JP5133960B2 - Circuit board for semiconductor mounting and manufacturing method thereof - Google Patents
Circuit board for semiconductor mounting and manufacturing method thereof Download PDFInfo
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- JP5133960B2 JP5133960B2 JP2009243029A JP2009243029A JP5133960B2 JP 5133960 B2 JP5133960 B2 JP 5133960B2 JP 2009243029 A JP2009243029 A JP 2009243029A JP 2009243029 A JP2009243029 A JP 2009243029A JP 5133960 B2 JP5133960 B2 JP 5133960B2
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- 239000002184 metal Substances 0.000 claims description 143
- 238000005219 brazing Methods 0.000 claims description 42
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- 239000000463 material Substances 0.000 claims description 34
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- 239000010949 copper Substances 0.000 claims description 17
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- 230000017525 heat dissipation Effects 0.000 claims description 10
- 238000005530 etching Methods 0.000 claims description 9
- PMHQVHHXPFUNSP-UHFFFAOYSA-M copper(1+);methylsulfanylmethane;bromide Chemical compound Br[Cu].CSC PMHQVHHXPFUNSP-UHFFFAOYSA-M 0.000 claims description 8
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- 238000007747 plating Methods 0.000 description 6
- ORTQZVOHEJQUHG-UHFFFAOYSA-L copper(II) chloride Chemical compound Cl[Cu]Cl ORTQZVOHEJQUHG-UHFFFAOYSA-L 0.000 description 4
- 239000011888 foil Substances 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 229910017944 Ag—Cu Inorganic materials 0.000 description 3
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
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- 229910000679 solder Inorganic materials 0.000 description 3
- 229910052719 titanium Inorganic materials 0.000 description 3
- 229910052726 zirconium Inorganic materials 0.000 description 3
- 229910052782 aluminium Inorganic materials 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
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- 229910000838 Al alloy Inorganic materials 0.000 description 1
- 229910052582 BN Inorganic materials 0.000 description 1
- PZNSFCLAULLKQX-UHFFFAOYSA-N Boron nitride Chemical compound N#B PZNSFCLAULLKQX-UHFFFAOYSA-N 0.000 description 1
- 229910000881 Cu alloy Inorganic materials 0.000 description 1
- 229910021578 Iron(III) chloride Inorganic materials 0.000 description 1
- CERQOIWHTDAKMF-UHFFFAOYSA-M Methacrylate Chemical compound CC(=C)C([O-])=O CERQOIWHTDAKMF-UHFFFAOYSA-M 0.000 description 1
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- RBTARNINKXHZNM-UHFFFAOYSA-K iron trichloride Chemical compound Cl[Fe](Cl)Cl RBTARNINKXHZNM-UHFFFAOYSA-K 0.000 description 1
- 230000007257 malfunction Effects 0.000 description 1
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- Structure Of Printed Boards (AREA)
- Cooling Or The Like Of Semiconductors Or Solid State Devices (AREA)
Description
本発明は、半導体搭載用回路基板及びその製造方法に関する。 The present invention relates to a circuit board for mounting a semiconductor and a manufacturing method thereof.
エレクトロニクス技術の発展に伴い、半導体の高出力化が進む中、半導体搭載用回路基板（以下、単に「回路基板」という。）が達成すべき今日の課題は、耐熱サイクル特性を一段と向上させることである。 Along with the development of high-power semiconductors as electronics technology develops, today's challenge for semiconductor-mounted circuit boards (hereinafter simply referred to as “circuit boards”) is to further improve the thermal cycle characteristics. is there.
回路基板は、セラミックス基板の表面に金属回路を、裏面に金属放熱板を有することを基本構造とし、上記金属回路と上記金属放熱板には、通常、無電解Ｎｉめっきが施される。Ｎｉめっきがないときは防錆剤が施される。モジュールの組み立ては、回路基板の金属回路に半導体を、また金属放熱板面に放熱部材をはんだ付けして行われる。 The circuit board has a basic structure having a metal circuit on the surface of a ceramic substrate and a metal heat sink on the back, and the metal circuit and the metal heat sink are usually subjected to electroless Ni plating. When there is no Ni plating, a rust inhibitor is applied. The assembly of the module is performed by soldering the semiconductor to the metal circuit of the circuit board and soldering the heat radiating member to the metal heat radiating plate surface.
近年、電気自動車、電鉄等のパワーモジュール用途や、エアコン、エレベータ等の一般用途においては、環境負荷軽減のため、インバータ制御を可能とするモジュールが採用されている。モジュールには複数個の半導体が搭載されるので総発熱量が増加し、誤作動の原因となる。これをなくするために、回路基板には一段と高い放熱特性が要求されている。加えて、半導体稼働により発生する熱サイクルは、回路基板に直接負荷されるので、これまで以上の耐熱サイクル特性が必要となる。そこで、これまでに、回路基板の金属回路ないしは金属放熱板の端部を変形しやすい金属で構成する（特許文献１）、多段構造とする（特許文献２）、などの提案があるが、十分な耐熱サイクル特性を確保できていない。 In recent years, modules that enable inverter control have been adopted in power module applications such as electric vehicles and electric railways and general applications such as air conditioners and elevators in order to reduce environmental impact. Since a plurality of semiconductors are mounted on the module, the total amount of heat generation increases, causing malfunction. In order to eliminate this, circuit boards are required to have higher heat dissipation characteristics. In addition, since the heat cycle generated by the semiconductor operation is directly loaded on the circuit board, the heat cycle characteristics more than ever are required. So far, there have been proposals such as forming the metal circuit of the circuit board or the end of the metal heat sink with a metal that is easily deformed (Patent Document 1), or a multistage structure (Patent Document 2). The heat cycle characteristics are not secured.
