JP3824044B2 - Silicon nitride circuit board manufacturing method - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は窒化ケイ素回路基板、特に高熱伝導率及び高信頼性が要求される自動車、電車、新幹線などの交通手段に使用するパワーモジュール及びペルチェ素子の実装に最適な窒化ケイ素回路基板製造方法に関するものである。
【０００２】
【従来の技術】
従来、パワーモジュール及びペルチェ素子の実装には銅張り窒化アルミニウム回路基板が広く使用されている。
【０００３】
銅と窒化アルミニウムとはその熱膨張係数が互いに異なるため、高温で接合し室温で冷却した場合、基板の内部で大きな熱応力が発生する。この熱応力の影響で、使用中に窒化アルミニウム基板の内部にクラックが発生し、基板の表裏に貫通するクラックによる絶縁破壊が発生する。
【０００４】
クラックの発生を防止する為に窒化ケイ素回路基板が開発されるようになった。窒化ケイ素は窒化アルミニウムに比べてクラック発生に対する抵抗力が大きい。材料のクラックの進展に対する抵抗力を通常破壊靱性値で評価するが、窒化ケイ素の破壊靱性値は窒化アルミニウムの２倍以上もあるため、窒化ケイ素回路基板の使用により、クラックの発生は押さえられ、基板の信頼性は大きく改善された。
【０００５】
特開平４−２１２４４１号公報、特開平７−４８１７４号公報に窒化ケイ素回路基板が開示されている。この例では、窒化ケイ素回路基板にＡｌ、Ｙ、Ｙｂ、Ｍｇ、Ｚｒ、Ｔｉ、 Ｈｆ、 Ｖ、Ｎｂ、Ｔａ、 Ｃｒ、 Ｍｏ、Ｗなどの酸化物、炭化物、窒化物、けい化物、硼化物からなる群より選択された少なくとも１種を添加し、焼結している。
【０００６】
また、特開平９−６９５９０号公報、特開平９−６９６７２号公報にも窒化ケイ素回路基板及びその製造方法が開示されている。
【０００７】
【発明が解決しようとする課題】
近年環境保護の機運が高まり、電子機器作動時のロスの低減に対する要望は日増しに強くなっている。そのため基板の絶縁抵抗改善に対する要望も高まってきている。
【０００８】
また、パワーモジュールの使用時には基板の温度が最高125℃に達する場合があり、高温での絶縁抵抗も重要視されるようになったが、従来のものは高温での絶縁抵抗が低く、所期の目的を達成できない欠点があった。
【０００９】
本発明者はかかる問題を解決するために鋭意研究した結果、窒化ケイ素基板の上に活性金属ろう材を介して銅回路を形成したのち、窒素雰囲気に於いて加熱することによって、窒化ケイ素回路基板の絶縁抵抗が向上することを見出した。
【００１０】
本発明はかかる知見を基に成されたものである。
【００１１】
【課題を解決するための手段】
本発明者が検討したところ絶縁抵抗が低いと基板の使用時に頻繁にリーク電流が発生し、作動時の誤動作を起こす恐れがある。絶縁抵抗は２０００ＭΩ以上であることが必要で好ましくは１００００ＭΩ以上が良いことがわかった。２０００ＭΩ以上で作動時のロスが１／２０以下に低減できる。
【００１２】
本発明の窒化ケイ素回路基板製造方法は、窒化ケイ素基板に活性金属を含むろう材を介して銅板を対接する工程と、ろう材の融点以上、銅の融点以下に加熱して上記窒化ケイ素基板に上記銅板を接合する工程と、上記銅板にエッチングにより銅回路を形成する工程と、更に窒素雰囲気中３３０℃以上で加熱する工程とより成ることを特徴とする。
【００１３】
上記ろう材の活性金属は、Ｔｉ、Ｚｒ、またはＨｆを含むことを特徴とする。
【００１４】
上記窒化ケイ素基板は、窒化ケイ素にＡｌ、Ｙ、Ｙｂ、Ｍｇ、Ｚｒ、Ｔｉ、 Ｈｆ、Ｖ、Ｎｂ、Ｔａ、 Ｃｒ、 Ｍｏ、Ｗなどの酸化物、炭化物、窒化物、けい化物、硼化物からなる群より選択された少なくとも１種を添加し、焼結して形成したものであることを特徴とする。
