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JP2008066561A - Method of manufacturing semiconductor device - Google Patents

Method of manufacturing semiconductor device Download PDF

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Publication number
JP2008066561A
JP2008066561A JP2006243840A JP2006243840A JP2008066561A JP 2008066561 A JP2008066561 A JP 2008066561A JP 2006243840 A JP2006243840 A JP 2006243840A JP 2006243840 A JP2006243840 A JP 2006243840A JP 2008066561 A JP2008066561 A JP 2008066561A
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Japan
Prior art keywords
lead frame
heat spreader
welding
laser
gap
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Application number
JP2006243840A
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JP4765853B2 (en
Inventor
Katsuhiko Yoshihara
克彦 吉原
Tomoaki Gotou
友彰 後藤
Keisuke Sato
圭輔 佐藤
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Fuji Electric Co Ltd
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Fuji Electric Holdings Ltd
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Publication of JP2008066561A publication Critical patent/JP2008066561A/en
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Publication of JP4765853B2 publication Critical patent/JP4765853B2/en
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  • Engineering & Computer Science (AREA)
  • Computer Hardware Design (AREA)
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  • Power Engineering (AREA)
  • Laser Beam Processing (AREA)

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser welding method of a lead frame which is improved so that a welding of little welding variation could be achieved with a high reproducibility by using a laser beam irradiation of low power. <P>SOLUTION: In a method of manufacturing a semiconductor device comprising the steps of: loading a heat spreader 5 on a top face main electrode of a semiconductor chip mounted on an insulating substrate; laying a strap-like lead frame 6 as a lead material for internal wiring among a conductor pattern of the insulating substrate, the heat spreader 5, and input/output terminals; piling a bonding part thereof on a bonding partner member; irradiating a laser beam to a top face of the bonding part of the lead frame in this state; and making a wiring structure by carrying out a pile welding on the bonding partner member, after forming an air gap g at a bonding surface between the lead frame 6 and the heat spreader 5 which is the bonding partner member corresponding to a laser welding part, the laser beam is irradiated to a top face of the lead frame to carry out a welding, and as a practical embodiment thereof a spacer 14 with an air gap hole 14a is interposed at a position corresponding to the laser welding part between the lead frame 6 and the heat spreader 5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は、パワー半導体モジュールなどを対象とした半導体装置の製造方法に関し、詳しくは半導体装置の構成部品間に配線したリードフレームのレーザ溶接方法に係わる。   The present invention relates to a method of manufacturing a semiconductor device intended for a power semiconductor module, and more particularly to a laser welding method of a lead frame wired between components of the semiconductor device.

頭記のパワー半導体モジュールは、電流容量の増大，小形化に伴い半導体チップが高電流密度で使用されることから、ハイパワー動作での信頼性を確保するには半導体チップの発生熱を効率よく放熱することが重要課題となっている。この観点から絶縁基板にマウントした半導体チップの配線構造について、在来のボンディングワイヤに代えて通電，伝熱容量の大きなストラップ状のリードフレーム（Ｃｕ箔）を半導体チップの主電極面に接合し、該リードフレームを伝熱経路として半導体チップの発生熱を上面側からも放熱させるようにした配線構造、およびこの配線構造においてリードフレームと配線用端子との間の接合にスポット溶接，超音波接合のほか、レーザ溶接法を用いるようにしたことが知られている（例えば、特許文献１参照）。   The power semiconductor modules mentioned above use semiconductor chips with high current density as current capacity increases and downsizing. Therefore, to ensure reliability in high power operation, the heat generated from the semiconductor chips is efficiently used. Dissipating heat is an important issue. From this point of view, regarding the wiring structure of the semiconductor chip mounted on the insulating substrate, a strap-like lead frame (Cu foil) having a large energization and heat transfer capacity is joined to the main electrode surface of the semiconductor chip instead of the conventional bonding wire, A wiring structure that uses the lead frame as a heat transfer path to dissipate the heat generated by the semiconductor chip from the top surface, and in this wiring structure, the joint between the lead frame and the wiring terminal includes spot welding and ultrasonic bonding. It is known that the laser welding method is used (see, for example, Patent Document 1).

また、半導体チップの上面側からの放熱性を高め、併せて温度分布の集中を緩和させる手段として、伝熱性の高い金属板で作られたヒートスプレッダを半導体チップの上面に伝熱的に接合し、このヒートスプレッダを介して半導体チップの中央部分に集中する発生熱を周囲に分散させ、チップ全体での温度分布を平均化させるようにした構成も知られている（例えば、特許文献２参照）。   In addition, as a means of improving the heat dissipation from the upper surface side of the semiconductor chip and also reducing the concentration of temperature distribution, a heat spreader made of a highly heat conductive metal plate is thermally transferred to the upper surface of the semiconductor chip, There is also known a configuration in which generated heat concentrated in the central portion of the semiconductor chip is distributed to the periphery via this heat spreader, and the temperature distribution in the entire chip is averaged (see, for example, Patent Document 2).