すなわち、従来、耐熱サイクル特性の評価は、１２５℃で３０分、−４０℃で３０分を１サイクルとするヒートサイクル試験により行われているが、この評価法では回路基板の放熱部材へのはんだ付け温度（３５０℃近傍）が考慮されていないので適切であるとはいえない。そこで、より厳しい通炉試験（注：３５０℃で５分、室温まで放熱、−７８℃で５分、室温まで放熱を１サイクルとするヒートサイクル試験を１０サイクル行う試験のこと。）にて評価すると、特許文献１、２の回路基板では、金属回路の下部に水平クラックが発生し、場合によっては回路基板が割れた。 That is, conventionally, the heat cycle characteristics are evaluated by a heat cycle test in which one cycle is 125 ° C. for 30 minutes and −40 ° C. for 30 minutes. In this evaluation method, the solder to the heat dissipation member of the circuit board is used. Since the attaching temperature (around 350 ° C.) is not taken into account, it cannot be said that it is appropriate. Therefore, it was evaluated in a more severe furnace test (note: a test in which a heat cycle test is performed for 10 cycles at 350 ° C. for 5 minutes, heat dissipation to room temperature, 5 minutes at −78 ° C. and heat dissipation to room temperature for 1 cycle). Then, in the circuit board of patent document 1, 2, the horizontal crack generate | occur | produced in the lower part of the metal circuit, and the circuit board cracked depending on the case.
本発明の目的は、耐熱サイクル特性を一段と向上させた回路基板とその製造方法を提供する。 The objective of this invention provides the circuit board which improved the heat-resistant cycle characteristic further, and its manufacturing method.
本発明の回路基板は、セラミックス基板１の表面には１又は２以上の金属回路２が、裏面には金属放熱板３が、それぞれろう材層４を介して接合されていること、上記ろう材層が金属回路の端部から８０μｍ以下（０を含まず）の長さにはみ出ていること、上記ろう材層の厚みがいかなる部分においても１０〜２５μｍであること、上記金属回路及び上記金属放熱板の端部はいずれも段差構造を有し、その段差構造は、長さ（Ｓ１、Ｓ２）が１００〜３００μｍ、厚み（ｔ）が２０〜７０μｍのステップ部５と、このステップ部５に連続したスロープ部６とから構成されており、しかも上記スロープ部６のセラミックス基板に対する角度（金属回路のスロープ角度α１、金属放熱板のスロープ角度α２）がいずれも３０°〜７０°であること、ろう材層端部からステップ部側壁までの合計長さを、金属回路ではＬ１、金属放熱板ではＬ２とし、またろう材層端部からセラミックス基板端部までの長さを、金属回路ではＥ１、金属放熱板ではＥ２としたときに、Ｌ１≦Ｌ２で、しかもＬ１＋Ｅ１≧Ｌ２＋Ｅ２であることを特徴とするものである。 In the circuit board of the present invention, one or more metal circuits 2 are bonded to the front surface of the ceramic substrate 1, and a metal heat sink 3 is bonded to the back surface thereof via a brazing material layer 4. The layer protrudes from the end of the metal circuit to a length of 80 μm or less (excluding 0), the thickness of the brazing material layer is 10 to 25 μm in any part, the metal circuit and the metal heat dissipation Each end portion of the plate has a step structure, and the step structure has a length (S1, S2) of 100 to 300 μm and a thickness (t) of 20 to 70 μm, and the step portion 5 is continuous with the step portion 5. In addition, the angle of the slope portion 6 with respect to the ceramic substrate (the slope angle α1 of the metal circuit and the slope angle α2 of the metal heat sink) is 30 ° to 70 °. The total length from the end of the material layer to the side wall of the step part is L1 for the metal circuit, L2 for the metal heat sink, and the length from the end of the brazing material layer to the end of the ceramic substrate is E1, for the metal circuit, When the heat sink is set to E2, L1 ≦ L2 and L1 + E1 ≧ L2 + E2 are satisfied.
本発明の回路基板にあっては、（イ）Ｌ１＜Ｌ２であり、しかもＬ１＋Ｅ１＞Ｌ２＋Ｅ２であること、（ロ）α１≧α２であること、特にα１>α２であること、（ハ）Ｌｌが１１０〜５００μｍ、Ｌ２が１１０〜５００μｍ、Ｅ１が３．０〜１．０ｍｍ、Ｅ２が０．１〜１．０ｍｍ、α１が３０〜４０°及びα２が３０〜４０°であること、（ニ）セラミックス基板が、厚み０．５〜３ｍｍの窒化アルミニウム基板であり、金属回路と金属放熱板がいずれも銅であって、金属回路と金属放熱板の厚みがいずれも０．１〜０．３ｍｍであること、から選ばれた少なくとも１つの実施態様を有していることが好ましい。 In the circuit board of the present invention, (b) L1 <L2, and L1 + E1> L2 + E2, (b) α1 ≧ α2, particularly α1> α2, and (c) Ll 110 to 500 μm, L2 to 110 to 500 μm, E1 to 3.0 to 1.0 mm, E2 to 0.1 to 1.0 mm, α1 to 30 to 40 ° and α2 to 30 to 40 °, (d) The ceramic substrate is an aluminum nitride substrate having a thickness of 0.5 to 3 mm, the metal circuit and the metal heat sink are both copper, and the thickness of the metal circuit and the metal heat sink is both 0.1 to 0.3 mm. It is preferable to have at least one embodiment selected from:
本発明の製造方法は、本発明の回路基板を製造する方法であって、セラミックス基板に金属回路形成用、金属放熱板形成用の金属板を活性金属ろう付け法で接合した後、エッチングによって、金属回路形成用金属板から金属回路の段差構造のスロープ部を形成する一方、金属放熱板形成用の金属板から金属放熱板の段差構造のスロープ部を形成させた後、切削加工によりそれぞれのステップ部を形成することを特徴とするものである。 The manufacturing method of the present invention is a method of manufacturing the circuit board of the present invention, and after bonding a metal plate for forming a metal circuit and a metal heat sink to the ceramic substrate by an active metal brazing method, etching is performed. The slope part of the step structure of the metal circuit is formed from the metal plate for forming the metal circuit, while the step part of the step structure of the metal heat sink is formed from the metal plate for forming the metal heat sink, and then each step is performed by cutting. Forming a part.
