JP2004241712A - Ultrasonic bonding method - Google Patents

Ultrasonic bonding method Download PDF

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Publication number
JP2004241712A
JP2004241712A JP2003031227A JP2003031227A JP2004241712A JP 2004241712 A JP2004241712 A JP 2004241712A JP 2003031227 A JP2003031227 A JP 2003031227A JP 2003031227 A JP2003031227 A JP 2003031227A JP 2004241712 A JP2004241712 A JP 2004241712A
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Prior art keywords
bonding
pressing
ultrasonic
joined
load
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Akihisa Noshita
明久 野下
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Panasonic Holdings Corp
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Matsushita Electric Industrial Co Ltd
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Priority to JP2003031227A priority Critical patent/JP2004241712A/en
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Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic bonding method capable of bonding an object to be joined with high junction quality with simple facility. <P>SOLUTION: In the ultrasonic bonding method, a press load is allowed to operate on the object to be joined by a press means and a vibrator allows ultrasonic vibration to operate for joining to the object to be joined. A bonding process is constituted of a first press process for pressing the object to be joined by first press load F1; and a second press process for pressing the object to be joined by second press load F2 being lower than the first one F1 after the first press process. Constant alternating voltages +V1 to -V1 are applied to the vibrator from the halfway of the first press process to the end of bonding, thus controlling ultrasonic output in the bonding process to appropriate conditions without performing any complicated control and bonding the object to be joined with the high junction quality with simple facilities. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、ワイヤやバンプなどの接合対象物を電子部品や基板の電極などの被接合物に超音波振動によって接合する超音波ボンディング方法に関するものである。
【０００２】
【従来の技術】
半導体素子の電極にバンプを形成する方法として、ワイヤボンド法を用いる技術が知られている（例えば特許文献１参照）。この方法は、端部が球状に整形されたワイヤを超音波ボンディングによって電極に圧接し、この後ワイヤを引きちぎることにより圧接された球状のワイヤを電極上に残置してバンプを形成するものである。
【０００３】
この技術を用いて微小なバンプを安定して形成するためには、ボンディング過程における超音波出力を適正条件に制御する必要がある。このための技術として、超音波発生装置と変換器との間に可変インピーダンス回路網を挿入し、適正条件によるボンディング処理のために予め選定された所望の出力レベルに維持するように回路網インピーダンスを設定する方式が知られている（例えば特許文献２参照）。
【０００４】
【特許文献１】
特開２００１−２８４３８６号公報
【特許文献２】
特開平７−６８２２０号公報
【０００５】
【発明が解決しようとする課題】
近年の電子機器の小型化・高機能化および低コスト化の要請に伴い、半導体素子などの電子部品の製造過程においても、微小サイズの電子部品を対象としてバンプ形成や部品実装などの各種作業を高品質且つ低コストで実行するための技術が求められている。しかしながら上述の従来技術による超音波ボンディングにおいては、このような高接合品質のボンディングを低コストで実現することが困難になっている。
【０００６】
すなわち、特許文献１記載の技術においては、バンプ形成において初期段階から大きな超音波出力でボンディングが行われるため、ボンディング初期にバンプが部分的に接合面に拘束され、その後のボンディングにおける十分な金属接合面の確保がかえって阻害される傾向があり、最終的なバンプ接合強度を低下させる場合があった。
【０００７】
