Apparatus for applying sintering force through compressible film

Abstract

To provide a sintering apparatus for simultaneously sintering an electronic device on a substrate and a metal sheet on the electronic device.SOLUTION: A sintering apparatus includes a sintering tool and a compressible film positionable over a metal sheet and an electronic device, the compressible film has a thickness greater than a height of the metal sheet, the compressible film conforms to the shapes of the metal sheet and the electronic device to simultaneously cover at least a portion of the metal sheet and the electronic device when the sintering tool applies a sintering force onto the compressible film during the sintering process.SELECTED DRAWING: Figure 4D

Description

[Technical Field]

[0001] The present invention relates to the sintering of electronic devices, such as during the manufacture of sintered packages containing high power electronic devices. [Background technology]

[0002] Sintering is the process of compressing and forming a solid mass of material by heat and / or pressure without melting to the liquidus point. The atoms in the material diffuse across the grain boundaries, fusing the grains together and creating one solid piece. Sintering is commonly utilized to attach semiconductor dies within high-power electronic devices, where the sintered material replaces solder in high-temperature applications.

[0003] Current sintering systems and solutions for stacked power structures require a two-step sintering process. During the first step, a power semiconductor die is sintered onto a substrate. During the second step, a thin metal sheet is then sintered onto the power semiconductor die. The metal sheet may be in the form of a foil made of copper, silver, gold, nickel, or other metals, or may include an alloy. The metal sheet may also include a plated layer, such as a silver layer plated onto a copper foil. An example of such a thin metal sheet is the so-called die-top system ("DTS"). The metal sheet may include pre-applied sinter paste and adhesive to provide die protection to enable high-yield copper wire bonding and simplify its assembly onto the semiconductor die.

[0004] 1 is a plan view of a substrate 100 having multiple semiconductor chips or dies 102 and a metal sheet 104 mounted thereon. The substrate 100 may be a direct bonded copper (DBC) ceramic substrate. Typically, there are multiple semiconductor dies 102 mounted on a single DBC substrate 100 that is sintered, and there may be height variations between the various semiconductor dies 102.

[0005] 2A is a side view of a prior art sintering approach using a sintering tool 110 and an incompressible film 108 separating the semiconductor die 102. The incompressible film 108 is used as a cushion to improve compression uniformity. Such an incompressible film 108 has a volume that remains constant when a force is applied to deform it. As such, the material is typically pushed sideways by the deformation force to establish the volumetric conserved state of the incompressible film 108. The semiconductor die 102 rests on a layer of sinter paste 106 on the substrate 100. The solidified sinter paste 106 bonds the semiconductor die 102 to the substrate 100 after sintering.

[0006] 2B shows a sintering force 112 being applied onto the semiconductor die 102 through the incompressible film 108. After the semiconductor die 102 is bonded onto the sinter paste 106 and substrate 100, the sintering tool 110 and incompressible film 108 are moved away from the semiconductor die 102.

[0007] 2C then shows the metal sheet 104 placed on top of the semiconductor die 102 bonded to the substrate 100 after the sintering tool 110 and incompressible film 108 have been moved away from the semiconductor die 102. A layer of sinter paste 106 is present between the metal sheet 104 and the semiconductor die 102 to bond the metal sheet 104 to the semiconductor die 102.

[0008] 2D shows a sintering tool 110 applying a sintering force 112 through the incompressible film 108, this time onto the metal sheet 104. After the sintering paste 106 has hardened, the metal sheet 104 is successfully bonded onto the semiconductor die 102.

[0009] Current two-step sintering processes that rely on an incompressible film 108, such as a typical incompressible PTFE (polytetrafluoroethylene) film, to transmit the sintering force 112 have several drawbacks. First, the die-top metallization is contaminated by the PTFE film, which comes into direct contact with the semiconductor die top during the first sintering step, and sintering the metal sheet requires a dedicated cleaning process to clean or reactivate the semiconductor die-top metallization. This increases assembly time and operational cost and complexity.