本発明によれば、耐熱サイクル特性を一段と向上させた回路基板とその容易な製造方法が提供される。 ADVANTAGE OF THE INVENTION According to this invention, the circuit board which improved the heat cycle characteristic further, and its easy manufacturing method are provided.
本発明で用いられるセラミックス基板１の材質は、例えばアルミナ、窒化ケイ素、窒化アルミニウム、窒化ホウ素等の熱伝導性絶縁材料である。これらの中でも、熱伝導性（放熱特性）を重視する場合は窒化アルミニウムが好ましく、強度と低熱抵抗を重視する場合は窒化ケイ素が好ましい。セラミックス基板の厚みは０．２〜３ｍｍが一般的であり、目的によって変更される。例えば、窒化ケイ素基板は、他のセラミックス基板よりも機械的強度が強いので、０．２〜０．５ｍｍに薄化し熱抵抗を小さくして用いることができる。これによって回路基板の薄化がより可能となる。一方、窒化アルミニウム基板は、他のセラミックス基板よりも熱伝導性が大きいので、その特徴を放熱特性、絶縁耐圧等の向上に利用するべく例えば０．５〜３ｍｍの厚物が用いられる。 The material of the ceramic substrate 1 used in the present invention is a thermally conductive insulating material such as alumina, silicon nitride, aluminum nitride, or boron nitride. Among these, aluminum nitride is preferable when emphasizing thermal conductivity (heat dissipation characteristics), and silicon nitride is preferable when emphasizing strength and low thermal resistance. The thickness of the ceramic substrate is generally 0.2 to 3 mm, and is changed depending on the purpose. For example, since the silicon nitride substrate has a higher mechanical strength than other ceramic substrates, it can be used by reducing the thermal resistance to 0.2 to 0.5 mm. As a result, the circuit board can be made thinner. On the other hand, since the aluminum nitride substrate has higher thermal conductivity than other ceramic substrates, a thickness of, for example, 0.5 to 3 mm is used in order to use the characteristics for improving heat dissipation characteristics, dielectric strength, and the like.
本発明で用いられる金属回路２、金属放熱板３の材質は、電気的・熱的特性の点から、アルミニウム、銅、銅合金、アルミニウム合金の単体又はこれらのクラッドが用いられる。熱容量を重視する場合はアルミニウムが好ましく、低電気抵抗を重視する場合は銅が好ましい。厚みは、金属回路、金属放熱板のいずれも０．１〜０．３ｍｍであることが好ましい。金属回路２は、セラミックス基板の表面に１又は２以上の適宜数が形成される。金属放熱板３は、通常、ベタ金属板が設けられる。 As the material for the metal circuit 2 and the metal heat sink 3 used in the present invention, aluminum, copper, a copper alloy, an aluminum alloy or a clad thereof is used from the viewpoint of electrical and thermal characteristics. Aluminum is preferable when the heat capacity is important, and copper is preferable when the low electric resistance is important. As for thickness, it is preferable that both a metal circuit and a metal heat sink are 0.1-0.3 mm. As for the metal circuit 2, one or two or more appropriate numbers are formed on the surface of the ceramic substrate. The metal heat sink 3 is usually provided with a solid metal plate.
金属回路又は金属放熱板とセラミックス基板との接合は、ろう材層４を介して行われる。このろう材層は、Ａｇ、Ｃｕ又はＡｇ−Ｃｕ合金と、Ｔｉ、Ｚｒ、Ｈｆ等の活性金属成分とを含むろう材を用いる活性金属ろう付け法によって形成される。本発明で重要なことは、ろう材層の厚みがいかなる部分においても１０〜２５μｍ、特に１５〜２２μｍとすることである。厚みが１０μｍ未満である部分があると、耐熱サイクル特性を一段と向上させる効果が乏しくなり、また２５μｍをこえる部分があると、金属回路及び金属放熱板へのろう材成分の拡散が進み、かえって耐熱サイクル特性が劣化する。従来、ろう材層の厚みを１０〜２５μｍとした回路基板は知られているが、いかなる部分においてもそのようにすることの開示はなく、また後述する回路基板の端部の段差構造との関連でそのように規定し、耐熱サイクル特性を一段と向上させることについては知られていない。 The metal circuit or the metal heat sink and the ceramic substrate are joined through the brazing material layer 4. This brazing material layer is formed by an active metal brazing method using a brazing material containing Ag, Cu, or an Ag—Cu alloy and an active metal component such as Ti, Zr, or Hf. What is important in the present invention is that the thickness of the brazing material layer is 10 to 25 μm, particularly 15 to 22 μm, in any part. If there is a part where the thickness is less than 10 μm, the effect of further improving the heat cycle characteristics will be poor, and if there is a part exceeding 25 μm, the diffusion of the brazing filler metal component into the metal circuit and the metal heat sink will proceed, and instead heat resistance Cycle characteristics deteriorate. Conventionally, a circuit board with a brazing material layer thickness of 10 to 25 μm is known, but there is no disclosure of doing so in any part, and the relationship with the step structure at the end of the circuit board described later However, it is not known how to further improve the heat cycle characteristics.
