JP2006179538A - Semiconductor power module - Google Patents

Semiconductor power module Download PDF

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JP2006179538A
JP2006179538A JP2004368629A JP2004368629A JP2006179538A JP 2006179538 A JP2006179538 A JP 2006179538A JP 2004368629 A JP2004368629 A JP 2004368629A JP 2004368629 A JP2004368629 A JP 2004368629A JP 2006179538 A JP2006179538 A JP 2006179538A
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resin
chip
power module
semiconductor power
solder
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Tasao Soga
太佐男 曽我
Daisuke Kawase
大助 川瀬
Chikara Tanaka
主税 田中
Hidekazu Morizaki
英一 森崎
Kazuhiro Suzuki
和弘 鈴木
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Hitachi Ltd
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Hitachi Ltd
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    • H01L2224/26—Layer connectors, e.g. plate connectors, solder or adhesive layers; Manufacturing methods related thereto
    • H01L2224/31—Structure, shape, material or disposition of the layer connectors after the connecting process
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    • H01L2224/83—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a layer connector
    • H01L2224/83909—Post-treatment of the layer connector or bonding area
    • H01L2224/83951—Forming additional members, e.g. for reinforcing, fillet sealant
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    • H01L2224/85—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a wire connector
    • H01L2224/85909—Post-treatment of the connector or wire bonding area
    • H01L2224/8592—Applying permanent coating, e.g. protective coating
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Abstract

<P>PROBLEM TO BE SOLVED: To improve thermal fatigue life and moisture resistance of a solder connection part of a resin sealing semiconductor power module. <P>SOLUTION: In the semiconductor power module, a silicon chip and a connection conductor, which are soldered to a ceramic insulating substrate or a resin insulating metal substrate through a thermal diffusion board, are precoated with polyimide resin superior in heat resistance and moisture resistance. Precoat resin is coated and sealed with epoxy resin of a coefficient of linear expansion, which is adjusted to that of solder with a low Young's modulus. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

本願発明は、家電用、産業用、車両用等に広く用いられる半導体パワーモジュールに関する。   The present invention relates to a semiconductor power module widely used for home appliances, industrial use, vehicles, and the like.

半導体パワーモジュールの中ではＩＧＢＴモジュールが広く使用されている。ＩＧＢＴモジュールはＩＧＢＴとＦＷＤ(Free Wheeling Diode) チップとがペアで複数個搭載された構造をとり、通常各４〜６チップが搭載される。電流は２５Ａ〜１８００Ａ、電圧は２００〜３３００Ｖを対象にしている。端子数は信号を含めて少なくとも４端子以上である。   Among semiconductor power modules, IGBT modules are widely used. The IGBT module has a structure in which a plurality of IGBTs and FWD (Free Wheeling Diode) chips are mounted in pairs, and usually 4 to 6 chips are mounted. The current is 25A to 1800A, and the voltage is 200 to 3300V. The number of terminals is at least 4 or more including signals.

半導体パワーモジュールは、発熱量の大きな中容量〜大容量の製品、コスト対応で、セラミックス絶縁基板、樹脂絶縁金属基板等の使い分けがなされている。これらの基板をシリコーンゲルで充填し、その上を硬いエポキシ樹脂で封止する構造が一般に使用されている。他方、低コスト、高信頼化のためエポキシ系樹脂で直接封止する構造が中、小型品で採用されている。   Semiconductor power modules are used for medium- to large-capacity products with a large calorific value, and for cost, ceramic insulating substrates, resin-insulated metal substrates, etc. are used properly. A structure is generally used in which these substrates are filled with silicone gel and the top is sealed with a hard epoxy resin. On the other hand, a structure that is directly sealed with an epoxy-based resin for low cost and high reliability is used for medium-sized products.

特許文献１には、部品類の全面保護としてシリコーンゲルが注入され、その上にエポキシ樹脂が注入された構造が記されている。しかし、チップ、基板等がシリコーンゲルで直接に被覆されている構造なのでヤング率が低く、チップ、基板等を拘束できないのでハンダの寿命向上が達成できない。   Patent Document 1 describes a structure in which a silicone gel is injected as an overall protection of parts, and an epoxy resin is injected thereon. However, since the chip, the substrate, etc. are directly covered with the silicone gel, the Young's modulus is low, and the chip, the substrate, etc. cannot be constrained, so that the life of the solder cannot be improved.

特許文献２には、樹脂封止型半導体装置の、耐湿性と、封止用樹脂との密着性とを良くするため、封止用樹脂より低硬度、例えばポリイミド系樹脂を第２の樹脂の層として設けることが開示されている。リードフレームと封止外装用樹脂との界面での剥離に起因する耐湿性の低下を防止することを目的としている。   In Patent Document 2, in order to improve the moisture resistance of the resin-encapsulated semiconductor device and the adhesion to the sealing resin, a hardness lower than that of the sealing resin, for example, a polyimide resin is used. Providing as a layer is disclosed. The object is to prevent a decrease in moisture resistance due to peeling at the interface between the lead frame and the sealing exterior resin.

また、特許文献３には樹脂封止型半導体装置において、パワー素子部をポリイミド系、またはポリアミドイミド系でコーテイング後、線膨張係数が３×１０-6／℃〜１７×１０-6／℃の樹脂でトランスファーモールドし、熱膨張係数のバランスを取り、熱応力を低減させ寿命向上、密着性を向上させることが開示されている。 Patent Document 3 discloses a resin-encapsulated semiconductor device having a linear expansion coefficient of 3 × 10 −6 / ° C. to 17 × 10 −6 / ° C. after coating the power element portion with polyimide or polyamideimide. It is disclosed that transfer molding is performed with a resin to balance the thermal expansion coefficient, thereby reducing thermal stress and improving life and adhesion.

特開平６−５７４２号公報（全体）JP-A-6-5742 (Overall) 特開平１１−１６３０２３号公報（図１、図２、全体）Japanese Patent Laid-Open No. 11-163023 (FIGS. 1 and 2, overall) 特開平２００１−１５６８２号公報（図１、全体）Japanese Patent Laid-Open No. 2001-15682 (FIG. 1, overall)

パワーサイクル、温度サイクル試験でのシリコーンゲル構造における破壊モードは、Ｓｉチップとセラミックス基板間、もしくはセラミックス基板とＣｕもしくはＡｌベース基板間のハンダである。Ｓｉチップの大型化によるチップ下ハンダの寿命、ＡｌＮ基板を用いた場合のＡｌＮ基板下ハンダの寿命が厳しい状況にあり、さらに寿命を向上させる必要がある。このため、エポキシ系樹脂で封止することでシリコーンゲル構造に比べ、寿命を大幅に向上させることを見出した。しかし、この樹脂だけで封止した場合、チップの大型化、厳しい環境試験条件においては、チップ端部に作用する応力が大きくなり、樹脂との界面が剥離し、パワーサイクル、温度サイクルの寿命低下を起し、耐湿性の低下をもたらすことがある。   The failure mode in the silicone gel structure in the power cycle and temperature cycle tests is solder between the Si chip and the ceramic substrate, or between the ceramic substrate and the Cu or Al base substrate. The life of the solder under the chip due to the increase in the size of the Si chip and the life of the solder under the AlN substrate when using the AlN substrate are severe, and it is necessary to further improve the life. For this reason, it discovered that lifetime was significantly improved by sealing with an epoxy resin compared with a silicone gel structure. However, when sealing with only this resin, the stress acting on the end of the chip increases and the interface with the resin peels off when the chip is enlarged and severe environmental test conditions are used, and the life of the power cycle and temperature cycle is reduced. May cause a decrease in moisture resistance.

本願発明の目的は、ハンダの熱疲労寿命と耐湿性を同時に向上させ、かつ素子部の保護を兼ねた半導体パワーモジュールを提供することである。   An object of the present invention is to provide a semiconductor power module that simultaneously improves the thermal fatigue life and moisture resistance of solder and also serves to protect the element portion.

そこで、予め、柔らかいポリイミド系もしくはポリアミドイミド系樹脂で表面を薄く塗布し硬化後、物性を特定化したエポキシ系樹脂で封止することで、低コスト、高性能、高信頼半導体パワーモジュールを実現するものである。特に、耐パワーサイクル、耐温度サイクル及び耐湿性向上を目的として、２種類の樹脂の特長を生かした構造のパワーモジュールを提案するものであり、従来のシリコーンゲルによる封止構造では、構造からくるハンダ寿命の限界にほぼ達しているのに対し、本案は寿命を大幅に向上することができて、界面剥離を防止し、耐湿性を向上させる技術である。   Therefore, a low-cost, high-performance, high-reliability semiconductor power module is realized by applying a thin surface with a soft polyimide-based or polyamide-imide-based resin in advance, and then sealing with an epoxy-based resin with specific physical properties. Is. In particular, we propose a power module with a structure that takes advantage of the characteristics of two types of resin for the purpose of improving power cycle resistance, temperature cycle resistance, and moisture resistance. Although the limit of the solder life is almost reached, this proposal is a technology that can greatly improve the life, prevent interfacial peeling, and improve moisture resistance.

本案はエポキシ系樹脂のチップ拘束によるハンダの寿命が大幅に向上する現象を活用する上で、厳しい条件で発生し易いチップ及びセラミックス端部の界面剥離、素子部の界面剥離及び破壊、チップ破壊等の防止、及びモジュール反り防止を目的として、第２の樹脂（ポリイミド系）を設けて緩和したものである。   This plan uses the phenomenon that the life of the solder is greatly improved due to the chip restraint of epoxy resin, interfacial delamination of the chip and the ceramic end that are likely to occur under severe conditions, interfacial delamination and destruction of the element part, chip destruction, etc. The second resin (polyimide type) is provided and relaxed for the purpose of preventing the above and module warpage.

これに対して、本願発明は３ＧＰａ〜２０ＧＰａの低いヤング率でハンダの線膨張係数２１×１０-6／℃に線膨張係数を合わせたエポキシ系樹脂（１４×１０-6／℃〜２４×１０-6／℃）と薄い柔らかいポリイミド系樹脂との組み合わせによって、チップ拘束によって発生しがちな、チップ端部、素子部の応力による樹脂との界面剥離や、チップ破壊や、モジュールの反りを防止した。 In contrast, the present invention has an epoxy resin (14 × 10 −6 / ° C. to 24 × 10 × 10 × 10 −6 / ° C. to 24 × 10 8) with a low Young's modulus of 3 GPa to 20 GPa and a linear expansion coefficient of solder of 21 × 10 −6 / ° C. -6 / ° C) and a thin soft polyimide resin, which prevents interface debonding from the resin due to stress at the chip edge and element, chip breakage, and module warpage that tend to occur due to chip restraint. .

封止用エポキシ系樹脂のヤング率を下げ、線膨張係数をハンダに合わすことで、ベース基板の線膨張係数に近く、ハンダ付け後の基板の反りを抑え、接続の高い歩留まり化と長寿命化を達成することができる。このエポキシ系樹脂の線膨張係数は、具体的には１４×１０-6／℃〜２４×１０-6／℃である。このような、封止用エポキシ系樹脂のヤング率、線膨張係数の選定により、ハンダのクラック起点での応力集中を抑えることで長寿命化を達成し、かつ、Ｓｉチップ１の破壊を起さないレベルの応力で拘束し、チップ端部及び素子を保護することができる。 By lowering the Young's modulus of the epoxy resin for sealing and matching the linear expansion coefficient to the solder, it is close to the linear expansion coefficient of the base substrate, suppresses the warpage of the substrate after soldering, increases the yield of the connection, and extends the life. Can be achieved. Specifically, the linear expansion coefficient of the epoxy resin is 14 × 10 −6 / ° C. to 24 × 10 −6 / ° C. By selecting the Young's modulus and linear expansion coefficient of the epoxy resin for sealing as described above, it is possible to extend the life by suppressing the stress concentration at the crack starting point of the solder, and to destroy the Si chip 1. It can be constrained by a low level of stress to protect the chip edges and elements.

