TWI917112B - Method of diffusion bonding workpiece - Google Patents

Abstract

A method of diffusion bonding workpiece is provided. The method includes disposing a workpiece to be joined in a hot-pressing equipment, in which the workpiece to be joined includes two substances to be joined; and performing a hot-pressing operation to the workpiece to be joined, in which the hot-pressing operation includes a first-stage hot-pressing step and a second-stage hot-pressing step. Various stages of hot-pressing steps are performed to bond the workpiece to be joined with different briquettes. Therefore, a bonding strength and a bonding rate of the workpiece can be increased.

Description

Methods for diffusion bonding of workpieces

This invention relates to a method for diffusion bonding of workpieces, and more particularly to a method for diffusion bonding of workpieces using multi-stage hot pressing.

Diffusion bonding is a solid-state bonding technique that typically involves applying high temperature and pressure in a vacuum environment to reduce the distance between the contact surfaces of two workpieces (e.g., metal workpieces) to the interatomic distance, allowing atoms to intercalate and diffuse, thus bonding materials such as metals and ceramics. Compared to traditional bonding techniques, diffusion bonding provides a stronger joint surface and reduces workpiece deformation. For example, vacuum diffusion welding involves plastic deformation of the contact surfaces of two or more objects under specific temperature and pressure conditions. After holding at temperature/pressure or temperature/pressure for a period of time, the atoms on the surfaces to be welded diffuse, achieving metallurgical bonding of the surfaces.

The advantages of diffusion bonding technology are that it does not require flux, there is no stress effect on the joint surface, and the material strength and corrosion resistance are identical to the original material. Applications of diffusion bonding technology include mold inserts, heat exchangers, automotive parts, aerospace components, medical equipment and implants, and precious metal jewelry. The key to successful bonding lies in the temperature and pressure conditions.

Hot pressing is a manufacturing process that uses high temperature and high pressure to press materials. It is commonly used in the manufacture of high-density and high-performance materials, such as ceramics, metals, and composites. Hot presses are known pressure equipment for diffusion bonding processes. Their upper pressure limit depends on the design and structural strength of the hydraulic system; a common upper pressure limit for hot presses is 250 tons. For example, when bonding high-purity copper plates, the diffusion bonding temperature must be no less than 420°C, the bonding stress greater than 10 MPa, and the bonding strength greater than or equal to 60 MPa (or the backplate must break). To clarify, the bonding stress is calculated by dividing the force applied by the hot press by the contact area of the workpieces to be bonded; while the bonding strength refers to the adhesive strength between the two materials at the bonding interface, that is, the ability of the bonding interface to resist separation or fracture under stress. A successful bond generally requires a bonding rate exceeding 99%. It should be noted that the bonding rate is calculated as the ratio of the successfully bonded area to the total area to be bonded, and the standard for a successful bond can be determined by ultrasonic testing (UT) of the interface. However, conventional diffusion bonding techniques still have many inconveniences and drawbacks, making it difficult to reliably achieve the above conditions in the process.

Chinese patent publication CN 113727801A proposes using a punch to apply pressure to the workpieces to be joined. The punch is designed for flatbed hot presses and is often specifically shaped to adapt to different processing requirements. While it can apply pressure to the workpieces, it cannot flexibly adjust the joining area and joining force. A pressure block can be used between the punch and the workpieces to be joined to ensure that the workpieces are not moved when pressure is applied. The prior art typically uses a pressure block with a single size to perform joining under optimal temperature and pressure conditions. However, when joining large workpieces, the hot press is limited by the upper limit of the applied force due to the large joining range and contact area, often failing to meet the joining stress requirements.

Furthermore, the position of the heating rods in the hot press can limit the uniformity of heating, causing local areas to fail to reach the required bonding temperature or resulting in temperature differences between all workpieces, thus reducing the quality of the bond. Moreover, uneven workpiece bonding interfaces, the presence of oxide layers or contaminants on the interfaces can lead to insufficient local stress, further reducing the bonding rate and increasing the risk of bonding failure. These problems cause many workpieces to fail during the bonding process, becoming irreparable and requiring scrap, thus wasting materials and production costs.