ろう材層の厚みの測定は、回路基板、但し回路基板が大きい等、そのまま測定することが困難であるときは、その一部が切り出された回路基板を、エポキシ樹脂に包埋、固化した後、接合断面が垂直面になるように切断し、その切断面を鏡面研磨した後、ろう材層の厚みを電子顕微鏡にて測定することによって行われる。耐熱サイクル特性が十分に高まらない回路基板では、ろう材が金属回路及び金属放熱板に拡散していて、ろう材層の厚みが０〜１０μｍになっている部分があるか、又は２５μｍをこえている部分がある。これに対し、耐熱サイクル特性を一段と向上した回路基板では、いかなる部分においても、ろう材層の厚みが１０〜２５μｍの範囲内にあることを本発明者は確認した。これらの現象から、いかなる部分においても１０〜２５μｍの厚みとなったろう材層には、熱サイクルに起因する金属回路及び金属放熱板からの応力を緩和する作用のあることが推察される。 When measuring the thickness of the brazing material layer is difficult to measure as it is, such as a circuit board, but the circuit board is large, after embedding the solidified circuit board in epoxy resin and solidifying it This is done by cutting so that the joining cross section becomes a vertical surface, mirror-polishing the cut surface, and then measuring the thickness of the brazing material layer with an electron microscope. In a circuit board where the heat cycle characteristics are not sufficiently improved, the brazing material is diffused in the metal circuit and the metal heat sink, and the thickness of the brazing material layer is 0 to 10 μm or exceeds 25 μm. There is a part. On the other hand, the present inventor has confirmed that the thickness of the brazing material layer is in the range of 10 to 25 μm in any part of the circuit board having further improved heat cycle characteristics. From these phenomena, it is presumed that the brazing filler metal layer having a thickness of 10 to 25 μm in any part has an action of relieving stress from the metal circuit and the metal heat sink caused by the thermal cycle.
後述するはみ出しろう材層を除き、回路基板のいかなる部分においても厚みが１０〜２５μｍの範囲内にあるろう材層は、Ａｇ粉末及びＣｕ粉末（又はＡｇ−Ｃｕ合金粉末）と、例えばＴｉ、Ｚｒ、Ｈｆ等の活性金属粉末と、例えばポリイソブタンメタクリレート等のバインダーとを混合してペーストを調製し、例えばスクリーン印刷法、ロールコーター法等によって、セラミックス基板の表面及び裏面に塗布量を調整して塗布する際に、上記Ａｇ粉末として、例えばアトマイズ処理等をして表面に酸化被膜を形成させたＡｇ粉末又はＡｇ−Ｃｕ合金粉末を用いることによって形成させることができる。 Except for the brazing filler metal layer described later, the brazing filler metal layer having a thickness in the range of 10 to 25 μm in any part of the circuit board is composed of Ag powder and Cu powder (or Ag—Cu alloy powder), for example, Ti, Zr. A paste is prepared by mixing an active metal powder such as Hf and a binder such as polyisobutane methacrylate, and the coating amount is adjusted on the front and back surfaces of the ceramic substrate by, for example, a screen printing method or a roll coater method. At the time of application, the Ag powder can be formed by using, for example, an Ag powder or an Ag—Cu alloy powder having an oxide film formed on the surface by an atomizing process or the like.
また、Ａｇ、Ｃｕ及び例えばＴｉ、Ｚｒ、Ｈｆ等の活性金属を含む合金箔を介して、セラミックス基板の表面に金属回路形成用金属板を、裏面に放熱板形成用金属板を配置し、真空炉中にて加熱してろう材層を形成させる際に、上記合金箔は酸化皮膜を有する合金箔を用いることによっても形成させることができる。 Further, a metal circuit forming metal plate is arranged on the surface of the ceramic substrate and a heat sink forming metal plate is arranged on the back surface through an alloy foil containing active metal such as Ag, Cu and Ti, Zr, Hf, etc. When the brazing material layer is formed by heating in a furnace, the alloy foil can also be formed by using an alloy foil having an oxide film.
耐熱サイクル特性を更に一段と向上させるため、図２に示されるように、ろう材層４はスロープ部６の先端から８０μｍ以下（０を含まず）の長さにはみ出ていることが好ましい。なお、ろう材層の成分の一例を示せば、上記ペースト法、合金箔法のいずれにあっても、Ａｇが６５〜７２質量％、Ｃｕが２３〜２９質量％、活性金属成分が３〜７質量％である。 In order to further improve the heat cycle characteristics, it is preferable that the brazing filler metal layer 4 protrudes from the tip of the slope portion 6 to a length of 80 μm or less (not including 0) as shown in FIG. In addition, if an example of the component of a brazing material layer is shown, it will be 65-72 mass% of Ag, 23-29 mass% of Cu, and 3-7 of an active metal component also in any of the said paste method and an alloy foil method. % By mass.
本発明の回路基板の金属回路及び金属放熱板の端部は、ステップ部５とこのステップ部に連続したスロープ部６とからなる段差構造を有しており、しかもステップ部の長さＳ１、Ｓ２がそれぞれ１００〜３００μｍ、厚みｔが２０〜７０μｍ、スロープ部のセラミックス基板に対する角度（金属回路のスロープ角度α１、金属放熱板のスロープ角度α２）がいずれも３０°〜７０°である。これを図２に基づいて説明する。 The ends of the metal circuit and the metal heat sink of the circuit board according to the present invention have a step structure including a step portion 5 and a slope portion 6 continuous to the step portion, and the lengths S1 and S2 of the step portions. Are respectively 100 to 300 μm, thickness t is 20 to 70 μm, and the angle of the slope portion with respect to the ceramic substrate (the slope angle α1 of the metal circuit and the slope angle α2 of the metal heat sink) is 30 ° to 70 °. This will be described with reference to FIG.
ステップ部５は、熱サイクルに起因する金属回路及び金属放熱板の端部に発生する垂直方向の引張応力を水平方向へ変換、分散させる機能を担う。ステップ部の長さが１００μｍよりも短いとこの機能が十分でなくなり、セラミックス基板にクラックを生じさせる恐れがある。一方、ステップ部の長さが３００μｍをこえると半導体を搭載する領域を十分に確保することができなくなる場合がある。上記のことから、ステップ部の長さＳ１、Ｓ２はそれぞれ１００〜３００μｍ、好ましくは１００〜２５０μｍである。 The step unit 5 has a function of converting and dispersing the vertical tensile stress generated at the ends of the metal circuit and the metal heat sink due to the thermal cycle in the horizontal direction. If the length of the step portion is shorter than 100 μm, this function is not sufficient, and there is a risk of causing cracks in the ceramic substrate. On the other hand, if the length of the step portion exceeds 300 μm, it may not be possible to secure a sufficient area for mounting the semiconductor. From the above, the lengths S1 and S2 of the step portions are 100 to 300 μm, preferably 100 to 250 μm, respectively.
