Preparation method of non-brazing high-thermal-conductivity copper-clad substrate

Abstract

The invention discloses a preparation method of a non-brazing high-thermal-conductivity copper-clad substrate. The preparation method comprises the following steps: selecting an insulating medium substrate comprising a silicon nitride ceramic substrate or a diamond film; metal layers grow on the insulating medium substrate, the outermost layer in the metal layers is a copper layer, and copper is electroplated on the copper layer until the thickness of the copper layer is 15-35 microns; polishing the surface copper layer on the copper-plated insulating medium substrate; preparing a copper foil with the thickness of 0.3-0.8 mm, and polishing the surface of the copper foil; carrying out plasma surface activation treatment on the polished surfaces of the polished insulating medium substrate and the copper foil; bonding of the insulating medium substrate and the copper foil is completed under the vacuum condition that the temperature is higher than 150 DEG C to form a copper-clad substrate; and carrying out vacuum high-temperature treatment at 600-900 DEG C on the bonded copper-clad substrate, so that the insulating medium substrate fully reacts with the metal layer in contact with the surface of the insulating medium substrate, thereby obtaining the high-thermal-conductivity copper-clad substrate. The heat conduction durability of the copper-clad substrate prepared by the method meets the requirements of a high-power module.

Description

Technical Field

[0001] The present invention relates to the technical fields of semiconductor processes and semiconductor packaging, and more particularly to a method for preparing a lead-free high thermal conductivity copper-clad substrate. Background Art

[0002] Currently, high thermal conductivity substrates in the market include silicon nitride AMB / DPC substrates, aluminum nitride AMB / DPC substrates, diamond AMB / DPC thermal conductivity substrates, etc., which use AMB technology and DPC technology to complete copper cladding on the insulating dielectric substrate. The AMB (Active Metal Bonding) technology is to print active solders such as silver-copper-titanium on the substrate surface or place solder pads, and complete copper cladding by means of vacuum high-temperature brazing. The DPC (Direct plating copper) technology is to metallize the substrate surface by PVD (Physical Vapor Deposition) method, and increase the copper thickness by electroplating after metallization to complete the production of copper-clad boards.

[0003] However, the printed active solder or the solder pads used in the AMB technology account for about one-third of the material cost, resulting in high costs. In addition, voids are likely to appear between the copper layer and the substrate after copper cladding by the AMB technology.

[0004] The bonding force between the metal layer and the substrate of the DPC technology is lower than that of the AMB technology, and DPC products are not suitable for high-power modules that require high durability. The copper thickness of the substrate circuit of the DPC technology is low and cannot reach the circuit thickness of the high thermal conductivity substrate. Summary of the Invention

[0005] An embodiment of the present invention provides a method for preparing a lead-free high thermal conductivity copper-clad substrate, and its thermal durability can meet the requirements of high-power modules.

[0006] To achieve the above object, an embodiment of the present invention provides a method for preparing a lead-free high thermal conductivity copper-clad substrate, including:

[0007] Select an insulating dielectric substrate that meets predetermined conditions, and the insulating dielectric substrate includes a silicon nitride ceramic substrate, an aluminum nitride ceramic substrate or a diamond thin film;

[0008] Grow a metal layer on the insulating dielectric substrate, the metal layer includes one or more layers and the outermost layer is a copper layer, and the thickness of the metal layer is 20 - 3500 nm;

[0009] Electroplate copper on the copper layer of the metal layer until the thickness of the copper layer is 15 - 35 μm;

[0010] The surface copper layer on the copper-plated insulating dielectric substrate is polished so that the surface roughness Ra value of the polished copper layer is between 1 nm and 200 nm;

[0011] Copper foil with a thickness of 0.3 - 0.8 mm is prepared, and the surface of the copper foil is polished so that the surface roughness Ra value of the polished copper foil is between 1 nm and 200 nm;

[0012] The polished surfaces of the polished insulating dielectric substrate and the copper foil are subjected to plasma surface activation treatment using one or more gases among argon, hydrogen, helium, nitrogen, oxygen, and carbon tetrafluoride;

[0013] The activated copper foil is placed on the surface of the activated insulating dielectric substrate, and the bonding of the insulating dielectric substrate and the copper foil is completed under a vacuum condition at a temperature greater than 150 °C to form a copper-clad substrate;

[0014] The bonded copper-clad substrate is subjected to a vacuum high-temperature treatment at 600 °C - 900 °C so that the insulating dielectric substrate fully reacts with the metal layer in contact with the surface of the insulating dielectric substrate, thereby obtaining a high thermal conductivity copper-clad substrate.

