JP3888085B2

JP3888085B2 - Substrate design method, implementation method of the substrate design method, and substrate structure designed by the substrate design method

Info

Publication number: JP3888085B2
Application number: JP2001185463A
Authority: JP
Inventors: 聖文別所
Original assignee: Omron Corp
Current assignee: Omron Corp
Priority date: 2001-06-19
Filing date: 2001-06-19
Publication date: 2007-02-28
Anticipated expiration: 2021-06-19
Also published as: JP2003008168A

Description

【０００１】
【発明の属する技術分野】
本発明は、プリント配線基板などに対して表面実装部品の配置位置を決定する際の、基板設計方法およびその実施手段ならびに基板設計方法により設計された基板構造に関する。
【０００２】
【従来の技術】
表面実装部品（以下、部品）を基板にはんだ付けする工法として、リフロが使用されている。リフロ中の基板上の各部品は，熱容量や伝熱性の差などから部品間で温度のばらつきが生じる。ばらつきが大きいと部品の熱損傷やはんだ付け不良が発生し，製品の信頼性や歩留まりに悪影響をおよぼす。
【０００３】
特に，近年使用され始めたＰｂフリーはんだをリフロに使用すると，融点が高いために，許容できる温度ばらつきが小さくなる。このため，従来のはんだでは問題なくリフロできる基板でも，部品の熱損傷やはんだ付け不良が発生する可能性が高まる。
【０００４】
新商品の基板設計を行う際に、部品選定で大型で大熱容量の部品や耐熱性の低い部品を選んだり、部品レイアウトを試行錯誤で行ったりすると、基板の再設計が必要になるなど、商品の開発期間や開発コストの増大を招く。また、部品の熱損傷は検査で発見できないことが多く、市場に流出して故障の原因となりかねない。このため温度ばらつきを事前に予測し、リフロを容易にする基板設計を実現することが望まれる。
【０００５】
表面実装部品の配置位置を決定する際の従来の基板設計方法としては、例えば、信号遅延時間を抑制するとともに電気的ノイズを低減するため、ＭＰＵ（超小型演算処理装置）とメモリ（記憶装置）とをなるべく近くに配置するという方法がある。
【０００６】
また、表面実装部品を配置する際の従来の他の基板設計方法としては、加熱中の基板温度を逐次シミュレートし、シミュレーションの結果から温度ばらつきを評価することによつて部品間隔を決定する方法（特開平１１−２０１６４７号公報の開示技術）がある。
【０００７】
【発明が解決しようとする課題】
しかしながら、上記した従来の前者の基板設計方法にあっては、部品をはんだ付けするために基板を加熱する際、部品の熱容量の差などによって発生する基板表面上の温度ばらつきが不明であり、温度の過上昇によって一部の部品が熱的損傷を受けたり、あるいは局所的に温度上昇が不十分ではんだ付け不良が発生したりする危険性があるという問題点があった。
【０００８】
また、従来の後者の基板設計方法にあっては、解析モデルの作成に時間を要する上、加熱のシミュレーシヨンを実施した後に初めて加熱時の基板表面上の温度ばらつきが評価できるため、部品間隔の決定にはシミュレーシヨンによる試行錯誤が必要であるという問題点があった。
【０００９】
本発明は、上記の問題点に着目して成されたものであって、その第１の目的とするところは、あらかじめ測定した温度データに基づいて、加熱時における部品からの距離と基板温度との関係（以下、部品周辺の基板温度分布）を定量的に予測し、部品同士が互いのはんだ付け温度を確保するために必要な部品間隔を基板設計時に簡単な方法で算出できる基板設計方法を提供することである。
【００１０】
また、本発明の第２の目的とするところは、良好なはんだ付けが得られる加熱温度の確保に必要な部品間隔が適性であるか否かをチェックすることができる基板設計方法の実施方法を提供することである。
【００１１】
また、本発明の第３の目的とするところは、部品の影響による基板温度の低下が大きい位置に耐熱保証温度を越えやすい部品を配置することで、さらに加熱時の温度ばらつきが小さい基板を設計できる基板構造を提供することである。
