Method for bonding at least one hard object to a film

Abstract

A method for bonding at least one hard object to a film is provided, comprising the following steps: S1: at a predefined stacking temperature and a predefined stacking pressure: providing a stack of at least two layers, one of which is made of a hard object and the other of which is a film layer, wherein a liquid substance is arranged between the layers, wherein the film layer a is designed to cure at a predefined temperature higher than the stacking temperature and a predefined pressure higher than the stacking pressure, so that it bonds to the hard object;S2: Placing the at least one stack in an autoclave chamber and applying an autoclave process to the at least one stack by S21: increasing the temperature and pressure so that the liquid substance is substantially forced out of gaps between the layers, and the film layer hardens and is thus bonded to the hard object; then S23: lowering the temperature and pressure until the autoclave chamber can be opened.

Description

[0001] The present invention relates to a manufacturing process that simplifies an autoclave process, wherein the autoclave process is preferably used to bond at least one hard object to each side of a film.

[0002] An autoclave is a promising alternative method for bonding a hard object to a flexible film originally designed for bonding using a mechanical press at a specific pressure and temperature. While the film is modified from the one originally designed for use in a mechanical press, it is fundamentally manufactured to cure at pressures higher than atmospheric pressure and temperatures higher than room temperature. High-pressure air as the pressing medium allows any external shape of the hard object to be the pressable surface, whereas a press, in principle, only permits a flat external surface. An autoclave ensures consistent pressure across the entire pressing area, whereas mechanical pressing requires frequent adjustments across the entire pressing plate to maintain uniformity.

[0003] KR 10 2024 0 158 276 A discloses a method for manufacturing a composite consisting of an electronic component, a circuit and an electrically insulating layer.

[0004] US patent 2003 / 0071348A1 discloses a semiconductor module with multiple semiconductor chips and a corresponding manufacturing process.

[0005] In the autoclave process, it is crucial to avoid creating voids or air bubbles at the contact interface between the hard object and the film. In the prior art, the air at the contact interface is evacuated before and during the autoclave process using a vacuum pump to expel any remaining air. Therefore, a so-called vacuum bag method is employed, in which the stack of hard object and film, placed on a rack plate, is wrapped with a vacuum bag film, and the area enclosed by the film is evacuated by a vacuum pump. In this way, the interface between the hard object and the film is securely contacted, and they are bonded together without voids across the entire contact interface.

[0006] Although the vacuum bagging process is crucial for the autoclave process, it is laborious and expensive. Skipping the vacuum bagging step would significantly reduce process costs, but it is difficult to avoid creating gaps at the contacting interface, for example, by simply using clamps to grip the stack and placing the gripped stack into the autoclave chamber.

[0007] The purpose of this invention is to eliminate the presence of air at the contacting interface between the hard object and the film before and during the autoclave process and to ensure the connection across the entire interface even without the use of a vacuum pump.

[0008] A method for bonding at least one hard object to a film is provided, comprising the following steps: S1: at a predefined stacking temperature and a predefined stacking pressure: providing a stack of at least two layers, one of which is made from a hard object and the other layer is a film layer, wherein a liquid substance is arranged between the layers, wherein the film layer a is designed to cure at a predefined temperature higher than the stacking temperature and a predefined pressure higher than the stacking pressure, so that it is bonded to the hard object;S2: Placing the at least one stack in an autoclave chamber and applying an autoclave process to the at least one stack by S21: increasing the temperature and pressure so that the liquid substance is substantially forced out of gaps between the layers, and the film layer hardens and is thus bonded to the hard object; thereafter S23: lowering the temperature and pressure until the autoclave chamber can be opened.

[0009] In one embodiment, step S1 provides a stack of at least three layers, wherein an upper layer is made of a hard object, a middle layer is formed of a film, and a lower layer is formed of a hard object, wherein a liquid substance is arranged in gaps between the upper layer and the film layer and between the film layer and the lower layer.

[0010] According to the invention, in a step S22, which is carried out between step S21 and step S23, the temperature is maintained and the pressure is reduced to the predetermined stacking pressure, so that the remaining liquid substance is evaporated.

