Sinterable silver film

Abstract

A method of making a combined sinter-ready silver film and carrier (1), the method comprising the steps of: a) forming a carrier (2) comprising a design opening (5); b) casting a silver film layer (7) into the design opening (5); e.g. casting a silver paste; and c) drying the carrier (2) and the silver film layer (7) to form the combined sinter-ready silver film and carrier (1). The carrier (2) can comprise a plastic carrier, which can be formed by permanently bonding two plastic films using a plasma bonding method or using a temperature-stable glue. The carrier (2) can comprise a stencil layer (3) and a backing layer (4). The stencil layer (3) can define the design opening (5). The backing layer (4) can be configured for sealing a bottom of the design opening (5), wherein a top of the design opening (5) can be open for receiving the cast silver film layer (7) at the beginning of step b).

Description

[0001] This application is a divisional application of the invention patent application filed on May 5, 2020, with application number 202080031579.1 and invention title "Sintered Silver Film".

[0002] This specification relates to methods of joining electrical or mechanical components, and more specifically to methods of attaching electronic components and associated devices to a circuit board. Background Technology

[0003] Sintered silver films that can be used with attached pipe cores combine the physical properties and chemical formulation of nano-silver powder into products that allow bonding of various electronic devices to create thermally and electrically conductive interfaces.

[0004] According to its specification summary, US20120114927A1 describes methods for die attachment for multi-chip and single-component applications that may involve printing a sintering paste onto a substrate or the back side of a die. Printing may involve stencil printing, screen printing, or a dispensing process. The paste may be printed onto the entire back side of a wafer or onto the back side of an individual die prior to dicing. A sintered film may also be fabricated and transferred onto a wafer, die, or substrate. Post-sintering steps can increase throughput. Summary of the Invention

[0005] In a first aspect, this disclosure provides a method for preparing a combined sintered silver film and a support, the method comprising the following steps:

[0006] a) Forming a carrier that includes designed openings;

[0007] b) Cast the silver film layer into the designed opening; and

[0008] c) Dry the carrier and silver film layer to form a combined sintered silver film and carrier.

[0009] The method may also include the following steps:

[0010] d) The combined sintered silver film and carrier are rolled or cut into individual sheets ready for industrial use.

[0011] In some implementations, the carrier may include a plastic carrier.

[0012] In some embodiments, the carrier can be formed by permanently bonding two plastic films. In some embodiments, a plasma bonding process can be used to bond the two plastic films. In other embodiments, a temperature-stable adhesive can be used to bond the two plastic films.

[0013] The carrier may include a template layer and a backing layer.

[0014] In some implementations, the template layer may define the design openings.

[0015] In some embodiments, the template layer may have a thickness of 100 to 200 micrometers, optionally 150 micrometers. Additionally or alternatively, the template layer may include a PET film.

[0016] In some implementations, the template layer can be punched to create the designed opening. In some implementations, the designed opening can be rectangular or square.

[0017] The backing layer can be constructed to seal the bottom of the design opening.

[0018] In some embodiments, the backing layer may have a thickness of 50 micrometers. Additionally or alternatively, the backing layer may comprise a PET film.

[0019] In some implementations, the backing layer may be pretreated with oxygen plasma.

[0020] In some implementations, a laminator can be used to optionally bond the template layer and the backing layer at a pressure of 5 MPa and a temperature of 150°C.

[0021] At the start of step b), the top of the designed opening can be opened to receive the cast silver film layer.

[0022] In some implementations, the casting of the silver film layer may include casting of silver paste.

[0023] In some embodiments, the silver film layer in step b) may contain a solvent. After step c), the amount of solvent is reduced, and preferably, the solvent is substantially absent from the combined sintered silver film and support. However, some solvent residue may remain.

[0024] In some embodiments, drying the carrier and silver film layer to form a combined, i.e., sintered silver film and carrier, can be carried out in an oven, optionally at 130°C for 20 minutes.

[0025] In a second aspect, this disclosure provides a combined sintered silver film and carrier comprising a carrier having a designed opening and a silver film layer cast into the designed opening.

[0026] In some implementations, the carrier may include a plastic carrier.

[0027] In some implementations, the carrier may include two permanently bonded plastic films.

[0028] The carrier may include a template layer and a backing layer.

