JP3541709B2 - Method of forming light emitting diode - Google Patents

Method of forming light emitting diode Download PDF

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Publication number
JP3541709B2
JP3541709B2 JP03926299A JP3926299A JP3541709B2 JP 3541709 B2 JP3541709 B2 JP 3541709B2 JP 03926299 A JP03926299 A JP 03926299A JP 3926299 A JP3926299 A JP 3926299A JP 3541709 B2 JP3541709 B2 JP 3541709B2
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Japan
Prior art keywords
light
light emitting
resin
fluorescent substance
emitting element
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JP03926299A
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Japanese (ja)
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JP2000286455A (en
Inventor
広昭 為本
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Nichia Corp
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Nichia Corp
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Description

【０００１】
【発明の属する技術分野】
本発明は発光素子から放出される発光波長の少なくとも一部を蛍光物質により変換して放出する発光ダイオードに係わり、特に、発光むら、色むらや形成された発光ダイオード間における発光バラツキが少なく歩留りの高い発光ダイオードに関するものである。
【０００２】
【従来の技術】
半導体発光素子は、小型で効率よく鮮やかな色の発光をする。また、半導体素子であるため球切れがない。駆動特性が優れ、振動やＯＮ／ＯＦＦ点灯の繰り返しに強いという特徴を有する。そのため、各種インジケータや種々の光源として利用されている。しかしながら、このような発光素子は単色性のピーク波長を有するが故に白色系（白、ピンクや電球色など）の発光のみを得る場合においても、２種類以上の発光素子を利用せざるを得なかった。また、種々の発光色を簡単に得ることはできなかった。
【０００３】
単色性のピーク波長を発するＬＥＤチップと蛍光物質を利用して種々の発光色を発光させる発光ダイオードとして、特開平７−９９３４５号公報などに記載されたものが知られている。これらの発光ダイオードは、発光チップの発光を発光観測面側に反射するカップの底部に発光チップを積載させると共にカップ内部に充填された樹脂と、全体を覆った樹脂から構成することができる。内部に充填された樹脂中には発光チップからの光を吸収し、波長変換する蛍光物質を含有させてある。
【０００４】
蛍光物質が含有された樹脂は、液状のエポキシ樹脂などを発光素子が搭載されたカップ上に滴下注入し、加熱硬化させ色変換部材とさせる。カップ内部以外の樹脂は液状のエポキシ樹脂などを注型したキャスティングケース内に、色変換部材及び発光チップが形成されたフレーム部材先端を浸漬配置し、これをオーブンに入れ加熱硬化させることにより形成する。これにより、発光チップからの発光波長を蛍光物質によって波長変換した発光ダイオードとすることができる。例えば、ＬＥＤチップからの青色系の光と、その青色系の光を吸収し補色関係にある黄色系を発光する蛍光体からの光との混色により白色が発光可能な発光ダイオードとすることができる。
【０００５】
このような発光ダイオードを用いて、所望の白色系などを発光させるためには、それぞれの光を極めて精度良く発光させ混色調整させる必要がある。ＬＥＤチップからの光は、その半導体及び駆動電流などにより調節させることができる。一方、蛍光物質からの波長変換された光も蛍光物質の組成や粒径を制御することによってある程度調整することができる。
【０００６】
【発明が解決しようとする課題】
しかし、蛍光物質自体には密着力がない、或いは弱いため発光素子上に配置固定させるためには、種々の樹脂中など発光素子及び蛍光物質それぞれの光が放出可能な密着性を有するバインダー中に含有させる必要がある。このようなバインダー中に含有された蛍光物質は、その蛍光物質の含有量や分布などによってＬＥＤチップから放出された光量及び蛍光物質から放出された光量が大きく左右される。これらが制御できず、また発光素子から放出される可視光と蛍光物質から放出される光が可視光の混色によって色表現させる場合には、それぞれの可視光量の違いが大きな問題となる。特に、白色系は人間の目が僅かな色温度差でも識別することができるため大きな問題となる。したがって、本発明は上記問題点を解決し、極めて精度良く蛍光物質の含有量及び分布を均一とさせ発光特性の優れた、歩留りの高い発光ダイオードを提供することにある。
【０００７】
【課題を解決するための手段】
本発明者は種々実験の結果、蛍光物質を利用した発光ダイオードにおいて、発光ダイオード間のバラツキや発光ダイオードの色むらや発光むらは、蛍光物質の分布に大きく起因していること及び特定の形成方法により制御しうることを見出し本発明を成すに至った。
【０００８】
即ち、蛍光物質が含有された液状の透光性樹脂を発光素子が配置された上に注入して形成させる場合、注型での充填性を考慮し、粘度が５００〜１０００ｃｐｓ程度の低粘度のものが用いられる。蛍光物質と樹脂との比重が大きく異なるため、このような透光性樹脂中に蛍光物質を混合すると、両者は容易に分離する。したがって、軽い有機蛍光物質などを利用した場合は浮遊し、重い無機蛍光物質などを利用した場合は沈降する傾向にある。このような分離は蛍光物質の分散不均一を生ずる。
【０００９】
特に、バッチ式に樹脂と蛍光物質を混合した混合体を少量ずつ注型していく方法を繰り返して製造する場合、混合体の樹脂と蛍光物質の分離は時間と共に進行する。したがって、混合直後に注型して製造された発光ダイオードと、混合後しばらく後に注型して製造された発光ダイオードでは、蛍光物質の含有量が異なってしまう傾向にある。
【００１０】
また、注型が完了した発光ダイオードを加熱硬化させる時、樹脂が固体化するまでの間、温度上昇に伴い粘度が低下する。そのため、キャスティングケース内でも樹脂と蛍光物質の比重差による分離が発生し易い傾向にある。特に、発光素子からの可視発光と蛍光物質からの可視蛍光との混色光を発生させる発光ダイオードにおいては、蛍光物質の含有量変化及び封止樹脂内での分布不均一がすべて発光色の色温度変化として顕著に現れる。このような問題を以下の本発明によって解決することができる。即ち、本発明は、発光素子と、該発光素子からの発光の少なくとも一部を吸収し蛍光を発する蛍光物質を含有する透光性樹脂とを有し、前記発光素子からの発光と前記蛍光物質からの蛍光との白色系混色光を発光する発光ダイオードの形成方法であって、成型前に蛍光物質と固体状の透光性樹脂とを均一に混合する第一の工程と、固体状の透光性樹脂を軟化させて、発光素子が固定された金型中に射出・注入し、該発光素子の少なくとも一部を被覆する第二の工程と、再び上記透光性樹脂を固体状とする第三の工程と、発光素子の少なくとも一部が被覆された蛍光物質含有透光性樹脂の外側に透光性樹脂を注型成型にて形成させる第四の工程と、を有する発光ダイオードの形成方法である。蛍光物質含有透光性樹脂は射出成型によって発光素子の少なくとも一部を被覆してなる。これによって、制御性よく均一発光可能な発光ダイオードとすることができる。
【００１１】
特に、本発明の発光ダイオードの形成方法は、発光素子の少なくとも一部が被覆された蛍光物質含有透光性樹脂の外側に透光性樹脂を注型成型にて形成させる第四の工程を有する。これにより、封止部材のレンズ作用のバラツキを防止することができる。
【００１２】
また、本発明の発光ダイオードの形成方法は、第三の工程によって再び固体状とされた前記蛍光物質含有透光性樹脂を硬化させる工程を有することもできる。
【００１３】
また、本発明の発光ダイオードの形成方法は、発光素子の発光層が少なくとも窒化物半導体からなると共に蛍光物質がセリウムで付活されたイットリウム・アルミニウム・ガーネット系蛍光体（以下、ＹＡＧ蛍光体と呼ぶこともある。）である。これにより、形成された発光ダイオード間のバラツキがより少なく発光むらや色むらの少ない白色光が発光可能な発光ダイオードを形成させることができる。