In view of this, there is an urgent need to provide a diffusion bonding method to improve bonding quality and reduce the risk of bonding failure.

One aspect of this invention is to provide a method for diffusion bonding of workpieces, which involves performing a hot pressing operation on the workpieces to be bonded, including a multi-stage hot pressing step, thereby improving the bonding quality of the workpieces.

According to one aspect of the present invention, a method for diffusion-joining workpieces is provided, comprising placing the workpieces to be joined in a hot pressing apparatus, wherein the workpieces to be joined comprise two overlapping objects to be joined; and performing a hot pressing operation on the workpieces to be joined, wherein the hot pressing operation includes a first-stage hot pressing step and a second-stage hot pressing step. The first-stage hot pressing step includes placing a first pressing block on the workpieces to be joined, wherein the contact area between the first pressing block and the surface of the workpieces to be joined is a first area, wherein the first area is 20% to 100% of the surface area of the workpieces to be joined. The second-stage hot pressing step includes placing a second pressing block on the workpiece to be joined, wherein the contact area between the second pressing block and the surface of the workpiece to be joined is the second area, and based on the first area being 100%, the overlap area between the first area and the second area is 1% to 60%.

According to one embodiment of the present invention, the hot pressing operation further includes at least one third-stage hot pressing step, which includes placing a third pressing block on the workpiece to be joined, wherein the contact area between the third pressing block and the surface of the workpiece to be joined is the third area, and based on the first area being 100%, the overlap area between the first area and the third area is 1% to 60%.

According to one embodiment of the present invention, the first stage hot pressing step includes applying a first pressure, and the second stage hot pressing step includes applying a second pressure, wherein the first pressure and the second pressure are the same or different.

According to one embodiment of the present invention, the first stage hot pressing step includes applying a first pressure, the second stage hot pressing step includes applying a second pressure, and the third stage hot pressing step includes applying a third pressure, wherein the first pressure, the second pressure, and the third pressure may be the same or different.

According to one embodiment of the present invention, the second area is less than or equal to the first area.

According to one embodiment of the present invention, the third area is less than or equal to the first area.

According to one embodiment of the present invention, the hot pressing operation is carried out at a temperature of 100°C to 1000°C.

According to one embodiment of the present invention, the first stage hot pressing step and the second stage hot pressing step are performed for 1 minute to 8 hours.

According to one embodiment of the present invention, the first pressing block and the second pressing block are discs, rings, quadrilaterals or polygons.

According to one embodiment of the present invention, the workpiece to be joined is selected from a group consisting of ceramics, metals and composite materials.

The diffusion bonding method of this invention is used to perform a hot pressing operation on the workpieces to be bonded, which includes multiple hot pressing steps. Each hot pressing step uses different pressing blocks to bond the workpieces to be bonded, and the contact areas between the different pressing blocks and the workpieces to be bonded have a specific overlap range, thereby achieving the effect of improving the bonding strength and bonding rate of the workpieces.

The following disclosure provides numerous different embodiments or illustrations to implement various features of the invention. The specific examples of components and configurations described below are for the purpose of simplifying this disclosure. These are, of course, merely illustrative and are not intended to be limiting. For example, a description in which a first feature is formed on or above a second feature includes embodiments where the first and second features are in direct contact, as well as embodiments where other features are formed between the first and second features such that the first and second features are not in direct contact. Furthermore, element symbols and/or letters are repeated in various specific instances in this disclosure. This repetition is for the purpose of simplification and clarity and does not imply a relationship between the various embodiments and/or configurations discussed.

Furthermore, spatial relative terms, such as "beneath," "below," "lower," "above," and "upper," are used to easily describe the relationship between parts or features depicted in the drawings and other parts or features. In addition to the directions depicted in the drawings, spatial relative terms also include different orientations of the components during use or operation. The device may be oriented in other ways (rotated 90 degrees or in other directions), and the spatial relative descriptions used in this disclosure can also be interpreted in this way.

As used in this invention, “around,” “about,” “approximately,” or “substantially” generally mean within 20 percent, 10 percent, or 5 percent of the stated value or range.

