably, the number of placement slots is N, where N is an integer greater than or equal to 2.

[0009] Preferably, the area of ​​the boss accounts for less than 20% of the area of ​​the placement groove.

[0010] Preferably, the bottom surface of the boss and the bottom surface of the heat spreader are on the same plane.

[0011] Preferably, there is a height difference between the bottom surface of the boss and the bottom surface of the heat spreader.

[0012] Preferably, the thickness of the boss is in the range of 1mm to 3mm.

[0013] Preferably, the atmosphere inside the welding furnace includes one of a nitrogen atmosphere, a nitrogen-hydrogen mixed atmosphere, and a nitrogen-formic acid mixed atmosphere.

[0014] Preferably, the heat spreader comprises a Ti-6Al-4V heat spreader.

[0015] Preferably, positioning slots are symmetrically arranged on both sides of the frame.

[0016] The present invention also provides a welding method, the welding method comprising at least the following steps:

[0017] Provide the welding furnace described above;

[0018] Provide the workpiece to be welded;

[0019] The workpiece is placed in the placement slot of the welding carrier;

[0020] The welding carrier is placed in the welding furnace for preheating;

[0021] The temperature of the heating plate is set and the heating plate is moved to the bottom of the welding carrier. Heat is transferred to the workpiece by radiation for welding.

[0022] The welded workpiece is cooled, and after cooling is complete, the workpiece is removed.

[0023] As described above, the welding furnace and welding method of the present invention have the following beneficial effects:

[0024] 1. In this invention, the workpiece is positioned only by the placement groove, without the need for an additional pressure plate, thus avoiding problems such as indentations and microcracks on the workpiece surface.

[0025] 2. By creating a stable gap between the bottom of the workpiece and the heating plate, the heat is mainly transferred through radiation and convection coupling, which can avoid local low temperature areas caused by fluctuations in the contact area and effectively reduce the peak temperature difference during operation.

[0026] 3. This invention places the workpiece in a suspended state within the welding carrier, reducing contact thickness and accelerating thermal response. Simultaneously, the suspended area of ​​the workpiece creates a "thermal short-circuit" effect, which, combined with the high-emissivity coating on the heating plate surface, significantly improves the heating rate. During the cooling phase, since there is no contact thermal resistance between the workpiece and the cold plate, heat dissipation efficiency is greatly improved, thereby achieving an overall reduction in single-cycle time.

[0027] 4. The suspended structure designed in this invention can effectively prevent flux volatiles from forming carbon residues on the contact surface, thereby achieving seamless adaptation to various atmospheric environments and meeting the requirements of various power modules for high-reliability fluxless welding processes.

[0028] 5. This invention uses radiative heat transfer, which is independent of the contact area. It can maintain a stable welding void rate even when the workpiece warpage changes within a certain range, thereby widening the process window and significantly reducing the cost of incoming material screening.

[0029] 6. The welding carrier of the present invention can be adapted to various contact welding furnaces without changing the heater, sensor or control program, and can realize equipment replacement without stopping production. Attached Figure Description

[0030] Figure 1 The diagram shown is a structural schematic of the welding carrier in an embodiment of the present invention.

[0031] Figure 2 The diagram shows the positional structure of the welding carrier and the heating plate in an embodiment of the present invention.

[0032] Component designation explanation

[0033] 100 Welding carrier 110 frame 111 Fixed groove 120 heat spreader 121 Placement slot 122 boss 123 Fasteners 200 heating plate Detailed Implementation

[0034] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0035] Please see Figure 1 and Figure 2 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0036] This invention provides a welding furnace, which includes at least:

[0037] A welding carrier 100 includes a frame 110 and at least one heat spreader 120. The frame 110 has a fixing groove 111 inside, and the heat spreader 120 has a fixing member 123. The fixing member 123 cooperates with the fixing groove 111 to fix the heat spreader 120 inside the frame 110. The heat spreader 120 has a placement groove 121 for accommodating workpieces. The placement groove 121 penetrates the heat spreader 120. The side wall of the placement groove 121 has a boss 122 for supporting the workpiece.

[0038] Heating plate 200, wherein a radiation coating is provided on the heating plate 200.

[0039] In this embodiment, the welding furnace further includes a conveying device (not shown), a preheating chamber (not shown), a welding chamber (not shown), and a cooling chamber (not shown). It should be understood that the components listed above are merely examples and are not intended to limit the configuration of the welding furnace of this invention. In practical applications, the components of the welding furnace can be adaptively added or removed according to specific process requirements without departing from the core protection scope of this invention.

