WO2020196132A1 - 接合構造体 - Google Patents

接合構造体 Download PDF

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Publication number
WO2020196132A1
WO2020196132A1 PCT/JP2020/011883 JP2020011883W WO2020196132A1 WO 2020196132 A1 WO2020196132 A1 WO 2020196132A1 JP 2020011883 W JP2020011883 W JP 2020011883W WO 2020196132 A1 WO2020196132 A1 WO 2020196132A1
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Prior art keywords
particles
sqrt
bonding material
conductive bonding
circuit pattern
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PCT/JP2020/011883
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English (en)
French (fr)
Inventor
史朗 石川
朋彦 山口
弘太郎 増山
広太郎 岩田
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三菱マテリアル株式会社
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Application filed by 三菱マテリアル株式会社 filed Critical 三菱マテリアル株式会社
Priority to KR1020217025349A priority Critical patent/KR20210141927A/ko
Priority to EP20779040.3A priority patent/EP3944303A4/en
Priority to CN202080009858.8A priority patent/CN113330559A/zh
Priority to US17/419,800 priority patent/US20220093553A1/en
Publication of WO2020196132A1 publication Critical patent/WO2020196132A1/ja

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Definitions

  • the present invention relates to a bonded structure.
  • the present application claims priority based on Japanese Patent Application No. 2019-0553666 filed in Japan on March 22, 2019, the contents of which are incorporated herein by reference.
  • a metal base substrate is known as one of the substrates for mounting electronic components such as LED chips and power modules.
  • the metal base substrate is a laminate in which a metal substrate, an insulating layer, and a circuit layer are laminated in this order.
  • the circuit layer is formed into a predetermined circuit pattern, and the electrode terminals of the electronic component are joined onto the circuit pattern via a conductive bonding material such as solder (Patent Document 1).
  • solder solder
  • a bonded structure in which a member to be joined having electrode terminals such as electronic components and a circuit pattern are joined can efficiently release the heat generated by the member to be joined to the outside, that is, has high heat dissipation. Is preferable.
  • Patent Documents 2 to 5 it has been studied to improve the thermal conductivity of the conductive bonding material.
  • the amount of heat generated in the bonded structure tends to increase with the increase in capacity and output of electronic devices in recent years.
  • the present invention has been made in view of the above circumstances, and an object of the present invention is to improve the heat dissipation of a bonded structure in which a member to be bonded having electrode terminals such as electronic components and a circuit pattern are bonded. That is, it is an object of the present invention to provide a bonded structure capable of efficiently releasing the heat generated in the member to be bonded to the outside.
  • the bonding structure of one aspect of the present invention includes a substrate having a circuit pattern and a member to be bonded having electrode terminals. Is a bonding structure bonded via a conductive bonding material, the contact area between the circuit pattern and the conductive bonding material is X, and the contact area between the electrode terminal and the conductive bonding material is Y. , The following equation (1) is satisfied when the thermal conductivity of the conductive bonding material is ⁇ . SQRT (X) / SQRT (Y) ⁇ 2.9209 ⁇ ⁇ -0.141 (1)
  • the contact area X between the circuit pattern and the conductive bonding material, the contact area Y between the electrode terminal and the conductive bonding material, and the thermal conductivity ⁇ of the conductive bonding material are the above equations ( Since the relationship of 1) is satisfied, the thermal resistance of the bonded structure is reduced. Therefore, the heat generated in the member to be joined can be efficiently released to the outside.
  • the member to be joined may be an LED chip or a power module.
  • the amount of heat generated by the LED chip and the power module is increasing with the recent increase in functionality and miniaturization of electronic devices.
  • the bonded structure of the present invention has high heat dissipation, the member to be bonded is Even LED chips and power modules exhibit excellent heat dissipation, and deterioration of the LED chips and power modules due to heat can be suppressed.
  • the conductive bonding material is a sintered body of at least one metal particle selected from the group consisting of silver particles, copper particles, and copper particles coated with tin. Is preferable.
  • the conductive bonding material has high thermal conductivity, the heat generated by the member to be bonded can be more reliably released to the outside. Further, since the sintered body of metal particles does not melt and have fluidity even in a high temperature state, the member to be joined can be stably fixed.
  • FIG. 1 is a schematic cross-sectional view of a bonded structure according to an embodiment of the present invention.
  • the joint structure 1 is a structure in which a metal base substrate 10 and a member 70 to be joined are joined.
  • the metal base substrate 10 is a laminate in which the metal substrate 20, the insulating layer 30, and the circuit pattern 40 are laminated in this order.
  • the member 70 to be joined includes an electrode terminal 71.
  • the circuit pattern 40 of the metal base substrate 10 and the electrode terminals 71 of the member to be joined 70 are joined via the conductive bonding material 60.
  • the joint structure 1 includes a contact area X (unit: mm 2 ) between the circuit pattern 40 and the conductive joint material 60, a contact area Y (unit: mm 2 ) between the electrode terminal 71 and the conductive joint material 60, and the like.
  • the thermal conductivity ⁇ (unit: W / mK) of the conductive bonding material 60 is set to satisfy the following formula (1). SQRT (X) / SQRT (Y) ⁇ 2.9209 ⁇ ⁇ -0.141 (1)
  • SQRT represents the square root. That is, SQRT (X) / SQRT (Y) is the ratio of the square root of the contact area X between the circuit pattern 40 and the conductive bonding material 60 to the square root of the contact area Y between the electrode terminal 71 and the conductive bonding material 60. ..
  • the SQRT (X) / SQRT (Y) is preferably 100 or less.
  • the thermal resistance is reduced by setting the contact area X and the contact area Y so as to satisfy the above formula (1) with respect to the conductive bonding material 60 having a thermal conductivity ⁇ , and the electrode
  • the heat conductivity from the terminal 71 to the circuit pattern 40 is improved, and the heat transferred to the circuit pattern 40 is easily diffused in the metal base substrate 10.
