Stress-free bonding of dissimilar materials

Stress-free bonding method between different materials

<p>10. . . HIP binding device</p><p>12. . . High pressure chamber</p><p>14. . . Insulator</p><p>16. . . level one</p><p>18. . . Second floor</p><p>20. . . Bonding layer</p><p>twenty two. . . Upper heating element</p><p>twenty four. . . Lower heating element</p><p>26. . . Fixture</p><p>28. . . Upper head assembly</p><p>30. . . Lower head assembly</p><p>32. . . Power guided feed slot</p><p>34. . . Thermocouple feed slot</p><p>36. . . aisle</p><p>37. . . Spring drive mechanism</p><p>38. . . spring</p><p>50. . . Pulse wave heating device</p><p>52. . . Pulse wave heating element</p><p>54. . . Hot slot</p><p>56. . . Pulse power</p><p>58. . . power cable</p>

Figure 1 shows the pressure-temperature critical line of the expansion of the base material and the bonding material in conjunction with the expansion of the polycrystalline drill;

Figure 2 shows a hot isostatic pressure (HIP) bonding device used in an embodiment of the present invention;

Figure 3 shows a pulse heating device used in another embodiment of the present invention;

Figure 4 is based on 380watts/cm ² The heat pulse effect generated by the current density, the temperature graph as a function of the thickness of the ZnSe substrate after a time of 30msec;

Figure 5 is a temperature graph with the pulse of Figure 4 applied for 270msec and then turned off, and after 30msec, the temperature is a function of the thickness of the ZnSe substrate (represents the temperature when the heat pulse is turned off);

Figure 6 shows that ZnSe () and chalcogenide glass () are maintained at the same physical size as the polycrystalline diamond layer in the pressure-temperature diagram.

The present invention relates to a method and device for combining two or more (including) materials with different thermal expansion coefficients to form a composite structure, and particularly relates to applying a large isostatic pressure in the actual combining process to generate a general Method and device for stress-free composition structure.

The forward-looking infrared (FLIR) system is well known, especially for military aircraft that need to fly at a low altitude and can find a destination at night to transport armor or ordnance. The current state of the art FLIR system requires two different infrared rays. The sensing system, which operates in turn in different states, one of which has a wide field of view, can develop a forward-looking infrared photo of the aircraft to provide pilot information (in navigation mode), this system is the so-called aviation FLIR; the other The FLIR system is installed on the aircraft to set the target mode. It has a narrow field of view and can provide zoom and telephoto functions, so that the target can be located. The FLIR system for setting the target can provide a high magnification image, so that the pilot can watch and find the target in time And assault and transport weapons.

Complex optical imaging systems on airplanes usually require some kind of sealing, especially when these components are exposed. When these optical imaging systems are installed on airplanes, especially high-performance airplanes, the smaller the size of the seal, the better to keep the air away. The impact of power on the aircraft is minimized. The package itself has some kind of infrared window, so that the internal optical imaging system can see the outside world. In order to increase the efficiency of the system, the larger the window, the better, so that the amount of light can be collected as much as possible.

The above-mentioned FLIR system and traditional infrared search and tracking (IRST) applications both use an infrared window to enable the internal optical imaging system to see the outside world. However, these infrared windows are often exposed to harsh environments, such as sand at about 470mph and 1.5 Mach's raindrops.

There is a method of manufacturing infrared windows, which uses a layer of bonding material to bond a standard ZnSe window substrate to a very wear-resistant polycrystalline diamond (PCD). The bonding material can be a soft organic polymer or a hard Chalcogenide glass, when the temperature rises (above 150°C) to solidify (polymerize or solidify) the bonding material, the difference in the thermal expansion coefficient between the diamond (bonding material) and the base material will cause the composition structure when it falls back to room temperature There are large stresses in the medium, and these stresses often exceed the damage limit of the diamond, the bonding material, or the substrate.

In order to solve the above problems, the present invention combines the diamond and the substrate with the same width and length under room temperature and pressure. Because the CTE of the substrate is greater than that of the diamond, the length and width of the substrate after heating will be greater than Diamond, however, if isostatic pressure is applied to the diamond and the substrate and the temperature is maintained, both will shrink. The volume elastic modulus of the material is defined as the ratio of the applied pressure to the volume reduction rate. Because the volume elastic modulus of the diamond is greater than the volume elastic modulus of the substrate, an isostatic pressure can be found to make the diamond and the substrate have the same again Of course, the length and width are different from the length and width under room temperature room pressure.