[0040] Specifically, such as Figure 1 and Figure 2 As shown, during the welding process, the workpiece and the heating plate 200 form a certain suspended structure, which prevents the carbonization residue of welding flux volatiles at the contact interface. Within the suspended structure area, heat is mainly transferred by radiation through the formation of a "thermal short circuit" effect combined with the radiation coating on the surface of the heating plate 200. This heat transfer mechanism is independent of the contact area, thus effectively avoiding problems such as unstable heat conduction caused by changes in the contact area. Furthermore, since heat transfer is independent of the contact area, the allowable warpage range of the workpiece can be expanded, and the weld void rate can still be maintained at a low level. As a result, the process window is widened, significantly reducing the requirements for incoming material screening and related costs.

[0041] As an example, the number of placement slots 121 is N, where N is an integer greater than or equal to 2. The specific number can be set according to actual needs.

[0042] In this embodiment, as Figure 1 As shown, there are 6 placement slots 121, which are arranged in an array in the heat spreader 120. Each heat spreader 120 is divided into 3 equal-width regions along the longitudinal direction, and 2 placement slots 121 are distributed in each region along the length of the heat spreader 120.

[0043] Specifically, the placement groove 121 structure is used to position and fix the workpiece, and the boss 122 provides auxiliary support, so that the surface of the workpiece does not bear additional pressure, thereby effectively avoiding damage problems such as indentation and micro-cracks, and thus achieving precision welding without pressure damage on the surface of the workpiece.

[0044] As an example, the area of ​​the boss 122 is less than 20% of the area of ​​the placement groove 121.

[0045] Specifically, the area of ​​the boss 122 is controlled to be less than 20% of the area of ​​the placement groove 121 in order to ensure that the area of ​​the workpiece exposed to radiation in the welding carrier 100 is greater than 80%; at the same time, the smaller proportion of the boss 122 can reduce the shielding of radiant heat energy by the support structure, avoid the formation of temperature gradient due to local heat reception differences, and ensure the uniformity and efficiency of radiant heating.

[0046] As an example, the bottom surface of the boss 122 is on the same plane as the bottom surface of the heat spreader 120.

[0047] As an example, in another embodiment, there is a height difference between the bottom surface of the boss 122 and the bottom surface of the heat spreader 120.

[0048] Specifically, during the welding process, when the heating plate 200 contacts the bottom surface of the heat spreader 120, if there is a height difference between the bottom surface of the boss 122 and the bottom surface of the heat spreader 120, that is, the bottom surface of the boss 122 is higher than the bottom surface of the heat spreader 120, the boss 122 and the heating plate 200 do not directly contact each other, which can avoid the workpiece from being heated unevenly in the area of ​​the boss 122 due to local contact with the heating plate 200.

[0049] It should be noted that the position of the boss 122 is set according to the actual process and is not limited here.

[0050] As an example, the shape of the boss 122 may include a fan shape, but is not limited to this.

[0051] In this embodiment, as Figure 1 As shown, fan-shaped bosses are used and are positioned at the four corners of the placement slot 121. It should be noted that the shape, number, and positional relationship of the bosses 122 can be adjusted according to the actual working conditions.

[0052] As an example, the thickness of the boss 122 ranges from 1 mm to 3 mm.

[0053] Specifically, the thickness of the boss 122 can be set according to actual process requirements and is not limited to the specific dimensions mentioned above. In practical applications, it is sufficient to ensure that the thickness of the boss 122 does not exceed the overall thickness of the heat spreader 120.

[0054] As an example, the atmosphere in the welding furnace may include one of a nitrogen atmosphere, a nitrogen-hydrogen mixed atmosphere, or a nitrogen-formic acid mixed atmosphere, but is not limited to these.

[0055] Specifically, the protective atmosphere inside the welding furnace can be flexibly set according to the actual working conditions such as the welding material and process requirements. During the welding process, the airflow inside the welding furnace cavity will form directional thermal convection, which will drive the heat emitted by the heating plate 200 to the surface of the workpiece, further helping to improve the uniformity of the workpiece heating.

[0056] As an example, the heat spreader 120 may include a Ti-6Al-4V heat spreader, but is not limited thereto.

[0057] Specifically, in this embodiment, the heat spreader 120 is preferably a Ti-6Al-4V heat spreader, as the Ti-6Al-4V alloy has a low heat capacity of only 0.18 kJ / kg. -1 ꞏK -1 Furthermore, the suspended structure design creates a "thermal short circuit" between the workpiece and the heating plate 200, thereby significantly improving the heating and cooling rates. This effectively shortens the single-cycle time and improves overall production efficiency.