  • the contact area Y between the electrode terminal 71 and the conductive bonding material 60 varies depending on the power supply voltage of the member to be bonded 70 and the like, but is preferably within the range of 50% or more and 90% or less of the bottom area of the member 70 to be bonded. ..
  • the contact area Y is within the above range, electric power can be stably supplied to the member to be joined 70, and the heat generated in the member 70 to be joined has conductivity from the electrode terminal 71 to the circuit pattern 40. improves.
  • the metal substrate 20 is a member that serves as a base for the metal base substrate 10.
  • a copper plate, an aluminum plate, and a laminated plate thereof can be used as the metal substrate 20.
  • the insulating layer 30 is a layer for insulating the metal substrate 20 and the circuit pattern 40.
  • the insulating layer 30 is formed of an insulating resin composition containing an insulating resin 31 and ceramic particles 32 (thermally conductive filler).
  • a metal substrate is formed from the circuit pattern 40 while maintaining the insulating property. The thermal resistance of the entire metal base substrate 10 up to 20 can be further reduced.
  • the insulating resin 31 is preferably a polyimide resin, a polyamide-imide resin, or a mixture thereof. Since the polyimide resin and the polyamide-imide resin have an imide bond, they have excellent heat resistance and mechanical properties.
  • the ceramic particles 32 silica (silicon dioxide) particles, alumina (aluminum oxide) particles, boron nitride (BN) particles, titanium oxide particles, alumina-doped silica particles, alumina hydrate particles, aluminum nitride particles and the like can be used. It can.
  • the ceramic particles 32 one type may be used alone, or two or more types may be used in combination. Among these ceramic particles, alumina particles are preferable because they have high thermal conductivity.
  • the form of the ceramic particles 32 is not particularly limited, but is preferably agglomerated particles of fine ceramic particles or single crystal ceramic particles.
  • the aggregated particles of the fine ceramic particles may be agglomerates in which the primary particles are relatively weakly connected, or may be aggregates in which the primary particles are relatively strongly connected. Further, the aggregated particles may form a particle aggregate in which the aggregated particles are further aggregated. Since the primary particles of the ceramic particles 32 form aggregated particles and are dispersed in the insulating layer 30, a network is formed by mutual contact between the ceramic particles 32, and heat is conducted between the primary particles of the ceramic particles 32. This facilitates the process and improves the thermal conductivity of the insulating layer 30.
  • Alu65 manufactured by Nippon Aerosil Co., Ltd.
  • alumina particles such as AA-04 (manufactured by Sumitomo Chemical Co., Ltd.), boron nitride particles such as AP-170S (manufactured by Maruka), AEROXIDE (R) TiO2 P90 Titanium oxide particles such as (manufactured by Nippon Aerosil Co., Ltd.), alumina-doped silica particles such as MOX170 (manufactured by Nippon Aerosil Co., Ltd.), alumina hydrate particles manufactured by Sasol, and the like can be used.
  • the single crystal ceramic particles are preferably ⁇ -alumina single crystal particles having a crystal structure of ⁇ -alumina ( ⁇ Al2O3).
  • ⁇ -alumina single crystal particles include AA-03, AA-04, AA-05, AA-07, and AA-1.5 of the Advanced Alumina (AA) series sold by Sumitomo Chemical Co., Ltd. Can be used.
  • the content of the ceramic particles 32 in the insulating layer 30 is preferably in the range of 5% by volume or more and 60% by volume or less. If the content of the ceramic particles 32 is too small, the thermal conductivity of the insulating layer 30 may not be sufficiently improved. On the other hand, if the content of the ceramic particles 32 becomes too large, the content of the insulating resin 31 may be relatively reduced, and the shape of the insulating layer 30 may not be stably maintained. In addition, the ceramic particles 32 tend to form excessively large aggregated particles, and the surface roughness Ra of the insulating layer 30 may increase. In order to surely improve the thermal conductivity of the insulating layer 30, the content of the ceramic particles 32 is preferably 10% by volume or more.
  • the content of the ceramic particles 32 is particularly preferably 50% by volume or less.
  • the film thickness of the insulating layer 30 is not particularly limited, but is preferably in the range of 1 ⁇ m or more and 200 ⁇ m or less, and particularly preferably in the range of 3 ⁇ m or more and 100 ⁇ m or less.
  • the material of the circuit pattern 40 aluminum, copper, silver, gold, tin, iron, nickel, chromium, molybdenum, tungsten, palladium, titanium, zinc and alloys of these metals can be used.
  • aluminum and copper are preferable, and aluminum is particularly preferable.
  • the molding method of the circuit pattern 40 is not particularly limited, and for example, an etching method can be used.
  • the film thickness of the circuit pattern 40 is preferably in the range of 10 ⁇ m or more and 1000 ⁇ m or less, and particularly preferably in the range of 20 ⁇ m or more and 100 ⁇ m or less. If the film thickness of the circuit pattern 40 becomes too thin, the thermal resistance may increase. On the other hand, if the film thickness of the circuit pattern 40 becomes too thick, it may be difficult to form the circuit pattern by the etching method. Further, if the film thickness of the circuit pattern 40 becomes too thick, the thermal stress applied to the circuit pattern 40 increases due to the difference in the coefficient of thermal expansion of each material constituting the joint structure 1, and insulation is performed during the thermal cycle. The layer 30 and the circuit pattern 40 may be easily separated from each other.
  • Examples of the member 70 to be joined are not particularly limited, and examples thereof include semiconductor elements, resistors, capacitors, and crystal oscillators.
  • semiconductor elements include MOSFETs (Metal-oxide-semiconductor field effect transducers), IGBTs (Insulated Gate Bipolar Transistors), LSIs (Large Scale Integration), LEDs (light emitting diodes), LED chips, and LED-CSPs (LED-Chips). Size Package).