【００１５】
上記窒化ケイ素基板と銅板は、窒素雰囲気中で３８０℃以上の温度で加熱処理されることを特徴とする。
【００１６】
上記ろう材はＡｇ−Ｃｕ−Ｔｉペースト状ろう材であることを特徴とする。
【００１７】
上記銅回路を形成する工程のエッチング液として、塩化鉄の溶液で不要部分の銅を溶かし、次いでフッ化アンモニアを含む硝酸溶液で不要なろう材を除去することを特徴とする。
【００１８】
上記ろう材は、有機バインダー及び溶剤を含み、銅板を接合する工程の前に、低温で加熱しろう材中の有機バインダー及び溶剤を蒸発せしめる工程を有することを特徴とする。
【００１９】
【発明の実施の形態】
以下本発明の実施例を説明する。
【００２０】
本発明においては、窒化ケイ素基板の両面にＡｇ−Ｃｕ−Ｔｉペースト状ろう材をスクリーン印刷法で全面或いはパターン形状に印刷した後、この窒化ケイ素基板をその両面に銅板を対接した状態で真空中において低温で加熱し、ペースト状ろう材中の有機バインダー及び溶剤を蒸発させてから、更にろう材の融点以上、銅の融点以下の高温度に加熱し、銅板と窒化ケイ素基板をろう接する。
【００２１】
次いで、銅板の表面にエッチングレジストを所望のパターン形状に印刷し、塩化鉄の溶液でエッチングして不要部分の銅を溶かし、銅回路を形成する。
【００２２】
次いで、フッ化アンモニウムと硝酸の混液に銅回路の形成された回路基板を浸漬し、基板上に付着している余分のろう材を除去する。
【００２３】
最後に、上述の方法で作製した銅張り窒化ケイ素回路基板を窒素雰囲気に於いて加熱し、高温での回路基板の絶縁抵抗を高める。
【００２４】
なお、窒素中で加熱すると銅板の表面は黒く変色する。この変色層を除去するためには、硫酸と硝酸との混液でエッチング処理すれば良い。
【００２５】
更に作製した銅張り窒化ケイ素回路基板の一部又は全面に対して、無電解メッキ法でニッケルめっき層を形成しても良い。
【００２６】
本発明によれば窒素雰囲気中での加熱は絶縁抵抗の向上に有効であることを示しているが、其の理由についてはまだ解明されていない。なお、比較例に示すように水素を含む窒素雰囲気で同じ温度に加熱する場合絶縁抵抗はむしろ悪くなったことと、空気中に於いては水の蒸発温度以上の125 ℃で長時間加熱しても絶縁抵抗の改善は見られなかったことから、エッチングの時に基板の表面に付着している水の影響ではないと考えられる。
【００２７】
また、ろう接時に窒化ケイ素の分解が起こり、基板の表面にわずかなケイ素層が形成された可能性があり、これが何等かの働きをしていると思われる。
【００２８】
（実施例１）
【００２９】
銀粉72重量部、銅粉28重量部、合計１００重量部に対して、Ｔｉ粉末２重量部及びバインダー７重量部、溶剤８重量部を添加し、ペースト状のろう材を作成した。
【００３０】
このろう材を厚さ0.3mm の窒化ケイ素基板の一面上に所定のパターン形状に厚さ２０μｍ印刷し、８０℃に加熱して溶剤分を蒸発し、ろう材を乾燥させた。ついでに反対面も同じようにろう材を印刷した。
【００３１】
このろう材の印刷された基板の両面に厚さ0.25mmの銅板を積層し、 10 -5torrの真空中に於いて６００℃で３時間保温し、ろう材中のバインダーを十分に除去してから８３０℃に加熱し、３０分間保温して銅板と窒化ケイ素基板をろう接し、次いで、銅板の表面にエッチングレジストを所定のパターン状に印刷し、塩化鉄の溶液でエッチングして不要部分の銅を溶かし、所定の回路パターンを形成した。
【００３２】
次いで、この回路基板を１０％のフッ化アンモニアを含む硝酸溶液に浸漬し、窒化ケイ素回路基板の表面に付着している不要なろう材を除去した。