ステップ部５の厚みは、ステップ部自体の垂直方向の応力が小さくなるため、薄いほうが有利であるが、その反面、ろう材層に亀裂が生じやすくなる。したがって、ステップ部の材料強度を確保する点から、ステップ部の厚みは２０μｍ以上が必要である。一方、ステップ部の厚みが７０μｍをこえるとステップ部に垂直方向の応力が加わり耐熱サイクル特性に悪影響を与え水平クラックが生じやすくなる。上記のことから、ステップ部の厚みｔは２０〜７０μｍ、好ましくは２５〜４５μｍである。 The thickness of the step portion 5 is advantageous because the stress in the vertical direction of the step portion itself is small, and it is advantageous that the thickness is small, but on the other hand, the brazing material layer is likely to crack. Therefore, the thickness of the step portion needs to be 20 μm or more from the viewpoint of securing the material strength of the step portion. On the other hand, if the thickness of the step portion exceeds 70 μm, a stress in the vertical direction is applied to the step portion, adversely affecting the heat resistance cycle characteristics, and horizontal cracks are likely to occur. From the above, the thickness t of the step portion is 20 to 70 μm, preferably 25 to 45 μm.
また、耐熱サイクル特性の向上のためには、スロープ部６のスロープ角度は小さいほどよいが、小さくすればするほど半導体の搭載領域が小さくなる。一方、スロープ角度が７０°をこえると耐熱サイクル特性に悪影響を及ぼし水平クラックが生じやすくなる。上記のことから、スロープ角度はα１、α２とも３０°〜７０°、好ましくは３０°〜４５°である。なかでも、α１≧α２、特にα１>α２であることが好ましい。 Further, in order to improve the heat cycle characteristics, the slope angle of the slope portion 6 is preferably as small as possible, but the semiconductor mounting area becomes smaller as the slope angle is smaller. On the other hand, if the slope angle exceeds 70 °, the heat cycle characteristics are adversely affected and horizontal cracks are likely to occur. From the above, the slope angles of both α1 and α2 are 30 ° to 70 °, preferably 30 ° to 45 °. Of these, α1 ≧ α2, particularly α1> α2 is preferable.
上記段差構造にあっても、ろう材層端部からステップ部側壁までの合計長さを、金属回路ではＬ１、金属放熱板ではＬ２とし、またろう材端部からセラミックス基板端部までの長さを、金属回路ではＥ１、金属放熱板ではＥ２としたときに、Ｌ１≦Ｌ２、特にＬ１＜Ｌ２であり、しかもＬ１＋Ｅ１≧Ｌ２＋Ｅ２、特にＬ１＋Ｅ１＞Ｌ２＋Ｅ２であることが好ましい。なかでも、Ｌｌは１１０〜５００μｍ、Ｌ２が１１０〜５００μｍ、Ｅ１が３〜１ｍｍ、Ｅ２が０．１〜１ｍｍが好ましい。特許文献１、２の回路基板も段差構造を有しているが、Ｌｌ、Ｌ２、Ｅ１、Ｅ２を本発明のように関連させることについては記載がない。通常、沿面放電防止の観点からＥ１＞Ｅ２にされる。 Even in the above step structure, the total length from the end of the brazing material layer to the side wall of the step portion is L1 for the metal circuit, L2 for the metal heat sink, and the length from the end of the brazing material to the end of the ceramic substrate. Is E1 in the metal circuit and E2 in the metal heat sink, it is preferable that L1 ≦ L2, particularly L1 <L2, and L1 + E1 ≧ L2 + E2, particularly L1 + E1> L2 + E2. Among these, Ll is preferably 110 to 500 μm, L2 is 110 to 500 μm, E1 is 3 to 1 mm, and E2 is 0.1 to 1 mm. The circuit boards of Patent Documents 1 and 2 also have a step structure, but there is no description about associating L1, L2, E1, and E2 as in the present invention. Usually, E1> E2 is set from the viewpoint of preventing creeping discharge.
Ｌｌ、Ｌ２、Ｅ１、Ｅ２を上記のように関連させた理由を説明する。金属回路と金属放熱板の厚みが同じである場合、回路基板の放熱部材へのはんだ付け時に金属放熱板側が凸に反るので、はんだボイドは防止できるが、所望する回路パターンによっては反り量が大きくなり、回路基板の端部近傍をはんだ接合できない場合や、回路基板の金属回路端部近傍に半導体をはんだ接合できない場合がある。これを解決するため、従来、金属放熱板の厚みを変更してはんだ付け時の反り量を調整してきたが、この方法では一般に入手可能な金属板の厚みに限定されるので反り量の微調整ができない。その結果、耐熱サイクル特性を一段と向上させることは困難であった。 The reason why L1, L2, E1, and E2 are related as described above will be described. When the thickness of the metal circuit and the metal heatsink is the same, the metal heatsink side warps convexly when soldering to the heatsink member of the circuit board, so solder voids can be prevented, but the amount of warp may vary depending on the desired circuit pattern In some cases, the vicinity of the end of the circuit board cannot be soldered or the semiconductor cannot be soldered to the end of the metal circuit of the circuit board. In order to solve this, conventionally, the thickness of the metal heat sink has been changed to adjust the amount of warpage during soldering, but this method is limited to the thickness of metal plates that are generally available, so fine adjustment of the amount of warpage I can't. As a result, it has been difficult to further improve the heat resistance cycle characteristics.