  • the conductive bonding material 60 As the material of the conductive bonding material 60, a metal or an alloy can be used.
  • the conductive bonding material 60 is preferably a sintered body of metal particles.
  • metal particles silver particles, copper particles, and tin-coated copper particles (tin-coated copper particles) can be used. One type of these metal particles may be used alone, or two or more types may be used in combination.
  • the thickness of the conductive bonding material 60 is preferably in the range of 1 ⁇ m or more and 100 ⁇ m or less.
  • the metal particle sintered body is heated with a paste containing the metal particles interposed between the circuit pattern 40 of the metal base substrate 10 and the electrode terminal 71 of the member 70 to be joined to sintered the metal particles. It can be done by letting it do.
  • the bonded structure includes, for example, a coating process of applying a metal particle paste to a circuit pattern of a metal base substrate to form a metal particle paste layer, and a loading process of loading a member to be bonded on the metal particle paste layer. It can be manufactured by a method including a joining step of heating a metal base substrate on which a member to be joined is loaded to form a metal particle sintered body.
  • the amount of the metal particle paste applied is the same as that of the metal particle sintered body produced by heating the metal particle paste by obtaining the thermal conductivity ⁇ of the metal particle sintered body generated by heating the metal particle paste in advance.
  • the contact area X with the circuit pattern and the contact area Y between the metal particle sintered body and the electrode terminal are set so as to satisfy the above equation (1).
  • a method of applying the metal particle paste to the circuit pattern of the metal base substrate a method such as a screen printing method can be used.
  • the member to be joined is loaded so that the electrode terminal of the member to be joined is in contact with the metal particle paste layer.
  • the heating temperature of the metal base substrate is the temperature at which the metal particles of the metal particle paste are sintered, and is preferably in the range of 200 ° C. or higher and 350 ° C. or lower.
  • the heating atmosphere is preferably a non-oxidizing atmosphere.
  • the bonding structure 1 of the present embodiment having the above configuration, the contact area X between the circuit pattern 40 and the conductive bonding material 60, the electrode terminals 71 of the member to be bonded 70, and the conductive bonding material 60 Since the contact area Y with and the thermal conductivity ⁇ of the conductive bonding material 60 satisfies the relationship of the above formula (1), the thermal resistance of the bonding structure 1 is reduced. Therefore, the heat generated in the member to be joined can be efficiently released to the outside.
  • the member 70 to be joined exhibits excellent heat dissipation even if it is an LED chip or a power module, and deterioration of the LED chip and the power module due to heat can be suppressed. ..
  • the conductive bonding material 60 is a sintered body of at least one metal particle selected from the group consisting of silver particles, copper particles, and copper particles coated with tin.
  • the conductive bonding material 60 has high thermal conductivity, the heat generated by the member to be bonded 70 can be more reliably released to the outside.
  • the present invention is not limited to this, and can be appropriately changed without departing from the technical idea of the invention.
  • the conductive bonding material 60 a sintered body of metal particles such as silver particles, copper particles, and copper particles coated with tin has been exemplified, but the conductive bonding material has been exemplified. 60 is not limited to these.
  • solder may be used as the conductive bonding material 60.
  • FIG. 2 is a cross-sectional view schematically showing a joint structure used in the simulation for verifying the equation (1).
  • FIG. 3 is a plan view of the joint structure of FIG. The simulation was performed using a LISA finite element analysis system (manufactured by Sonnenhof Holdings).
  • the metal base substrate 10S is a laminate in which the metal substrate 20S, the insulating layer 30S, and the copper foil 40S are laminated in this order.
  • the copper foil 40S is entirely formed on the insulating layer 30S.
  • the member 70S to be joined is connected to the electrode terminal 71S via an AIN (aluminum nitride) member 72S.
  • the member 70S to be joined was an LED chip, and the electrode terminal 71S was a copper terminal.
  • the characteristics of each member of the joint structure 1S are as follows.
  • Metal substrate 20S Plane size: 5 mm x 5 mm, heat transfer coefficient: 300 W / m 2 K Insulation layer 30S: Thickness: 100 ⁇ m, Thermal conductivity: 10 W / mK Copper foil 40S: Thickness: 35 ⁇ m, Thermal conductivity: 400 W / mK Conductive bonding material 60S: Thickness and thermal conductivity are shown in Table 1 below.
  • Electrode terminal 71S Thickness: 35 ⁇ m, Thermal conductivity: 400 W / mK AIN member 72S: Thickness: 635 ⁇ m, Thermal conductivity: 170 W / mK Member to be joined 70S: Thickness: 100 ⁇ m, Thermal conductivity: 1000000000 W / mK, Heat generation density: 20 W / m 3
  • the contact area X (mm 2 ) between the copper foil 40S and the conductive bonding material 60S, the contact area Y (mm 2 ) between the electrode terminal 71S and the conductive bonding material 60S, and SQRT (X) / SQRT (Y) are as follows. It is described in Table 1 of.
  • the heat distribution of the joint structure 1S when the member 70S to be joined generates heat was obtained. Then, the maximum temperature (° C.), the minimum temperature (° C.), and the temperature difference between the maximum temperature and the minimum temperature (maximum temperature-minimum temperature) in each member of the joint structure 1S were obtained. The results are shown in Table 1. Further, the thermal resistance in the joint structure 1S was calculated from the temperature difference between the maximum temperature and the minimum temperature of the joint structure 1S and the calorific value (W) of the member 70S to be joined from the following formula.
  • FIG. 4 is a graph showing the relationship between the SQRT (X) / SQRT (Y) obtained by the simulation and the relative thermal resistance.
