JP2004342715A - Method and apparatus for forming bump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make formable bumps of various shapes and microbumps, and make bump pitch very fine while enhancing productivity. <P>SOLUTION: The method of forming a bump comprises a step for ejecting a liquid drop of conductive paste toward a substrate from the ejection opening of a nozzle having inside diameter of 30 μm or less by charging the conductive paste produced by dispersing conductive fine particles becoming a bump material into liquid and applying an ejection voltage to the conductive paste in the nozzle 103, and a step for sintering the ejected liquid drop of conductive paste. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

で表される流域において駆動することが好ましい。
ただし、γ：液体の表面張力、ε０：真空の誘電率、ｒ：ノズル半径、ｈ：ノズル形状−基材間距離、ｋ：ノズル形状に依存する比例定数（１．５＜ｋ＜８．５）とする。
（５）上記各請求項の構成、上記（１）、（２）、（３）又は（４）の構成において、吐出電圧として印加する任意波形電圧が１０００［Ｖ］以下であることが好ましい。
（６）上記各請求項の構成、上記（１）、（２）、（３）、（４）又は（５）の構成において、吐出電圧として印加する任意波形電圧が５００［Ｖ］以下であることが好ましい。
（７）上記各請求項の構成、上記（１）〜（６）いずれかの構成において、ノズルの吐出口と基板との距離が５００［μｍ］以下とすることが、ノズル径を微細にした場合でも高い着弾精度を得ることができるので好ましい。
（８）上記各請求項の構成、上記（１）〜（７）いずれかの構成において、ノズル内の導電流体（導電ペースト）に圧力を印加するように構成することが好ましい。
（９）上記各請求項の構成、上記（１）〜（８）いずれかの構成において、単一パルスによって吐出する場合、
【数２】

により決まる時定数τ以上のパルス幅Δｔを印加する構成としても良い。ただし、ε：流体の誘電率、σ：導電率とする。
【００４３】
【発明の実施の形態】
以下、本発明の実施形態を図１から図８を参照して説明する。図１は本発明の実施形態たるバンプ形成装置１０の概略的な全体構成を示す構成図である。
【００４４】
（バンプ形成装置の全体構成）
バンプ形成装置１０は、下地電極（図示略）が設けられた基板Ｋを保持する基板保持手段２０と、この基板保持手段２０上の基板Ｋに向けて、バンプ材料となる導電性の微粒子を液体中に分散させてなる導電ペーストの液滴を吐出する液滴吐出手段としての吐出ヘッド１００と、基板保持手段２０上の基板に対する吐出ヘッド１００による吐出位置を位置決めする位置決め手段としてのＸ−Ｙステージ４０と、吐出された導電ペーストの液滴を焼結する焼結手段としてのレーザ出射手段５０とを備えている。
【００４５】
（基板保持手段及びＸ−Ｙステージ）
上記基板保持手段２０は、上部に水平となる基板Ｋの載置面を有する基板ステージ２１とこの基板ステージ２１上で基板Ｋの挟持と解放とを切替可能な挟持手段２２とを備えている。
かかる基板保持手段２０は、Ｘ−Ｙステージ４０の上部に設けられている。このＸ−Ｙステージ４０は、水平面上で互いに直交するＸ軸方向とＹ軸方向とに基板保持手段２０を移動位置決めすることが可能である。このＸ―Ｙステージ４０は、基板Ｋを吐出ヘッド１００に対する所定のバンプ形成作業開始位置に位置決めすると共に、バンプ形成作業時には吐出ヘッド１００から逐次吐出される導電ペーストの液滴が下地電極上の所定の位置に命中するように基板保持手段２０を介して基板Ｋの駆動を行う。
【００４６】
（レーザ出射手段）
レーザ出射手段５０は、レーザ光源とその光学系からなり、基板保持手段２０の上方において図示しない装置フレームに支持されると共に、基板保持手段２０の保持された基板Ｋの上面にレーザ光を照射する。そして、かかるレーザ光の照射により基板Ｋに吐出された導電ペーストの液滴は加熱され、焼結される。なお、かかるレーザ光の照射はバンプ形成作業時において連続的に照射し続けても良いし、導電ペーストの吐出時にのみ間欠的に行っても良い。
【００４７】
（導電ペースト）
導電ペーストについては、熱硬化性樹脂と有機溶剤とを含む液体中に微粒子を分散してなる導電ペーストを使用する。なお、微粒子としては、金，銀，銅，白金，パラジウム，タングステン，ニッケル，タンタル，ビスマス，鉛，インジウム，錫，亜鉛，チタン又はアルミニウムのいずれか一つからなる金属若しくはその酸化物又は各金属の内のいずれか二種以上からなる合金を含有するものが使用される。特に、「ナノペースト（ＮＰシリーズ）」（商標：ハリマ化成株式会社）を導電ペーストとして使用すると、より微細なバンプの形成に好適である。
また、導電ペーストに含まれる微粒子は１００［ｎｍ］以下とすることが望ましく、これにより、微細なバンプ形成を図ることができる。
【００４８】
（吐出ヘッド）
図２は、吐出ヘッド１００の使用時において底面となる面（基板Ｋとの対向面）を紙面手前側にして示すとともに吐出ヘッド１００を一部破断して示した分解斜視図である。図２に示すように、吐出ヘッド１００は、複数の液室１０１を内部に形成した液室構造体１０２と、液室構造体１０２の底部（使用時における底部）に取り付けられ，帯電可能な導電ペーストを液滴としてその先端部から吐出するための超微小径のノズル１０３をそれぞれの液室１０１に対応して具備したノズル板１０４と、を備える。なお、図２における符号Ｎは吐出ヘッド１００における液滴の吐出方向を示すものとし、当該吐出方向Ｎは図１における上下方向と一致するものとする。
【００４９】
液室構造体１０２について説明する。図３は、液室構造体１０２の一つの液室１０１について主に示した吐出方向Ｎの法面に沿った断面図である。図２に示すように、液室構造体１０２は、図２における下方に位置する液室側壁体１０５と、この液室側壁体１０５の図２における上方に位置するカバープレート１１０と一体的に接合して構成されている。
液室側壁体１０５には、一体的に突条に形成された複数の第一液室隔壁１０６，１０６，．．．が互いに平行となるように設けられている。それぞれの第一液室隔壁１０６には第二液室隔壁１０７が積み重なっており、第二液室隔壁１０７は接着剤層１０８を介して第一液室隔壁１０６に接着固定されている。これにより、液室側壁体１０５上においては、第一液室隔壁１０６及び第二液室隔壁１０７の一対からなる突条が複数互いに平行に配列していることによって複数の溝が形成されている。そして、カバープレート１１０が、液室側壁体１０５に対向するように且つ前記複数の溝を被覆するようにして、第二液室隔壁１０７，１０７，．．．上に接着剤層１０９を介して接着固定されている。これにより、両側の第一液室隔壁１０６及び第二液室隔壁１０７と、液室側壁体１０５と、カバープレート１１０とによって区画された液室１０１が複数形成される。この液室構造体１０２の底面においては、各液室１０１の底が開口しており、液室構造体１０２の底面に後述するノズル板１０４を接着固定することで各液室１０１を塞ぐ。ノズル板１０４には、各液室１０１に対応してノズル１０３が形成されている。
【００５０】
また、各液室１０１は、液室側壁体１０５の上端面１１１に近いところで浅くなっており、上端面１１１付近に浅溝１１８が形成されている。カバープレート１１０の上部には、液体導入口１１９、それに接続したマニホールド１２０が形成されている。そして、各液室１０１がカバープレート１１０で覆われることにより、各液室１０１の上端部がマニホールド１２０及び液体導入口１１９を介して導電ペーストを貯蔵したペースト供給源に接続される。この吐出ヘッド１００は各液室１０１への導電ペーストの供給圧力を付与する図示しない供給ポンプを具備しており、この供給ポンプによって付与された圧力によりペースト供給源から各液室１０１に導電ペーストが供給される。この供給ポンプは、後述するノズル１０３の先端部から導電ペーストがこぼれ出さない範囲の供給圧力を維持して導電ペーストの供給を行う。
【００５１】
液室隔壁１０６，１０７の壁面には電極１２１が設けられており、電極１２１上に絶縁層１２５が設けられている。液室側壁体１０５における液室１０１の形成面とは反対となる面に取り付けられた駆動基板１２２には、各液室１０１に対応した導電パターン１２３が形成され、その導電パターン１２３と電極１２１とはワイヤボンディング法によって導線１２４で接続されている。
【００５２】
ここで、液室側壁体１０５の液室隔壁１０６と液室隔壁１０７はいずれも圧電セラミックプレートで、強誘電性を有するチタン酸ジルコン酸鉛系（ＰＺＴ）の圧電セラミック材料で形成されており、積層方向でかつ互いに相反する方向（図３矢印参照）に分極されている。液室隔壁１０６，１０７は、電極１２１に電圧が印加されることで変形し、液室１０１の容積を縮小せしめて内部の導電ペーストに圧力を付与するが、液滴隔壁１０６，１０７単独での圧力では、後述するノズル１０３の先端部から液滴が吐出せずに、ノズル１０３の先端部から外部に突出した凸状メニスカスが形成されるだけである。つまり、これら各液室隔壁１０６，各液室隔壁１０７，各電極１２１，各導線１２４及び駆動基板１２２は、各ノズル１０３に設けられたノズル内流路１４５の導電ペーストがノズル１０３の先端部から凸状に盛り上がった状態を形成する凸状メニスカス形成手段の構成に含まれることになる。
【００５３】
次に、ノズル板１０４について説明する。図４は、ノズル板１０４の底面図（図１における下方から見た図）であり、図５は、ノズル板１０４を切断線Ａ−Ａ’で破断して示した断面図である。ノズル板１０４は、ベースとなる電気絶縁性の基板１４１と、基板１４１の表面１４１ａに形成された複数の吐出電極１４２，１４２，．．．と、複数の吐出電極１４２，１４２，．．．を挟んで基板１４１の表面１４１ａ一面に積層されたノズル層１４３と、を備える。
【００５４】
基板１４１の裏面１４１ｂは、上記の液室構造体１０２の底面に接着剤等を介して固着している。また、基板１４１には複数の貫通孔１４１ｃ，１４１ｃ，．．．が形成されており、これら貫通孔１４１ｃ，１４１ｃ，．．．はそれぞれ液室１０１に対応するように配列されており、それぞれの液室１０１に連通している。つまり、貫通孔１４１ｃは、液室１０１の下部を構成している。
【００５５】
吐出電極１４２，１４２，．．．は、それぞれの貫通孔１４１ｃに対応するように形成されている。各吐出電極１４２は対応する貫通孔１４１ｃを塞ぐようにして基板１４１の表面１４１ａに形成されており、底面視した場合に各吐出電極１４２が対応する貫通孔１４１ｃに重なっている。つまり、各吐出電極１４２は、対応する液室１０１に面しており、対応する液室１０１の底面を構成している。
吐出電極１４２には、貫通孔１４１ｃに重なった部分において貫通穴１４２ａが形成されており、この貫通穴１４２ａは対応した液室１０１に連通している。また、それぞれの吐出電極１４２には一体的に形成された配線１４４が接続されており、それぞれの配線１４４は後述するバイアス電源３０に接続されている。図面においては、底面視した場合に吐出電極１４２がリング状を呈しており、配線１４４が方状を呈しているが、本発明はこのような形状に限定されるわけではない。
【００５６】
ノズル層１４３には複数のノズル１０３，１０３，．．．が一体的に形成されており、複数のノズル１０３，１０３，．．．が一列になって並んでいる。かかる一列に並んだ各ノズル１０３は、基板Ｋに設けられる下地電極の配設ピッチの一般的な規格値と等しい間隔で設けられており、これにより、複数の下地電極に対して同時にバンプ形成を行うことを可能としている。なお、各ノズル１０３の間隔は、種々の各基板の下地電極の配設ピッチに等しく設定しても良いことはいうまでもない。
【００５７】
さらに、各ノズル１０３は、基板１４１に対して略直角に立設するように（垂下するように）形成されている。これらノズル１０３，１０３，．．．はそれぞれ液室１０１に対応するように配列されており、底面視した場合に各ノズル１０３のノズル孔１０３ａが対応する貫通孔１４１ｃに重なっている。
【００５８】
各ノズル１０３にはその先端部からその中心線に沿って貫通するノズル内流路１４５が形成されており、ノズル内流路１４５の末端となるノズル孔１０３ａが各ノズル１０３の先端部に形成されている。ノズル内流路１４５は、吐出電極１４２の貫通穴１４２ａを通じて対応する液室１０１に連通しており、吐出電極１４２がノズル内流路１４５に面している。
各液室１０１に供給された導電ペーストは、貫通孔１４１ｃ及びノズル内流路１４５内にも供給され、各液室１０１及び各ノズル内流路１４５内において吐出電極１４２に直接接触する。なお、図面においては、複数のノズル１０３，１０３，．．．が一列になって並んでいるが、二列以上になって並んでいても良いし、マトリクス状に並んでいても良いが、基板Ｋの各下地電極の配置に一致することが望ましい。
【００５９】
これらノズル１０３，１０３，．．．を含めてノズル層１４３は電気絶縁性を有しており、ノズル内流路１４５の内面も電気絶縁性を有している。また、これらノズル１０３，１０３，．．．を含めてノズル層１４３が撥水性を有するか（例えば、ノズル層１４３がフッ素を含有した樹脂で形成されている。）、ノズル１０３，１０３，．．．の表層に撥水性を有する撥水膜が形成されていることが好ましい（例えば、ノズル１０３，１０３、．．．の表面に金属膜が形成され、更にその金属膜上にその金属と撥水性樹脂との共析メッキによる撥水層が形成されている。）。ここで撥水性とは、ノズル１０３で吐出する導電ペーストに対してはじく性質である。
【００６０】
それぞれのノズル１０３についてさらに詳説する。ノズル１０３は、前述の通り、超微小径で形成されている。ノズル１０３の形状は、先端部に向かうにつれて径が細くなるように先端部で尖鋭に形成されており、限りなく円錐形に近い円錐台形に形成されている。具体的な各部の寸法の一例を挙げると、ノズル内流路１４５の内部直径は１［μｍ］、ノズル１０３の先端部における外部直径は２［μｍ］、ノズル１０３の根元の直径は５［μｍ］、ノズル１０３の高さは１００［μｍ］に設定されている。
なお、ノズル１０３の各寸法は、上記一例に限定されるものではない。特にノズル内径については、後述する電界集中の効果により液滴の吐出を可能とする吐出電圧が１０００［Ｖ］未満を実現する範囲であって、例えば、ノズル直径３０［μｍ］以下であり、より望ましくは、直径２０［μｍ］以下であって、現行のノズル形成技術により導電ペーストを通す貫通穴を形成することが実現可能な範囲である直径をその下限値とする。また、これらノズル１０３，１０３，．．．の形状は互いに同じであることが望ましいが、異なる形状であっても良い。
【００６１】
次に、ノズル板１０４を駆動するための回路構成について説明する。この吐出ヘッド１００は、上記吐出電極１４２，１４２，．．．に個別に吐出電圧を印加する吐出電圧印加手段２５（便宜上図４に図示）と、上記ノズル１０３，１０３，．．．に対向する対向面２３ａと共にその対向面２３ａで液滴の着弾を受ける基板Ｋを支持する基板ステージ２１内に設けられる対向電極２３（図５に図示）と、を備える。
【００６２】
吐出電圧印加手段２５は、吐出電極１４２に直流のバイアス電圧を印加するバイアス電源３０と、バイアス電圧に重畳して吐出に要する電位とするパルス電圧を吐出電極１４２に印加する吐出電源２９と、をそれぞれの吐出電極１４２に対応して備えている。バイアス電源３０及び吐出電源２９は全ての吐出電極１４２，１４２，．．．に共通であっても良いが、この場合には吐出電源２９はこれら吐出電極１４２，１４２，．．．個別にパルス電圧を印加する。
【００６３】
バイアス電源３０によるバイアス電圧は、導電ペーストの吐出が行われない範囲で常時電圧印加を行うことにより、吐出時に印加すべき電圧の幅を予め低減し、これによる吐出時の反応性の向上を図っている。
【００６４】
吐出電圧電源２９は、導電ペーストの吐出を行う時にのみパルス電圧をバイアス電圧に重畳させて吐出電極１４２，１４２，．．．個別に印加する。このときの重畳電圧Ｖは次式の条件を満たすようにパルス電圧の値が設定されている。
【数１】