また所望の超音波出力をバンプに印加するためには、特許文献２に示すように、インピーダンス制御回路網を用いた複雑な制御を必要とすることから、設備面でのコスト高が避けられなかった。したがって実用上には、特許文献１に示すような、ボンディング過程における超音波出力を適正条件に制御して良好な接合品質を確保する効果を享受できるのは限定された場合のみであり、高接合品質のボンディングを低コストで実現することが困難であった。そしてこの課題は、電子部品に形成されたバンプを基板の電極に超音波ボンディングによって接合する場合にも共通していた。
【０００８】
そこで本発明は、簡便な設備により高い接合品質で接合対象物をボンディングすることができる超音波ボンディング方法を提供することを目的とする。
【０００９】
【課題を解決するための手段】
請求項１記載の超音波ボンディング方法は、接合対象物に押圧手段によって押圧荷重を作用させるとともに振動子によって超音波振動を作用させて被接合物に接合する超音波ボンディング方法であって、前記接合対象物を第１の押圧荷重で押圧する第１押圧工程と、第１押圧工程の後第１の押圧荷重よりも低い第２の押圧荷重で接合対象物を押圧する第２押圧工程とを含み、前記第１押圧工程の途中からボンディング終了に至るまで前記振動子に一定の駆動電圧を印加する。
【００１０】
請求項２記載の超音波ボンディング方法は、請求項１記載の超音波ボンディング方法であって、前記接合対象物がワイヤであり、前記振動子を有するホーンに設けられたキャピラリに挿通した前記ワイヤの端部を、電子部品の電極に超音波ボンディングにより接合する。
【００１１】
請求項３記載の超音波ボンディング方法は、請求項１記載の超音波ボンディング方法であって、前記接合対象物が電子部品に形成された外部接続用のバンプであり、前記振動子を有するホーンに設けられた当接ツールによって前記電子部品を基板に押圧することにより、前記バンプを基板の電極に超音波ボンディングにより接合する。
【００１２】
本発明によれば、超音波ボンディング工程を、接合対象物を第１の荷重で押圧する第１押圧工程と、第１押圧工程の後、第１の荷重よりも低い第２の荷重で接合対象物を押圧する第２押圧工程とで構成し、第１押圧工程の途中からボンディング終了に至るまで振動子に一定の駆動電圧を印加する定電圧制御を用いることにより、複雑な制御を行うことなくボンディング過程における超音波出力を適正条件に制御することができ、簡便な設備により高い接合品質で接合対象物をボンディングすることができる。
【００１３】
【発明の実施の形態】
（実施の形態１）
図１は本発明の実施の形態１のワイヤボンディング装置の構成を示すブロック図、図２は本発明の実施の形態１のワイヤボンディングによるバンプ形成方法のフロー図、図３は本発明の実施の形態１のワイヤボンディングによるバンプ形成方法における超音波ボンディング条件を示すグラフ、図４は本発明の実施の形態１のワイヤボンディングによるバンプ形成方法における超音波ボンディング過程の説明図である。
【００１４】
本実施の形態１は、超音波ボンディングの接合対象物がワイヤであり、このワイヤを被接合物である電子部品の電極に接合するワイヤボンディングの例を示している。このワイヤボンディングにおいては、振動子を有するホーンに設けられたキャピラリに挿通したワイヤの端部を、電子部品の電極に超音波ボンディングにより接合する。
【００１５】
まず図１を参照してワイヤボンディング装置のボンディング機構について説明する。図１において、ホーン駆動機構１は水平方向に延出したホーン２を備えている。ホーン２の先端部にはキャピラリ２ａが装着されており、ホーン２の後端部には超音波振動を発生する振動子４が結合されている。振動子４はＵＳドライバ９によって駆動され、これによりホーン２を介してキャピラリ２ａには超音波振動が印加される。
【００１６】
この振動子４の駆動において、制御部１０が記憶部１２に記憶された電圧指令値を読み取り、ＵＳドライバ９にこの電圧指令値を出力することにより、ＵＳドライバ９は常に電圧指令値に応じた一定の駆動電圧、すなわち一定電圧値の交番電圧を振動子４に印加するように構成されている。
【００１７】
ホーン２は駆動ブロック３によって支持されており、Ｚ軸ドライバ８に駆動されるＶＣＭモータ５によって、駆動ブロック３は水平な回転軸３ａ廻りに所定角度の回動が可能となっている。この回動はエンコーダ６によってその回動量が検出され、検出信号はアンプ７を介してＺ軸ドライバ８に伝達される。ＶＣＭモータ５を駆動してホーン２を回転軸３ａ廻りに回動させることにより、キャピラリ２ａが昇降するとともに、キャピラリ２ａを下方に対して押圧する。ＶＣＭモータ５は、接合対象物に押圧荷重を作用させる押圧手段となっている。このキャピラリ２ａの動作において、制御部１０が記憶部１２に記憶された荷重指令値を読み取り、荷重制御部１１を介してＺ軸ドライバ８にこの荷重指令値を出力することにより、キャピラリ２ａは荷重指令値に応じた押圧荷重を発生する。
【００１８】
ボンディング動作は、キャピラリ２ａにボンディングワイヤを挿通させ、ボンディングワイヤの下端にボール１３（図４参照）を形成させた状態で行われる。すなわち制御部１０によってキャピラリ２ａの昇降押圧動作と超音波振動の印加を制御して、ボール１３をキャピラリ２ａによって被接合物である電子部品の電極１４の接合面に押し付け、ボール１３に押圧荷重と超音波振動を作用させることにより、電子部品へのワイヤボンディングによるバンプ形成が行われる。
【００１９】
このワイヤボンディング装置のボンディング機構は上記の様に構成されており、次に図２のフローに沿って，図３、図４を参照して、ワイヤボンディングによるバンプ形成方法について説明する。図３はこのワイヤボンディング過程における超音波ボンディング条件を示しており、図３（ａ）、（ｂ）、（ｃ）は、キャピラリ２ａによってボール１３を押圧する押圧荷重、ＵＳドライバ９によって振動子４に印加される駆動電圧、および振動子４が発生する超音波出力の各項目の時間的変化をそれぞれ示している。
【００２０】
まずキャピラリ２ａを上方から挿通したボンディングワイヤの先端部をスパークによって溶融させて、キャピラリ２ａの下端部に球状のボール１３を形成する（ＳＴ１）。次いでキャピラリ２ａをボール１３とともに下降させて、ボール１３を電極１４に当接させる（ＳＴ２）。そしてこの後、キャピラリ２ａによってボール１３を電極１４に対して押圧する押圧工程が開始される（図４（ａ）参照）。
【００２１】
ここではまず図３（ａ）に示すように、押圧開始のタイミングｔ１から、ボール１３を上下方向に塑性変形させるのに必要十分な第１の押圧荷重Ｆ１で押圧する（ＳＴ３）（第１押圧工程）。図４（ａ）は、第１の押圧工程において、ボール１３を第１の押圧荷重Ｆ１で押圧した状態を示している。この第１の押圧工程では、ボール１３の略球面状の下端部が電極１４の接合面１４ａに接触した状態から第１の押圧荷重Ｆ１で押圧される。
【００２２】
これにより、ボール１３は上下方向に幾分押しつぶされるとともに、ボール１３の下端部は接合面１４ａにならって水平方向に拡がるように塑性変形する。これにより、当初は下端部のみで接合面１４ａと接触していたボール１３は、より広い範囲で接合面１４ａと接触するようになる。