By repeating this method at each temperature, a critical line can be obtained on the pressure-temperature (P-T) diagram. When the bonding layer is solidified, if the pressure and temperature are maintained on this line, the diamond and the substrate will be roughly There will be no stress.

An important feature of the present invention is to use a large isostatic pressure to obtain a substantially stress-free composition structure (at a temperature lower than the freezing point of the bonding layer). The present invention discloses how to learn from known material parameters To determine the static pressure.

The above stress-free state can be achieved by a method used to combine two different materials to produce a substantially stress-free composition structure at a selectable reference temperature and reference isostatic pressure, including the following steps: (a) Preparation A first layer and a second layer; (b) determine the critical line of the first and second layers in a pressure-temperature diagram, wherein the position of the critical line is based on the reference temperature and reference isostatic pressure, and the first The volume elastic modulus of the material of the first and second layers is determined, and the critical line shows a complex number of temperature-pressure, which corresponds to the structure of the composition to be substantially stress-free; (c) controlling a temperature and isostatic during bonding Pressure so that the temperature and isostatic pressure represent a point on the critical line; (d) combine the first layer and the second layer under the temperature and isostatic pressure in step (c); (e) combine After completion, return to the reference temperature and the reference pressure along a path in the pressure-temperature diagram that avoids the stress of rupture in the structure of the composition.

The above stress-free state can also be achieved by a device used to combine two different materials to produce a uniformly stress-free composition structure at a selectable reference temperature and reference isostatic pressure, including: (a) for support A first-layer and a second-layer device; (b) A device used to determine the critical line of the first and second layers in a pressure-temperature diagram, wherein the position of the critical line is based on the reference temperature and reference It depends on the isostatic pressure and the elastic modulus of the material volume of the first and second layers, and the critical line shows a complex number of temperature-pressure, which corresponds to the structure of the composition substantially without stress; (c) during bonding A device for controlling a temperature and isostatic pressure so that the temperature and isostatic pressure represent a point on the critical line; (d) used to combine the first layer and the first layer under the temperature and isostatic pressure in step (c) The device of the second layer; (e) a device used to return to the reference temperature and reference pressure along a path in the pressure-temperature diagram that avoids the stress of cracking in the composition structure after the completion of the bonding .

The above stress-free state can also be achieved by a method used to combine two layers of different materials to produce a stress-free bond under ambient temperature and pressure, including the following steps: (a) Prepare a first layer and a second layer, the The thermal expansion coefficient and thickness of the first layer are smaller than the thermal expansion coefficient and thickness of the second layer, and the thermal conductivity of the first layer is greater than the thermal conductivity of the second layer; (b) preparing a bonding layer under the ambient pressure, the The thickness of the bonding layer is substantially smaller than the thickness of the first layer, and the softening temperature of the bonding layer is higher than the ambient temperature; (c) arranging the first and second layers so that the bonding layer is between the first and second layers (D) Make a thermal bath thermally contact one surface of the second layer, and the other surface of the second layer contact the bonding layer; (e) Make a pulse heat source thermally contact one surface of the first layer, The other side of the first layer is in contact with the bonding layer; (f) applying a pressure between the pulse heat source and the heat bath to compress the first and second layers so that the temperature reaches the softening or melting of the bonding layer The bonding layer will flow at temperature; and (g) applying a heat pulse at a predetermined current density and time to melt or soften the bonding layer, and make the interface temperature of the second layer higher than the melting or softening of the bonding layer Temperature, but will not heat the other parts of the second layer.

The above stress-free state can also be achieved by a device used to combine two layers of different materials to produce a stress-free bond under ambient temperature and pressure, including: a device for supporting the first, second and thin thermosetting bonding layers , The thermal expansion coefficient and thickness of the first layer are less than the thermal expansion coefficient and thickness of the second layer, and the thermal conductivity of the first layer is greater than the thermal conductivity of the second layer, and the softening temperature of the thermosetting bonding layer is higher than the ambient temperature; The bonding layer is placed between the first and second layers; a thermal groove is in thermal contact with one surface of the second layer, and the other surface of the second layer is in contact with the bonding layer; a pulsed heat source is in thermal contact with One side of the first layer and the other side of the first layer are in contact with the bonding layer; a force applying device applies a pressure between the pulse heat source and the heat bath to compress the first and second layers so that the temperature When reaching the softening or melting temperature of the bonding layer, the bonding layer will flow; wherein the pulsed heat source applies a heat pulse at a predetermined current density for a predetermined time to melt or soften the bonding layer and make the interface temperature of the second layer It is higher than the melting or softening temperature of the bonding layer, but does not heat the other parts of the second layer.