しかし、チップ端部界面の応力集中部及び強い応力が作用して欲しくない素子部においては、ヤング率が低いエポキシ系樹脂を使用しても、エポキシ系樹脂は相対的にはヤング率が高い部類の樹脂であること、及びＳｉチップ、セラミックス基板等における樹脂の密着力等を考慮すると、このエポキシ系樹脂だけでは界面での負担がかかり過ぎるため、大型チップ及び厳しい環境条件には耐えられない恐れがある。そこで、この構造における弱点であるチップ端部、素子部界面及びセラミックス端部を予め、より柔らかいポリイミド系樹脂で薄く保護することで、その樹脂のせん断方向の変形能とその上を覆うエポキシ系樹脂によるチップ、基板の拘束力によりチップ端部等における応力集中を緩和し、耐パワーサイクル性、耐温度サイクル性、耐湿性の向上、界面における剥離防止、チップ破壊を防止することができる。これにより、より厳しい環境においても耐えられる高信頼パワーモジュールを提供することができる。   However, even in the case of using an epoxy resin with a low Young's modulus in the stress concentration part at the chip end interface and an element part where a strong stress is not desired, the epoxy resin has a relatively high Young's modulus. In view of the resin and adhesion of the resin on the Si chip, ceramic substrate, etc., this epoxy resin alone is too burdensome at the interface, so it may not be able to withstand large chips and severe environmental conditions. There is. Therefore, the chip end, the element interface, and the ceramic end, which are weak points in this structure, are preliminarily protected with a softer polyimide resin, so that the deformability in the shear direction of the resin and the epoxy resin covering it are covered. The stress concentration at the end of the chip or the like can be relaxed by the binding force of the chip and the substrate due to the above, and power cycle resistance, temperature cycle resistance, moisture resistance can be improved, peeling at the interface can be prevented, and chip breakage can be prevented. As a result, it is possible to provide a highly reliable power module that can withstand even a harsh environment.

本願発明は、他の一面において、前記エポキシ系樹脂の選定に加え、室温（１５℃〜２０℃）における前記エポキシ系樹脂のヤング率を３ＧＰａ〜２０ＧＰａとする。   In another aspect of the present invention, in addition to selecting the epoxy resin, the Young's modulus of the epoxy resin at room temperature (15 ° C. to 20 ° C.) is 3 GPa to 20 GPa.

即ち、Ｓｉチップ周辺を、ハンダと同レベルに柔らかくし、かつ密着力のあるエポキシ系樹脂と柔らかい変形性に優れたポリイミドもしくはポリアミドイミド系樹脂を予め界面に塗布して取り囲む。なお、ポリイミド系樹脂に限らずポリイミドとシリコーンの変性体、フィラーを含むポリイミド、封止樹脂より硬度が低いものであれば本願発明に適用することができる。これにより、半導体素子及びチップ端部に大きな応力を作用させないように隔離するように機械的に保護し、Ｓｉチップの保護、界面剥離防止、耐湿性を向上させ、かつ、パワーサイクル、温度サイクルにおけるハンダの寿命を向上させ、さらにモジュールの反りを抑えることができる。   That is, the periphery of the Si chip is softened to the same level as that of solder, and an epoxy resin having adhesion and a polyimide or polyamideimide resin excellent in soft deformability are preliminarily applied to the interface and surrounded. In addition, not only polyimide resin but the modified body of polyimide and silicone, the polyimide containing a filler, and what has hardness lower than sealing resin are applicable to this invention. This mechanically protects the semiconductor element and the chip end so as not to apply a large stress, and protects the Si chip, prevents interfacial delamination, improves moisture resistance, and in power cycle and temperature cycle. The life of the solder can be improved and the warpage of the module can be suppressed.

また、本願発明は、他の一面において、前記樹脂の選定に加え、ガラス転移温度（Ｔｇ）が１５０℃以上の樹脂を使用する。これにより、ガラス転移温度に達することによる線膨張係数の急激な（２倍〜３倍）上昇を避けることで、半導体パワーモジュールの特に高温での信頼性を向上させることができる。   Moreover, this invention uses resin whose glass transition temperature (Tg) is 150 degreeC or more in addition to selection of the said resin in other one surface. Thereby, the reliability of the semiconductor power module at a particularly high temperature can be improved by avoiding a rapid (2 to 3 times) increase in the linear expansion coefficient due to reaching the glass transition temperature.

本願発明においては、封止用エポキシ系樹脂のヤング率を、３ＧＰａ〜２０ＧＰａ、より望ましくは５ＧＰａ〜１０ＧＰａとする。本願発明で、エポキシ系樹脂のヤング率が比較的高くても可能な理由は柔らかいポリイミド系樹脂との複合作用による。   In the present invention, the Young's modulus of the epoxy resin for sealing is 3 GPa to 20 GPa, more preferably 5 GPa to 10 GPa. In the present invention, the reason that is possible even when the Young's modulus of the epoxy resin is relatively high is due to the combined action with a soft polyimide resin.

これにより、Ｓｉチップを拘束できて、Ｓｉチップ界面剥離を防止でき、耐湿性を向上させ、ハンダの寿命向上が期待でき、かつ電気的絶縁、機械的保護等を兼ねる高性能・小型・軽量モジュールが実現できる。   This makes it possible to constrain the Si chip, prevent peeling of the Si chip interface, improve moisture resistance, increase the life of the solder, and provide high performance, small size, and light weight for electrical insulation and mechanical protection. Can be realized.

本願発明は、他の一面において、前記エポキシ系樹脂の選定に加え、室温（１５℃〜２０℃）における前記エポキシ系樹脂のヤング率を３ＧＰａ〜２０ＧＰａとする。即ち、Ｓｉチップ周辺を、ハンダと同レベルに柔らかくし、かつ密着力のあるエポキシ系樹脂と柔らかい変形性に優れたポリイミドもしくはポリアミドイミド系樹脂を予め界面に塗布して取り囲む。これらの材料として、例えば、日立化成製ＨＬ−１２００（ヤング率；２.８ＧＰａ、Ｔｇ；２３０℃）がある。表面被覆用として望ましい物性は０.１ＧＰａ〜３ＧＰａと考えている。弾性率が極端に小さいシリコーンゲル（０.０５ＭＰａ）ではエポキシ樹脂によるチップ等を拘束する効果が伝わり難く、ある程度の弾性率を有する表面被覆用樹脂である必要がある。なお、ポリイミド系樹脂に限らずポリイミドとシリコーンの変性体、フィラーを含むポリイミド、封止樹脂より硬度が低いものであれば本願発明に適用することができる。これにより、半導体素子及びチップ端部に大きな応力を作用させないように隔離するように機械的に素子部等を保護し、チップ等の界面剥離防止、耐湿性を向上させ、かつ、パワーサイクル、温度サイクルにおけるハンダの寿命を大幅に向上させ、さらにモジュールの反りを抑えることができる。   In another aspect of the present invention, in addition to selecting the epoxy resin, the Young's modulus of the epoxy resin at room temperature (15 ° C. to 20 ° C.) is 3 GPa to 20 GPa. That is, the periphery of the Si chip is softened to the same level as that of solder, and an epoxy resin having adhesion and a polyimide or polyamideimide resin excellent in soft deformability are preliminarily applied to the interface and surrounded. As these materials, for example, Hitachi Chemical's HL-1200 (Young's modulus; 2.8 GPa, Tg; 230 ° C.) is available. Desirable physical properties for surface coating are considered to be 0.1 GPa to 3 GPa. A silicone gel (0.05 MPa) having an extremely low elastic modulus hardly transmits the effect of restraining a chip or the like by an epoxy resin, and needs to be a surface coating resin having a certain elastic modulus. In addition, not only polyimide resin but the modified body of polyimide and silicone, the polyimide containing a filler, and what has hardness lower than sealing resin are applicable to this invention. This mechanically protects the element part and the like so as to isolate the semiconductor element and the end of the chip so as not to exert a large stress, prevents interfacial delamination of the chip and the like, improves moisture resistance, power cycle, temperature The life of the solder in the cycle can be greatly improved, and the warpage of the module can be further suppressed.

また、本願発明は、他の一面において、前記樹脂の選定に加え、ガラス転移温度（Ｔｇ）が１５０℃以上の樹脂を使用すると良い。これにより、ガラス転移温度に達することによる線膨張係数の急激な（２倍〜３倍）上昇を避けることで、半導体パワーモジュールの特に高温での信頼性を向上させることができる。   In another aspect of the present invention, in addition to the selection of the resin, a resin having a glass transition temperature (Tg) of 150 ° C. or higher may be used. Thereby, the reliability of the semiconductor power module at a particularly high temperature can be improved by avoiding a rapid (2 to 3 times) increase in the linear expansion coefficient due to reaching the glass transition temperature.

本願発明の望ましい実施形態においては、封止用エポキシ系樹脂のヤング率を、３ＧＰａ〜２０ＧＰａ、より望ましくは５ＧＰａ〜１０ＧＰａとする。エポキシ系樹脂のヤング率が比較的高くても可能な理由は柔らかいポリイミド系樹脂との複合作用による。   In a desirable embodiment of the present invention, the Young's modulus of the epoxy resin for sealing is 3 GPa to 20 GPa, more desirably 5 GPa to 10 GPa. The reason why the Young's modulus of the epoxy resin is relatively high is due to the combined action with the soft polyimide resin.

これにより、Ｓｉチップを拘束できて、Ｓｉチップ界面剥離を防止でき、耐湿性を向上させ、ハンダの寿命向上が期待でき、かつ電気的絶縁、機械的保護等を兼ねる高性能・小型・軽量モジュールが実現できる。   This makes it possible to constrain the Si chip, prevent peeling of the Si chip interface, improve moisture resistance, increase the life of the solder, and provide high performance, small size, and light weight for electrical insulation and mechanical protection. Can be realized.

本願発明によれば、２つの異なった機能を有する樹脂の組合せにより、大型チップ、厳しいパワーサイクル、温度サイクル試験に対してもより耐えられる構造となり、ハンダの熱疲労寿命と耐湿性を同時に向上させ、かつ素子部の保護を兼ねた半導体パワーモジュールを提供することができる。   According to the present invention, the combination of resins having two different functions makes the structure more resistant to large chips, severe power cycle and temperature cycle tests, and improves the thermal fatigue life and moisture resistance of the solder at the same time. In addition, a semiconductor power module that also serves to protect the element portion can be provided.

以下、本願発明の詳細を図面を参照しながら説明する。   Hereinafter, details of the present invention will be described with reference to the drawings.

図１は、本実施例による、エポキシ系樹脂１０で封止した構造のＡｌ2Ｏ3製のセラミックス基板１０２を用いた半導体パワーモジュール（以下、パワーモジュールと略す。）の断面図である。 FIG. 1 is a cross-sectional view of a semiconductor power module (hereinafter abbreviated as a power module) using a ceramic substrate 102 made of Al 2 O 3 having a structure sealed with an epoxy resin 10 according to the present embodiment.

以下、Ａｌ2Ｏ3製のセラミックス基板１０２を用いた場合を説明するが、セラミックス基板１０２に代えて、メタライズされたＳｉチップ裏面ハンダ付けできる熱拡散板を用い、この熱拡散板の裏面を樹脂絶縁性の金属ベース基板にハンダ付けしてもよい。 Hereinafter, although the case where the ceramic substrate 102 made of Al 2 O 3 is used will be described, instead of the ceramic substrate 102, a heat diffusion plate that can be soldered to the back surface of the metallized Si chip is used, and the back surface of the heat diffusion plate is made of resin. Soldering may be performed on an insulating metal base substrate.

