Method for fluxless soldering of Kovar carrier and annular isolator

Abstract

This invention provides a method for fluxless tinning of a Kovar carrier and a ring isolator, relating to the field of microwave device processing technology. The method for fluxless tinning of a Kovar carrier includes: sequentially placing a ceramic sheet, a fluxless tin-enameled solder sheet, and a device to be de-tinned in a tinning fixture; placing a tinning press block above the device to be de-tinned, assembling it into a de-tinned assembly; placing the assembly in a vacuum sintering furnace, evacuating the furnace, and filling the furnace cavity with formic acid gas to expose the tinning fixture to a formic acid atmosphere; heating the vacuum sintering furnace to a preset temperature to allow the formic acid to react with the tinning interface of the device, melting all the solder sheet; lowering the temperature inside the vacuum sintering furnace and removing the formic acid to obtain the de-tinned device. The de-tinning method provided by this invention can reduce yield loss and enable mass production.

Description

Technical Field

[0001] This invention relates to the field of microwave device processing technology, and in particular to a method for fluxless tinning of Kovar carriers and a ring isolator. Background Technology

[0002] In the field of microwave components, when sintering signal transmitting antennas, such as loop isolators, into the component housing, the gold-plated Kovar substrate at the bottom of the loop isolator needs to be de-goldened and tin-plated to prevent gold embrittlement. De-goldening and tin-plating not only prevents gold embrittlement but also improves the sintering quality.

[0003] In related technologies, the main methods for removing gold and tinning electronic components are high-temperature solder baths and flux baths with manually adjustable temperatures. The component is held manually with a pen, and the part of the component to be gold-removed and tinned is immersed in the flux bath to apply flux. Then, the part of the component to be gold-removed and tinned is immersed in a high-temperature solder bath to remove gold. After gold removal, the component is held manually again and the part of the component to be gold-removed and tinned is immersed in the flux bath to apply flux. Then, the part of the component to be gold-removed and tinned is immersed in a high-temperature pure tin bath to tin-plate. After tin-plate, the flux residue on the leads is wiped off with an alcohol swab.

[0004] However, current manual gold removal and tinning methods are inefficient, involve complicated steps, produce inconsistent tinning results, and have a high scrap rate. Summary of the Invention

[0005] This invention provides a method for fluxless tinning of Kovar carriers and a ring isolator to solve the problems of low efficiency and low yield of current manual gold removal tinning methods.

[0006] In a first aspect, embodiments of the present invention provide a method for fluxless soldering of a Kovar carrier, comprising:

[0007] A ceramic sheet, a fluxless tin-plated solder sheet, and a device to be de-goldened and tin-plated are placed sequentially in a tin-plating fixture, and a tin-plating pressure block is placed above the device to be de-goldened and tin-plated to assemble a device to be de-goldened and tin-plated; wherein, the gold-plated Kovar carrier of the device to be de-goldened and tin-plated is in contact with the tin-plated solder sheet.

[0008] The tin-plated assembly to be de-plated is placed in a vacuum sintering furnace, a vacuum is drawn, and formic acid gas is filled into the cavity of the vacuum sintering furnace so that the tin-plating fixture is in a formic acid atmosphere.

[0009] The vacuum sintering furnace is heated to a preset temperature so that formic acid reacts with the tin-plating interface of the device and the tin-plating solder sheet is completely melted.

[0010] The temperature inside the vacuum sintering furnace is lowered and formic acid gas is discharged to obtain a device with de-gold tin plating.

[0011] In one possible implementation, heating the vacuum sintering furnace to a preset temperature to cause formic acid to react with the tin-plating interface of the device and to completely melt the tin-plating solder sheet includes:

[0012] The vacuum sintering furnace is heated to a first preset temperature and maintained at the first preset temperature for a first preset time so that formic acid reacts with the tin-plating interface of the device.

[0013] The vacuum sintering furnace is heated to a second preset temperature and maintained at the second preset temperature for a second preset time so that the tin-plated solder sheet is completely melted.

[0014] In one possible implementation, heating the vacuum sintering furnace to a second preset temperature and maintaining it at the second preset temperature for a second preset time to completely melt the solder sheet includes:

[0015] The vacuum sintering furnace is heated to a third preset temperature and maintained at the third preset temperature for a third preset time to preheat the tin-plated solder sheet; wherein the third preset temperature is greater than the first preset temperature and less than the second preset temperature;

[0016] The vacuum sintering furnace is heated to the second preset temperature and maintained at the second preset temperature for a fourth preset time so that the tin-plated solder sheet is completely melted.