The above-mentioned stress-free state exists in a multi-layer structure in which two layers of different materials are bonded without stress under ambient temperature and pressure. This multi-layer structure includes: a first layer; a second layer, the thermal expansion coefficient of the second layer and The thickness is greater than the thermal expansion coefficient and thickness of the first layer, and the thermal conductivity of the second layer is less than the thermal conductivity of the first layer; a thin bonding layer, the softening temperature of the bonding layer is higher than the ambient temperature at ambient temperature ; Wherein the bonding layer is between the first layer and the second layer.

The above-mentioned stress-free state can be achieved by a method used to combine the three layers to generate a substantially stress-free state at a selectable reference temperature and reference isostatic pressure, including the following steps: (a) preparing a first layer, a second layer The second layer and the bonding layer; (b) Determine the critical line of the first layer and the second layer in a pressure-temperature diagram, wherein the position of the critical line is based on the reference temperature and reference isostatic pressure, and the first The volume elastic modulus and thermal expansion coefficient of the first and second layers are determined, and the critical line shows a complex array of temperature-pressure, which corresponds to the structure to be substantially stress-free; (c) select the bonding layer so that the The slope of the bonding layer on the critical line is smaller than the slopes of the first layer and the second layer; (d) combining the first layer and the second layer with the bonding layer; (e) adding the temperature of the three-layer structure to The bonding layer is above the softening temperature; (f) increase the pressure of the three-layer structure along a path near the critical line; (g) decrease the pressure and temperature of the three-layer structure along a path near the critical line until The pressure of the three-layer structure reaches the point corresponding to the softening temperature of the bonding layer; (h) A heat pulse is applied to the outer surface of the first layer and the bonding layer for a sufficient time and current density so that the temperature just exceeds the The softening temperature of the bonding layer while maintaining the pressure unchanged, so that when the three-layer structure returns to the reference temperature and reference isostatic pressure, the bonding layer hardens but is substantially stress-free; (i) along the critical line A path brings the pressure and temperature of the three-layer structure back to the reference temperature and reference isostatic pressure.

The aforementioned stress-free state can also be achieved by a device used to combine the three layers to generate a substantially stress-free state at a selectable reference temperature and reference isostatic pressure. This device includes; providing a first layer, a second layer, And bonding layer device; determine the critical line device of the first layer and the second layer in the pressure-temperature diagram, wherein the position of the critical line is based on the reference temperature and reference isostatic pressure, and the first and second layers The volumetric elastic modulus and thermal expansion coefficient of the two layers are determined, and the critical line shows a complex array of temperature-pressure, which corresponds to the device being substantially stress-free; the bonding layer is selected so that the bonding layer is on the critical line A device with a slope smaller than the slope of the first layer and the second layer; a device that combines the first layer and the second layer with the bonding layer; a device that increases the temperature of the three-layer structure above the softening temperature of the bonding layer; A device that increases the pressure of the three-layer structure along a path near the critical line; decreases the pressure and temperature of the three-layer structure along a path near the critical line until the pressure of the three-layer structure reaches the pressure corresponding to the combination A device at the point of the softening temperature of the layer; a heat pulse is applied to the outer surface of the first layer and the bonding layer at a sufficient time and current density so that the temperature just exceeds the softening temperature of the bonding layer while maintaining the pressure unchanged , When the three-layer structure returns to the reference temperature and reference isostatic pressure, the bonding layer is hardened but substantially stress-free device; along a path near the critical line, the pressure and temperature of the three-layer structure return The reference temperature and reference isostatic pressure device.