本実施例では、裏面に薄膜メタライズを施したＭＯＳＦＥＴ、ＩＧＢＴなどのパワー半導体チップであるＳｉチップ１を、セラミックス基板１０２（Ａｌ2Ｏ3絶縁基板）にＳｎ−３Ａｇ−０.５Ｃｕ の鉛フリーハンダを用いて水素雰囲気の加熱炉（以下、水素炉と称する。）でハンダ付けする。さらに、セラミックス基板１０２の裏のメタライズ膜５（本実施例ではＣｕ／Ｎｉメッキ）と、Ｃｕ板にＮｉメッキしたベース基板４とを、Ｓｎ−３Ａｇ−０.５Ｃｕ の鉛フリーハンダ箔を挟んで水素炉でハンダ付けした。自重等で溶融ハンダが潰れないように、また半導体チップが傾かないようにするために、スペーサを用いても良い。なお、チップ下のハンダ３と基板下のハンダ１６とを同時に接続する方法も可能である。 In this embodiment, a Si chip 1 which is a power semiconductor chip such as a MOSFET or IGBT having a thin film metallized on the back surface, and a lead-free solder of Sn-3Ag-0.5Cu on a ceramic substrate 102 (Al 2 O 3 insulating substrate). And soldering in a hydrogen atmosphere heating furnace (hereinafter referred to as a hydrogen furnace). Further, the metallized film 5 (Cu / Ni plating in this embodiment) on the back of the ceramic substrate 102 and the base substrate 4 plated with Ni on the Cu plate are sandwiched with a Sn-3Ag-0.5Cu lead-free solder foil. Soldered in a hydrogen furnace. A spacer may be used so that the molten solder is not crushed by its own weight and the semiconductor chip is not tilted. It is also possible to connect the solder 3 under the chip and the solder 16 under the substrate at the same time.

本実施例では、チップ下のハンダ３と、基板下のハンダ１６とに融点が同じハンダを用いているので、基板下のハンダ付けは、先に接合したチップ下ハンダが再溶融する方法で検討したが、振動による位置ズレ等の問題はない。また、Ａｌ2Ｏ3製のセラミックス基板１０２を接続する際に、電気回路部品、リード等も同時に、ペーストハンダを用いて、真空ハンダ付けをしても良い。ペーストハンダを用いた場合は、洗浄後に接続導線であるＡｌ線８を超音波ワイヤボンド（ＷＢと略す。）接続する。 In this embodiment, since solder having the same melting point is used for the solder 3 under the chip and the solder 16 under the substrate, the soldering under the substrate is examined by a method in which the solder under the chip previously bonded is remelted. However, there is no problem such as displacement due to vibration. Further, when connecting the ceramic substrate 102 made of Al 2 O 3 , electric circuit components, leads, etc. may be vacuum-soldered using paste solder at the same time. In the case of using paste solder, the Al wire 8 which is a connecting conductor is connected by ultrasonic wire bonding (abbreviated as WB) after cleaning.

次にＳｉチップ１、Ａｌ等に対して密着力があり、柔軟なポリイミド系、あるいはポリアミドイミド系樹脂を、実装した側のＳｉチップ１及びセラミックス基板１０２の表面と側面、及びベース基板４の表面に、溶媒で薄め、均一に薄く散布もしくは塗布し、硬化後のポリイミド系樹脂９の厚さを１０μｍ〜５０μｍとした。次に、低いヤング率でハンダの線膨張係数(２０.５×１０-6／℃) にほぼ線膨張係数を合わせたエポキシ系樹脂１０を、先に塗布した樹脂の上からポッテイングして硬化させた。 Next, the surface of the Si chip 1 and the ceramic substrate 102 on which the flexible polyimide-based or polyamide-imide-based resin is mounted and the side surface and the side surface of the base substrate 4 are adhered. The polyimide resin 9 after curing was thinned with a solvent and uniformly spread or applied to a thickness of 10 μm to 50 μm. Next, the epoxy resin 10 having a low Young's modulus and a linear expansion coefficient of solder (20.5 × 10 −6 / ° C.) substantially matched with the linear expansion coefficient is potted from above the previously applied resin and cured. It was.

ハンダ接続部分の寿命を向上するには、Ｓｉチップ１、セラミックス基板１０２、ベース基板４等を拘束できて、かつ素子部、Ｓｉチップ１外周部の応力集中を緩和できる、低いヤング率でハンダに合わせた線膨張係数を有するエポキシ系樹脂１０の拘束効果が必要である。但し、エポキシ系樹脂１０だけでは、大型のＳｉチップ１や、温度差が大きく厳しい試験条件では、Ｓｉチップ１界面における応力歪みの対応に限界がある。従って、本実施例では、パワーサイクル、温度サイクル試験でも、エポキシ系樹脂構造の弱点とされる樹脂とＳｉチップ１、セラミックス基板１０２であるＡｌ2Ｏ3絶縁基板、ベース基板４等の端部、界面における応力による剥離破壊、及びそれに伴って起きる耐湿性の低下を、２種類の樹脂の異なった機能を組合わせて防止した。 In order to improve the life of the solder connection portion, the Si chip 1, the ceramic substrate 102, the base substrate 4 and the like can be constrained, and the stress concentration on the element portion and the outer periphery of the Si chip 1 can be reduced. The restraining effect of the epoxy resin 10 having the combined linear expansion coefficient is necessary. However, with the epoxy resin 10 alone, there is a limit to the stress strain correspondence at the Si chip 1 interface under the large Si chip 1 and under severe test conditions with a large temperature difference. Therefore, in this embodiment, the resin and the Si chip 1 which are weak points of the epoxy resin structure in the power cycle and temperature cycle tests, the ends of the Al 2 O 3 insulating substrate which is the ceramic substrate 102, the base substrate 4 and the like, The peeling failure due to the stress at the interface and the accompanying decrease in moisture resistance were prevented by combining different functions of the two types of resins.

本実施例では、セラミックス基板１０２、Ａｌ、エポキシ系樹脂１０との密着力に優れ、柔らかく変形性に富み、かつ耐熱性でガラス転移点温度（Ｔｇと略す。）が２３０℃の前記日立化成製ＨＬ−１２００ポリイミド系樹脂９をまず薄く塗布し、応力、歪みが強く作用する端部、界面で、このポリイミド系樹脂９自体が変形して、界面の剥離、破壊等を防止し、併せて、耐湿性も確保する。なお、本実施例に適用できるポリイミド系樹脂９のガラス転移温度Ｔｇは、１００℃〜２５０℃、好ましくは１５０℃から２５０℃の範囲である。   In this example, the adhesive made with the ceramic substrate 102, Al, and the epoxy resin 10 is soft, highly deformable, heat resistant, and has a glass transition temperature (abbreviated as Tg) of 230 ° C. First, the HL-1200 polyimide resin 9 is thinly applied, and the polyimide resin 9 itself is deformed at the end portion and interface where stress and strain act strongly to prevent peeling and destruction of the interface. Ensures moisture resistance. In addition, the glass transition temperature Tg of the polyimide resin 9 applicable to a present Example is 100 to 250 degreeC, Preferably it is the range of 150 to 250 degreeC.

本実施例で、線膨張係数が１８×１０-6／℃、室温のヤング率が１０ＧＰａのエポキシ系樹脂１０を用いて、パワーサイクル試験を行った結果、ジャンクション温度Ｔｊが５０℃〜１５０℃では、１００００サイクルでも破壊せず、ハンダのクラック進展は殆ど認められず無視でき得る状態であった。また、温度サイクル試験でも、ハンダのクラック進展は殆ど認められなかった。 In this example, a power cycle test was performed using an epoxy resin 10 having a linear expansion coefficient of 18 × 10 −6 / ° C. and a Young's modulus at room temperature of 10 GPa. As a result, when the junction temperature Tj was 50 ° C. to 150 ° C. Even at 10,000 cycles, no breakage occurred, and almost no solder cracks were observed. Also, in the temperature cycle test, almost no solder crack growth was observed.

以下、本願発明のエポキシ系樹脂１０とポリイミド系樹脂９との役割を詳述する。図１に示すポリイミド系樹脂９のヤング率を下げ、Ｓｉチップ１に応力的な負担をかけない物性のエポキシ系樹脂１０でＳｉチップ１の周囲を取り囲むことで、素子への影響、Ｓｉチップ１の界面剥離等の問題から開放する。そして、エポキシ系樹脂１０がハンダ３とＳｉチップ１を取り囲み拘束する補強効果、即ち、エポキシ系樹脂１０がＳｉチップ１の端部でのハンダ３の応力集中を緩和する役割を果たすことにより、ハンダ３のクラック進展を阻止する。   Hereinafter, the roles of the epoxy resin 10 and the polyimide resin 9 of the present invention will be described in detail. By lowering the Young's modulus of the polyimide resin 9 shown in FIG. 1 and surrounding the periphery of the Si chip 1 with an epoxy resin 10 having physical properties that do not apply a stress load to the Si chip 1, the influence on the element can be reduced. Free from problems such as interface peeling. The epoxy resin 10 surrounds and restrains the solder 3 and the Si chip 1, that is, the epoxy resin 10 plays a role of relaxing the stress concentration of the solder 3 at the end of the Si chip 1. 3 crack growth is prevented.

この場合、エポキシ系樹脂１０の応力−歪特性は熱弾性で近似できるが、ハンダ３の場合は熱弾塑性で近似される。このため、ハンダ３のヤング率(Ｓｎ−３Ａｇ−０.５Ｃｕ；２０℃で４１.５ＧＰａ)はエポキシ系樹脂１０に比べ高くても、応力が作用するとハンダ３が塑性変形するので、温度変化域では、見掛け上のハンダ３のヤング率が低くなる。このように、見掛け上のハンダ３のヤング率が１０ＧＰａ以下になるので、エポキシ系樹脂１０と同様の柔らかさになる。Ｓｉチップ１の周囲を柔らかい材料であるポリイミド系樹脂９で包むことでＳｉチップ１を保護できる。低温に変化した時に、エポキシ系樹脂１０に大きな応力が作用した場合、ポリイミド系樹脂９が存在しないと、Ｓｉチップ１の周囲に大きな応力が作用し、エポキシ系樹脂１０とＳｉチップ１との界面で剥離、破壊を起こす恐れがある。   In this case, the stress-strain characteristic of the epoxy resin 10 can be approximated by thermoelasticity, but in the case of the solder 3, it is approximated by thermoelasticity. For this reason, even if the Young's modulus (Sn-3Ag-0.5Cu; 41.5 GPa at 20 ° C.) of the solder 3 is higher than that of the epoxy resin 10, the solder 3 is plastically deformed when stress is applied. Then, the apparent Young's modulus of the solder 3 is lowered. Thus, since the apparent Young's modulus of the solder 3 is 10 GPa or less, the softness similar to that of the epoxy resin 10 is obtained. The Si chip 1 can be protected by wrapping the periphery of the Si chip 1 with a polyimide resin 9 which is a soft material. When a large stress is applied to the epoxy resin 10 when the temperature is changed to a low temperature, if the polyimide resin 9 is not present, a large stress is applied around the Si chip 1, and the interface between the epoxy resin 10 and the Si chip 1. May cause peeling or destruction.