The manufacture and use of embodiments of the present invention will now be discussed in detail. However, it is understood that the embodiments provide many applicable inventive concepts that can be implemented in a wide variety of specific contexts. The specific embodiments discussed are for illustrative purposes only and are not intended to limit the scope of the present invention.

As described above, this invention provides a method for diffusion-bonding workpieces, which involves performing a multi-stage hot pressing operation on the workpieces to be joined. Each stage of the hot pressing process uses different pressing blocks to join the workpieces, and the contact areas between the different pressing blocks and the workpieces have a specific overlap range. This achieves the effect of improving the bonding strength and bonding rate of the workpieces.

Please refer to Figure 1, which is a schematic diagram of a diffusion bonding process apparatus 100 according to some embodiments of the present invention. The diffusion bonding method of the present invention includes placing the workpiece 120 to be bonded 120 in a hot press 110. In some embodiments, the workpiece 120 to be bonded includes two overlapping elements 122 and 125. Specifically, this method involves diffusion bonding of elements 122 and 125. In some embodiments, the workpiece 120 to be bonded may be ceramic, metal, or a composite material. In some embodiments, the workpiece 120 to be bonded is placed on a lower pressure block 130.

Next, a hot pressing operation is performed on the workpieces 120 to be joined. The hot pressing operation includes multiple stages, the number of which can be adjusted according to application requirements. The present invention does not limit the number of hot pressing stages performed. The hot pressing step includes placing an upper pressure block 140 on the workpieces 120 to be joined. The upper pressure block 140 shown in FIG1 is merely an example, and the present invention is not limited thereto. In fact, the upper pressure block 140 can have different shapes and contact areas. In some embodiments, the upper pressure block 140 can be a disk, a ring, or a polygon, wherein the polygon can be, for example, a quadrilateral. Please refer to Figures 2A to 2D, which are schematic diagrams illustrating various upper pressure blocks 140 disposed on the workpieces 120 to be joined. Generally, especially for large workpieces (e.g., larger than 1000 ^cm² ), an annular pressure block must be used at least once to apply pressure to the periphery of the workpieces to be joined, thereby increasing the joint strength of the surrounding area of the workpieces to be joined.

In some embodiments, the hot pressing operation includes a first hot pressing step and a second hot pressing step. In this embodiment, the first hot pressing step involves placing a first pressing block on the workpiece 120 to be joined, and the second hot pressing step involves placing a second pressing block on the workpiece 120 to be joined.

The contact area between the first pressing block and the surface 120A of the workpiece 120 to be joined is the first area, and the contact area between the second pressing block and the surface 120A of the workpiece 120 to be joined is the second area. In some embodiments, the first area is about 20% to about 100% of the area of the surface 125A of the workpiece 120 to be joined, preferably about 50% to about 100%. If the first area is less than approximately 20% of the area of the surface 125A to be joined, meaning the contact area between the first pressing block and the workpiece 120 to be joined is too small, it may lead to uneven pressure applied by the pressing block to the workpiece 120, affecting the diffusion effect and resulting in insufficient interatomic bonding force between the joint interfaces. This may increase joining defects, thus reducing the joining efficiency. Furthermore, a small contact area between the first pressing block and the workpiece 120 may also cause uneven local pressure across the entire workpiece 120, preventing the effective formation of a stable diffusion bonding layer and resulting in unstable bonding strength. If the strength of the joint does not meet expectations, the workpiece 120 may be prone to delamination, cracking, or deformation when subjected to subsequent mechanical stress. Generally speaking, the contact area between the pressure block used in hot pressing and the surface 120A of the workpiece 120 to be joined is not greater than the surface 120A of the workpiece 120 to be joined.

The hot pressing area of the second stage hot pressing step must at least partially overlap with that of the first stage hot pressing step to help improve the bonding quality of the workpiece (i.e., bonding strength and bonding rate). In some embodiments, based on the first area being 100%, the overlap area between the first and second areas is about 1% to about 60%, preferably about 20% to about 55%, and more preferably about 30% to about 50%. If the overlap area between the first and second areas is less than 1%, the hot pressing ranges of the two stages almost do not overlap in the same area, and the bonding process cannot effectively achieve the cumulative pressure effect. Conversely, if the overlap area between the first and second areas is greater than 60%, the segmented pressure effect cannot be effectively improved, and the manufacturing cost of the pressure block design is increased. It should be understood that the first area is essentially equal to the contact area of the first pressure block, and the second area is essentially equal to the contact area of the second pressure block. In some embodiments, the second area is less than or equal to the first area, so the contact area of the second block is less than or equal to the contact area of the first block.