但し、γ：導電ペーストの表面張力、ε０：真空の誘電率、ｒ：ノズル半径、ｋ：ノズル形状に依存する比例定数（１．５＜ｋ＜８．５）とする。
一例を挙げると、バイアス電圧はＤＣ３００［Ｖ］で印加され、パルス電圧は１００［Ｖ］で印される。従って、吐出の際の重畳電圧は４００［Ｖ］となる。
【００６５】
対向電極２３は、ノズル１０３，１０３，．．．に垂直な対向面２３ａを備えており、かかる対向面２３ａは基板ステージ２１の載置面上に配置され、基板Ｋを載置する。ノズル１０３，１０３，．．．の先端部から対向電極２３の対向面２３ａまでの距離は、一例としては１００［μｍ］に設定される。
また、この対向電極２３は接地されているため、常時，接地電位を維持している。従って、パルス電圧の印加時にはそれぞれのノズル１０３の先端部と対向面２３ａとの間に生じる電界による静電力により吐出された液滴を対向電極２３側に誘導する。
【００６６】
なお、吐出ヘッド１００は、ノズル１０３，１０３，．．．の超微小化によるそれぞれのノズル１０３，１０３，．．．先端部での電界集中により電界強度を高めることで液滴の吐出を行うことから、対向電極２３による誘導がなくとも液滴の吐出を行うことは可能ではあるが、ノズル１０３，１０３，．．．と対向電極２３との間での静電力による誘導が行われた方が望ましい。また、帯電した液滴の電荷を対向電極２３の接地により逃がすことも可能である。
【００６７】
（実施形態の動作説明）
図１及び図６に基づいて上記バンプ形成装置１０の動作説明を行う。図６はバンプ形成の途中過程を示す動作説明図であり、図中の二点鎖線は形成しようとしているバンプＢの形状を示している。
バンプＢの形成作業においては、まず、基板Ｋが基板保持手段２０に装着されると、吐出ヘッド１００の複数のノズル部３７がそれぞれ個別に基板Ｋの各下地電極に向けて吐出が行われるようにＸ−Ｙステージ４０により基板Ｋがその初期位置に位置決めされる。
【００６８】
そして、基板Ｋにレーザ出射手段５０によるレーザ光の照射が行われた状態で（焼結工程）、各ノズル部３７から導電ペーストの液滴が吐出される（吐出工程）。吐出された液滴は基板Ｋの下地電極に命中すると同時にレーザ光に照射され、加熱により焼結される。このとき、導電ペーストの液滴中に含まれる液状状態を維持する有機溶媒が蒸発し、熱硬化樹脂が硬化を生じると共に金属粒子が焼結することで命中位置に固着する。
【００６９】
この導電ペーストの液滴はその滴径がバンプＢよりも充分小さく、繰り返し吐出が行われることで積み上げられるようにしてバンプ形成が行われる。即ち、図６に示すように、液滴一つ分の高さで一つの層が形成されると、その上にまた新たな層を積み上げるように形成し、これを繰り返すことで所定の形状のバンプＢを形成する。
【００７０】
上記吐出工程における吐出ヘッド１００の吐出動作を捕捉して詳細に説明する。図７は導電ペーストの吐出動作と導電ペーストに印加される電圧との関係を示す説明図であって、図７（Ａ）は吐出を行わない状態であり、図７（Ｂ）は吐出状態を示す。
供給ポンプによって液体導入口１１９及びマニホールド１２０を介してそれぞれのノズル１０３のノズル内流路１４５には帯電可能な導電ペーストが供給された状態にあり、かかる状態でそれぞれのバイアス電源３０によりそれぞれの吐出電極１４２を介してバイアス電圧が導電ペーストに印加されている。かかる状態で、導電ペーストは帯電すると共に、それぞれのノズル１０３の先端部において導電ペーストによる凹状に窪んだメニスカスが形成される（図７（Ａ））。
【００７１】
そして、ノズル１０３，１０３，．．．のうち液滴を吐出するノズル１０３については、吐出電圧電源２９によりパルス電圧が吐出電極１４２を介して導電ペーストに印加されるとともに、このパルス電圧に同期して電極１２１にもパルス電圧が印加される。電極１２１にパルス電圧が印加されると、液室隔壁１０６，１０７が膨張して液室１０１の容積が減少することなり、これにより液室１０１内の導電ペーストの圧力が増加する。従って、ノズル１０３の先端部において外部に突出した凸状のメニスカスが形成される。更に、電極１２１にパルス電圧が印加されるのとほぼ同時に吐出電極１４２にもパルス電圧が印加されるから、外部に突出した凸状メニスカスの頂点により電界が集中し、ついには導電ペーストの表面張力に抗して微小液滴が対向電極側に吐出される（図７（Ｂ））。
【００７２】
そして、吐出電極１４２に印加されるパルス電圧が終了すると共に、電極１２１に印加されるパルス電圧が終了すると、液室１０１の容積が増大することでノズル１０３の先端部において導電ペーストが凹状に窪んだメニスカスが形成されるとともに、液体導入口１１９及びマニホールド１２０を介して導電ペーストを吐出したノズル１０３のノズル内流路１４５に導電ペーストが供給される。
【００７３】
このように、微小ノズル径の液滴吐出手段に、ノズル内で吐出電圧を印加することにより、低電圧で微小な導電ペーストの液滴を吐出することができるので、微細なバンプも形成することが可能である。
【００７４】
なお、上記説明では電極１２１にパルス電圧が印加されることで液室隔壁１０６，１０７が膨張して液室１０１の容積が増大したが、逆に電極１２１にパルス電圧が印加されることで液室隔壁１０６，１０７が収縮して液室１０１の容積が減少するように動作しても良い。但しこの場合には、吐出の際において吐出電極１４２にパルス電圧が印加されている時には電極１２１にパルス電圧が印加されておらず、吐出しない際において吐出電極１４２にバイアス電圧が印加されている時には電極１２１にパルス電圧が印加される。
【００７５】
上述のように、バンプ形成装置１０は、導電ペーストの液滴を吐出する工程とこれを焼結する工程とでバンプ形成を行うことから、各工程の作業自体は単純であり、フォトレジストやマスク等の前準備を不要とし、作業の容易化及び迅速化を図ると共にこれによる生産性の向上を図ることが可能である。また、バンプ形成作業にフォトレジスト等の薬剤を不要とし、作業後の廃棄物の発生を低減することから周囲の環境に及ぼす影響を十分に低減することが可能である。
また、バンプ形成装置１０では、導電ペーストの液滴を吐出すると共にこれを焼結することで複数の層を積み上げるようにバンプの形成を行うことができるので、各層ごとの形状に変化を設けることで、例えば、図８（Ａ）〜（Ｃ）に示すような種々の形状のバンプＢを形成することが可能となる。
【００７６】
（その他）
なお、吐出口の内径が、形成するバンプのサイズの１／３以下であることが、平坦や突起付き等の任意の微細で正確な形状のバンプを形成する上では好ましい。特に形成するバンプの容積の１／１０以下の体積の液滴を複数回吐出し、液滴を積み重ねることが好ましい。また、形成するバンプのサイズが５０［μｍ］以下であるときに、特に、形成するバンプのサイズの１／３以下とし、液滴の体積をバンプの体積の１／１０とすることが好ましい。
【００７７】
例えば、バンプが１５［μｍ］×１５［μｍ］の正方形（バンプのサイズが２１［μｍ］）、高さ４［μｍ］の上面は平坦型のバンプを形成する場合、吐出口の内径が２［μｍ］のノズルにより、１液滴分量（液滴の体積）を４×１０^−１８［ｍ^３］（４フェムトリットル）とし、液滴を直径２［μｍ］の球形の液滴と考えると、分散液の揮発分を考慮すると、およそ２５０滴の液滴を吐出することにより、バンプを形成することができる。
また、上記と同じ大きさのバンプを形成するために、始めは吐出口の内径が４［μｍ］のノズルで３×３×２＝１８滴（１滴＝３３フェムトリットル）積み重ねた後（約６００フェムトリットル分）、吐出口の内径が２［μｍ］のノズルで形を整えるように残りの３００フェムトリットル分を積み上げる（分散液の揮発分を考慮して、約１００滴程度）ことにより、１１８液滴で形成可能なため、微細で正確な形状のバンプを形成することが可能である。
【００７８】
なお、焼結手段は、上述したレーザ光出射手段に限られず、電子ビームや赤外線を照射することで加熱を行う構成としても良い。レーザ光出射手段、電子ビームや赤外線を照射する手段を用いて焼結させることにより、局所的に加熱可能のため、熱に弱い部分を備えた基板にバンプを形成する場合でも部品を傷めることを抑制することが可能であり、又は基板の熱による変形も抑制可能である。また、基板を裏面側から加熱するヒートステージを設ける構成としても良い。また、各種の光照射手段とヒートステージとを併用しても良い。
【００７９】
また、レーザ出射手段５０のレーザ光の照射位置については、基板Ｋの上面を照射する場合に限定されるものではなく、吐出された液滴がレーザ光に照射されればいずれに照射しても良い。例えば、図９に示すように、吐出液滴が通過する途中の領域を照射するようにその向きを設定しても良い。
また、焼結を行うタイミングとしては、液滴が基板Ｋ側に着弾してから行っても良いし、予め基板Ｋを加熱した状態で吐出を行い焼結させても良い。
【００８０】
また、位置決め手段は基板Ｋを移動させるＸ−Ｙステージに限らず、吐出ヘッド２０を移動位置決めする手段を用いても良い。また、基板を一定の直線に沿った方向についてのみ移動位置決めする手段と、吐出ヘッドをこれと交差する他の直線方向に沿って移動位置決めする手段とから構成しても良い。
【００８１】
また、バンプの形成にあっては、予め基板Ｋの下地電極形成面にフォトレジスト層を設けると共に下地電極位置のみ除去することでバンプ形成の為の除去部を設けるフォトレジスト層形成工程を設けても良い。かかる工程の後にフォトレジスト層の除去部に導電ペーストの液滴を充填を行うことにより、バンプＢの形状を有り安定して形成し得る。
【００８２】
また、上記実施形態では、基板Ｋを水平面内（Ｘ軸方向とＹ軸方向）について位置決めを行っているが、さらに上下方向についても位置決め調節可能としても良い。なお、吐出ヘッド１００について上下方向に位置決めを行っても良い。
【００８３】
また、吐出ヘッド１００にあっては、ノズル１０３にエレクトロウェッティング効果を得るために、ノズル１０３の外周に電極（例えば上述した撥水膜下に形成された金属膜である。）を設けるか、また或いは、ノズル内流路１４５の内面に電極を設け、その上から絶縁膜で被覆しても良い。そして、この電極に電圧を印加することで、吐出電極１４２により電圧が印加されている導電ペーストに対して、エレクトロウェッティング効果によりノズル内流路１４５の内面のぬれ性を高めることができ、ノズル内流路１４５への導電ペーストの供給を円滑に行うことができ、良好に吐出を行うと共に、吐出の応答性の向上を図ることが可能となる。
【００８４】
（好ましいノズルの吐出口の内径の捕捉説明）
上記実施形態で説明する吐出ヘッド１００に備わった各ノズルのノズルの吐出口の内径（内部直径）は、３０［μｍ］以下であることが好ましく、さらに好ましくは２０［μｍ］未満、さらに好ましくは８［μｍ］以下、さらに好ましくは４［μｍ］以下とすることが好ましい。また、ノズルの吐出口の内径は、０．２［μｍ］より大きくすることにより、液滴の飛翔安定性を向上させることができる。
【００８５】
ノズルの吐出口の内径がφ２０［μｍ］未満とすることにより電界強度分布を狭くできるので、ノズルと対向電極の距離の自由度を増すことができる。
ノズルの吐出口の内径がφ８［μｍ］以下であれば、対向電極の位置精度及び基板Ｋ（特に、下地電極）の材料特性のバラ付きや厚さのバラツキの影響を受けずに安定した吐出が可能となる。
【００８６】
さらに、ノズルの吐出口の内径がφ４［μｍ］以下になると、導電ペーストの初期吐出速度を大きくすることができるので、液滴の飛翔安定性が増すと共に、メニスカス部での電荷の移動速度が増すために吐出応答性が向上する。
【００８７】
また、ノズルの吐出口の内径がφ４［μｍ］以下の範囲において、液滴の吐出効率を向上させることができ、該範囲において安定した吐出が行える。
【００８８】
［液体吐出装置の理論説明］
本発明では、静電吸引型流体ジェット方式において果たすノズルの役割を再考察し、
【数３】

