Copper sheet rapid oxidation method for optimizing DCB inter-island insulativity

Abstract

The invention relates to the technical field of copper-clad ceramic substrate processing, in particular to a copper sheet rapid oxidation method for optimizing DCB inter-island insulativity. Comprising the following steps that 1, a copper sheet is pretreated, specifically, the copper sheet is sequentially subjected to the technological processes of acid pickling, alkali washing oil removal, presoaking, roughening and film stripping, and a copper sheet A is obtained; 2, copper sheet oxidation, wherein the copper sheet A is oxidized in air, and a copper sheet B is obtained; and 3, sintering the copper sheet: sintering the copper sheet B at a high temperature to obtain a finished product. The preparation method has the beneficial effects that an interface product during sintering is mixed with insulating components through a rapid oxidation mode, so that the resistivity is increased, the insulativity is enhanced, and overlarge leakage current generated when high voltage is applied between islands is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of copper-clad ceramic substrate processing, in particular to a copper sheet rapid oxidation method for optimizing insulation between DCB islands. Background Art

[0002] The DCB process, full name Direct Copper Bonding, is a special process method that directly bonds copper foil to the surface of a ceramic substrate. The ceramic substrate with copper cladding manufactured by this process has high thermal conductivity, high electrical performance and high reliability, so it is widely used in electronic packaging and radiator manufacturing.

[0003] The basic principle of the DCB process is to introduce an appropriate amount of oxygen between copper and ceramic (aluminum oxide) before or during the bonding process. Within a certain temperature range, copper and oxygen form a Cu-O eutectic liquid, which can wet both the metal copper foil and the Al2O3 ceramic substrate well. After cooling to room temperature and solidifying, a strong bond can be formed between the two. The current common copper sheet pretreatment method is to pass oxygen in a high-temperature tunnel furnace, which has harsh process conditions and low production efficiency. In addition, this oxidation method will form a thicker oxide layer, resulting in the interface phase produced after sintering being mostly CuAlO2. CuAlO2 has a hexagonal crystal structure and is a transparent p-type semiconductor with a band gap range of 2.7 to 3.5eV and a low resistivity (1.4–74kΩ-cm), so it will cause the inter-island insulation of the DCB product pattern to be greatly reduced.

[0004] Therefore, in summary, in order to solve the above problems, the present invention provides a method for rapid oxidation of copper sheets for optimizing the insulation between DCB islands. Summary of the invention

[0005] The object of the present invention is to provide a method for rapid oxidation of copper sheets for optimizing the insulation between DCB islands, so as to solve the problems raised in the above-mentioned background technology.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A method for rapid oxidation of copper sheets for optimizing insulation between DCB islands comprises the following steps:

[0008] Step 1: Pretreatment of the copper sheet: The copper sheet is sequentially subjected to the processes of pickling, alkaline washing and degreasing, pre-impregnation, roughening, and film stripping to obtain copper sheet A;

[0009] Step 2: Copper sheet oxidation: Copper sheet A is oxidized in air to obtain copper sheet B;

[0010] Step 3: Sintering of copper sheet: Sinter copper sheet B at high temperature to obtain a finished product.

[0011] More optimally, the specific parameters of the pickling are: temperature 25-40° C., duration 30-45 seconds, and the pickling solution is 6-12wt% sulfuric acid. Pickling can remove oxides on the surface of the copper sheet.

[0012] More optimally, the specific parameters of the alkaline washing and degreasing are: temperature 40-50°C, duration 30-45s, and alkaline washing liquid is 8-12wt% sodium hydroxide solution. Alkaline washing and degreasing can remove fingerprints, grease, etc. on the surface of the copper sheet.

[0013] More optimally, the specific parameters of the pre-dip are: temperature 25-30°C, duration 15-30s, the pre-dip liquid is a benzotriazole aqueous solution with a concentration of 4±1vol%, so that a thin oxide layer is formed on the copper surface and benzotriazole (BTA) is evenly adsorbed on the lattice, so that it can react quickly and evenly after entering the roughening tank.