【００１４】
【発明の実施の形態】
本発明の実施態様例による発光ダイオードとして図１に、白色発光可能な発光ダイオード１００の模式的断面図を示してある。銅あるいは鉄系合金材の表面に銀あるいは金等のメッキ処理が施されたマウント・リード１０４の先端にＬＥＤチップを搭載するカップ上部を有する。搭載されたＬＥＤチップは単体では青色系の可視光を発光する発光素子１０３であり、マウント部材１０６となるエポキシ樹脂によりマウント固着されている。発光素子１０３の各電極は、金等よりなるワイヤ１０７でマウント・リード１０４及びインナー・リード１０５とワイヤボンド結合している。耐熱性に優れた透光性樹脂１０１としてノルボネン系樹脂、ポリメチルペンテン樹脂（ＴＰＸ）、非晶質ナイロン樹脂などの熱可塑性樹脂や脂環式エポキシ樹脂や含窒素エポキシ樹脂等の熱硬化性樹脂によって封止してある。透光性樹脂中には、青色光を照射すると黄色の蛍光を発するＣｅで付活されたＹＡＧ蛍光体１０２を約５質量％混合してある。
【００１５】
発光ダイオードは、リードフレームにＬＥＤチップをマウント、ワイヤボンドしたものを成形型にインサートし、１個が数十ｍｍ3程度のペレット状の樹脂とＹＡＧ蛍光体をホッパに攪拌しながら収容したもの、或いは予め樹脂ペレット内にＹＡＧ蛍光体を混ぜ込んだものをホッパ内に収容した射出成形機で、射出成形し封止する。射出成型は樹脂を成型機のスクリュー内で数秒程度の短時間で加熱溶融、攪拌圧送し、型内に樹脂を注入し、型内に注入された樹脂は速やかに冷却され、数十秒で固化する。
【００１６】
本発明で透光性樹脂は、成型前状態において固体状とできる。成型機投入前に均一に樹脂ペレットと蛍光物質とを混合しておけば、液体のように樹脂中の蛍光物質が自由に沈降あるいは浮遊することはない。そのため、蛍光物質の混合状態は型内に投入前の状態まま保持される。また、成形時に樹脂が溶融し液体で存在する期間は数分から数十秒と、注型成形により熱硬化形成する方法の数時間と比較して極めて短い。また、射出される際にスクリューで加圧攪拌される場合、樹脂中での蛍光物質の分布はより均一にすることができる。さらに、固化までの時間も極めて短く樹脂と蛍光物質との分離もほとんど発生しない。
【００１７】
すなわち、成形前及び成形後固化までの間に樹脂と蛍光物質との分離が極めて発生し難い。これにより本発明の発光ダイオードでは、樹脂と蛍光物質の比重差によらず樹脂中に均一分散させることができる。そのため、発光ダイオード内の蛍光物質の分布均一だけでなく、製造ロット毎の蛍光物質の含有量バラツキも極めて少ない。
【００１８】
特にＹＡＧ：Ｃｅ蛍光体を蛍光物質として含有した白色発光が可能な発光ダイオードとした場合、樹脂に較べ比重の大きいＹＡＧ：Ｃｅ蛍光体でも常時極めて均一な分布のものができる。そのため色温度の均一な発光ダイオードが安定して形成し得る。以下、本発明に用いられる各構成について詳述する。
【００１９】
（射出成形機４００）
本発明に用いられる射出成形機４００としては、図４の如き蛍光物質含有の透光性樹脂を加熱溶融させプランジャー４０２でノズルを通して金型４０５内に射出し成形させられるために好適に用いられる。したがって、射出成型機は予め蛍光物質が一定量含有された透光性樹脂のペレット４０１を軟化溶融させ射出するためのプランジャー、プランジャーで押し出される融解樹脂を金型内に導くノズル及び成型品の形を与える金型から主として構成することができる。特に、発光ダイオードが発光素子からの可視光と、この可視光によって励起されると共に発光する蛍光物質との混色発光させる場合、混合分布量がごく微少量でも異なるとその発光色の変動が大きくなる。そのため、蛍光物質が含有された透光性樹脂を予備可塑化装置などを利用して撹拌溶融させることが好ましい。このような撹拌は、透光性樹脂中に含有される蛍光物質の密度が変化しない限り連続的、間欠的になど種々行うことができる。また、撹拌回転数は撹拌部となるスクリュー４０３の大きさ、蛍光物質の粒径や形状、バインダーの粘度、材質などによって種々選択させることができる。
【００２０】
（透光性樹脂１０１）
本発明に用いられる透光性樹脂は蛍光物質を内部に含有させ射出により一定の形状をとることができる樹脂である。具体的には、ノルボネン樹脂、ポリメチルペンテン樹脂、非晶質ナイロン樹脂、ポリアリレートやポリカーボネート樹脂など透光性がありかつ耐熱性に優れた熱可塑性樹脂、ポリアミドや酢酸ビニル等の１００℃から２６０℃程度の比較的低温、１から２５Ｋｇｆ／ｃｍ2程度の比較的低圧にていわゆるホットメルト成形と称される射出成形が可能でかつ透光性を有する熱可塑性樹脂及び脂環式エポキシ樹脂、含窒素エポキシ樹脂等の熱硬化性樹脂が好適に挙げられる。これらの樹脂中に蛍光物質を溶融分散させ一定の大きさに形成させることで射出形成の軟化溶融材料となるペレットなどとすることができる。これらの透光性樹脂には所望の波長をカットする着色剤、所望の光を拡散させる拡散材、樹脂の耐光性を高める紫外線吸収剤、酸化防止剤や硬化促進剤など種々の添加剤を含有させることができる。
【００２１】
（蛍光物質１０２）
本発明に用いられる蛍光物質としては、発光素子から発光された電磁波で励起されて蛍光を発する蛍光物質をいう。蛍光物質は一般に発光波長よりも励起波長が短波長の方が効率が良いため、発光素子からの発光波長よりも長波長の蛍光を発する蛍光体を用いることが好ましい。具体的蛍光物質として青色の発光素子との混色により白色を発光させるためには、セリウムで付活されたイットリウム・アルミニウム・ガーネット系蛍光体、ペリレン系誘導体、銅で付活されたセレン化亜鉛など種々のものが挙げられる。特に、イットリウム・アルミニウム・ガーネット系蛍光体は、発光素子に窒化物半導体を用いた場合、耐光性や効率などの観点から特に好ましい。
【００２２】
セリウムで付活されたイットリウム・アルミニウム・ガーネット系蛍光体は、ガーネット構造のため、熱、光及び水分に強く、励起スペクトルのピークが４５０ｎｍ付近にさせることができる。また、発光ピークも５３０ｎｍ付近にあり７００ｎｍまで裾を引くブロードな発光スペクトルを持たすことができる。なお、本発明においてセリウムで付活されたイットリウム・アルミニウム・ガーネット系蛍光体とは、最も広義に解釈するものとしてＹ3Ａｌ5Ｏ12：Ｃｅのイットリウム（Ｙ）の代わりにＬｕ、Ｓｃ、Ｌａ、Ｇｄ、Ｓｍから選択される少なくとも一種と置き換えることができるものである。また、アルミニウム（Ａｌ）の代わりにＧａ、Ｉｎ、Ｂ、Ｔｌから選択される少なくとも一種と置き換えることができるものである。組成を変化させることで発光色を連続的に調節することが可能である。即ち、長波長側の強度がＧｄの組成比で連続的に変えられるなど窒化物半導体の青色系発光を白色系発光に変換するための理想条件を備えている。同様に、Ｌｕ、Ｌｃ、ＳｃやＳｍなどを加えて所望の特性を得るようにしても良い。
【００２３】
このような蛍光物質は、Ｙ、Ｇｄ、Ｃｅ、Ｓｍ、Ｌａ、Ａｌ及びＧａの原料として酸化物、又は高温で容易に酸化物になる化合物を使用し、それらを化学量論比で十分に混合して原料を得る。又は、Ｙ、Ｇｄ、Ｃｅ、Ｓｍ、Ｌａの希土類元素を化学量論比で酸に溶解した溶解液を蓚酸で共沈したものを焼成して得られる共沈酸化物と、酸化アルミニウム、酸化ガリウムとを混合して混合原料を得る。これにフラックスとしてフッ化アンモニウム等のフッ化物を適量混合して坩堝に詰め、空気中１３５０〜１４５０°Ｃの温度範囲で２〜５時間焼成して焼成品を得、次に焼成品を水中でボールミルして、洗浄、分離、乾燥、最後に篩を通すことで得ることができる。
【００２４】
本発明の発光ダイオードにおいて、このような蛍光物質を２種類以上混合させてもよい。具体的には、Ａｌ、Ｇａ、Ｙ及びＧｄ、ＬａやＳｍの含有量が異なる２種類以上のセリウムで付活されたイットリウム・アルミニウム・ガーネット系蛍光体を混合させてＲＧＢの波長成分を増やすことなどができる。このような場合、異なる蛍光物質間の比重が異なっていても量産性よく発光特性の均一な発光ダイオードを形成することができる。
【００２５】
（発光素子１０３、２０３）
本発明に用いられる発光素子１０３とは、蛍光物質を励起可能な発光波長を発光できる発光層を有する半導体発光素子である。このような半導体発光素子としてＺｎＳｅやＧａＮなど種々の半導体を挙げることができるが、蛍光物質を効率良く励起できる短波長が発光可能な窒化物半導体（ＩｎXＡｌYＧａ1-X-YＮ、０≦Ｘ、０≦Ｙ、Ｘ＋Ｙ≦１）が好適に挙げられる。半導体の構造としては、ＭＩＳ接合、ＰＩＮ接合やｐｎ接合などを有するホモ構造、ヘテロ構造あるいはダブルへテロ構成のものが挙げられる。半導体層の材料やその混晶度によって発光波長を種々選択することができる。また、半導体活性層を量子効果が生ずる薄膜に形成させた単一量子井戸構造や多重量子井戸構造とすることもできる。
【００２６】