即ち、
【数４】

或いは
【数５】

という従来吐出不可能として試みられていなかった領域において、マクスウェル力などを利用することで、微細液滴を形成することができる。
【００８９】
このような駆動電圧低下および微少量吐出実現の方策のための吐出条件等を近似的に表す式を導出したので以下に述べる。
以下の説明は、上記各本発明の実施形態で説明した吐出ヘッド１００に適用可能である。
いま、半径ｒのノズルに流体を注入し、基板Ｋとしての無限平板導体からｈの高さに垂直に位置させたと仮定する。この様子を図１０に示す。このとき、ノズル先端部に誘起される電荷は、ノズル先端の半球部に集中すると仮定し、以下の式で近似的に表される。
【数６】

ここで、Ｑ：ノズル先端部に誘起される電荷、ε_０：真空の誘電率、ε：基板の誘電率、ｈ：ノズル−基板間距離、ｒ：ノズル内径の半径、Ｖ：ノズルに印加する電圧である。α：ノズル形状などに依存する比例定数で、１〜１．５程度の値を取り、特にｒ＜＜ｈのときほぼ１程度となる。
【００９０】
また、基材としての基板が導体基板の場合、基板内の対称位置に反対の符号を持つ鏡像電荷Ｑ’が誘導されると考えられる。基板が絶縁体の場合は、誘電率によって定まる対称位置に同様に反対符号の映像電荷Ｑ’が誘導される。
ところで、ノズル先端部に於ける電界強度Ｅｌｏｃ．は、先端部の曲率半径をＲと仮定すると、
【数７】

で与えられる。ここでｋ：比例定数で、ノズル形状などにより異なるが、１．５〜８．５程度の値をとり、多くの場合５程度と考えられる。（Ｐ． Ｊ． Ｂｉｒｄｓｅｙｅ ａｎｄ Ｄ．Ａ．Ｓｍｉｔｈ， Ｓｕｒｆａｃｅ Ｓｃｉｅｎｃｅ， ２３ （１９７０） １９８−２１０）。
【００９１】
今簡単のため、ｒ＝Ｒとする。これは、ノズル先端部に表面張力で流体（導電ペースト）がノズルの吐出口の内径ｒと同じ半径を持つ半球形状に盛り上がっている状態に相当する。
ノズル先端の液体に働く圧力のバランスを考える。まず、静電的な圧力は、ノズル先端部の液面積をＳとすると、
【数８】

（６）、（７）、（８）式よりα＝１とおいて、
【数９】

と表される。
【００９２】
一方、ノズル先端部に於ける液体（導電ペースト）の表面張力をＰｓとすると、
【数１０】

ここで、γ：表面張力、である。
静電的な力により流体の吐出が起こる条件は、静電的な力が表面張力を上回る条件なので、
【数１１】

となる。十分に小さいノズルの吐出口の内径ｒをもちいることで、静電的な圧力が、表面張力を上回らせる事が可能である。
この関係式より、Ｖとｒの関係を求めると、
【数１２】

が吐出の最低電圧を与える。すなわち、式（５）および式（１２）より、
【数１３】

が、本発明の動作電圧となる。
【００９３】
ある半径ｒのノズルに対し、吐出限界電圧Ｖｃの依存性を前述した図１１に示す。この図より、微細ノズルによる電界の集中効果を考慮すると、吐出開始電圧は、ノズルの吐出口の内径の減少に伴い低下する事が明らかになった。
従来の電界に対する考え方、すなわちノズルに印加する電圧と対向電極間の距離によって定義される電界のみを考慮した場合では、微小ノズルになるに従い、吐出に必要な電圧は増加する。一方、局所電界強度に注目すれば、微細ノズル化により吐出電圧の低下が可能となる。
【００９４】
静電吸引による吐出は、ノズル端部における流体（導電ペースト）の帯電が基本である。帯電の速度は誘電緩和によって決まる時定数程度と考えられる。
【数１４】

ここで、ε：流体の比誘電率、σ：流体の導電率である。流体の比誘電率を１０、導電率を１０^−６ Ｓ／ｍ を仮定すると、τ＝１．８５４×１０^−５ｓｅｃとなる。あるいは、臨界周波数をｆｃとすると、
【数１５】