[0029] In some implementations, the template layer may define the design openings.

[0030] In some embodiments, the template layer may have a thickness of 100 to 200 micrometers, optionally 150 micrometers. Additionally or alternatively, the template layer may include a PET film.

[0031] In some implementations, the opening can be designed as a rectangle or a square.

[0032] The backing layer has a sealable design at the bottom of the opening.

[0033] In some embodiments, the backing layer may have a thickness of 50 micrometers. Additionally or alternatively, the backing layer may comprise a PET film.

[0034] The silver film can be formed by casting silver paste. The silver film may contain solvent during casting.

[0035] In a third aspect, this disclosure provides a method for assembling a component onto a substrate, the method comprising the following steps:

[0036] a) Position the combined sintered silver film and carrier on top of the substrate, the combined sintered silver film and carrier including a carrier with a design opening and a silver film layer cast into the design opening such that the silver film layer is facing down.

[0037] b) Transfer the silver film layer onto the substrate by lamination;

[0038] c) Remove the combined sintered silver film and the carrier;

[0039] d) Place the component onto the substrate, bringing it into contact with the transferred silver film layer to form the assembly; and

[0040] e) Sinter the components to form silver junctions between the components and the substrate.

[0041] In some embodiments, in step b), the laminator can be used with a pressure of 3 MPa to 8 MPa, optionally 3 MPa to 6 MPa, optionally 8 MPa, and a temperature of 130°C to 150°C, optionally 130°C.

[0042] In some implementations, in step e), sintering can be carried out at a pressure of 10 MPa and a temperature of 250°C.

[0043] In some implementations, the substrate may include direct-bonded copper (DBC), lead frames, clips or clip arrays, wafers, or any other components for assembling electronic devices and having metallized surfaces.

[0044] In some implementations, the components may include Si devices or SiC devices and / or dies.

[0045] In some implementations, the combined sintered silver film and carrier may be as defined in the second aspect above.

[0046] In a fourth aspect, this disclosure provides an assembly of a component and a substrate joined together by sintered silver contacts, which can be obtained by the method described in the third aspect above. Attached Figure Description

[0047] One or more embodiments of this disclosure will now be described by way of example only with reference to the accompanying drawings, in which:

[0048] Figures 1a to 1c This is a schematic diagram of the manufacturing process of the combination of sintered silver film and carrier according to the present disclosure;

[0049] Figure 2a and Figure 2b This is a schematic diagram of the lamination process;

[0050] Figure 3a This is a photograph of a carrier with a square opening formed from PET film;

[0051] Figure 3b This is after the silver film layer is cast into the opening. Figure 3a The photograph on the carrier;

[0052] Figure 3c The flatness profile of the silver film layer is shown;

[0053] Figure 4a and Figure 4b This illustrates a direct-bonded copper (DBC) substrate laminated with a patterned silver film according to the present disclosure; and

[0054] Figure 5 To show the placement Figure 4a and Figure 4b A photograph of a die sintered onto a silver film and then onto a DBC substrate. Detailed Implementation

[0055] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by a reader in the field to which the claimed subject matter pertains. It should be understood that the foregoing summary of this disclosure and the following examples are merely illustrative and not intended to limit any of the claimed subject matter.

[0056] The following description relates to embodiments of this disclosure. The description of embodiments is not intended to include all possible embodiments of this disclosure claimed in the appended claims. Many modifications, alterations, and equivalents not expressly stated in the following embodiments may fall within the scope of the appended claims. Unless the context clearly requires otherwise, a feature described as part of one embodiment may be combined with features of one or more other embodiments.

[0057] In some cases, a preferred method for using sinterable silver films is to laminate the sinterable silver film onto a substrate, such as direct-bonded copper (DBC), lead frames, or clips. This disclosure describes an extension of existing sintering film technologies to form silver films with unique patterns, thereby providing selective lamination onto specific areas of the substrate. This process is suitable for high-volume manufacturing of a variety of power modules and discrete packages via sintering processes. The process utilizes the capability of sinterable silver films and specialized patterning techniques to ensure accurate component positioning and reliable connection.

[0058] Figures 1a to 1c A schematic diagram of the patterning process is shown. First, a carrier 2 is formed by permanently bonding two plastic films 3 and 4 together. In some embodiments, the carrier 2 may consist of two layers of polyethylene terephthalate (PET) films bonded together.