In some embodiments, the first hot pressing step includes applying a first pressure, and the second hot pressing step includes applying a second pressure. The first and second pressures may be the same or different. Generally, a hot press can apply the same force for hot pressing, so the first and second pressures are the applied force divided by the first and second areas, respectively. Therefore, the first and second pressures are the bonding stresses. Thus, if the second area is smaller than the first area, the second pressure is greater than the first pressure. It should be understood that the magnitude of the applied force is generally limited by the equipment. Therefore, if it is desired to increase the pressure of the hot pressing operation, it can be achieved by reducing the contact area between the pressure block and the workpiece 120 to be joined. Thus, the present invention utilizes a multi-stage hot pressing process to increase the flexibility of adjusting the size and shape of the pressure block, thereby improving the bonding strength of each area of the workpiece 120 to be joined.

In some embodiments, the hot pressing operation may optionally include a third-stage hot pressing step. The third-stage hot pressing step involves placing a third pressure block on the workpiece 120 to be joined, and the contact area between the third pressure block and the surface 120A of the workpiece 120 is the third area. Similarly, in some embodiments, based on the first area being 100%, the overlap area between the first and third areas is approximately 1% to approximately 60%, preferably approximately 20% to approximately 55%, and more preferably approximately 30% to approximately 50%. In some embodiments, the third area is less than or equal to the first area. In some embodiments, the third-stage hot pressing step includes applying a third pressure, where the second and third pressures may be the same or different. If the joint surface 125A of the workpiece 120 to be joined (i.e. the interface between the workpiece 122 and the workpiece 125) is not flat, it is preferable to perform at least one third-stage hot pressing step to increase the joint strength of the workpiece in the area of uneven interface, thereby improving the joint rate.

In some embodiments, the various stages of the hot pressing operation described above (e.g., the first, second, and third hot pressing stages) are performed at temperatures ranging from approximately 100°C to approximately 1000°C, depending on the material of the workpieces 120 to be joined. In some embodiments, the aforementioned temperature is controlled by gradually increasing, holding, and decreasing the temperature to avoid damage or performance degradation of the workpiece material due to rapid temperature changes.

In some embodiments, the various stages of the hot pressing operation described above (e.g., the first stage hot pressing, the second stage hot pressing, and the third stage hot pressing) are performed for about 1 minute to about 8 hours, depending on the material of the workpiece 120 to be joined.

The following examples illustrate the application of the invention, but they are not intended to limit the invention. Those with ordinary knowledge in the art can make various modifications and embellishments without departing from the spirit and scope of the invention.

Implementation Example 1

In Embodiment 1, the area of the surfaces to be joined is 1500 ^cm² , and the surface flatness is good. Embodiment 1 involves a two-stage hot-pressing process, with both stages performed at 425°C and the hot press force set to 250 tons. The first stage of hot-pressing uses an 800 ^cm² annular pressing block (as shown in Figure 2B) to pressurize the periphery of the workpieces. The second stage of hot-pressing uses an 800 ^cm² circular pressing block (as shown in Figure 2C) to pressurize the central area of the workpieces. The overlapping area of the pressure applied to the workpieces by the pressure blocks in the first and second hot pressing steps is 100 ^cm² (i.e., 12.5% of the first area). The bonding strength of the workpieces after diffusion bonding was determined by measuring tensile strength, and the bonding rate was determined by ultrasonic scanning. The results are shown in Table 1 below.