The aforementioned stress-free state can also be realized by a three-layer structure that is substantially stress-free at a selectable reference temperature and reference isostatic pressure. The three-layer structure includes: a first layer, a second layer, and a bonding layer ; Where the critical line of the first and second layers in a pressure-temperature diagram is determined; wherein the position of the critical line is based on the selectable reference temperature and reference isostatic pressure, and the first and second layers The volumetric elastic modulus and thermal expansion coefficient of the layer are determined; wherein the critical line shows a complex number of temperature-pressure, and the corresponding three-layer structure is substantially stress-free; wherein the slope of the bonding layer on the critical line is less than the first The slope of the first layer and the second layer; wherein the bonding layer combines the first layer and the second layer; wherein the temperature of the three-layer structure is increased above the softening temperature of the bonding layer; wherein the pressure of the three-layer structure is along the The pressure and temperature of the three-layer structure decrease along a path near the critical line of the first and second layers until the pressure of the three-layer structure reaches the softening corresponding to the bonding layer The point of temperature; where a heat pulse is applied to the outer surface of the first layer and the bonding layer for sufficient time and current density so that the temperature just exceeds the softening temperature of the bonding layer, while maintaining the pressure constant, so that the three When the layer structure returns to the reference temperature and reference isostatic pressure, the bonding layer hardens but is substantially stress-free; wherein the pressure and temperature of the three-layer structure return to the reference temperature and reference etc. along a path near the critical line Static pressure.

Schematic description

Figure 1 shows the pressure-temperature critical line of the expansion of the base material and the bonding material in conjunction with the expansion of the polycrystalline drill;

Figure 2 shows a hot isostatic pressure (HIP) bonding device used in an embodiment of the present invention;

Figure 3 shows a pulse heating device used in another embodiment of the present invention;

Figure 4 is based on 380watts/cm ² The heat pulse effect generated by the current density, the temperature graph as a function of the thickness of the ZnSe substrate after a time of 30msec;

Figure 5 is a temperature graph with the pulse of Figure 4 applied for 270msec and then turned off, and after 30msec, the temperature is a function of the thickness of the ZnSe substrate (represents the temperature when the heat pulse is turned off);

Figure 6 shows that ZnSe () and chalcogenide glass () are maintained at the same physical size as the polycrystalline diamond layer in the pressure-temperature diagram.

Symbol description of main components

10. . . HIP binding device

12. . . High pressure chamber

14. . . Insulator

16. . . level one

18. . . Second floor

20. . . Bonding layer

twenty two. . . Upper heating element

twenty four. . . Lower heating element

26. . . Fixture

28. . . Upper head assembly

30. . . Lower head assembly

32. . . Power guided feed slot

34. . . Thermocouple feed slot

36. . . aisle

37. . . Spring drive mechanism

38. . . spring

50. . . Pulse wave heating device

52. . . Pulse wave heating element

54. . . Hot slot

56. . . Pulse power

58. . . power cable

The preferred embodiments of the present invention are described with reference to the drawings.

Among the many methods of bonding materials and substrates, there are three methods that can ensure proper bonding. They are vacuum pressurization (VP), rapid pulse heating (RPH), and hot isostatic pressing (HIP). The invention uses hot isostatic pressing as one of the embodiments.

The present invention relates to chalcogenide glass, organic polymers, or other bonding materials that can be remelted and resolidified. The method and advantages are described below.

The present invention is a novel device and method that can reduce or eliminate residual stress when two or more different materials are thermally bonded. Although the present invention can be widely used in various combinations, the preferred embodiments below only describe optical combinations. (Including visible light and infrared light), it combines a thin layer of polycrystalline diamond (PCD) on a thick layer of zinc selenide (ZnSe) substrate, using elevated temperature and pressure to bond PCD and ZnSe together, When it cools and returns to atmospheric pressure, there is no stress when it solidifies.

The difference between the coefficient of thermal expansion (CTE) of PCD and ZnSe is a stress consideration. It is assumed that the bonding material is quite hard so that there is no sliding between the PCD and ZnSe contact surfaces during the cooling process. Arsenic sulfide glass conforms to this assumption, and its composition is approximately As ₂ S ₃ , And the softening temperature is about 200 °C, in As ₂ S ₃ Other chemical elements, such as germanium and/or selenium, can be added to produce entire families of similar materials.

In mathematical analysis, the Youngs modulus and CTE value of diamond and ZnSe are found using the engineering manual, which shows that the long bunches of PCD and ZnSe are in As ₂ S ₃ The solidification temperature (approximately 200°C) and atmospheric pressure combine to produce high stress when returning to room temperature.

If the thickness of the bonding material is neglected, when a 300μm thick PCD is combined with a half-inch thick ZnSe bundle, a compressive stress of 500MPa will be generated. The interface between ZnSe and PCD will have a tensile stress of about 48MPa, and there will be a compressive stress of about 25MPa on other surfaces. Stress, the engineering manual lists the damage stress of diamond as 700MPa and ZnSe as 50MPa. Therefore, it is very important to make these stress values tend to zero at (or close to) room temperature.