一方、前記したストラップ状のリードフレームをヒートスプレッダと組合せてチップ上面側からの放熱性を高めるようにした配線構造の開発も進められており、次にその半導体装置の組立構造を図３に示す。なお、図示はブリッジ回路になる多相インバータ装置の一相分に対応するＩＧＢＴ (Insulated Gate Bipolar Transistor) モジュールである。
図３において、１は放熱用銅ベース、２Ａ，２Ｂは左右に並べて銅ベース１に搭載した絶縁基板（セラミックス基板表，裏両面に銅箔を直接接合して導体パターンを形成したＤＣＢ（Direct Copper Bonding）基板）、２ａ〜２ｅは絶縁基板２Ａ，２Ｂの上面に形成した導体パターン、３は絶縁基板２Ａ，２Ｂの導体パターン２ａ，２ｄにマウントしたＩＧＢＴチップ、４はＦＷＤ（Free Wheel Diode）、５はＩＧＢＴチップ３およびＦＷＤ４の上面電極に重ねて接合した銅，アルミ板，あるいはＭｏ，Ｗ等の焼結体に銅を含浸させた複合材で作られたヒートスプレッダ、６はヒートスプレッダ５の上面と絶縁基板２の導体パターン２ｂ，２ｅとの間に配線したリードフレーム（Ｃｕ，Ｃｕ合金箔）、７は絶縁基板２Ａと２Ｂの間に跨がって導体パターン２ｃと２ｄ，および２ｂと２ｅとの間に配線したリードフレーム、８(+)，８(-)，８(o)は入力，出力端子として導体パターン２ｂ，２ｃ，２ｅの端部から引出したリードフレームである。 On the other hand, development of a wiring structure in which the above-described strap-like lead frame is combined with a heat spreader so as to improve heat dissipation from the upper surface side of the chip is also underway. Next, an assembly structure of the semiconductor device is shown in FIG. The figure shows an IGBT (Insulated Gate Bipolar Transistor) module corresponding to one phase of a multiphase inverter device that becomes a bridge circuit.
In FIG. 3, 1 is a copper base for heat dissipation, 2A and 2B are insulation substrates mounted on the copper base 1 side by side (DCB (Direct Copper Bonding) substrate), 2a to 2e are conductor patterns formed on the top surfaces of the insulating substrates 2A and 2B, 3 is an IGBT chip mounted on the conductor patterns 2a and 2d of the insulating substrates 2A and 2B, and 4 is an FWD (Free Wheel Diode), 5 is a heat spreader made of a composite material in which copper, an aluminum plate, or a sintered body of Mo, W or the like is impregnated with copper and joined to the upper surface electrodes of the IGBT chip 3 and FWD 4. 6 is an upper surface of the heat spreader 5. A lead frame (Cu, Cu alloy foil) wired between the conductive patterns 2b and 2e of the insulating substrate 2 and 7 extends between the insulating substrates 2A and 2B. Lead frames 8 (+), 8 (-), 8 (o) wired between c and 2d, and 2b and 2e are drawn out from the ends of the conductor patterns 2b, 2c and 2e as input and output terminals. Lead frame.

ここで、銅ベース１と絶縁基板２Ａ，２Ｂの間、絶縁基板２Ａ，２Ｂの導体パターン２ａ，２ｄとここに搭載したＩＧＢＴチップ３，ＦＷＤ４との間、およびＩＧＢＴチップ２，ＦＷＤ３とヒートスプレッダ５との間がそれぞれ半田９で接合されている。
これに対して、リードフレーム６，７，８を接合相手部材であるヒートスプレッダ５の上面，絶縁基板２Ａ，２Ｂの各導体パターンに接合する方法として、次記のようにレーザ溶接法で重ね溶接するようにしており、その接合部（溶融部）を符号１０で示す。 Here, between the copper base 1 and the insulating substrates 2A and 2B, between the conductor patterns 2a and 2d of the insulating substrates 2A and 2B and the IGBT chips 3 and FWD 4 mounted thereon, and between the IGBT chips 2 and FWD 3 and the heat spreader 5 Are joined by solder 9.
On the other hand, as a method of joining the lead frames 6, 7 and 8 to the upper surface of the heat spreader 5 which is a joining partner member and each conductor pattern of the insulating substrates 2A and 2B, lap welding is performed by laser welding as described below. The joint portion (melting portion) is indicated by reference numeral 10.