Implementation Example 2

In Embodiment 2, the area of the surfaces to be joined is 1000 ^cm² , and the interface of the surfaces to be joined has local unevenness. Embodiment 2 involves a two-stage hot pressing process on the workpieces to be joined, with both stages performed at a temperature of 425°C. The first stage hot press is set to a force of 250 tons, and the second stage hot press is set to a force of 200 tons. The first stage hot pressing process uses a pressure block with an area of 1000 ^cm² and the same shape as the workpieces to be joined to apply full-area pressure to the workpieces. The second-stage hot pressing step involves applying pressure to the uneven areas of the workpieces to be joined using a circular pressure block with an area of 300 ^cm² (as shown in Figure 2C). The overlapping area of the pressure applied by the pressure blocks in the first and second-stage hot pressing steps is 300 ^cm² (i.e., 30% of the first area). After diffusion bonding, the joint strength of the workpieces to be joined is determined by measuring tensile strength, and the joint rate is determined by ultrasonic scanning. The results are shown in Table 1 below.

Implementation Example 3

In Embodiment 3, the area of the surfaces to be joined is 1500 ^cm² , and the interface of the surfaces to be joined is uneven. Embodiment 3 involves a three-stage hot pressing process on the workpieces to be joined, with each hot pressing step performed at a temperature of 425°C. The hot press force is set to 250 tons in the first and second stages, and to 200 tons in the third stage. The first stage of the hot pressing process involves applying full-area pressure to the workpieces using a 1500 ^cm² pressure block with the same shape as the workpieces to be joined. The second stage of hot pressing involves applying pressure to a localized area of the workpieces to be joined using an 800 ^cm² ring-shaped pressure block (as shown in Figure 2D). The third stage of hot pressing involves reinforcing the localized area of the workpieces to be joined using a 300 ^cm² circular pressure block (as shown in Figure 2C). The overlapping area of the pressure applied by the pressing blocks in the first and second hot pressing steps to the workpieces to be joined is 800 ^cm² (53.3% of the first area), while the overlapping area of the pressure applied by the pressing blocks in the second and third hot pressing steps to the workpieces to be joined is 300 ^cm² (20% of the first area). The bonding strength of the workpieces after diffusion bonding was determined by measuring tensile strength, and the bonding rate was determined by ultrasonic scanning. The results are shown in Table 1 below.

Comparative example one

In Comparative Example 1, the area of the surfaces to be joined is 1500 ^cm² , and the surface flatness is good. Comparative Example 1 involves a single hot-pressing step on the workpieces to be joined, with each hot-pressing step performed at a temperature of 425°C and the hot press force set to 250 tons. The hot-pressing step utilizes a 1500 ^cm² pressure block with the same shape as the workpieces to be joined to apply full-area pressure. The bonding strength of the workpieces after diffusion bonding was determined by measuring tensile strength, and the bonding rate was determined by ultrasonic scanning. The results are shown in Table 1 below.

Comparative Example 2

In Comparative Example 2, the area of the surfaces to be joined is 1000 ^cm² , and the interface of the surfaces to be joined is locally uneven. In Comparative Example 1, a single hot-pressing step was performed on the workpieces to be joined, with each hot-pressing step conducted at a temperature of 425°C and the hot press force set to 250 tons. The hot-pressing step used a pressure block with an area of 1000 ^cm² and the same shape as the workpieces to be joined to apply full-area pressure. The bonding strength of the workpieces after diffusion bonding was determined by measuring tensile strength, and the bonding rate was determined by ultrasonic scanning. The results are shown in Table 1 below.

Table 1

According to Table 1, the workpieces of Examples 1 to 3, which use multi-stage hot pressing, all have a joint strength of over 60 MPa and a joint rate of over 99%, and therefore can all be judged as successfully joined.

In contrast, the workpieces to be joined in Comparative Example 1 were larger, so a single hot-pressing process was used, resulting in uneven stress distribution across the entire joint surface. Consequently, the joint stress at the contact point of the pressure block edges was less than 10 MPa. Furthermore, the larger workpiece size could also lead to uneven local temperatures, resulting in lower joint strength in these areas. This meant that the joint strength varied significantly across different locations, resulting in an overall joint rate of only 76%, which failed to meet the expected joint standard, thus causing the joint to fail.

Comparative Example 2 involves a single hot-press bonding of a workpiece with an uneven interface. As a result, the bonding is not complete in some areas. The bonding strength at the uneven areas and around the workpiece is only 48 MPa, which is insufficient in some areas. Therefore, the bonding rate is only 82%, which means the bonding fails.