[0015] In an alternative embodiment, growing a metal layer on the insulating dielectric substrate includes: growing a titanium layer with a thickness of 10 - 500 nm on the insulating dielectric substrate; and, growing a copper layer with a thickness of 10 - 3000 nm on the titanium layer.

[0016] In an alternative embodiment, the preparation method further includes performing plasma surface activation treatment on the insulating dielectric substrate using a plasma surface modification gas before growing a metal layer on the insulating dielectric substrate.

[0017] In an alternative embodiment, the plasma surface modification gas includes argon.

[0018] In an alternative embodiment, the preparation method further includes performing activation treatment on the plasma surface-activated insulating dielectric substrate and copper foil with formic acid having a concentration of 5% - 10% and a temperature of 20 °C - 60 °C before the step of placing the activated copper foil on the surface of the activated insulating dielectric substrate.

[0019] In an alternative embodiment, metal layers are grown on two opposite surfaces of the insulating dielectric substrate.

[0020] In an alternative embodiment, the surface roughness Ra value of the copper layer is 1 nm, and / or, the surface roughness Ra value of the copper foil is 1 nm; and, the bonding of the insulating dielectric substrate and the copper foil is completed under a vacuum condition at a temperature of 250 °C to form a copper-clad substrate.

[0021] In an alternative embodiment, the Ra value of the surface roughness of the copper layer is 200 nm, and / or the Ra value of the surface roughness of the copper foil is 200 nm; and, the bonding of the insulating dielectric substrate and the copper foil is completed under a vacuum condition where the temperature is greater than 250 °C to form a copper-clad substrate.

[0022] In an alternative embodiment, the step of completing the bonding of the insulating dielectric substrate and the copper foil under a vacuum condition where the temperature is greater than 150 °C to form a copper-clad substrate includes completing the bonding of the insulating dielectric substrate and the copper foil under a vacuum condition where the temperature is in the range of 200 to 250 °C to form a copper-clad substrate.

[0023] By using the preparation method of the high thermal conductivity copper-clad substrate according to the technical solution of the present invention, the active soldering process is eliminated, but the thermal conductivity durability of the prepared copper-clad substrate can also meet the requirements of high-power modules. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic diagram of a method for preparing a solderless high thermal conductivity copper-clad substrate according to an embodiment of the present invention.

[0025] Figure 2 is a flowchart of a method for preparing a solderless high thermal conductivity copper-clad substrate according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The technical solutions of the embodiments will be clearly and completely described below with reference to the accompanying drawings of the present application. Those skilled in the art can understand that the embodiments described in the specification are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments described in this application without creative efforts shall fall within the scope of protection of the present invention.

[0027] In the description of this patent specification, the orientation or positional relationships indicated by "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", "longitudinal", "transverse", "center", "vertical", "horizontal", "length", "width", "thickness", "clockwise", "counterclockwise", etc. are based on the accompanying drawings of the specification. These orientation and positional relationships are only for the convenience of describing the embodiments related to the technical innovation of the present invention and should not be construed as limiting the scope of protection of the claims. In addition, those skilled in the art can understand that the terms "first" and "second" used in this specification to describe various components are only for distinguishing one component from another and have no meaning of sequence, and the corresponding components should not be limited by these terms.

[0028] Such as Figure 1 and Figure 2As shown, a preparation method of a lead-free soldering high thermal conductivity copper-clad substrate according to an embodiment of the present invention includes the following steps:

[0029] Step S101, select an insulating dielectric substrate that meets predetermined conditions.

[0030] In an alternative embodiment of the present invention, the insulating dielectric substrates that meet the predetermined conditions include aluminum nitride ceramic sheets and silicon nitride ceramic sheets. In another alternative embodiment, the qualified insulating dielectric substrates further include diamond films. In this case, diamond films can be grown on a silicon wafer growth substrate, and then the silicon wafer growth substrate is removed to leave the diamond films.

[0031] The above-mentioned predetermined conditions include the following:

[0032] 1) Insulation requirement, volume resistivity (25°C) > 10 14 Ω·cm;

[0033] 2) The breakdown strength meets ≥ 20 KV / mm;

[0034] 3) The material thermal conductivity meets the packaging requirements;

[0035] For example, the thermal conductivity of diamond films is 500 - 1800 W / m·K; the thermal conductivity of silicon nitride substrates > 80 W / m·K;

[0036] The thermal conductivity of aluminum nitride substrates > 170 W / m·K.