[0014] More optimally: the specific parameters of the roughening are: temperature 35-45°C, duration 40-60s, the ingredients of the roughening solution include the following components: 20±2vol% benzotriazole, 3±1vol% sulfuric acid, 2±1vol% hydrogen peroxide, and the rest is pure water. The oxidant (hydrogen peroxide) oxidizes copper into Cu2O, and then benzotriazole (BTA) and Cu2O form a protective organic metal film to isolate copper from the solution, preventing further reaction of copper. The organic metal film is continuously dissolved in the solution (sulfuric acid + hydrogen peroxide jointly form micro-etching on copper). After the thinner part of the metal film is dissolved, the copper in the lower layer will continue to be etched by the micro-etching solution, and the organic metal film is also continuously generated. The etched surface will become smaller and smaller, and finally a honeycomb structure will be formed, thereby improving the roughness of the copper surface and increasing the surface area during subsequent oxidation.

[0015] More optimally, the specific parameters of the film stripping are: temperature 40-55° C., duration 75-90 s, and the film stripping liquid is 2-7 wt % sodium hydroxide solution.

[0016] More optimally: the specific parameters of the oxidation are: peak temperature at 280-350°C, heating time at 30-60min, and holding time at 5-15min. Although both sides of the copper sheet are oxidized, the oxidation time is short and the oxidation layer is thin, so the oxidation layer on the non-sintered side can be removed in the subsequent wet process. In addition, the thinner oxidation layer can simultaneously precipitate CuAlO2 and CuAl2O4 as interface products during the subsequent sintering of the copper sheet and the ceramic sheet; the copper islands of the DCB product pattern have sufficient insulation, avoiding excessive leakage current when a high voltage is applied between the islands.

[0017] More optimally, the specific parameters of the high temperature sintering are: temperature 1065-1083°C, oxygen 100±10ppm.

[0018] More optimally: When DCB is sintered, there is a layer of amorphous Cu-Al-O glass phase on the interface, which crystallizes into interface products CuAlO2 and CuAl2O4 phases during annealing. The composition and purity of the precipitated phase are related to the ratio of Cu:Al:O and the rate of temperature change, that is, when Al is relatively excessive and Cu is lacking, and the temperature drops relatively quickly, it is easier to precipitate the CuAl2O4 phase. The CuAl2O4 phase is a chocolate brown spinel compound with a cubic crystal structure and an optical band gap of 4eV; on the one hand, when the CuAl2O4 content in the precipitated phase increases, the band gap energy will increase, that is, the resistivity between islands will increase. On the other hand, the alternating existence of CuAlO2 and CuAl2O4 in the precipitated phase will limit the conductivity of CuAlO2 to a smaller range, so that it will not be completely conductive and cause insulation failure.

[0019] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0020] 1. The efficiency of pre-oxidation of copper sheets is improved by using a high-temperature oven to quickly oxidize the copper sheets in an air atmosphere;

[0021] 2. Through the integration of the copper cleaning section, the surface of the copper sheet is roughened to obtain a larger surface roughness, increase its reaction area and wettability, and avoid the problem of insufficient oxidation caused by air oxidation;

[0022] 3. Through this rapid oxidation method, the interface product during sintering is mixed with insulating components, which increases its resistivity and enhances its insulation, thus avoiding excessive leakage current when high voltage is applied between islands. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0024] Figure 1 The XRD characterization results of the interface products of the poorly-insulated product obtained by conventional oxidation sintering in Comparative Example 1;

[0025] Figure 2 This is the XRD characterization result of the interface product of the well-insulated product obtained by fresh oxidation sintering in Example 3. DETAILED DESCRIPTION

[0026] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] It should be noted that there is no special restriction on the purchasing manufacturers of all the raw materials involved in the present invention, and they are all common and general raw materials and can be purchased directly.

[0028] Embodiment 1: A method for rapid oxidation of copper sheets to optimize insulation between DCB islands, comprising the following steps:

[0029] Step 1: Use a horizontal spray device to sequentially perform pickling, alkali washing, pre-impregnation, roughening, and film stripping operations on the copper sheet to obtain a copper sheet A; wherein the pickling is performed at 25°C, using 6wt% sulfuric acid, and cleaning for 30s to remove oxides on the surface of the copper sheet; the alkali washing is performed at 40°C, using 8wt% sodium hydroxide solution, and cleaning for 30s to remove fingerprints, grease, etc. on the surface of the copper sheet; the pre-impregnation is performed at 25°C for 15s, using a 4vol% benzotriazole aqueous solution; the roughening is performed at 35°C for 40s, using a mixed solution of benzotriazole, sulfuric acid, hydrogen peroxide, and pure water (20vol% benzotriazole, 3vol% sulfuric acid, 2vol% hydrogen peroxide, and the rest is pure water); the film stripping is performed at 40°C, using 2wt% sodium hydroxide solution, and cleaning for 75s;