One of the characteristics of the present invention is the application of isostatic pressure during actual bonding (a stress-free structure is produced below the freezing point temperature of the bonding layer). The present invention determines the isostatic pressure value according to known material parameters to achieve a stress-free state.

In order to show the progress of the present invention, consider a PCD sheet and a ZnSe sheet that have been machined, which have the same width and length under room temperature and pressure (the thickness is not important), and the two sheets are heated above room temperature. Because the CTE of ZnSe is about 4 times that of PCD, the length and width of ZnSe are also larger than PCD after the temperature rises. However, if the two pieces are subjected to isostatic pressure and maintained at the same temperature, both of them will shrink. The ratio of pressure to volume reduction is called the bulk modulus of the material, because of the volume elasticity of PCD The modulus is more than 8 times that of ZnSe, so it is easy to recognize that PCD and ZnSe sheets have the same length and width under isostatic pressure. Of course, this length and width are different from those under room temperature and atmospheric pressure.

Repeat this method at each temperature, and then draw a critical line on the pressure-temperature (P-T) diagram. If the pressure and temperature remain on this line when the bonding layer is solidified, as long as one of them is on the critical line and the bonding layer When the induced stress is negligible, the two sheets will remain substantially stress-free. If the bonding layer is very thin, the stress in the PCD and ZnSe can be ignored. However, it will be discussed below that a thick bonding layer may also be stress-free.

Derive the mathematical equation of the critical line on the P-T diagram, starting from the change in length caused by temperature and pressure:

<maths><img file="TW513346B_D0001.tif" /></maths>

The subscripts d and s stand for diamond and substrate, respectively, t and p stand for temperature and pressure. CTE is represented by α and is a function of temperature and pressure. The volume modulus of elasticity is represented by β and is also a function of temperature and pressure. , Tr and Pr are the reference temperature and pressure, respectively, T and P are the temperature and pressure on the P-T diagram, the coefficient 3 in the equations (3) and (4) represents the volume change rate 3 times the length change rate, when <img file="TW513346B_D0002.tif" /> / <img file="TW513346B_D0003.tif" /> When &lt;&lt;1, this approximate estimate is very accurate.

Make the difference between (1) and (3) equal to the difference between (2) and (4), then the critical line can be obtained on the PT diagram. If the CTE and volume modulus of elasticity are regarded as constants, then a To simplify the example, in this example, the critical line becomes (P-P _r )(β _d -Β _s )=3β _d β _s (α _s -Α _d )(T-T _r ) (5) The relationship between volumetric modulus and Young's modulus is E=3β(1-2μ) (6) Where μ is Poisson's ratio, use the engineering manual to find out Young's modulus, Poisson's ratio, And the CTE of PCD can calculate the necessary value and draw the formula (5). In the first figure, the formula (5) of three pairs of different materials with Pr=1 and Tr=25°C is shown. PCD-ZnSe is represented by the symbol .

It is obvious from Figure 1 that at 200°C, it takes 26000 psi to bring the PCD and ZnSe chips back to the same size, and this pressure and temperature can be achieved by commercial HIP equipment. Therefore, the present invention relates to a device and method. , It determines the appropriate pressure and temperature in the HIP environment to thermosolidify the different materials together, and can avoid the stress problem (if the proper pressure is not applied, stress will be generated after cooling).

As mentioned above, if the bonding layer is not very thin, stress will be generated in the bonding material. In many instances, the bonding layer cannot be very thin. Therefore, it is necessary to find a suitable bonding material. Even if the bonding layer is quite thick, it will not Generate stress.

Regarding the above-mentioned PCD and ZnSe, formula (5) can be applied to bonding materials and substrates. If the CTE, Young's modulus, and Poisson ratio of the bonding material make the critical line of the PCD bonding material on the PT chart and the PCD If the critical line of the substrate is consistent, the three-layer structure at any point on the line will be substantially stress-free. Similarly, the stress of the material close to the critical line on the P-T diagram will be less than the stress of the material far away from the critical line. In this example, the bonding material is selected so that the critical line is consistent with the critical line of the future substrate.

In the first figure, there are also two sets of other critical lines. The upper line is PCD and the composition is As ₃₂ S ₄₈ Se ₂₀ (Composition K) glass, the line below is PCD and the composition is As ₄₀ S ₅₀ Se ₁₀ (Composition I) glass, the measured CTE of these two compositions is 41.6 and 29.6 (in 10 ^-6 ℃ ^-1 Unit below), the critical line of the intermediate material is very likely to be very close to the critical line of ZnSe.

