Method for filling through hole of DPC ceramic substrate

Abstract

The invention discloses a DPC ceramic substrate through hole filling method, which comprises the following steps: S1, laser drilling: a through hole is drilled in a ceramic substrate by adopting laser, and parameters of the laser are configured to enable the inner wall of the through hole to form a microscopic rough surface; s2, cleaning: cleaning the ceramic substrate with the through holes; s3, activating and forming a metal transition layer: performing catalytic activation treatment on the cleaned ceramic substrate, and then chemically plating a metal transition layer on the inner wall of the through hole; s4, magnetron sputtering of a seed layer: sequentially depositing a bonding layer and a conductive seed layer on the surface of the ceramic substrate coated with the metal transition layer and in the through hole by adopting a magnetron sputtering mode; and S5, pattern electroplating and hole filling: performing pattern thickening on the conductive seed layer through an electroplating process until the through hole is completely filled with the conductive metal. According to the invention, the laser coarsening and the chemical nickel plating transition layer are combined, so that the difficulty in binding force between the metal layer and the ceramic substrate is fundamentally solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fixing parts, and particularly relates to a method for filling a through hole of a DPC ceramic substrate. BACKGROUND

[0002] In high-end electronic packaging such as power semiconductors and radio frequency devices, DPC ceramic substrates are widely used due to their excellent heat conduction, insulation and mechanical properties. In order to realize three-dimensional interconnection, conductive through holes need to be made on the ceramic substrate.

[0003] In the prior art, ceramic through hole metallization often faces two major challenges: first, the ceramic surface has high chemical inertness, and the metal layer has poor adhesion; second, when the through hole has a large depth-diameter ratio, it is difficult to achieve uniform and void-free metal filling in the hole. By using the direct sputtering method, due to the small diameter of the through hole and the poor adhesion of the ceramic, a plating layer of about 1000 angstroms can generally be achieved, which has poor conductivity and a long pattern plating time. SUMMARY

[0004] TECHNICAL PROBLEM The purpose of the present application is to make up for the shortcomings of the prior art, and provide a method for filling a through hole of a DPC ceramic substrate.

[0005] TECHNICAL SCHEME In order to achieve the above-mentioned purpose, the present application provides the following technical scheme: a method for filling a through hole of a DPC ceramic substrate, comprising the following steps: S1. Laser drilling: laser drilling a through hole on a ceramic substrate, wherein the parameters of the laser are configured to form a micro-rough surface on the inner wall of the through hole; S2. Cleaning: cleaning the ceramic substrate with the through hole; S3. Activation and formation of a metal transition layer: catalytically activating the cleaned ceramic substrate, and then chemically plating a metal transition layer on the inner wall of the through hole; S4. Magnetic control sputtering seed layer: using a magnetic control sputtering method to sequentially deposit a bonding layer and a conductive seed layer on the surface of the ceramic substrate and in the through hole covered with the metal transition layer; S5. Pattern plating hole filling: pattern thickening on the conductive seed layer by electroplating process until the through hole is completely filled with conductive metal.

[0006] In the above, the laser is ultraviolet laser or picosecond laser, and the surface roughness Ra of the micro-rough surface is 0.5-3 microns.

[0007] In the above, in step S2, the cleaning comprises: S2a. Ultrasonic cleaning of the ceramic substrate using an alkaline solution; S2b. Dry cleaning and surface activation of the ceramic substrate by oxygen and / or argon plasma.

[0008] In step S3, the catalytic activation treatment is a colloidal palladium activation method, specifically including: The cleaned ceramic substrate is immersed in a palladium activation solution for 3 to 10 minutes, allowing the palladium catalytic nucleus to be adsorbed on the surface.

[0009] In the above, the metal transition layer is a chemical nickel plating layer.

[0010] In the above, the thickness of the chemical nickel plating layer is 3 to 7 microns.

[0011] In the above, after forming the chemical nickel plating layer, it further includes the step of heat treatment at 250 to 400°C in an inert atmosphere or vacuum environment.

[0012] In step S4, the bonding layer is a titanium layer or a titanium-tungsten alloy layer with a thickness of 0.1 to 0.3 microns; the conductive seed layer is a copper layer with a thickness of 0.5 to 2 microns.

[0013] In step S5, the patterned electroplating hole filling specifically includes: S5a. Apply dry film on the conductive seed layer, expose and develop to form an electroplating pattern window; S5b. Fill the through hole with copper by electroplating and thicken the surface circuit pattern; S5c. Remove the dry film and remove the conductive seed layer and bonding layer not covered by the patterned electroplated copper through a rapid etching process.

[0014] Advantages: Compared with the prior art, the method for filling holes in DPC ceramic substrate through holes has the following advantages: Strong adhesion: laser roughening combined with chemical nickel plating transition layer fundamentally solves the problem of adhesion between metal layer and ceramic substrate.

[0015] High hole filling quality: uniform transition layer and seed layer ensure that electroplated copper can completely fill the high aspect ratio through hole without voids or gaps.

[0016] Good process compatibility: the whole process is a low-temperature process (main steps below 95°C), which avoids thermal stress damage to the ceramic substrate and possible sensitive devices caused by high temperature.

[0017] Excellent reliability: the formed metal through hole structure is dense, and the thermal expansion coefficient matching is better, which performs well in thermal cycle and other reliability tests.

[0018] Additional advantages, objects, and features of the application will be apparent to those skilled in the art upon examination of the following detailed description, it being understood that each BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The whole process of the present application is shown in the schematic diagram. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0021] As Figure 1 shown, the present application provides a technical solution: a method for filling a through hole of a DPC ceramic substrate.