となる。このｆｃよりも早い周波数の電界の変化に対しては、応答できず吐出は不可能になると考えられる。上記の例について見積もると、周波数としては１０ ｋＨｚ程度となる。このとき、ノズル半径２μｍ、電圧５００Ｖ弱の場合、Ｇは１０−１３ｍ３／ｓと見積もることができるが、上記の例の液体の場合、１０ｋＨｚでの吐出が可能なので、１周期での最小吐出量は１０ｆｌ（フェムトリットル、１ｆｌ：１０−１５ ｌ）程度を達成できる。
【００９５】
なお、各上記本実施の形態においては、図１０に示したようにノズル先端部に於ける電界の集中効果と、対向基板に誘起される鏡像力の作用を特徴とする。このため、先行技術のように基板または基板支持体を導電性にしたり、これら基板または基板支持体に電圧を印加する必要はない。すなわち、基板として絶縁性のガラス基板、ポリイミドなどのプラスチック基板、セラミックス基板、半導体基板などを用いることが可能である。
また、上記各実施形態において電極への印加電圧はプラス、マイナスのどちらでも良い。
さらに、ノズルと基板Ｋとの距離は、５００［μｍ］以下に保つことにより、流体の吐出を容易にすることができる。また、図示しないが、ノズル位置検出によるフィードバック制御を行い、ノズルを基板Ｋに対し一定に保つようにする。
また、基板Ｋを、導電性または絶縁性の基板Ｋホルダーに裁置して保持するようにしても良い。
【００９６】
図１２は、前述したの吐出ヘッド１００の他の基本例の一例としての液体吐出装置の側面断面図を示したものである。ノズル１の側面部には電極１５が設けられており、ノズル内流体３との間に制御された電圧が引加される。この電極１５の目的は、Ｅｌｅｃｔｒｏｗｅｔｔｉｎｇ 効果を制御するための電極である。十分な電場がノズルを構成する絶縁体にかかる場合この電極がなくともＥｌｅｃｔｒｏｗｅｔｔｉｎｇ効果は起こると期待される。しかし、本基本例では、より積極的にこの電極を用いて制御することで、吐出制御の役割も果たすようにしたものである。ノズル１を絶縁体で構成し、その厚さが１μｍ、ノズル内径が２μｍ、印加電圧が３００Ｖの場合、約３０気圧のＥｌｅｃｔｒｏｗｅｔｔｉｎｇ効果になる。この圧力は、吐出のためには、不十分であるが流体のノズル先端部への供給の点からは意味があり、この制御電極により吐出の制御が可能と考えられる。
【００９７】
前述した図１１は、本発明における吐出開始電圧のノズルの吐出口の内径依存性を示したものである。液体吐出装置として、図２に示した吐出ヘッド１００に示すものを用いた。微細ノズルになるに従い吐出開始電圧が低下し、従来より低電圧で吐出可能なことが明らかになった。
上記各実施形態において、流体吐出の条件は、ノズル基板間距離（Ｌ）、印加電圧の振幅（Ｖ）、印加電圧振動数（ｆ）のそれぞれの関数になり、それぞれにある一定の条件を満たすことが吐出条件として必要になる。逆にどれか一つの条件を満たさない場合他のパラメーターを変更する必要がある。
【００９８】
この様子を図１２を用いて説明する。
まず吐出のためには、それ以上の電界でないと吐出しないというある一定の臨界電界Ｅｃが存在する。この臨界電界は、ノズルの吐出口の内径、流体の表面張力、粘性などによって変わってくる値で、Ｅｃ以下での吐出は困難である。臨界電界Ｅｃ以上すなわち吐出可能電界強度において、ノズル基板間距離（Ｌ）と印加電圧の振幅（Ｖ）の間には、おおむね比例の関係が生じ、ノズル間距離を縮めた場合、臨界印加電圧Ｖを小さくする事が出来る。
逆に、ノズル基板間距離Ｌを極端に離し、印加電圧Ｖを大きくした場合、仮に同じ電界強度を保ったとしても、コロナ放電による作用などによって、流体液滴の破裂すなわちバーストが生じてしまう。そのため良好な吐出特性を得るためには、ノズル基板間距離は１００μｍ程度以下に抑えることが吐出特性並びに、着弾精度の両面から望ましい。
【００９９】
【発明の効果】
本発明は、導電ペースト液滴を液滴吐出手段により吐出し、焼結することでバンプ形成が行われるので、バンプ形成を容易且つ迅速に行うことができ、その生産性の向上を図ることが可能となる。また、パターニングされたマスクを不要とできるので、少量生産下でもコストを低減することできる。さらに、液滴吐出手段と基板との相対的に位置関係を調節することで種々の形状のバンプ形成を容易に行うことが可能となる。さらに、液滴の積み上げ作業によりバンプ形成を行えば、種々の形状のバンプ形成が可能となる。
【０１００】
また、本発明は、ノズルの吐出口を３０［μｍ］以下とすることでノズル先端部に電界を集中させて電界強度を高めると共にその際に誘導される基板側の鏡像電荷或いは映像電荷までの間に生じる電界の静電力により液滴の飛翔を行っている。このため、従来の静電吸引方式の原理では吐出電圧が過度に高電位となるためにその採用が困難とされていた吐出口３０［μｍ］以下のノズルでの液滴の吐出が低電位で行うことが可能となり、これにより微細な液滴を吐出することが可能となった。これにより、より微細なバンプ形成が可能となると共に、バンプの微細化に伴うバンプピッチの縮小化も可能となった。
【０１０１】
また、ノズルの吐出口を形成するバンプサイズの１／３以下とするか、吐出する液滴をバンプ体積の１／１０以下とするか、又は、形成するバンプサイズを７０［μｍ］以下とすることにより、平坦や突起付き等の任意の微細で正確な形状のバンプを形成することが可能となる。
【図面の簡単な説明】
【図１】本発明の実施形態たるバンプ形成装置の概略的な全体構成を示す構成図である。
【図２】吐出ヘッドの底面を紙面手前側にして示すとともに吐出ヘッドを一部破断して示した分解斜視図である。
【図３】液室構造体の一つの液室について主に示した吐出方向の法面に沿った断面図である。
【図４】図２に示された吐出ヘッドを示した底面図である。
【図５】図４に示された切断線Ａ−Ａ’で破断して示した断面図である。
【図６】バンプ形成の途中過程を示す動作説明図である。
【図７】導電ペーストの吐出動作と導電ペーストに印加される電圧との関係を示す説明図であって、図７（Ａ）は吐出を行わない状態であり、図７（Ｂ）は吐出状態を示す。
【図８】図８（Ａ）〜（Ｃ）は種々の形状のバンプを例を示す説明図である。
【図９】レーザ出射手段の照射位置の他の例を示す説明図である。
【図１０】吐出ヘッドの基本例として、ノズルの電界強度の計算を説明するために示したものである。
【図１１】ノズルのノズル径とメニスカス部で吐出する液滴が飛翔を開始する吐出開始電圧、該初期吐出液滴のレイリー限界での電圧値及び吐出開始電圧とレイリー限界電圧値の比との関係を示す線図である。
【図１２】吐出ヘッドの他の基本例としての液体吐出機構の側面断面図を示したものである。
【図１３】吐出ヘッドにおける距離−電圧の関係による吐出条件を説明した図である。
【符号の説明】
１０ バンプ形成装置
２０ 基板保持手段
３０ 吐出ヘッド（液滴吐出手段）
４０ Ｘ−Ｙステージ（位置決め手段）
５０ レーザ出射手段（焼結手段）
１０３ ノズル
Ｂ バンプ
Ｋ 基板[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a bump forming method and a bump forming apparatus for forming a bump on a substrate of a semiconductor element such as a diode or an IC (integrated circuit device) or an electrode surface of a printed circuit board.
[0002]
[Prior art]
As a method of forming a bump, a method of using a photoresist film on a base electrode forming surface side of a substrate is known (for example, see Patent Document 1). In such a bump forming method, a photoresist film is formed on a substrate, holes are formed at base electrode positions, a conductive paste is filled therein with a dispenser, a spinner is rotated at a high speed, and the paste on the photoresist film is removed. By shaking off the paste, only the holes are filled with the paste to remain, and prebaked. Further, bumps are formed on the substrate by sintering the conductive paste after removing the photoresist film.
[0003]
As another bump forming method, a method using screen printing is known (for example, see Patent Document 2). In such a bump forming method, a mask on which a bump forming pattern is formed is positioned on a base electrode forming surface side of a substrate, a conductive paste is printed through the mask, and after the mask is removed, sintering is performed to form a bump on the base electrode. The formation of.
[0004]
[Patent Document 1]
JP-A-9-64047 (FIG. 1-5)
[0005]
[Patent Document 2]
JP-A-6-204229 (FIG. 1)
[0006]
[Problems to be solved by the invention]
However, in the case of the conventional example described in Patent Literature 1, since the paste is applied to the photoresist film other than the holes due to the use of the dispenser, it is troublesome to remove the paste other than the holes by using a spinner. There was a problem that it took.
[0007]
Further, in the case of the conventional example described in Patent Document 2, since a patterned mask is required for forming the bumps, the shape of the bumps is restricted in advance, and it is not easy to respond to changes and improvements. There was an inconvenience. Further, since a mask is required, there is also a problem that the cost is increased in the small-scale production.
[0008]
Also, with the recent increase in the density of semiconductor elements, the underlying electrodes on the substrate have been miniaturized and densified. In order to cope with this, it has been necessary to miniaturize the bumps and increase the density. With the bump formation technology described in each patent document, it has been difficult to achieve further miniaturization and higher density.
[0009]
An object of the present invention is to improve productivity by speeding up pump formation. Still another object of the present invention is to easily form bumps of various shapes. Still another object is to reduce costs in the case of small-scale production.
Another object of the present invention is to further reduce the size and density of bumps.
[0010]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided a nozzle having a discharge port having an inner diameter of 30 [μm] or less, a conductive paste formed by dispersing conductive fine particles serving as a bump material in a liquid, and a discharge voltage in the nozzle. And a sintering step of sintering the ejected conductive paste droplets to remove the liquid component. , Is adopted. The inner diameter of the discharge port of the nozzle refers to the internal diameter of the discharge port of the nozzle (the same applies hereinafter).
[0011]
In the above configuration, in the discharging step, the bumps are formed by sequentially discharging droplets of the conductive paste on the substrate and stacking a plurality of droplets according to a predetermined shape.
In the above configuration, in the discharging step, droplets of the conductive paste are discharged onto the substrate, and further, sintering is performed in the sintering step to form bumps. The sintering in the sintering step may be performed after the bumps are stacked according to the overall shape, or may be performed each time a single discharge is performed. Further, the sintering of the droplets may be performed immediately after the discharge and before hitting the substrate, or may be performed on the substrate. Sintering may be performed intermittently or continuously.
The “substrate” includes a substrate of a semiconductor element such as a diode and an IC, and a printed circuit board. In addition, “on the substrate” may be on the substrate, and includes on a base electrode provided on the substrate. Except where specifically described, the same applies to the entire description of the present specification (including inventions described in other claims).
[0012]
Further, in the above-mentioned discharge step, the inner diameter of the discharge port of the nozzle for discharge is 30 [μm] or less, preferably 20 [μm] or less, more preferably 8 [μm] or less, more preferably 4 [μm]. The following is a feature of increasing the electric field strength by concentrating the electric field at the nozzle tip (the configuration of the invention according to claims 2, 3, and 4). The reduction in the diameter of the nozzle will be described in detail later. In such a case, it is possible to discharge droplets even if there is no counter electrode facing the tip of the nozzle. For example, in a state where the counter electrode is not present, when the substrate is arranged so as to face the nozzle tip portion, and when the substrate is a conductor, the nozzle tip portion is located at a plane symmetric position with respect to the facing surface of the substrate. Inverted mirror image charges are induced, and when the substrate is an insulator, the oppositely polarized image charges are induced at symmetrical positions determined by the dielectric constant of the substrate with reference to the opposing surface of the substrate. The droplet is caused to fly by electrostatic force between the charge induced at the nozzle tip and the mirror image charge or the image charge.
Accordingly, it is possible to avoid a high potential of the discharge voltage that has hindered the discharge of the conductive paste from the nozzle, to enable the discharge from the fine nozzle at a low potential, and to discharge the fine droplets due to the fine diameter, It is possible to miniaturize the bumps and to make the pitch finer with the miniaturization.
[0013]
A fifth aspect of the present invention has a configuration similar to that of the first, second, third, or fourth aspect of the present invention, and a configuration in which a sintering step is performed for each of one or more discharge steps. .
In the above configuration, the same operation as that of the first, second, third, or fourth aspect of the invention is performed, and sintering is performed every discharge of the conductive paste droplet or every predetermined number of discharges.
[0014]
The invention according to claim 6 has the same configuration as the invention according to claim 1, 2, 3, 4 or 5, and the fine particles of the conductive paste are made of gold, silver, copper, platinum, palladium, tungsten, nickel, Tantalum, bismuth, lead, indium, tin, zinc, titanium or aluminum containing a metal or an oxide thereof, or an alloy containing any two or more of these metals I have.
With the above configuration, a bump made of any one of the above-described materials is formed.
[0015]
The invention according to claim 7 has the same configuration as the invention according to any one of claims 1 to 6, and in the sintering step, irradiation of at least one of infrared rays, laser light, and an electron beam is performed. A configuration is adopted in which droplets of the conductive paste are heated.
With the above configuration, in the sintering step, droplets of the conductive paste are irradiated with any one of infrared, laser, and electron beams on the discharge path or on the substrate and sintered.
[0016]
The invention described in claim 8 has the same configuration as the invention described in any one of claims 1 to 7, and adopts a configuration in which the particle diameter of the fine particles is 100 [nm] or less.
With the above configuration, the same operation as the invention described in any one of claims 1 to 7 is performed, and the discharge is performed in units of ultrafine particles of 100 [nm] or less.
The “particle size of fine particles” refers to the number average value of the diameter of a circumscribed circle obtained by measuring 100 arbitrary fine particle samples by electron microscopy. Except where specifically described, the same applies to the entire description of the present specification (including inventions described in other claims).
[0017]
According to a ninth aspect of the present invention, there is provided a configuration similar to the first aspect of the present invention, wherein the discharging step is performed a plurality of times, and the droplets are stacked to form a bump. I am taking it.
In the above configuration, in the discharging step, the conductive paste droplets are discharged onto the substrate a plurality of times, and the plurality of droplets are stacked according to a predetermined shape to form a bump.
[0018]
A tenth aspect of the present invention has a configuration similar to that of any one of the first to ninth aspects and has a configuration in which the sintering step is performed in parallel with the discharge step.