[0058] As an example, positioning slots (not shown) are symmetrically arranged on both sides of the frame 110.

[0059] Specifically, the positioning slot can be directly adapted and installed with the conveying device of the welding furnace, so that the welding carrier 100 can be compatible with a variety of contact welding furnaces; without replacing the heater, sensor and control program of the furnace body, the equipment can be switched and adapted without stopping production.

[0060] As an example, the radiation coating may include a NiCrAlY blackbody coating, but is not limited to this.

[0061] In this embodiment, the radiation coating is preferably a NiCrAlY blackbody coating. By coating the surface of the heating plate 200 with a 50μm thick NiCrAlY blackbody coating, its emissivity can be significantly increased from 0.25 to 0.90, and the radiation power density can be increased by 3.6 times. In addition, the NiCrAlY blackbody coating has high hardness and high bonding strength with the heating plate 200, and can remain intact even after multiple thermal shock cycles without peeling off.

[0062] Table 1 below further illustrates the parameter comparison between the welding furnace provided in this embodiment and the existing contact welding furnace during use.

[0063] Table 1

[0064] parameter Existing contact welding furnace Welding furnace of the present invention multiple heating rate <![CDATA[90 Kꞏmin -1 ]]> <![CDATA[150 Kꞏmin -1 ]]> 1.67 cooling rate <![CDATA[80 Kꞏmin -1 ]]> <![CDATA[180 Kꞏmin -1 ]]> 2.25 ΔT in the same batch 8.1 °C 1.9 °C 4.3 void ratio 5.2 % 0.7 % 7.4 Clamping force 0.25 MPa 0 MPa 250 Compatible with warp ≤0.2 mm ≤0.5 mm 2.5

[0065] As shown in Table 1, in this embodiment, by maintaining a 12mm gap between the bottom of the workpiece and the heating plate 200, heat is transferred via 88% radiation and 12% natural convection, thus avoiding the traditional "point-to-surface" contact heat transfer mode. Furthermore, the suspended structure creates a "thermal short circuit" between the workpiece and the heating plate 200, thereby reducing the heating rate from 90KΩ / min. -1 Increased to 150K kmin -1 This represents an increase of approximately 1.37 times, while the cooling rate has increased from 80K kmin. -1 Increased to 180K kmin -1 This represents an improvement of approximately 2.25 times. Consequently, the single-cycle time decreased from 180s to 112s, effectively increasing overall production capacity. Since radiative heat transfer is unaffected by contact area, when the allowable warpage range of the workpiece is widened from 0~0.2mm to 0~0.5mm, the warpage range expands by 2.5 times, resulting in an 18% reduction in incoming material scrap and rework costs. Simultaneously, the weld void rate decreased from 5.2% to 0.7%, a reduction of approximately 7.4 times, and the weld void rate can be stably maintained below 1%, meeting the current technical requirements for weld void rate in high-reliability packaging. Under these conditions, the measured peak temperature difference of the same batch of workpieces decreased from 8.1°C to 1.9°C, and the temperature uniformity was correspondingly improved to approximately 4.3 times the original. In existing contact welding processes, the clamping force is typically set at 0.25MPa. In contrast, the welding carrier 100 used in this invention does not require a clamping mechanism, thus completely eliminating the clamping force. Compared with existing technologies, its equivalent clamping force is reduced by 250 times. This invention, through an integrated design of "carrier-radiation-process", can eliminate contact damage, improve temperature uniformity and shorten process cycle, while meeting the high reliability welding requirements of power modules and thin-walled ceramic packages.

[0066] Example 2

[0067] This invention also provides a welding method, which includes at least the following steps:

[0068] Provide a welding furnace as described in Example 1;

[0069] Provide the workpiece to be welded;

[0070] The workpiece is placed in the placement slot 121 of the welding carrier 100;

[0071] The welding carrier 100 is placed in the welding furnace for preheating;

[0072] The temperature of the heating plate 200 is set and the heating plate 200 is moved to the bottom of the welding carrier 100. Heat is transferred to the workpiece by radiation for welding.

[0073] The welded workpiece is cooled, and after cooling is complete, the workpiece is removed.

[0074] Specifically, the welding method provided in this embodiment is implemented based on the welding furnace described in Embodiment 1. Its specific structure and working process can be referred to the aforementioned relevant descriptions, and will not be repeated here.