[0022] Substrate and drilling: a 96% alumina ceramic substrate with a thickness of 0.5 and a diameter of 100 microns is used. An ultraviolet laser (wavelength 355 nm) is used, with a pulse energy of 20 μJ, a frequency of 30 kHz, and a scanning speed of 500 mm / s, to drill a through hole with a diameter of 150 μm. After drilling, the roughness Ra of the inner wall of the through hole is about 1.2 μm.

[0023] Cleaning: first, ultrasonic cleaning in an alkaline cleaning solution at 50°C for 10 minutes, then rinsing with deionized water. Then put into a plasma cleaning machine, use O2 / Ar mixed gas at 200 Pa pressure and 200 W power for 5 minutes.

[0024] Activation and electroless nickel plating: immerse the substrate in a palladium activation solution (pH=1.5) for 3-5 minutes. Then, immerse in an electroless nickel plating solution (using sodium hypophosphite as a reducing agent, pH 4.8) at 85°C for 40 minutes to obtain a layer of Ni-P alloy with a thickness of about 3 μm and a phosphorus content of about 9%.

[0025] Then heat treatment at 300°C for 30 minutes.

[0026] Because the outer surface of the ceramic substrate removed from the through hole is smooth, and the inner wall of the through hole is rough under the action of the laser, the activation solution can stay in the through hole, and the other smooth outer surface is not easy to stay, and is easy to be cleaned.

[0027] Magnetron sputtering: In a magnetron sputtering apparatus, a 3000 angstrom thick titanium layer is first sputtered at a rate of 0.3 nm / s, and then an 8000 angstrom thick copper layer is sputtered at a rate of 0.8 nm / s.

[0028] Pre-plating copper: Its core function is to perform a slight global thickening on the fragile sputtered copper seed layer, transforming the sputtered thin film into a thicker, continuous plating layer, filling microscopic defects, and increasing conductivity.

[0029] Pattern plating: A 25μm thick dry film is deposited on the sputtered seed layer. After exposure and development, the vias and the circuit pattern areas requiring thickening are exposed. Electroplating is performed in a sulfate copper plating solution at a current density of 2.0 ASD for 180 minutes, completely filling the vias and increasing the surface pattern copper thickness to approximately 55μm. Finally, the dry film is removed with NaOH solution, and the seed layer and titanium layer on the surface are rapidly removed with an etching solution.

[0030] The through-hole resistance obtained in this embodiment was less than 2mΩ after testing. No cracking or significant increase in resistance was observed after passing the thermal shock test (-55℃~125℃, 1000 cycles).

[0031] It should be noted that in this document, the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used solely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "fixed," "installed," "connected," and "linked" should be interpreted broadly. For example, "installed" can be a fixed connection, a detachable connection, or an integral connection; "connected" can be a mechanical connection or an electrical connection; "linked" can be a direct connection, an indirect connection through an intermediate medium, or a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for filling through-holes in a DPC ceramic substrate, characterized in that, Includes the following steps: S1. Laser drilling: A laser is used to drill through holes in a ceramic substrate, wherein the parameters of the laser are configured to create a micro-rough surface on the inner wall of the through hole; S2. Cleaning: Clean the ceramic substrate with through holes; S3. Activation and formation of metal transition layer: The cleaned ceramic substrate is subjected to catalytic activation treatment, and then a metal transition layer is chemically plated on the inner wall of the through hole; S4. Magnetron sputtering seed layer: On the surface of the ceramic substrate covered with the metal transition layer and inside the via, a bonding layer and a conductive seed layer are sequentially deposited by magnetron sputtering. S5. Patterned Electroplating Filling: The conductive seed layer is patterned and thickened by electroplating until the through hole is completely filled with conductive metal.

2. The method according to claim 1, characterized in that, In step S1, the laser is an ultraviolet laser or a picosecond laser, and the surface roughness Ra of the micro-rough surface is 0.5 μm to 3 μm.

3. The method according to claim 1, characterized in that, In step S2, the cleaning includes: S2a. Ultrasonic cleaning of the ceramic substrate using an alkaline solution; S2b. Dry cleaning and surface activation of the ceramic substrate using oxygen and / or argon plasma.

4. The method according to claim 1, characterized in that, In step S3, the catalytic activation treatment is a palladium activation method, specifically including: The cleaned ceramic substrate is immersed in palladium activation solution for 3 to 10 minutes to allow palladium catalytic nuclei to be adsorbed onto the surface.

5. The method according to claim 4, characterized in that, The metal transition layer is a chemically plated nickel layer.

6. The method according to claim 5, characterized in that, The thickness of the electroless nickel plating layer is 3 μm to 7 μm.

7. The method according to claim 6, characterized in that, After forming the electroless nickel plating layer, the process further includes a heat treatment step at 250°C to 400°C in an inert atmosphere or vacuum environment.

8. The method according to claim 1, characterized in that, In step S4, the bonding layer is a titanium layer or a titanium-tungsten alloy layer with a thickness of 0.1 μm to 0.3 μm; the conductive seed layer is a copper layer with a thickness of 0.5 μm to 2 μm.

9. The method according to claim 1, characterized in that, In step S5, the pattern electroplating filling specifically includes: S5a. A dry film is attached to the conductive seed layer, and then exposed and developed to form an electroplated pattern window; S5b. Fill the through-holes and thicken the surface circuit pattern by electroplating copper; S5c. Remove the dry film and remove the conductive seed layer and bonding layer that are not covered by the patterned copper plating through a rapid etching process.

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