[0037] 4) The mechanical strength meets the usage requirements.

[0038] Step S102, perform plasma surface activation treatment on the insulating dielectric substrate with argon or other similar gases.

[0039] Step S103, after activation, grow a metal layer containing a copper layer on the surface of the insulating dielectric substrate by PVD (Physical Vapor Deposition). In one embodiment, metal layers can be grown on two opposite surfaces of the insulating dielectric substrate. The metal layer can be one or more layers. For example, the metal layer can include a Ti layer of 10 - 500 nm and a copper layer of 10 - 3000 nm, so that the total thickness of the metal layer is in the range of 20 - 3500 nm. When implementing this step, a 10 - 500 nm Ti layer is first grown on two surfaces of the insulating dielectric substrate, and then a 10 - 3000 nm copper layer is grown. In other alternative embodiments, it can also be to grow a metal layer on one surface of the insulating dielectric substrate by PVD according to needs or requirements.

[0040] Step S104, electroplate copper on the surface of the copper layer until the thickness of the copper layer is 15 - 35 μm.

[0041] Step S105: Polish the surface copper layer on the copper-plated insulating dielectric substrate so that the surface roughness Ra value of the polished copper layer is between 0.001 and 0.2000 um.

[0042] Step S106: Prepare another copper foil with a thickness of 0.3 - 0.8 mm, and polish the surface of the copper foil so that the surface roughness Ra value of the polished surface is between 0.001 and 0.2000 um.

[0043] Step S107: Use one or more gases among argon, hydrogen, helium, nitrogen, oxygen, and carbon tetrafluoride to perform plasma surface activation treatment on the polished surfaces of the polished insulating dielectric substrate and the copper foil.

[0044] Step S018: Then, use formic acid with a concentration of 5% - 10% and a temperature of 20°C - 60°C to perform activation treatment on the polished surfaces of the polished insulating dielectric substrate and the copper foil for 1 - 5 minutes.

[0045] Step S109: Bond the insulating dielectric substrate and the copper foil under a vacuum condition with a temperature greater than 150°C to form a copper-clad substrate. In a preferred embodiment, a temperature of 200 - 250°C is most suitable for the bonding of the insulating dielectric substrate and the copper foil.

[0046] Step S110: Perform vacuum high-temperature treatment on the bonded copper-clad substrate at 600°C - 900°C so that the insulating dielectric substrate and the metal layer in contact with the surface of the insulating dielectric substrate react sufficiently, thereby obtaining a high-thermal-conductivity copper-clad substrate. In the embodiments of the present invention, the treatment time is approximately 60 - 120 minutes.

[0047] In the embodiments of the present invention, when the insulating dielectric matrix substrate is a diamond film, Ti and diamond materials react sufficiently. When the insulating dielectric matrix substrate is a silicon nitride ceramic sheet, Ti and Si3N4 materials react sufficiently, so that a bonding force similar to that of the AMB process can be generated. This is because the inventor found that the reaction between titanium Ti and diamond or Ti and silicon nitride ceramic is incomplete during the PVD process, and the proportion of TiC (diamond PVD Ti), TiN / TiSi (Si3N4 substrate PVD Ti) compounds is not as fully reacted as in the AMB process, resulting in lower durability than the AMB process. Under a vacuum condition where the temperature is greater than 600°C and less than the self-decomposition temperature of silicon nitride (about 1800°C), Ti at the PVD process interface can react more fully with C in diamond or N and Si in silicon nitride Si3N4 material to form TiC or TiN / TiSi compounds, so that the interfacial bonding strength between the metal layer and the diamond or silicon nitride substrate is greatly improved from 30 - 50 MPa to 50 - 70 MPa.

[0048] In other alternative embodiments of the present invention, growing a metal layer on an insulating dielectric substrate may involve first growing a molybdenum layer on the surface of the insulating dielectric substrate and then growing a copper layer. In this case, molybdenum at the PVD process interface reacts sufficiently with C in diamond or N and Si in silicon nitride (Si3N4) material, thereby obtaining a high thermal conductivity copper-clad substrate.

[0049] Finally, the copper-clad substrate after high-temperature baking can complete the manufacturing of the heat-conducting substrate circuit by using the publicly disclosed laser or printed circuit board manufacturing process.