【００３３】
次いで、この基板を窒素雰囲気連続炉で３０分かけて３３０℃に加熱し、１０分間保温してから、２０分かけて室温に冷却した。
【００３４】
次いで、窒素雰囲気中で加熱された基板を硫酸20％と硝酸10％の水溶液に浸漬し、銅表面の変色層を除去し、本発明の銅張り窒化ケイ素回路基板を作製した。この回路基板の１２５℃での絶縁抵抗を測定したところ、２０００ＭΩ以上有ることが分かった。
【００３５】
（実施例２）
【００３６】
実施例１の工程中窒素雰囲気炉での処理温度を３８０℃にした以外は実施例１と同一にした。この銅張窒化ケイ素回路基板の１２５℃の絶縁抵抗を測定したところ、１００００ＭΩ以上あることがわかった。
【００３７】
（実施例３）
【００３８】
実施例１と同じ工程を施した後、通常の無電解めっき法で銅板の上に厚み３μｍのニッケルめっき層を形成した。この銅張り窒化ケイ素回路基板の１２５℃の絶縁抵抗を測定したところ、１００００ＭΩ以上あることが分かった。
【００３９】
（比較例１）
【００４０】
実施例１の工程中、基板を窒素雰囲気中で加熱処理することを除いて実施例１と同一に処理した。この銅張り窒化ケイ素回路基板の１２５℃の絶縁抵抗を測定したところ、１００ＭΩ未満であることが分かった。
【００４１】
（比較例２）
【００４２】
実施例１の工程中基板を窒素雰囲気中で加熱温度が３２０℃であることを除いて実施例１と同一に処理した。この銅張り窒化ケイ素回路基板の１２５℃の絶縁抵抗を測定したところ１００ＭΩ未満であることがわかった。
【００４３】
（比較例３）
【００４４】
実施例１の工程中、基板を窒素雰囲気連続炉で加熱処理する代りに空気中において１２５℃で４時間加熱したことを除いて実施例１と同一に処理した。この銅張り窒化ケイ素回路基板の１２５℃の絶縁抵抗を測定したところ、１００ＭΩ未満であることが分かった。
【００４５】
（比較例４）
【００４６】
実施例１の工程中、上記加熱処理を水素20％、窒素80％の雰囲気中で行ったことを除いて実施例１と同一に処理した。この銅張り窒化ケイ素回路基板の１２５℃の絶縁抵抗を測定したところ、１ＭΩ未満であることが分かった。
【００４７】
表１は、上記実施例及び比較例におけるサンプル１〜５を比較した表である。
【００４８】
【表１】
【発明の効果】
上記のように本発明によれば、窒素中での加熱処理によって１２５℃においても高絶縁抵抗を有する銅張り窒化ケイ素回路基板を作製でき、この回路基板を使って組み立てたパワーモジュールの作動時のロスを大幅に低下させる大きな効果が得られる。[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a silicon nitride circuit board, and more particularly to a power module used for transportation such as automobiles, trains, and bullet trains that require high thermal conductivity and high reliability, and a silicon nitride circuit board manufacturing method optimal for mounting a Peltier device. It is.
[0002]
[Prior art]
Conventionally, copper-clad aluminum nitride circuit boards have been widely used for mounting power modules and Peltier elements.