[0011] In one embodiment, the stacking is carried out by stacking the top layer, the foil layer, and the bottom layer such that a gap remains between the layers, and then filling the gaps with the liquid substance. In an alternative embodiment, the stacking is carried out by providing a liquid substance on the bottom layer, stacking the foil layer on top of the liquid substance, and, if there are more than two layers, providing a further liquid substance on the foil layer and stacking the top layer on top of this further liquid substance.

[0012] In one embodiment, the main part of the film layer is made of resin and / or the film layer is elastic at the predefined stacking temperature and predefined stacking pressure, which include room temperature and atmospheric pressure.

[0013] In one embodiment, the liquid substance is a substance whose unit volume contains molecules that are at least two orders of magnitude larger than air, and / or wherein the liquid substance is a liquid substance or a colloid with a liquid substance as a dispersion medium, a liquid substance comprising water or an aqueous solution or an alcohol, or an alcoholic solution, or an organic solvent, or an organic solution or a surfactant, or a mixture of any of the aforementioned substances or water.

[0014] In one embodiment, in a step S12, which is carried out after step S1 and before step S2, clamping means are applied to the stack so that the position of the layers is pre-fixed.

[0015] In one embodiment, the clamping pressure is such that at least part of the liquid substance is forced out of the gaps.

[0016] In one embodiment, the upper layer is divided into several parts, each of which is an encapsulated power semiconductor device, wherein the foil layer is electrically non-conductive, and wherein the part of the lower layer that is connected to the foil layer is a top surface of a heat sink.

[0017] In one embodiment, several stacks are lined up inside the autoclave chamber, or several stacks are placed in a transport device and inserted into the autoclave chamber, or the stack is assembled in step S1 in a transport device which is inserted into the autoclave chamber in step S2.

[0018] For a better understanding of the invention, it is explained in more detail below with reference to the accompanying drawings. The detailed description will illustrate and describe what are considered preferred embodiments of the invention. It is understood that various modifications and changes in form or detail are readily feasible without departing from the inventive concept. It is therefore intended that the invention cannot be limited to the exact form and detail shown and described here, nor to anything less than the entire invention disclosed herein, as claimed below. Furthermore, the features described in the description, the figures, and the claims disclosing the invention may be essential to the invention, whether considered alone or in combination. In particular, any reference numerals in the claims are not to be interpreted as limiting the scope of the invention.

[0019] In the enclosed figures: shows Fig. 1A a three-layer stack prepared for a state-of-the-art autoclave process; shows Fig. Figure 1B shows a three-layer stack that is fixed by clamping means in accordance with the prior art; show Fig. 2 and Fig. 4 each a three-layer stack to be processed according to an embodiment of the invention. show Fig. 3 and Fig. 5 each the three-layer stack of the Fig. 2 or 4 shortly before an autoclave process. shows Fig. 6 a three-layer stack which is fixed by clamping means according to an embodiment of the invention. shows Fig. 7 a flowchart according to an embodiment of the invention. shows Fig. 8 a sequence according to the method of an embodiment of the invention in a three-phase point diagram.

[0020] While the present disclosure is subject to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the figures and are described here in detail. The invention is to be understood as not being limited to the individual disclosed forms, but on the contrary, is intended to cover all modifications, equivalents, and alternatives that fall within the spirit and scope of the present disclosure.

[0021] Fig. Figure 1A shows a three-layer stack 100 prepared for processing by an autoclave according to the prior art. During the autoclave process, it is important to avoid creating any voids or air bubbles at the contacting interface between the hard object, i.e., layers 1 and 3, and the film layer 2. According to the prior art, the air at the contacting interface is evacuated before and during the autoclave process using a vacuum pump to expel any remaining air at the contacting interface, as already mentioned in the introduction. The three-layer stack 100, placed on a rack plate 4, is wrapped by a vacuum bag film 5 with a venting fabric 50 beneath the film 5. The edge of the film 5 and the rack plate 4 are sealed by a vacuum sealing material 6, which is also encased by the vacuum bag film 5.An evacuation tube 51 pierces the vacuum bag film 5, which is sealed with vacuum sealing material 6, and the area surrounded by the vacuum bag film 5, the vacuum sealing material 6, and the rack plate 4 is evacuated by the vacuum pump through the evacuation tube 51 even during the autoclave process. In this way, the interface between the hard object and the film is securely contacted, and they are joined at the entire contacting interface without any gaps.