  • the simulation results obtained in the joint structure 1S having the same thermal conductivity ⁇ of the conductive joint material 60S are connected by a line. From the results of FIG. 4, it can be seen that when the thermal conductivity ⁇ of the conductive bonding material 60S is the same, the relative thermal resistance decreases as the SQRT (X) / SQRT (Y) increases. Further, it can be seen that as the thermal conductivity ⁇ of the conductive bonding material 60S increases, the amount of decrease in relative thermal resistance as the SQRT (X) / SQRT (Y) increases increases.
  • FIG. 5 is a graph showing the relationship between the thermal conductivity ⁇ of the conductive bonding material obtained by the simulation and SQRT (X) / SQRT (Y) when the relative thermal resistance of the bonded structure is reduced by 2%. ..
  • the black circles in the graph shown in FIG. 5 indicate the thermal conductivity ⁇ of the conductive bonding material 60S and the relative thermal resistance of the bonding structure S1 is reduced by 2% (the relative thermal resistance is 98 in the graph shown in FIG. 4). It is a point where the relationship with SQRT (X) / SQRT (Y) of (when it becomes%) is plotted.
  • the curve in the graph is a power approximation curve obtained by data fitting the plotted black circle points.
  • the region above the power approximation curve is a region in which the relative thermal resistance of the joint structure S1 is reduced by 2% or more. Therefore, from the result of FIG. 5, the contact area (X) between the copper foil 40S (circuit pattern) of the bonding structure S1 and the conductive bonding material 60S, and the contact area between the electrode terminal 71S and the conductive bonding material 60S (Y).
  • Example 2 Bonding structure using a silver particle sintered body as a conductive bonding material
  • An insulating layer (thickness: 30 ⁇ m, alumina particle content: 60% by volume) containing an alumina particle-containing polydimide resin and a copper layer (thickness: 35 ⁇ m) are formed on a copper substrate (30 mm ⁇ 20 mm ⁇ 0.3 mmt). Copper base substrates were prepared by laminating them in order. The copper layer of this copper base substrate was etched by an etching method to form a circuit pattern.
  • a silver particle paste (average particle diameter of silver particles: 150 nm) was applied to the circuit pattern of the copper base substrate to form a silver particle paste coating layer (width: 10 mm, thickness: 50 ⁇ m).
  • the electrode terminals of the LED chip (terminal size: 1.65 mm ⁇ 0.45 mm) were loaded on the silver particle paste.
  • pressurizing (10 Pa) the loaded LED chip it is heated at 300 ° C. in a nitrogen atmosphere to sintered the silver particles of the silver particle paste, and the copper base substrate and the LED chip are sintered with silver particles.
  • a bonded structure joined via a body was produced.
  • Example 3 A bonding structure using a copper particle sintered body as a conductive bonding material