【００２３】
このとき、ボール１３の下面と接合面１４ａとの接触面における面圧分布は全接触範囲にわたって必ずしも均一ではなく、ばらついている場合が多い。すなわち、ボール１３下面の凹凸やキャピラリ２ａの下端部がボール１３を押圧する位置によって、ボール１３が高面圧で集中的に接合面１４ａに押圧された高面圧部Ａ（図４（ａ）において太線で示す）と、比較的面圧が低い低面圧部が存在する。
【００２４】
そして押圧開始から、上述のボール１３の塑性変形に要する所定時間Ｔ１（例えば５ｍｓｅｃ．程度）経過後に、図４（ｂ）に示すように、ＵＳドライバ９によって振動子４に一定の駆動電圧を印加する（ＳＴ４）。これにより、振動子４には＋Ｖ１〜−Ｖ１の高周波の交番電圧が印加され、振動子４はこの駆動電圧に応じた超音波振動を発生する。そしてこの超音波振動がホーン２，キャピラリ２ａを介してボール１３に伝達されることにより、ボール１３の下面は接合面１４ａに対して面方向に相対振動し、超音波ボンディングによる接合界面の金属接合が開始される。
【００２５】
上述の第１押圧工程での超音波ボンディング（ボンディング初期）は、ボール１３に塑性変形を生じさせる程度の高い押圧荷重下で行われ、ボール１３と接合面１４ａの接合界面には、高拘束状態で超音波振動が作用する。そして駆動電圧一定の条件下では、接合界面における超音波振動の振幅は拘束状態に応じたものとなることから、第１押圧工程のように高拘束状態における接合界面での超音波振動の振幅は小さい。この結果、図３（ｃ）に示すように、この間の超音波出力は低出力Ｗ１に保たれる。
【００２６】
換言すれば、このボンディング初期においては、上述の高面圧部Ａに低出力の超音波振動を作用させる形態になっている。すなわち、まずボール１３の表面および接合面１４ａの酸化膜を高面圧によって破壊し易い状態にして、両者の金属面が直接接触するようにした後に、小振幅の超音波振動を作用させる。これにより、まず高面圧部Ａにおいてボール１３は電極１４の接合面１４ａと金属接合され、後続過程においては高面圧部Ａを起点として金属接合範囲が徐々に拡大する。
【００２７】
したがって、超音波ボンディング過程の初期において、未だ電極１４に対して拘束されていない状態のボール１３が振動方向に大きく移動する、いわゆる「ばたつき」を発生することなく、ボール１３と接合面１４ａとの接触面を徐々になじませながら、安定したボンディング進行を実現するようになっている。
【００２８】
この後、図３（ｂ）に示すように、タイミングｔ２から初期ボンディング時間Ｔ２（例えば５〜１０ｍｓｅｃ．）が経過したタイミングｔ３において、押圧荷重を第１の押圧荷重Ｆ１よりも低い第２の押圧荷重Ｆ２に切り換え、この状態で＋Ｖ１〜−Ｖ１の高周波の交番電圧の印加を継続する（ＳＴ５）（第２押圧工程）。
【００２９】
この第２押圧工程での超音波ボンディング（ボンディング後期）は、第１の押圧荷重Ｆ１よりも低い低押圧荷重下で行われ、ボール１３と接合面１４ａの接合界面には、第１押圧工程での振幅と比べて大きな振幅の超音波振動が作用する。この結果、図３（ｃ）に示すように、第２押圧工程における超音波出力はＷ１よりも大きい高出力Ｗ２に保たれる。
【００３０】
すなわち、このボンディング後期においては、ボール１３と接合面１４ａとの接触面の面圧が全体的に低下した状態で、ボンディング初期よりも高出力の超音波振動を作用させる形態となっている。したがって、ボール１３と電極１４の接合界面には、図４（ｃ）に示すように、大きな振幅の超音波振動によって高応力が作用する。
【００３１】
これにより、ボンディング初期においては高面圧部Ａの周囲に限定されていた金属接合面が全体に拡大し、より均一な金属接合状態が実現される。そしてこの間、ボール１３には塑性変形を発生させるような高押圧荷重が負荷されないことから、ボール１３のつぶれ変形が進行せず、ボール１３が過度に押しつぶされることによるバンプ形状不良が発生しない。
【００３２】
そして図３に示す所定の全体ボンディング時間Ｔ（例えば３５〜５５ｍｓｅｃ．）が経過したタイミングｔ４において、駆動電圧の印加および押圧を停止する（ＳＴ６）。これにより、ボール１３は電極１４に荷重と超音波振動によって接合された状態となる。この後、キャピラリ２ａを上昇させてボール１３の上端に結合した状態のボンディングワイヤを切断することにより、ボール１３が電極１４上に接合された状態で残置されて、バンプが形成される。これにより、バンプ形成が比較的困難なＳＡＷフィルターチップ等のチップにおける電極に対しても良好なバンプを形成することができる。
【００３３】
（実施の形態２）
図５は本発明の実施の形態２の電子部品ボンディング装置の構成を示すブロック図、図６は本発明の実施の形態２の電子部品ボンディング装置によるバンプボンディング動作の工程説明図である。
【００３４】
本実施の形態２は、超音波ボンディングの接合対象物が電子部品に設けられた外部接続用のバンプであり、このバンプを被接合物としての基板の電極に接合するバンプボンディング（いわゆるフリップチップボンディング）の例を示している。このバンプボンディングにおいては、振動子を有するホーンに設けられた当接ツールによって電子部品を基板に押圧することにより、バンプを基板の電極に超音波ボンディングにより接合する。
【００３５】
図６において基板保持部２０上には、電極２１ａが形成された基板２１が保持されている。基板保持部２０の上方には、ボンディング部２３が配設されている。ボンディング部２３はモータおよびエンコーダを内蔵したツール昇降押圧駆動部２４を備えており、ツール昇降押圧駆動部２４はホルダ２５に保持されたボンディングツール２６を昇降駆動する。
【００３６】
ボンディングツール２６は、下方に突出した接合作用部２６ａ（当接ツール）を備えており、接合作用部２６ａはバンプ付きの電子部品２２を吸着して保持するとともに、電子部品２２を基板２１に対して押圧する。ツール昇降押圧駆動部２４は、接合対象物に押圧荷重を作用させる押圧手段となっている。このときボンディングツール２６に装着された振動子２７を駆動することにより、電子部品２２には超音波振動が印加される。なお押圧手段として空圧シリンダを用いてもよい。
【００３７】
図６において、制御部３１、荷重制御部３２，Ｚ軸ドライバ３０、アンプ２９およびＵＳドライバ２８は、実施の形態１における制御部１０、荷重制御部１１，Ｚ軸ドライバ８、アンプ７およびＵＳドライバ９と同様の機能を有しており、記憶部３３には、実施の形態１における記憶部１２と同様のデータが記憶されている。
【００３８】