そこで、予め、さらに柔らかいポリイミド系樹脂９を薄く塗布し、界面でこのポリイミド系樹脂９が変形して、応力を緩和する。なお、柔らかいポリイミド系樹脂９を必要以上に厚く塗布し過ぎるとＳｉチップ１の破壊防止の効果はあっても、エポキシ系樹脂１０のＳｉチップ１、セラミックス基板、ベース基板を拘束する作用が緩慢になる可能性がある。そこで、ポリイミド系樹脂９の厚さは、通常は１０μｍ〜５０μｍが望ましいが、例え１μｍ〜１０μｍ厚さでもポリイミド系樹脂９が変形し、応力を緩和できることは言うまでもない。   Therefore, a softer polyimide resin 9 is thinly applied in advance, and the polyimide resin 9 is deformed at the interface to relieve stress. If the soft polyimide resin 9 is applied too thickly more than necessary, the effect of restraining the Si chip 1, the ceramic substrate, and the base substrate of the epoxy resin 10 is slow although the effect of preventing the destruction of the Si chip 1 is obtained. There is a possibility. Therefore, the thickness of the polyimide resin 9 is usually preferably 10 μm to 50 μm, but it goes without saying that even if the thickness is 1 μm to 10 μm, the polyimide resin 9 can be deformed to relieve the stress.

なお柔らかいポリイミド系樹脂９を厚めに塗布することで、封止用のエポキシ系樹脂１０のヤング率を、Ｓｉチップ１の寸法等にも依存するが、Ｓｉチップ１、ベース基板４等を強く拘束できて、かつＳｉチップ１に負担がかからない低いヤング率とし、かつエポキシ系樹脂１０の線膨張係数をハンダの線膨張係数に合わせることもできる。このポリイミド系樹脂９が塗布されている場合、Ｓｉチップ１の寸法や、試験条件の厳しさにもよるが、エポキシ系樹脂のヤング率が、２０ＧＰａと高めであってもＳｉチップ１を破壊から防止できる。   By applying a soft polyimide resin 9 thickly, the Young's modulus of the epoxy resin 10 for sealing depends on the dimensions of the Si chip 1 and the like, but strongly restrains the Si chip 1, the base substrate 4 and the like. In addition, the Young's modulus can be made low so that the Si chip 1 is not burdened, and the linear expansion coefficient of the epoxy resin 10 can be matched with the linear expansion coefficient of the solder. When this polyimide resin 9 is applied, the Si chip 1 can be destroyed even if the Young's modulus of the epoxy resin is as high as 20 GPa, depending on the dimensions of the Si chip 1 and the severity of the test conditions. Can be prevented.

本実施例のように、Ｓｉチップ１、ベース基板４等をエポキシ系樹脂１０で覆う方式により、Ｓｉチップ１の応力の負担は大きいが、特に温度サイクル試験やパワーサイクル試験の条件では、シリコーンゲルを封入した従来技術の構造に比べ、ハンダ３の寿命が大幅に改善されるメカニズムを以下説明する。   As in this embodiment, the Si chip 1, the base substrate 4 and the like are covered with the epoxy resin 10, so that the stress of the stress on the Si chip 1 is large. However, especially in the conditions of the temperature cycle test and the power cycle test, the silicone gel The mechanism by which the life of the solder 3 is greatly improved compared to the structure of the prior art in which is encapsulated is described below.

Ａｌ2Ｏ3基板をセラミックス基板１０２として適用したものを、図１を用いて説明する。これまで、樹脂封止型モジュールの寿命に対する樹脂の設計指針が明らかにされていない。以下に示すように、適正な樹脂物性値を選定することで、従来技術のシリコーンゲル充填構造に比べ、温度サイクル、パワーサイクル試験における熱疲労寿命を大幅に向上できることが分かった。また、有限要素法解析でも、実験結果の妥当性を確認できた。 An application of an Al 2 O 3 substrate as the ceramic substrate 102 will be described with reference to FIG. Until now, the resin design guideline for the life of the resin-encapsulated module has not been clarified. As shown below, it was found that the thermal fatigue life in the temperature cycle and power cycle tests can be greatly improved by selecting appropriate resin physical property values as compared with the conventional silicone gel filling structure. The validity of the experimental results was confirmed by finite element analysis.

以下に示した物性を示すエポキシ系樹脂で封止することで、シリコーンゲル封止構造より格段に優れた熱疲労寿命を示すことはＡｌ2Ｏ3基板のフリップチップ実装における樹脂充填構造でも確認済みであり、このことは、例えば、電子情報通信学会論文誌Ｃ−II、Ｖol.Ｊ７３−Ｃ−II Ｎo.９，ｐｐ５１６−５２４に記載されている。 It has been confirmed in the resin-filled structure of flip-chip mounting of Al 2 O 3 substrates that it exhibits a thermal fatigue life much better than the silicone gel sealing structure by sealing with epoxy resin showing the physical properties shown below This is described, for example, in IEICE Transactions C-II, Vol. J73-C-II No. 9, pp 516-524.

従って、高出力、大型Ｓｉチップ、あるいはセラミックス絶縁基板とＣｕベース基板との接続に対しても高信頼性を確保できる見通しを得た。全体を封止する樹脂の線膨張係数をハンダの線膨張係数（２１×１０-6／℃）に合わせることと、全体を封止する樹脂を低ヤング率化することとで、ハンダ接合部の寿命を向上させ、Ｓｉチップ、セラミックス絶縁基板の界面剥離を防止し、かつモジュールの反りを防止できる。従って、主に条件が厳しいＳｉチップとＣｕ板のハンダ付けモデルを例にとり、選定すべきエポキシ系樹脂１０の物性値の詳細を以下に示す。なお、Ｓｉチップ１とＡｌ2Ｏ3基板とについても同様な見方ができることを確認してある。 Therefore, a high output, large-sized Si chip, or a prospect of ensuring high reliability for the connection between the ceramic insulating substrate and the Cu base substrate was obtained. By matching the linear expansion coefficient of the resin that seals the whole with that of the solder (21 × 10 −6 / ° C.) and by reducing the Young's modulus of the resin that seals the entire, The service life can be improved, interface peeling between the Si chip and the ceramic insulating substrate can be prevented, and module warpage can be prevented. Therefore, the physical property values of the epoxy resin 10 to be selected will be described in detail below, taking an example of a soldering model of a Si chip and a Cu plate whose conditions are severe. It has been confirmed that the same view can be made for the Si chip 1 and the Al 2 O 3 substrate.

図２は、樹脂封止構造パワーモジュールの設計指針を得るための封止用のエポキシ系樹脂１０の線膨張係数に対する、Ｓｉチップ１の応力と、ハンダ歪との関係を示すグラフである。図２（ａ）のグラフ中に示す断面モデル構造で、パワーサイクル試験におけるＳｉチップ１の端部Ｂの相当応力と、ハンダ３のクラック起点Ａの相当歪とを、有限要素法による３次元弾塑性解析を行った。温度プロファイルは、実績のある１２０℃→２０℃→１２０℃→２０℃の変化で、１.５ サイクルの温度変化で発生したＳｉチップ１端部Ｂの相当応力振幅及びハンダ３のクラック起点Ａでの相当歪振幅を求めた。なお、Ｓｉチップ１表面に作用する応力として、相当応力の他に主応力、σｘ、σｙ、σｚ等での評価も行ったが、ほぼ相当応力に比例していることから、ここでは相当応力で評価した。図２（ａ）、図２（ｂ）中に示した各枠の内側はエポキシ系樹脂１０の線膨張係数の適正領域（１４×１０-6／℃〜２４×１０-6／℃）を示す。 FIG. 2 is a graph showing the relationship between the stress of the Si chip 1 and the solder strain with respect to the linear expansion coefficient of the epoxy resin 10 for sealing to obtain a design guideline for the resin-encapsulated power module. In the cross-sectional model structure shown in the graph of FIG. 2 (a), the equivalent stress at the end B of the Si chip 1 and the equivalent strain at the crack starting point A of the solder 3 in the power cycle test are expressed by a three-dimensional Plastic analysis was performed. The temperature profile is a proven change of 120 ° C. → 20 ° C. → 120 ° C. → 20 ° C., and the equivalent stress amplitude of the end B of the Si chip 1 generated by the temperature change of 1.5 cycles and the crack starting point A of the solder 3. The equivalent distortion amplitude was obtained. In addition to the equivalent stress, the principal stress, σx, σy, σz, etc. were also evaluated as the stress acting on the surface of the Si chip 1. evaluated. The inside of each frame shown in FIG. 2A and FIG. 2B shows an appropriate region (14 × 10 −6 / ° C. to 24 × 10 −6 / ° C.) of the linear expansion coefficient of the epoxy resin 10. .

図２（ａ）から、封止用のエポキシ系樹脂１０のヤング率が、Ｓｉチップ１の端部Ｂの応力に直接に影響を与えることが分かる。同一ヤング率の場合、ヤング率が低い１５ＧＰａレベルでは、エポキシ系樹脂１０の線膨張係数が１０×１０-6／℃〜４０×１０-6／℃の広い範囲で、相当応力は変わらない。適正領域ではさらにその傾向が強い。封止用のエポキシ系樹脂１０のヤング率が約２０ＧＰａを超える（図２（ａ）では２０ＧＰａの曲線を省略している。）とＳｉチップ１の端部Ｂにかかる相当応力は、線膨張係数３０×１０-6／℃以上で上昇する傾向が強い。封止用のエポキシ系樹脂１０のヤング率が高いと、Ｓｉチップ１の端部Ｂの相当応力が上昇し、またエポキシ系樹脂１０のヤング率が約２０ＧＰａより小さいと、封止用のエポキシ系樹脂１０の線膨張係数が３０×１０-6／℃より小さい場合には、小さくなるにつれて相当応力が多少上昇する傾向はあるが、線膨張係数１０×１０-6／℃〜３０×１０-6／℃の広い範囲で、相当応力はあまり変わらない。 From FIG. 2A, it can be seen that the Young's modulus of the epoxy resin 10 for sealing directly affects the stress at the end B of the Si chip 1. In the case of the same Young's modulus, at a 15 GPa level where the Young's modulus is low, the equivalent stress does not change in a wide range where the linear expansion coefficient of the epoxy resin 10 is 10 × 10 −6 / ° C. to 40 × 10 −6 / ° C. This tendency is even stronger in appropriate areas. When the Young's modulus of the epoxy resin 10 for sealing exceeds about 20 GPa (the curve of 20 GPa is omitted in FIG. 2A), the equivalent stress applied to the end B of the Si chip 1 is the linear expansion coefficient. The tendency to increase at 30 × 10 −6 / ° C. or higher is strong. When the Young's modulus of the epoxy resin 10 for sealing is high, the equivalent stress at the end B of the Si chip 1 is increased, and when the Young's modulus of the epoxy resin 10 is less than about 20 GPa, the epoxy system for sealing is used. When the linear expansion coefficient of the resin 10 is smaller than 30 × 10 −6 / ° C., the equivalent stress tends to slightly increase as the resin becomes smaller, but the linear expansion coefficient 10 × 10 −6 / ° C. to 30 × 10 −6. The equivalent stress does not change much over a wide range of / ° C.

図２（ｂ）から、封止用のエポキシ系樹脂１０のヤング率が同じ場合、エポキシ系樹脂１０の線膨張係数が増す程、ハンダ３のクラック起点Ａの相当歪が大きくなる。しかし、破線で示した従来技術のシリコーンゲル充填構造の値と比べると、エポキシ系樹脂１０の線膨張係数が１０×１０-6／℃〜４０×１０-6／℃を超える広い範囲で、ハンダ３の相当歪は低い値を示しており、シリコーンゲル充填構造よりハンダ３の寿命が長いことを示している。実際のパワーサイクル加速試験でも、この樹脂構造では、ハンダ３に起因する寿命低下は生じていないことを確認した。これらのことは、封止用のエポキシ系樹脂１０の物性を適切に選定すればハンダ３の応力集中を緩和することを示し、有限要素法解析でも確認できた。 2B, when the Young's modulus of the epoxy resin 10 for sealing is the same, the equivalent strain at the crack starting point A of the solder 3 increases as the linear expansion coefficient of the epoxy resin 10 increases. However, when compared with the value of the conventional silicone gel filling structure shown by the broken line, the soldering resin is in a wide range where the linear expansion coefficient of the epoxy resin 10 exceeds 10 × 10 −6 / ° C. to 40 × 10 −6 / ° C. The equivalent strain of 3 shows a low value, indicating that the life of the solder 3 is longer than that of the silicone gel filled structure. Even in an actual power cycle acceleration test, it was confirmed that this resin structure did not cause a decrease in life due to the solder 3. These facts show that if the physical properties of the epoxy resin 10 for sealing are appropriately selected, the stress concentration of the solder 3 is relaxed, and can be confirmed by finite element analysis.