[0059] The two plastic films may include a template layer 3 and a backing layer 4, such as Figure 1a As shown. Template layer 3 can be referred to as "layer 1", and backing layer 4 can be referred to as "layer 2".

[0060] The top plastic film (i.e., template layer 3) is pre-cut to form an opening / hole 5 according to the desired pattern design. The opening / hole 5 can also be referred to as design opening 5. The main body of template layer 3 is... Figure 1a The number 6 is used to represent the hole 5. The hole 5 can be formed by punching through the template layer 3. The opening / hole 5 can be square, rectangular, or other shapes. The template layer 3 can be formed of PET and can have a thickness of 100 to 200 micrometers. In a non-limiting embodiment, the template layer 3 of the carrier 2 is composed of a 150-micrometer-thick PET film, which is punched to produce a 13×13mm diameter. 2 5 square openings / holes.

[0061] The bottom plastic film (i.e., backing layer 4) can be formed from PET and can have a thickness of 50 micrometers. Backing layer 4 can be formed from PET film on a roller.

[0062] The template layer 3 and the backing layer 4 are bonded together using conventional plasma bonding processes or temperature-stabilized adhesives to form the carrier 2, such as... Figure 1b As shown. Figure 3a A non-limiting example of carrier 2 is shown in the figure.

[0063] In some embodiments, the backing layer 4 or both the template layer 3 and the backing layer 4 may be pretreated with oxygen plasma. In one non-limiting embodiment, the oxygen plasma pretreatment is performed with oxygen plasma for 10 minutes.

[0064] In some embodiments, the template layer 3 and the backing layer 4 can be bonded together under pressure and temperature. In a non-limiting embodiment, bonding is performed using a laminator at a pressure of 5 MPa and a temperature of 150°C.

[0065] Once the carrier 2 is formed, a special silver paste is poured into the openings / holes 5 of the carrier 2. The silver paste may contain a solvent. In one non-limiting embodiment, the silver paste may be Argomax, purchased from MacDermid Alpha - Assembly Solutions of Somerset, NJ, USA. ® Slurry.

[0066] The carrier 2 containing silver paste is dried in an oven to form a pattern of sintered silver film 7, such as... Figure 1c As shown. In a non-limiting embodiment, the carrier 2 and the silver paste are dried at 130°C for 20 minutes. The drying step removes at least some solvent from the silver paste. After the drying step is completed, the amount of solvent is reduced, and preferably, there is essentially no solvent in the sintered silver film 7. However, some solvent residue may remain.

[0067] In this disclosure, the carrier 2 and the sintered silver film 7 are collectively referred to as a combined sintered silver film and carrier 1. The combined sintered silver film and carrier 1 can be rolled or cut into individual sheets for industrial use. Non-limiting examples of the combination of the sintered silver film and carrier 1 are shown in... Figure 3b As shown in the image.

[0068] In one non-limiting embodiment, the sintered silver film 7 has a thickness of approximately 100 micrometers and the thickness is uniform across the entire pattern, such as... Figure 3c The flatness profile is shown.

[0069] To utilize the combined sinterable silver film and carrier 1 in an application, a patterned sinterable silver film 7 is laminated onto a substrate 10. The substrate 10 can be a DBC, lead frame, clip or clip array, wafer, or any other component used for assembling electronic devices and having a metallized surface. Once the sinterable silver film 7 is laminated onto the substrate 10, the component is ready for assembly using a sintering process.

[0070] Figure 2a and Figure 2b An exemplary lamination process is schematically illustrated. Lamination can be performed using a laminator, such as... Figure 2aAs shown schematically, the laminator may include a top platen 11 and a bottom platen 12 for applying compressive pressure to the combined, i.e., sintered silver film, carrier 1, and substrate 10. The top platen 11 and bottom platen 12 may be heated to 130°C.

[0071] Graphite sheet 13 can be inserted between upper plate 11 and the combined sintered silver film and carrier 1. The combined sintered silver film and carrier 1 are positioned on top of substrate 10 (e.g., DBC), with the sintered silver film 7 facing down. The sintered silver film 7 is transferred from carrier 2 to substrate 10 in a laminator under a pressure of 5 MPa or 8 MPa and a temperature of 130°C. Figure 2b Schematic illustration. A non-limiting example of a substrate 10 (DBC in this example) on which a sintered silver film 7 is laminated is shown. Figure 4a and Figure 4b middle.