[0022] Although the vacuum bag procedure is crucial for the autoclave process, it is laborious and expensive. Skipping the vacuum bag step would significantly reduce process costs, but it is difficult to avoid the creation of voids at the contacting interface, for example, as in Fig. 1B shown by having only clamping means 8 grip the stack 100 and placing the gripped stack 100 into the autoclave chamber.

[0023] The purpose of this invention is therefore to eliminate the presence of air at the contacting interface between the hard object and the film before and during the autoclave process and to ensure the connection across the entire interface even without the use of a vacuum pump.

[0024] In the Fig. 2 and Fig. Figure 4 shows a preferred embodiment of a three-layer stack 100 to be processed. Fig. 3 and Fig. 5 is the three-layer stack 100 of the Fig. 2 or 4 are shown shortly before processing by an autoclave process. In Fig. 2 and Fig. Figure 4 shows an upper layer 1 and a lower layer 3 with a foil layer 2 between the upper layer 1 and the lower layer 3. A gap 9 is shown between layers 1 and 2 and between layers 2 and 3. As shown in... Fig. 3 and Fig. 5 shows a liquid substance being poured in before the three-layer stack100 is subjected to an autoclave process. Fig. 3 and Fig. A liquid substance 7 is introduced into the gap 9 between the upper layer 1 and the foil layer 2, and between the lower layer 3 and the foil layer 2, with the foil layer 2 being the middle layer that connects layers 1 and 3. The surface of the foil layer 2 is therefore designed such that it bonds to the contacting object (layers 1 and 3) through the curing process.

[0025] It is important that the liquid substance 7 is introduced into the gap 9 in such a way that no air bubbles or voids remain in the gap 9 or within the liquid substance 7. Therefore, the liquid substance 7 must be denser than air, preferably two or more orders of magnitude denser. This means that it contains at least two orders of magnitude more molecules than air. However, it still requires sufficient fluidity so that it can be completely or substantially forced out of the gap 9 during the autoclave process. Examples of liquid substances 7 that can be used for the process according to the invention are, for example, a liquid substance containing water, or an aqueous solution, or an alcohol, or an alcoholic solution, or an organic solvent, or an organic solution, or a surfactant, or a mixture of any of the aforementioned substances, or water; or a colloid with such a liquid substance as a dispersion medium.

[0026] The material of film layer 2 is selected such that it is elastic at a predefined temperature and pressure, preferably room temperature and atmospheric pressure, and cures (hardens) at another predefined temperature and pressure, which depends on the film material. The main part of film layer 2 is preferably made of resin. In most cases, a higher temperature and pressure are required to cure the material of film layer 2. Furthermore, the surface of the film is designed so that it is firmly bonded to the contacting object, i.e., layers 1 and 3, through the curing process (also called the hardening process).Additionally, particularly in an embodiment in which encapsulated power semiconductor components are used as the upper layer 1, the material of the foil layer 2 should be electrically insulated and preferably have a high thermal conductivity, so that the heat generated at the power semiconductors can be effectively dissipated through the foil layer 2 to the heat-emitting fin structure 30.

[0027] In one embodiment, no fixing means need to be provided to fix the layers 1-3, since the layers 1-3 are held in position due to the surface tension between the surfaces of the layers 1-3 and the liquid substance 7.