すなわち、制御部３１が記憶部３３に記憶された電圧指令値を読み取り、ＵＳドライバ２８にこの電圧指令値を出力することにより、ＵＳドライバ２８は常に電圧指令値に応じた一定の駆動電圧、すなわち一定電圧値の交番電圧を振動子２７に印加するように構成されている。またツール昇降押圧駆動部２４によるボンディングツール２６の昇降押圧動作において、制御部３１が記憶部３３に記憶された荷重指令値を読み取り、荷重制御部３２を介してＺ軸ドライバ３０にこの荷重指令値を出力することにより、ツール昇降押圧駆動部２４は荷重指令値に応じた押圧荷重で押圧する。
【００３９】
ボンディングツール２６による電子部品２２の超音波ボンディング工程においては、まずボンディングツール２６の接合作用部２６ａの下端部に、バンプ２２ａが設けられた電子部品２２を保持させ、図６（ａ）に示すように、ボンディングツール２６を移動させてバンプ２２ａを基板２１の電極２１ａに位置合わせする。
【００４０】
次いでボンディングツール２６を電子部品２２とともに下降させて、バンプ２２ａを電極２１ａに当接させる（ＳＴ２）。そしてこの後、ボンディングツール２６によって電子部品２２を押圧して、バンプ２２ａを電極２１ａに対して押圧する押圧工程が開始される。この押圧工程においては、実施の形態１の図３に示すボンディング条件と同様の条件、すなわち押圧荷重の高低切換制御と振動子２７の駆動電圧の定電圧制御が適用される。
【００４１】
まず押圧開始のタイミングｔ１から、図６（ｂ）に示すように、バンプ２２ａを上下方向に塑性変形させるのに必要十分な第１の押圧荷重Ｆ１で押圧する（第１押圧工程）。そして押圧開始から、上述のバンプ２２ａの塑性変形に要する所定時間Ｔ１経過後のタイミングｔ２に、ＵＳドライバ２８によって振動子２７に一定の駆動電圧Ｖを印加する（ＳＴ４）。これにより、振動子２７には＋Ｖ１〜−Ｖ１の高周波の交番電圧が印加され、振動子２７は超音波振動を発生する。そしてこの超音波振動がホーン２６，接合作用部２６ａを介してバンプ２２ａに伝達されることにより、図６（ｃ）に示すように、バンプ２２ａの下面は電極２１ａの接合面に対して面方向に相対振動し、超音波ボンディングが開始される。
【００４２】
この後、駆動電圧印加開始から実施の形態１と同様の初期ボンディング時間Ｔ２が経過したタイミングｔ３において、図６（ｄ）に示すように、押圧荷重を第１の押圧荷重Ｆ１よりも低い第２の押圧荷重Ｆ２に切り換え、＋Ｖ１〜−Ｖ１の交番電圧の印加を継続する（第２押圧工程）。そして所定の全体ボンディング時間Ｔが経過したタイミングｔ４において、駆動電圧の印加および押圧を停止する。これにより、バンプ２２ａは電極２１に荷重と超音波振動によって接合される。この後、ボンディングツール２６を上昇させることにより、バンプ２２ａが電極２１ａに接合されて、電子部品２２の超音波ボンディングによる実装が完了する。
【００４３】
上述の実施の形態２においても、バンプ２２ａを電極２１ａに超音波ボンディングする過程において、実施の形態１と同様に押圧荷重の高低切換制御を行い、振動子の駆動電圧を定電圧制御することにより、良好なボンディング結果を得ることができる。
【００４４】
上記説明したように、各実施の形態に示す超音波ボンディング方法においては、接合対象物を第１の押圧荷重で押圧する第１押圧工程と、第１押圧工程の後、第１の荷重よりも低い第２の押圧荷重で接合対象物を押圧する第２押圧工程とでボンディング工程を構成し、第１押圧工程の途中からボンディング終了に至るまで、振動子に一定の駆動電圧を印加するようにしている。
【００４５】
これにより、ボンディング初期において接合対象物は適度に押しつぶされて接合面との接触状態が均一化されるとともに、接触面中の高面圧領域では金属面が相互に押し付けられて酸化膜などの異物層が破壊されやすくなる。そしてこの状態で駆動電圧を振動子に印加することにより、前述の高面圧領域では異物層が除去された金属面が相互に接触して金属接合される。
【００４６】
このとき、前述のように超音波出力は低出力に保たれることから、接合界面における金属接合面の形成は小振幅の超音波振動によって行われる。これにより、接合界面では高面圧領域を起点として金属接合面が徐々に拡大し、接触面相互をなじませつつ安定した状態でボンディングを進行させることができる。
【００４７】
そしてこの状態で、押圧荷重を低荷重に切り換えることにより、接合界面における超音波振動の振幅が増大する。これにより、これ以降のボンディング後期においては大振幅によって接合界面に高応力を作用させて効率よくボンディングを進行させ、接合対象物と接合面との広い範囲により均一な金属接合面を形成することができる。
【００４８】
そして上述の超音波ボンディング方法においては、押圧荷重の高低切換制御と、振動子の駆動電圧の定電圧制御のみによって、適正な超音波出力の制御を実現するようにしている。このため、従来において所望の超音波出力を印加するために必要とされたインピーダンス制御回路網などを用いた複雑な制御装置を用いることなく、簡便な設備によって高い接合品質のボンディングを実現することができる。
【００４９】
【発明の効果】
本発明によれば、接合対象物を第１の押圧荷重で押圧する第１押圧工程と、第１押圧工程の後、第１の押圧荷重よりも低い第２の押圧荷重で接合対象物を押圧する第２押圧工程とを含み、第１押圧工程の途中からボンディング終了に至るまで前記振動子に一定の駆動電圧を印加することにより、複雑な制御を行うことなくボンディング過程における超音波出力を低出力から高出力へ変化させることができ、簡便な設備により高い接合品質でボンディングすることができる。
【図面の簡単な説明】
【図１】本発明の実施の形態１のワイヤボンディング装置の構成を示すブロック図
【図２】本発明の実施の形態１のワイヤボンディングによるバンプ形成方法のフロー図
【図３】本発明の実施の形態１のワイヤボンディングによるバンプ形成方法における超音波ボンディング条件を示すグラフ
【図４】本発明の実施の形態１のワイヤボンディングによるバンプ形成方法における超音波ボンディング過程の説明図
【図５】本発明の実施の形態２の電子部品ボンディング装置の構成を示すブロック図
【図６】本発明の実施の形態２の電子部品ボンディング装置によるバンプボンディング動作の工程説明図
【符号の説明】
１ ホーン駆動機構
２ａ キャピラリ
４、２７ 振動子
９、２８ ＵＳドライバ
１０、３１ 制御部
１１、３２ 荷重制御部
１３ ボール
１４ 電極
２１ 基板
２１ａ 電極
２２ 電子部品
２２ａ バンプ
２４ ツール昇降押圧駆動部
２６ ボンディングツール
２６ａ 接合作用部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ultrasonic bonding method for bonding an object such as a wire or a bump to an object such as an electronic component or an electrode of a substrate by ultrasonic vibration.