By designing the glass, the desired critical line can be obtained, thereby generating a composition window structure that is stress-free at the selected temperature. Diamond, glass, and ZnSe are stress-free and can be combined under thermal equilibrium without the use of complex pulse waves. heating.

However, if the critical line of the bonding material in the design is not consistent with the critical line of ZnSe in the first figure, as long as the HIP bonding method is pulsed heating, the desired result can still be obtained (that is, at the reference temperature Completely stress-free).

Now consider the glass component I. Figure 1 shows that the pressure during solidification (about 200°C) is approximately 21000 psi. Figure 1 also shows that the size of ZnSe is too large at this time (because 26000 psi is the critical pressure of ZnSe at this temperature). However, if the temperature drop of the HIP is low enough and the pressure is kept at 21000psi, you can find a point that makes the ZnSe exactly match the size of the diamond and glass component I, and then heat the diamond, chalcogenide, and ZnSe surfaces with pulse waves Returning to about 200°C to form a stress-free bond, the size of ZnSe is only slightly increased. In fact, by starting heating at a temperature lower than the correct size, the thermal expansion of ZnSe caused by pulse heating can be offset.

FIG. 2 shows an embodiment of the HIP bonding device 10 of the present invention, which includes a high-pressure chamber 12 formed by a 3 1/2-inch thick wall, which is insulated by an insulator 14. The first layer 16, the second layer 18, and the optional bonding layer 20 are placed between the upper and lower heating elements (with thermocouples) 22 and 24 in the high-pressure chamber 12. The bonding layer 20 can be selected because the first layer 16 and the second layer 18 can be combined by the HIP bonding device 10 under the above-mentioned temperature, pressure and force. The bonding layer 20 uses thermal diffusion to bond the first layer 16 and the second layer 18, and the first layer 16 and the second layer 18 are combined in the high-pressure chamber 12 with a clamp 26. The first layer 16, the second layer 18, and the bonding layer 20 are clamped, and the high-pressure chamber 12 also serves as a vacuum chamber. The HIP coupling device 10 includes an upper head assembly 28 and a lower head assembly 30, both of which are eight inches thick. The lower head assembly 30 includes a power guide feed slot 32, a thermocouple feed slot 34, and an argon channel 36. The upper head assembly 28 includes a tube of a vacuum feed slot and a spring drive mechanism 37. The spring drive mechanism 37 transmits force to the spring 38 so that the first and second layers 16, 18 are together in the high pressure chamber 12.

The computer will draw the critical line according to formulas (1)-(6), calculate the temperature and pressure, and then input it to the HIP coupling device 10.

In summary, the present invention provides a method to solve the different heat shrinkage in the multi-layer structure. It should be noted that the calculation in Figure 1 is based on the critical line at room temperature and atmospheric pressure at the same time, but room temperature may not be used. Other temperatures below the freezing point of the bonding layer can be used. Generally speaking, the midpoint of the actual application temperature range will be used. In this way, the stress state of the structure can fully conform to the actual application. In this way, the applicable temperature range will be doubled (because the stress-free state can be reached above and below the temperature, and the bonding layer does not need to be remelted). If there is no help of pressure, even the bonding temperature will be reached. Cannot create a stress-free state.

In this embodiment, polycrystalline diamonds are used, but this layer can also be made of sapphire or other materials suitable for infrared windows. It has sufficient optical properties and good mechanical protection, and can resist environmental damage, such as rain, gruel, sand, And insects, which often act on car windows. In this embodiment, a ZnSe substrate is also used, but other materials, such as zinc sulfide, silicon, or germanium, can also be used, which have the optical characteristics required for the infrared window as part of the FLIR or IRST system. In this embodiment, a combination material of glass components is used. The glass may include any mixture of arsenic and sulfur, or further include selenium and/or germanium and/or tellurium, so as to achieve the desired optical properties and softening temperature at the same time.

As described above, three methods can be used including vacuum press (VP), rapid pulse heating (RPH), and hot isostatic pressing (HIP). The first embodiment of the present invention relates to the HIP method, and the second embodiment below relates to the RPH method.

The traditional VP method used to combine PCD and ZnSe is carried out under a high vacuum to prevent bubbles from forming in the chalcogenide layer and at the interface with PCD and ZnSe. The temperature of each component is raised to melt sulfur. When the viscosity of the chemical compound reaches a sufficiently low level (240°C for most chalcogenide glasses), it is pressed together, and then (the temperature remains unchanged) nitrogen is injected to raise the vacuum system to atmospheric pressure. Then lower to room temperature. In some cases, keeping the composition structure at an intermediate temperature for a period of time and annealing can eliminate residual stress.