[0072] The component can then be bonded to the substrate 10 by sintering, i.e., sintered silver film, to form a silver contact. Figure 5 A non-limiting example is shown in which the die 22 is mounted on a laminated, i.e., sintered silver film 7 and sintered onto the substrate 10 at 10 MPa and 250 °C in a sintering press.

[0073] Industrial applicability

[0074] The patterned, sintered silver film and carrier 1 can be composed of a plastic carrier 2 with designed openings 5 ​​and a sintered silver film layer 7 cast into the openings 5. The layout of the patterned sintered silver film 7 is advantageously defined by the design of the electronic device to be assembled. The patterned sintered silver film 7 is produced using a two-step process. In the first step, the sintered silver film 7 is transferred from the carrier 2 onto the substrate 10 by lamination at a typical pressure of 3 MPa to 6 MPa and a temperature of 130°C to 150°C. Typical substrates used are ceramic DBCs, lead frames, clips, and wafers with Si or SiC devices. In the second step, the component is placed on the substrate 10 and sintered at a typical pressure of 10 MPa and a temperature of 250°C to form highly reliable silver contacts. Advantageously, this process is well-suited for high-volume manufacturing of power modules, discrete components, and various other devices.

[0075] The combined sinterable silver film and carrier 1 of this disclosure can be advantageously positioned to be adapted to existing manufacturing equipment and processes for high-volume manufacturing. In one example, the sinterable silver film 7 can be laminated to an individual die or laminated to a wafer (followed by dicing). The laminated die can then be placed on a substrate and sintered under applied heat and pressure. The resulting junction between the die and the substrate is metallic silver, with the structure and properties shown below:

[0076] Typical Argomax ® contact

[0077] Composition: Sintered silver particles

[0078] Density: 85% to 95%

[0079] Thermal conductivity: approximately 200 W / mK

[0080] Electrical conductivity: approximately 3 µΩ·cm

[0081] Young's modulus: approximately 20 GPa

[0082] The combined sintered silver film and carrier 1 disclosed herein can be used for attachment of components in a variety of devices and applications, ranging from large-area thyristors and power modules for electrical and automotive equipment to miniature discrete components for mobile technology and LED lighting. Compared to conventional bonding techniques, this technology can improve the performance of existing devices by 5 to 30 times in terms of power or light output or reliability. The film enables the use of novel high-temperature SiC and GaN semiconductors, as well as new device designs, producing electrical efficiencies unattainable with existing technologies.

[0083] Other aspects of this disclosure are set forth in the following provisions.

[0084] Terms and Conditions :

[0085] Clause 1: A method for preparing a combined sintered silver film and a support, the method comprising the following steps:

[0086] a) Forming a carrier that includes designed openings;

[0087] b) Cast the silver film layer into the designed opening; and

[0088] c) Dry the carrier and the silver film layer to form the combined sintered silver film and carrier.

[0089] Clause 2: The method described in Clause 1 further includes the following steps:

[0090] d) Roll or cut the combined sintered silver film and carrier into individual sheets ready for industrial use.

[0091] Clause 3: The method described in accordance with Clause 1 or Clause 2, wherein the carrier includes a plastic carrier.

[0092] Clause 4: The method according to any one of the preceding clauses, wherein the carrier is formed by permanently bonding two plastic films together.

[0093] Clause 5: The method described in Clause 4, wherein the two plastic films are bonded using a plasma bonding process.

[0094] Clause 6: The method described in Clause 4, wherein the two plastic films are bonded using a temperature-stable adhesive.

[0095] Clause 7: The method according to any one of the preceding clauses, wherein the carrier comprises a template layer and a backing layer.

[0096] Clause 8: The method described in Clause 7, wherein the template layer defines the design opening.

[0097] Clause 9: The method described in accordance with Clause 7 or Clause 8, wherein the template layer has a thickness of 100 micrometers to 200 micrometers, optionally 150 micrometers.

[0098] Clause 10: The method according to any one of Clauses 7 to 9, wherein the template layer comprises a PET film.