窒化物半導体を使用した場合、半導体用基板にはサファイヤ、スピネル、ＳｉＣ、Ｓｉ、ＺｎＯ等の材料が好適に用いられる。結晶性の良い窒化物半導体を量産性よく形成させるためにはサファイヤ基板を用いることが好ましい。このサファイヤ基板上にＭＯＣＶＤ法などを用いて窒化物半導体を形成させることができる。サファイア基板上にＧａＮ、ＡｌＮ、ＧａＡＩＮ等のバッファー層を形成しその上にｐｎ接合を有する窒化物半導体を形成させる。
【００２７】
窒化物半導体を使用したｐｎ接合を有する発光素子例として、バッファ層上に、ｎ型窒化ガリウムで形成した第１のコンタクト層、ｎ型窒化アルミニウム・ガリウムで形成させた第１のクラッド層、窒化インジウム・ガリウムで形成した活性層、ｐ型窒化アルミニウム・ガリウムで形成した第２のクラッド層、ｐ型窒化ガリウムで形成した第２のコンタクト層を順に積層させたダブルへテロ構成などが挙げられる。
【００２８】
窒化物半導体は、不純物をドープしない状態でｎ型導電性を示す。発光効率を向上させるなど所望のｎ型窒化物半導体を形成させる場合は、ｎ型ドーパントとしてＳｉ、Ｇｅ、Ｓｅ、Ｔｅ、Ｃ等を適宜導入することが好ましい。一方、ｐ型窒化物半導体を形成させる場合は、ｐ型ドーパントであるＺｎ、Ｍｇ、Ｂｅ、Ｃａ、Ｓｒ、Ｂａ等をドープさせる。窒化物半導体は、ｐ型ドーパントをドープしただけではｐ型化しにくいためｐ型ドーパント導入後に、炉による加熱やプラズマ照射等により加熱処理することで低抵抗化させることが好ましい。電極形成後、半導体ウエハーからチップ状にカットさせることで窒化物半導体からなる発光素子を形成させることができる。
【００２９】
本発明の発光ダイオードにおいて白色系を発光させる場合は、蛍光物質からの発光波長との補色関係や透光性樹脂の劣化等を考慮して発光素子の発光波長は４００ｎｍ以上５３０ｎｍ以下が好ましく、４２０ｎｍ以上４９０ｎｍ以下がより好ましい。発光素子と蛍光物質との励起、発光効率をそれぞれより向上させるためには、４５０ｎｍ以上４７５ｎｍ以下がさらに好ましい。なお、４００ｎｍより短い紫外域の波長を利用できることは言うまでもない。
【００３０】
（マウント・リード１０４、２０４）
マウント・リード１０４としては、発光素子を配置させるものであり、ダイボンド機器などで積載するのに十分な大きさがあれば良い。また、発光素子を複数設置しマウント・リードを発光素子の共通電極として利用する場合においては、十分な電気伝導性とボンディングワイヤ等との接続性が求められる。また、マウント・リード上のカップ内に発光素子を配置すると共に蛍光体を内部に充填させる場合は、近接して配置させた別の発光ダイオードからの光により疑似点灯することを防止することができる。
【００３１】
発光素子とマウント・リードのカップとの接着はマウント部材１０６として熱硬化性樹脂などによって行うことができる。具体的には、エポキシ樹脂、アクリル樹脂、シリコン樹脂やイミド樹脂などが挙げられる。また、フリップチップ型の発光素子によりマウント・リードと接着させると共に電気的に接続させるためにはＡｇペースト、Ｃｕペースト、カーボンペースト、金属バンプや金属酸化物が含有された樹脂等を用いることができる。また、マウント・リードの具体的な電気抵抗としては３００μΩ・ｃｍ以下が好ましく、より好ましくは、３μΩ・ｃｍ以下である。また、マウント・リード上に複数の発光素子を積載する場合は、発光素子からの発熱量が多くなるため熱伝導度がよいことが求められる。具体的には、０．０１ｃａｌ／ｃｍ2／ｃｍ／℃以上が好ましくより好ましくは ０．５ｃａｌ／ｃｍ2／ｃｍ／℃以上である。これらの条件を満たす材料としては、鉄、銅、鉄入り銅、錫入り銅、メタライズパターン付きセラミック等が挙げられる。
【００３２】
（インナー・リード１０５、２０５）
インナー・リードとしては、マウント・リード上に配置された発光素子と導電性ワイヤなどを介して電気的に接続を図るものである。インナー・リードは、ボンディングワイヤ等との接続性及び電気伝導性が良いことが求められる。具体的な電気抵抗としては、３００μΩ・ｃｍ以下が好ましく、より好ましくは３μΩ・ｃｍ以下である。これらの条件を満たす材料としては、鉄、銅、鉄入り銅、錫入り銅及び銅、金、銀をメッキしたアルミニウム、鉄、銅等が挙げられる。
【００３３】
（ワイヤ１０７、２０７）
ワイヤ１０７としては、発光素子の電極とのオーミック性、密着性、電気伝導性及び熱伝導性がよいものが求められる。熱伝導度としては０．０１ｃａｌ／ｃｍ2／ｃｍ／℃以上が好ましく、より好ましくは０．５ｃａｌ／ｃｍ2／ｃｍ／℃以上である。また、作業性などを考慮してワイヤの直径は、好ましくは、Φ１０μｍ以上、Φ４５μｍ以下である。このようなワイヤとして具体的には、金、銅、白金、アルミニウム等の金属及びそれらの合金を用いたワイヤが挙げられる。このようなワイヤは、各発光素子の電極と、インナー・リード及びマウント・リードなどとをワイヤボンディング機器によって容易に接続させることができる。
【００３４】
（モールド部材２０８）
モールド部材２０８は、発光ダイオードの使用用途に応じて発光素子１０３、ワイヤ１０７、蛍光物質１０２などを外部から保護するために設けることができる。モールド部材は、一般には樹脂を用いて形成させることができる。また、蛍光体を含有させることによって視野角を増やすことができるが、樹脂モールドに拡散剤を含有させることによって発光素子からの指向性を緩和させ視野角をさらに増やすことができる。更にまた、モールド部材を所望の形状にすることによって発光素子からの発光を集束させたり拡散させたりするレンズ効果を持たせることができる。したがって、モールド部材は複数積層した構造でもよい。具体的には、凸レンズ形状、凹レンズ形状さらには、発光観測面から見て楕円形状やそれらを複数組み合わせた物である。モールド部材の具体的材料としては、主としてエポキシ樹脂、ユリア樹脂、シリコーン樹脂などの耐候性に優れた透明樹脂や硝子などが好適に用いられる。また、拡散剤としては、チタン酸バリウム、酸化チタン、酸化アルミニウム、酸化珪素等が好適に用いられる。また、屈折率差を考慮してモールド部材と結着剤とを同じ材質のものを用いて形成させても良い。以下、本発明の具体的実施例について詳述するがこれのみに限定されないことは言うまでもない。
【００３５】
【実施例】
（実施例１）
ＬＥＤチップは、発光層として発光ピークが４５０ｎｍのＩｎ0.2Ｇａ0.8Ｎ半導体を用いた。ＬＥＤチップは、洗浄させたサファイヤ基板上にＴＭＧ（トリメチルガリウム）ガス、ＴＭＩ（トリメチルインジウム）ガス、窒素ガス及びドーパントガスをキャリアガスと共に流し、ＭＯＣＶＤ法で窒化物半導体を成膜させることにより形成させた。ドーパントガスとしてＳｉＨ4とＣｐ2Ｍｇとを切り替えることによってｎ型やｐ型導電性の窒化物半導体を形成させる。発光素子としてはｎ型導電性を有する窒化ガリウム半導体であるコンタクト層と、ｐ型導電性を有する窒化アルミニウムガリウム半導体であるクラッド層、ｐ型導電性を有する窒化ガリウムであるコンタクト層を形成させた。ｎ型コンタクト層とｐ型クラッド層との間に厚さ約３ｎｍであり、単一量子井戸構造となるＩｎＧａＮの活性層を形成してある。（なお、サファイヤ基板上には低温で窒化ガリウムを形成させバッファ層とさせてある。また、ｐ型半導体は、成膜後４００℃以上で熱処理させてある。）
エッチングによりサファイア基板上の窒化物半導体に同一面側で、ｐｎ各コンタクト層表面を露出させる。各コンタクト層上に、スパッタリング法を用いて正負各台座電極をそれぞれ形成させた。なお、ｐ型窒化物半導体上の全面には金属薄膜を透光性電極として形成させた後に、透光性電極の一部に台座電極を形成させてある。出来上がった半導体ウエハーをスクライブラインを引いた後、外力により分割させ半導体発光素子であるＬＥＤチップを形成させた。
【００３６】
一方、打ち抜き及びスタンピングによりタイバーで接続されマウント・リード先端にカップが形成された鉄入り銅製リードフレームを形成する。ＬＥＤチップはエポキシ樹脂を用いて銀メッキした鉄入り銅製リードフレームの先端カップ内にダイボンドした。ＬＥＤチップの各電極と、カップが設けられたマウント・リードやインナー・リードとをそれぞれ金線でワイヤボンディングし電気的導通を取った。
【００３７】
蛍光物質は、Ｙ、Ｇｄ、Ｃｅの希土類元素を化学量論比で酸に溶解した溶解液を蓚酸で共沈させた。これを焼成して得られる共沈酸化物と、酸化アルミニウムと混合して混合原料を得る。これにフラックスとしてフッ化アンモニウムを混合して坩堝に詰め、空気中１４００°Ｃの温度で３時間焼成して焼成品を得た。焼成品を水中でボールミルして、洗浄、分離、乾燥、最後に篩を通して形成させた。
【００３８】