“Performing the sintering step in parallel with the discharging step” means that the discharging step and the sintering step overlap with each other in terms of time. That is, sintering to droplets may be started from the ejection of the droplets to the landing on the substrate, or the ejection may be performed to the substrate in a state where the processing required for sintering has already been started. good. Except where specifically described, the same applies to the entire description of the present specification (including inventions described in other claims).
[0019]
An eleventh aspect of the present invention has a configuration similar to the one of the first to ninth aspects, wherein the sintering step is performed immediately after the discharge step.
In the above configuration, sintering starts immediately after the ejection of the droplet.
[0020]
According to a twelfth aspect of the present invention, there is provided a resist film forming step of forming a resist film on a substrate, wherein the resist film has an opening similar to that of any one of the first to eleventh aspects. And forming an opening. The discharging step discharges droplets to the opening.
[0021]
In the above configuration, the same operation as the invention according to any one of claims 1 to 11 is performed, a photoresist film is formed on the substrate in advance, and an opening is formed at a bump formation position. Is done. Then, droplets are ejected toward the opening, and a bump is formed in accordance with the opening. After the sintering of the droplets, the photoresist film is removed.
[0022]
According to a thirteenth aspect of the present invention, there is provided the same configuration as the one of the first to twelfth aspects, wherein the inner diameter of the discharge port is equal to or less than 1/3 of the bump size to be formed. I am taking it.
With the above configuration, a bump having a size three times or more the inner diameter of the discharge port is formed.
The “bump size” indicates the diameter of a circle circumscribing the bump. same as below.
[0023]
The invention according to a fourteenth aspect has the same configuration as the invention according to any one of the first to thirteenth aspects, and in the discharging step, a plurality of droplets each having a volume of 1/10 or less of the volume of the bump to be formed are provided. A configuration is adopted in which the bumps are formed by ejecting the droplets once and stacking the droplets.
In the above configuration, in the discharging step, a conductive paste droplet having a volume of 1/10 or less of the volume of the bump to be formed on the substrate is discharged a plurality of times, and the plurality of droplets are stacked to form the bump. I do.
[0024]
According to a fifteenth aspect of the present invention, there is provided a configuration similar to that of the first aspect of the present invention, wherein the size of the bump to be formed is set to 70 [μm] or less.
[0025]
According to a sixteenth aspect of the present invention, there is provided a substrate holding means for holding a substrate, and a droplet of a charged conductive paste obtained by dispersing conductive fine particles serving as a bump material in a liquid, onto the substrate on the substrate holding means. A nozzle having an inner diameter of a discharge port of 30 [μm] or less, a discharge voltage applying means for applying a discharge voltage to the conductive paste in the nozzle, and a positioning means for positioning the nozzle with respect to the substrate on the substrate holding means And a sintering unit for sintering the discharged conductive paste droplets.
[0026]
In the above configuration, the droplets of the conductive paste are discharged from the nozzles whose discharge positions are positioned by the positioning means at predetermined positions on the substrate held by the substrate holding means. Such discharge is performed by sequentially changing the discharge position by the positioning means, and is stacked so as to form a pump having a predetermined shape.
The sintering by the sintering means may be performed after the bumps are stacked according to the overall shape, or may be performed once or every time a predetermined number of ejections are performed. Further, the sintering of the droplets may be performed immediately after the discharge and before hitting the substrate, or may be performed on the substrate. The sintering may be performed intermittently or continuously while the droplets are being discharged.
[0027]
Also in the case of the above configuration, similarly to the first aspect of the present invention, the electric field is concentrated at the tip of the nozzle by increasing the discharge nozzle to 30 [μm] or less, which is not conventionally used, to increase the electric field strength. It has a special feature. Therefore, the droplet is caused to fly by the electrostatic force between the charge induced at the nozzle tip and the mirror image charge or the image charge. The reduction in the diameter of the nozzle will be described in detail later.
[0028]
According to the first and sixteenth aspects of the present invention, it is possible to eliminate the necessity of the counter electrode which is indispensable in the conventionally known electrostatic suction type droplet discharge technology. A counter electrode may be used in combination. By using the counter electrode together, it is also possible to use the electrostatic force due to the electric field between the nozzle and the counter electrode to guide the flying electrode, and if the counter electrode is grounded, the charge of the charged droplet is reduced. Since it is possible to escape through the counter electrode and obtain an effect of reducing the accumulation of electric charge, it can be said that it is rather desirable to use them together.
[0029]
Further, the inner diameter of the discharge port of the nozzle for discharging is set to 30 [μm] or less, preferably 20 [μm] or less, more preferably 8 [μm] or less, and more preferably 4 [μm] or less. It is possible to further increase the electric field intensity by concentrating the electric field in the portion (the configuration of the invention according to claims 17, 18, and 19).
[0030]
The invention according to claim 20 has the same configuration as the invention according to claim 16, 17, 18 or 19, and sinters the droplets once or more than once by the droplet discharging means. And a control means for controlling the sintering means.
In the above configuration, the same operation as that of the invention according to claim 16, 17, 18, or 19 is performed, and sintering is performed every discharge of the conductive paste droplet or every plural times.
[0031]
The invention according to claim 21 has the same configuration as the invention according to claim 16, 17, 18, 19, or 20, and the fine particles of the conductive paste include gold, silver, copper, platinum, palladium, tungsten, nickel, Tantalum, bismuth, lead, indium, tin, zinc, titanium or aluminum containing a metal or an oxide thereof, or an alloy containing any two or more of these metals I have.
With the above configuration, a bump containing any one of the above-described materials is formed.
[0032]
The invention according to claim 22 has the same configuration as the invention according to any one of claims 16 to 21, and the sintering means performs any one of infrared, laser light, and electron beam irradiation. The configuration is adopted.
With the above configuration, the sintering unit sinters the droplets of the conductive paste by receiving any one of infrared rays, laser light, and electron beams on the discharge path or on the substrate.
[0033]
The invention according to claim 23 has the same configuration as the invention according to any one of claims 16 to 22, and has a configuration in which the particle diameter of the fine particles is 100 [nm] or less.
In the above configuration, the same operation as that of the invention according to any one of claims 16 to 22 is performed, and ejection is performed in units of ultrafine particles of 100 nm or less.
[0034]
According to a twenty-fourth aspect of the present invention, in addition to the same configuration as the one of the sixteenth to twenty-third aspects, a droplet is ejected a plurality of times and droplets are stacked so as to form a bump by stacking the droplets. The means of controlling the means is adopted.
In the above configuration, the bump is formed by discharging the conductive paste droplets onto the substrate a plurality of times by the discharging means and stacking the plurality of droplets according to a predetermined shape.
[0035]
The invention according to claim 25 has the same configuration as the invention according to any one of claims 16 to 24, and the sintering of the droplet by the sintering means is performed in parallel with the ejection by the droplet discharging means. The sintering means is controlled so as to be performed.
The expression “performed in parallel with the discharge” means that the discharge by the droplet discharge means and the sintering by the sintering means overlap with each other in terms of time. That is, sintering to droplets may be started from the ejection of the droplets to the landing on the substrate, or the ejection may be performed to the substrate in a state where the processing required for sintering has already been started. good. Except where specifically described, the same applies to the entire description of the present specification (including inventions described in other claims).
[0036]
The invention according to claim 26 has the same configuration as the invention according to any one of claims 16 to 24, and the sintering of the droplet by the sintering unit is performed immediately after the ejection by the droplet ejection unit. The sintering means is controlled so as to be performed.
In the above configuration, sintering starts immediately after the ejection of the droplet.
[0037]
The invention according to claim 27 has the same configuration as the invention according to any one of claims 16 to 26, and the positioning means discharges droplets to the opening of the resist film formed on the substrate. In such a case, the position of the droplet discharge means is determined with respect to the substrate.
[0038]
In the above configuration, the same operation as the invention according to any one of claims 16 to 26 is performed, a photoresist film is formed in advance on the substrate, and an opening is formed in a bump formation position. Is done. Then, droplets are ejected toward the opening, and a bump is formed in accordance with the opening. After the sintering of the droplets, the photoresist film is removed.
[0039]
The invention according to claim 28 has the same configuration as the invention according to any one of claims 16 to 27, and further has a configuration in which the inner diameter of the discharge port is 1/3 or less of the bump size to be formed. I am taking it.
With the above configuration, a bump having a size three times or more the inner diameter of the discharge port is formed.
[0040]
The invention according to claim 29 has the same configuration as the invention according to any one of claims 16 to 28, and the discharging step discharges the droplet having a volume of 1/10 or less of the volume of the bump to be formed. A configuration is adopted in which the bumps are formed by discharging a plurality of times and stacking the droplets.
In the above structure, a conductive paste droplet having a volume of 1/10 or less of the volume of the bump to be formed on the substrate is discharged a plurality of times, and the plurality of droplets are stacked to form a bump.
[0041]
The invention according to claim 30 has the same structure as the invention according to any one of claims 16 to 29, and adopts a structure in which the size of a bump to be formed is 70 [μm] or less.
[0042]
Further, in the configuration of each of the above claims,
(1) It is preferable that the shape of the nozzle is made of an electrically insulating material, and an electrode is inserted or plated in the nozzle.
(2) In the configuration of each claim or the configuration of (1), it is preferable that the nozzle is formed of an electrically insulating material and an electrode is provided outside the nozzle.
According to (1) and (2), in addition to the functions and effects described in the above claims, the ejection force can be improved, so that the liquid can be ejected at a low voltage even if the nozzle diameter is further reduced.
(3) In the structure of each of the above-mentioned claims and the structure of the above (1) or (2), it is preferable to arrange a flat plate made of a conductive material or an insulating material behind the substrate.
(4) In the configuration of each of the above claims, the configuration of (1), (2) or (3), the voltage V applied to the nozzle is
(Equation 1)