[0017] In one possible implementation, the first preset temperature is 200℃-230℃, the third preset temperature is 230℃-250℃, and the second preset temperature is 250℃-280℃;

[0018] The first preset duration is 2-4 minutes, the third preset duration is 2-4 minutes, the fourth preset duration is 1-2 minutes, and the second preset duration is 3-6 minutes.

[0019] In one possible implementation, the tinning fixture includes a plurality of grooves for placing devices, and the size of the grooves is larger than the size of the device to be de-tinned, the size of the fluxless tinned solder sheet is the same as the size of the device to be de-tinned, and the size of the ceramic sheet is the same as the size of the device to be de-tinned.

[0020] In one possible implementation, each of the grooves corresponds to a weight, all of the weights constitute the tin-plating pressing block, and all of the weights are disposed on the pressing plate;

[0021] The process involves placing a solder pad on top of the device to be de-plated and assembling it into a solder pad assembly, including:

[0022] After placing the tinning press block above the device to be detinned, the press plate is fixed to the tinning fixture.

[0023] In one possible implementation, the weight of the weight block is 10-20g.

[0024] In one possible implementation, the oxygen content of the fluxless tin-enameled solder sheet is less than 50 ppm.

[0025] In one possible implementation, the thickness of the gold plating layer on the surface of the device to be de-plated is less than or equal to 0.003 mm.

[0026] In a second aspect, embodiments of the present invention provide a ring isolator, including a ring isolator and a gold-plated Kovar carrier disposed below the ring isolator, wherein the gold plating on the gold-plated Kovar carrier is removed based on the fluxless tinning method of the Kovar carrier described in any of the first aspects, and tin is applied to the Kovar carrier after the gold plating is removed.

[0027] This invention provides a method for fluxless tinning of a Kovar carrier. By sequentially placing a ceramic sheet, fluxless tin-enameled solder sheet, and the component to be tinned in a tinning fixture, the tin-enameled solder sheet can be brought into contact with the ceramic sheet, and then into contact with the gold-plated Kovar carrier of the component to be tinned, ensuring the flatness of the tin-plated surface of the Kovar carrier. Placing a tinning press block above the component to be tinned ensures sufficient contact between the gold-plated Kovar carrier and the tin-enameled solder sheet, guaranteeing solder quality. After assembling the component to be tinned, it is placed in a vacuum sintering furnace filled with formic acid gas, allowing the tin-enameled solder sheet to fully melt and tin-enamele in a high-temperature formic acid atmosphere. Furthermore, in this high-temperature formic acid atmosphere, formic acid can remove oxides from the surface of the gold-plated Kovar carrier, improving solder flowability, enhancing tinning quality and consistency, reducing defective product losses, and enabling rapid mass production. Attached Figure Description

[0028] Figure 1 This is a flowchart of the method for fluxless tinning of Kovar carrier provided in an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of the structure of the assembled tin-plated component to be de-plated according to an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the structure of the ring isolator provided in an embodiment of the present invention;

[0031] Figure 4This is a SEM image of the intermetallic compound distribution on the tin-plated surface of the device prepared according to the present invention, provided in an embodiment of the present invention.

[0032] Figure 5 This is an EDS analysis diagram of intermetallic compounds provided in an embodiment of the present invention;

[0033] Figure 6 This is an EDS analysis diagram of the free intermetallic compound provided in an embodiment of the present invention;

[0034] Figure 7 This is a local EDS line scan image of the cross-section near the device phase interface provided in the embodiment of the present invention. Detailed Implementation

[0035] The present application will be described more clearly below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the function of the present application, but do not limit the present application in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application. These all fall within the protection scope of the present application.

[0036] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0037] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0038] In the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0039] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0040] Furthermore, the term "multiple" mentioned in the embodiments of this application should be interpreted as two or more.

[0041] First, the terms used in the embodiments of this application will be explained:

[0042] Kovar carriers: These are carrier or base components made of Kovar alloy used for encapsulating electronic components. Kovar alloy is a precision alloy with iron, nickel, and cobalt as its main components, with a core composition of approximately 36% nickel, 18% cobalt, and 46% iron. Kovar alloy has a coefficient of thermal expansion that matches that of materials such as glass and ceramics, ensuring high airtightness after sealing.