[0028] In another embodiment, if strict positioning of layers 1-3 is required, clamping means 8 are used as pre-fixing means before the stack 100 is placed in the autoclave chamber. Such strict positioning at a specific position may be necessary if the upper layer 1 consists of encapsulated power semiconductor devices, since these usually need to be arranged at a specific position relative to each other, for example, to be connected to the terminals of a control board whose spatial arrangement is already defined elsewhere. The clamping means 8 can be positioned so that most of the liquid substance 7 is already squeezed out of the gaps 9. Alternatively, the clamping means 8 can be positioned so that only the position of layer 1 is correctly fixed.Since the pressure exerted on the stack 100 is not very strong, there is no significant loss of dimensional freedom in the shape of the metal plate on the other side of the contacting interface; that is, a rib structure 30 can still be provided without being damaged by the clamping pressure. The clamping means 8 can also serve as a transport device for moving the stack 100 into the autoclave chamber.

[0029] The liquid substance between layers 1-3 can be provided in different ways. One possibility is to provide the bottom layer 3, provide the liquid substance 7 on the bottom layer 3, and then place the foil layer 2 on the liquid substance 7. Then, another liquid substance 7 is placed on the foil layer 2. The top layer 1 is then placed on top of this liquid substance 7. Another way to provide the liquid substance 7 in the spaces 9 is to stack all three layers 1-3 so that spaces 9 remain between them, and then fill the spaces 9 with the liquid substance 7, for example, by pressing it into the spaces 9.

[0030] As can be seen, layers 1-3 are preferably essentially flat on the side where they are bonded to another layer 1-3. Therefore, in the autoclave process, it is possible that the facing surfaces of layers 1 and 2, or 2 and 3, are not flat, but these surfaces are at least substantially parallel to each other. On the side where they are not bonded to another layer 1-3, they may have a structure as shown in Fig. Figure 4 shows an example of a rib structure 30 on the underside of the lower layer 3.

[0031] In all embodiments, the stack of 100 must be transported into the autoclave chamber, as stacking takes place outside the chamber. Several options exist for getting the stack of 100 into the autoclave chamber. One possibility is to place each stack of 100 into the autoclave chamber separately. Another possibility is to provide transport means, such as the clamping means 8 or a tray, onto which one or more stacks of 100 are placed and then transported into the autoclave chamber. Preferably, all or some of the stacks of 100 to be placed into an autoclave chamber for processing in the same process are placed on a transport means, such as a rack tray 4, before stacking; that is, the stacking takes place directly on the transport means. This facilitates the transport of the stacks of 100 into the autoclave chamber.

[0032] As is easy to understand, the described procedure is not limited to processing three layers 1-3. More or even just two layers can be joined using the described procedure, i.e., by filling a liquid substance 7 into the gaps 9 between the layers to be joined and subsequently applying an autoclave process to complete the joining.

[0033] In Fig. A flowchart of the described process is shown. In a first step S1, the stack 100 is produced, i.e., layers 1-3 are stacked and the liquid substance 7 is introduced into the spaces 9 between layers 1-3. In step S2, one or more of the stacks 100 are placed in an autoclave chamber and an autoclave process is applied to the stacks 100, as described below with reference to Fig. 8 described.

[0034] In Fig. Figure 8 illustrates the process carried out in the autoclave chamber using water as an example of a liquid substance. Figure 7. Fig. Figure 8 shows a three-phase point diagram in which the three states (phases) of a material are indicated, namely solid phase, gaseous phase and liquid phase.

[0035] The point where the graphs meet is called the three-phase point. This point, also known as the triple point, is the temperature and pressure at which the three phases of this substance coexist in thermodynamic equilibrium.

[0036] As mentioned previously, in step S2 one or more of the stacks of 100 are placed in an autoclave chamber. This is done under a predefined stack temperature and a predefined stack pressure, which in this example are room temperature and atmospheric pressure. As from Fig. As can be seen in 8 (example water), water (the liquid substance 7) is in a liquid state at room temperature and atmospheric pressure (number “1” in Fig. 8).