[0099] Clause 11: The method according to any one of Clauses 7 to 10, wherein the template layer is punched to produce the design opening.

[0100] Clause 12: The method according to any one of Clauses 7 to 11, wherein the design opening is rectangular or square.

[0101] Clause 13: The method according to any one of Clauses 7 to 12, wherein the backing layer is configured to seal the bottom of the design opening.

[0102] Clause 14: The method according to any one of Clauses 7 to 13, wherein the backing layer has a thickness of 50 micrometers.

[0103] Clause 15: The method according to any one of Clauses 7 to 14, wherein the backing layer comprises a PET film.

[0104] Clause 16: The method according to any one of Clauses 7 to 15, wherein the backing layer is pretreated with oxygen plasma.

[0105] Clause 17: The method according to any one of Clauses 7 to 16, wherein the template layer and the backing layer are optionally bonded using a laminator at a pressure of 5 MPa and a temperature of 150°C.

[0106] Clause 18: The method according to any one of Clauses 7 to 17, wherein at the beginning of step b), the top of the design opening is opened to receive the cast silver film layer.

[0107] Clause 19: The method according to any one of the preceding clauses, wherein casting the silver film layer includes casting silver paste.

[0108] Clause 20: The method according to any one of the preceding clauses, wherein the silver film layer contains a solvent.

[0109] Clause 21: The method according to any one of the preceding clauses, wherein the drying of the carrier and the silver film layer to form the combined sintered silver film and carrier is carried out in an oven, optionally at 130°C for 20 minutes.

[0110] Clause 22: A combined sintered silver film and carrier comprising a carrier having a designed opening and a silver film layer cast into the designed opening.

[0111] Clause 23: The combination of sintered silver film and carrier as described in Clause 22, wherein the carrier includes a plastic carrier.

[0112] Clause 24: The combination of a sintered silver film and a carrier as described in Clause 22 or Clause 23, wherein the carrier comprises two permanently bonded plastic films.

[0113] Clause 25: A combination of a sintered silver film and a carrier according to any one of Clauses 22 to 24, wherein the carrier comprises a template layer and a backing layer.

[0114] Clause 26: The combination of sintered silver film and carrier as described in Clause 25, wherein the template layer defines the design opening.

[0115] Clause 27: The combination of sintered silver film and carrier according to Clause 25 or Clause 26, wherein the template layer has a thickness of 100 micrometers to 200 micrometers, optionally 150 micrometers.

[0116] Clause 28: A combination of a sintered silver film and a carrier according to any one of Clauses 25 to 27, wherein the template layer comprises a PET film.

[0117] Clause 29: A combination of sintered silver film and carrier according to any one of Clauses 25 to 28, wherein the design opening is rectangular or square.

[0118] Clause 30: A combination of a sintered silver film and a carrier according to any one of Clauses 25 to 29, wherein the backing layer seals the bottom of the design opening.

[0119] Clause 31: A combination of a sintered silver film and a carrier according to any one of Clauses 25 to 30, wherein the backing layer has a thickness of 50 micrometers.

[0120] Clause 32: A combination of a sintered silver film and a carrier according to any one of Clauses 25 to 31, wherein the backing layer comprises a PET film.

[0121] Clause 33: A combination of a sintered silver film and a carrier according to any one of Clauses 22 to 32, wherein the silver film layer is formed by casting silver paste.

[0122] Clause 34: A combination of a sintered silver film and a carrier according to any one of Clauses 22 to 33, wherein the silver film layer contains a solvent during casting.

[0123] Clause 35: A method of assembling a component onto a substrate, the method comprising the steps of:

[0124] a) Position the combined sintered silver film and carrier on top of the substrate, the combined sintered silver film and carrier including a carrier having a design opening and a silver film layer cast into the design opening such that the silver film layer is facing down.

[0125] b) The silver film layer is transferred to the substrate by lamination;

[0126] c) Remove the sintered silver film and the carrier from the combination;

[0127] d) Place the component onto the substrate, bringing it into contact with the transferred silver film layer to form an assembly; and

[0128] e) Sinter the component to form a silver junction between the component and the substrate.

[0129] Clause 36: The method according to Clause 35, wherein in step b), the lamination is performed using a laminator at a pressure of 3 MPa to 8 MPa, optionally 3 MPa to 6 MPa, optionally 8 MPa and a temperature of 130°C to 150°C, optionally 130°C.