図３は、封止用のエポキシ系樹脂１０の線膨張係数に対する、Ｓｉチップの端部Ｂの応力と、ハンダ歪の関係図である。図３中に示した枠内は、エポキシ系樹脂１０の線膨張係数の適正領域（１４×１０-6／℃〜２４×１０-6／℃）を示す。図３は、エポキシ系樹脂１０の線膨張係数を横軸とり、縦軸にハンダのクラック起点Ａの相当歪（左）とＳｉチップ１表面素子端部Ｂに作用する相当応力（右）をとって、プロットしたものである。また、破線はシリコーンゲルで全体を充填した従来技術のモジュールのハンダのクラック起点の相当歪を示す。エポキシ系樹脂１０の線膨張係数が１４×１０-6／℃〜２４×１０-6／℃の範囲では、ハンダ３のクラック起点Ａでの相当歪は、シリコーンゲルで全体を被覆した構造のハンダの相当歪よりも小さい。従って、図３に示すように、線膨張係数が１４×１０-6／℃〜２４×１０-6／℃ の範囲のエポキシ系樹脂１０を用いると、シリコーンゲル封止構造に比べ、ハンダ３の歪は小さくなることから、ハンダ３に起因する断線の確率がより少くなる。また、Ｓｉチップ１の端部Ｂの相当応力σ（窓枠部）の値も小さく、Ｓｉチップ１の破壊応力（１００ＭＰａ）以下であり、素子部の破壊、界面での剥離等が起こり難くなる。 FIG. 3 is a relationship diagram between the stress at the end B of the Si chip and the solder strain with respect to the linear expansion coefficient of the epoxy resin 10 for sealing. The inside of the frame shown in FIG. 3 shows an appropriate region (14 × 10 −6 / ° C. to 24 × 10 −6 / ° C.) of the linear expansion coefficient of the epoxy resin 10. FIG. 3 shows the linear expansion coefficient of the epoxy resin 10 on the horizontal axis, and the vertical axis shows the equivalent strain (left) at the crack starting point A of the solder and the equivalent stress (right) acting on the surface element end B of the Si chip 1. And plotted. The broken line indicates the equivalent strain at the crack starting point of the solder of the prior art module filled entirely with silicone gel. When the linear expansion coefficient of the epoxy resin 10 is in the range of 14 × 10 −6 / ° C. to 24 × 10 −6 / ° C., the equivalent strain at the crack starting point A of the solder 3 is solder having a structure in which the whole is covered with silicone gel. Is less than the equivalent distortion. Therefore, as shown in FIG. 3, when an epoxy resin 10 having a linear expansion coefficient in the range of 14 × 10 −6 / ° C. to 24 × 10 −6 / ° C. is used, the solder 3 Since the distortion becomes smaller, the probability of disconnection due to the solder 3 becomes smaller. Further, the value of the equivalent stress σ (window frame portion) at the end B of the Si chip 1 is small and is equal to or less than the fracture stress (100 MPa) of the Si chip 1, so that the element portion is less likely to be broken and peeled off at the interface. .

さらに、有限要素法解析結果によって、変位を拘束する樹脂のヤング率は少なくとも１ＧＰａ以上であることが必要であり、しかもＳｉチップを１拘束する効果が確実に現われる封止用のエポキシ系樹脂１０のヤング率が３ＧＰａ以上であることを確認した。ヤング率が１５ＧＰａ以上では変位は余り変わらないが、Ｓｉチップ１の界面に作用する応力が大きくなり、チップ素子部への影響、Ｓｉチップ１界面剥離、素子部の破壊、チップ割れ等を起こしやすくなる。このため、弱いＳｉチップ１表面を保護する意味からも、ヤング率が高い樹脂は問題がある。   Further, according to the finite element method analysis result, the Young's modulus of the resin that restrains the displacement needs to be at least 1 GPa or more, and the effect of restraining the Si chip by 1 appears surely. It was confirmed that the Young's modulus was 3 GPa or more. When the Young's modulus is 15 GPa or more, the displacement does not change much, but the stress acting on the interface of the Si chip 1 becomes large, and the influence on the chip element part, the peeling of the Si chip 1 interface, destruction of the element part, chip cracking, etc. are likely to occur. Become. For this reason, there is a problem with a resin having a high Young's modulus from the viewpoint of protecting the weak Si chip 1 surface.

また、実際に製造する製品では、弱い素子もあり、高い歩留まりで高い信頼性を確保するには封止用のエポキシ系樹脂１０のヤング率を下げることが重要である。有限要素法による３次元弾塑性解析でも物性による違いを確認できた。なお、ヤング率（曲げ弾性率）の測定は、樹脂硬化物を５×１０×１００mmに切削し、ＪＩＳ−６９１１規定の曲げ試験片を作製した。これを、島津製作所製オートグラフＤＳＳ−５０００を用いて、曲げ速度１mm／min 、支点間距離８０mmの条件で、両端指示中央集中荷重法によって測定した。   In addition, products actually manufactured include weak elements, and it is important to lower the Young's modulus of the epoxy resin 10 for sealing in order to ensure high reliability with a high yield. Differences due to physical properties were also confirmed by three-dimensional elasto-plastic analysis using the finite element method. The Young's modulus (bending elastic modulus) was measured by cutting a cured resin to 5 × 10 × 100 mm to prepare a bending test piece defined in JIS-6911. This was measured using a Shimadzu Autograph DSS-5000 with a bending speed of 1 mm / min and a fulcrum distance of 80 mm by a both-end directed centralized load method.

以上の検討結果をまとめ素子への影響を考慮し、高い信頼性を得るための封止用エポキシ系樹脂１０の物性を整理すると次の（１）〜（６）に示すようになる。
（１）線膨張係数：１４×１０-6／℃〜２４×１０-6／℃。
（２）ヤング率：３ＧＰａ〜２０ＧＰａ、望ましくは５ＧＰａ〜１０ＧＰａ。
（３）先に塗布されるポリイミド系樹脂９に対して密着性に優れること。
（４）ガラス転移温度Ｔｇが１５０℃以上、望ましくは１７０℃以上であること。
（５）シリコーンゲル等の高温で安定な微粒子ゴムをエポキシ系樹脂に分散させて衝撃を緩和。
（６）不純物濃度：Ｎａ+，Ｋ+≦１ppm、Ｃｌ-≦５ppm
さらに、以下の新たな機能が追加されることになる。
（７）エポキシ系樹脂で封止する前に、実装したＳｉ基板表面を、予め耐熱性のある柔らかいポリアミドイミド系、あるいはポリイミド系樹脂を、薄くスプレー等で塗布する。耐熱性に優れる柔らかいポリイミド系樹脂を薄く塗布することでエポキシ系樹脂にはない新たな変形機能付加により、応力を逃がす役割を果たす。この結果、半導体パワーモジュールで、高信頼実装を実現することが可能になった。 Summarizing the above examination results and considering the influence on the element, the physical properties of the sealing epoxy resin 10 for obtaining high reliability are arranged as shown in the following (1) to (6).
(1) Linear expansion coefficient: 14 × 10 −6 / ° C. to 24 × 10 −6 / ° C.
(2) Young's modulus: 3 GPa to 20 GPa, desirably 5 GPa to 10 GPa.
(3) Excellent adhesion to the polyimide resin 9 applied earlier.
(4) The glass transition temperature Tg is 150 ° C. or higher, desirably 170 ° C. or higher.
(5) Mitigating impact by dispersing high temperature stable particulate rubber such as silicone gel in epoxy resin.
(6) Impurity concentration: Na + , K + ≦ 1 ppm, Cl − ≦ 5 ppm
In addition, the following new functions will be added.
(7) Before sealing with the epoxy resin, the mounted Si substrate surface is preliminarily coated with a heat-resistant soft polyamide-imide or polyimide resin thinly by spraying or the like. By thinly applying a soft polyimide resin with excellent heat resistance, it plays a role of releasing stress by adding a new deformation function not found in epoxy resins. As a result, it has become possible to achieve highly reliable mounting with a semiconductor power module.

本実施例では、大型Ｓｉチップ１に対する封止用のエポキシ系樹脂１０の効果を確認するため、Ａｌ2Ｏ3基板及びＡｌＮ基板等のセラミックス基板を用いたパワーサイクル、温度サイクルの各試験を行った。予め溶剤で希釈したポリアミドイミド系樹脂を、１０μｍ〜５０μｍの厚さにモジュール実装面全体に薄く塗布し、硬化後、ヤング率；１３.５ＧＰａ、線膨張係数１８×１０-6／℃の封止用のエポキシ系樹脂１０で封止してモジュールとした。 In this example, in order to confirm the effect of the epoxy resin 10 for sealing on the large Si chip 1, each test of a power cycle and a temperature cycle using a ceramic substrate such as an Al 2 O 3 substrate and an AlN substrate was performed. It was. Polyamideimide resin diluted in advance with a solvent is thinly applied to the entire module mounting surface to a thickness of 10 μm to 50 μm, and after curing, it is sealed with Young's modulus: 13.5 GPa and linear expansion coefficient of 18 × 10 −6 / ° C. The module was sealed with epoxy resin 10 for use.

Ｓｉチップ１には、１辺が７mm及び９mmの概略正方形のものを用いた。なお、比較用にシリコーンゲルで充填したモジュールも評価した。チップ下ハンダ（Ｓｉチップと絶縁基板間を意味する。Ｓｎ−３Ａｇ−０.５Ｃｕ ）及び基板下ハンダ（絶縁基板とベース基板間を意味する。Ｓｎ−３Ａｇ−０.５Ｃｕ）の疲労劣化度を断面観察で評価した。パワーサイクル試験及び温度サイクル試験は、本実施例のモジュールのクラック進展が、従来構造のシリコーンゲル充填構造のモジュールに比べ少ないことを確認した。また、本実施例のモジュールでは、Ｓｉチップ１界面での剥離も防止できた。   A Si chip 1 having a substantially square shape with sides of 7 mm and 9 mm was used. For comparison, a module filled with silicone gel was also evaluated. The fatigue degradation degree of solder under the chip (meaning between the Si chip and the insulating substrate; Sn-3Ag-0.5Cu) and solder under the substrate (meaning between the insulating substrate and the base substrate; Sn-3Ag-0.5Cu) Evaluation was made by cross-sectional observation. The power cycle test and the temperature cycle test confirmed that the crack growth of the module of this example was less than that of the conventional silicone gel filled structure module. Further, in the module of this example, peeling at the interface of the Si chip 1 could be prevented.