【００１２】
【課題を解決するための手段】
上記の第１の目的を達成するために、本発明に係る基板設計方法は、基板設計時において、あらかじめ測定した温度データに基づいて加熱時における部品周辺の基板温度分布（部品からの距離と基板温度との関係）を予測し、部品が基板を介して他の部品のはんだ接合部におよぼす温度変化を計算することによつて、良好なはんだ付けが得られる加熱温度の確保に必要な部品間隔を決定するようにした。
【００１３】
そして、温度データとして生基板温度と部品周辺の基板温度分布を使用するようにしてもよく、温度データは生基板や部品を限定して測定するようにしてもよい。
【００１４】
ここで、部品とは基板に搭載させる電子部品であり、例えば、ＱＦＰなどのパッケージ部品、ＢＧＡなどである。また、生基板とは、部品が搭載されていない基板である。また、部品間隔とは、例えば２つの部品の対向する側端部間の間隔や２つの部品の中心同士の間隔である。
【００１５】
したがって、リフロ条件を一定にした場合の基板温度ばらつきのうち、部品による基板の温度低下を予測可能とし、生基板の温度と部品による基板の温度低下の許容値から、はんだ付け温度の確保に必要な部品間隔を決定できるようになる。
【００１６】
また、温度上昇しにくい大型部品の影響による隣接部品の温度低下と、部品間隔の関係を数値化することが可能になる。このように、部品間隔を何ｍｍ以上に設定すればよいかが具体的な数値でわかるため、リフロ温度に問題がないかどうか定量的な判断が可能になる。
【００１７】
また、本発明に係る基板設計方法は、上記した本発明に係る基板設計方法において、部品が搭載されていない生基板の温度と、いくつかの部品について加熱時における、それぞれの部品周辺の基板温度の分布をあらかじめ測定しておくことで、加熱時における部品周辺の基板温度分布を、部品の種類やサイズおよび生基板の厚さや層数や材質など、熱容量、比熱、熱伝導、熱伝達、熱複写に影響する因子をパラメータとして数式化し、部品周辺の基板温度分布を定量的に予測できるようにした。
【００１８】
したがって、生基板の温度に対する部品の影響による基板温度の変化と、その影響が及ぶ範囲が簡単に評価できて、リフロ条件を一定にした場合の基板温度ばらつきのうち、部品による基板の温度低下を予測可能とし、生基板の温度と部品による基板の温度低下の許容値から、はんだ付け温度の確保に必要な部品間隔を決定できるようになる。
【００１９】
そして、部品の種類をパラメータに用いて部品周辺の基板温度分布を予測する場合には、部品の分類は、測定した部品周辺の基板温度分布の違いに基づくようにしてもよい。
【００２０】
また、部品の分類に、部品の形状を用いるようにしてもよいし、部品の分類に、部品の内部構造を用いるようにしてもよいし、部品の分類に、部品の材質を用いるようにしてもよいし、部品の分類に、はんだ接合部の位置を用いるようにしてもよい。
【００２１】
また、部品のサイズをパラメータに用いて、部品周辺の基板温度分布を予測する場合には、部品サイズとして部品の長さと幅を使用するようにしてもよい。この際、部品の長さと幅は、端子部を除いたサイズでもよい。
【００２２】
そして、部品の長さ方向と幅方向に分けて部品周辺の基板温度分布を予測するようにしてもよい。また、部品サイズとして部品の厚さを使用するようにしてもよい。この際、部品の厚さは、端子部を除いたサイズでもよい。
【００２３】
また、生基板の層数をパラメータに用いて部品周辺の基板温度分布を予測する場合には、生基板の層数として内層の有無に着目するようにしてもよい。
【００２４】
また、本発明に係る基板設計方法は、上記した本発明に係る基板設計方法において、部品周辺の基板温度分布の予測結果に基づいて基板温度を大きく低下させる部品を選択し、他の部品のはんだ接合部に及ぼす温度低下を計算して、それぞれの部品がはんだ付け温度を確保できる部品間隔を算出できるようにした。
【００２５】
したがって、加熱時の基板温度をシミュレーションする方法と比較して、良好なはんだ付けが得られる加熱温度の確保に必要な部品間隔が試行錯誤なく、短時間で簡単に決定できる。
【００２６】
そして、本発明に係る基板設計方法は、上記した本発明に係る基板設計方法において、部品周辺の基板温度分布は前記部品の中心を基準に求めるようにしてもよいし、部品周辺の基板温度分布は部品中心に最も近い部品端部を基準に求めるようにしてもよい。
【００２７】