As mentioned above, the residual stress in different materials is a big problem, and this stress is derived from the different coefficients of thermal expansion between the materials. If 10 ^-6 ℃ ^-1 As the unit, the temperature dependence coefficient of diamond is 1.13+0.0065×T, ZnSe is 7.1+0.0060×T, and the general chalcogenide is about 25. At 100°C, the CTE of ZnSe is more than 4 times that of PCD. In order to explain the stress induced by these values of CTE, the equation of the thermal bonding between the Young's modulus of the three materials and the thermal bonding of the two metal bars can be used. This method shows one A 300μm diamond layer, a 50μm chalcogenide, and half an inch of ZnSe at room temperature will produce (if the chalcogenide solidifies at 200°C) a compressive stress of about 500MPa in the diamond, and 36MPa in the chalcogenide The tensile stress and the tensile stress at the interface between the chalcogenide and ZnSe are 48MPa, while the other surface of ZnSe is about 25MPa compressive stress.

These stress values are too high for actual manufacturing. It is known that the failure stress of diamond is 700 MPa, chalcogenide is 18 MPa, and ZnSe is 50 MPa. When the existing cracks start to grow, or the flaws in the stressed material produce new cracks, Damage occurs, so that the known value can only be used as a reference. When the flat composition specimen is cooled to room temperature, the chalcogenide layer will often break, and ZnSe will produce a network near the interface with the chalcogenide. crack.

The specimen will not delaminate before reaching room temperature. The direct evidence can be obtained by measuring the curvature of the back side of ZnSe to know that it is in a high pressure state. The two-metal beam equation predicts (as discussed in the previous paragraph) that the radius of curvature is about 12m, and the magnitude of the curvature It can be seen from the experiment.

One of the ways to solve the stress problem is to choose a material with a compatible thermal coefficient. Unfortunately, it is difficult to choose such a material (the thermal coefficient can be matched, and it also meets the optical characteristics of the infrared window in the FLIR system). The second embodiment of the present invention greatly reduces the stress problem by generating a dynamic and unbalanced thermal state in the composition structure, so that the diamond and chalcogenide layers are above the chalcogenide softening temperature at the same time, but only ZnSe The interface reaches this temperature, and the other parts are at its initial (cooling) temperature.

The thermal energy of the hot part of the composition will diffuse to the cold part of ZnSe at the beginning. When the softening temperature is reached, the chalcogenide will solidify. However, the ZnSe is still cold at this time, so the heat has hardly diffused evenly, resulting in solidification. The diamond is hot and thermally expands when it occurs. However, although the ZnSe interface is hot, it does not expand thermally (because it is integrated with the cold ZnSe substrate and is limited). The structure of the composition obtained by this method is either diamond or ZnSe cannot detect stress at room temperature.

FIG. 3 shows an embodiment of the present invention using a pulse wave heating device 50. The pulse wave heating device 50 includes a pulse wave heating element 52 and a heat bath 54. The pulse wave heating element 52 is connected to a pulse wave power source 56 by a power cord 58. The first layer 16, the second layer 18, and the selective bonding layer 20 are placed between the pulse wave heating element 52 and the heat bath 54, except for the heat pulse In addition, force is applied to the pulse heating element 52 and the heat bath 54, whether with or without the bonding material 20, to bond the first layer 16 to the second layer 18. The bonding layer is selective because the first layer 16 and The second layer 18 can be joined together by heating and pressing. If the bonding layer 20 is used, the bonding layer 20 and the first and second layers 16, 18 are combined by thermal diffusion. In a preferred embodiment, use a computer to draw the 4th and 5th diagrams and tell the pulse heating device 50 required potential.

This pulse heating concept has been used in one-inch diameter flat specimens, a commercial flat heater (which deposits a thin pyrolytic carbon heating element on a six-inch thick boron nitride substrate) Used to provide heat pulse, this heater uses 125watts/cm ² The current density and the pulse time slightly smaller than 1 minimize the stress. The initial temperature of the test piece, the heater close to room temperature, and the structure of the composition that are in thermal contact with the pyrolytic carbon surface of the heater should be used during use. Drill face.