温度変化が大きい試験条件の場合には、封止用樹脂のヤング率が高いと大きな応力を発生し、特に、Ｓｉチップ端部の接着界面で剥離を起こす可能性がある。エポキシ系樹脂だけでは線膨張係数を下げて、ヤング率を下げることに限界がある。そこで、本実施例では、実施例１と同様に、予めポリイミド系樹脂９を塗布してあるので、このポリイミド系樹脂９の被膜が変形して、応力を緩和し、封止用エポキシ系樹脂１０のヤング率が低減したことと同じ作用をする。それでも、封止用エポキシ系樹脂１０自体のヤング率を下げることは有効であり、このことは、パワーサイクル、温度サイクルに対して、Ｓｉチップ１端部の界面及びＳｉチップ１の保護するために重要である。   In the test conditions where the temperature change is large, if the Young's modulus of the sealing resin is high, a large stress is generated, and in particular, there is a possibility of causing peeling at the adhesive interface at the end of the Si chip. There is a limit to lowering the Young's modulus by lowering the linear expansion coefficient with epoxy resin alone. Therefore, in this embodiment, since the polyimide resin 9 is applied in advance as in the case of the first embodiment, the coating film of the polyimide resin 9 is deformed to relieve stress, and the epoxy resin 10 for sealing. This has the same effect as reducing the Young's modulus. Nevertheless, it is effective to lower the Young's modulus of the sealing epoxy resin 10 itself, which is to protect the Si chip 1 interface and the Si chip 1 against power cycle and temperature cycle. is important.

さらに、本実施例では、封止用のエポキシ系樹脂１０にシリコーン系のゴムの微細粒子を５〜１０重量％分散させることで、ヤング率を下げた。このようにシリコーン系の微細粒子のゴムを分散させると、そのマクロなヤング率を下げるだけでなく、ゴム添加による耐熱衝撃緩和材として優れた効果があることも確認した。   Furthermore, in this example, Young's modulus was lowered by dispersing 5 to 10% by weight of silicone rubber fine particles in the epoxy resin 10 for sealing. It was also confirmed that the dispersion of silicone fine particle rubber not only lowers the macro Young's modulus but also has an excellent effect as a thermal shock reducing material by adding rubber.

比較のために検討した、従来技術のシリコーンゲル充填構造のモジュールでは、Ａｌ2Ｏ3基板では、チップ下ハンダ、基板下ハンダ共、ほぼ同等の寿命であることが分かった。また、シリコーンゲル充填構造では、ＡｌＮ基板とＡｌ2Ｏ3基板とでの寿命を比較した結果、ＡｌＮ基板では基板下ハンダの劣化に起因して寿命が来ることが分かった。 In the module of the prior art silicone gel filling structure examined for comparison, it was found that the Al 2 O 3 substrate has almost the same lifetime for both the solder under the chip and the solder under the substrate. Further, as a result of comparing the lifetimes of the AlN substrate and the Al 2 O 3 substrate in the silicone gel-filled structure, it was found that the AlN substrate has a lifetime due to deterioration of the solder under the substrate.

一方、本実施例の樹脂構成ではＡｌ2Ｏ3基板及びＡｌＮ基板共に、従来技術のシリコーンゲルを充填した構造ものに比べ、３倍以上の長さのハンダの耐熱疲労寿命があった。 On the other hand, in the resin configuration of this example, both the Al 2 O 3 substrate and the AlN substrate had a heat fatigue life of solder that was three times longer than that of a structure filled with silicone gel of the prior art.

本実施例で用いた上記組成のハンダは、Ｓｎ系ハンダの典型的な組成であるが、他の組成のハンダとして、Ｓｎ−Ａｇ−Ｃｕ系では、例えばＳｎ−１Ａｇ−０.５Ｃｕが、Ｓｎ−Ｃｕ系では、例えばＳｎ−０.７Ｃｕが本実施例のモジュールに適用できる。あるいは、これらのハンダにＩｎ、Ｂｉ、Ｇｅ、Ｚｎ、Ｎｉ等を１種類以上微量添加した組成でもよい。   The solder of the above composition used in this example is a typical composition of Sn-based solder. However, Sn-Ag-Cu-based solder, for example, Sn-1Ag-0.5Cu is Sn as a solder of other composition. In the -Cu system, for example, Sn-0.7Cu can be applied to the module of this embodiment. Alternatively, a composition in which one or more kinds of In, Bi, Ge, Zn, Ni, etc. are added in a small amount to these solders may be used.

また、環境を考慮した高温系鉛フリーハンダとして、Ｓｎ−Ｓｂ系のＳｎ−（５〜１０）Ｓｂ（融点：２３２℃〜２４０℃）を用いることができる。このハンダでモジュールを組み立て、他の基板にモジュールを実装する場合には、この組成と温度階層を可能とする、低温系ハンダとして、Ｓｎ−Ａｇ−Ｃｕ、Ｓｎ−Ｃｕ共晶系にＩｎを５〜１０％添加した低融点高信頼ハンダを用いることができる。この低融点高信頼ハンダは、機械的性質に優れ、比較的柔軟であり、温度分布の優れた炉の使用によりｍａｘ２３０℃での接続が可能である。同様に低温系でさらに融点を下げられるハンダとして、Ｓｎ−９Ｚｎ（融点；１９９℃）もしくはＳｎ−９Ｚｎに微量のＩｎ、Ｂｉ、Ａｇ、Ｃｕ、Ａｌ、Ｇｅ、Ｎｉ等を１種類以上添加したハンダも用いることができる。   Further, Sn—Sb-based Sn— (5-10) Sb (melting point: 232 ° C. to 240 ° C.) can be used as a high-temperature lead-free solder considering the environment. When a module is assembled with this solder and the module is mounted on another substrate, Sn—Ag—Cu, Sn—Cu eutectic-based In is used as a low-temperature solder that enables this composition and temperature hierarchy. A low melting point high reliability solder added with 10% to 10% can be used. This low melting point and high reliability solder is excellent in mechanical properties, is relatively flexible, and can be connected at a maximum of 230 ° C. by using a furnace having an excellent temperature distribution. Similarly, as solder capable of further lowering the melting point in a low-temperature system, Sn-9Zn (melting point: 199 ° C.) or Sn-9Zn is added with a trace amount of In, Bi, Ag, Cu, Al, Ge, Ni, etc. Can also be used.

本実施例では、高信頼性実装をもたらすエポキシ系樹脂で封止する構造のモジュールの封止用樹脂の検討結果を詳述する。本実施例のモジュールは、（１）パワーサイクル、温度サイクルにおけるハンダの熱疲労寿命向上、（２）Ｓｉチップ端部における樹脂との界面剥離防止、（３）素子部の樹脂からの応力に対する保護、（４）界面からの浸水防止（耐湿性向上）、（５）モジュール基板の反り低減、（６）機械的負荷に対する保護等を満たす。   In the present embodiment, the results of study on a resin for sealing a module having a structure sealed with an epoxy-based resin that provides highly reliable mounting will be described in detail. The module of the present embodiment has (1) improvement of thermal fatigue life of solder in power cycle and temperature cycle, (2) prevention of interfacial delamination with resin at the end of the Si chip, and (3) protection against stress from the resin in the element portion. (4) Prevention of infiltration from the interface (improvement of moisture resistance), (5) Reduction of warpage of the module substrate, (6) Protection against mechanical load, etc.

機械的に特定した物性を有するエポキシ系樹脂１０で封止することで、チップ下ハンダの寿命を大幅に向上できる。この寿命向上のためには、樹脂の線膨張係数を２０×１０-6／℃〜４５×１０-6／℃にすればよい。また、基板の反り防止のためには、基板の線膨張係数に合わすか、それより線膨張係数を低めにすることで、基板の反りを中央部が凸状に外側に変形させて、熱伝導性グリースとの接触を良くする。例えば、ベース基板がＣｕの場合、基板の線膨張係数１７×１０-6／℃であり、ばらつきを考慮し、エポキシ系樹脂１０の線膨張係数の下限を１４×１０-6／℃に設定した。 By sealing with the epoxy resin 10 having mechanically specified physical properties, the life of the solder under the chip can be greatly improved. In order to improve the lifetime, the linear expansion coefficient of the resin may be set to 20 × 10 −6 / ° C. to 45 × 10 −6 / ° C. In order to prevent the warpage of the substrate, the warpage of the substrate is deformed outwardly in a convex shape by matching the coefficient of linear expansion of the substrate or lowering the coefficient of linear expansion. Make good contact with functional grease. For example, when the base substrate is Cu, the linear expansion coefficient of the substrate is 17 × 10 −6 / ° C., and the lower limit of the linear expansion coefficient of the epoxy resin 10 is set to 14 × 10 −6 / ° C. in consideration of variation. .

また、Ａｌ基板の場合は、線膨張係数が２４×１０-6／℃、Ｃｕ基板の場合は線膨張係数１７×１０-6／℃であり、Ｓｎ系ハンダの線膨張係数２０.５×１０-6／℃であることを考慮し、エポキシ系樹脂１０の線膨張係数の上限を２４×１０-6／℃とした。 In the case of an Al substrate, the linear expansion coefficient is 24 × 10 −6 / ° C., and in the case of a Cu substrate, the linear expansion coefficient is 17 × 10 −6 / ° C., and the linear expansion coefficient of Sn solder is 20.5 × 10 6. Considering that it is −6 / ° C., the upper limit of the linear expansion coefficient of the epoxy resin 10 was set to 24 × 10 −6 / ° C.

このように、本実施例のモジュールでは、１４×１０-6／℃〜２４×１０-6／℃の線膨張係数を有し、低いヤング率のエポキシ系樹脂１０を使用することで、基板の反り防止、ハンダの寿命向上等を同時に達成することができる。 Thus, in the module of this example, the linear expansion coefficient of 14 × 10 −6 / ° C. to 24 × 10 −6 / ° C. is used, and the low Young's modulus epoxy-based resin 10 is used. Warpage prevention, improvement of solder life, etc. can be achieved at the same time.

さらに、本実施例のモジュールでは、ポリイミド系樹脂９を予め薄く被覆することで、エポキシ系樹脂１０だけではクリアできない厳しい条件でも、チップ端部、素子部等における剥離、破壊を防止する。このようにして、本実施例のパワーモジュール構造では、制御回路部に必要な、割れ易く膨張が小さな大型セラミックスチップコンデンサー等が面実装してあっても、ポリイミド系樹脂９を予め薄く被覆してあるので、熱応力による破損を防止できる。   Furthermore, in the module of the present embodiment, the polyimide resin 9 is previously thinly coated to prevent the chip end portion, the element portion, and the like from being peeled off or broken even under severe conditions that cannot be cleared by the epoxy resin 10 alone. In this way, in the power module structure of the present embodiment, the polyimide resin 9 is thinly coated in advance even if a large ceramic chip capacitor or the like that is necessary for the control circuit portion and is easily cracked and has a small expansion is surface-mounted. Therefore, damage due to thermal stress can be prevented.

また、本実施例では、水の侵入経路である界面における樹脂との密着性等の解決策として、予め、耐高温特性に優れたガラス転移温度Ｔｇが高く、柔らかいポリイミド系樹脂９をチップ側のモジュール表面全体に塗布した。ポリイミド系樹脂９の硬化後、ハンダと同じ２１×１０-6／℃前後の線膨張係数のエポキシ系樹脂１０で封止して、エポキシ系樹脂１０とポリイミド系樹脂９及びハンダ３がＳｉチップ１を取り囲んで、応力による素子の破壊を防止できる。同時にハンダの寿命を向上させるため、Ｓｉチップ１及びセラミックス基板、ベース基板等も拘束できる樹脂の補強効果が必要である。即ち、応力的に最も厳しい位置であるＳｉチップ１の端部でのハンダ３の応力集中を緩和する役割を果たすことにより、ハンダ３のクラック進展を阻止することができる。このため、Ｓｉチップ１に対しては保護する柔らかさと、強い拘束力も必要となる。相矛盾する性質なので、エポキシ系樹脂１０だけでは役割を担えないので、チップ保護、チップ端部保護に対しては、薄く塗布したポリイミド系樹脂９との組合せで補うこととした。 Further, in this example, as a solution such as adhesion to the resin at the interface that is the water intrusion route, a glass transition temperature Tg excellent in high-temperature resistance characteristics is high, and a soft polyimide resin 9 is applied on the chip side in advance. It was applied to the entire module surface. After the polyimide resin 9 is cured, the polyimide resin 9 is sealed with an epoxy resin 10 having a linear expansion coefficient of about 21 × 10 −6 / ° C., which is the same as the solder, and the epoxy resin 10, the polyimide resin 9 and the solder 3 are bonded to the Si chip 1. The element can be prevented from being damaged by stress. At the same time, in order to improve the life of the solder, it is necessary to have a resin reinforcing effect capable of restraining the Si chip 1, the ceramic substrate, the base substrate, and the like. That is, cracks of the solder 3 can be prevented from progressing by relaxing the stress concentration of the solder 3 at the end of the Si chip 1 that is the most severely stressed position. For this reason, the Si chip 1 needs to be protected and have a strong restraining force. Because of the contradictory nature, the epoxy resin 10 alone cannot play a role, so that chip protection and chip end protection are supplemented by a combination with a thinly applied polyimide resin 9.