[0037] In a first step S21, the curing process of the film layer 2, the temperature and pressure are increased to a predetermined temperature and pressure until the film is sufficiently hardened, i.e., cured. In the case of water as the liquid substance 7, a temperature of 150°C and a pressure of 1 MPa are the required temperature and pressure to cure the film. In this step, the liquid substance 7 remaining in the gap 9 is preferably completely forced out of the gap 9 without leaving air bubbles or cavities, while the expelled liquid substance 7 remains in the vicinity of each hard object 1 and the film layer 2.

[0038] However, if substance 7 is not vaporized, it can only be essentially forced out of the gap 9, i.e., residues of substance 7 remain in the gap 9.

[0039] The hardening process can be controlled by maintaining the temperature and increasing the pressure up to a predefined limit (number "2" in Fig. 8) and subsequently maintaining high pressure and raising the temperature (number “3” in Fig. 8) take place. Alternatively, the temperature and pressure increase can occur simultaneously, as long as the liquid substance 7 remains liquid.

[0040] In the next step S22 (after the film has cured), the temperature is maintained and the pressure is increased to the specified stack pressure, i.e., atmospheric pressure (number "4" in Fig. 8) lowered. As from Fig. As can be seen in Figure 8 (example: water), in this sub-step S22, the water (as a liquid substance 7) transitions into a gaseous phase state by lowering the pressure and maintaining the temperature. It is important that the evaporation step is long enough so that the expelled, evaporated liquid substance 7 can completely evaporate and be removed from the vicinity of any hard object 1 and the foil layer 2.

[0041] If the squeezed-out residue of the liquid substance 7, which remains in the vicinity of the hard object 1 and the layer of foil 2, does not evaporate due to material properties or intrinsic factors, the residue is removed by other means after the stack 100 has been removed from the autoclave chamber, or it is left as is if the residue is not detrimental to the final product. The specific removal method depends on the material of the liquid substance 7 and is outside the scope of this invention.

[0042] In a final step, S23, the temperature is lowered again to a temperature at which the autoclave chamber can be safely opened. If the evaporation of the liquid substance 7 does not occur, S22 can be skipped and the temperature can be lowered before the pressure reduction, or both can even be lowered simultaneously. Preferably, the temperature is lowered until room temperature is reached (number "5" in Fig. 8) However, once the temperature is low enough to safely open the autoclave chamber, this can be done. At this point, the liquid substance 7 remaining in the vicinity of the hard object 1 and the layer of foil 2 may be left as a residue, depending on the material of the liquid substance 7.

[0043] In one embodiment, step S12 is performed after step S1 and before step S2. In this step S12, as already described, clamping means 8 are applied to the stack 100 for pre-fixation.

[0044] In general, the described method can be applied to any upper layer 1 and any lower layer 3 made of hard objects, between which a middle layer of foil (foil layer 2) 2 is placed to join the layers 1 and 3.

[0045] In a preferred embodiment, the lower layer 3 is a heat sink, as shown in the Fig. 4 and Fig. Figure 5 shows that the upper layer 1 consists of several separately encapsulated power semiconductor devices. The heat sink can be equipped with a fin structure 30 (pins or another structure that aids heat dissipation can also be used). In this embodiment, the material of the part of the upper layer 1 that is in contact with the foil layer 2 can be a metal, and the other side of the metal is electrically connected to the back of a semiconductor chip within the potting compound. The entire lower layer 3 can also be made of metal. Since semiconductor devices must be positioned quite precisely, it is advantageous to use clamping means 8, as shown in Figure 5. Fig. 6 described, to be used to strictly pre-fix the semiconductor devices before applying the autoclave process.

[0046] A major advantage of the proposed method is that a large number of stacks (100) can be processed in a single batch simply by lining them up within the autoclave chamber. This results in a significant reduction in process costs compared to using an autoclave process with vacuum bagging or mechanical pressing. Unlike mechanical pressing, the shape on the other side of the contacting interface between the upper and lower metal plates can be freely designed, for example, as a cooling fin structure (30) for power electronics circuits mounted on the upper metal plate (top layer 1).

[0047] Encapsulated power semiconductors typically have contact pins on their surface. In autoclave processes requiring vacuum bagging, these pins tend to puncture the vacuum bag film. The proposed method eliminates this conflict between the contact pins and the vacuum bag film.