[0002]
[Prior art]
As a method of forming a bump on an electrode of a semiconductor element, a technique using a wire bonding method is known (for example, see Patent Document 1). According to this method, a wire whose end is shaped into a sphere is pressed against an electrode by ultrasonic bonding, and then the wire is torn off to leave a pressed spherical wire on the electrode to form a bump. .
[0003]
In order to stably form minute bumps using this technique, it is necessary to control the ultrasonic output in the bonding process to appropriate conditions. As a technique for this, a variable impedance network is inserted between the ultrasonic generator and the transducer, and the network impedance is adjusted so as to maintain a desired output level selected in advance for a bonding process under appropriate conditions. A setting method is known (for example, see Patent Document 2).
[0004]
[Patent Document 1]
JP 2001-284386 A [Patent Document 2]
JP-A-7-68220
[Problems to be solved by the invention]
With the recent demand for miniaturization, higher functionality, and lower cost of electronic equipment, in the manufacturing process of electronic components such as semiconductor devices, various operations such as bump formation and component mounting for micro-sized electronic components are performed. There is a need for a technique for performing high quality and low cost. However, in the above-described ultrasonic bonding according to the related art, it is difficult to realize such high bonding quality bonding at low cost.
[0006]
That is, in the technique described in Patent Document 1, since bonding is performed with a large ultrasonic output from the initial stage in the formation of bumps, the bumps are partially restrained on the bonding surface at the initial stage of bonding, and sufficient metal bonding in subsequent bonding is performed. There is a tendency that the securing of the surface is rather hindered, and the final bump bonding strength may be reduced.
[0007]
In addition, in order to apply a desired ultrasonic output to the bump, as shown in Patent Document 2, complicated control using an impedance control network is required, so that the cost in equipment is unavoidable. Was. Therefore, in practical use, the effect of controlling the ultrasonic output in the bonding process to an appropriate condition and ensuring good joining quality as shown in Patent Document 1 can be enjoyed only in limited cases, It has been difficult to achieve quality bonding at low cost. This problem is common to the case where a bump formed on an electronic component is bonded to an electrode on a substrate by ultrasonic bonding.
[0008]
Therefore, an object of the present invention is to provide an ultrasonic bonding method that can bond an object to be bonded with high bonding quality using simple equipment.
[0009]
[Means for Solving the Problems]
2. The ultrasonic bonding method according to claim 1, wherein the pressing means applies a pressing load to the object to be bonded and applies ultrasonic vibration by a vibrator to bond the object to the object. A first pressing step of pressing the object with a first pressing load, and a second pressing step of pressing the joining object with a second pressing load lower than the first pressing load after the first pressing step And applying a constant drive voltage to the vibrator from the middle of the first pressing step to the end of the bonding.
[0010]
The ultrasonic bonding method according to claim 2 is the ultrasonic bonding method according to claim 1, wherein the object to be bonded is a wire, and the bonding object is a wire that is inserted through a capillary provided in a horn having the vibrator. The ends are joined to the electrodes of the electronic component by ultrasonic bonding.
[0011]
The ultrasonic bonding method according to claim 3 is the ultrasonic bonding method according to claim 1, wherein the object to be bonded is a bump for external connection formed on an electronic component, and the horn having the vibrator. The bump is bonded to the electrode of the substrate by ultrasonic bonding by pressing the electronic component against the substrate with the provided contact tool.
[0012]
According to the present invention, the ultrasonic bonding step includes: a first pressing step of pressing the object to be bonded with the first load; and, after the first pressing step, the bonding object with the second load lower than the first load. A second pressing step of pressing an object, and using a constant voltage control for applying a constant driving voltage to the vibrator from the middle of the first pressing step to the end of bonding, without performing complicated control. The ultrasonic output in the bonding process can be controlled to an appropriate condition, and the object to be bonded can be bonded with high bonding quality using simple equipment.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
(Embodiment 1)
FIG. 1 is a block diagram showing a configuration of a wire bonding apparatus according to Embodiment 1 of the present invention, FIG. 2 is a flowchart of a bump forming method by wire bonding according to Embodiment 1 of the present invention, and FIG. FIG. 4 is a graph showing ultrasonic bonding conditions in the method for forming a bump by wire bonding according to the first embodiment. FIG. 4 is an explanatory diagram of an ultrasonic bonding process in the method for forming a bump by wire bonding according to the first embodiment of the present invention.
[0014]
The first embodiment shows an example of wire bonding in which an object to be bonded by ultrasonic bonding is a wire, and the wire is bonded to an electrode of an electronic component to be bonded. In this wire bonding, an end of a wire inserted into a capillary provided on a horn having a vibrator is bonded to an electrode of an electronic component by ultrasonic bonding.
[0015]
First, the bonding mechanism of the wire bonding apparatus will be described with reference to FIG. In FIG. 1, a horn drive mechanism 1 includes a horn 2 extending in a horizontal direction. A capillary 2a is mounted on the tip of the horn 2, and a vibrator 4 for generating ultrasonic vibration is connected to a rear end of the horn 2. The vibrator 4 is driven by a US driver 9, whereby ultrasonic vibration is applied to the capillary 2 a via the horn 2.
[0016]
In driving the vibrator 4, the control unit 10 reads the voltage command value stored in the storage unit 12 and outputs this voltage command value to the US driver 9, so that the US driver 9 always responds to the voltage command value. A constant drive voltage, that is, an alternating voltage having a constant voltage value is applied to the vibrator 4.