[0010] Furthermore, a typical thickness of a non-compressible film such as a PTFE film is 0.05 mm. Because a PTFE film having a thickness of 0.05 mm can typically only cover a maximum height variation of about 0.01 mm, this thickness is usually not sufficient to cover the height variation of the semiconductor die 102 or the metal sheet 104. On the other hand, the actual variation of the semiconductor die 102 or the metal sheet 104 may be 0.05 mm.

[0011] If such height variations are not fully compensated for, the bond quality of the subsequently sintered semiconductor die 102 or metal sheet 104 will be adversely affected.

[0012] Incompressible materials in the form of elastomers, such as silicone rubber, can also be used as pressure pads when bonded to the upper sintering tool to compensate for any thickness variations within the product. However, the elastomer itself is a solid material, and therefore the pressure distribution inside the pressure pad is inherently uneven. This unevenness can cause yield or damage problems, as areas of lower pressure tend to have lower die bond strength, and areas of higher pressure are at higher risk of semiconductor die cracking.

[0013] Furthermore, the use of elastomer as a pressure pad does not allow for selection of the area or component that is pressure sintered. Because such selection is not possible, this concept is likely to induce damage to the substrate, such as cracks or fractures, during sintering, especially when the substrate is a panel-type ceramic substrate.

[0014] It would be useful to provide a one-step sintering process for metal sheets and power semiconductor dies that avoids the aforementioned drawbacks of current sintering approaches, such as the inability to selectively apply sintering pressure over predetermined areas. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] International Publication No. 2021 / 177292 [Patent Document 2] Patent No. 6667879 [Patent Document 3] US Patent Application Publication No. 2005 / 0277244 [Patent Document 4] Special Publication No. 06-504880 Summary of the Invention [Problem to be solved by the invention]

[0016] It is therefore an object of the present invention to seek to provide an effective one-step sintering process by deploying a compressible material such as a force distribution medium during sintering. [Means for solving the problem]

[0017] According to a first aspect of the present invention, there is provided a sintering apparatus for simultaneously sintering an electronic device on a substrate and a metal sheet on the electronic device, the sintering apparatus comprising a sintering tool and a compressible film positionable over the metal sheet and the electronic device, the compressible film having a thickness greater than a height of the metal sheet, and the compressible film adapted to conform to the shapes of the metal sheet and the electronic device to simultaneously cover at least a portion of the metal sheet and the electronic device when the sintering tool applies a sintering force onto the compressible film during the sintering process.

[0018] According to a second aspect of the present invention, there is provided a method for simultaneously sintering an electronic device on a substrate and a metal sheet on the electronic device, the method comprising the steps of placing the electronic device on the substrate and the metal sheet on the electronic device; placing a compressible film on the metal sheet and the electronic device, wherein a thickness of the compressible film is greater than a height of the metal sheet; and then applying a sintering force on the compressible film during the sintering process with a sintering tool such that the compressible film conforms to the shapes of the metal sheet and the electronic device and simultaneously covers at least a portion of the metal sheet and the electronic device with the compressible film.

[0019] According to a third aspect of the present invention, there is provided a method for manufacturing a sintered package by simultaneously sintering an electronic device on a substrate and a metal sheet on the electronic device, the method comprising the steps of placing the electronic device on the substrate and the metal sheet on the electronic device; placing a compressible film on the metal sheet and the electronic device, wherein a thickness of the compressible film is greater than a height of the metal sheet; and then applying a sintering force on the compressible film during the sintering process with a sintering tool such that the compressible film conforms to the shapes of the metal sheet and the electronic device and simultaneously covers at least a portion of the metal sheet and the electronic device with the compressible film.