  • the copper base substrate and the LED chip are via the copper particle sintered body, except that the copper particle paste (average particle size of copper particles: 150 nm) is used instead of the silver particle paste.
  • a bonded structure was prepared. Contact area (X) between the circuit pattern of the obtained bonded structure and the silver particle sintered body, contact area (Y) between the electrode terminal of the LED chip and the silver particle sintered body, thermal conductivity of the copper particle sintered body Degree ⁇ was measured respectively.
  • Example 4 A bonding structure using a tin-coated copper particle sintered body as a conductive bonding material
  • the copper base substrate and the LED chip are made of tin-coated copper, except that tin-coated copper particle paste (average particle size of tin-coated copper particles: 9 ⁇ m) is used instead of silver particle paste.
  • a bonded structure bonded via a particle sintered body was produced.
  • the thermal conductivity ⁇ was measured respectively.
  • the joint structure of the present invention can efficiently release the heat generated in the member to be joined to the outside. Therefore, even if the member to be joined is an electronic component such as an LED chip or a power module that generates a large amount of heat, deterioration due to heat can be suppressed.

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Abstract

本発明の接合構造体は、回路パターンを有する基板と、電極端子を備えた被接合部材とが導電性接合材を介して接合した接合構造体であって、前記回路パターンと前記導電性接合材との接触面積をXとし、前記電極端子と前記導電性接合材との接触面積をYとし、前記導電性接合材の熱伝導度をλとしたときに下記の式(1)を満足することを特徴とする。 SQRT(X)/SQRT(Y)≧2.9209×λ-0.141 (1)

Description

接合構造体
 本発明は、接合構造体に関するものである。
 本願は、2019年3月22日に、日本に出願された特願2019-055366号に基づき優先権を主張し、その内容をここに援用する。
 LEDチップやパワーモジュールなどの電子部品を実装するための基板の一つとして、金属ベース基板が知られている。金属ベース基板は、金属基板と、絶縁層と、回路層とがこの順で積層された積層体である。回路層は、所定の回路パターンに成形され、電子部品の電極端子は、回路パターンの上に、半田などの導電性接合材を介して接合される(特許文献1)。このような構成とされた金属ベース基板では、電子部品にて発生した熱は、絶縁層を介して金属基板に伝達され、金属基板から外部に放熱される。
 電子部品などの電極端子を備えた被接合部材と、回路パターンとを接合した接合構造体は、被接合部材にて発生した熱を、外部に効率よく放出させることができること、すなわち放熱性が高いことが好ましい。接合構造体の放熱性を高めるために、導電性接合材の熱伝導度を向上させることが検討されている(特許文献2~5)。
特開2014-103314号公報 特開2018-172792号公報 特開2018-168226号公報 特開2018-152176号公報 特開2016-204733号公報
 ところで、近年の電子機器の高容量化や高出力化に伴って、接合構造体にて発生する熱量は増加する傾向にある。しかしながら、接合材の熱伝導度を向上させることだけでは、電子機器のさらなる高容量化や高出力化に対応するには限界がある。
 本発明は、前述した事情に鑑みてなされたものであって、その目的は、電子部品などの電極端子を備えた被接合部材と、回路パターンとを接合した接合構造体の放熱性を向上させること、すなわち被接合部材にて発生した熱を、外部に効率よく放出させることができる接合構造体を提供することにある。
 上記の課題を解決するために、本発明の一態様の接合構造体(以下、「本発明の接合構造体」と称する)は、回路パターンを有する基板と、電極端子を備えた被接合部材とが導電性接合材を介して接合した接合構造体であって、前記回路パターンと前記導電性接合材との接触面積をXとし、前記電極端子と前記導電性接合材との接触面積をYとし、前記導電性接合材の熱伝導度をλとしたときに下記の式(1)を満足することを特徴とする。
   SQRT(X)/SQRT(Y)≧2.9209×λ-0.141 (1)
 本発明の接合構造体では、回路パターンと導電性接合材との接触面積Xと電極端子と導電性接合材との接触面積Yと、導電性接合材の熱伝導度λとが上記の式(1)の関係を満足するので、接合構造体の熱抵抗が低減する。このため、被接合部材にて発生した熱を、外部に効率よく放出させることができる。
 ここで、本発明の接合構造体においては、前記被接合部材が、LEDチップ、もしくはパワーモジュールであってもよい。
 この場合、LEDチップ及びパワーモジュールは、近年の電子機器の高機能化や小型化に伴って発熱量が増加しているが、本発明の接合構造体は放熱性が高いため、被接合部材が、LEDチップやパワーモジュールであっても優れた放熱性を示し、熱によるLEDチップ及びパワーモジュールの劣化を抑制することができる。
 また、本発明の接合構造体においては、前記導電性接合材が、銀粒子、銅粒子、スズで被覆された銅粒子からなる群より選ばれる少なくとも1種の金属粒子の焼結体であることが好ましい。