[0017]
The horn 2 is supported by a drive block 3, and the drive block 3 can be turned at a predetermined angle around a horizontal rotation axis 3 a by a VCM motor 5 driven by a Z-axis driver 8. The amount of this rotation is detected by the encoder 6, and a detection signal is transmitted to the Z-axis driver 8 via the amplifier 7. By driving the VCM motor 5 to rotate the horn 2 around the rotation shaft 3a, the capillary 2a moves up and down and presses the capillary 2a downward. The VCM motor 5 is a pressing means for applying a pressing load to the joining object. In the operation of the capillary 2a, the control unit 10 reads the load command value stored in the storage unit 12 and outputs this load command value to the Z-axis driver 8 via the load control unit 11, whereby the capillary 2a A pressing load is generated according to the command value.
[0018]
The bonding operation is performed with a bonding wire inserted through the capillary 2a and a ball 13 (see FIG. 4) formed at the lower end of the bonding wire. That is, the controller 13 controls the vertical pressing operation of the capillary 2 a and the application of ultrasonic vibration, and presses the ball 13 against the bonding surface of the electrode 14 of the electronic component to be bonded by the capillary 2 a, and applies a pressing load to the ball 13. By applying ultrasonic vibration, bump formation is performed on the electronic component by wire bonding.
[0019]
The bonding mechanism of this wire bonding apparatus is configured as described above. Next, a bump forming method by wire bonding will be described with reference to FIGS. 3 and 4 along the flow of FIG. FIG. 3 shows the ultrasonic bonding conditions in the wire bonding process. FIGS. 3A, 3B, and 3C show a pressing load for pressing the ball 13 by the capillary 2a and a vibrator 4 by the US driver 9. , And the temporal change of each item of the ultrasonic output generated by the transducer 4 is shown.
[0020]
First, the tip of the bonding wire, through which the capillary 2a is inserted from above, is melted by a spark to form a spherical ball 13 at the lower end of the capillary 2a (ST1). Next, the capillary 2a is lowered together with the ball 13, and the ball 13 is brought into contact with the electrode 14 (ST2). Thereafter, a pressing step of pressing the ball 13 against the electrode 14 by the capillary 2a is started (see FIG. 4A).
[0021]
Here, first, as shown in FIG. 3A, the ball 13 is pressed with a first pressing load F1 necessary and sufficient to vertically deform the ball 13 from a pressing start timing t1 (ST3) (first pressing). Process). FIG. 4A shows a state in which the ball 13 is pressed by the first pressing load F1 in the first pressing step. In the first pressing step, the substantially spherical lower end of the ball 13 is pressed by the first pressing load F1 from a state in which the ball 13 contacts the joint surface 14a of the electrode 14.
[0022]
As a result, the ball 13 is somewhat crushed in the vertical direction, and the lower end of the ball 13 is plastically deformed so as to expand in the horizontal direction following the joint surface 14a. As a result, the ball 13 initially in contact with the joint surface 14a only at the lower end portion comes into contact with the joint surface 14a in a wider range.
[0023]
At this time, the surface pressure distribution on the contact surface between the lower surface of the ball 13 and the joint surface 14a is not always uniform over the entire contact range, and often varies. That is, depending on the unevenness of the lower surface of the ball 13 and the position where the lower end of the capillary 2a presses the ball 13, the high surface pressure portion A where the ball 13 is intensively pressed against the bonding surface 14a at a high surface pressure (FIG. 4A) , There is a low surface pressure portion having a relatively low surface pressure.
[0024]
After a lapse of a predetermined time T1 (for example, about 5 msec.) Required for the plastic deformation of the ball 13 from the start of pressing, a fixed driving voltage is applied to the vibrator 4 by the US driver 9 as shown in FIG. (ST4). As a result, a high-frequency alternating voltage of + V1 to -V1 is applied to the vibrator 4, and the vibrator 4 generates ultrasonic vibration according to the drive voltage. When this ultrasonic vibration is transmitted to the ball 13 via the horn 2 and the capillary 2a, the lower surface of the ball 13 is vibrated relative to the bonding surface 14a in the surface direction, and the metal bonding of the bonding interface by ultrasonic bonding is performed. Is started.
[0025]
The ultrasonic bonding (initial bonding) in the above-described first pressing step is performed under a pressing load high enough to cause plastic deformation of the ball 13, and the bonding interface between the ball 13 and the bonding surface 14 a is in a highly restricted state. The ultrasonic vibration works. Then, under the condition of a constant drive voltage, the amplitude of the ultrasonic vibration at the bonding interface depends on the constrained state, so that the amplitude of the ultrasonic vibration at the bonding interface in the high constrained state as in the first pressing step is small. As a result, as shown in FIG. 3C, the ultrasonic output during this period is kept at the low output W1.
[0026]
In other words, in the initial stage of the bonding, a low-output ultrasonic vibration is applied to the high surface pressure portion A. That is, first, the surface of the ball 13 and the oxide film on the bonding surface 14a are easily broken by a high surface pressure so that the two metal surfaces are in direct contact with each other, and then a small-amplitude ultrasonic vibration is applied. Thereby, first, the ball 13 is metal-bonded to the bonding surface 14a of the electrode 14 at the high surface pressure portion A, and the metal bonding range gradually increases starting from the high surface pressure portion A in the subsequent process.
[0027]
Therefore, at the beginning of the ultrasonic bonding process, the ball 13 that has not yet been restrained with respect to the electrode 14 moves largely in the vibration direction, that is, does not generate so-called “fluttering”, and the ball 13 and the bonding surface 14 a A stable bonding progress is realized while gradually adjusting the contact surface.
[0028]
Thereafter, as shown in FIG. 3B, at a timing t3 when an initial bonding time T2 (for example, 5 to 10 msec.) Has elapsed from the timing t2, the pressing load is changed to the second pressing lower than the first pressing load F1. The load is switched to the load F2, and in this state, the application of the high-frequency alternating voltage of + V1 to -V1 is continued (ST5) (second pressing step).
[0029]
The ultrasonic bonding (late bonding) in the second pressing step is performed under a low pressing load lower than the first pressing load F1, and the bonding interface between the ball 13 and the bonding surface 14a is formed in the first pressing step. The ultrasonic vibration having a larger amplitude than the amplitude of the ultrasonic wave acts. As a result, as shown in FIG. 3C, the ultrasonic output in the second pressing step is kept at a high output W2 larger than W1.