[0020] The present invention will now be described in more detail by reference to the accompanying drawings, which illustrate, for convenience, certain preferred embodiments of the invention. It is to be understood that the particulars of the drawings and the related description do not supersede the broad equivalent generality of the invention as defined by the claims.

[0021] An exemplary sintering process according to the present invention will now be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a plan view of a substrate having multiple semiconductor dies and a metal sheet mounted thereon. [Figure 2-1] FIG. 2A is a side view of a prior art sintering approach using a non-compressible film to separate the sintering tool and semiconductor die, and FIG. 2B is a diagram illustrating the sintering force exerted on the semiconductor die through the non-compressible film. [Figure 2-2] FIG. 2C shows a metal sheet placed on top of a semiconductor die, and FIG. 2D shows a sintering tool applying a sintering force onto the metal sheet through an incompressible film. [Figure 3A] FIG. [Figure 3B] FIG. 1 shows a substrate placed on a carrier. [Figure 3C] FIG. 1 illustrates a semiconductor die placed on a substrate. [Figure 3D] FIG. 1 illustrates multiple metal sheets placed over a semiconductor die. [Figure 3E] FIG. 1 shows a compressible film piece placed on a substrate. [Figure 4A] FIG. 1 is a side view of a sintering apparatus including a compressible film according to a preferred embodiment of the present invention. [Figure 4B] FIG. 1 illustrates a sintering tool contacting a compressible film. [Figure 4C] FIG. 1 illustrates a compressible film being compressed over a metal sheet and a portion of a semiconductor die. [Figure 4D]FIG. 1 illustrates a sintering apparatus in a sintering position where the compressible film substantially conforms to the shape of the metal sheet and semiconductor die. [Figure 5] 1 is a schematic diagram of modules that may be included in a sintering machine for performing a sintering process, according to a preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] For purposes of illustrating how multiple electronic devices (such as semiconductor dies 18) and metal sheets 20 are bonded onto a substrate 16 by sintering in a sintering apparatus, FIG. 3A is a plan view of a carrier 10 used to support multiple substrates 16 during sintering, according to a preferred embodiment of the present invention. The carrier 10 is adapted to be received by the sintering apparatus when it supports at least one substrate 16 for sintering. The illustrated carrier 10 has multiple pockets 12 with through-holes, each configured to receive one substrate 16. The periphery of each pocket 12 incorporates a step 14 onto which the edge of the substrate 16 can rest for support.

[0024] 3B shows four substrates placed on carrier 10, each supported by steps 14 within a respective pocket 12. In FIG. 3C, multiple semiconductor dies 18 are placed on substrates 16. In this illustration, each substrate 16 is configured to hold four semiconductor dies 18. Each semiconductor die 18 is to be placed on a layer of sinter paste 24 in preparation for the sintering process to follow.

[0025] 3D shows multiple metal sheets 20 placed over semiconductor dies 18, with each semiconductor die 18 configured to hold one metal sheet 20. Each metal sheet 20 may have a layer of sintering paste 24 on its surface when placed over the semiconductor die 18 in preparation for the sintering process. Finally, FIG. 3E shows four pieces of compressible film 22 placed over substrate 16, the multiple pieces of compressible film 22 fitting into the space allotted by carrier 10 to cover the metal sheets 20 and semiconductor dies 18 prior to the sintering process.

[0026] Unlike the incompressible film 108, the volume of the compressible film 22 is specifically configured to change when a deformation force is applied onto the compressible material. These four pieces of compressible film 22 may be placed onto the substrate 16 at the compressible film loading station using a pick-and-place operation and act to transfer a compressive force onto the metal sheet 20 and semiconductor die 18 when a sintering force is applied thereon during the sintering process.

[0027] 4A is a side view of a sintering apparatus including a compressible film 22 according to a preferred embodiment of the present invention. In this side view, a pair of semiconductor dies 18 and a metal sheet 20 are visible. A substrate 16 is placed in a pocket 12 of a carrier 10, and a bottom sintering tool 32, which is insertable into and protrudes through a through-hole in the pocket 12, lifts the substrate 16 away from a step 14 within the pocket 12. The bottom sintering tool 32 provides a firm support for the substrate 16 during sintering.