すなわち、図４はヒートスプレッダ５の上面にリードフレーム６を接合するレーザ溶接法の工程図であり、ヒートスプレッダ５の上面にリードフレーム６の接合部を重ね合わせた状態で、レーザ発振器（例えば半導体レーザ）１１から光ファイバーを通じてレーザヘッダ１２に導光したレーザ光１３を集光し、レーザヘッダ１２からリードフレーム６の接合部上面にスポット状に照射する。これにより、レーザ光１３の光エネルギーが金属の自由電子に吸収されることで、リードフレーム６が局部的に加熱されて表面から溶融し、熱伝導的に溶融領域の深さがヒートスプレッダ５の表面まで拡大して図示のような溶接部１０が形成されることは周知の通りである。なお、レーザ溶接箇所は、ヒートスプレッダ５，リードフレーム６の外形サイズ，通電容量に応じて、１〜６箇所に分散してスポット状に溶接する。
特開２００４−９６１３５号公報 特開２０００−３０７０５８号公報（図１） That is, FIG. 4 is a process diagram of a laser welding method in which the lead frame 6 is joined to the upper surface of the heat spreader 5, and a laser oscillator (for example, a semiconductor laser) with the joined portion of the lead frame 6 superimposed on the upper surface of the heat spreader 5. The laser beam 13 guided from 11 to the laser header 12 through the optical fiber is condensed and irradiated from the laser header 12 to the upper surface of the joint portion of the lead frame 6 in a spot shape. As a result, the light energy of the laser beam 13 is absorbed by the metal free electrons, so that the lead frame 6 is locally heated and melted from the surface, and the depth of the melted region is thermally conductive to the surface of the heat spreader 5. It is well known that the welded portion 10 as shown in the figure is formed by enlarging to the above. The laser welding locations are dispersed in 1 to 6 locations and welded in a spot shape according to the heat spreader 5, the outer size of the lead frame 6, and the current carrying capacity.
JP 2004-96135 A Japanese Patent Laid-Open No. 2000-307058 (FIG. 1)

ところで、図３に示した配線構造の半導体装置について、発明者等はリードフレーム６（厚さ0.５ｍｍの無酸素銅板）の接合部をヒートスプレッダ６の上に重ね合わせ、リードフレーム６の上面側から半導体レーザ（波長：８０８ｎｍ）により、照射条件（パワー密度：０．１〜０．３ＭＷ／ｃｍ２，照射時間：１〜４ｓｅｃ）を変えて溶接し、その溶接部１０を検証したところ、溶接強度に大きなバラツキの生じることが認められた。 Incidentally, in the semiconductor device having the wiring structure shown in FIG. 3, the inventors superimpose the joint portion of the lead frame 6 (oxygen-free copper plate having a thickness of 0.5 mm) on the heat spreader 6, and the upper surface side of the lead frame 6. And welding with a semiconductor laser (wavelength: 808 nm) under different irradiation conditions (power density: 0.1 to 0.3 MW / cm 2 , irradiation time: 1 to 4 sec), and the welded portion 10 was verified. It was recognized that large variations in strength occurred.

すなわち、図５（ａ），（ｂ）のようにリードフレーム６の接合部と接合相手部材であるヒートスプレッダ５との間を密着状態に重なり合わせて溶接すると、レーザ光照射地点に生じたリードフレーム６の溶融部からヒートスプレッダ５に伝熱して放散する放熱量が多くなってリードフレーム／ヒートスプレッダ間の接合界面に十分な熱エネルギーが蓄積されず、その結果として前記したレーザ照射条件では、（ｂ）図で表すようにレーザ光照射によりリードフレーム６に生じた溶融部１０の溶け込み深さが接合相手部材であるヒートスプレッダ５の領域まで成長せずにリードフレーム６／ヒートスプレッダ５間が溶接不良となる。また、前記とは逆にレーザ光のパワー密度を高く設定すると、溶融部の溶け込み深さが接合相手部材であるヒートスプレッダ５，絶縁基板２の導体パターン２ａを貫通してしまい、そのためにセラミック基板，半導体チップ３，ＦＷＤ４を破壊するといったダメージが発生することがある。   That is, as shown in FIGS. 5 (a) and 5 (b), when the welded portion of the lead frame 6 and the heat spreader 5 which is a joining partner member are overlapped and welded, the lead frame generated at the laser light irradiation point As a result, the amount of heat dissipated and dissipated from the melted part 6 to the heat spreader 5 is increased and sufficient thermal energy is not accumulated at the joint interface between the lead frame and the heat spreader. As a result, under the laser irradiation conditions described above, (b) As shown in the figure, the penetration depth of the melted portion 10 generated in the lead frame 6 by the laser beam irradiation does not grow to the region of the heat spreader 5 which is the joining partner member, and the weld between the lead frame 6 and the heat spreader 5 becomes poor. On the contrary, when the power density of the laser beam is set high, the penetration depth of the melted portion penetrates through the heat spreader 5, which is a bonding partner member, and the conductor pattern 2a of the insulating substrate 2, and therefore, the ceramic substrate, Damage such as destruction of the semiconductor chip 3 and the FWD 4 may occur.

本発明は上記の点に鑑みなされたものであり、前述したレーザ溶接の検証，考察結果を基に、配線部材であるリードフレームの接合部を接合相手部材であるヒートスプレッダ，絶縁基板の導体パターンの上に重ねてレーザ溶接する際に、低パワーのレーザ光照射で、溶接バラツキの少ない溶接が高い再現性で実現できるように改良した半導体装置の製造方法を提供することを目的とする。   The present invention has been made in view of the above points, and based on the above-described verification and consideration results of laser welding, the joint portion of the lead frame, which is a wiring member, is connected to the heat spreader, which is a joint member, and the conductor pattern of the insulating substrate. An object of the present invention is to provide a method for manufacturing a semiconductor device which is improved so that welding with little welding variation can be realized with high reproducibility by laser beam irradiation with low power when superposed on the top.