[0043] Flux is an auxiliary material used in welding. Its core function is to remove oxides from the welding surface, reduce the surface tension of the solder, help the solder wet the base metal, and form a reliable joint. The main purpose of using flux in welding is to ensure the reliability and stability of the weld joint and to solve key problems such as oxidation and poor wetting during the welding process.

[0044] Gold removal and tin plating: This refers to the process of dissolving and removing the gold or other metal plating layers on a device in a high-temperature molten tin bath. This ensures that the gold plating layer does not cause solder joint brittleness during subsequent component soldering. After gold removal, flux is added to the surface of the component, and it is then immersed in a high-temperature molten pure tin bath to plate a layer of tin metal onto the component, ensuring solderability during the soldering process.

[0045] The inventors discovered that when performing gold removal and soldering on large-area annular isolators, typically with a maximum size of 8*10mm, it is difficult to guarantee the amount of solder used and achieve a flatness of less than 30µm on the soldered surface using current manual soldering methods. Solder sheets must be used to specify the amount of solder used while ensuring the flatness of the soldered surface, with a flatness of less than 30µm.

[0046] In traditional soldering, flux is essential. The flux reduces oxides on the solder and Kovar carrier surfaces, increases the fluidity of the molten solder, and ensures a full reaction between the solder and the Kovar carrier surface. Without flux, traditional soldering methods result in incomplete wetting after melting, and the oxides on the solder or Kovar carrier surface cannot be removed. This leads to localized areas where the solder and Kovar carrier do not react, causing poor soldering and failing to achieve the desired soldering purpose.

[0047] Refer to together Figure 1 and Figure 2 , Figure 1 This is a flowchart illustrating a method for fluxless tinning of a Kovar carrier, as provided in an embodiment of the present invention. Figure 2This is a schematic diagram of the structure of the tin-plated assembly to be de-goldened after assembly using the Kovar carrier flux-free tinning method provided in this embodiment of the invention. The Kovar carrier flux-free tinning method provided in this embodiment of the invention is applied in a ring isolator. The Kovar carrier flux-free tinning method includes:

[0048] S110. Place the ceramic sheet, the fluxless tin-enameled solder sheet, and the device to be de-goldened and tin-enameled in sequence into the tin-enameling fixture, and place the tin-enameling pressing block on top of the device to be de-goldened and tin-enameled to assemble it into a de-goldened and tin-enameled assembly.

[0049] Before assembling the gold-plated tin-plated assembly 240, it is necessary to first prepare a ceramic sheet 220 and a fluxless tin-plated solder sheet 230.

[0050] It should be noted that the bottom of the device to be de-goldened and tinned has a Kovar carrier with gold plating. The gold-plated Kovar carrier on the bottom of the device to be de-goldened and tinned needs to be de-goldened and tinned. Therefore, the gold-plated Kovar carrier of the device to be de-goldened and tinned only needs to be in contact with the tinning solder sheet. The other sides do not need to be de-goldened and tinned. Therefore, the other sides do not need to be tinned and tinned.

[0051] In some embodiments, since oxides can cause poor solder joints and hinder the spread of solder on the base material surface, in order to reduce soldering defects and improve solder joint reliability, it is necessary to use clean, flux-free tin-enameled solder sheets with low oxygen content.

[0052] In this embodiment, the oxygen content of the fluxless tin-enameled solder sheet 230 is less than 50 ppm, thereby reducing the impact of oxides on tinning.

[0053] In some embodiments, in order to ensure the flatness of the final tinning of the device 240 to be de-goldened and tinned, a ceramic sheet 220 and a fluxless tinning solder sheet 230 that match the size and shape of the device 240 to be de-goldened and tinned can be prepared first.

[0054] In this embodiment, a ceramic sheet 220 and a fluxless tin-plated solder sheet 230 with the same size and shape as the device 240 to be de-goldened and tin-plated can be prepared.

[0055] In this embodiment, the thickness of the gold plating layer on the surface of the device 240 to be de-goldened and tinned can be <0.003mm, the thickness of the clean tin-plated solder sheet 230 without flux can be 0.04mm, the thickness of the ceramic sheet 220 can be 0.06mm, and the size of the tinning fixture can be slightly larger than the size of the device 240 to be de-goldened and tinned. For example, the size of the tinning fixture can be 0.03mm larger than the size of the device to be de-goldened and tinned.