[0075] In this embodiment, based on the welding furnace described in Embodiment 1, the welding carrier 100 is installed on a conveying device, and the workpiece to be welded is placed in the welding carrier 100. The conveying device is then activated to move the welding carrier 100 into the welding furnace chamber. First, it is moved to the preheating chamber for preheating of the workpiece and the welding carrier 100. After preheating, the conveying device moves the welding carrier 100 to the welding chamber for welding. Inside the welding chamber, the heating plate 200 is moved to the bottom of the welding carrier 100. Because a preset gap is maintained between the workpiece and the heating plate 200, and the surface of the heating plate 200 is covered with a radiation coating, and airflow is present in the furnace chamber, heat is transferred to the workpiece via radiation-convection coupling, achieving uniform welding. After welding is completed, the conveying device moves the welding carrier 100 to the cooling chamber for cooling. After cooling, the welding carrier 100 is removed from the furnace chamber, and the welded workpiece is taken out.

[0076] In summary, the welding carrier, welding furnace, and welding method provided by this invention allow the workpiece to be positioned solely by a placement slot, eliminating the need for additional pressure plates and thus avoiding damage issues such as indentations and microcracks on the workpiece surface. By creating a gap between the bottom of the workpiece and the heating plate, heat is transferred through radiation and convection coupling, avoiding localized low-temperature areas caused by fluctuations in contact area and reducing the peak temperature difference of the workpiece. The workpiece is suspended within the welding carrier, reducing the contact area with the carrier, effectively lowering the heat capacity and increasing the thermal response speed. Combined with the "thermal short-circuit" effect formed by the suspended area and the high-emissivity coating on the heating plate surface, the heating rate is significantly improved. During the cooling stage, the lack of contact thermal resistance between the workpiece and the cooling plate significantly improves heat dissipation efficiency, thereby shortening the overall process cycle time. Furthermore, the suspended structure effectively prevents flux volatiles from forming carbonized residues on the contact surface and is adaptable to various atmospheric environments, meeting the requirements of various power modules for high-reliability fluxless welding processes. This invention is based on radiative heat transfer, whose heat transfer efficiency is independent of the contact area. Even if the workpiece has a certain range of warpage, it can still maintain the stability of the weld void ratio, which helps to broaden the process window and reduce the stringent requirements for the flatness of incoming materials and the screening costs. Furthermore, the welding carrier is compatible with various contact welding furnaces, and no changes to heaters, sensors, or control programs are required; changes can be completed without interrupting production. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and has high industrial application value.

[0077] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A welding furnace, characterized in that, The welding furnace includes at least: A welding carrier, comprising a frame and at least one heat spreader, wherein the frame has a fixing groove inside, the heat spreader has a fixing member, the fixing member cooperates with the fixing groove to fix the heat spreader inside the frame, the heat spreader has a placement groove for accommodating a workpiece, the placement groove penetrates the heat spreader, and the side wall of the placement groove has a boss for supporting the workpiece. A heating plate, wherein the heating plate is provided with a radiation coating.

2. The welding furnace according to claim 1, characterized in that: The number of placement slots is N, where N is an integer greater than or equal to 2.

3. The welding furnace according to claim 1, characterized in that: The area of ​​the boss accounts for less than 20% of the area of ​​the placement groove.

4. The welding furnace according to claim 1, characterized in that: The bottom surface of the boss is on the same plane as the bottom surface of the heat spreader.

5. The welding furnace according to claim 1, characterized in that: There is a height difference between the bottom surface of the boss and the bottom surface of the heat spreader.

6. The welding furnace according to claim 1, characterized in that: The thickness of the boss ranges from 1mm to 3mm.

7. The welding furnace according to claim 1, characterized in that: The atmosphere inside the welding furnace includes one of the following: nitrogen atmosphere, nitrogen-hydrogen mixed atmosphere, and nitrogen-formic acid mixed atmosphere.

8. The welding furnace according to claim 1, characterized in that: The heat spreader includes a Ti-6Al-4V heat spreader.

9. The welding furnace according to claim 1, characterized in that: The frame has symmetrical positioning slots on both sides.

10. A welding method, characterized in that, The welding method includes at least the following steps: Provide a welding furnace as described in any one of claims 1 to 9; Provide the workpiece to be welded; The workpiece is placed in the placement slot of the welding carrier; The welding carrier is placed in the welding furnace for preheating; The temperature of the heating plate is set and the heating plate is moved to the bottom of the welding carrier. Heat is transferred to the workpiece by radiation for welding. The welded workpiece is cooled, and after cooling is complete, the workpiece is removed.

Images