上記目的を達成するために、本発明によれば、半導体装置の内部配線用リード材としてリードフレームを用い、このリードフレームの接合部を接合相手部材の上に重ね合わせた上で、前記リードフレームの接合部上面にレーザ光を照射してリードフレームと接合相手部材との間を重ね溶接してなる半導体装置の製造方法において、
前記リードフレームのレーザ溶接部位に対応して前記リードフレームと接合相手部材との間の接合面に空隙を形成した上で、リードフレームの上面にレーザ光を照射して溶接するようにし（請求項１）、その空隙は具体的に次記のよう形態で形成する。
（１）前記リードフレームと接合相手部材との間に、レーザ溶接部位に対応する位置に穴を開口した空隙形成用スペーサを介挿して空隙を形成する（請求項２）。
（２）前記リードフレームの接合部裏面，該接合部裏面に対峙する接合相手部材の上面のいずれか一方，もしくは双方に、レーザ溶接箇所と対応する位置に窪み（凹部）を設けて空隙を形成する（請求項３）。
（３）前項（１），（２）において、リードフレームと接合相手部材との間に形成した空隙の適正な深さを約１０μｍとする（請求項４）。
（４）リードフレームへのレーザ光の吸収率を高めるために、リードフレームの母材表面にＮｉもしくはＳｎのメッキが施す（請求項５）。 In order to achieve the above object, according to the present invention, a lead frame is used as a lead material for internal wiring of a semiconductor device, and a joint portion of this lead frame is superimposed on a mating member, and then the lead frame is used. In the manufacturing method of the semiconductor device formed by lap welding between the lead frame and the bonding partner member by irradiating the upper surface of the bonding portion with laser light,
A gap is formed in a joint surface between the lead frame and a mating member corresponding to a laser welding portion of the lead frame, and then the upper surface of the lead frame is irradiated with laser light for welding. 1) The void is specifically formed in the following form.
(1) A gap is formed between the lead frame and the joining partner member by inserting a gap forming spacer having a hole opened at a position corresponding to the laser welding portion.
(2) A void is formed by providing a recess (concave portion) at a position corresponding to the laser welding location on one or both of the bonding portion back surface of the lead frame and the upper surface of the bonding partner member facing the bonding portion back surface. (Claim 3).
(3) In the preceding items (1) and (2), the appropriate depth of the gap formed between the lead frame and the bonding partner member is about 10 μm.
(4) Ni or Sn plating is applied to the surface of the base material of the lead frame in order to increase the absorption rate of the laser beam into the lead frame.

上記のように、リードフレームの接合部上面に照射するレーザ光の照射部位に合わせてリードフレームの裏面と接合相手部材との間の接合界面に空隙を形成しておくことにより、この空隙が伝熱抵抗部となってリードフレームの溶融部から接合界面を経て接合相手部材に放散する放熱量が制限される。これにより、空隙部が熱溜まりとして機能し、リードフレームの溶融部から伝熱してきた熱エネルギーが十分に蓄積されるようになる。その結果、低パワーのレーザ照射でもリードフレームに生じた溶融部の深さがリードフレームの裏面まで十分に成長し、さらにリードフレームの溶融金属が前記空隙を埋めつくすように浸透してリードフレーム／接合相手部材間が広い面域で接合されるようになる。   As described above, a gap is formed at the bonding interface between the back surface of the lead frame and the bonding partner member in accordance with the irradiation site of the laser beam irradiated on the upper surface of the bonding portion of the lead frame. The amount of heat dissipated from the melted part of the lead frame to the joining partner member via the joining interface is limited. As a result, the gap functions as a heat reservoir, and the heat energy transferred from the melted portion of the lead frame is sufficiently accumulated. As a result, the depth of the melted portion generated in the lead frame is sufficiently grown to the back surface of the lead frame even with low-power laser irradiation, and the molten metal in the lead frame penetrates to fill the gaps. The joining partner members are joined in a wide area.

なお、この場合にリードフレームの接合部裏面／接合相手部材間の間に形成した空隙深さが極端に小さいと殆ど密着状態となって前記した熱溜まり効果が発揮できず、逆に空隙深さが極端に大きても溶融深さの成長が阻害される。かかる点、空隙深さを１０μｍ程度に設定すれば前記の熱溜まり効果を有効に発揮でき、かつその間隙範囲を照射するレーザ光のスポット径よりも大きく設定することにより、広い接合面積で接合強度の高い溶接部を形成できることが実験結果から確認されている。   In this case, if the depth of the gap formed between the back surface of the joint portion of the lead frame / the mating member is extremely small, the contact state is almost inadequate and the above-described heat accumulation effect cannot be exhibited. Even if is extremely large, the growth of the melt depth is inhibited. In this respect, if the gap depth is set to about 10 μm, the above-mentioned heat accumulation effect can be effectively exhibited, and by setting the gap range larger than the spot diameter of the laser beam to irradiate, the bonding strength can be obtained with a wide bonding area. It has been confirmed from the experimental results that a high weld area can be formed.