 この場合、導電性接合材は高い熱伝導性を有するので、より確実に、被接合部材にて発生した熱を、外部に効率よく放出させることができる。また、金属粒子の焼結体は、高温状態であっても溶融して流動性を持つことがないので、被接合部材を安定して固定することができる。
 本発明によれば、被接合部材にて発生した熱を、外部に効率よく放出させることができる接合構造体を提供することが可能となる。
本発明の一実施形態に係る接合構造体の概略断面図である。 式(1)を検証するためのシミュレーションに用いた接合構造体を模式的に示す断面図である。 図2に示す接合構造体の平面図である。 シミュレーションで得られたSQRT(X)/SQRT(Y)と相対熱抵抗との関係を示すグラフである。 シミュレーションで得られた導電性接合材の熱伝導度λと接合構造体の相対熱抵抗が2%減少するときのSQRT(X)/SQRT(Y)との関係を示すグラフである。
 以下に、本発明の実施形態である接合構造体について、添付した図面を参照して説明する。
 図1は、本発明の一実施形態に係る接合構造体の概略断面図である。
 図1において、接合構造体1は、金属ベース基板10と、被接合部材70とが接合した構造体である。金属ベース基板10は、金属基板20、絶縁層30と、回路パターン40とがこの順で積層された積層体である。被接合部材70は電極端子71を備える。金属ベース基板10の回路パターン40と、被接合部材70の電極端子71とが、導電性接合材60を介して接合されている。
 接合構造体1は、回路パターン40と導電性接合材60との接触面積X(単位:mm)と、電極端子71と導電性接合材60との接触面積Y(単位:mm)と、導電性接合材60の熱伝導度λ(単位:W/mK)が、下記の式(1)を満足するようにされている。
   SQRT(X)/SQRT(Y)≧2.9209×λ-0.141 (1)
 式(1)において、SQRTは平方根を表す。すなわち、SQRT(X)/SQRT(Y)は、電極端子71と導電性接合材60との接触面積Yの平方根に対する回路パターン40と導電性接合材60との接触面積Xの平方根の比である。SQRT(X)/SQRT(Y)は100以下であることが好ましい。
 接合構造体1は、熱伝導度λの導電性接合材60に対して、上記式(1)を満足するように接触面積Xと接触面積Yとを設定することによって熱抵抗が低減し、電極端子71から回路パターン40への熱の伝導性が向上すると共に、回路パターン40に伝わった熱が金属ベース基板10内に拡散しやすくなる。
 電極端子71と導電性接合材60との接触面積Yは、被接合部材70の電源電圧などによって異なるが、被接合部材70の底面積の5割以上9割以下の範囲内にあることが好ましい。接触面積Yが上記の範囲内にあると、被接合部材70に対して電力を安定して供給でき、かつ被接合部材70にて発生した熱の電極端子71から回路パターン40への伝導性が向上する。
 金属基板20は、金属ベース基板10のベースとなる部材である。金属基板20としては、銅板、アルミニウム板及びこれらの積層板を用いることができる。
 絶縁層30は、金属基板20と回路パターン40とを絶縁するための層である。絶縁層30は、絶縁性樹脂31とセラミック粒子32(熱伝導性フィラー)とを含む絶縁性樹脂組成物から形成されている。絶縁層30を、絶縁性が高い絶縁性樹脂31と、熱伝導度が高いセラミック粒子32とを含む絶縁性樹脂組成物から形成することによって、絶縁性を維持しつつ、回路パターン40から金属基板20までの金属ベース基板10全体の熱抵抗をより低減させることができる。
 絶縁性樹脂31は、ポリイミド樹脂又はポリアミドイミド樹脂、もしくはこれらの混合物であることが好ましい。ポリイミド樹脂及びポリアミドイミド樹脂は、イミド結合を持つので、優れた耐熱性と機械特性を有する。
 セラミック粒子32としては、シリカ(二酸化ケイ素)粒子、アルミナ(酸化アルミニウム)粒子、窒化ホウ素(BN)粒子、酸化チタン粒子、アルミナドープシリカ粒子、アルミナ水和物粒子、窒化アルミニウム粒子などを用いることができる。セラミック粒子32は、1種を単独で使用してもよいし、2種以上を組合せて使用してもよい。これらのセラミック粒子の中では、アルミナ粒子は熱伝導性が高い点で好ましい。セラミック粒子32の形態は、特に制限はないが、微細なセラミック粒子の凝集粒子、あるいは単結晶のセラミック粒子であることが好ましい。
 微細なセラミック粒子の凝集粒子は、一次粒子が比較的弱く連結しているアグロメレートであってもよいし、一次粒子が比較的強く連結しているアグリゲートであってもよい。また、凝集粒子同士がさらに集合した粒子集合体を形成していてもよい。セラミック粒子32の一次粒子が凝集粒子を形成して絶縁層30中に分散していることによって、セラミック粒子32間の相互接触によるネットワークが形成されて、セラミック粒子32の一次粒子間を熱が伝導しやすくなり、絶縁層30の熱伝導度が向上する。
 微細なセラミック粒子の凝集粒子の市販品としては、AE50、AE130、AE200、AE300、AE380、AE90E(いずれも、日本アエロジル株式会社製)、T400(ワッカー社製)、SFP-20M(デンカ株式会社製)などのシリカ粒子、Alu65(日本アエロジル株式会社製)、AA-04(住友化学株式会社製)などのアルミナ粒子、AP-170S(Maruka社製)などの窒化ホウ素粒子、AEROXIDE(R)TiO2 P90(日本アエロジル株式会社製)などの酸化チタン粒子、MOX170(日本アエロジル株式会社製)などのアルミナドープシリカ粒子、Sasol社製のアルミナ水和物粒子などを用いることができる。
 単結晶のセラミック粒子は、αアルミナ(αAl2O3)の結晶構造を有するαアルミナ単結晶粒子であることが好ましい。αアルミナ単結晶粒子の市販品としては、住友化学株式会社から販売されているアドバンストアルミナ(AA)シリーズのAA-03、AA-04、AA-05、AA-07、AA-1.5などを用いることができる。
 絶縁層30のセラミック粒子32の含有量は、5体積%以上60体積%以下の範囲内にあることが好ましい。セラミック粒子32の含有量が少なくなりすぎると、絶縁層30の熱伝導性が十分に向上しないおそれがある。一方、セラミック粒子32の含有量が多くなりすぎると、絶縁性樹脂31の含有量が相対的に減少して、絶縁層30の形状を安定に維持できなくなるおそれがある。また、セラミック粒子32が過剰に大きな凝集粒子を形成しやすくなり、絶縁層30の表面粗さRaが大きくなるおそれがある。絶縁層30の熱伝導性を確実に向上させるためには、セラミック粒子32の含有量は10体積%以上であることが好ましい。また、絶縁層30の形状の安定性を確実に向上させ、表面粗さRaを低くするためには、セラミック粒子32の含有量は50体積%以下であることが特に好ましい。
 絶縁層30の膜厚は、特には制限されるものではないが、1μm以上200μm以下の範囲内にあることが好ましく、3μm以上100μm以下の範囲内にあることが特に好ましい。