[0048] Another advantage is that the vacuum pump can be eliminated from the autoclave system due to the absence of a vacuum bag procedure. Reference numbers 100 three-layer stacks 1 upper layer (hard object) 2 layers of foil 3 bottom layer (hard object) 30 rib structure 4 frame plate 5 vacuum bag film 50 ventilation fabrics 51 Evacuation pipe 6 Vacuum sealing material 7 liquid substance 8 clamping devices 9 columns

Claims

[1] Method for joining at least one hard object (3) to a film, comprising the steps: - S1: at a predefined stacking temperature and a predefined stacking pressure: providing a stack (100) of at least two layers (2, 3), wherein one is made of a hard object (3) and the other is a film layer (2), wherein a liquid substance (7) is arranged between the layers (2, 3), wherein the film layer (2) is designed to harden at a predefined higher temperature than the stacking temperature and a predefined higher pressure than the stacking pressure, so that it is bonded to the hard object (3); - S2: Placing the at least one stack (100) in an autoclave chamber and applying an autoclave process to the at least one stack (100) by - S21: Increasing the temperature and pressure so that the liquid substance (7) is substantially forced out of gaps (9) between the layers (2, 3), and the foil layer (2) hardens and is thus bonded to the hard object (3); then - S23: Lowering temperature and pressure until the autoclave chamber can be opened - wherein in a step S22, which is carried out between step S21 and step S23, the temperature is maintained and the pressure is reduced to the predetermined stack pressure so that the remaining liquid substance (7) is evaporated. [2] Method according to claim 1, wherein in step S1 a stack (100) of at least three layers is provided, wherein an upper layer (1) is made of a hard object, a middle layer is made of a film and a lower layer (3) is formed of a hard object, wherein the liquid substance (7) is arranged in gaps between the upper layer (1) and the film layer (2) and between the film layer (2) and the lower layer (3). [3] Method according to any of the preceding claims, wherein the stacking is carried out - such that the upper layer (1), the foil layer (2) and the lower layer (3) are stacked in such a way that a gap (9) is left between the layers (1-2, 2-3), and then the liquid substance (7) is filled into the gaps (9), or - such that the liquid substance (7) is provided on the lower layer (3), the foil layer (2) is stacked on the liquid substance (7), and in the case of more than two layers, a further liquid substance (7) is provided on the foil layer (2) and the upper layer (1) is stacked on the further liquid substance (7). [4] Method according to any of the preceding claims, wherein the main part of the film layer (2) is made of resin and / or the film layer (2) is elastic at the predefined stacking temperature and predefined stacking pressure, which include room temperature and atmospheric pressure. [5] Method according to any of the preceding claims, wherein the liquid substance (7) is a substance whose unit volume contains molecules that are at least two orders of magnitude larger than air, and / or wherein the liquid substance (7) is a liquid substance or a colloid with a liquid substance as a dispersion medium, a liquid substance comprising water or an aqueous solution, or an alcohol or an alcohol solution, or an organic solvent or an organic solution, or a surfactant, or a mixture of any of the aforementioned substances, or water. [6] Method according to one of the preceding claims, wherein in a step S12, which is carried out after step S1 and before step S2, clamping means (8) are applied to the stack (100) such that the position of the layers (1-3) is pre-fixed. [7] Method according to claim 6, wherein the clamping pressure is such that at least a part of the liquid substance (7) is forced out of the gaps (9). [8] Method according to any one of claims 2 to 7, wherein the upper layer (1) is divided into several parts, each of which is an encapsulated power semiconductor device, and wherein the foil layer (2) is electrically non-conductive, and wherein the part of the lower layer (3) which is connected to the foil layer (2) is a top surface of a heat sink. [9] Method according to any one of the preceding claims, wherein - a large number of stacks (100) are lined up inside the autoclave chamber, or - a large number of stacks (100) are placed in a transport device and into the autoclave chamber, or - In step S1, the stack (100) is assembled in the transport device, which is placed in the autoclave chamber in step S2.

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