本発明者が種々検討したところ、上記Ｌ１、Ｌ２と、Ｅ１、Ｅ２とが、はんだ付けの際の加熱による反り量に大きく影響していることを見いだした。すなわち、Ｌ１＞Ｌ２であると、加熱時に金属回路側の反り量が大きくなり、回路基板端部のはんだ付けが困難となるか、金属放熱板からの熱サイクルに起因する応力が増大し、耐熱サイクル特性に悪影響を及ぼす。Ｌ１＋Ｅ１＜Ｌ２＋Ｅ２であると、はんだ付けの際、金属放熱板側が凹に反り、はんだボイドを生じやすくなることを見いだしたものである。 As a result of various studies by the present inventor, it has been found that the above-described L1, L2 and E1, E2 have a great influence on the amount of warpage due to heating during soldering. That is, when L1> L2, the amount of warp on the metal circuit side during heating increases, and soldering of the circuit board end becomes difficult, or stress due to the heat cycle from the metal heat sink increases, It adversely affects cycle characteristics. It has been found that when L1 + E1 <L2 + E2, the metal heat sink side is warped in the soldering and solder voids are likely to occur.
本発明の回路基板の製造方法について説明する。 A method for manufacturing a circuit board according to the present invention will be described.
本発明の回路基板の製造方法は、上記本発明の回路基板を製造する方法であって、セラミックス基板に金属回路形成用、金属放熱板形成用の金属板を活性金属ろう付け法で接合して接合体を製造した後、エッチングによって、金属回路形成用金属板から金属回路の段差構造のスロープ部を形成する一方、金属放熱板形成用の金属板から金属放熱板の段差構造のスロープ部を形成させた後、切削加工によりそれぞれのステップ部を形成することを特徴とするものである。この場合において、セラミックス基板に金属回路形成用、金属放熱板形成用の金属板を、ろう材層の厚みがいかなる部分においても１０〜２５μｍにすることは上記した。 A method for manufacturing a circuit board according to the present invention is a method for manufacturing the circuit board according to the present invention, wherein a metal plate for forming a metal circuit and a metal heat sink is joined to a ceramic substrate by an active metal brazing method. After manufacturing the joined body, the slope portion of the step structure of the metal circuit is formed from the metal plate for forming the metal circuit by etching, while the slope portion of the step structure of the metal heat sink is formed from the metal plate for forming the metal heat sink. Then, each step portion is formed by cutting. In this case, as described above, the metal plate for forming the metal circuit and the metal heat dissipating plate is formed on the ceramic substrate so that the brazing material layer has a thickness of 10 to 25 μm at any portion.
接合体の金属板から段差構造を有する金属回路と金属放熱板を形成するには、従来、エッチング法が採用されていた。すなわち、エッチングレジストを金属板に所望のパターンに塗布した後、塩化第二銅、塩化第二鉄等の水溶液をエッチャントとして、回路パターン及び放熱パターンを形成した。その後、エッチングレジストを剥離し、所望のパターンよりも、使用している金属板厚みと同程度、好ましくはそれ以上小さく縮小したパターンをレジスト印刷し、再度エッチングして行われていた。しかしながら、エッチャントと金属の反応は等方的に進行するため、本発明のような段差構造の形成は極めて困難である。 In order to form a metal circuit having a step structure and a metal heat radiating plate from a metal plate of a joined body, an etching method has been conventionally employed. That is, after applying an etching resist to a metal plate in a desired pattern, a circuit pattern and a heat radiation pattern were formed using an aqueous solution of cupric chloride, ferric chloride, or the like as an etchant. After that, the etching resist was peeled off, and a pattern which was reduced in size to the same thickness as the metal plate used, preferably smaller than the desired pattern, was printed with resist and etched again. However, since the reaction between the etchant and the metal proceeds isotropically, it is very difficult to form a step structure as in the present invention.
そこで本発明が採用した方法は、まず接合体の金属板に所望のパターンにエッチングレジストを塗布した後、所定のスロープ角度となるようにエッチャント濃度及び送り速度等を調整して回路パターン及び放熱板パターンを形成させ、その後、例えば立形マシニングセンタにて所定形状のステップ部を切削加工する。これによって、本発明の回路基板が製造される。回路基板は、必要に応じ、膜厚が１〜８μｍ程度の無電解Ｎｉめっきが施される。Ｎｉめっきを施さないときは、研削、物理研磨、化学研磨等によって金属表面の傷をＲａ≦０．５μｍに平滑化した後、防錆剤が塗布される。 Therefore, the method employed by the present invention is to first apply an etching resist in a desired pattern to the metal plate of the joined body, and then adjust the etchant concentration, feed rate, etc. so as to obtain a predetermined slope angle. A pattern is formed, and then a step portion having a predetermined shape is cut by a vertical machining center, for example. Thus, the circuit board of the present invention is manufactured. The circuit board is subjected to electroless Ni plating with a film thickness of about 1 to 8 μm as necessary. When Ni plating is not applied, the metal surface is smoothed to Ra ≦ 0.5 μm by grinding, physical polishing, chemical polishing or the like, and then a rust inhibitor is applied.
実施例１〜１７ 比較例１〜１２
アトマイズＡｇ粉末(酸素量：０．６質量％、平均粒径０．４μｍ、タップ密度２．３ｇ／ｃｍ３、比表面積３．７ｍ２／ｇ)、Ｃｕ粉末（特級試薬）、Ｚｒ粉末（特級試薬）、ＴｉＨ２粉末（特級試薬）を、Ａｇ／Ｃｕ／Ｚｒ／ＴｉＨ２＝６８．４／２６．６／３／２（質量比）にして混合した。この粉末１００質量部に、テレピネオール１５質量部、ポリイソブチルメタクリレートのトルエン溶液を固形分として１．５質量部を混合してろう材ペーストを調整した。これを、厚み０．６３５ｍｍ×２６．５ｍｍ×３５．２ｍｍの窒化アルミニウム基板（熱伝導率１７０Ｗ／ｍＫ、３点曲げ強度４００ＭＰａ）の表面及び裏面に、表１に示されるろう材層の厚み（乾燥後の厚み）にロールコーターを用いて塗布した。その後、表面に回路形成用銅板（厚み０．２５ｍｍ、無酸素銅板）を、裏面に放熱板形成用銅板（厚み０．２５ｍｍ、無酸素銅板）を重ね、６．７×１０−４Ｐａの真空炉中、８３０℃×５０分保持した後、２℃／分の降温速度で冷却し、銅板と窒化アルミニウム基板の接合体を製造した。
Examples 1-17 Comparative Examples 1-12
Atomized Ag powder (oxygen amount: 0.6 mass%, average particle size 0.4 μm, tap density 2.3 g / cm 3 , specific surface area 3.7 m 2 / g), Cu powder (special grade reagent), Zr powder (special grade) Reagent) and TiH 2 powder (special grade reagent) were mixed with Ag / Cu / Zr / TiH 2 = 68.4 / 26.6 / 3/2 (mass ratio). To 100 parts by mass of this powder, 15 parts by mass of terpineol and 1.5 parts by mass of a toluene solution of polyisobutyl methacrylate were mixed to prepare a brazing material paste. The thickness of the brazing material layer shown in Table 1 (on the front and back surfaces of an aluminum nitride substrate (thermal conductivity 170 W / mK, 3-point bending strength 400 MPa) having a thickness of 0.635 mm × 26.5 mm × 35.2 mm ( The thickness after drying was applied using a roll coater. Then, a copper plate for circuit formation (thickness 0.25 mm, oxygen-free copper plate) is stacked on the front surface, and a copper plate for heat dissipation plate formation (thickness 0.25 mm, oxygen-free copper plate) is stacked on the rear surface, and a vacuum of 6.7 × 10 −4 Pa. After holding at 830 ° C. for 50 minutes in the furnace, it was cooled at a rate of temperature decrease of 2 ° C./min to produce a joined body of a copper plate and an aluminum nitride substrate.