[0056] In some embodiments, in order to ensure uniform tinning on the surface of the device to be de-tinned, a tinning block 250 is placed above the device to be de-tinned. This ensures that the surface of the device 240 to be de-tinned is in full contact with the fluxless tinning solder sheet 230, and that the fluxless tinning solder sheet 230 is in full contact with the ceramic sheet 220, thus avoiding uneven tinning due to poor contact.

[0057] In this embodiment, the tinning block 250 can be made of aluminum alloy. Since there are typically one or two permanent magnets on the ring isolator chip, an aluminum alloy tinning block 250 is required to ensure it is non-ferromagnetic and does not attract the permanent magnets. Furthermore, the bottom of the tinning block 250 conforms to the surface of the device to be de-tinned, ensuring full contact with the permanent magnets and uniform force distribution on the device.

[0058] In some embodiments, since the device size 240 to be de-plated is relatively small, multiple devices to be de-plated can be de-plated simultaneously to improve manufacturing efficiency.

[0059] In this embodiment, as Figure 2 As shown, the tinning fixture 210 may include multiple grooves 2110 for placing devices 240 to be de-tinned. In order to ensure that the devices 240 to be de-tinned can have sufficient gold removal and uniform tinning, the size of the grooves 2110 may be larger than the size of the devices 240 to be de-tinned, so that all devices 240 to be de-tinned can be placed inside the grooves 2110.

[0060] like Figure 3 As shown, in the structure of the ring isolator, there is a permanent magnet above the chip. During the tinning process, the devices to be de-goldened and tinned are close together, which can easily cause them to attract each other. The grooves in the tinning fixture can effectively prevent the devices from attracting each other.

[0061] For example, the size of the groove 2110 may be 0.03 mm larger than the size of the device 240 to be de-goldened and de-tinned. The size of the fluxless tin-plated solder sheet 230 is the same as the size of the device 240 to be de-goldened and de-tinned, and the size of the ceramic sheet 220 is the same as the size of the device 240 to be de-goldened and de-tinned.

[0062] In this embodiment, as Figure 2As shown, since the tinning fixture 210 includes multiple grooves 2110 for placing the components to be de-tinned, in order to ensure that the surface of the components to be de-tinned is in full contact with the flux-free tinning solder sheet, and that the flux-free tinning solder sheet 230 is in full contact with the ceramic sheet 220, and to avoid uneven tinning due to poor contact, a weight can be set for each groove 2110, and all the weights 2510 form a tinning pressure block 250.

[0063] For example, each weight 2510 can weigh 10-20g, and the material of weight 2510 can be aluminum alloy.

[0064] For example, to facilitate assembly, all weights 2510 are set on the pressure plate 260, and fixing buckles are provided on both the pressure plate 260 and the tinning fixture 210. After placing the tinning pressure block 250 on top of the device 240 to be de-tinned, the pressure plate 260 and the tinning fixture 210 can be fixed.

[0065] In this embodiment, screws and screw holes can be provided at corresponding positions on the pressure plate 260 and the tinning fixture 210, respectively. After placing the tinning block 250 on top of the device 240 to be de-tinned, the screws on the pressure plate 260 and the tinning fixture 210 can be tightened to achieve fixation.

[0066] In this embodiment, clips / spring clips can be installed at the corresponding positions of the pressure plate 260 and the tin-plated fixture 210 for fixation: the elastic structure is used for engagement.

[0067] In this embodiment, pins / pins can be installed at corresponding positions on the pressure plate 260 and the tin-plated fixture 210 for fixation: cylindrical pins and conical pins are used for positioning and fixing to ensure the coaxiality or relative position of the parts.

[0068] In this embodiment, magnetic fixation can be performed at the corresponding positions of the pressure plate 260 and the tin-plated fixture 210.

[0069] S120. Place the tin-plated assembly to be de-plated into a vacuum sintering furnace, evacuate the furnace, and fill the cavity with formic acid gas so that the tin-plating fixture is in a formic acid atmosphere.

[0070] After the assembly of the components to be de-plated with tin is completed, the de-plating process can begin.

[0071] Place the tin-plated assembly to be de-plated into the vacuum sintering furnace, close the furnace door, and evacuate the furnace.

[0072] In some embodiments, in order to greatly reduce the oxygen content in the vacuum sintering furnace, the vacuum sintering furnace can be evacuated and then nitrogen can be released before evacuating again, thereby reducing the oxygen content in the vacuum sintering furnace.