[0003]
Since copper and aluminum nitride have different thermal expansion coefficients, large thermal stresses are generated inside the substrate when they are bonded at a high temperature and cooled at room temperature. Under the influence of this thermal stress, cracks are generated inside the aluminum nitride substrate during use, and dielectric breakdown occurs due to cracks penetrating the front and back of the substrate.
[0004]
Silicon nitride circuit boards have been developed to prevent the occurrence of cracks. Silicon nitride has a greater resistance to cracking than aluminum nitride. The resistance against the development of cracks in the material is usually evaluated by the fracture toughness value. Since the fracture toughness value of silicon nitride is more than twice that of aluminum nitride, the use of a silicon nitride circuit board suppresses the occurrence of cracks. Substrate reliability has been greatly improved.
[0005]
Japanese Patent Laid-Open Nos. 4-212441 and 7-48174 disclose silicon nitride circuit boards. In this example, the silicon nitride circuit board is made of oxides, carbides, nitrides, silicides, borides such as Al, Y, Yb, Mg, Zr, Ti, Hf, V, Nb, Ta, Cr, Mo, and W. At least one selected from the group is added and sintered.
[0006]
Japanese Patent Laid-Open Nos. 9-69590 and 9-69672 also disclose a silicon nitride circuit board and a method for manufacturing the same.
[0007]
[Problems to be solved by the invention]
In recent years, the demand for environmental protection has increased, and the demand for reducing the loss during the operation of electronic devices has been increasing day by day. Therefore, there is an increasing demand for improving the insulation resistance of the substrate.
[0008]
In addition, when the power module is used, the substrate temperature may reach up to 125 ° C, and insulation resistance at high temperatures has become important. Conventional products have low insulation resistance at high temperatures, and are expected There was a drawback that could not achieve the purpose.
[0009]
As a result of diligent research to solve such problems, the present inventor formed a copper circuit on a silicon nitride substrate through an active metal brazing material, and then heated in a nitrogen atmosphere to thereby form a silicon nitride circuit substrate. It has been found that the insulation resistance is improved.
[0010]
The present invention has been made based on such knowledge.
[0011]
[Means for Solving the Problems]
As a result of studies by the present inventor, if the insulation resistance is low, a leak current frequently occurs when the substrate is used, which may cause malfunction during operation. It has been found that the insulation resistance needs to be 2000 MΩ or more, and preferably 10,000 MΩ or more. Loss during operation can be reduced to 1/20 or less at 2000 MΩ or more.
[0012]
Silicon nitride circuit board manufacturing method of the present invention includes the steps of contacting pair copper plate via a brazing material containing an active metal on a silicon nitride substrate, above the melting point of the brazing material, the silicon nitride substrate is heated to below the melting point of copper to the step of bonding the copper plate, and forming a copper circuit by etching the copper plate, wherein more adult Rukoto the process of heating further above 330 ° C. in a nitrogen atmosphere.
[0013]
The active metal of the brazing material contains Ti, Zr, or Hf .
[0014]
The silicon nitride substrate is made of silicon nitride such as Al, Y, Yb, Mg, Zr, Ti, Hf, V, Nb, Ta, Cr, Mo, W, and other oxides, carbides, nitrides, silicides, and borides. It is characterized in that it is formed by adding at least one selected from the group consisting of and sintering.
[0015]
The silicon nitride substrate and the copper plate are heat-treated at a temperature of 380 ° C. or higher in a nitrogen atmosphere .
[0016]
The brazing material is an Ag-Cu-Ti paste brazing material.
[0017]
As an etching solution for forming the copper circuit, an unnecessary portion of copper is dissolved with an iron chloride solution, and then an unnecessary brazing material is removed with a nitric acid solution containing ammonia fluoride .
[0018]
The brazing material contains an organic binder and a solvent, and has a step of evaporating the organic binder and the solvent in the brazing material by heating at a low temperature before the step of joining the copper plates .