An enlarged pulse heating device can accommodate flat specimens with a diameter of 6 inches and 380 watts/cm ² For the input current density, the specific heat, thermal conductivity, and component density of the composition structure should be used in the analysis. Figure 4 shows the results of ZnSe temperature (as a function of substrate thickness) and time. The heat pulse lasts for 270msec in the 30msec time interval. The nine curves in Figure 4 correspond to the temperature in each interval.

The substrate in Figure 4 is so thick that the heat pulse cannot reach the other side. The right side of the curve in Figure 4 corresponds to a thickness of 3/8 inch. The surface temperature is about 270°C at 270msec, but it is one side below the surface. The temperature is less than 60°C, which shows that the surface of ZnSe is hot, but not thermally expanded much.

To achieve substantially no stress, the current density and heat pulse time can be determined by experience or standard mathematical analysis of transient heat flow, which is a conventional technique.

Figure 5 shows the calculated ZnSe surface cooling. The line that intersects the ordinate at 270°C is the 270msec line in Figure 4, which corresponds to the temperature during the heat pulse. The other three lines in Figure 5 are displayed at 30, In the case of heat after 50 and 90msec, 360msec after the first heat pulse, the ZnSe interface temperature almost drops to 180°C. Therefore, in practice, pulse heating is used to make the expansion of diamond and ZnSe equal, and the stored energy can be 3/ The 8-inch thick substrate has an average increase of 40°C compared to the surroundings. This average temperature value can be used to estimate the expansion of ZnSe when the chalcogenide softens. Using the known thermal expansion coefficient, it can be known that the ZnSe expansion is insufficient in this case and needs to be more Low current density and longer pulses will work.

If the diamond and ZnSe meet the requirements in this way, the chalcogenide will be subjected to high pressure. For the PCD/chalcogenide/ZnSe composition structure, even if the best pulse heating combination is used, the chalcogenide will be subjected to high pressure. High stress (because the equilibrium temperature of the PCD/chalcogenide/PCD composition is combined), the stress in the chalcogenide can be reduced by reducing its CTE. If there is no stress, the CTE and PCD must be the same. This problem can be mixed The fine diamond powder and chalcogenide are greatly improved. However, it should be noted that if the CTE of PCD and chalcogenide is not matched and stress occurs in ZnSe and PCD, the stress can still be changed by reducing the thickness of chalcogenide. Is very small.

If a very thin chalcogenide layer can be used for bonding, pulse heating technology can be used to produce a composition in which both PCD and ZnSe are substantially stress-free. But if the bonding layer cannot be very thin (for some reasons in fact), this pulse heating method must be used in combination with the first embodiment of the present invention to produce a completely stress-free composition. As described in the first embodiment, there is a line in the pressure-temperature diagram, and its PCD is the same size as ZnSe. The two lines are shown in Figure 6. The upper line represents ZnSe. Determine the method of these two lines. It is described in the first embodiment. The chalcogenide in Figure 6 softens at about 200°C. Therefore, if this combination method is used, the chalcogenide will solidify at a pressure of approximately 21,000 psi. Figure 6 shows that the PCD and chalcogenide will have the same size at this time. However, the size of ZnSe should be consistent only at this temperature. Figure 6 shows that ZnSe expands too much at 21000psi and 200°C, but the size will be correct at 21000psi and about 175°C.

Therefore, the use of pulse heating combined with the HIP method (starting from an equilibrium state of 21000 psi and about 175°C) will obtain a three-layer composition structure that is stress-free at room temperature and pressure. The HIP method can make PCD and sulfur at the moment of combination. The size of the attribute is the same, and the pulse heating method can adjust the size of ZnSe at this moment.

Obviously, the pulse heating assisted combination method can be applied to other materials besides PCD/chalcogenide/ZnSe. The condition is to generate a suitable thermal gradient according to the thickness of the composition structure to compensate for the difference in CTE, and the smaller CTE The temperature of the material is relatively high under this gradient. This method can be used only when the temperature of the thinner layer with high thermal conductivity (such as PCD) is about the same, and the other layers are only hot near one side (such as ZnSe). The pulse heating device 50 of Fig. 3 can also be used in combination with the HIP bonding device of Fig. 2 to produce a substantially stress-free multilayer structure.

Although the present invention has been disclosed in preferred embodiments as above, it is not intended to limit the present invention. Anyone familiar with the art can make changes and modifications without departing from the spirit and scope of the present invention. Therefore, the present invention The scope of protection shall be subject to the scope of the attached patent application.