したがって、リードフレーム／接合相手部材間の接合面にあらかじめ前記設定の空隙を形成した上で、これに合わせてリードフレームの上面に照射するレーザ光の照射条件（パワー密度，照射時間）を適正管理して溶接を行うことにより、低パワーで、しかも溶接部のバラツキを抑えた接合品質の高いレーザ溶接を再現性よく実現できる。   Therefore, after the above-mentioned gap is formed in the joint surface between the lead frame and the mating member, the irradiation conditions (power density, irradiation time) of the laser beam irradiated to the upper surface of the lead frame are appropriately managed accordingly. By performing welding, laser welding with low power and high joint quality with suppressed variation in the welded portion can be realized with good reproducibility.

以下、本発明の実施の形態を図１，図２に示す実施例に基づいて説明する。なお、図示実施例は図５と同様にリードフレーム６とヒートスプレッダ５との溶接部を対象としている。   DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on the examples shown in FIGS. The illustrated embodiment is intended for the welded portion between the lead frame 6 and the heat spreader 5 as in FIG.

まず、本発明の請求項１，２に対応する実施例を図１（ａ）〜（ｃ）により説明する。この実施例では、図３（ａ），（ｂ）に示したＩＧＢＴチップ３，ＦＷＤ４の上面電極に重ねて接合したヒートスプレッダ５とリードフレーム６（Ｃｕ）の接合部との間にスペーサ１４を介挿し、該スペーサ１４の板面に空隙穴１４ａを開口してリードフレーム／ヒートスプレッダ間に空隙ｇを形成している。   First, an embodiment corresponding to claims 1 and 2 of the present invention will be described with reference to FIGS. In this embodiment, a spacer 14 is interposed between the heat spreader 5 joined to the upper surface electrode of the IGBT chip 3 and FWD 4 shown in FIGS. 3A and 3B and the joined portion of the lead frame 6 (Cu). The gap 14a is opened in the plate surface of the spacer 14 to form a gap g between the lead frame and the heat spreader.

ここで、リードフレーム６は銅板（Ｃｕ）で作られた帯状の導体片で、半導体装置の電流容量などに応じてその導体幅，厚さを設定しており、本実施例では厚さ１ｍｍ，幅５ｍｍの銅板を用いたが、他の実施例でも同様である。なお、リードフレーム６は厚さの薄い銅箔を使用することも可能であるが、後述する実施例２のようにリードフレーム６の接合部に形成する窪み状空隙の寸法精度を確保するために、剛性のある板状の銅板を用いる方が有利である。   Here, the lead frame 6 is a strip-shaped conductor piece made of a copper plate (Cu), and its conductor width and thickness are set according to the current capacity of the semiconductor device. In this embodiment, the thickness is 1 mm, Although a copper plate with a width of 5 mm was used, the same applies to other examples. It is possible to use a thin copper foil for the lead frame 6, but in order to ensure the dimensional accuracy of the hollow space formed in the joint portion of the lead frame 6 as in Example 2 described later. It is more advantageous to use a rigid plate-like copper plate.

一方、スペーサ１４は、リードフレーム６とヒートスプレッダ５との間に所望の空隙ｇを形成するための部材であり、リードフレーム６とヒートスプレッダ５との間に高さ１０μｍ程度の空隙ｇを形成するのであれば、厚さ１０μｍ程度の板材、線径が１０μｍ程度である線材、あるいはリードフレーム５，ヒートスプレッダ６のいずれかの表面に形成した成層，突起なども適用できる。   On the other hand, the spacer 14 is a member for forming a desired gap g between the lead frame 6 and the heat spreader 5, and forms a gap g having a height of about 10 μm between the lead frame 6 and the heat spreader 5. If there are, a plate material having a thickness of about 10 μm, a wire material having a wire diameter of about 10 μm, or stratification and protrusions formed on any surface of the lead frame 5 and the heat spreader 6 can be applied.