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Examples of the present invention will be described below.
[0020]
In the present invention, an Ag-Cu-Ti paste brazing material is printed on both surfaces of a silicon nitride substrate by screen printing on a whole surface or a pattern shape, and then the silicon nitride substrate is vacuum-bonded with a copper plate in contact with both surfaces. After heating at a low temperature to evaporate the organic binder and solvent in the paste-like brazing material, it is further heated to a high temperature not lower than the melting point of the brazing material and not higher than the melting point of copper to braze the copper plate and the silicon nitride substrate.
[0021]
Next, an etching resist is printed in a desired pattern shape on the surface of the copper plate, and an unnecessary portion of copper is dissolved by etching with an iron chloride solution to form a copper circuit.
[0022]
Next, the circuit board on which the copper circuit is formed is immersed in a mixed solution of ammonium fluoride and nitric acid to remove excess brazing material adhering to the board.
[0023]
Finally, the copper-clad silicon nitride circuit board produced by the above method is heated in a nitrogen atmosphere to increase the insulation resistance of the circuit board at a high temperature.
[0024]
When heated in nitrogen, the surface of the copper plate turns black. In order to remove the discolored layer, an etching process may be performed with a mixed solution of sulfuric acid and nitric acid.
[0025]
Furthermore, a nickel plating layer may be formed by an electroless plating method on part or the entire surface of the produced copper-clad silicon nitride circuit board.
[0026]
According to the present invention, it has been shown that heating in a nitrogen atmosphere is effective in improving the insulation resistance, but the reason has not yet been elucidated. In addition, as shown in the comparative example, when heating to the same temperature in a nitrogen atmosphere containing hydrogen, the insulation resistance rather deteriorated, and in the air, it was heated for a long time at 125 ° C, which is higher than the evaporation temperature of water. However, since the insulation resistance was not improved, it is considered that it is not an influence of water adhering to the surface of the substrate at the time of etching.
[0027]
In addition, silicon nitride may be decomposed during brazing, and a slight silicon layer may be formed on the surface of the substrate, which seems to have some function.
[0028]
Example 1
[0029]
2 parts by weight of Ti powder, 7 parts by weight of binder and 8 parts by weight of solvent were added to 72 parts by weight of silver powder and 28 parts by weight of copper powder, to prepare a paste-like brazing material.
[0030]
This brazing material was printed on one surface of a 0.3 mm thick silicon nitride substrate in a predetermined pattern shape with a thickness of 20 μm, heated to 80 ° C. to evaporate the solvent, and the brazing material was dried. The other side was printed with the same brazing material.
[0031]
A copper plate with a thickness of 0.25 mm was laminated on both sides of the printed board of the brazing material and kept at 600 ° C. for 3 hours in a vacuum of 10 −5 torr to sufficiently remove the binder in the brazing material. Then, the copper plate and the silicon nitride substrate are brazed with each other by heating to 830 ° C., and then an etching resist is printed in a predetermined pattern on the surface of the copper plate and etched with an iron chloride solution to remove unnecessary portions of copper. Was melted to form a predetermined circuit pattern.
[0032]
Next, this circuit board was immersed in a nitric acid solution containing 10% ammonia fluoride to remove unnecessary brazing material adhering to the surface of the silicon nitride circuit board.
[0033]
Next, the substrate was heated to 330 ° C. in a nitrogen atmosphere continuous furnace over 30 minutes, kept at temperature for 10 minutes, and then cooled to room temperature over 20 minutes.
[0034]
Next, the substrate heated in a nitrogen atmosphere was immersed in an aqueous solution of 20% sulfuric acid and 10% nitric acid to remove the discolored layer on the copper surface, thereby producing a copper-clad silicon nitride circuit substrate of the present invention. When the insulation resistance of this circuit board at 125 ° C. was measured, it was found to be 2000 MΩ or more.