[0030]
That is, in the latter stage of the bonding, the ultrasonic vibration having a higher output than the initial stage of the bonding is applied while the surface pressure of the contact surface between the ball 13 and the bonding surface 14a is entirely reduced. Therefore, high stress acts on the bonding interface between the ball 13 and the electrode 14 by ultrasonic vibration having a large amplitude, as shown in FIG.
[0031]
As a result, the metal bonding surface limited to the periphery of the high surface pressure portion A in the initial stage of bonding is enlarged as a whole, and a more uniform metal bonding state is realized. During this time, since a high pressing load that causes plastic deformation is not applied to the ball 13, the crushing deformation of the ball 13 does not progress, and a bump shape defect due to excessive crushing of the ball 13 does not occur.
[0032]
Then, at a timing t4 when a predetermined overall bonding time T (for example, 35 to 55 msec.) Shown in FIG. 3 has elapsed, the application of the driving voltage and the pressing are stopped (ST6). Thereby, the ball 13 is in a state of being joined to the electrode 14 by the load and the ultrasonic vibration. Thereafter, the capillary 2a is raised to cut the bonding wire connected to the upper end of the ball 13, leaving the ball 13 bonded to the electrode 14 to form a bump. As a result, it is possible to form a good bump even on an electrode of a chip such as a SAW filter chip in which bump formation is relatively difficult.
[0033]
(Embodiment 2)
FIG. 5 is a block diagram showing a configuration of an electronic component bonding apparatus according to the second embodiment of the present invention, and FIG. 6 is a process explanatory view of a bump bonding operation by the electronic component bonding apparatus according to the second embodiment of the present invention.
[0034]
In the second embodiment, an object to be joined by ultrasonic bonding is a bump for external connection provided on an electronic component, and the bump is joined to an electrode of a substrate as an object to be joined (so-called flip-chip bonding). ) Is shown. In this bump bonding, an electronic component is pressed against a substrate by a contact tool provided on a horn having a vibrator, so that a bump is bonded to an electrode of the substrate by ultrasonic bonding.
[0035]
In FIG. 6, a substrate 21 on which an electrode 21a is formed is held on a substrate holding unit 20. Above the substrate holding section 20, a bonding section 23 is provided. The bonding unit 23 includes a tool lifting / lowering driving unit 24 having a motor and an encoder built therein. The tool lifting / lowering pressing driving unit 24 drives the bonding tool 26 held by the holder 25 up and down.
[0036]
The bonding tool 26 includes a bonding operation portion 26a (contact tool) protruding downward. The bonding operation portion 26a sucks and holds the electronic component 22 with the bump, and also attaches the electronic component 22 to the substrate 21. And press. The tool lifting / lowering drive unit 24 is a pressing unit that applies a pressing load to the object to be joined. At this time, an ultrasonic vibration is applied to the electronic component 22 by driving the vibrator 27 mounted on the bonding tool 26. Note that a pneumatic cylinder may be used as the pressing means.
[0037]
In FIG. 6, the control unit 31, the load control unit 32, the Z-axis driver 30, the amplifier 29, and the US driver 28 are the control unit 10, the load control unit 11, the Z-axis driver 8, the amplifier 7, and the US driver in the first embodiment. The storage unit 33 has the same function as that of the storage unit 12, and stores the same data as the storage unit 12 in the first embodiment.
[0038]
That is, the control unit 31 reads the voltage command value stored in the storage unit 33 and outputs this voltage command value to the US driver 28, so that the US driver 28 always has a constant drive voltage according to the voltage command value, that is, The alternating voltage having a constant voltage value is applied to the vibrator 27. Further, in the lifting / lowering operation of the bonding tool 26 by the tool lifting / lowering driving unit 24, the control unit 31 reads the load command value stored in the storage unit 33 and sends the load command value to the Z-axis driver 30 via the load control unit 32. Is output, the tool lifting / lowering drive unit 24 presses with a pressing load corresponding to the load command value.
[0039]
In the ultrasonic bonding process of the electronic component 22 by the bonding tool 26, first, the electronic component 22 provided with the bump 22a is held at the lower end of the joining action portion 26a of the bonding tool 26, as shown in FIG. Next, the bonding tool 26 is moved to align the bumps 22 a with the electrodes 21 a of the substrate 21.
[0040]
Next, the bonding tool 26 is lowered together with the electronic component 22 to bring the bump 22a into contact with the electrode 21a (ST2). Thereafter, a pressing step of pressing the electronic component 22 by the bonding tool 26 to press the bump 22a against the electrode 21a is started. In this pressing step, the same conditions as the bonding conditions shown in FIG. 3 of the first embodiment, that is, the control of switching the pressing load between high and low and the constant voltage control of the driving voltage of the vibrator 27 are applied.
[0041]
First, from the pressing start timing t1, as shown in FIG. 6B, the bump 22a is pressed with a first pressing load F1 necessary and sufficient to cause the bump 22a to be plastically deformed in the vertical direction (first pressing step). Then, at the timing t2 after the elapse of the predetermined time T1 required for the plastic deformation of the bump 22a from the start of pressing, the US driver 28 applies a constant drive voltage V to the vibrator 27 (ST4). As a result, a high-frequency alternating voltage of + V1 to -V1 is applied to the vibrator 27, and the vibrator 27 generates ultrasonic vibration. Then, the ultrasonic vibration is transmitted to the bump 22a via the horn 26 and the bonding action portion 26a, so that the lower surface of the bump 22a is in a direction perpendicular to the bonding surface of the electrode 21a, as shown in FIG. And the ultrasonic bonding is started.
[0042]
Thereafter, at timing t3 when the same initial bonding time T2 as in the first embodiment has elapsed from the start of the application of the driving voltage, as shown in FIG. 6D, the pressing load is set to the second pressing lower than the first pressing load F1. And the application of the alternating voltage of + V1 to -V1 is continued (second pressing step). Then, at a timing t4 when a predetermined overall bonding time T has elapsed, the application and the pressing of the driving voltage are stopped. Thereby, the bump 22a is joined to the electrode 21 by the load and the ultrasonic vibration. Thereafter, by raising the bonding tool 26, the bump 22a is joined to the electrode 21a, and the mounting of the electronic component 22 by ultrasonic bonding is completed.