[0030] Step 2: insert copper sheet A into the plug-in board rack, put it into an oven, and use air for oxidation, wherein the peak temperature is 280°C, the heating time is 30 minutes, and the heat preservation time is 5 minutes, to obtain copper sheet B;

[0031] Step 3: Pass the copper sheet B through a tunnel furnace and sinter it at a high temperature of 1065°C and 100ppm oxygen to combine it with the ceramic sheet to obtain a finished product.

[0032] Embodiment 2: A method for rapid oxidation of a copper sheet for optimizing insulation between DCB islands, comprising the following steps:

[0033] Step 1: Use a horizontal spray device to sequentially perform pickling, alkali washing, pre-impregnation, roughening, and film stripping operations on the copper sheet to obtain a copper sheet A; wherein the pickling is performed at 40°C, using 12wt% sulfuric acid, and cleaning for 45s to remove oxides on the surface of the copper sheet; the alkali washing is performed at 50°C, using 12wt% sodium hydroxide solution, and cleaning for 45s to remove fingerprints, grease, etc. on the surface of the copper sheet; the pre-impregnation is performed at 30°C for 30s, using a 4vol% benzotriazole aqueous solution; the roughening is performed at 45°C for 60s, using a mixed solution of benzotriazole, sulfuric acid, hydrogen peroxide, and pure water (20vol% benzotriazole, 3vol% sulfuric acid, 2vol% hydrogen peroxide, and the rest is pure water); the film stripping is performed at 55°C, using a 7wt% sodium hydroxide solution, and cleaning for 90s;

[0034] Step 2: insert copper sheet A into the plug-in board rack, put it into an oven, and use air for oxidation, wherein the peak temperature is 350°C, the heating time is 60 minutes, and the heat preservation time is 15 minutes, to obtain copper sheet B;

[0035] Step 3: Pass the copper sheet B through a tunnel furnace and sinter it at a high temperature of 1083°C and 100ppm oxygen to combine it with the ceramic sheet to obtain a finished product.

[0036] Embodiment 3: A method for rapid oxidation of copper sheets for optimizing insulation between DCB islands, comprising the following steps:

[0037] Step 1: Use a horizontal spray device to sequentially perform pickling, alkali washing, pre-impregnation, roughening, and film stripping operations on the copper sheet to obtain a copper sheet A; wherein the pickling is performed at 30°C, using 10wt% sulfuric acid, and cleaning for 40s to remove oxides on the surface of the copper sheet; the alkali washing is performed at 45°C, using 10wt% sodium hydroxide solution, and cleaning for 40s to remove fingerprints, grease, etc. on the surface of the copper sheet; the pre-impregnation is performed at 28°C for 20s, using a 4vol% benzotriazole aqueous solution; the roughening is performed at 40°C for 50s, using a mixed solution of benzotriazole, sulfuric acid, hydrogen peroxide, and pure water (20vol% benzotriazole, 3vol% sulfuric acid, 2vol% hydrogen peroxide, and the rest is pure water); the film stripping is performed at 50°C, using a 5wt% sodium hydroxide solution, and cleaning for 80s;

[0038] Step 2: insert copper sheet A into the plug-in board rack, put it into an oven, and use air for oxidation, wherein the peak temperature is 300°C, the heating time is 50 minutes, and the heat preservation time is 10 minutes, to obtain copper sheet B;

[0039] Step 3: Pass the copper sheet B through a tunnel furnace and sinter it at a high temperature of 1070°C and 100ppm oxygen to combine it with the ceramic sheet to obtain a finished product.