It is preferable to drive in a basin represented by
Here, γ: surface tension of liquid, ε0: dielectric constant of vacuum, r: nozzle radius, h: distance between nozzle shape and substrate, k: proportional constant depending on nozzle shape (1.5 <k <8.5) ).
(5) In the configuration of each of the above-mentioned claims, the above-mentioned (1), (2), (3) or (4), it is preferable that the arbitrary waveform voltage applied as the ejection voltage is 1000 [V] or less.
(6) In the configuration of each of the above-described claims, and in the configuration of (1), (2), (3), (4) or (5), the arbitrary waveform voltage applied as the ejection voltage is 500 [V] or less. Is preferred.
(7) In the configuration of any one of the above-described claims, and in any one of the above-described (1) to (6), the distance between the discharge port of the nozzle and the substrate is set to 500 [μm] or less to make the nozzle diameter fine. Even in such a case, it is preferable because high landing accuracy can be obtained.
(8) In the configuration of each of the above-described claims and any one of the above-described configurations (1) to (7), it is preferable that a pressure is applied to the conductive fluid (conductive paste) in the nozzle.
(9) In the configuration according to any one of the claims, and in any one of the configurations (1) to (8), when discharging by a single pulse,
(Equation 2)

May be applied to apply a pulse width Δt that is equal to or greater than a time constant τ determined by the following equation. Here, ε: dielectric constant of fluid, σ: electrical conductivity.
[0043]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram showing a schematic overall configuration of a bump forming apparatus 10 according to an embodiment of the present invention.
[0044]
(Overall configuration of bump forming apparatus)
The bump forming apparatus 10 includes a substrate holding unit 20 for holding a substrate K on which a base electrode (not shown) is provided, and conductive fine particles serving as a bump material are applied to the substrate K on the substrate holding unit 20 by a liquid. A discharge head 100 serving as a droplet discharge means for discharging droplets of conductive paste dispersed therein, and an XY stage serving as a positioning means for positioning a discharge position of the discharge head 100 with respect to the substrate on the substrate holding means 20 40, and a laser emitting means 50 as a sintering means for sintering the discharged droplets of the conductive paste.
[0045]
(Substrate holding means and XY stage)
The substrate holding means 20 includes a substrate stage 21 having a horizontal mounting surface for the substrate K thereon and a holding means 22 capable of switching between holding and releasing the substrate K on the substrate stage 21.
The substrate holding means 20 is provided above the XY stage 40. The XY stage 40 can move and position the substrate holding means 20 in an X-axis direction and a Y-axis direction orthogonal to each other on a horizontal plane. The XY stage 40 positions the substrate K at a predetermined bump forming operation start position with respect to the discharge head 100, and at the time of the bump forming operation, droplets of the conductive paste sequentially discharged from the discharge head 100 are supplied to a predetermined position on the base electrode. The substrate K is driven via the substrate holding means 20 so as to hit the position.
[0046]
(Laser emitting means)
The laser emitting means 50 is composed of a laser light source and its optical system, is supported by a device frame (not shown) above the substrate holding means 20, and irradiates the upper surface of the substrate K on which the substrate holding means 20 is held with laser light. . Then, the droplets of the conductive paste discharged to the substrate K by the irradiation of the laser beam are heated and sintered. Note that the laser beam irradiation may be continuously performed during the bump forming operation, or may be performed intermittently only when the conductive paste is discharged.
[0047]
(Conductive paste)
As the conductive paste, a conductive paste obtained by dispersing fine particles in a liquid containing a thermosetting resin and an organic solvent is used. The fine particles may be a metal made of any one of gold, silver, copper, platinum, palladium, tungsten, nickel, tantalum, bismuth, lead, indium, tin, zinc, titanium or aluminum, or an oxide thereof, or each metal Those containing an alloy composed of any two or more of these are used. In particular, when "Nanopaste (NP series)" (trademark: Harima Chemicals, Inc.) is used as a conductive paste, it is suitable for forming finer bumps.
Further, the fine particles contained in the conductive paste are desirably 100 [nm] or less, whereby fine bumps can be formed.
[0048]
(Ejection head)
FIG. 2 is an exploded perspective view showing a surface serving as a bottom surface (a surface facing the substrate K) when the ejection head 100 is used, with the ejection head 100 partially cut away. As shown in FIG. 2, the discharge head 100 includes a liquid chamber structure 102 having a plurality of liquid chambers 101 formed therein, and a bottom (a bottom part in use) of the liquid chamber structure 102, which is electrically conductive. A nozzle plate 104 provided with an ultra-fine nozzle 103 corresponding to each of the liquid chambers 101 for discharging the paste as droplets from the tip thereof. Note that reference numeral N in FIG. 2 indicates a discharge direction of the droplet in the discharge head 100, and the discharge direction N corresponds to the vertical direction in FIG.
[0049]
The liquid chamber structure 102 will be described. FIG. 3 is a cross-sectional view of one liquid chamber 101 of the liquid chamber structure 102 along a slope mainly in the ejection direction N mainly shown. As shown in FIG. 2, the liquid chamber structure 102 is integrally joined to a liquid chamber side wall 105 located below in FIG. 2 and a cover plate 110 located above the liquid chamber side wall 105 in FIG. It is configured.
The liquid chamber side wall 105 has a plurality of first liquid chamber partition walls 106, 106,. . . Are provided so as to be parallel to each other. A second liquid chamber partition 107 is stacked on each first liquid chamber partition 106, and the second liquid chamber partition 107 is bonded and fixed to the first liquid chamber partition 106 via an adhesive layer 108. Thus, a plurality of grooves are formed on the liquid chamber side wall body 105 by arranging a plurality of pairs of the first liquid chamber partition walls 106 and the second liquid chamber partition walls 107 in parallel with each other. . Then, the second liquid chamber partition walls 107, 107,... Are arranged such that the cover plate 110 faces the liquid chamber side wall body 105 and covers the plurality of grooves. . . It is adhered and fixed via an adhesive layer 109 thereon. As a result, a plurality of liquid chambers 101 defined by the first liquid chamber partition walls 106 and the second liquid chamber partition walls 107 on both sides, the liquid chamber side walls 105, and the cover plate 110 are formed. At the bottom of the liquid chamber structure 102, the bottom of each liquid chamber 101 is opened, and each liquid chamber 101 is closed by bonding and fixing a nozzle plate 104 described below to the bottom of the liquid chamber structure 102. Nozzles 103 are formed in the nozzle plate 104 corresponding to the respective liquid chambers 101.
[0050]
Each liquid chamber 101 is shallow near the upper end face 111 of the liquid chamber side wall body 105, and a shallow groove 118 is formed near the upper end face 111. At the upper part of the cover plate 110, a liquid inlet 119 and a manifold 120 connected to the liquid inlet 119 are formed. Then, by covering each liquid chamber 101 with the cover plate 110, the upper end of each liquid chamber 101 is connected to the paste supply source storing the conductive paste via the manifold 120 and the liquid inlet 119. The discharge head 100 includes a supply pump (not shown) that applies a supply pressure of the conductive paste to each liquid chamber 101. The conductive paste is supplied from the paste supply source to each liquid chamber 101 by the pressure applied by the supply pump. Supplied. The supply pump supplies the conductive paste while maintaining a supply pressure in a range that does not cause the conductive paste to spill out from the tip of the nozzle 103 described later.
[0051]
An electrode 121 is provided on the wall surfaces of the liquid chamber partition walls 106 and 107, and an insulating layer 125 is provided on the electrode 121. A conductive pattern 123 corresponding to each liquid chamber 101 is formed on a drive substrate 122 attached to a surface of the liquid chamber side wall body 105 opposite to the surface on which the liquid chamber 101 is formed. Are connected by a wire 124 by a wire bonding method.
[0052]
Here, both the liquid chamber partition wall 106 and the liquid chamber partition wall 107 of the liquid chamber side wall body 105 are piezoelectric ceramic plates, and are formed of a piezoelectric ceramic material of lead zirconate titanate (PZT) having ferroelectricity. It is polarized in the stacking direction and in mutually opposite directions (see arrows in FIG. 3). The liquid chamber partition walls 106 and 107 are deformed when a voltage is applied to the electrode 121 to reduce the volume of the liquid chamber 101 and apply pressure to the internal conductive paste. With the pressure, a liquid drop is not ejected from the tip of the nozzle 103, which will be described later, and only a convex meniscus protruding outward from the tip of the nozzle 103 is formed. That is, each of the liquid chamber partition walls 106, each of the liquid chamber partition walls 107, each of the electrodes 121, each of the conductive wires 124, and the drive substrate 122 are formed by the conductive paste of the nozzle flow path 145 provided in each of the nozzles 103. This is included in the configuration of the convex meniscus forming means for forming a convexly raised state.
[0053]
Next, the nozzle plate 104 will be described. FIG. 4 is a bottom view of the nozzle plate 104 (a view as viewed from below in FIG. 1), and FIG. 5 is a cross-sectional view of the nozzle plate 104 cut along a cutting line AA ′. The nozzle plate 104 includes an electrically insulating substrate 141 serving as a base and a plurality of ejection electrodes 142, 142,... Formed on the surface 141a of the substrate 141. . . And a plurality of ejection electrodes 142, 142,. . . And a nozzle layer 143 laminated on one surface of the surface 141a of the substrate 141.
[0054]
The back surface 141b of the substrate 141 is fixed to the bottom surface of the liquid chamber structure 102 via an adhesive or the like. The substrate 141 has a plurality of through holes 141c, 141c,. . . Are formed, and the through holes 141c, 141c,. . . Are arranged so as to correspond to the respective liquid chambers 101, and communicate with the respective liquid chambers 101. That is, the through hole 141c forms the lower part of the liquid chamber 101.
[0055]
The ejection electrodes 142, 142,. . . Are formed so as to correspond to the respective through holes 141c. Each discharge electrode 142 is formed on the surface 141a of the substrate 141 so as to cover the corresponding through hole 141c, and when viewed from the bottom, each discharge electrode 142 overlaps the corresponding through hole 141c. That is, each discharge electrode 142 faces the corresponding liquid chamber 101 and forms the bottom surface of the corresponding liquid chamber 101.
The discharge electrode 142 has a through hole 142a formed in a portion overlapping the through hole 141c, and the through hole 142a communicates with the corresponding liquid chamber 101. In addition, wirings 144 formed integrally are connected to the respective ejection electrodes 142, and the respective wirings 144 are connected to a bias power supply 30 described later. In the drawing, the discharge electrode 142 has a ring shape and the wiring 144 has a square shape when viewed from the bottom, but the present invention is not limited to such a shape.
[0056]
The nozzle layer 143 includes a plurality of nozzles 103, 103,. . . Are formed integrally, and a plurality of nozzles 103, 103,. . . Are lined up in a row. The nozzles 103 arranged in a line are provided at an interval equal to a general standard value of the arrangement pitch of the base electrodes provided on the substrate K, whereby the bumps can be simultaneously formed on a plurality of base electrodes. It is possible to do. Needless to say, the interval between the nozzles 103 may be set to be equal to the pitch of the base electrodes of the various substrates.
[0057]
Further, each of the nozzles 103 is formed so as to stand substantially vertically (to hang down) with respect to the substrate 141. These nozzles 103, 103,. . . Are arranged so as to correspond to the liquid chambers 101, respectively. When viewed from the bottom, the nozzle holes 103a of the respective nozzles 103 overlap the corresponding through holes 141c.
[0058]
Each of the nozzles 103 is formed with an in-nozzle flow path 145 penetrating from the tip of the nozzle 103 along the center line thereof. ing. The flow path 145 in the nozzle communicates with the corresponding liquid chamber 101 through the through hole 142 a of the discharge electrode 142, and the discharge electrode 142 faces the flow path 145 in the nozzle.
The conductive paste supplied to each liquid chamber 101 is also supplied to the through-hole 141c and the nozzle flow path 145, and directly contacts the discharge electrode 142 in each liquid chamber 101 and each nozzle flow path 145. In the drawings, a plurality of nozzles 103, 103,. . . Are arranged in one row, but may be arranged in two or more rows, or may be arranged in a matrix. However, it is desirable that the arrangement conforms to the arrangement of each base electrode of the substrate K.
[0059]
These nozzles 103, 103,. . . The nozzle layer 143 has electrical insulation properties, and the inner surface of the in-nozzle flow path 145 also has electrical insulation properties. The nozzles 103, 103,. . . , Including the nozzle layer 143 (for example, the nozzle layer 143 is formed of a resin containing fluorine), or the nozzles 103, 103,. . . (For example, a metal film is formed on the surfaces of the nozzles 103, 103,..., And the metal and the water-repellent resin are further formed on the metal film). A water-repellent layer is formed by eutectoid plating.) Here, the water repellency is a property repelling the conductive paste discharged from the nozzle 103.
[0060]
Each nozzle 103 will be described in more detail. As described above, the nozzle 103 is formed with a very small diameter. The shape of the nozzle 103 is sharply formed at the distal end so that the diameter becomes smaller toward the distal end, and is formed as a truncated cone that is almost conical. As an example of specific dimensions of each part, the internal diameter of the nozzle internal flow path 145 is 1 [μm], the external diameter at the tip of the nozzle 103 is 2 [μm], and the root diameter of the nozzle 103 is 5 [μm] ], The height of the nozzle 103 is set to 100 [μm].
The dimensions of the nozzle 103 are not limited to the above example. In particular, the inner diameter of the nozzle is within a range in which a discharge voltage enabling discharge of a droplet by an effect of electric field concentration described later is less than 1000 [V], for example, a nozzle diameter of 30 [μm] or less. Desirably, the lower limit value is a diameter of 20 [μm] or less, which is a range in which it is feasible to form a through-hole through which the conductive paste is formed by the current nozzle forming technology. The nozzles 103, 103,. . . Are preferably the same as each other, but may be different.
[0061]
Next, a circuit configuration for driving the nozzle plate 104 will be described. The ejection head 100 includes the ejection electrodes 142, 142,. . . And an ejection voltage applying means 25 (shown in FIG. 4 for convenience) for individually applying an ejection voltage to the nozzles 103, 103,. . . And a counter electrode 23 (shown in FIG. 5) provided in a substrate stage 21 that supports a substrate K that receives droplets landing on the counter surface 23a.
[0062]
The ejection voltage applying means 25 includes a bias power supply 30 for applying a DC bias voltage to the ejection electrode 142 and an ejection power supply 29 for applying a pulse voltage superimposed on the bias voltage to a potential required for ejection to the ejection electrode 142. It is provided corresponding to each ejection electrode 142. The bias power supply 30 and the discharge power supply 29 are connected to all the discharge electrodes 142, 142,. . . However, in this case, the ejection power supply 29 supplies the ejection electrodes 142, 142,. . . A pulse voltage is applied individually.
[0063]
The bias voltage from the bias power supply 30 is always applied within a range in which the conductive paste is not ejected, so that the width of the voltage to be applied at the time of ejection is reduced in advance, thereby improving the reactivity at the time of ejection. ing.
[0064]
The discharge voltage power supply 29 superposes a pulse voltage on a bias voltage only when discharging the conductive paste, and discharges the discharge electrodes 142, 142,. . . Apply individually. At this time, the value of the pulse voltage is set so that the superimposed voltage V satisfies the following condition.
(Equation 1)