また、スペーサ１４の材質は、金属，耐熱性樹脂などの適用が可能であるが、リードフレーム／ヒートスプレッダ間の導電性，熱伝導性を勘案して、例えば銅，銅合金，アルミニウム，アルミニウム合金などが安価で好適である。なお、本実施例では厚さが約１０μｍの銅板（銅箔）を採用した。
なお、本実施例ではリードフレーム／ヒートスプレッダ間のスポット溶接箇所を４点として、前記スペーサ１４の板面には４箇所に分散して空隙穴１４ａを開口し（図１（ｂ）参照）、その空隙穴１４ａの穴径φはリードフレーム６の上面に照射するレーザビーム径の１／２〜２倍程度の範囲に設定した。これにより、ヒートスプレッダ５の上にスペーサ１４を挟んでリードフレーム６を重ね合わせた状態では、リードフレーム／ヒートスプレッダ間に高さ１０μｍ程度の空隙ｇが形成されることになる。 The material of the spacer 14 can be metal, heat-resistant resin, etc., but considering the conductivity between the lead frame / heat spreader and the thermal conductivity, for example, copper, copper alloy, aluminum, aluminum alloy, etc. Is inexpensive and suitable. In this example, a copper plate (copper foil) having a thickness of about 10 μm was employed.
In this embodiment, there are four spot welds between the lead frame / heat spreader, and the spacer 14 is dispersed in four places on the plate surface to open the gap holes 14a (see FIG. 1 (b)). The hole diameter φ of the air gap hole 14 a was set in a range of about 1/2 to 2 times the diameter of the laser beam irradiated on the upper surface of the lead frame 6. As a result, in a state where the lead frame 6 is superimposed on the heat spreader 5 with the spacer 14 interposed therebetween, a gap g having a height of about 10 μm is formed between the lead frame and the heat spreader.

この状態で前記の溶接箇所に位置を合わせてリードフレーム６の上面にレーザ光１３を照射すると、リードフレーム５が表面から局部的に溶け込んでいく。また、このレーザ光照射の過程では接合相手部材であるヒートスプレッダ５との間に前記したスペーサ１４の空隙ｇが形成されているために、溶融部からヒートスプレッダ５に逃げる放熱量は低く抑えられて深さ方向の溶け込みが進行する。そして、溶融部の溶け込み深さがリードフレーム６の板厚を超えると、溶融金属が前記空隙ｇに浸透してスペーサ１４の空隙穴１４ａを埋めて、リードフレーム／ヒートスプレッダ間に図１（ｃ）で表すような溶融部１０が形成される。これにより、リードフレーム６とヒートスプレッダ５との間が広い面域で確実に接合され、低パワーで溶接バラツキの少ないレーザ溶接が達成される。   In this state, when the laser beam 13 is irradiated on the upper surface of the lead frame 6 with the position being aligned with the above-mentioned welding location, the lead frame 5 melts locally from the surface. Further, in the process of laser light irradiation, since the gap g of the spacer 14 is formed between the heat spreader 5 which is a bonding partner member, the amount of heat released from the melted portion to the heat spreader 5 is suppressed to a low level. Melting in the vertical direction proceeds. When the penetration depth of the melted part exceeds the plate thickness of the lead frame 6, the molten metal penetrates into the gap g and fills the gap hole 14a of the spacer 14, and between the lead frame and the heat spreader, FIG. As shown, a melted portion 10 is formed. Thereby, the lead frame 6 and the heat spreader 5 are reliably joined in a wide surface area, and laser welding with low power and less welding variation is achieved.

なお、レーザ溶接は接合部材と非接触式にレーザ光を照射するので、前記したスペーサ１４はリードフレーム６とヒートスプレッダ５との間に重ね合わせるだけで固着する必要なない。
この実施例では、上記のようにスペーサ１４に空隙穴１４ａを穿孔して空隙ｇをその周囲が閉じた「室」の状態で形成している。このようにすることで、レーザ光照射による熱が空隙部に蓄熱され、この空隙を溶融部１０で満たすようになるので大きな接合面積を確保する上で効果的である。 Since laser welding irradiates laser light in a non-contact manner with the joining member, the above-described spacer 14 does not need to be fixed only by being overlapped between the lead frame 6 and the heat spreader 5.
In this embodiment, as described above, the gap 14 is formed in the spacer 14 and the gap g is formed in a “chamber” state in which the periphery is closed. By doing in this way, the heat | fever by laser beam irradiation is heat-accumulated in a space | gap part, and since this space | gap will be filled with the fusion | melting part 10, it is effective in ensuring a big joining area.

一方、前記空隙ｇの高さ（例えば、１０μｍ程度）はリードフレーム６の板幅に比べて非常に小さく、また一箇所の接合箇所に照射するレーザ光の照射時間も１０ｍｓｅｃ程度で非常に短い。したがって、空隙ｇを図示例のスペーサ１４のように周囲が閉じた「室」とせずに、空隙に周囲壁がなくてもレーザ照射中にその熱が空隙の側方に拡散してしまうことは殆どない。そこで、板材のスペーサ１４に代えて、例えば線材のスペーサを接合箇所から外れた位置に並べてリードフレーム６とヒートスプレッダ５との間に隙間を確保しても、この隙間が前記空隙と同様に熱溜まりとして有効に機能し、再現性よく大きな接合面積を確保できる。なお、スペーサ１４は上記のものに限定されるものではなく、リードフレーム／ヒートスプレッダ間に所望高さの空隙ｇを形成できるものであれば、その形態に関係なく採用できる。   On the other hand, the height of the gap g (for example, about 10 μm) is very small as compared with the plate width of the lead frame 6, and the irradiation time of the laser beam applied to one joining portion is as short as about 10 msec. Therefore, the gap g does not become a “chamber” whose periphery is closed like the spacer 14 in the illustrated example, and even if there is no surrounding wall in the gap, the heat diffuses to the side of the gap during laser irradiation. Almost no. Therefore, instead of the plate spacer 14, for example, even if a wire spacer is arranged at a position deviated from the joining location and a gap is secured between the lead frame 6 and the heat spreader 5, this gap accumulates heat similarly to the gap. As a result, the large bonding area can be secured with good reproducibility. The spacer 14 is not limited to the above, and any spacer can be used as long as it can form a gap g having a desired height between the lead frame and the heat spreader.