[0028] The semiconductor dies 18 are each placed on a layer of sintering paste 24 on the substrate 16, and the metal sheet 20 is then placed on top of the layer of sintering paste on each semiconductor die 18. A compressible film 22 fits within the pocket 12 of the carrier 10 and covers the upper surface of the metal sheet 20. An upper sintering tool 30 is placed in a waiting position above the compressible film 22 in a vertical position corresponding to the positions of the semiconductor dies 18 and the metal sheet 20.

[0029] FIG. 4B shows the upper sintering tool 30 contacting the compressible film 22, but the compressible film 22 is not yet compressed. FIG. 4C shows the compressible film 22 being compressed by the upper sintering tool 30 to create a depressed compressible film 34 that begins to form a conformal surface area as it is compressed toward the substrate 16. By having the thickness of the compressible film 22 greater than the height of the metal sheet 20 so that the compressible film 22 is thicker than the thickness of the metal sheet 20 (including the layer of sinter paste 24 on which the metal sheet rests), the compressible film 22 conforms to the shapes of the metal sheet 20 and the semiconductor die 18, thereby covering the entire exposed area of ​​the metal sheet 20 and a portion of the semiconductor die 18. If possible, the compressible film 22 may also be selected with a thickness that covers the entire exposed area of ​​the semiconductor die 18 and the metal sheet 20.

[0030] 4D shows the sintering apparatus in a sintering position in which the compressible film 22 substantially conforms to the shapes of the metal sheet 20 and the semiconductor die 18. This conforming compressible film 36, which covers the metal sheet 20 and the semiconductor die 18 during sintering, conforms at its base to the surface of the metal sheet 20, the sintering paste 24 between the metal sheet 20 and the semiconductor die 18, and some of the top and side surfaces of the semiconductor die 18. Thus, the conforming compressible film 36 can simultaneously cover at least a portion of the metal sheet 20 and the semiconductor die 18 when the upper sintering tool 30 applies a sintering force onto the compressible film 22 during the sintering process.

[0031] On top of that, the conforming compressible film 36 conforms to cover the bottom surface and a portion of the sidewall of the upper sintering tool 30 as the upper sintering tool 30 applies a sintering force onto the conforming compressible film 36. At this point, sintering may be performed to bond the semiconductor die 18 to the substrate 16 and the metal sheet 20 to the semiconductor die 18 in a one-step process.

[0032] 5 is a schematic diagram of modules that may be included within a sintering machine 40 for carrying out a sintering process in accordance with a preferred embodiment of the present invention. The sintering machine has a product input store 42 into which carriers 10 bearing substrates 16, semiconductor dies 18, and metal sheets are introduced and fed into the sintering machine 40. An input vision system 44 inspects the carriers 10 and their contents to ensure they are free of defects.

[0033] The carrier 10 is then fed to a preheat station 48 via use of an input track 46. At this point, a compressible film input station 52 receives a supply of compressible film 22 of a particular predetermined size, which is then lifted and placed onto the carrier 10 to cover the substrate 16 and any devices to be bonded to the substrate 16. An on-loader 50 then feeds the carrier 10 into one of a number of sintering presses 54 for the sintering process, as described in detail above with reference to Figures 4A-4D.

[0034] After the devices in the form of semiconductor die 18 and metal sheet 20 are bonded to substrate 16 by sintering, carrier 10 is moved from sinter press 54 to cooling station 56 for cooling and hardening, and carrier 10 is then unloaded by off-loader 58. There may be more than one cooling station 56 deployed to improve throughput in case a production bottleneck is encountered at cooling station 56. After cooling, carrier 10 is moved via unloading truck 60 to product unloading storage station 62 where the sintered product can then be retrieved and compressible film 22 can be disposed of.