さらに、樹脂特有の問題として、ガラス転移温度Ｔｇがある。特にパワーモジュールにおいては高温時の特性が重視されるので、ガラス転移温度Ｔｇは信頼性に大きく影響を及ぼす。一般に、ガラス転移温度Ｔｇが低い樹脂は作業性に優れることから、使い勝手性に優れるが、ガラス転移温度Ｔｇ以上の温度では線膨張係数が約３倍に急上昇するので、高温でのマージンが少ないと良い結果が得られない場合がある。従って、使用環境条件、加速試験等はガラス転移温度Ｔｇ以下であることが高信頼性確保の必要条件である。厳しいパワーサイクル試験を考慮すると、ガラス転移温度Ｔｇは１５０℃以上が必要で、１７０℃位であることが望ましい。これにより厳しい環境条件、熱処理等の高温での熱影響によるダメージを最小限に抑え、高信頼性を確保できる。なお、ガラス転移点温度Ｔｇの上限は２５０℃であれば十分である。   Furthermore, there is a glass transition temperature Tg as a problem specific to the resin. In particular, in a power module, since characteristics at high temperatures are important, the glass transition temperature Tg greatly affects the reliability. In general, a resin having a low glass transition temperature Tg is excellent in workability, so it is excellent in usability. However, since the linear expansion coefficient rapidly increases about three times at a temperature higher than the glass transition temperature Tg, there is little margin at high temperature. Good results may not be obtained. Therefore, it is a necessary condition for ensuring high reliability that the use environment condition, the acceleration test, and the like are not higher than the glass transition temperature Tg. Considering a severe power cycle test, the glass transition temperature Tg needs to be 150 ° C. or higher, and is preferably about 170 ° C. As a result, damage due to severe environmental conditions and heat effects at high temperatures such as heat treatment can be minimized and high reliability can be ensured. The upper limit of the glass transition temperature Tg is sufficient if it is 250 ° C.

線膨張係数とガラス転移温度Ｔｇの測定は、真空理工製の熱物理試験機ＴＭＡ−１５００を用いて測定した。厚さ４mmの硬化試験片を圧縮モード、毎分１℃の速度で昇温し、伸びの温度特性を測定した。線膨張係数αは伸びの温度特性から求め、ガラス転移温度は伸びの温度特性グラフの変曲点とした。   The linear expansion coefficient and the glass transition temperature Tg were measured using a thermophysical tester TMA-1500 manufactured by Vacuum Riko. A cured specimen having a thickness of 4 mm was heated in a compression mode at a rate of 1 ° C. per minute, and the temperature characteristics of elongation were measured. The linear expansion coefficient α was determined from the temperature characteristic of elongation, and the glass transition temperature was the inflection point of the temperature characteristic graph of elongation.

本実施例のパワーモジュールの断面を図４に示す。本実施例では、Ｓｉチップ１の上方及びその周辺にフェライト部材１１６を配置し、応力的負担のない位置に高周波ノイズ対策、電磁的遮断効果を持たせた構造とした。フェライト部材１１６はフェライト板をモジュール上面に固定してもよいし、フェライト粉末を耐熱性のある接着剤で固着した板でも良く、あるいは封止用樹脂のフィラー材として混合してもよい。本実施例に用いるフェライト粉末には一例として、ＮｉＦｅ2Ｏ4・ＺｎＦｅ2Ｏ4があるが、これに限定されるものではない。図４に示す構造でパワーサイクル試験を行った結果、ジャンクション温度Ｔｊが５０〜１５０℃では、１００００サイクルでも破壊せず、ハンダのクラック進展は殆ど認められないことが分かった。 A cross section of the power module of this example is shown in FIG. In the present embodiment, the ferrite member 116 is disposed above and around the Si chip 1 so as to have a high frequency noise countermeasure and an electromagnetic shielding effect at a position where there is no stress load. The ferrite member 116 may fix a ferrite plate on the upper surface of the module, may be a plate in which ferrite powder is fixed with a heat-resistant adhesive, or may be mixed as a filler material for a sealing resin. An example of the ferrite powder used in this example is NiFe 2 O 4 .ZnFe 2 O 4, but is not limited to this. As a result of conducting a power cycle test with the structure shown in FIG. 4, it was found that when the junction temperature Tj was 50 to 150 ° C., it did not break even at 10,000 cycles, and almost no crack growth of solder was observed.

図５、図６に本実施例のパワーモジュールの断面図を示す。パワー素子のため大電流を流す必要からチップ当たり１０本レベルのφ３００μｍのＡｌ線を超音波ワイヤボンディング接続する方式に比べ、ワイヤボンディングより放熱効果に優れるリードフレームが注目されている（例えば、池田他５；リードフレームハンダ接合と熱特性の検討；Mate．２００４，ｐ３７５）。本実施例のパワーモジュールは、Ａｌ線の代わりにＣｕリードフレーム等をＳｉチップ１にハンダ付けした。   5 and 6 are sectional views of the power module of this embodiment. Due to the necessity of flowing a large current because of the power element, lead frames that have a heat dissipation effect superior to wire bonding are attracting attention compared to the method of connecting 10-level φ300 μm Al wires per chip by ultrasonic wire bonding (for example, Ikeda et al. 5; Examination of lead frame soldering and thermal characteristics; Mate. 2004, p375). In the power module of this example, a Cu lead frame or the like was soldered to the Si chip 1 instead of the Al wire.

図５はリードフレームの伸び剛性による影響が直接にハンダ付け部である素子部に及ぼさないために、ベローズ状の折り曲げ部分を有するベローズ型リードフレーム１７にした。このベローズ型リードフレーム１７は、無酸素Ｃｕをプレス圧延加工で型を形成後、アニールすることで柔らかくなる。Ｓｉチップ１のジャンクション部で発生した熱は、チップ下に伝導されるだけでなく、熱容量のあるＳｉチップ１上のローズ型リードフレーム１７のＣｕブロック部で一旦均熱化され、リードフレームを伝わってセラミックス基板１０２、ベース基板４に伝導される。   FIG. 5 shows a bellows type lead frame 17 having a bellows-like bent portion so that the influence of the rigidity of the lead frame does not directly affect the element portion which is a soldering portion. The bellows type lead frame 17 is softened by forming an oxygen-free Cu die by press rolling and then annealing it. The heat generated at the junction portion of the Si chip 1 is not only conducted under the chip, but is also soaked once at the Cu block portion of the rose-type lead frame 17 on the Si chip 1 having a heat capacity, and is transmitted through the lead frame. Then, it is conducted to the ceramic substrate 102 and the base substrate 4.

本実施例では、セラミックス基板１０２の熱流路となっているチップ下ではない部分も、新たな熱流路になるため、効率の良い熱引きが期待できる。Ｓｉチップ１とリードフレーム間は線膨張係数の差が大きいので、シリコーンゲル等で被覆しただけでは、ハンダの寿命が短く特性への影響が大きい問題がある。そこで、本実施例のモジュールの樹脂構造では、リードフレームに伸縮して熱応力を緩和できるベローズ部を備えたことによって、チップ上のハンダ接合部１１６の寿命が向上するので、特性への影響を小さくできる。本実施例のモジュールの構造で高い出力のモジュールには、特にＣｕのリードフレーム、ＡｌＮ基板、Ｃｕのベース基板の組合せが優れる。   In this embodiment, a portion of the ceramic substrate 102 that is not under the chip that is the heat flow path is also a new heat flow path, so that efficient heat sinking can be expected. Since the difference in coefficient of linear expansion between the Si chip 1 and the lead frame is large, there is a problem that the life of the solder is short and the influence on the characteristics is large only by coating with silicone gel or the like. Therefore, in the resin structure of the module of the present embodiment, the life of the solder joint portion 116 on the chip is improved by providing the bellows portion that can expand and contract on the lead frame to relieve the thermal stress. Can be small. The combination of the Cu lead frame, the AlN substrate, and the Cu base substrate is particularly excellent for the high output module having the module structure of this embodiment.

図６は図５と同様に、リードフレームの伸び剛性を下げるためのリードフレームの変形例を示す。図６の折り曲げリードフレーム１９は、接続部の間に折り曲げ部を備えた形状である。   FIG. 6 shows a modification of the lead frame for reducing the elongation rigidity of the lead frame, similarly to FIG. The bent lead frame 19 in FIG. 6 has a shape having a bent portion between connecting portions.

リードフレーム方式ではチップへの熱衝撃は緩和されるが、ジャンクション部に直接ハンダ付けされる構造のため、接合部の温度は高く、融点が低いハンダでは熱疲労による劣化に課題がある。そこで、本実施例では、実施例１から実施例４と同様の樹脂物性を有し、かつ、ガラス転移温度Ｔｇが１５０℃以上のエポキシ系樹脂１０で封止することで、樹脂によるハンダの熱疲労劣化の少ない、高出力モジュールを得る。   In the lead frame method, the thermal shock to the chip is alleviated, but due to the structure that is soldered directly to the junction, there is a problem of deterioration due to thermal fatigue in the solder where the temperature of the joint is high and the melting point is low. Therefore, in this example, the resin physical properties similar to those of Example 1 to Example 4 and the glass transition temperature Tg is sealed with the epoxy resin 10 having a glass transition temperature of 150 ° C. or higher, so that the heat of soldering by the resin can be achieved. A high output module with little fatigue deterioration is obtained.

リードフレームとしては無酸素Ｃｕ以外に柔らかい高純度Ａｌリード（ＮｉもしくはＮｉ／Ａｕフラッシュメッキ）、熱伝導率がＣｕ並みに優れ、線膨張係数が約６×１０-6／℃であるＣｕ−Ｃ複合材（Ｃｕと高純度カーボングラファイトのナノレベルの粒径で作られた粉末もしくは繊維とを焼結した複合材。）等も可能である。このＣｕ−Ｃ複合材は、アルミナ並みの線膨張係数であり、かつ柔らかいことから、Ｓｉチップ１への応力の負担が少なく、樹脂で補強することで高い信頼性が確保できる。 The lead frame is soft, high-purity Al lead (Ni or Ni / Au flash plating) in addition to oxygen-free Cu, Cu-C, which has excellent thermal conductivity similar to Cu, and a linear expansion coefficient of about 6 × 10 −6 / ° C. A composite material (composite material obtained by sintering powder or fiber made of Cu and high-purity carbon graphite with a particle size of nano-level) is also possible. Since this Cu-C composite material has a linear expansion coefficient similar to that of alumina and is soft, the stress load on the Si chip 1 is small, and high reliability can be ensured by reinforcing it with resin.