Here, γ: surface tension of the conductive paste, ε0: dielectric constant of vacuum, r: nozzle radius, and k: proportional constant depending on the nozzle shape (1.5 <k <8.5).
In one example, the bias voltage is applied at 300 [V] DC and the pulse voltage is marked at 100 [V]. Therefore, the superimposed voltage at the time of ejection is 400 [V].
[0065]
The counter electrode 23 includes nozzles 103, 103,. . . Is provided on the mounting surface of the substrate stage 21, and the substrate K is mounted on the mounting surface. The nozzles 103, 103,. . . Is set to 100 [μm] as an example.
Further, since the counter electrode 23 is grounded, the ground potential is always maintained. Therefore, when the pulse voltage is applied, the discharged liquid droplets are guided to the counter electrode 23 side by electrostatic force due to an electric field generated between the tip of each nozzle 103 and the opposing surface 23a.
[0066]
The ejection head 100 has nozzles 103, 103,. . . Of the nozzles 103, 103,. . . Since the droplets are discharged by increasing the electric field strength by the electric field concentration at the tip, the droplets can be discharged without the guidance by the counter electrode 23, but the nozzles 103, 103,. . . It is desirable that induction by electrostatic force be performed between the electrode and the counter electrode 23. It is also possible to release the charge of the charged droplet by grounding the counter electrode 23.
[0067]
(Description of operation of the embodiment)
The operation of the bump forming apparatus 10 will be described with reference to FIGS. FIG. 6 is an operation explanatory view showing a process in the middle of bump formation, and the two-dot chain line in the figure indicates the shape of the bump B to be formed.
In the forming operation of the bump B, first, when the substrate K is mounted on the substrate holding means 20, the plurality of nozzle portions 37 of the discharge head 100 are individually discharged toward the respective base electrodes of the substrate K. Then, the substrate K is positioned at the initial position by the XY stage 40.
[0068]
Then, in a state where the substrate K is irradiated with the laser beam by the laser emitting means 50 (sintering step), droplets of the conductive paste are ejected from each nozzle portion 37 (ejection step). The discharged droplet hits a base electrode of the substrate K and is simultaneously irradiated with a laser beam and sintered by heating. At this time, the organic solvent that maintains the liquid state contained in the droplets of the conductive paste evaporates, the thermosetting resin is cured, and the metal particles are sintered and fixed to the hit position.
[0069]
The droplets of the conductive paste are sufficiently smaller in diameter than the bumps B, and the bumps are formed by being repeatedly ejected and stacked up. That is, as shown in FIG. 6, when one layer is formed at the height of one droplet, a new layer is formed on top of it, and this is repeated to form a predetermined shape. A bump B is formed.
[0070]
The discharge operation of the discharge head 100 in the discharge step will be described in detail. 7A and 7B are explanatory diagrams showing the relationship between the operation of discharging the conductive paste and the voltage applied to the conductive paste. FIG. 7A shows a state in which discharge is not performed, and FIG. Show.
A chargeable conductive paste is supplied to the in-nozzle flow path 145 of each nozzle 103 via the liquid inlet 119 and the manifold 120 by the supply pump, and in this state, each discharge is performed by each bias power supply 30. A bias voltage is applied to the conductive paste via the electrode 142. In this state, the conductive paste is charged, and a concave meniscus is formed at the tip of each nozzle 103 by the conductive paste (FIG. 7A).
[0071]
Then, the nozzles 103, 103,. . . Among the nozzles 103 that eject droplets, a pulse voltage is applied from the ejection voltage power supply 29 to the conductive paste via the ejection electrode 142, and a pulse voltage is also applied to the electrode 121 in synchronization with the pulse voltage. You. When a pulse voltage is applied to the electrode 121, the liquid chamber partitions 106 and 107 expand, and the volume of the liquid chamber 101 decreases, whereby the pressure of the conductive paste in the liquid chamber 101 increases. Therefore, a convex meniscus protruding outward is formed at the tip of the nozzle 103. Further, since the pulse voltage is applied to the ejection electrode 142 almost simultaneously with the application of the pulse voltage to the electrode 121, the electric field is concentrated by the apex of the convex meniscus projecting to the outside, and finally the surface tension of the conductive paste is increased. Micro droplets are ejected to the counter electrode side against the pressure (FIG. 7B).
[0072]
When the pulse voltage applied to the ejection electrode 142 ends and the pulse voltage applied to the electrode 121 ends, the volume of the liquid chamber 101 increases, so that the conductive paste is concavely recessed at the tip of the nozzle 103. As a result, a conductive meniscus is formed, and the conductive paste is supplied through the liquid inlet 119 and the manifold 120 to the nozzle passage 145 of the nozzle 103 that has discharged the conductive paste.
[0073]
As described above, by applying a discharge voltage in the nozzle to the droplet discharge means having a fine nozzle diameter, fine droplets of the conductive paste can be discharged at a low voltage, so that a fine bump can also be formed. Is possible.
[0074]
In the above description, when the pulse voltage is applied to the electrode 121, the liquid chamber partitions 106 and 107 expand and the volume of the liquid chamber 101 increases, but conversely, when the pulse voltage is applied to the electrode 121, The operation may be performed such that the chamber partitions 106 and 107 contract to reduce the volume of the liquid chamber 101. However, in this case, when a pulse voltage is applied to the ejection electrode 142 during ejection, no pulse voltage is applied to the electrode 121, and when a bias voltage is applied to the ejection electrode 142 when ejection is not performed. A pulse voltage is applied to the electrode 121.
[0075]
As described above, since the bump forming apparatus 10 forms the bumps in the step of discharging the droplets of the conductive paste and the step of sintering the same, the operation itself in each step is simple, and the photoresist or the mask is used. This eliminates the need for pre-preparation, etc., thereby facilitating and speeding up the work and improving productivity. Further, chemicals such as photoresist are not required for the bump forming operation, and the generation of waste after the operation is reduced, so that the influence on the surrounding environment can be sufficiently reduced.
In addition, in the bump forming apparatus 10, since the bumps can be formed so as to stack a plurality of layers by discharging and sintering the droplets of the conductive paste, it is necessary to change the shape of each layer. Thus, for example, bumps B of various shapes as shown in FIGS. 8A to 8C can be formed.
[0076]
(Other)
In addition, it is preferable that the inner diameter of the discharge port be equal to or less than 1/3 of the size of the bump to be formed, in order to form a bump of any fine and accurate shape such as flat or with a projection. In particular, it is preferable that droplets having a volume of 1/10 or less of the volume of the bump to be formed are ejected a plurality of times and the droplets are stacked. When the size of the bump to be formed is 50 [μm] or less, it is particularly preferable that the size of the bump to be formed is set to 1/3 or less, and the volume of the droplet is set to 1/10 of the volume of the bump.
[0077]
For example, when the bumps are 15 [μm] × 15 [μm] square (bump size is 21 [μm]) and the upper surface with a height of 4 [μm] is a flat bump, the inner diameter of the discharge port is 2 μm. [Μm] nozzle, one drop amount (droplet volume) is 4 × 10 ^-18 [M ³ (4 femtoliters), and considering that the droplet is a spherical droplet having a diameter of 2 [μm], in consideration of the volatile content of the dispersion, approximately 250 droplets are ejected to form a bump. be able to.
In order to form bumps of the same size as above, 3 × 3 × 2 = 18 drops (1 drop = 33 femtoliters) were first stacked with a nozzle having an inner diameter of the discharge port of 4 [μm] (approximately By stacking the remaining 300 femtoliters (approximately 100 drops in consideration of the volatile content of the dispersion liquid) so as to adjust the shape with a nozzle having an inner diameter of the discharge port of 2 [μm], Since it can be formed with 118 droplets, it is possible to form a fine and accurate bump.
[0078]
The sintering unit is not limited to the laser beam emitting unit described above, and may be configured to perform heating by irradiating an electron beam or infrared rays. By sintering using laser light emitting means and means for irradiating electron beam or infrared rays, it is possible to locally heat, so that even if bumps are formed on a substrate with heat-sensitive parts, parts can be damaged. It can be suppressed, or deformation of the substrate due to heat can be suppressed. Further, a configuration may be adopted in which a heat stage for heating the substrate from the back side is provided. Further, various light irradiation means and a heat stage may be used in combination.
[0079]
Further, the irradiation position of the laser beam from the laser emitting means 50 is not limited to the case of irradiating the upper surface of the substrate K. good. For example, as shown in FIG. 9, the direction may be set so as to irradiate an area in the middle of the passage of the discharged droplet.
The sintering may be performed after the droplet lands on the substrate K side, or may be performed by discharging while the substrate K is heated in advance and sintering.
[0080]
Further, the positioning means is not limited to the XY stage for moving the substrate K, but a means for moving and positioning the ejection head 20 may be used. Further, it may be constituted by a means for moving and positioning the substrate only in a direction along a certain straight line, and a means for moving and positioning the ejection head along another linear direction intersecting the same.
[0081]
In the formation of the bumps, a photoresist layer forming step is provided in which a photoresist layer is provided in advance on the base electrode forming surface of the substrate K and only the base electrode position is removed to provide a removed portion for bump formation. Is also good. By filling the removed portion of the photoresist layer with the droplet of the conductive paste after such a process, the shape of the bump B can be formed stably.
[0082]
In the above embodiment, the substrate K is positioned in the horizontal plane (the X-axis direction and the Y-axis direction). However, the positioning may be adjusted in the vertical direction. Note that the ejection head 100 may be positioned vertically.
[0083]
In the ejection head 100, an electrode (for example, the above-described metal film formed under the water-repellent film) is provided on the outer periphery of the nozzle 103 in order to obtain an electrowetting effect on the nozzle 103. Alternatively, an electrode may be provided on the inner surface of the in-nozzle flow path 145, and covered with an insulating film from above. By applying a voltage to this electrode, the wettability of the inner surface of the in-nozzle flow path 145 can be improved by the electrowetting effect on the conductive paste to which the voltage is applied by the ejection electrode 142. The supply of the conductive paste to the inner channel 145 can be performed smoothly, and the discharge can be performed satisfactorily, and the response of the discharge can be improved.
[0084]
(Explanation of capturing the inner diameter of the discharge port of a preferred nozzle)
The inner diameter (inner diameter) of the discharge port of each nozzle provided in the discharge head 100 described in the above embodiment is preferably 30 [μm] or less, more preferably less than 20 [μm], more preferably It is preferably 8 [μm] or less, more preferably 4 [μm] or less. By setting the inner diameter of the discharge port of the nozzle to be larger than 0.2 [μm], the flying stability of the droplet can be improved.
[0085]
When the inner diameter of the discharge port of the nozzle is less than φ20 [μm], the electric field intensity distribution can be narrowed, so that the degree of freedom of the distance between the nozzle and the counter electrode can be increased.
If the inner diameter of the discharge port of the nozzle is φ8 [μm] or less, stable discharge can be performed without being affected by the positional accuracy of the counter electrode and the material characteristics of the substrate K (particularly, the base electrode) and the thickness. Becomes possible.
[0086]
Further, when the inner diameter of the discharge port of the nozzle is φ4 [μm] or less, the initial discharge speed of the conductive paste can be increased, so that the flight stability of the droplet is increased and the moving speed of the electric charge in the meniscus portion is reduced. As a result, the ejection response is improved.
[0087]
Further, when the inner diameter of the discharge port of the nozzle is φ4 [μm] or less, the droplet discharge efficiency can be improved, and stable discharge can be performed in this range.
[0088]
[Theoretical explanation of liquid ejection device]
In the present invention, the role of the nozzle that plays in the electrostatic suction type fluid jet system is reconsidered,
[Equation 3]

That is,
(Equation 4)

Or
(Equation 5)

By using Maxwell force or the like in a region which has not been conventionally attempted to be undischargeable, fine droplets can be formed.
[0089]
An expression that approximately derives ejection conditions and the like for such a drive voltage reduction and a technique for realizing minute ejection is described below.
The following description is applicable to the ejection head 100 described in each of the embodiments of the present invention.
Now, it is assumed that a fluid is injected into a nozzle having a radius r, and the fluid is vertically positioned at a height h from an infinite plate conductor as the substrate K. This is shown in FIG. At this time, it is assumed that the electric charge induced at the nozzle tip concentrates on the hemisphere at the nozzle tip, and is approximately represented by the following equation.
(Equation 6)

Here, Q: electric charge induced at the tip of the nozzle, ε ₀ : Dielectric constant of vacuum, ε: dielectric constant of substrate, h: distance between nozzle and substrate, r: radius of nozzle inner diameter, V: voltage applied to nozzle. α is a proportionality constant depending on the nozzle shape and the like, and takes a value of about 1 to 1.5, and particularly becomes about 1 when r << h.
[0090]
When the substrate as the base material is a conductive substrate, it is considered that a mirror image charge Q ′ having an opposite sign is induced at a symmetric position in the substrate. When the substrate is an insulator, the image charge Q ′ having the opposite sign is similarly induced at a symmetric position determined by the dielectric constant.
By the way, the electric field strength Eloc. Assuming that the radius of curvature at the tip is R,
(Equation 7)

Given by Here, k is a proportional constant, which varies depending on the nozzle shape and the like, but takes a value of about 1.5 to 8.5, and is considered to be about 5 in many cases. (PJ Birdsey and DA Smith, Surface Science, 23 (1970) 198-210).
[0091]
For the sake of simplicity, r = R. This corresponds to a state in which the fluid (conductive paste) rises into a hemispherical shape having the same radius as the inner diameter r of the discharge port of the nozzle due to surface tension at the nozzle tip.
Consider the balance of the pressure acting on the liquid at the nozzle tip. First, assuming that the liquid pressure at the tip of the nozzle is S, the electrostatic pressure is
(Equation 8)

From equations (6), (7) and (8), setting α = 1,
(Equation 9)

It is expressed as
[0092]
On the other hand, when the surface tension of the liquid (conductive paste) at the nozzle tip is Ps,
(Equation 10)

Here, γ: surface tension.
The condition under which the ejection of fluid occurs due to the electrostatic force is a condition where the electrostatic force exceeds the surface tension.
(Equation 11)

It becomes. By using the sufficiently small inner diameter r of the discharge port of the nozzle, it is possible to make the electrostatic pressure exceed the surface tension.
When the relationship between V and r is obtained from this relational expression,
(Equation 12)

Gives the lowest voltage for ejection. That is, from Equations (5) and (12),
(Equation 13)

Is the operating voltage of the present invention.
[0093]
FIG. 11 shows the dependence of the discharge limit voltage Vc on the nozzle having a certain radius r. From this figure, it was clarified that, considering the electric field concentration effect of the fine nozzle, the discharge start voltage decreases as the inner diameter of the discharge port of the nozzle decreases.
In the conventional concept of an electric field, that is, when only the electric field defined by the voltage applied to the nozzle and the distance between the opposing electrodes is considered, the voltage required for ejection increases as the size of the nozzle becomes smaller. On the other hand, if attention is paid to the local electric field strength, the discharge voltage can be reduced by making the nozzle fine.
[0094]
Discharge by electrostatic suction is basically based on charging of a fluid (conductive paste) at the nozzle end. It is considered that the charging speed is about a time constant determined by dielectric relaxation.
[Equation 14]