形成された（Ｙ0.8Ｇｄ0.2）3Ａｌ5Ｏ12：Ｃｅ蛍光物質２５重量部、ポリカーボネート樹脂１００重量部をよく混合して１個が十ｍｍ3程度のペレットとさせた。このペレットを図４に示す射出成型機のホッパ中に入れた。他方、リード端子と電気的に接続されたＬＥＤチップを金型中に入れ固定させる。ペレットを加熱可塑化させ撹拌させながらプランジャーにより射出温度２８０℃射出圧力８００ｋｇｆ／ｃｍ2で金型中に注入した。金型を冷却後、樹脂モールドされたリードを取り出しタイバーを切断することでＬＥＤチップ、マウント・リード及びインナー・リードの一部を蛍光物質が含有された熱可塑性樹脂で被覆して砲弾型に形成された発光ダイオードを得ることができる。こうした発光ダイオードを５００個形成させバラツキを測定した。得られた白色系が発光可能な発光ダイオードの色度点を測定しＣＩＥ座標上にプロットした。また、一個ずつの発光ダイオードにおいて外観上の発光むらがないことを確認した。なお、砲弾型発光ダイオードだけではなく、チップタイプＬＥＤやセグメントディスプレイなどにおいても利用することができることは言うまでもない。
【００３９】
（比較例）
（Ｙ0.8Ｇｄ0.2）3Ａｌ5Ｏ12：Ｃｅ蛍光物質をエポキシ樹脂中に混合したものを用いて注型によりカップ内に配置させた後に、硬化形成した以外は実施例１と同様の発光ダイオードを形成させた。形成された発光ダイオードの５００個平均と実施例１の発光ダイオードとを比較して色温度の製造バラツキを調べた。比較例の発光ダイオードに較べ実施例の発光ダイオードは、色温度の製造バラツキが明らかに小さくなった。なお、比較例の発光ダイオードは、モールド部材の先端に蛍光物質が固まった状態であった。
【００４０】
（実施例２）
図２に示すようにＬＥＤチップ２０３周辺を上述と同様の蛍光物質２０２を含有した熱可塑性樹脂２０１で射出成形封止した後、注型成形にて透光性のエポキシ樹脂をモールド部材２０８として外側に形成した以外は実施例１と同様にして発光ダイオード２００を形成させた。これにより、上述の硬化に加え、射出成形時に封止樹脂表面に型のミスマッチやバリが発生しても、これをさらに注型で覆うことができる。そのため、封止樹脂のレンズ作用のバラツキや発光ダイオード実装時のバリ脱落によるはんだ付け不良等が防止される。また、比較的高価な高透光性かつ高耐熱性の熱可塑性樹脂の使用量を減らすことも可能である。
【００４１】
（実施例３）
図３に示すように表面実装型の発光ダイオード３００を形成させた。ＬＥＤチップ３０３は、発光層として発光ピークが４７５ｎｍのＩｎ0.2Ｇａ0.8Ｎ半導体を有する窒化物半導体素子を用いた。より具体的にはＬＥＤチップ３０３は、洗浄させたサファイヤ基板上にＴＭＧ（トリメチルガリウム）ガス、ＴＭＩ（トリメチルインジウム）ガス、窒素ガス及びドーパントガスをキャリアガスと共に流し、ＭＯＣＶＤ法で窒化物半導体を成膜させることにより形成させることができる。ドーパントガスとしてＳｉＨ4とＣｐ2Ｍｇを切り替えることによってｎ型窒化物半導体やｐ型窒化物半導体となる層を形成させる。
【００４２】
ＬＥＤチップの素子構造としてはサファイア基板上に、アンドープの窒化物半導体であるｎ型ＧａＮ層、Ｓｉドープのｎ型電極が形成されｎ型コンタクト層となるＧａＮ層、アンドープの窒化物半導体であるｎ型ＧａＮ層、次に発光層を構成するバリア層となるＧａＮ層、井戸層を構成するＩｎＧａＮ層、バリア層となるＧａＮ層を１セットとしＧａＮ層に挟まれたＩｎＧａＮ層を５層積層させた多重量子井戸構造としてある。発光層上にはＭｇがドープされたｐ型クラッド層としてＡｌＧａＮ層、Ｍｇがドープされたｐ型コンタクト層であるＧａＮ層を順次積層させた構成としてある。（なお、サファイヤ基板上には低温でＧａＮ層を形成させバッファ層とさせてある。また、ｐ型半導体は、成膜後４００℃以上でアニールさせてある。）
エッチングによりサファイア基板上の窒化物半導体に同一面側で、ｐｎ各コンタクト層表面を露出させる。各コンタクト層上に、スパッタリング法を用いて正負各台座電極をそれぞれ形成させた。なお、ｐ型窒化物半導体上の全面には金属薄膜を透光性電極として形成させた後に、透光性電極の一部に台座電極を形成させてある。出来上がった半導体ウエハーをスクライブラインを引いた後、外力により分割させ半導体発光素子であるＬＥＤチップを形成させた。
【００４３】
一方、打ち抜き及び射出成形により一対のリード電極３０４、３０５となる金属片が絶縁性樹脂３０９によって固定された基板を形成する。ＬＥＤチップ３０３はエポキシ樹脂３０６を用いて銀メッキした鉄入り銅製のリード電極上にダイボンドした。ＬＥＤチップの各電極と、各リード電極とをそれぞれ金線３０７でワイヤボンディングし電気的導通を取った。
【００４４】
蛍光物質３０２は、Ｙ、Ｇｄ、Ｃｅの希土類元素を化学量論比で酸に溶解した溶解液を蓚酸で共沈させた。これを焼成して得られる共沈酸化物と、酸化アルミニウムと混合して混合原料を得る。これにフラックスとしてフッ化アンモニウムを混合して坩堝に詰め、空気中１４００°Ｃの温度で３時間焼成して焼成品を得た。焼成品を水中でボールミルして、洗浄、分離、乾燥、最後に篩を通して形成させた。
【００４５】
形成された（Ｙ0.6Ｇｄ0.4）3Ａｌ5Ｏ12：Ｃｅ蛍光物質２５重量部、含窒素エポキシ樹脂であるトリグリシジルイソシアヌレート１００重量部と酸無水物及び硬化促進剤を６５℃で撹拌させ２４時間反応させ室温で冷却する。この反応によりある程度硬化させた固体となる。室温に冷却後、取り出した固体を粉砕しプレスして固体状のタブレットを形成させる。なお、蛍光物質を透光性樹脂中に含有させたタブレットを形成させるためには、上述のように原材料透光性樹脂中に含有させても良いし、均一性を保てる限りにおいて、ある程度硬化させた透光性樹脂粉体と蛍光物質とを混合撹拌させ固めたタブレットを利用することもできる。
【００４６】
次にポットを加熱後、上記で形成させたＬＥＤチップと導通を取った基板が配置された金型に軟化させたタブレットを射出させ１５０℃５分で一時硬化させた。次に、金型から射出成形させた発光ダイオードを取り出した後、１５０℃４時間で二次硬化させた。蛍光物質が含有された透光性樹脂３０１は、ＬＥＤチップが配置された基板上に突出した形状で形成させることができた。
【００４７】
形成させたチップタイプＬＥＤは上述と同様に形成された発光ダイオードのばらつきが極めて少ないと共に各発光ダイオードの色むらが極めて少ない白色ＬＥＤとすることができる。また、蛍光物質を含有させた樹脂を維持させるためにキャビティー構造となる側壁を形成させる必要もなく極めて小型な白色発光ダイオードを形成させることができる。さらに、ある程度硬化させたとはいえ熱硬化性樹脂を用いるため、射出成型時に比較的粘度が高い熱可塑性樹脂を用いた場合と比較してＬＥＤチップを電気的に接続させるワイヤなどの損傷を防ぎつつ形成させることができる。
【００４８】
【発明の効果】
本発明による製造方法を用いることによって、発光特性が安定した蛍光物質を有する白色系が発光可能な発光ダイオードを量産性良く製造させることができる。また、長時間量産時においても最初に形成された発光ダイオードと、後に形成された発光ダイオード間の発光ばらつきが極めて小さくさせることができる。さらに、比較的簡便に形成された発光ダイオード内における発光むらを低減させることができるため量産性と歩留りを向上させることができる。
【図面の簡単な説明】
【図１】図１は本発明の発光ダイオードを示す模式的断面図である。
【図２】図２は本発明の他の発光ダイオードを示す模式的断面図である。
【図３】図３は本発明の別の発光ダイオードを示す模式的断面図である。
【図４】図４は本発明の製造に用いられる射出成型機の模式的断面図である。
【符号の説明】
１００、２００、３００・・・発光ダイオード
１０１、２０１、３０１・・・蛍光物質を含有する透光性樹脂
１０２、２０２、３０２・・・蛍光物質
１０３、２０３、３０３・・・発光素子
１０４、２０４・・・マウント・リード
１０５、２０５・・・インナー・リード
１０６、２０６、３０６・・・ＬＥＤを接着させるマウント部材
１０７、２０７、３０７・・・ワイヤ
２０８・・・モールド部材
３０４、３０５・・・リード電極
３０９・・・リード電極間を絶縁する樹脂
４００・・・射出成形機
４０１・・・ペレット
４０２・・・射出ピストン
４０３・・・スクリュー
４０４・・・電熱線
４０５・・・金型
４０６・・・発光素子がマウントされたマウントリード[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light-emitting diode that emits light by converting at least a part of the emission wavelength emitted from a light-emitting element with a fluorescent substance, and in particular, uneven light emission, uneven color and light-emitting variation between the formed light-emitting diodes and a low yield. It concerns high light emitting diodes.