According to the above embodiments, the present invention provides a method for diffusion-bonding workpieces, which involves performing a multi-stage hot pressing operation on the workpieces to be joined. Each stage of the hot pressing process uses different pressing blocks to join the workpieces, providing different hot pressing conditions for workpieces with different dimensions or flatness. Furthermore, the contact areas between the different pressing blocks and the workpieces have a specific overlap range. This achieves the effect of improving the bonding strength and bonding rate of the workpieces.

Although the present invention has been disclosed above with several embodiments, it is not intended to limit the present invention. Anyone with ordinary knowledge in the art to which the present invention pertains may make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended patent application.

100: Process apparatus; 110: Hot pressing equipment; 120: Workpiece to be joined; 122, 125: Item to be joined; 130: Lower pressure block; 140: Upper pressure block; 120A: Surface; 125A: Surface to be joined.

A better understanding of the features disclosed herein will be achieved by referring to the following detailed description and accompanying figures. It should be noted that, as is standard practice in the industry, many features are not drawn to scale. In fact, the dimensions of many features can be arbitrarily scaled for clarity of discussion. Figure 1 is a schematic diagram illustrating a diffusion bonding process apparatus according to some embodiments of the present invention. Figures 2A to 2D are schematic diagrams illustrating various upper pressure blocks disposed on the workpieces to be bonded.

Domestic storage information (please record in order of storage institution, date, and number): None. International storage information (please record in order of storage country, institution, date, and number): None.

100: Process Equipment

110: Hot pressing equipment

120: Workpieces to be joined

122, 125: Items to be received

130: Lower block

140: Top Press

120A: Surface

125A: Surface to be joined

Claims (10)

A method for diffusion-joining workpieces includes: placing a workpiece to be joined in a hot pressing apparatus, wherein the workpiece to be joined comprises two objects to be joined stacked vertically; and performing a hot pressing operation on the workpiece to be joined, wherein the hot pressing operation includes: a first-stage hot pressing step, comprising placing a first pressing block on the workpiece to be joined, wherein the contact area between the first pressing block and one surface of the workpiece to be joined is a first area, wherein the first area is 20% to 100% of the area of one joining surface of the two objects to be joined; and A second-stage hot pressing step includes placing a second pressing block on the workpiece to be joined, wherein the contact area between the second pressing block and the surface of the workpiece to be joined is a second area, and based on the first area being 100%, the overlap area between the first area and the second area is 1% to 60%. The method for diffusion bonding of workpieces as described in claim 1, wherein the hot pressing operation further comprises: at least a third-stage hot pressing step, comprising placing a third pressing block on the workpiece to be bonded, wherein the contact area between the third pressing block and the surface of the workpiece to be bonded is a third area, and based on the first area being 100%, the overlap area between the first area and the third area is 1% to 60%. The method for diffusion bonding of workpieces as described in claim 1, wherein the first stage hot pressing step includes applying a first pressure, the second stage hot pressing step includes applying a second pressure, and the first pressure and the second pressure are the same or different. The method for diffusion bonding of workpieces as described in claim 2, wherein the first stage hot pressing step includes applying a first pressure, the second stage hot pressing step includes applying a second pressure, the at least one third stage hot pressing step includes applying a third pressure, and the first pressure, the second pressure, and the third pressure are the same or different. The method for diffusing and bonding workpieces as described in claim 1, wherein the second area is less than or equal to the first area. The method for diffusing and bonding workpieces as described in claim 2, wherein the third area is less than or equal to the first area. The method for diffusion bonding of workpieces as described in claim 1, wherein the hot pressing operation is performed at a temperature of 100°C to 1000°C. The method for diffusion bonding of workpieces as described in claim 1, wherein the first stage hot pressing step is performed for 1 minute to 8 hours, and the second stage hot pressing step is performed for 1 minute to 8 hours. The method for diffusion bonding of workpieces as described in claim 1, wherein the first pressure block and the second pressure block are discs, rings or polygons. The method for diffusion bonding of workpieces as described in claim 1, wherein the workpieces to be bonded are selected from a group consisting of ceramics, metals and composite materials.