接合体の金属板に、スクリーン印刷によりＵＶ硬化型エッチングレジストを図１に示すパターンに印刷しＵＶ硬化させた後、金属放熱面にベタパターンを印刷しＵＶ硬化させた。これを塩化第２銅水溶液（エッチャント）の濃度及びエッチャントへの搬送速度を調整してエッチングしスロープ角度を変更した。その後、６０℃のフッ化アンモニウム水溶液で処理する際、その濃度及び搬送速度を調整して各パターン間、及びスロープ部先端からセラミックス基板先端までの間に残留するろう材量を変更した。このようにして、スロープ部の構造及びろう材層のはみ出し長さが異なる回路基板の中間体を種々製造した。 A UV curable etching resist was printed on the metal plate of the joined body by screen printing in the pattern shown in FIG. 1 and UV cured, and then a solid pattern was printed on the metal heat radiation surface and UV cured. This was etched by adjusting the concentration of the cupric chloride aqueous solution (etchant) and the transport speed to the etchant to change the slope angle. Then, when processing with 60 degreeC ammonium fluoride aqueous solution, the density | concentration and the conveyance speed were adjusted and the amount of brazing | wax materials remaining between each pattern and between a slope part front-end | tip and a ceramic substrate front-end | tip was changed. In this way, various circuit board intermediates having different slope portions and different brazing layer protrusion lengths were produced.
ついで、中間体の金属回路パターン、金属放熱板パターンに種々のステップ部を立形マシニングセンタ（牧野フライス製作所社製商品名「Ｖ２２」、加工条件；φ０．８スクエアエンドミル使用、切削加工回転数２４０００回転／分、加工送り速度１２００ｍｍ／分）を用いて切削加工した後、無電解Ｎｉ−Ｐめっきを施して図１、図２、表１、２に示される回路基板を製造し、以下の評価を行った。それらの結果を表３に示す。 Next, various steps are formed on the intermediate metal circuit pattern and metal heat sink pattern. Vertical machining center (trade name “V22” manufactured by Makino Milling Mfg. Co., Ltd.), machining conditions: φ0.8 square end mill used, cutting rotation speed 24,000 rotations / Min, machining feed rate of 1200 mm / min), then electroless Ni-P plating is applied to produce the circuit boards shown in FIGS. 1, 2, and 1 and 2, and the following evaluation is performed. went. The results are shown in Table 3.
寸法評価：パターン間及び半導体搭載領域の寸法を、工具顕微鏡（ミツトヨ社製商品名「ＭＦ−１０１０」）を用いて測定し、寸法許容範囲を基準にして寸法判定をおこなった。 Dimensional evaluation: The dimensions between the patterns and the semiconductor mounting area were measured using a tool microscope (trade name “MF-1010” manufactured by Mitutoyo Corporation), and the dimension was determined based on the allowable dimension range.
加熱時反り評価：回路基板の窒化アルミニウム基板の重心点となる部位を測定点とし、３５０℃のホットプレート上にて、回路面を基準(すなわちゼロ点)として、回路面と放熱面の変位差をレーザー変位計（キーエンス社製商品名「ＬＫ−Ｇ８０」）にて測定した。反り評価の基準は、測定値が正の場合、正反りとなり、負の場合、逆反りとし、逆反りの場合、また正反りであっても変位差１５０μｍ以上である場合を不可とした。 Warpage evaluation during heating: The difference between the circuit surface and the heat dissipation surface on the hot plate at 350 ° C with the circuit surface as a reference (ie, zero point) on the hot plate at 350 ° C. Was measured with a laser displacement meter (trade name “LK-G80” manufactured by Keyence Corporation). The criteria for warpage evaluation are positive warpage when the measured value is positive, reverse warpage when negative, and reverse warpage. .
耐熱サイクル特性評価：回路基板を、ホットプレート上で３５０℃×５分、２５℃まで放冷、その後ドライアイス冷却メタノール中で−７８℃×５分、２５℃まで大気中放冷を１サイクルとして、１０サイクル、１５サイクルを繰り返した後、エッチングによりめっき及び銅回路、銅放熱板を除去し、窒化アルミニウム基板の割れや水平クラックの有無を、光学実体顕微鏡を用いて観察した。水平クラックの無いものは、良好と評価し、評価において水平クラックのあるものは、以下の３段階で評価した。
水平クラックＡ：長さ５０μｍ未満
水平クラックＢ：長さ５０μｍ以上１００μｍ未満
水平クラックＣ：長さ１００μｍ以上
Thermal cycle characteristics evaluation: The circuit board is allowed to cool to 350 ° C. for 5 minutes and 25 ° C. on a hot plate, and then cooled to dry air-cooled methanol in −78 ° C. for 5 minutes and allowed to cool to 25 ° C. in one cycle. After repeating 10 cycles and 15 cycles, plating, a copper circuit, and a copper heat sink were removed by etching, and the presence or absence of cracks or horizontal cracks in the aluminum nitride substrate was observed using an optical stereomicroscope. Those without horizontal cracks were evaluated as good, and those with horizontal cracks were evaluated in the following three stages.