[0002]
[Prior art]
The semiconductor light emitting device is small and efficiently emits bright colors. In addition, the ball is not broken because of the semiconductor element. It has excellent driving characteristics and is resistant to vibration and ON / OFF lighting. Therefore, it is used as various indicators and various light sources. However, since such a light emitting element has a monochromatic peak wavelength, even when only white light (white, pink, light bulb color, etc.) is obtained, two or more kinds of light emitting elements must be used. Was. Further, various luminescent colors could not be easily obtained.
[0003]
2. Description of the Related Art A light emitting diode which emits various light colors using an LED chip emitting a monochromatic peak wavelength and a fluorescent substance is disclosed in, for example, JP-A-7-99345. These light-emitting diodes can be composed of a resin in which the light-emitting chip is mounted on the bottom of a cup that reflects light emitted from the light-emitting chip toward the light emission observation surface side, and which is filled in the cup and a resin that covers the whole. The resin filled therein contains a fluorescent substance that absorbs light from the light emitting chip and converts the wavelength.
[0004]
The resin containing the fluorescent substance is dropped into a cup on which a light emitting element is mounted, such as a liquid epoxy resin, and is heated and cured to form a color conversion member. The resin other than the inside of the cup is formed by immersing the tip of the frame member on which the color conversion member and the light emitting chip are formed in a casting case in which a liquid epoxy resin or the like is cast, and placing it in an oven and heating and curing. . Thus, a light emitting diode in which the emission wavelength from the light emitting chip is wavelength-converted by the fluorescent substance can be obtained. For example, a light-emitting diode capable of emitting white light by mixing color of blue light from an LED chip and light from a phosphor that absorbs the blue light and emits a yellow light in a complementary color relationship can be obtained. .
[0005]
In order to emit a desired white light or the like using such a light emitting diode, it is necessary to emit each light with extremely high accuracy and to perform color mixing adjustment. The light from the LED chip can be adjusted by its semiconductor and driving current. On the other hand, the wavelength-converted light from the fluorescent substance can also be adjusted to some extent by controlling the composition and particle size of the fluorescent substance.
[0006]
[Problems to be solved by the invention]
However, since the fluorescent substance itself has no or weak adhesive force, in order to arrange and fix it on the light emitting element, it is necessary to use a light emitting element and a fluorescent substance each in a binder having an adhesive property capable of emitting light, such as in various resins. Must be included. Regarding the fluorescent substance contained in such a binder, the amount of light emitted from the LED chip and the amount of light emitted from the fluorescent substance largely depend on the content and distribution of the fluorescent substance. When these cannot be controlled, and when the visible light emitted from the light emitting element and the light emitted from the fluorescent substance are expressed in color by mixing the visible light, the difference between the respective visible light amounts becomes a serious problem. In particular, the white system poses a serious problem since human eyes can identify even a slight color temperature difference. Accordingly, an object of the present invention is to solve the above problems and to provide a high-yield light emitting diode having excellent emission characteristics by making the content and distribution of the fluorescent substance uniform with high accuracy.
[0007]
[Means for Solving the Problems]
As a result of various experiments, the present inventor has found that, in a light emitting diode using a fluorescent substance, variations between the light emitting diodes and uneven color and uneven light emission of the light emitting diode largely depend on the distribution of the fluorescent substance and a specific forming method. And found that the present invention can be controlled.
[0008]
That is, in the case where a liquid translucent resin containing a fluorescent substance is injected and formed on the light emitting element, the viscosity is as low as about 500 to 1000 cps in consideration of the filling property in casting. Things are used. Since the specific gravity of the fluorescent substance is significantly different from that of the resin, when the fluorescent substance is mixed in such a translucent resin, the two are easily separated. Therefore, when a light organic fluorescent substance is used, it tends to float, and when a heavy inorganic fluorescent substance is used, it tends to settle. Such separation results in non-uniform dispersion of the phosphor.
[0009]
In particular, when a method of repeatedly casting a mixture of a resin and a fluorescent substance in a batch manner by small amounts is manufactured repeatedly, the separation of the resin and the fluorescent substance of the mixture proceeds with time. Therefore, the content of the fluorescent substance tends to be different between a light emitting diode manufactured by casting immediately after mixing and a light emitting diode manufactured by casting a while after mixing.
[0010]
In addition, when the light emitting diode for which casting is completed is cured by heating, the viscosity decreases as the temperature increases until the resin is solidified. Therefore, even in the casting case, separation due to a difference in specific gravity between the resin and the fluorescent substance tends to occur easily. In particular, in a light emitting diode that generates mixed light of visible light emission from a light emitting element and visible fluorescent light from a fluorescent substance, the change in the content of the fluorescent substance and the uneven distribution in the sealing resin are all caused by the color temperature of the emission color. Appears remarkably as a change. Such a problem can be solved by the present invention described below. That is, the present invention has a light-emitting element and a light-transmitting resin containing a fluorescent substance that absorbs at least a part of light emitted from the light-emitting element and emits fluorescence, and emits light from the light-emitting element and the fluorescent substance. A method for forming a light emitting diode that emits white-colored mixed light with fluorescent light from a substrate, comprising: a first step of uniformly mixing a fluorescent substance and a solid translucent resin before molding; A second step of softening the light-sensitive resin, injecting and injecting the light-emitting element into a mold in which the light-emitting element is fixed, and covering at least a part of the light-emitting element, and solidifying the light-transmitting resin again A third step, Fourth step of forming the light-transmitting resin by casting on the outside of the phosphor-containing light-transmitting resin in which at least a part of the light emitting element is coated And a method for forming a light emitting diode comprising: The fluorescent substance-containing translucent resin covers at least a part of the light emitting element by injection molding. Thus, a light emitting diode capable of emitting light uniformly with good controllability can be obtained.
[0011]
In particular, the method for forming a light-emitting diode of the present invention has a fourth step of forming a light-transmitting resin by casting on the outside of a phosphor-containing light-transmitting resin that covers at least a part of the light-emitting element. . Accordingly, it is possible to prevent the lens function of the sealing member from varying.
[0012]
Further, the method for forming a light emitting diode of the present invention may include a step of curing the phosphor-containing translucent resin that has been solidified again in the third step.
[0013]
In the method of forming a light emitting diode according to the present invention, the light emitting layer of the light emitting element is made of at least a nitride semiconductor and the phosphor is activated with cerium. An yttrium aluminum garnet phosphor (hereinafter referred to as a YAG phosphor). Sometimes.) Accordingly, it is possible to form a light emitting diode capable of emitting white light with less variation between the formed light emitting diodes and less light emission unevenness and color unevenness.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a schematic sectional view of a light emitting diode 100 capable of emitting white light as a light emitting diode according to an embodiment of the present invention. It has a cup upper portion for mounting an LED chip on the tip of a mount lead 104 in which the surface of a copper or iron alloy material is plated with silver or gold. The mounted LED chip is a light emitting element 103 that emits blue-based visible light by itself, and is mounted and fixed by an epoxy resin serving as a mounting member 106. Each electrode of the light emitting element 103 is wire-bonded to the mount lead 104 and the inner lead 105 by a wire 107 made of gold or the like. Thermoplastic resin such as norbornene resin, polymethylpentene resin (TPX), amorphous nylon resin and the like, and thermosetting resin such as alicyclic epoxy resin and nitrogen-containing epoxy resin as translucent resin 101 having excellent heat resistance Sealed by. The translucent resin contains about 5% by mass of Ce activated YAG phosphor 102 that emits yellow fluorescence when irradiated with blue light.