[0035] The compressible film 22 is preferably made of expanded PTFE (heat and acid treated) or expanded graphite to form an expanded, highly fibrous structure membrane at a predetermined stretch ratio, which should be a high stretch ratio to expand the PTFE. Expanded PTFE membranes can be described as porous structures with a significantly lower density than similar unexpanded PTFE structures. Expanded PTFE membranes have a density of 0.1 g / cm. 3 ~1.9g / cm 3The expanded PTFE film may have a specific gravity of 0.5 g / cm and a porosity of 25% to 96%. Small pore sizes of less than 1 micron can lead to porosities up to 90%, while larger pore sizes of 1 micron to 6 microns can contribute to promoting porosity to at least 95%. One preferred expanded PTFE film has a specific gravity of 0.5 g / cm. 3 ~0.9g / cm 3 and a compressibility of 50% to 90%. The expanded PTFE film may comprise multiple separate conformal expanded PTFE layers, optionally sandwiched between one or more rigid PTFE layers. The thickness of the compressible film 22 as used in preferred embodiments of the present invention may be in the region of 0.1 mm to 3.0 mm. The expanded graphite film has a density of 0.5 g / cm 3 ~1.5g / cm 3 and a compressibility of 15% to 70%.

[0036] The compressible film 22 may be introduced as separate pieces of material as shown in Figure 3E, but may also be introduced as a continuous film to simplify waste disposal. The compressible film 22 may also comprise a single compressible layer, multiple layers, or may be made from a composite material including a compressible material adapted to cover the metal sheet 20 and the semiconductor die 18.

[0037] It should be appreciated that the use of compressible film 22 as described in the preferred embodiment of the present invention allows for successful sintering of semiconductor die 18 and metal sheet 20 to be completed in a one-step process. This helps save costs, simplify the assembly process, and increase yield. Furthermore, much more variation in the height of semiconductor die 18 and metal sheet 20 can be compensated for to improve sintering quality.

[0038] The user can allocate specific areas for selective application of sintering pressure, which is not possible with conventional techniques. The compressible film 22 is a consumable item that can be loaded onto a product in an automated process before the product is loaded into a sintering press for pressure sintering. Electronic devices manufactured using the above method exhibit no delamination at the sintering interface of the device, and die shear strength tests have shown high bond strength.

[0039] It is to be understood that the invention described herein may be susceptible to variations, modifications and / or additions other than those specifically described, and the invention includes all such variations, modifications and / or additions that fall within the spirit and scope of the above description. [Explanation of symbols]

[0040] 10. Career 12 pockets 14 steps 16 boards 18 Semiconductor Dies 20 metal sheets 22 Compressible Film 24 Sintering paste 30 Upper sintering tool 32 Bottom Sintering Tool 34 Compressible Film 36 Compressible Film 40 Sintering Machine 42 Product loading storage area 44 Insertion Vision System 46 Input Truck 48 Preheating Station 50 Onloader 52 Compressible Film Input Station 54 Sintering Press 56 Cooling Station 58 Off-roader 60 Extraction Truck 62 Product removal and storage station 100 boards 102 Semiconductor chip or die 104 Metal Sheet 106 Sintering paste 108 Incompressible Film 110 Sintering Tools 112 Sintering force

Claims

1. 1. A sintering apparatus for simultaneously sintering an electronic device on a substrate and a metal sheet on the electronic device, comprising: a sintering tool; a compressible film positionable over the metal sheet and the electronic device; a thickness of the compressible film is greater than a height of the metal sheet, and the compressible film conforms to the shapes of the metal sheet and the electronic device to simultaneously cover the exposed area of ​​the metal sheet and at least a portion of the exposed area of ​​the electronic device when the sintering tool applies a sintering force onto the compressible film during a sintering process; a sintering apparatus configured such that a volume of the compressible film changes when the sintering force is applied onto the compressible film to apply a uniform sintering pressure distribution to the exposed areas of the metal sheet and the electronic device located at different heights.