Horizontal crack A: Length less than 50 μm Horizontal crack B: Length 50 μm or more and less than 100 μm Horizontal crack C: Length 100 μm or more
各評価を勘案し、総合評価として以下の４段階で評価した。
◎：すべての評価において良好な結果であったもの。
○：耐熱サイクル特性の１５サイクルにて水平クラックＡがみられるが、その他の評価において良好な結果であり、実用上、問題無いと考えられるもの。
△：耐熱サイクル特性の１５サイクルにて水平クラックＢがみられるが、その他の評価において良好な結果であり、実用上、問題無いと考えられるもの。
×：耐熱サイクル特性の１０サイクルやその他の評価が悪く、実用上の問題を生じる可能性のあるもの。
Considering each evaluation, the following four levels were evaluated as a comprehensive evaluation.
A: Good results in all evaluations.
○: A horizontal crack A is observed in 15 cycles of the heat resistance cycle characteristics, but other evaluations are good results, and it is considered that there is no problem in practical use.
Δ: Although horizontal cracks B are observed in 15 cycles of the heat resistance cycle characteristics, it is a good result in other evaluations, and it is considered that there is no problem in practical use.
X: 10 cycles of heat-resistant cycle characteristics and other evaluations are bad, and there is a possibility of causing practical problems.
本発明の回路基板は、複数の半導体を搭載する回路基板として使用され、具体的には、例えば電鉄、電気自動車、一般産業用のインバータ等に用いられる。 The circuit board of the present invention is used as a circuit board on which a plurality of semiconductors are mounted. Specifically, for example, it is used for electric railways, electric vehicles, general industrial inverters, and the like.
１ セラミックス基板
２ 金属回路
３ 金属放熱板
４ ろう材層
５ 段差構造のステップ部
６ 段差構造のスロープ部
Ｓ１ 金属回路のステップ部の長さ
Ｓ２ 金属放熱板のステップ部の長さ
ｔ ステップ部の厚み
Ｌ１ 金属回路２の、ろう材層端部からステップ部側壁までの合計長さ
Ｌ２ 金属放熱板３の、ろう材層端部からステップ部側壁までの合計長さ
Ｅ１ 金属回路２の、ろう材層端部の先端からセラミックス基板端部までの長さ
Ｅ２ 金属放熱板３の、ろう材層端部の先端からセラミックス基板端部までの長さ
α１ 金属回路のスロープ角度
α２ 金属放熱板のスロープ角度
DESCRIPTION OF SYMBOLS 1 Ceramic substrate 2 Metal circuit 3 Metal heat sink 4 Brazing material layer 5 Step part of step structure 6 Slope part of step structure S1 Length of step part of metal circuit S2 Length of step part of metal heat sink t Thickness of step part L1 Total length of the metal circuit 2 from the end portion of the brazing material layer to the side wall of the step portion L2 Total length of the metal radiator plate 3 from the end portion of the brazing material layer to the side wall of the step portion E1 The brazing material layer of the metal circuit 2 Length E2 from the end of the end to the end of the ceramic substrate E2 Length of the metal heat sink 3 from the end of the brazing material layer end to the end of the ceramic substrate α1 Slope angle of the metal circuit α2 Slope angle of the metal heat sink
Claims (7)
上記ろう材層が金属回路の端部から８０μｍ以下（０を含まず）の長さにはみ出ていること、
上記ろう材層の厚みがいかなる部分においても１０〜２５μｍであること、
上記金属回路及び上記金属放熱板の端部はいずれも段差構造を有し、その段差構造は、長さ（Ｓ１、Ｓ２）が１００〜３００μｍ、厚み（ｔ）が２０〜７０μｍのステップ部（５）と、このステップ部（５）に連続したスロープ部（６）とから構成されており、しかも上記スロープ部（６）のセラミックス基板に対する角度（金属回路のスロープ角度α１、金属放熱板のスロープ角度α２）がいずれも３０°〜７０°であること、
ろう材層端部からステップ部側壁までの合計長さを、金属回路ではＬ１、金属放熱板ではＬ２とし、またろう材層端部からセラミックス基板端部までの長さを、金属回路ではＥ１、金属放熱板ではＥ２としたときに、Ｌ１≦Ｌ２で、しかもＬ１＋Ｅ１≧Ｌ２＋Ｅ２であること
を特徴とする半導体搭載用回路基板。 1 or 2 or more metal circuits (2) are bonded to the front surface of the ceramic substrate (1), and a metal heat sink (3) is bonded to the back surface of the ceramic substrate (1) via a brazing material layer (4),
The brazing filler metal layer protrudes from the end of the metal circuit to a length of 80 μm or less (excluding 0);
The thickness of the brazing filler metal layer is 10 to 25 μm in any part,
The end portions of the metal circuit and the metal heat dissipation plate both have a step structure, and the step structure has a step portion (5 having a length (S1, S2) of 100 to 300 μm and a thickness (t) of 20 to 70 μm. ) And a slope portion (6) continuous to the step portion (5), and the angle of the slope portion (6) with respect to the ceramic substrate (slope angle α1 of the metal circuit, slope angle of the metal heat sink) α2) are all 30 ° to 70 °,
The total length from the brazing material layer end to the step side wall is L1 for the metal circuit, L2 for the metal heat sink, and the length from the brazing material layer end to the ceramic substrate end is E1, for the metal circuit. A circuit board for mounting on a semiconductor, characterized in that L1 ≦ L2 and L1 + E1 ≧ L2 + E2 when E2 in the metal heat sink.
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