[0015]
A light emitting diode is mounted on a lead frame with an LED chip mounted and wire-bonded, and inserted into a molding die. Three Injection molding and sealing with an injection molding machine in which a pellet-shaped resin and YAG phosphor are accommodated in a hopper while stirring, or a resin pellet in which YAG phosphor is mixed in advance is accommodated in a hopper. I do. In the injection molding, the resin is heated and melted in a screw of the molding machine in a short time of about several seconds, stirred and pressure-fed, the resin is injected into the mold, and the resin injected into the mold is quickly cooled and solidified in several tens of seconds I do.
[0016]
In the present invention, the translucent resin can be solid before molding. If the resin pellets and the fluorescent substance are uniformly mixed before being put into the molding machine, the fluorescent substance in the resin does not freely settle or float like liquid. Therefore, the mixed state of the fluorescent substance is maintained in a state before being put into the mold. In addition, the period during which the resin is melted and present as a liquid at the time of molding is several minutes to several tens of seconds, which is extremely short as compared with several hours of the method of thermosetting by casting. Further, when the mixture is pressurized and stirred by a screw at the time of injection, the distribution of the fluorescent substance in the resin can be made more uniform. Furthermore, the time until solidification is extremely short, and there is almost no separation between the resin and the fluorescent substance.
[0017]
That is, it is extremely unlikely that the resin and the fluorescent substance are separated from each other before molding and before solidification after molding. Accordingly, in the light emitting diode of the present invention, the light emitting diode can be uniformly dispersed in the resin regardless of the specific gravity difference between the resin and the fluorescent substance. Therefore, not only the distribution of the fluorescent substance in the light emitting diode is uniform, but also the variation in the content of the fluorescent substance among the production lots is extremely small.
[0018]
In particular, in the case of a light emitting diode capable of emitting white light containing a YAG: Ce phosphor as a phosphor, a YAG: Ce phosphor having a higher specific gravity than a resin can always have an extremely uniform distribution. Therefore, a light emitting diode having a uniform color temperature can be formed stably. Hereinafter, each configuration used in the present invention will be described in detail.
[0019]
(Injection molding machine 400)
The injection molding machine 400 used in the present invention is suitably used because a transparent resin containing a fluorescent substance as shown in FIG. 4 is heated and melted, and is injected into a mold 405 through a nozzle with a plunger 402 to be molded. . Therefore, the injection molding machine is provided with a plunger for softening and injecting a transparent resin pellet 401 containing a predetermined amount of a fluorescent substance in advance, a nozzle for guiding the molten resin extruded by the plunger into a mold, and a molded product. Can be mainly composed of a mold giving the shape of In particular, when the light emitting diode emits mixed color light of the visible light from the light emitting element and a fluorescent substance which emits light while being excited by the visible light, the variation of the emission color becomes large if the amount of the mixed distribution is very small. . Therefore, it is preferable that the translucent resin containing the fluorescent substance is stirred and melted by using a pre-plasticizing device or the like. Such stirring can be performed variously, such as continuously or intermittently, as long as the density of the fluorescent substance contained in the translucent resin does not change. The number of rotations for stirring can be variously selected depending on the size of the screw 403 serving as the stirring section, the particle size and shape of the fluorescent substance, the viscosity and material of the binder, and the like.
[0020]
(Translucent resin 101)
The translucent resin used in the present invention is a resin capable of containing a fluorescent substance therein and taking a certain shape by injection. Specifically, a translucent and heat-resistant thermoplastic resin such as a norbonene resin, a polymethylpentene resin, an amorphous nylon resin, a polyarylate or a polycarbonate resin; Relatively low temperature of about 1 ℃, 1 to 25Kgf / cm Two Thermosetting resins such as thermoplastic resins and alicyclic epoxy resins, and nitrogen-containing epoxy resins that can be injection-molded and so-called hot-melt molding at a relatively low pressure and are preferably cited. Can be By melting and dispersing the fluorescent substance in these resins and forming them into a certain size, pellets or the like that can be used as injection-molded softened molten material can be obtained. These translucent resins contain various additives such as a colorant that cuts the desired wavelength, a diffusing material that diffuses the desired light, an ultraviolet absorber that increases the light resistance of the resin, an antioxidant and a curing accelerator. Can be done.
[0021]
(Fluorescent substance 102)
The fluorescent substance used in the present invention refers to a fluorescent substance that emits fluorescence when excited by an electromagnetic wave emitted from a light emitting element. In general, a fluorescent substance is more efficient when the excitation wavelength is shorter than the emission wavelength, and thus it is preferable to use a phosphor that emits fluorescence having a longer wavelength than the emission wavelength from the light emitting element. In order to emit white light by mixing with a blue light-emitting element as a specific fluorescent substance, yttrium aluminum garnet-based phosphor activated with cerium, perylene-based derivative, zinc selenide activated with copper, etc. Various things are mentioned. In particular, when a nitride semiconductor is used for a light emitting element, an yttrium / aluminum / garnet-based phosphor is particularly preferable in terms of light resistance and efficiency.
[0022]
The yttrium / aluminum / garnet-based phosphor activated with cerium has a garnet structure, and thus is strong against heat, light and moisture, and can have an excitation spectrum peak near 450 nm. Also, the emission peak is around 530 nm, and a broad emission spectrum with a tail extending to 700 nm can be obtained. In the present invention, the yttrium-aluminum-garnet-based phosphor activated with cerium is interpreted in the broadest sense as Y. Three Al Five O 12 : Can be replaced with at least one selected from Lu, Sc, La, Gd and Sm instead of yttrium (Y) of Ce. Further, it can be replaced with at least one selected from Ga, In, B, and Tl instead of aluminum (Al). The emission color can be continuously adjusted by changing the composition. That is, there is an ideal condition for converting blue light emission of the nitride semiconductor into white light emission such that the intensity on the long wavelength side can be continuously changed by the composition ratio of Gd. Similarly, desired characteristics may be obtained by adding Lu, Lc, Sc, Sm, and the like.
[0023]
Such a fluorescent substance uses an oxide or a compound which easily becomes an oxide at a high temperature as a raw material of Y, Gd, Ce, Sm, La, Al and Ga, and sufficiently mixes them in a stoichiometric ratio. To obtain the raw material. Alternatively, a coprecipitated oxide obtained by calcining a solution obtained by dissolving a rare earth element of Y, Gd, Ce, Sm, or La in an acid at a stoichiometric ratio with oxalic acid, aluminum oxide, gallium oxide To obtain a mixed raw material. An appropriate amount of a fluoride such as ammonium fluoride is mixed into the crucible as a flux, and the mixture is baked in air at a temperature of 1350 to 1450 ° C for 2 to 5 hours to obtain a baked product. It can be obtained by ball milling, washing, separating, drying and finally passing through a sieve.
[0024]
In the light emitting diode of the present invention, two or more kinds of such fluorescent substances may be mixed. Specifically, increasing the wavelength components of RGB by mixing yttrium / aluminum / garnet-based phosphors activated with two or more types of cerium having different contents of Al, Ga, Y, Gd, La and Sm. And so on. In such a case, even if the specific gravities of the different fluorescent materials are different, it is possible to form a light emitting diode with uniform light emitting characteristics with good mass productivity.
[0025]
(Light-emitting elements 103 and 203)
The light-emitting element 103 used in the present invention is a semiconductor light-emitting element having a light-emitting layer capable of emitting a light emission wavelength capable of exciting a fluorescent substance. As such a semiconductor light emitting device, various semiconductors such as ZnSe and GaN can be cited, and a nitride semiconductor (In) capable of emitting a short wavelength light capable of efficiently exciting a fluorescent substance can be used. X Al Y Ga 1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1) are preferred. Examples of the semiconductor structure include a homostructure having a MIS junction, a PIN junction, and a pn junction, a heterostructure, and a double heterostructure. Various emission wavelengths can be selected depending on the material of the semiconductor layer and the degree of mixed crystal thereof. Further, a single quantum well structure or a multiple quantum well structure in which the semiconductor active layer is formed as a thin film in which a quantum effect occurs can be used.
[0026]
When a nitride semiconductor is used, a material such as sapphire, spinel, SiC, Si, or ZnO is preferably used for the semiconductor substrate. In order to form a nitride semiconductor having good crystallinity with good mass productivity, it is preferable to use a sapphire substrate. A nitride semiconductor can be formed on the sapphire substrate by using the MOCVD method or the like. A buffer layer of GaN, AlN, GaAIN or the like is formed on a sapphire substrate, and a nitride semiconductor having a pn junction is formed thereon.
[0027]
As an example of a light emitting device having a pn junction using a nitride semiconductor, a first contact layer formed of n-type gallium nitride, a first cladding layer formed of n-type aluminum / gallium nitride, A double hetero structure in which an active layer formed of indium gallium, a second cladding layer formed of p-type aluminum gallium nitride, and a second contact layer formed of p-type gallium nitride are sequentially stacked.