[0073] Once the set vacuum level is reached, formic acid gas can be introduced into the cavity of the vacuum sintering furnace to place the tin-plating fixture in a formic acid atmosphere.

[0074] S130. Heat the vacuum sintering furnace to the preset temperature so that formic acid reacts with the tinning interface of the device and melts all the tinning solder sheet.

[0075] To ensure the smoothness and quality of the tinning process, oxides need to be removed and the fluidity of the solder needs to be increased to achieve a better tinning effect.

[0076] In some embodiments, multi-stage heating can be performed to achieve different heating effects. First, the vacuum sintering furnace is heated to a first preset temperature and held at the first preset temperature for a first preset time to allow formic acid to undergo a reduction reaction with the interface of the device to be tinned, removing the oxide film on the interface. Then, the vacuum sintering furnace is heated to a second preset temperature and held at the second preset temperature for a second preset time to allow the tin-plating solder sheet to completely melt.

[0077] In this embodiment, the second preset temperature is higher than the first preset temperature. Heating to the first preset temperature and maintaining it for a first preset time allows for the effective reduction of oxides by formic acid, ensuring that there are no oxides at the tin-plating interface and guaranteeing the final tin-plating quality.

[0078] In this embodiment, the first preset temperature is 200℃-230℃, and the second preset temperature is 250℃-280℃. The first preset duration is 2-4 minutes, and the second preset duration is 3-6 minutes.

[0079] For example, the first preset temperature can be 200℃, and the second preset temperature can be 270℃. The first preset duration can be 3 minutes, and the second preset duration can also be 3 minutes.

[0080] In this embodiment, in order to ensure that the solder sheet is fully melted and to improve the soldering effect, the vacuum sintering furnace is first heated to a third preset temperature and held at that temperature for a third preset time to preheat the solder sheet. Then, the vacuum sintering furnace is heated to a second preset temperature and held at that temperature for a fourth preset time to ensure that the solder sheet is fully melted.

[0081] The third preset temperature is greater than the first preset temperature and less than the second preset temperature.

[0082] The temperature is raised to a third preset temperature and maintained at that temperature for a certain duration. This third preset temperature serves as preheating for the solder sheets before soldering, ensuring that all solder sheets melt simultaneously in the next heating stage. The vacuum sintering furnace is then raised to a second preset temperature and maintained at that temperature for a fourth preset duration, ensuring that all solder sheets melt completely. This allows for the removal of gold plating and tinning on the gold-plated Kovar carrier of the assembly to be de-goldened and tinned, while maintaining the smoothness and quality of the tinned surface. This eliminates the need for cleaning due to flux contamination during conventional de-goldening and tinning processes, reducing yield losses and enabling rapid mass production.

[0083] In this embodiment, the third preset temperature is 230℃-250℃, the third preset duration is 2-4 min, and the fourth preset duration is 1-2 min.

[0084] For example, the third preset temperature can be 230°C, the third preset duration can be 4 minutes, and the fourth preset duration can be 1 minute.

[0085] S140. Reduce the temperature inside the vacuum sintering furnace and remove formic acid to obtain a device with de-gold tin plating.

[0086] After preparation, the temperature inside the vacuum sintering furnace is lowered and formic acid is removed, and the device to be de-plated with gold and tin can be taken out, with tin plating already completed on its Kovar carrier.

[0087] At a high temperature of 200℃~230℃, formic acid volatilizes and reacts with the oxides at the interface of the gold-plated Kovar carrier of the device to be tinned, increasing the flowability of the solder formed from the molten solder sheet. In addition, the pressure provided by the tinning block ensures that the molten solder flows fully. At this high temperature, the molten solder comes into contact with the Kovar gold-plated layer and undergoes a chemical reaction, completing the tinning process.

[0088] When using a vacuum sintering furnace, the solder can be melted in a formic acid atmosphere at high temperatures. The inventors discovered that in this high-temperature formic acid atmosphere, the solder exhibits a flowability effect comparable to that of added flux. Formic acid at high temperatures can remove oxides and increase wettability, thus achieving a tinning effect. By enhancing solder flowability, tinning quality and consistency can be improved, defective product losses can be reduced, and mass production can be rapidly achieved.