[0043]
Also in the second embodiment described above, in the process of ultrasonic bonding the bump 22a to the electrode 21a, the pressing load is controlled to be high and low similarly to the first embodiment, and the driving voltage of the vibrator is controlled by a constant voltage. And good bonding results can be obtained.
[0044]
As described above, in the ultrasonic bonding method described in each of the embodiments, the first pressing step of pressing the object to be bonded with the first pressing load, and the first pressing step, after the first pressing step, the first pressing step. A bonding step is constituted by a second pressing step of pressing the object to be bonded with a low second pressing load, and a constant drive voltage is applied to the vibrator from the middle of the first pressing step to the end of bonding. ing.
[0045]
As a result, in the initial stage of bonding, the object to be bonded is appropriately crushed and the contact state with the bonding surface is made uniform, and in the high surface pressure region in the contact surface, the metal surfaces are pressed against each other and foreign matter such as an oxide film is formed. The layer is easily broken. Then, by applying a drive voltage to the vibrator in this state, the metal surfaces from which the foreign material layer has been removed are brought into contact with each other in the high surface pressure region to form a metal joint.
[0046]
At this time, since the ultrasonic output is maintained at a low level as described above, the formation of the metal bonding surface at the bonding interface is performed by ultrasonic vibration of small amplitude. Thus, at the bonding interface, the metal bonding surface gradually expands from the high surface pressure region as a starting point, and bonding can proceed in a stable state while making the contact surfaces conform to each other.
[0047]
By switching the pressing load to a low load in this state, the amplitude of the ultrasonic vibration at the bonding interface increases. As a result, in the subsequent later stages of bonding, a high amplitude is applied to the bonding interface with a large amplitude to promote efficient bonding, and to form a more uniform metal bonding surface over a wide range between the bonding target and the bonding surface. it can.
[0048]
In the above-described ultrasonic bonding method, proper control of ultrasonic output is realized only by the control of switching the pressing load between high and low and the constant voltage control of the driving voltage of the vibrator. For this reason, it is possible to realize bonding of high bonding quality with simple equipment without using a complicated control device using an impedance control network or the like that was conventionally required to apply a desired ultrasonic output. it can.
[0049]
【The invention's effect】
According to the present invention, the first pressing step of pressing the object to be joined with the first pressing load, and after the first pressing step, the object to be bonded is pressed with the second pressing load lower than the first pressing load. And applying a constant drive voltage to the vibrator from the middle of the first pressing step to the end of bonding, thereby reducing the ultrasonic output in the bonding step without performing complicated control. The output can be changed from high to high, and bonding can be performed with high bonding quality using simple equipment.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a wire bonding apparatus according to a first embodiment of the present invention; FIG. 2 is a flowchart of a bump forming method by wire bonding according to a first embodiment of the present invention; FIG. FIG. 4 is a graph showing ultrasonic bonding conditions in the method of forming a bump by wire bonding according to the first embodiment. FIG. 4 is an explanatory diagram of an ultrasonic bonding process in the method of forming a bump by wire bonding in the first embodiment of the present invention. FIG. 6 is a block diagram showing a configuration of an electronic component bonding apparatus according to a second embodiment of the present invention. FIG. 6 is an explanatory diagram of a process of a bump bonding operation by the electronic component bonding apparatus according to the second embodiment of the present invention.
1 Horn driving mechanism 2a Capillary 4, 27 Vibrator 9, 28 US driver 10, 31 Control unit 11, 32 Load control unit 13 Ball 14 Electrode 21 Substrate 21a Electrode 22 Electronic component 22a Bump 24 Tool lifting / lowering driving unit 26 Bonding tool 26a Joint action part

Claims (3)

接合対象物に押圧手段によって押圧荷重を作用させるとともに振動子によって超音波振動を作用させて被接合物に接合する超音波ボンディング方法であって、前記接合対象物を第１の押圧荷重で押圧する第１押圧工程と、第１押圧工程の後第１の押圧荷重よりも低い第２の押圧荷重で接合対象物を押圧する第２押圧工程とを含み、前記第１押圧工程の途中からボンディング終了に至るまで前記振動子に一定の駆動電圧を印加することを特徴とする超音波ボンディング方法。An ultrasonic bonding method in which a pressing load is applied to an object to be joined by a pressing means and ultrasonic vibration is applied by a vibrator to join the object to be joined, wherein the object to be joined is pressed with a first pressing load. A first pressing step; and a second pressing step of pressing the object to be joined with a second pressing load lower than the first pressing load after the first pressing step, and the bonding is completed in the middle of the first pressing step. An ultrasonic bonding method, wherein a constant drive voltage is applied to the vibrator until the step (a). 前記接合対象物がワイヤであり、前記振動子を有するホーンに設けられたキャピラリに挿通した前記ワイヤの端部を、電子部品の電極に超音波ボンディングにより接合することを特徴とする請求項１記載の超音波ボンディング方法。2. The object to be joined is a wire, and an end of the wire inserted into a capillary provided on a horn having the vibrator is joined to an electrode of an electronic component by ultrasonic bonding. Ultrasonic bonding method. 前記接合対象物が電子部品に形成された外部接続用のバンプであり、前記振動子を有するホーンに設けられた当接ツールによって前記電子部品を基板に押圧することにより、前記バンプを基板の電極に超音波ボンディングにより接合することを特徴とする請求項１記載の超音波ボンディング方法。The object to be joined is a bump for external connection formed on the electronic component, and the bump is pressed against the substrate by pressing the electronic component against the substrate with a contact tool provided on a horn having the vibrator. 2. The ultrasonic bonding method according to claim 1, wherein the bonding is performed by ultrasonic bonding.
JP2003031227A 2003-02-07 2003-02-07 Ultrasonic bonding method Pending JP2004241712A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8308049B2 (en) 2008-10-22 2012-11-13 Kabushiki Kaisha Toshiba Wire bonding method

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8308049B2 (en) 2008-10-22 2012-11-13 Kabushiki Kaisha Toshiba Wire bonding method

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