[0028]
A nitride semiconductor shows n-type conductivity without doping impurities. When a desired n-type nitride semiconductor is formed, for example, to improve luminous efficiency, it is preferable to appropriately introduce Si, Ge, Se, Te, C, or the like as an n-type dopant. On the other hand, in the case of forming a p-type nitride semiconductor, the p-type dopant such as Zn, Mg, Be, Ca, Sr, or Ba is doped. Since it is difficult to convert a nitride semiconductor into a p-type simply by doping with a p-type dopant, it is preferable to reduce the resistance by performing a heat treatment by heating in a furnace, plasma irradiation, or the like after the introduction of the p-type dopant. After the electrodes are formed, a light emitting element made of a nitride semiconductor can be formed by cutting the semiconductor wafer into chips.
[0029]
In the case where a white light is emitted in the light emitting diode of the present invention, the emission wavelength of the light emitting element is preferably 400 nm or more and 530 nm or less, and 420 nm in consideration of a complementary color relationship with the emission wavelength from the fluorescent substance and deterioration of the light-transmitting resin. It is more preferably at least 490 nm. In order to further improve the excitation and luminous efficiency of the light emitting element and the fluorescent substance, respectively, the wavelength is more preferably 450 nm or more and 475 nm or less. Needless to say, an ultraviolet wavelength shorter than 400 nm can be used.
[0030]
(Mount leads 104, 204)
The mount lead 104 is for mounting a light emitting element, and it is sufficient that the mount lead 104 is large enough to be mounted on a die bonding device or the like. Further, when a plurality of light emitting elements are provided and the mount lead is used as a common electrode of the light emitting element, sufficient electric conductivity and connectivity with a bonding wire or the like are required. Further, when the light emitting element is arranged in the cup on the mount lead and the phosphor is filled in the inside, it is possible to prevent the false light from being caused by light from another light emitting diode arranged in the vicinity. .
[0031]
The light emitting element and the cup of the mount lead can be bonded to each other by using a thermosetting resin or the like as the mount member 106. Specifically, an epoxy resin, an acrylic resin, a silicone resin, an imide resin, or the like can be given. Further, in order to bond and electrically connect to the mount lead by using a flip-chip type light emitting element, an Ag paste, a Cu paste, a carbon paste, a resin containing a metal bump or a metal oxide, or the like can be used. . The specific electrical resistance of the mount lead is preferably 300 μΩ · cm or less, and more preferably 3 μΩ · cm or less. Further, when a plurality of light emitting elements are mounted on the mount lead, good heat conductivity is required because the amount of heat generated from the light emitting elements increases. Specifically, 0.01 cal / cm Two / Cm / ° C or higher, more preferably 0.5 cal / cm Two / Cm / ° C or more. Materials satisfying these conditions include iron, copper, copper with iron, copper with tin, and ceramic with a metallized pattern.
[0032]
(Inner leads 105, 205)
The inner leads are intended to be electrically connected to the light emitting elements disposed on the mount leads via conductive wires and the like. The inner leads are required to have good connectivity with a bonding wire and the like and good electrical conductivity. The specific electric resistance is preferably 300 μΩ · cm or less, and more preferably 3 μΩ · cm or less. Materials satisfying these conditions include iron, copper, copper with iron, copper with tin, and copper, gold, and silver-plated aluminum, iron, and copper.
[0033]
(Wires 107, 207)
The wire 107 is required to have good ohmic properties, adhesion, electrical conductivity, and thermal conductivity with the electrode of the light emitting element. 0.01 cal / cm as thermal conductivity Two / Cm / ° C. or higher, more preferably 0.5 cal / cm Two / Cm / ° C or more. Further, in consideration of workability and the like, the diameter of the wire is preferably Φ10 μm or more and Φ45 μm or less. Specific examples of such wires include wires using metals such as gold, copper, platinum, and aluminum and alloys thereof. With such a wire, the electrode of each light emitting element can be easily connected to the inner lead, the mount lead, and the like by a wire bonding device.
[0034]
(Mold member 208)
The mold member 208 can be provided to protect the light emitting element 103, the wire 107, the fluorescent substance 102, and the like from the outside according to the application of the light emitting diode. The mold member can be generally formed using a resin. Although the viewing angle can be increased by including the phosphor, the directivity from the light emitting element can be relaxed and the viewing angle can be further increased by including the diffusing agent in the resin mold. Further, by forming the mold member into a desired shape, it is possible to have a lens effect of converging or diffusing light emitted from the light emitting element. Therefore, a structure in which a plurality of mold members are stacked may be used. Specifically, the shape is a convex lens shape, a concave lens shape, an elliptical shape viewed from the light emission observation surface, or a combination of a plurality of shapes. As a specific material of the mold member, a transparent resin having excellent weather resistance, such as an epoxy resin, a urea resin, or a silicone resin, or glass is preferably used. As the diffusing agent, barium titanate, titanium oxide, aluminum oxide, silicon oxide and the like are preferably used. Further, the mold member and the binder may be formed using the same material in consideration of the difference in the refractive index. Hereinafter, specific examples of the present invention will be described in detail, but it is needless to say that the present invention is not limited thereto.
[0035]
【Example】
(Example 1)
The LED chip has an emission layer with an emission peak of 450 nm. 0.2 Ga 0.8 An N semiconductor was used. The LED chip is formed by flowing a TMG (trimethyl gallium) gas, a TMI (trimethyl indium) gas, a nitrogen gas, and a dopant gas together with a carrier gas on a cleaned sapphire substrate, and forming a nitride semiconductor by MOCVD. Was. SiH as dopant gas Four And Cp Two By switching to Mg, an n-type or p-type conductive nitride semiconductor is formed. As the light emitting element, a contact layer made of a gallium nitride semiconductor having n-type conductivity, a clad layer made of an aluminum gallium nitride semiconductor having p-type conductivity, and a contact layer made of gallium nitride having p-type conductivity were formed. . An InGaN active layer having a thickness of about 3 nm and a single quantum well structure is formed between the n-type contact layer and the p-type cladding layer. (Note that gallium nitride is formed at a low temperature on a sapphire substrate to serve as a buffer layer. The p-type semiconductor is heat-treated at 400 ° C. or higher after film formation.)
The surface of each pn contact layer is exposed on the same side of the nitride semiconductor on the sapphire substrate by etching. Positive and negative pedestal electrodes were formed on the respective contact layers using a sputtering method. A metal thin film is formed as a light-transmitting electrode on the entire surface of the p-type nitride semiconductor, and then a pedestal electrode is formed on a part of the light-transmitting electrode. After a scribe line was drawn on the completed semiconductor wafer, the semiconductor wafer was divided by external force to form LED chips as semiconductor light emitting elements.
[0036]
On the other hand, an iron-containing copper lead frame which is connected by a tie bar by punching and stamping and has a cup formed at the tip of the mount lead is formed. The LED chip was die-bonded into the cup at the tip of a copper lead frame containing iron, which was silver-plated using epoxy resin. Each electrode of the LED chip was wire-bonded to a mount lead or an inner lead provided with a cup with a gold wire to establish electrical continuity.
[0037]
As a fluorescent substance, a solution obtained by dissolving rare earth elements of Y, Gd, and Ce in an stoichiometric ratio in an acid was coprecipitated with oxalic acid. This is mixed with a coprecipitated oxide obtained by calcination and aluminum oxide to obtain a mixed raw material. This was mixed with ammonium fluoride as a flux, packed in a crucible, and fired in air at a temperature of 1400 ° C. for 3 hours to obtain a fired product. The calcined product was ball milled in water, washed, separated, dried, and finally formed through a sieve.
[0038]
Formed (Y 0.8 Gd 0.2 ) Three Al Five O 12 : 25 parts by weight of Ce fluorescent substance and 100 parts by weight of polycarbonate resin are mixed well, and one piece is 10 mm Three The pellets were of the order of magnitude. The pellets were placed in a hopper of an injection molding machine shown in FIG. On the other hand, the LED chip electrically connected to the lead terminal is put in a mold and fixed. The injection temperature is 280 ° C. and the injection pressure is 800 kgf / cm. Two And injected into the mold. After cooling the mold, take out the resin-molded lead, cut the tie bar, and cover a part of the LED chip, mount lead and inner lead with thermoplastic resin containing fluorescent material to form a shell type The light emitting diode thus obtained can be obtained. The dispersion was measured by forming 500 light emitting diodes. The chromaticity point of the obtained light emitting diode capable of emitting white light was measured and plotted on CIE coordinates. In addition, it was confirmed that there was no uneven light emission in appearance in each of the light emitting diodes. It is needless to say that the present invention can be used not only in a bullet type light emitting diode but also in a chip type LED or a segment display.
[0039]
(Comparative example)
(Y 0.8 Gd 0.2 ) Three Al Five O 12 : A light-emitting diode was formed in the same manner as in Example 1 except that a mixture of a Ce fluorescent material and an epoxy resin was used, and then placed in a cup by casting, followed by curing. The average of 500 light emitting diodes formed was compared with the light emitting diode of Example 1 to examine the variation in the production of the color temperature. The light emitting diode of the example had a significantly smaller variation in the production of the color temperature than the light emitting diode of the comparative example. Note that the light emitting diode of the comparative example was in a state where the fluorescent substance was solidified at the tip of the mold member.