[0089] The minimum thickness of the fluxless solder sheet can be determined by considering the thickness of the gold plating on the device to be de-goldened, the thickness of the fluxless solder sheet, the dimensions of the device to be de-goldened, the dimensions of the fluxless solder sheet, the density of gold, the density of the solder sheet, and the requirement that the gold mass ratio should be less than 3% to avoid gold embrittlement. See Table 1 below:

[0090] Table 1. Au Content Calculation Table

[0091]

[0092] In the theoretical calculation of the component ratio, when Y1 / (Y1+Y2) < 3%, gold embrittlement can be avoided. Since the size of the device to be de-goldened and tinned is fixed, the thickness k of the fluxless tin-plated solder sheet can be determined according to the above formula.

[0093] To demonstrate whether gold elements exhibit reverse aggregation after tinning using the method provided in this invention, EDS analysis was performed on the cross-section of the tinned device. The solder used in this tinning was SnSb10. The intermetallic compounds after the tinning reaction were classified into two states according to their location: one is the intermetallic compound formed at the grain boundaries or phase boundaries of the material, and the other is the intermetallic compound free within the phase of a certain material. Figure 4 As shown, the cross-section of the device after tinning was inspected by SEM. The red circle marks the intermetallic compound.

[0094] like Figure 5 As shown, an EDS scan was performed on the location of the gold-plated Kovar carrier attachment. The intermetallic compound at this location was primarily an interfacial NiSn compound, with very little Au content. Based on this phenomenon and data analysis, the gold layer near the Kovar carrier has been completely consumed, and all Au has reacted with Sn to form a stable AuSn compound. According to the scale in the figure, the thickness of the interfacial intermetallic compound is approximately 2–3 μm.

[0095] like Figure 6 As shown, EDS analysis of the white substance attached to the gold-plated Kovar carrier revealed that it is a free AuSn compound, AuSn2. The free intermetallic compound is uniformly distributed throughout the SnSb interface, without any segregation or enrichment.

[0096] The initial Au element originated from the surface of the gold-plated Kovar carrier, and EDS analysis was performed on this location. Local EDS line scans were performed on the cross-section near the phase interface of the device, such as... Figure 7 As can be seen from the elemental distribution in the figure, Au is evenly distributed without obvious elemental segregation or enrichment. It should be noted that... Figure 7 In the figure, Au-Lα represents the L-series α characteristic X-rays of gold, Ni-Kα represents the K-series α characteristic X-rays of nickel, Sb-Lα represents the L-series α characteristic X-rays of antimony, and Sn-Lα represents the L-series α characteristic X-rays of tin.

[0097] The above analysis shows that by using the Kovar carrier fluxless tinning method provided by the present invention, the purpose of gold removal tinning can be achieved, and there will be no dirt on the surface of the device after tinning, and the device does not need to be cleaned.

[0098] This application places a ceramic sheet, a fluxless tin-enameled solder sheet, and the component to be de-goldened and tin-enameled in a tinning fixture in sequence. This ensures that the tin-enameled solder sheet contacts the ceramic sheet and the gold-plated Kovar carrier of the component to be de-goldened and tin-enameled, guaranteeing the flatness of the tin-plated surface of the Kovar carrier. By placing a tinning press block above the component to be de-goldened and tin-enameled, sufficient contact between the gold-plated Kovar carrier and the tin-enameled solder sheet is ensured, guaranteeing solder quality. After assembling the component to be de-goldened and tin-enameled, it is placed in a vacuum sintering furnace and filled with formic acid gas. This allows the tin-enameled solder sheet to fully melt and tin-enameled in a high-temperature formic acid atmosphere. Furthermore, in a high-temperature formic acid atmosphere, formic acid can also remove oxides from the surface of the gold-plated Kovar carrier, improving the quality of tinning.

[0099] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0100] In a second aspect, the present invention also provides a ring isolator, comprising a ring isolator and a gold-plated Kovar carrier disposed below the ring isolator, wherein the gold plating on the Kovar carrier is removed by a fluxless tinning method according to any one of the first aspects, and tin is applied to the Kovar carrier after the gold plating is removed.

[0101] Still with Figure 3 For example, the ring isolator is also equipped with a permanent magnet. Therefore, the tinned block cannot be attracted to the permanent magnet on the ring isolator. The tinned block can be made of aluminum alloy.