2. 2. The sintering apparatus of claim 1, wherein the sintering apparatus is adapted to receive a carrier capable of supporting at least one substrate during sintering, the carrier being configured to fit with a piece of the compressible film to cover the metal sheet and the electronic device prior to performing the sintering process.

3. 3. The sintering apparatus of claim 2, further comprising a compressible film loading station for placing the piece of compressed film over the metal sheet and the electronic device supported by the carrier.

4. 3. The sintering apparatus of claim 2, wherein the carrier has a plurality of pockets, each pocket configured to hold a respective substrate, and the carrier further has through holes, and a bottom sintering tool can be insertable through the through holes to support the substrates.

5. The sintering apparatus of claim 1 , wherein the thickness of the compressible film is sufficient to further cover the entire exposed area of ​​the metal sheet and the electronic device during the sintering process.

6. 2. The sintering apparatus of claim 1, wherein the compressible film conforms to and covers a bottom surface and a portion of a sidewall of the sintering tool when the sintering tool applies a sintering force on the compressible film during the sintering process.

7. The sintering apparatus of claim 1 , wherein the compressible film comprises a highly fibrous structure membrane expanded at a predetermined stretch ratio.

8. 10. The sintering apparatus of claim 1, wherein the compressible film comprises expanded PTFE.

9. The expanded PTFE has a viscosity of 0.5 g / cm ３ ~0.9 g / cm ３ 9. The sintering apparatus of claim 8, wherein the sintering apparatus has a density of 0.1 to 1.0 MPa and a compressibility of 50% to 90%.

10. The expanded PTFE further has a viscosity of 0.1 g / cm ３ ~1.9 g / cm ３ 10. The sintering apparatus according to claim 9, wherein the sintering apparatus has a specific gravity of 0.1 to 0.5 and a porosity of 25% to 96%.

11. The sintering apparatus of claim 1 , wherein the compressible film comprises an expanded graphite film.

12. The expanded graphite film has a density of 0.5 g / cm ３ ~1.5g / cm ３ and a compressibility of 15% to 70%.

13. The sintering apparatus of claim 1 , wherein the compressible film comprises a plurality of separate conformable layers of compressible film.

14. 1. A method for simultaneously sintering an electronic device onto a substrate and a metal sheet onto the electronic device, comprising: placing the electronic device on the substrate and a metal sheet on the electronic device; placing a compressible film over the metal sheet and the electronic device, the compressible film having a thickness greater than a height of the metal sheet; then applying a sintering force onto the compressible film during a sintering process with a sintering tool such that the compressible film conforms to the shape of the metal sheet and the electronic device, and the compressible film simultaneously covers at least a portion of the exposed area of ​​the metal sheet and the exposed area of ​​the electronic device; The method is configured such that the volume of the compressible film changes when the sintering force is applied onto the compressible film to apply a uniform sintering pressure distribution to the exposed areas of the metal sheet and the electronic device located at different heights.

15. 1. A method for manufacturing a sintered package by simultaneously sintering an electronic device onto a substrate and a metal sheet onto the electronic device, comprising: placing the electronic device on the substrate and a metal sheet on the electronic device; placing a compressible film over the metal sheet and the electronic device, the compressible film having a thickness greater than a height of the metal sheet; then applying a sintering force onto the compressible film during a sintering process with a sintering tool such that the compressible film conforms to the shape of the metal sheet and the electronic device, simultaneously covering at least a portion of the exposed area of ​​the metal sheet and the exposed area of ​​the electronic device with the compressible film; The method is configured such that the volume of the compressible film changes when the sintering force is applied onto the compressible film to apply a uniform sintering pressure distribution to the exposed areas of the metal sheet and the electronic device located at different heights.

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