 回路パターン40の材料としては、アルミニウム、銅、銀、金、錫、鉄、ニッケル、クロム、モリブデン、タングステン、パラジウム、チタン、亜鉛及びこれら金属の合金を用いることができる。これらの金属の中では、アルミニウム、銅が好ましく、特にアルミニウムが好ましい。回路パターン40の成形方法としては、特に制限なく、例えば、エッチング法を用いることができる。
 回路パターン40の膜厚は、好ましくは10μm以上1000μm以下の範囲内、特に好ましくは20μm以上100μm以下の範囲内にある。回路パターン40の膜厚が薄くなりすぎると、熱抵抗が高くなるおそれがある。一方、回路パターン40の膜厚が厚くなりすぎると、エッチング法により回路パターンを形成するのが困難となるおそれがある。また、回路パターン40の膜厚が厚くなりすぎると、接合構造体1を構成する各材料の熱膨張係数の差異によって、回路パターン40に付与される熱応力が大きくなり、冷熱サイクル中に、絶縁層30と回路パターン40とが剥離しやすくなるおそれがある。
 被接合部材70の例としては、特に制限はなく、半導体素子、抵抗、キャパシタ、水晶発振器などが挙げられる。半導体素子の例としては、MOSFET(Metal-oxide-semiconductor field effect transistor)、IGBT(Insulated Gate Bipolar Transistor)、LSI(Large Scale Integration)、LED(発光ダイオード)、LEDチップ、LED-CSP(LED-Chip Size Package)が挙げられる。
 導電性接合材60の材料としては、金属もしくは合金を用いることができる。導電性接合材60は、金属粒子の焼結体であることが好ましい。金属粒子としては、銀粒子、銅粒子、スズで被覆された銅粒子(スズ被覆銅粒子)を用いることができる。これらの金属粒子は1種を単独で使用してもよいし、2種以上を組合せて使用してもよい。導電性接合材60の厚みは、1μm以上100μm以下の範囲内にあることが好ましい。
 金属粒子の焼結体は、金属ベース基板10の回路パターン40と、被接合部材70の電極端子71との間に金属粒子を含むペーストを介在させた状態で加熱して、金属粒子を焼結させることによって成させることができる。
 次に、本実施形態の接合構造体の製造方法について説明する。
 接合構造体は、例えば、金属ベース基板の回路パターンに金属粒子ペーストを塗布して金属粒子ペースト層を形成する塗布工程と、金属粒子ペースト層の上に、被接合部材を積載する積載工程と、被接合部材を積載した金属ベース基板を加熱して、金属粒子焼結体を生成させる接合工程とを含む方法によって製造することができる。
 塗布工程において、金属粒子ペーストの塗布量は、金属粒子ペーストの加熱によって生成する金属粒子焼結体の熱伝導度λを予め求めておき、金属粒子ペーストの加熱によって生成する金属粒子焼結体と回路パターンとの接触面積X、及び金属粒子焼結体と電極端子との接触面積Yが上記の式(1)を満足するように設定する。金属ベース基板の回路パターンに金属粒子ペーストを塗布する方法としては、スクリーン印刷法などの方法を用いることができる。
 積載工程では、被接合部材の電極端子が金属粒子ペースト層に接するように、被接合部材を積載する。
 接合工程において、金属ベース基板の加熱は、被接合部材を加圧しながら行うことが好ましい。金属ベース基板の加熱温度は、金属粒子ペーストの金属粒子が焼結する温度であり、200℃以上350℃以下の範囲内にあることが好ましい。加熱雰囲気は、非酸化雰囲気であることが好ましい。
 以上のような構成とされた本実施形態の接合構造体1によれば、回路パターン40と導電性接合材60との接触面積Xと、被接合部材70の電極端子71と導電性接合材60との接触面積Yと、導電性接合材60の熱伝導度λとが上記の式(1)の関係を満足するので、接合構造体1の熱抵抗が低減する。このため、被接合部材にて発生した熱を、外部に効率よく放出させることができる。
 また、本実施形態の接合構造体1においては、被接合部材70が、LEDチップやパワーモジュールであっても優れた放熱性を示し、熱によるLEDチップ及びパワーモジュールの劣化を抑制することができる。
 また、本実施形態の接合構造体1において、導電性接合材60が、銀粒子、銅粒子、スズで被覆された銅粒子からなる群より選ばれる少なくとも1種の金属粒子の焼結体である場合は、導電性接合材60は高い熱伝導性を有するので、より確実に、被接合部材70にて発生した熱を、外部に効率よく放出させることができる。
 以上、本発明の実施形態について説明したが、本発明はこれに限定されることはなく、その発明の技術的思想を逸脱しない範囲で適宜変更可能である。
 例えば、本実施形態の接合構造体1においては、導電性接合材60として、銀粒子、銅粒子、スズで被覆された銅粒子などの金属粒子の焼結体を例示したが、導電性接合材60はこれらに限定されるものではない。例えば、導電性接合材60として半田を用いてもよい。
 以下に、本発明の作用効果を実施例により説明する。
[本発明例1:シミュレーション]
 図2は、前記式(1)を検証するためのシミュレーションに用いた接合構造体を模式的に示す断面図である。図3は、図2の接合構造体の平面図である。シミュレーションはLISA有限要素解析システム(Sonnenhof Holdings社製)を用いて行った。
 図2、3に示す接合構造体1Sにおいて、金属ベース基板10Sは、金属基板20S、絶縁層30Sと、銅箔40Sとがこの順で積層された積層体である。銅箔40Sは絶縁層30Sの上に全体に形成されている。被接合部材70Sは、AIN(窒化アルミニウム)部材72Sを介して電極端子71Sと接続している。被接合部材70Sは、LEDチップとし、電極端子71Sは銅端子とした。接合構造体1Sの各部材の特性は、下記の通りとした。
 金属基板20S:平面のサイズ:5mm×5mm、熱伝達係数:300W/m
 絶縁層30S:厚み:100μm、熱伝導度:10W/mK
 銅箔40S:厚み:35μm、熱伝導度:400W/mK
 導電性接合材60S:厚み、熱伝導度は、下記の表1に記載した。
 電極端子71S:厚み:35μm、熱伝導度:400W/mK
 AIN部材72S:厚み:635μm、熱伝導度:170W/mK
 被接合部材70S:厚み:100μm、熱伝導度:1000000000W/mK、発熱密度:20W/m
 銅箔40Sと導電性接合材60Sとの接触面積X(mm)、電極端子71Sと導電性接合材60Sとの接触面積Y(mm)、SQRT(X)/SQRT(Y)は、下記の表1に記載した。
 シミュレーションにより、被接合部材70Sが発熱したときの接合構造体1Sの熱分布を得た。そして、接合構造体1Sの各部材中の最高温度(℃)と、最低温度(℃)と、最高温度と最低温度の温度差(最高温度-最低温度)を求めた。その結果を、表1に示す。