次に、本発明の請求項３に対応する実施例を図２に示す。この実施例では、先記実施例１のスペーサ１４を使用する代わりに、レーザ溶接の箇所に対応してリードフレーム６の裏面側にプレス，あるいはエッチング加工を施して窪み状の凹部６ａを形成しておき、リードフレーム６をヒートスプレッダ５の上面に重ね合わせた状態で両者の間に空隙ｇを確保するようにしている。なお、凹部６ａは、図１のスペーサ１４に形成した空隙穴１４ａと同様にその深さを１０μｍ程度，凹部径φをレーザビーム径の１／２〜２倍程度に設定する。   Next, an embodiment corresponding to claim 3 of the present invention is shown in FIG. In this embodiment, instead of using the spacer 14 of the first embodiment, the depression 6a is formed by pressing or etching on the back side of the lead frame 6 corresponding to the location of laser welding. In the state where the lead frame 6 is superposed on the upper surface of the heat spreader 5, a gap g is secured between them. The recess 6a is set to have a depth of about 10 μm and a recess diameter φ of about 1/2 to 2 times the laser beam diameter in the same manner as the gap hole 14a formed in the spacer 14 of FIG.

これにより、レーザ溶接時には前記凹部６ａが実施例１の空隙穴１４ａと同じように熱溜まりとして機能し、リードフレーム／ヒートスプレッダ間を低パワーでバラツキなしにレーザ溶接することができる。
なお、図２ではリードフレーム６の裏面に凹部６ａを形成しているが、これに代わる応用実施例としてヒートスプレッダ５の上面に同様な窪み状の凹部を形成するか、あるいはリードフレーム６の裏面とヒートスプレッダ５の上面の双方に浅い凹部を形成しても同様な効果を奏することができる。 Thereby, at the time of laser welding, the said recessed part 6a functions as a heat pool like the space | gap hole 14a of Example 1, and laser welding can be performed between the lead frame / heat spreader with low power and no variation.
In FIG. 2, the recess 6 a is formed on the back surface of the lead frame 6. However, as an alternative application example, a similar recess is formed on the upper surface of the heat spreader 5, or the back surface of the lead frame 6 is Even if shallow recesses are formed on both upper surfaces of the heat spreader 5, the same effect can be obtained.

なお、前記の各実施例において、レーザ光１３を照射するリードフレーム（Ｃｕ，Ｃｕ合金）６の表面にＮｉメッキを施してＮｉもしくはＳｎメッキを施しておくことにより、レーザ光１３の吸収率が大幅に向上するようになる。すなわち、リードフレーム６の母材であるＣｕに照射したレーザ光１３（半導体レーザ（波長０．８０８μｍ））の吸収率は高々約１５％であるのに対して、Ｎｉ，Ｓｎのメッキを施すと、レーザ光の吸収率は約３０％まで改善され、これにより低パワーでのレーザ溶接が可能となる。   In each of the above-described embodiments, the surface of the lead frame (Cu, Cu alloy) 6 that irradiates the laser beam 13 is Ni-plated and Ni or Sn-plated so that the absorption rate of the laser beam 13 is increased. It will be greatly improved. That is, the absorption rate of the laser beam 13 (semiconductor laser (wavelength: 0.808 μm)) irradiated to Cu which is the base material of the lead frame 6 is about 15% at most, but when Ni and Sn are plated. The absorption rate of the laser beam is improved to about 30%, which enables laser welding with low power.

また、前記の各実施例ではリードフレーム６／ヒートスプレッダ５間の溶接について述べたが、リードフレーム６の接合相手部材が図７に示した絶縁基板２Ａ，２Ｂの導体パターンであっても同様な効果を奏することは勿論である。
また、このレーザ溶接方法に適用するレーザ光は、各実施例で述べた半導体レーザ（波長：０．８０８μｍ）に限定されるものではなく、ＹＡＧレーザ，ＣＯ２レーザなどでも同様な効果が得られることが確認されている。 In each of the above-described embodiments, the welding between the lead frame 6 and the heat spreader 5 has been described. However, the same effect can be obtained even when the mating member of the lead frame 6 is the conductor pattern of the insulating substrates 2A and 2B shown in FIG. Of course.
The laser beam applied to this laser welding method is not limited to the semiconductor laser (wavelength: 0.808 μm) described in each example, and a similar effect can be obtained with a YAG laser, a CO 2 laser, or the like. It has been confirmed.