[0130] Clause 37: The method according to Clause 35 or Clause 36, wherein in step e), the sintering is carried out at a pressure of 10 MPa and a temperature of 250°C.

[0131] Clause 38: The method according to any one of Clauses 35 to 37, wherein the substrate comprises direct bonded copper (DBC), lead frame, fixture or fixture array, wafer or any other component for assembling electronic devices and having a metallized surface.

[0132] Clause 39: The method according to any one of Clauses 35 to 38, wherein the component comprises a Si device or a SiC device and / or a die.

[0133] Clause 40: The method according to any one of Clauses 35 to 39, wherein the combination of the sintered silver film and the carrier is as defined in any one of Clauses 22 to 34.

[0134] Clause 41: An assembly of a component and a substrate joined together by sintered silver contacts, the assembly being obtainable by any one of Clauses 35 to 40.

[0135] It should be understood that at least some of the figures and descriptions in this disclosure have been simplified to focus on elements relevant to a clear understanding of this disclosure, and other elements that would be familiar to a reader in the art may also be omitted for clarity. Because such elements are well-known to a reader in the art, and because they are not necessarily conducive to a better understanding of this disclosure, descriptions of such elements are not provided herein.

Claims

1. A method for preparing a combined sintered silver film and a support, the method comprising the following steps: a) Forming a carrier that includes designed openings; b) Cast the silver film layer into the designed opening; as well as c) Dry the carrier and the silver film layer to form the combined sintered silver film and carrier. in: The carrier is formed by permanently bonding two plastic films together; The carrier includes a template layer and a backing layer; and The template layer defines the design opening.

2. The method according to claim 1, further comprising the following steps: d) The combined sintered silver film and carrier are rolled or cut into individual sheets ready for industrial use.

3. The method of claim 1 or 2, wherein the backing layer is configured to seal the bottom of the design opening.

4. The method according to any one of claims 1 to 3, wherein at the beginning of step b), the top of the design opening is opened for receiving the cast silver film layer.

5. The method according to any one of the preceding claims, wherein casting the silver film layer comprises casting silver paste.

6. A combined sintered silver film and carrier, the combined sintered silver film and carrier comprising a carrier having a designed opening and a silver film layer cast into the designed opening, wherein: The carrier comprises two permanently bonded plastic films; The carrier includes a template layer and a backing layer; and The template layer defines the design opening.

7. The combined sintered silver film and carrier according to claim 6, wherein the template layer has a thickness of 100 micrometers to 200 micrometers, optionally 150 micrometers.

8. A method for assembling a component onto a substrate, the method comprising the steps of: a) Position the combined sintered silver film and carrier on top of the substrate, the combined sintered silver film and carrier comprising a carrier having a design opening and a silver film layer cast into the design opening such that the silver film layer faces downward. b) The silver film layer is transferred onto the substrate by lamination; c) Remove the carrier of the combination, namely the sintered silver film and the carrier; d) Placing the component onto the substrate, bringing the component into contact with the transferred silver film layer to form an assembly; and e) Sinter the assembly to form a silver junction between the component and the substrate. in: The carrier comprises two permanently bonded plastic films; The carrier includes a template layer and a backing layer; and The template layer defines the design opening.

9. The method of claim 8, wherein in step b), the lamination is performed using a laminator at a pressure of 3 MPa to 8 MPa, optionally 3 MPa to 6 MPa, optionally 8 MPa and a temperature of 130°C to 150°C, optionally 130°C.

10. The method according to claim 8 or claim 9, wherein in step e), the sintering is carried out at a pressure of 10 MPa and a temperature of 250°C.

11. The method according to any one of claims 8 to 10, wherein the substrate comprises direct bonded copper (DBC), a lead frame, a fixture or fixture array, a wafer, or any other component for assembling electronic devices and having a metallized surface.

12. The method according to any one of claims 8 to 11, wherein the component comprises a Si device or a SiC device and / or a die.

13. The method according to any one of claims 8 to 12, wherein the combination of the sintered silver film and the carrier is as defined in claim 6 or 7.

14. An assembly of a component and a substrate joined together by sintered silver contacts, said assembly being obtainable by any one of claims 8 to 13.

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