[0040]
(Example 2)
As shown in FIG. 2, the periphery of the LED chip 203 is injection-molded and sealed with a thermoplastic resin 201 containing the same fluorescent substance 202 as described above, and then a translucent epoxy resin is molded as a molding member 208 by casting. A light emitting diode 200 was formed in the same manner as in Example 1 except that the light emitting diode 200 was formed. Thus, in addition to the above-described curing, even if a mold mismatch or a burr occurs on the surface of the sealing resin during injection molding, it can be further covered by casting. For this reason, variations in the lens function of the sealing resin and poor soldering caused by falling off of burrs when mounting the light emitting diode are prevented. Further, it is also possible to reduce the amount of relatively expensive thermoplastic resin having high translucency and high heat resistance.
[0041]
(Example 3)
As shown in FIG. 3, a surface-mounted light emitting diode 300 was formed. The LED chip 303 has an emission peak of 475 nm as an emission layer. 0.2 Ga 0.8 A nitride semiconductor device having an N semiconductor was used. More specifically, the LED chip 303 is formed by flowing a TMG (trimethyl gallium) gas, a TMI (trimethyl indium) gas, a nitrogen gas and a dopant gas together with a carrier gas on a cleaned sapphire substrate, and forming a nitride semiconductor by MOCVD. It can be formed by forming a film. SiH as dopant gas Four And Cp Two By switching Mg, a layer to be an n-type nitride semiconductor or a p-type nitride semiconductor is formed.
[0042]
As the device structure of the LED chip, an n-type GaN layer as an undoped nitride semiconductor, a GaN layer as an n-type contact layer formed by forming an Si-doped n-type electrode on a sapphire substrate, and n as an undoped nitride semiconductor A GaN layer serving as a barrier layer, a GaN layer serving as a well layer, an InGaN layer serving as a well layer, and a GaN layer serving as a barrier layer are set as one set, and five InGaN layers sandwiched between GaN layers are stacked. It has a multiple quantum well structure. On the light emitting layer, an AlGaN layer as a Mg-doped p-type cladding layer and a GaN layer as a Mg-doped p-type contact layer are sequentially laminated. (Note that a GaN layer is formed on the sapphire substrate at a low temperature to serve as a buffer layer. The p-type semiconductor is annealed at 400 ° C. or higher after film formation.)
The surface of each pn contact layer is exposed on the same side of the nitride semiconductor on the sapphire substrate by etching. Positive and negative pedestal electrodes were formed on the respective contact layers using a sputtering method. A metal thin film is formed as a light-transmitting electrode on the entire surface of the p-type nitride semiconductor, and then a pedestal electrode is formed on a part of the light-transmitting electrode. After a scribe line was drawn on the completed semiconductor wafer, the semiconductor wafer was divided by external force to form LED chips as semiconductor light emitting elements.
[0043]
On the other hand, a substrate to which metal pieces to be a pair of lead electrodes 304 and 305 are fixed by an insulating resin 309 by punching and injection molding. The LED chip 303 was die-bonded on a silver-plated iron-containing copper lead electrode using an epoxy resin 306. Each electrode of the LED chip and each lead electrode were wire-bonded with a gold wire 307 to establish electrical continuity.
[0044]
As the fluorescent substance 302, a solution obtained by dissolving rare earth elements of Y, Gd, and Ce in an stoichiometric ratio in an acid was coprecipitated with oxalic acid. This is mixed with a coprecipitated oxide obtained by calcination and aluminum oxide to obtain a mixed raw material. This was mixed with ammonium fluoride as a flux, packed in a crucible, and fired in air at a temperature of 1400 ° C. for 3 hours to obtain a fired product. The calcined product was ball milled in water, washed, separated, dried, and finally formed through a sieve.
[0045]
Formed (Y 0.6 Gd 0.4 ) Three Al Five O 12 : 25 parts by weight of Ce fluorescent substance, 100 parts by weight of triglycidyl isocyanurate which is a nitrogen-containing epoxy resin, an acid anhydride and a curing accelerator are stirred and reacted at 65 ° C. for 24 hours, and cooled at room temperature. This reaction results in a solid that has been cured to some extent. After cooling to room temperature, the removed solid is crushed and pressed to form a solid tablet. In addition, in order to form a tablet containing a fluorescent substance in a light-transmitting resin, the tablet may be contained in the raw material light-transmitting resin as described above, or may be cured to some extent as long as uniformity can be maintained. It is also possible to use a tablet obtained by mixing and stirring the transparent resin powder and the fluorescent substance.
[0046]
Next, after heating the pot, the softened tablet was injected into a mold in which a substrate having electrical conductivity with the LED chip formed above was arranged, and was temporarily cured at 150 ° C. for 5 minutes. Next, after taking out the injection-molded light emitting diode from the mold, it was secondarily cured at 150 ° C. for 4 hours. The translucent resin 301 containing the fluorescent substance could be formed in a protruding shape on the substrate on which the LED chips were arranged.
[0047]
The formed chip type LED can be a white LED in which the variation of the light emitting diodes formed in the same manner as described above is extremely small and the color unevenness of each light emitting diode is extremely small. In addition, it is not necessary to form a side wall having a cavity structure in order to maintain a resin containing a fluorescent substance, so that a very small white light emitting diode can be formed. Furthermore, since the thermosetting resin is used even though it has been cured to some extent, it is possible to prevent damage to wires and the like that electrically connect the LED chips as compared with the case where a thermoplastic resin having a relatively high viscosity is used during injection molding. Can be formed.
[0048]
【The invention's effect】
By using the manufacturing method according to the present invention, a light emitting diode capable of emitting white light having a fluorescent substance with stable emission characteristics can be manufactured with high mass productivity. Further, even during mass production for a long time, the light emission variation between the light emitting diode formed first and the light emitting diode formed later can be made extremely small. Furthermore, since light emission unevenness in a light emitting diode formed relatively easily can be reduced, mass productivity and yield can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing a light emitting diode of the present invention.
FIG. 2 is a schematic sectional view showing another light emitting diode of the present invention.
FIG. 3 is a schematic sectional view showing another light emitting diode of the present invention.
FIG. 4 is a schematic sectional view of an injection molding machine used for manufacturing the present invention.
[Explanation of symbols]
100, 200, 300 ... light emitting diode
101, 201, 301: Translucent resin containing fluorescent substance
102, 202, 302 ... fluorescent substance
103, 203, 303 ... light emitting element
104, 204: Mount lead
105, 205 ・ ・ ・ Inner lead
106, 206, 306: mounting member for bonding the LED
107, 207, 307 ... wires
208: Mold member
304, 305: Lead electrode
309: Resin that insulates between lead electrodes
400 ・ ・ ・ Injection molding machine
401 ・ ・ ・ Pellets
402 ・ ・ ・ Injection piston
403 ・ ・ ・ Screw
404 ・ ・ ・ heating wire
405: mold
406... Mount lead on which light emitting element is mounted

Claims (2)

発光素子と、該発光素子からの発光の少なくとも一部を吸収し蛍光を発する蛍光物質を含有する透光性樹脂とを有し、前記発光素子からの発光と前記蛍光物質からの蛍光との白色系の混色光を発光する発光ダイオードの形成方法であって、
成型前に蛍光物質と固体状の透光性樹脂とを均一に混合する第一の工程と、
前記固体状の透光性樹脂を軟化させて、前記発光素子が固定された金型中に射出・注入し、該発光素子の少なくとも一部を被覆する第二の工程と、
再び前記透光性樹脂を固体状とする第三の工程と、
前記発光素子の少なくとも一部が被覆された蛍光物質含有透光性樹脂の外側に透光性樹脂を注型成型にて形成させる第四の工程と、を有する発光ダイオードの形成方法。A light-emitting element and a light-transmitting resin containing a fluorescent substance that absorbs at least a part of light emitted from the light-emitting element and emits fluorescence, and white light emission from the light-emitting element and fluorescence from the fluorescent substance A method of forming a light emitting diode that emits mixed light of a system,
A first step of uniformly mixing the fluorescent substance and the solid translucent resin before molding,
The second step of softening the solid translucent resin, injecting and injecting the light emitting element into a fixed mold, and covering at least a part of the light emitting element,
A third step of making the translucent resin solid again,
Forming a light- transmitting resin by casting on the outside of the fluorescent substance-containing light-transmitting resin on which at least a part of the light-emitting element is coated . 前記発光素子の発光層が少なくとも窒化物半導体からなると共に前記蛍光物質がセリウムで付活されたイットリウム・アルミニウム・ガーネット系蛍光体である請求項１に記載の発光ダイオードの形成方法。The method for forming a light-emitting diode according to claim 1, wherein the light-emitting layer of the light-emitting element is made of at least a nitride semiconductor and the fluorescent substance is a yttrium-aluminum-garnet-based phosphor activated with cerium.
JP03926299A 1998-02-17 1999-02-17 Method of forming light emitting diode Expired - Lifetime JP3541709B2 (en)

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