 また、接合構造体1Sの最高温度と最低温度の温度差と、被接合部材70Sの発熱量(W)から、下記の式より接合構造体1S内の熱抵抗を算出した。そして、導電性接合材60Sの熱伝導度λが同じで、SQRT(X)/SQRT(Y)が異なる接合構造体1Sについて、SQRT(X)/SQRT(Y)=1.2の熱抵抗を100とした場合の熱抵抗の相対値を求めた。この結果を、相対熱抵抗(%)として表1に示す。
  熱抵抗(K/W)=(最高温度-最低温度)/発熱量
Figure JPOXMLDOC01-appb-T000001
 図4は、シミュレーションで得られたSQRT(X)/SQRT(Y)と相対熱抵抗との関係を示すグラフである。図4において、導電性接合材60Sの熱伝導度λが同じ接合構造体1Sで得られたシミュレーション結果を線で結んでいる。図4の結果から、導電性接合材60Sの熱伝導度λが同じである場合は、SQRT(X)/SQRT(Y)が増加するに伴って、相対熱抵抗が低下することがわかる。また、導電性接合材60Sの熱伝導度λが大きくなるにしたがって、SQRT(X)/SQRT(Y)が増加することに伴う相対熱抵抗の低下量が大きくなることがわかる。
 図5は、シミュレーションで得られた導電性接合材の熱伝導度λと接合構造体の相対熱抵抗が2%減少するときのSQRT(X)/SQRT(Y)との関係を示すグラフである。図5に示すグラフ中の黒丸の点は、導電性接合材60Sの熱伝導度λと、接合構造体S1の相対熱抵抗が2%減少するとき(図4に示すグラフにおいて相対熱抵抗が98%となるとき)のSQRT(X)/SQRT(Y)との関係をプロットした点である。また、グラフ中の曲線は、プロットした黒丸の点をデータフィッテングした累乗近似曲線である。この累乗近似曲線は、SQRT(X)/SQRT(Y)=2.9209×λ-0.141で示されている。図5に示すグラフにおいて、この累乗近似曲線より上側の領域が、接合構造体S1の相対熱抵抗が2%以上低減する領域となる。したがって、この図5の結果から、接合構造体S1の銅箔40S(回路パターン)と導電性接合材60Sとの接触面積(X)、電極端子71Sと導電性接合材60Sとの接触面積(Y)、導電性接合材60Sの熱伝導度λが、SQRT(X)/SQRT(Y)≧2.9209×λ-0.141の関係を満たす場合は、相対熱抵抗を2%以上低減できることがわかる。
[本発明例2:導電性接合材に銀粒子焼結体を用いた接合構造体]
 銅基板(30mm×20mm×0.3mmt)の上に、アルミナ粒子含有ポリドイミド樹脂を含む絶縁層(厚み:30μm、アルミナ粒子含有量:60体積%)と、銅層(厚み:35μm)とがこの順で積層され銅ベース基板を作製した。この銅ベース基板の銅層をエッチング法によりエッチングして、回路パターンを形成した。
 銅ベース基板の回路パターンに銀粒子ペースト(銀粒子の平均粒子径:150nm)を塗布して銀粒子ペースト塗布層(幅:10mm、厚み:50μm)を形成した。次いで、銀粒子ペーストの上に、LEDチップの電極端子(端子のサイズ:1.65mm×0.45mm)を積載した。そして、積載したLEDチップを加圧(10Pa)しながら、窒素雰囲気下、300℃で加熱して、銀粒子ペーストの銀粒子を焼結させて、銅ベース基板とLEDチップとが銀粒子焼結体を介して接合した接合構造体を作製した。
 得られた接合構造体の回路パターンと銀粒子焼結体との接触面積(X)、LEDチップの電極端子と銀粒子焼結体との接触面積(Y)、銀粒子焼結体の熱伝導度λをそれぞれ測定した。そして、SQRT(X)/SQRT(Y)と、2.9209×λ-0.141とを算出した結果、SQRT(X)/SQRT(Y)は23.2であり、2.9209×λ-0.141は1.3であった。また、得られた接合構造体を目視で観察した結果、LEDチップの位置ずれや浮きは確認されなかった。
[本発明例3:導電性接合材に銅粒子焼結体を用いた接合構造体]
 銀粒子ペーストの代わりに銅粒子ペースト(銅粒子の平均粒子径:150nm)を用いたこと以外は、本発明例2と同様にして、銅ベース基板とLEDチップとが銅粒子焼結体を介して接合した接合構造体を作製した。
 得られた接合構造体の回路パターンと銀粒子焼結体との接触面積(X)、LEDチップの電極端子と銀粒子焼結体との接触面積(Y)、銅粒子焼結体の熱伝導度λをそれぞれ測定した。そして、SQRT(X)/SQRT(Y)と、2.9209×λ-0.141とを算出した結果、SQRT(X)/SQRT(Y)は23.2であり、2.9209×λ-0.141は1.3であった。また、得られた接合構造体を目視で観察した結果、LEDチップの位置ずれや浮きは確認されなかった。
 [本発明例4:導電性接合材にスズ被覆銅粒子焼結体を用いた接合構造体]
 銀粒子ペーストの代わりにスズ被覆銅粒子ペースト(スズ被覆銅粒子の平均粒子径:9μm)を用いたこと以外は、本発明例2と同様にして、銅ベース基板とLEDチップとがスズ被覆銅粒子焼結体を介して接合した接合構造体を作製した。
 得られた接合構造体の回路パターンと銀粒子焼結体との接触面積(X)、LEDチップの電極端子と銀粒子焼結体との接触面積(Y)、スズ被覆銅粒子焼結体の熱伝導度λをそれぞれ測定した。そして、SQRT(X)/SQRT(Y)と、2.9209×λ-0.141とを算出した結果、SQRT(X)/SQRT(Y)は23.2であり、2.9209×λ-0.141は1.8であった。また、得られた接合構造体を目視で観察した結果、LEDチップの位置ずれや浮きは確認されなかった。
 本発明の接合構造体は、被接合部材にて発生した熱を、外部に効率よく放出させることができる。このため、被接合部材がLEDチップやパワーモジュールなどの発熱量が多い電子部品であっても、熱による劣化を抑制することができる。
 1、1S 接合構造体
 10、10S 金属ベース基板
 20、20S 金属基板
 30、30S 絶縁層
 31 絶縁性樹脂
 32 セラミック粒子
 40 回路パターン
 40S 銅箔
 60、60S 導電性接合材
 70、70S 被接合部材
 71、71S 電極端子
 72S AIN(窒化アルミニウム)部材

Claims (3)

  1.  回路パターンを有する基板と、電極端子を備えた被接合部材とが導電性接合材を介して接合した接合構造体であって、
     前記回路パターンと前記導電性接合材との接触面積をXとし、前記電極端子と前記導電性接合材との接触面積をYとし、前記導電性接合材の熱伝導度をλとしたときに下記の式(1)を満足することを特徴とする接合構造体。
       SQRT(X)/SQRT(Y)≧2.9209×λ-0.141 (1)
  2.  前記被接合部材が、LEDチップ、もしくはパワーモジュールであることを特徴とする請求項1に記載の接合構造体。
  3.  前記導電性接合材が、銀粒子、銅粒子、スズで被覆された銅粒子からなる群より選ばれる少なくとも1種の金属粒子の焼結体であることを特徴とする請求項1または2に記載の接合構造体。
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