本発明の実施例１に対応するリードフレーム／ヒートスプレッダ間のレーザ溶接法の説明図で、（ａ）はレーザ光の照射状態を模式的に表す側面図、（ｂ）は空隙用スペーサの平面図、（ｃ）はレーザ溶接後の接合状態を表す断面図BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing of the laser welding method between the lead frame / heat spreader corresponding to Example 1 of this invention, (a) is a side view which represents typically the irradiation state of a laser beam, (b) is a top view of the spacer for space | gap. (C) is sectional drawing showing the joining state after laser welding 本発明の実施例２に対応するリードフレーム／ヒートスプレッダ間のレーザ溶接法の説明図でレーザ光の照射状態を模式的に表す側面図、The side view which represents typically the irradiation state of a laser beam by explanatory drawing of the laser welding method between the lead frame / heat spreader corresponding to Example 2 of this invention, 本発明の実施対象となる半導体装置の組立構造図で、（ａ）は平面図、（ｂ），（ｃ）はそれぞれ（ａ）の矢視Ａ−Ａ，Ｂ−Ｂに対応する断面側視図BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an assembly structure diagram of a semiconductor device to be implemented by the present invention, where (a) is a plan view, and (b) and (c) are cross-sectional side views corresponding to arrows AA and BB of (a), respectively. Figure レーザ光照射によるリードフレーム／ヒートスプレッダ間の溶接工程図Laser welding process between lead frame and heat spreader 従来のレーザ溶接法の説明図で、（ａ），（ｂ）はそれぞれレーザ光の照射状態、溶接接合部を表す模式図It is explanatory drawing of the conventional laser welding method, (a), (b) is a schematic diagram showing the irradiation state of a laser beam, and a welding joint part, respectively.

符号の説明Explanation of symbols

２Ａ，２Ｂ 絶縁基板
２ａ〜２ｅ 導体パターン
３ ＩＧＢＴチップ（半導体チップ）
４ ＦＷＤ（半導体チップ）
５ ヒートスプレッダ
５ａ 粗面（上面）
６〜８ リードフレーム
６ａ 凹部
１０ 溶融部
１３ レーザ光
１４ 空隙形成用スペーサ
１４ａ 空隙穴 2A, 2B Insulating substrate 2a-2e Conductor pattern 3 IGBT chip (semiconductor chip)
4 FWD (semiconductor chip)
5 Heat spreader 5a Rough surface (upper surface)
6 to 8 Lead frame 6a Concave portion 10 Melting portion 13 Laser beam 14 Spacer 14a for air gap formation Air gap hole

Claims (5)

半導体装置の内部配線用リード材としてのリードフレームの接合部を接合相手部材の上に重ね合わせ、この状態で前記接合部の上面にレーザ光を照射して前記リードフレームと前記接合相手部材とを重ね溶接してなる半導体装置の製造方法において、
前記リードフレームのレーザ溶接部位に対応して前記リードフレームと接合相手部材との間の接合面に空隙を形成した上で、リードフレームの上面にレーザ光を照射して溶接することを特徴とする半導体装置の製造方法。 A joint portion of a lead frame as a lead material for internal wiring of a semiconductor device is overlaid on a joint partner member, and in this state, the upper surface of the joint portion is irradiated with laser light to bond the lead frame and the joint partner member. In the manufacturing method of the semiconductor device formed by lap welding,
A gap is formed in the joint surface between the lead frame and the mating member corresponding to the laser welding part of the lead frame, and then the upper surface of the lead frame is irradiated with laser light and welded. A method for manufacturing a semiconductor device. 請求項１に記載の製造方法おいて、リードフレームと接合相手部材との間に、レーザ溶接部位に対応する位置に穴を開口した空隙形成用スペーサを介挿して空隙を形成したことを特徴とする半導体装置の製造方法。 The manufacturing method according to claim 1, wherein a gap is formed between a lead frame and a bonding partner member by inserting a gap forming spacer having a hole at a position corresponding to a laser welding site. A method for manufacturing a semiconductor device. 請求項１に記載の製造方法において、リードフレームの接合部裏面，該接合部裏面に対峙する接合相手部材の上面のいずれか一方，もしくは双方に、レーザ溶接部位と対応する位置に窪みを設けて空隙を形成したことを特徴とする半導体装置の製造方法。 2. The manufacturing method according to claim 1, wherein a recess is provided at a position corresponding to the laser welding site on one or both of the back surface of the joint portion of the lead frame and the top surface of the joint member facing the back surface of the joint portion. A method of manufacturing a semiconductor device, wherein a void is formed. 請求項１ないし３のいずれかの項に記載の製造方法において、リードフレームと接合相手部材との間に形成した空隙は、その深さが約１０μｍであることを特徴とする半導体装置の製造方法。 4. The method of manufacturing a semiconductor device according to claim 1, wherein the gap formed between the lead frame and the bonding partner member has a depth of about 10 [mu] m. . 請求項１ないし４に記載の製造方法において、リードフレームの母材表面がＮｉもしくはＳｎのメッキが施されていることを特徴とする半導体装置の製造方法。 5. The method of manufacturing a semiconductor device according to claim 1, wherein the surface of the base material of the lead frame is plated with Ni or Sn.
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