鉛フリーハンダとして、高温のＳｎ−５Ｓｂ（融点：２３２℃〜２４０℃）を使用することで、パワーサイクルに対してもジャンクション部での温度上昇に対しての温度マージンを確保できる。さらに高温対応としては、２８０℃でも強度を確保できるＣｕ粒子混入Ｓｎ系ハンダ複合材、例えば特開２００２−２６１１０５号公報に記載のもの等がある。なお、チップへの負荷が少なく、耐力が小さいＳｎ−０.７ＣｕもしくはＳｎ−０.７ＣｕにＩｎを添加した系でもよい。   By using high-temperature Sn-5Sb (melting point: 232 ° C. to 240 ° C.) as lead-free solder, it is possible to secure a temperature margin against a temperature rise at the junction portion even for a power cycle. Furthermore, as for high temperature, there are Cu-based Sn composite solder materials that can ensure strength even at 280 ° C., for example, those described in JP-A-2002-261105. In addition, a system in which In is added to Sn-0.7Cu or Sn-0.7Cu, which has a low load on the chip and a low yield strength, may be used.

実施例１の半導体パワーモジュールの断面図である。1 is a sectional view of a semiconductor power module of Example 1. FIG. 実施例１の半導体パワーモジュールの封止用樹脂の線膨張係数とチップ応力との関係や、封止用樹脂の線膨張係数とハンダ歪との関係を示すグラフ。6 is a graph showing the relationship between the linear expansion coefficient of the sealing resin and the chip stress of the semiconductor power module of Example 1 and the relationship between the linear expansion coefficient of the sealing resin and solder strain. 実施例１の半導体パワーモジュールの封止用樹脂の線膨張係数に対するチップ応力とハンダ歪みとを示すグラフ。3 is a graph showing chip stress and solder strain with respect to the linear expansion coefficient of the sealing resin for the semiconductor power module of Example 1; 実施例４の半導体パワーモジュールの断面図である。It is sectional drawing of the semiconductor power module of Example 4. FIG. 実施例５の半導体パワーモジュールの断面図である。FIG. 6 is a cross-sectional view of a semiconductor power module of Example 5. 実施例５の別の半導体パワーモジュールの断面図である。10 is a cross-sectional view of another semiconductor power module according to Embodiment 5. FIG.

符号の説明Explanation of symbols

１…Ｓｉチップ、２…外部リード、３…ハンダ、４…ベース基板、５…メタライズ膜、６…電気回路、８…Ａｌ線、９…ポリイミド系樹脂、１０…エポキシ系樹脂、１５…電極、１６…ハンダ、１７…ベローズ型リードフレーム、１９…折り曲げリードフレーム、１０２…セラミックス基板、１１０…ケース。   1 ... Si chip, 2 ... external lead, 3 ... solder, 4 ... base substrate, 5 ... metallized film, 6 ... electric circuit, 8 ... Al wire, 9 ... polyimide resin, 10 ... epoxy resin, 15 ... electrode, 16 ... solder, 17 ... bellows type lead frame, 19 ... bent lead frame, 102 ... ceramic substrate, 110 ... case.

Claims (17)

セラミックス絶縁基板の一方の面に配置した電極に、メタライズされたＳｉ半導体チップ裏面をハンダ付けし、該セラミックス絶縁基板上の他方の面をベース基板にハンダ付けした半導体パワーモジュールにおいて、
該半導体パワーモジュールが、前記Ｓｉ半導体チップ表面と前記セラミックス絶縁基板の他の電極とを接続する接続導体と、前記Ｓｉ半導体チップと前記セラミックス絶縁基板の一方の面とを被覆する第１の樹脂と、該第１の樹脂を被覆する第２の樹脂とによって、封止されていて、
前記第１の樹脂のヤング率が前記第２の樹脂のヤング率より小さく、
前記第２の樹脂は、ヤング率が３ＧＰａ〜２０ＧＰａであって、その線膨張係数が１０×１０-6／℃〜４０×１０-6／℃であるエポキシ系樹脂であって、
前記第２の樹脂を、ポッティング若しくはトランスファモールドで封止したことを特徴とする半導体パワーモジュール。 In a semiconductor power module in which a metallized Si semiconductor chip back surface is soldered to an electrode disposed on one surface of a ceramic insulating substrate, and the other surface on the ceramic insulating substrate is soldered to a base substrate.
The semiconductor power module includes a connection conductor that connects the surface of the Si semiconductor chip and the other electrode of the ceramic insulating substrate, and a first resin that covers the Si semiconductor chip and one surface of the ceramic insulating substrate. And sealed with a second resin covering the first resin,
Young's modulus of the first resin is smaller than Young's modulus of the second resin,
The second resin is an epoxy resin having a Young's modulus of 3 GPa to 20 GPa and a linear expansion coefficient of 10 × 10 −6 / ° C. to 40 × 10 −6 / ° C.
A semiconductor power module, wherein the second resin is sealed by potting or transfer molding. 請求項１において、前記第２の樹脂の線膨張係数が１４×１０／℃〜２４×１０-6／℃であることを特徴とする半導体パワーモジュール。 2. The semiconductor power module according to claim 1, wherein the second resin has a linear expansion coefficient of 14 × 10 / ° C. to 24 × 10 −6 / ° C. 3. 請求項１から請求項２の何れかにおいて、前記第１の樹脂の膜厚が前記Ｓｉ半導体チップ上面及び該チップ側面で、１μｍ〜５０μｍであることを特徴とする半導体パワーモジュール。   3. The semiconductor power module according to claim 1, wherein the thickness of the first resin is 1 μm to 50 μm on the upper surface of the Si semiconductor chip and the side surface of the chip. 請求項１から請求項３の何れかにおいて、前記第２の樹脂がシリコーン系のゴム粒子を５重量％〜１０重量％含むことを特徴とする半導体パワーモジュール。   4. The semiconductor power module according to claim 1, wherein the second resin contains 5 wt% to 10 wt% of silicone rubber particles. 請求項１から請求項４の何れかにおいて、前記第１の樹脂のヤング率が０.１ＧＰａ〜３ＧＰａであることを特徴とする半導体パワーモジュール。   5. The semiconductor power module according to claim 1, wherein Young's modulus of the first resin is 0.1 GPa to 3 GPa. 請求項１から請求項５の何れかにおいて、Ｓｉ半導体チップ裏面にハンダを介して接続するセラミックス絶縁基板の線膨張係数αが４.５×１０-6／℃〜７×１０-6／℃ であることを特徴とする半導体パワーモジュール。 6. The coefficient of linear expansion α of the ceramic insulating substrate connected to the back surface of the Si semiconductor chip via solder is 4.5 × 10 −6 / ° C. to 7 × 10 −6 / ° C. A semiconductor power module characterized by being. 請求項１から請求項６の何れかにおいて、前記Ｓｉ半導体チップ上面にフェライト層を備えた部材を前記第１の樹脂と第２の樹脂とを介して配置したことを特徴とする半導体パワーモジュール。   7. The semiconductor power module according to claim 1, wherein a member having a ferrite layer on the upper surface of the Si semiconductor chip is disposed via the first resin and the second resin. 請求項１から請求項７の何れかにおいて、前記セラミックス絶縁基板が、Ａｌ2Ｏ3基板もしくはＡｌＮ基板もしくはＳｉ3Ｎ4基板であることを特徴とする半導体パワーモジュール。 In any one of claims 1 to 7, a semiconductor power module, wherein the ceramic insulating substrate is Al 2 O 3 substrate or an AlN substrate or Si 3 N 4 substrate. 請求項１から請求項８の何れかにおいて、前記第１の樹脂のガラス転移温度Ｔｇが１５０℃〜２５０℃であることを特徴とする半導体パワーモジュール。   9. The semiconductor power module according to claim 1, wherein the glass transition temperature Tg of the first resin is 150 ° C. to 250 ° C. 10. メタライズされたＳｉチップ裏面を熱拡散板にハンダ付けし、該熱拡散板の裏面を樹脂絶縁性の金属ベース基板にハンダ付けした半導体パワーモジュールにおいて、
該半導体パワーモジュールが、前記Ｓｉ半導体チップ表面に配置した接続導体と、前記Ｓｉ半導体チップと前記熱拡散板の一方の面とを被覆する第１の樹脂と、該第１の樹脂を被覆する第２の樹脂とによって、封止されていて、
前記第１の樹脂のヤング率が前記第２の樹脂のヤング率より小さく、
前記第２の樹脂は、ヤング率が３ＧＰａ〜２０ＧＰａであって、その線膨張係数が１０×１０-6／℃〜４０×１０-6／℃であるエポキシ系樹脂であって、
前記第２の樹脂を、ポッティング若しくはトランスファモールドで封止したことを特徴とする半導体パワーモジュール。 In a semiconductor power module in which the back surface of the metallized Si chip is soldered to a heat diffusion plate, and the back surface of the heat diffusion plate is soldered to a resin insulating metal base substrate,
The semiconductor power module includes a connection conductor disposed on the surface of the Si semiconductor chip, a first resin that covers the Si semiconductor chip and one surface of the heat diffusion plate, and a first resin that covers the first resin. 2 is sealed with resin,
Young's modulus of the first resin is smaller than Young's modulus of the second resin,
The second resin is an epoxy resin having a Young's modulus of 3 GPa to 20 GPa and a linear expansion coefficient of 10 × 10 −6 / ° C. to 40 × 10 −6 / ° C.
A semiconductor power module, wherein the second resin is sealed by potting or transfer molding. 請求項１０において、前記熱拡散板がＣｕ−ＣあるいはＡｌ−Ｃの複合材を用いたことを特徴とする半導体パワーモジュール。   11. The semiconductor power module according to claim 10, wherein the thermal diffusion plate uses a Cu-C or Al-C composite material. 請求項１０から請求項１１の何れかにおいて、前記第２の樹脂の線膨張係数が１４×１０／℃〜２４×１０-6／℃であることを特徴とする半導体パワーモジュール。 12. The semiconductor power module according to claim 10, wherein a linear expansion coefficient of the second resin is 14 × 10 / ° C. to 24 × 10 −6 / ° C. 13. 請求項１０から請求項１２の何れかにおいて、前記第１の樹脂の膜厚が前記Ｓｉ半導体チップ上面及び該チップ側面で、１μｍ〜５０μｍであることを特徴とする半導体パワーモジュール。   13. The semiconductor power module according to claim 10, wherein the thickness of the first resin is 1 μm to 50 μm on the upper surface of the Si semiconductor chip and the side surface of the chip. 請求項１０から請求項１３の何れかにおいて、前記第２の樹脂がシリコーン系のゴム粒子を５重量％〜１０重量％含むことを特徴とする半導体パワーモジュール。   14. The semiconductor power module according to claim 10, wherein the second resin contains 5 wt% to 10 wt% of silicone rubber particles. 請求項１０から請求項１４の何れかにおいて、前記第１の樹脂のヤング率が０.１ＧＰａ〜３ＧＰａであることを特徴とする半導体パワーモジュール。   15. The semiconductor power module according to claim 10, wherein a Young's modulus of the first resin is 0.1 GPa to 3 GPa. 請求項１０から請求項１５の何れかにおいて、前記Ｓｉ半導体チップ上面にフェライト層を備えた部材を前記第１の樹脂と第２の樹脂とを介して配置したことを特徴とする半導体パワーモジュール。   16. The semiconductor power module according to claim 10, wherein a member having a ferrite layer on the upper surface of the Si semiconductor chip is disposed via the first resin and the second resin. 請求項１０から請求項１６の何れかにおいて、前記第１の樹脂のガラス転移温度Ｔｇが１５０℃〜２５０℃であることを特徴とする半導体パワーモジュール。   17. The semiconductor power module according to claim 10, wherein the glass transition temperature Tg of the first resin is 150 ° C. to 250 ° C. 17.
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