[0040] Comparative Example 1: The copper sheet is not subjected to a roughening operation, as follows:

[0041] Step 1: Use a horizontal spray device to sequentially perform acid washing and alkali washing operations on the copper sheet to obtain copper sheet A; wherein the acid washing is performed at 30° C. using 10wt% sulfuric acid for 40 seconds to remove oxides on the surface of the copper sheet; the alkali washing is performed at 45° C. using 10wt% sodium hydroxide solution for 40 seconds to remove fingerprints, grease, etc. on the surface of the copper sheet;

[0042] Step 2: Place copper sheet A flat on the alloy jig, and then place the alloy jig flat on the mesh belt of the tunnel furnace; pass through each temperature zone of the tunnel furnace in turn, where the peak temperature of the oxidation zone is 810°C, the oxygen flow rate is 100mL / min, and the mesh belt transmission speed is 175mm / min, to obtain copper sheet B;

[0043] Step 3: Pass the copper sheet B through a tunnel furnace and sinter it at a high temperature of 1070°C and 100ppm oxygen to combine it with the ceramic sheet to obtain a finished product.

[0044] Detection experiment: 10 master plates were prepared by the same process as in Example 3. After the pattern transfer was completed, a voltage of 1000 V was applied between the independent copper islands to measure the leakage current (nA) between the copper islands. The measured data are shown in the following table:

[0045]

[0046] Table 1

[0047] 18 motherboards were prepared by the same process as in Comparative Example 1. After the pattern transfer was completed, a voltage of 1000 V was applied between the independent copper islands to measure the leakage current (μA) between the copper islands. The measured data are shown in the following table:

[0048]

[0049]

[0050] Table 2

[0051] Conclusion: Comparative Example 1 adopts conventional oxidation sintering. From the XRD characterization results, it can be seen that its interface product is only CuAlO2, and the measured leakage current between copper islands is far beyond the normal value (normal value <100nA); Example 3 adopts new oxidation and sintering. From the XRD characterization results, it can be seen that its interface products are CuAlO2 and CuAl2O4, and the measured leakage current between copper islands is within the normal value and can meet the use requirements.

[0052] In the description of the specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0053] Finally, it should be noted that the above description is only a preferred example of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for rapid oxidation of copper sheets to optimize the insulation between DCB islands, characterized in that: The following steps are involved: Step 1: Pretreatment of the copper sheet: The copper sheet is sequentially subjected to the processes of pickling, alkaline washing and degreasing, pre-impregnation, roughening, and film stripping to obtain copper sheet A; Step 2: Copper sheet oxidation: Copper sheet A is oxidized in air to obtain copper sheet B; Step 3: Sintering of copper sheet: Sinter copper sheet B at high temperature to obtain a finished product.

2. A method for rapid oxidation of copper sheets for optimizing insulation between DCB islands according to claim 1, characterized in that: The specific parameters of the pickling are: temperature 25-40° C., duration 30-45 seconds, and the pickling liquid is 6-12wt% sulfuric acid.

3. A method for rapid oxidation of copper sheets for optimizing insulation between DCB islands according to claim 1, characterized in that: The specific parameters of the alkaline washing and oil removal are: temperature 40-50°C, duration 30-45s, and the alkaline washing liquid is 8-12wt% sodium hydroxide solution.

4. A method for rapid oxidation of copper sheets for optimizing insulation between DCB islands according to claim 1, characterized in that: The specific parameters of the pre-immersion are: temperature 25-30° C., duration 15-30 s, and the pre-immersion liquid is a benzotriazole aqueous solution with a concentration of 4±1 vol%.

5. The method for rapid oxidation of copper sheets for optimizing insulation between DCB islands according to claim 1, characterized in that: The specific parameters of the roughening are: temperature 35-45° C., duration 40-60 s, and the ingredients of the roughening solution include the following components: 20±2 vol% benzotriazole, 3±1 vol% sulfuric acid, 2±1 vol% hydrogen peroxide, and the rest is pure water.

6. A method for rapid oxidation of copper sheets for optimizing insulation between DCB islands according to claim 1, characterized in that: The specific parameters of the film stripping are: temperature 40-55° C., duration 75-90 s, and the film stripping liquid is 2-7 wt % sodium hydroxide solution.

7. A method for rapid oxidation of copper sheets for optimizing insulation between DCB islands according to claim 1, characterized in that: The specific parameters of the oxidation are: peak temperature at 280-350° C., heating time at 30-60 min, and heat preservation time at 5-15 min.

8. The method for rapid oxidation of copper sheets for optimizing insulation between DCB islands according to claim 1, characterized in that: The specific parameters of the high temperature sintering are: temperature 1065-1083° C., oxygen 100±10 ppm.

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