[0102] Furthermore, considering the permanent magnets on the ring isolators, which could cause them to attract each other when multiple ring isolators are simultaneously de-goldened and de-tinned, the tinning fixture includes multiple grooves for placing components. The dimensions of these grooves are larger than the dimensions of the components to be de-goldened and de-tinned. The dimensions of the fluxless tinning solder sheet and the ceramic sheet are the same as the dimensions of the components. By providing these grooves, the problem of components attracting each other can be effectively avoided.

[0103] The annular isolator prepared by using the Kovar carrier fluxless tinning method provided in the first aspect of the present invention can not only be mass-produced quickly, but also achieve gold removal and tinning without the use of flux or the addition of a cleaning process. Moreover, the quality of the tinning meets the product requirements after inspection and analysis.

[0104] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for fluxless tinning of a Kovar carrier, characterized in that, include: A ceramic sheet, a fluxless tin-enameled solder sheet, and a device to be de-goldened and tin-enameled are sequentially placed in a tinning fixture, and a tinning block is placed on top of the device to be de-goldened and tin-enameled, assembling them into a de-goldened and tin-enameled assembly. The gold-plated Kovar carrier of the device to be de-goldened and tin-enameled is in contact with the tin-enameled solder sheet, and the Kovar carrier has a gold plating layer. The mass ratio of the gold plating layer to the mass of the gold plating layer and the tin-enameled solder sheet is less than 3%. The tinning fixture includes multiple grooves for placing devices, and the size of the grooves is larger than the size of the device to be de-goldened and tin-enameled. The size of the fluxless tin-enameled solder sheet is the same as the size of the device to be de-goldened and tin-enameled, the size of the ceramic sheet is the same as the size of the device to be de-goldened and tin-enameled, and the tinning block is non-ferromagnetic. The tin-plated assembly to be de-plated is placed in a vacuum sintering furnace, a vacuum is drawn, and formic acid gas is filled into the cavity of the vacuum sintering furnace so that the tin-plating fixture is in a formic acid atmosphere. The vacuum sintering furnace is heated to a first preset temperature and maintained at the first preset temperature for a first preset time so that formic acid reacts with the tin-plating interface of the device to remove the oxides from the interface of the gold-plated Kovar carrier. The vacuum sintering furnace is heated to a third preset temperature and held at the third preset temperature for a third preset time to preheat the tin-plated solder sheet; wherein the third preset temperature is greater than the first preset temperature; The vacuum sintering furnace is heated to a second preset temperature and maintained at the second preset temperature for a fourth preset time, so that the tin-plated solder sheet is completely melted. The melted solder comes into contact with the gold-plated layer of the Kovar carrier and undergoes a chemical reaction, thereby removing the gold plating from the gold-plated Kovar carrier. The third preset temperature is lower than the second preset temperature. The first preset temperature is 200℃-230℃, the third preset temperature is 230℃-250℃, and the second preset temperature is 250℃-280℃. The temperature inside the vacuum sintering furnace is lowered and formic acid gas is discharged to obtain a device with de-gold tin plating.

2. The method for fluxless tinning of Kovar carrier as described in claim 1, characterized in that, The first preset duration is 2-4 minutes, the third preset duration is 2-4 minutes, and the fourth preset duration is 1-2 minutes.

3. The method for fluxless tinning of Kovar carrier as described in claim 1, characterized in that, Each groove corresponds to a weight, all of which together form the tin-plating pressing block, and all of which are mounted on the pressing plate. The process involves placing a solder pad on top of the device to be de-plated, assembling it into a solder pad assembly, including: After placing the tinning press block above the device to be detinned, the press plate is fixed to the tinning fixture.

4. The method for fluxless tinning of Kovar carrier as described in claim 3, characterized in that, The weight of the weight is 10-20g.

5. The method for fluxless soldering of Kovar carrier as described in any one of claims 1-4, characterized in that, The oxygen content of the fluxless tin-enameled solder sheet is less than 50 ppm.

6. The method for fluxless soldering of Kovar carrier as described in any one of claims 1-4, characterized in that, The thickness of the gold plating layer on the surface of the device to be de-plated is less than or equal to 0.003 mm.

7. A ring isolator, characterized in that, The device includes a ring isolator body and a gold-plated Kovar carrier disposed below the ring isolator body. The gold-plated Kovar carrier is removed by the fluxless tinning method of Kovar carrier according to any one of claims 1-6, and tin is applied to the Kovar carrier after the gold plating is removed.

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