[0035]
(Example 2)
[0036]
It was the same as Example 1 except that the treatment temperature in the nitrogen atmosphere furnace was changed to 380 ° C. during the process of Example 1. When the insulation resistance at 125 ° C. of this copper-clad silicon nitride circuit board was measured, it was found to be 10000 MΩ or more.
[0037]
Example 3
[0038]
After the same steps as in Example 1, a nickel plating layer having a thickness of 3 μm was formed on the copper plate by a normal electroless plating method. The insulation resistance at 125 ° C. of this copper-clad silicon nitride circuit board was measured and found to be 10000 MΩ or more.
[0039]
(Comparative Example 1)
[0040]
During the process of Example 1, the substrate was processed in the same manner as in Example 1 except that the substrate was heat-treated in a nitrogen atmosphere. When the insulation resistance at 125 ° C. of this copper-clad silicon nitride circuit board was measured, it was found to be less than 100 MΩ.
[0041]
(Comparative Example 2)
[0042]
During the process of Example 1, the substrate was treated in the same manner as in Example 1 except that the heating temperature was 320 ° C. in a nitrogen atmosphere. The insulation resistance at 125 ° C. of this copper-clad silicon nitride circuit board was measured and found to be less than 100 MΩ.
[0043]
(Comparative Example 3)
[0044]
During the process of Example 1, the substrate was processed in the same manner as in Example 1 except that the substrate was heated in air at 125 ° C. for 4 hours instead of being heated in a nitrogen atmosphere continuous furnace. When the insulation resistance at 125 ° C. of this copper-clad silicon nitride circuit board was measured, it was found to be less than 100 MΩ.
[0045]
(Comparative Example 4)
[0046]
During the process of Example 1, the same heat treatment as in Example 1 was performed except that the heat treatment was performed in an atmosphere of 20% hydrogen and 80% nitrogen. When the insulation resistance at 125 ° C. of this copper-clad silicon nitride circuit board was measured, it was found to be less than 1 MΩ.
[0047]
Table 1 is a table comparing Samples 1 to 5 in the above Examples and Comparative Examples.
[0048]
[Table 1]
【The invention's effect】
As described above, according to the present invention, a copper-clad silicon nitride circuit board having a high insulation resistance can be produced even at 125 ° C. by heat treatment in nitrogen, and a power module assembled using this circuit board can be operated. A great effect of greatly reducing the loss can be obtained.
Claims (6)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP25071299A JP3824044B2 (en) | 1999-09-03 | 1999-09-03 | Silicon nitride circuit board manufacturing method |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP25071299A JP3824044B2 (en) | 1999-09-03 | 1999-09-03 | Silicon nitride circuit board manufacturing method |
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| JP2001077245A JP2001077245A (en) | 2001-03-23 |
| JP3824044B2 true JP3824044B2 (en) | 2006-09-20 |
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| JP25071299A Expired - Lifetime JP3824044B2 (en) | 1999-09-03 | 1999-09-03 | Silicon nitride circuit board manufacturing method |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP4692708B2 (en) | 2002-03-15 | 2011-06-01 | Ｄｏｗａメタルテック株式会社 | Ceramic circuit board and power module |
| JP2015178424A (en) * | 2014-03-19 | 2015-10-08 | 日立金属株式会社 | Method of producing ceramic circuit board |
| TWI746807B (en) * | 2017-02-28 | 2021-11-21 | 日商三菱綜合材料股份有限公司 | Copper/ceramic bonded body, insulating circuit substrate, method of manufacturing copper/ceramic bonded body and method of manufacturing insulating circuit substrate |
| JP6965768B2 (en) | 2017-02-28 | 2021-11-10 | 三菱マテリアル株式会社 | Copper / Ceramics Joint, Insulated Circuit Board, Copper / Ceramics Joint Manufacturing Method, Insulated Circuit Board Manufacturing Method |
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