[0050] The preparation method of the high thermal conductivity copper-clad substrate according to the embodiment of the present invention eliminates the active solder, and can also obtain a copper-clad substrate whose thermal durability can meet the requirements of high-power modules. Compared with the silicon nitride substrate of the AMB process, the aluminum nitride plate of the AMB process, and the diamond substrate of the AMB process, the material cost is saved by about 1 / 3. Moreover, by using the bonding method between the substrate and the copper foil according to the embodiment of the present invention, the stress is minimized and the stability is high. The copper-clad substrate after heat treatment at a temperature above 600 degrees improves the problem that the interfacial bonding strength after depositing Ti and Cu layers by the general PVD process is lower than that of the AMB milling welding process.

[0051] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent substitution on some of the technical features. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a solderless high thermal conductivity copper-clad substrate, comprising: Selecting an insulating dielectric substrate that meets predetermined conditions, wherein the insulating dielectric substrate includes a silicon nitride ceramic substrate, an aluminum nitride ceramic substrate, or a diamond film; Growing a metal layer on the insulating dielectric substrate, wherein the metal layer comprises one or more layers and the outermost layer is a copper layer, and the thickness of the metal layer is 20 to 3500 nm; Electroplating copper on the copper layer of the metal layer until the thickness of the copper layer is 15-35 um; Polishing the copper layer on the insulating dielectric substrate after copper plating, so that the surface roughness Ra value of the copper layer after polishing is between 1nm and 200nm; Preparing a copper foil with a thickness of 0.3 to 0.8 mm, and polishing the surface of the copper foil so that the surface roughness Ra value of the polished copper foil is between 1 nm and 200 nm; The polished surfaces of the insulating dielectric substrate and the copper foil are subjected to plasma surface activation treatment using one or more gases selected from argon, hydrogen, helium, nitrogen, oxygen and carbon tetrafluoride; Placing the activated copper foil on the surface of the activated insulating dielectric substrate, and completing the bonding between the insulating dielectric substrate and the copper foil under vacuum conditions with a temperature greater than 150° C. to form a copper-clad substrate; The bonded copper-clad substrate is subjected to vacuum high-temperature treatment at 600° C. to 900° C., so that the insulating dielectric substrate and the metal layer contacting the surface of the insulating dielectric substrate fully react, thereby obtaining a high thermal conductivity copper-clad substrate.

2. The method for preparing a high thermal conductivity copper-clad substrate according to claim 1, characterized in that: Growing a metal layer on the insulating dielectric substrate comprises: Growing a titanium layer with a thickness of 10 to 500 nm on the insulating dielectric substrate; and, A copper layer with a thickness of 10 to 3000 nm is grown on the titanium layer.

3. The method for preparing a high thermal conductivity copper-clad substrate according to claim 1, characterized in that: The preparation method further comprises, before growing the metal layer on the insulating dielectric substrate, performing plasma surface activation treatment on the insulating dielectric substrate using a plasma surface modification gas.

4. The method for preparing a high thermal conductivity copper-clad substrate according to claim 1, characterized in that: The preparation method also includes the step of activating the insulating dielectric substrate and the copper foil after the plasma surface activation treatment with formic acid at a concentration of 5%-10% and a temperature of 20°C-60°C before placing the activated copper foil on the surface of the activated insulating dielectric substrate.

5. The method for preparing a high thermal conductivity copper-clad substrate according to claim 3, characterized in that: The plasma surface modification gas includes argon.

6. The method for preparing a high thermal conductivity copper-clad substrate according to claim 1, characterized in that: Metal layers are grown on two opposite surfaces of the insulating dielectric substrate.

7. The method for preparing a high thermal conductivity copper-clad substrate according to claim 1, characterized in that: The surface roughness of the copper layer The Ra value is 1 nm, and / or the surface roughness Ra value of the copper foil is 1 nm; and The insulating dielectric substrate and the copper foil are bonded together under vacuum conditions at a temperature of 250°C to form a copper-clad substrate.

8. The method for preparing a high thermal conductivity copper-clad substrate according to claim 1, characterized in that: The surface roughness of the copper layer The Ra value is 200 nm, and / or the surface roughness Ra value of the copper foil is 200 nm; and, The insulating dielectric substrate and the copper foil are bonded together under vacuum conditions at a temperature greater than 250°C to form a copper-clad substrate.

9. The method for preparing a high thermal conductivity copper-clad substrate according to claim 1, characterized in that: The step of bonding the insulating dielectric substrate and the copper foil to form the copper-clad substrate under vacuum conditions at a temperature greater than 150° C. includes bonding the insulating dielectric substrate and the copper foil to form the copper-clad substrate under vacuum conditions at a temperature of 200-250° C.

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