Here, ε: relative permittivity of the fluid, σ: conductivity of the fluid. The fluid has a dielectric constant of 10 and a conductivity of 10 ^-6 Assuming S / m, τ = 1.854 × 10 ^-5 sec. Alternatively, if the critical frequency is fc,
(Equation 15)

It becomes. It is considered that no response can be made to a change in the electric field having a frequency earlier than fc and ejection becomes impossible. Estimating the above example results in a frequency of about 10 kHz. At this time, when the nozzle radius is 2 μm and the voltage is slightly less than 500 V, G can be estimated to be 10-13 m 3 / s. However, in the case of the liquid of the above example, the discharge at 10 kHz is possible, so the minimum discharge amount in one cycle Can achieve about 10 fl (femtoliter, 1 fl: 10-15 l).
[0095]
Each of the above embodiments is characterized by the effect of concentrating the electric field at the nozzle tip and the effect of the image force induced on the opposing substrate, as shown in FIG. Thus, there is no need to make the substrate or substrate support conductive or to apply a voltage to these substrates or substrate support as in the prior art. That is, an insulating glass substrate, a plastic substrate such as polyimide, a ceramic substrate, a semiconductor substrate, or the like can be used as the substrate.
In each of the above embodiments, the voltage applied to the electrode may be either positive or negative.
Further, by keeping the distance between the nozzle and the substrate K at 500 [μm] or less, it is possible to easily discharge the fluid. Although not shown, feedback control based on nozzle position detection is performed to keep the nozzle constant with respect to the substrate K.
Alternatively, the substrate K may be placed and held in a conductive or insulating substrate K holder.
[0096]
FIG. 12 is a side sectional view of a liquid ejection apparatus as an example of another basic example of the ejection head 100 described above. An electrode 15 is provided on the side surface of the nozzle 1, and a controlled voltage is applied between the nozzle 15 and the fluid 3 in the nozzle. The purpose of this electrode 15 is an electrode for controlling the ElectroWetting effect. If a sufficient electric field is applied to the insulator forming the nozzle, the Electrowetting effect is expected to occur without this electrode. However, in this basic example, the role of the ejection control is also achieved by more positively controlling using this electrode. When the nozzle 1 is made of an insulator, has a thickness of 1 μm, an inner diameter of the nozzle of 2 μm, and an applied voltage of 300 V, an Electrowetting effect of about 30 atm is obtained. Although this pressure is insufficient for discharge, it is significant from the point of supply of fluid to the nozzle tip, and it is considered that discharge can be controlled by this control electrode.
[0097]
FIG. 11 described above shows the dependence of the discharge start voltage on the inner diameter of the discharge port of the nozzle in the present invention. As the liquid ejection device, the one shown in the ejection head 100 shown in FIG. 2 was used. It has been clarified that the discharge start voltage decreases as the nozzle becomes finer, and that discharge can be performed at a lower voltage than in the past.
In each of the above embodiments, the condition of the fluid discharge is a function of the distance (L) between the nozzle substrates, the amplitude (V) of the applied voltage, and the frequency (f) of the applied voltage, and each satisfies a certain condition. Is required as a discharge condition. Conversely, if any one of the conditions is not satisfied, it is necessary to change other parameters.
[0098]
This will be described with reference to FIG.
First, for discharge, there is a certain critical electric field Ec in which the discharge is performed only when the electric field is larger than that. The critical electric field varies depending on the inner diameter of the discharge port of the nozzle, the surface tension of the fluid, the viscosity, and the like, and it is difficult to discharge the liquid at Ec or less. Above the critical electric field Ec, that is, at the dischargeable electric field strength, there is a roughly proportional relationship between the distance (L) between the nozzle substrates and the amplitude (V) of the applied voltage, and when the distance between the nozzles is reduced, the critical applied voltage V Can be reduced.
Conversely, when the distance L between the nozzle substrates is extremely large and the applied voltage V is increased, even if the same electric field strength is maintained, the burst or burst of the fluid droplet occurs due to the action of corona discharge or the like. Therefore, in order to obtain good ejection characteristics, it is desirable to keep the distance between the nozzle substrates to about 100 μm or less in terms of both ejection characteristics and landing accuracy.
[0099]
【The invention's effect】
According to the present invention, since bumps are formed by discharging and sintering conductive paste droplets by droplet discharging means, bumps can be formed easily and quickly, and the productivity can be improved. It becomes possible. Further, since a patterned mask is not required, cost can be reduced even in small-quantity production. Further, by adjusting the relative positional relationship between the droplet discharging means and the substrate, it is possible to easily form bumps of various shapes. Furthermore, if bumps are formed by stacking droplets, bumps of various shapes can be formed.
[0100]
Further, according to the present invention, by reducing the discharge port of the nozzle to 30 [μm] or less, the electric field is concentrated at the tip of the nozzle to increase the electric field strength, and at the same time, up to the mirror image charge or the image charge on the substrate side induced at that time. The droplet flies by the electrostatic force of the electric field generated therebetween. For this reason, in the principle of the conventional electrostatic attraction method, the ejection voltage is excessively high, and it is considered difficult to employ the ejection voltage. This makes it possible to discharge fine droplets. As a result, finer bumps can be formed, and the bump pitch can be reduced as the bumps become finer.
[0101]
Further, the size of the bump to form the discharge port of the nozzle is set to 1/3 or less, the size of the discharged droplet is set to 1/10 or less of the bump volume, or the size of the formed bump is set to 70 [μm] or less. This makes it possible to form bumps of any fine and accurate shape, such as flat or with projections.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a schematic overall configuration of a bump forming apparatus according to an embodiment of the present invention.
FIG. 2 is an exploded perspective view showing a bottom surface of the ejection head on a front side of the drawing and showing the ejection head partially cut away.
FIG. 3 is a sectional view taken along a slope in a discharge direction mainly showing one liquid chamber of the liquid chamber structure.
FIG. 4 is a bottom view showing the ejection head shown in FIG. 2;
FIG. 5 is a cross-sectional view taken along a cutting line AA ′ shown in FIG.
FIG. 6 is an operation explanatory view showing an intermediate process of bump formation.
7A and 7B are explanatory diagrams showing a relationship between a discharging operation of a conductive paste and a voltage applied to the conductive paste, wherein FIG. 7A shows a state in which discharging is not performed, and FIG. 7B shows a discharging state. Is shown.
FIGS. 8A to 8C are explanatory views showing examples of bumps of various shapes.
FIG. 9 is an explanatory view showing another example of the irradiation position of the laser emitting means.
FIG. 10 is a diagram illustrating a calculation of electric field strength of a nozzle as a basic example of a discharge head.
FIG. 11 shows the relationship between the nozzle diameter of the nozzle, the discharge start voltage at which the droplet discharged from the meniscus portion starts to fly, the voltage value of the initial discharge droplet at the Rayleigh limit, and the ratio of the discharge start voltage to the Rayleigh limit voltage value. FIG. 4 is a diagram showing the relationship.
FIG. 12 is a side sectional view of a liquid ejection mechanism as another basic example of the ejection head.
FIG. 13 is a diagram illustrating ejection conditions based on a distance-voltage relationship in an ejection head.
[Explanation of symbols]
10 Bump forming equipment
20 Substrate holding means
30 ejection head (droplet ejection means)
40 XY stage (positioning means)
50 Laser emitting means (sintering means)
103 nozzle
B bump
K board

Claims (30)

A conductive paste formed by dispersing conductive fine particles serving as a bump material in a liquid is charged, and a discharge voltage is applied to the conductive paste in the nozzle to discharge droplets of the conductive paste so that the inner diameter of a discharge port is reduced. A discharge step of discharging to a substrate through a nozzle of 30 [μm] or less;
A sintering step of sintering the discharged droplets of the conductive paste. 2. The bump forming method according to claim 1, wherein the inner diameter of the nozzle is 20 [μm] or less. 2. The bump forming method according to claim 1, wherein the inner diameter of the nozzle is 8 [μm] or less. 2. The bump forming method according to claim 1, wherein the inner diameter of the nozzle is 4 [μm] or less. 5. The bump forming method according to claim 1, wherein the sintering step is performed for each of one or two or more discharge steps. The fine particles may be a metal or an oxide of any one of gold, silver, copper, platinum, palladium, tungsten, nickel, tantalum, bismuth, lead, indium, tin, zinc, titanium or aluminum, or an oxide of each metal. The bump forming method according to claim 1, 2, 3, 4, or 5, further comprising an alloy comprising at least two of the above. The bump formation according to any one of claims 1 to 6, wherein in the sintering step, the conductive paste droplets are heated by irradiation of at least one of infrared rays, laser light, and an electron beam. Method. The method according to claim 1, wherein a particle diameter of the fine particles is 100 nm or less. The bump forming method according to any one of claims 1 to 8, wherein the discharging step is performed a plurality of times, and the droplets are stacked to form a bump. 10. The bump forming method according to claim 1, wherein the sintering step is performed in parallel with the discharging step. 10. The bump forming method according to claim 1, wherein the sintering step is performed immediately after the discharging step. A resist film forming step of forming a resist film on the substrate,
An opening forming step of forming an opening in the resist film;
The method according to claim 1, wherein, in the discharging step, the droplet is discharged to the opening. 13. The bump forming method according to claim 1, wherein an inner diameter of the discharge port is equal to or less than 1/3 of a size of a bump to be formed. 14. The method according to claim 1, wherein, in the discharging step, the droplet is discharged a plurality of times of a volume equal to or less than 1/10 of the volume of the bump to be formed, and the droplet is stacked to form a bump. The bump forming method according to any one of the preceding claims. The bump forming method according to claim 1, wherein the size of the bump to be formed is 70 μm or less. Substrate holding means for holding a substrate,
A droplet of a charged conductive paste formed by dispersing conductive fine particles serving as a bump material in a liquid is discharged toward a substrate on the substrate holding means. The inner diameter of the discharge port is 30 [μm] or less. Nozzle and
Discharge voltage applying means for applying a discharge voltage to the conductive paste in the nozzle, positioning means for positioning the nozzle with respect to the substrate on the substrate holding means,
A sintering unit for sintering the discharged droplets of the conductive paste. 17. The bump forming apparatus according to claim 16, wherein the inner diameter of the nozzle is 20 [μm] or less. 14. The bump forming apparatus according to claim 13, wherein an inner diameter of the nozzle is 8 [μm] or less. 17. The bump forming apparatus according to claim 16, wherein the inner diameter of the nozzle is 4 [μm] or less. 19. A control unit for controlling the sintering unit so as to sinter the droplets at each time of one or a plurality of ejections by the droplet ejection unit. Or a bump forming apparatus according to claim 19; The fine particles may be a metal or an oxide of any one of gold, silver, copper, platinum, palladium, tungsten, nickel, tantalum, bismuth, lead, indium, tin, zinc, titanium or aluminum, or an oxide of each metal. 21. The bump forming apparatus according to claim 16, wherein the bump forming apparatus contains an alloy composed of any two or more of the above. 22. The bump forming apparatus according to claim 16, wherein the sintering unit irradiates at least one of infrared rays, laser light, and electron beams. 23. The bump forming apparatus according to claim 16, wherein the particle diameter of the fine particles is 100 [nm] or less. The bump forming apparatus according to any one of claims 16 to 23, wherein the discharging is performed a plurality of times, and the droplet discharging unit is controlled so that the droplets are stacked to form a bump. 25. The sintering unit according to claim 16, wherein the sintering unit is controlled such that the sintering of the droplet by the sintering unit is performed in parallel with the ejection by the droplet ejection unit. Item 5. The bump forming apparatus according to Item 1. 26. The sintering unit is controlled so that sintering of the droplet by the sintering unit is performed immediately after ejection by the droplet ejection unit. Item 5. The bump forming apparatus according to Item 1. 27. The method according to claim 16, wherein the positioning unit performs positioning of the droplet discharging unit with respect to the substrate such that the droplet is discharged to an opening of a resist film formed on the substrate. The bump forming apparatus according to claim 1. The bump forming apparatus according to any one of claims 16 to 27, wherein an inner diameter of the discharge port is 1/3 or less of a size of a bump to be formed. 29. The method according to claim 16, wherein, in the discharging step, the droplet is discharged a plurality of times with a volume equal to or less than 1/10 of the volume of the bump to be formed, and the droplet is stacked to form a bump. The bump forming apparatus according to claim 1. 30. The bump forming apparatus according to claim 16, wherein the size of the bump to be formed is 70 [μm] or less.

Images