また、部品周辺の基板温度分布は線形に近似することが好ましい。または、部品周辺の基板温度分布は曲線に近似することが好ましい。この場合、線形とは、例えば直線である。曲線とは、例えば、２次、３次などの多次式や、対数関数でもよい。
【００２８】
また、あらかじめ測定した温度データに基づいて基板温度への影響が小さく無視できると判断できる部品については、周辺の基板温度分布の予測を行わず、生基板上の任意の位置に配置するようにしてもよいし、また、部品周辺の基板温度分布を予測した結果、基板温度への影響が小さく無視できると判断できる部品については、生基板上の任意の位置に配置するようにしてもよい。基板温度への影響が小さく無視できるとは、計測誤差や炉の温度変化などを考慮して決定される。
【００２９】
また、複数の部品による基板温度の低下を重ね合わせて任意の位置における基板温度を予測し、良好なはんだ付けが得られる加熱温度の確保に必要な部品間隔を決定するようにしてもよい。
【００３０】
また、加熱時の前記基板温度に対する部品の影響を、部品周辺の基板温度と生基板の温度との差で評価し、個々の部品による影響を重ね合わせて部品のはんだ接合の温度を予測することで、良好なはんだ付けが得られる加熱温度の確保に必要な部品間隔を決定するようにしてもよい。
【００３１】
また、ある一定の加熱条件の下での加熱時における部品周辺の基板温度を予測するようにしてもよい。
【００３２】
また、複数の加熱条件の下での加熱時における部品周辺の基板温度を包括して平均値を予測するようにしてもよい。
【００３３】
また、加熱条件による加熱時における部品周辺の基板温度の違いを、測定データを追加することで数式を修正して補正するようにしてもよい。
【００３４】
また、本発明に係る基板設計方法は、上記した本発明に係る基板設計方法において、パソコンなどの表計算ソフトウェアを使用して加熱時における部品周辺の基板温度分布を算出するようにした。
【００３５】
そして、パソコンなどの表計算ソフトウェアを使用して加熱時における部品間隔を算出するようにした。
【００３６】
したがって、本発明に係る基板設計方法を簡単に使えるように、パソコンの表計算ソフトを使用してツール化し、設計者自身が基板の温度低下を予測して部品をレイアウトできる。
【００３７】
また、上記の第２の目的を達成するために、本発明に係る基板設計方法の実施方法は、基板設計時において、あらかじめ測定した温度データに基づいて加熱時における部品周辺の基板温度分布（部品からの距離と基板温度との関係）を予測し、部品が基板を介して他の部品のはんだ接合部におよぼす温度変化を計算することによつて、良好なはんだ付けが得られる加熱温度の確保に必要な部品間隔を決定し、部品間隔が適性であるか否かをチェックできる機能を有する。
【００３８】
ここで、あらかじめ測定した温度データとして生基板温度と部品周辺の基板温度分布を使用するようにしてもよく、温度データは生基板や部品を限定して測定するようにしてもよい。
【００３９】
また、部品配置後の基板で加熱時の予想最低温度部と予想最高温度部のいずれか一方もしくは双方が表示できるようにしてもよいし、また、加熱時の基板全体の予想温度が表示できるようにしてもよい。
【００４０】
また、必要な部品間隔を確保できない領域に部品を配置しようとした場合にその旨を表示するか、あるいは部品が配置できない機能を有するようにしてもよい。
【００４１】
したがって、チェック機能により、良好なはんだ付けが得られる加熱温度の確保に必要な部品間隔か否かをチェックすることができる。
【００４２】
また、上記の第３の目的を達成するために、本発明に係る回路基板構造は、基板設計時において、あらかじめ測定した温度データに基づいて加熱時における部品周辺の基板温度分布（部品からの距離と基板温度との関係）を予測し、基板温度が低い部分に耐熱保証温度を越えやすい部品を配置するようにした。
【００４３】
そして、耐熱保証温度を越えやすい部品がアルミ電解コンデンサであることが好ましい。また、耐熱保証温度を越えやすい部品がＬＥＤであることが好ましい。
【００４４】
したがって、部品の影響による基板温度の低下が大きい位置にアルミ電解コンデンサなど耐熱保証温度を越えやすい部品を配置することで、さらに加熱時の温度ばらつきが小さい基板を設計できる。
【００４５】
【発明の実施の形態】
以下、本発明の実施の形態を図面を参照して説明する。
【００４６】
リフロ時の基板温度ばらつきによって生じる問題は、部品の熱損傷とはんだ付け不良である。これらの問題が発生しないようにするには、部品のボディ温度が耐熱温度（部品によって異なる）以下であり、端子温度がはんだの融点以上であることが必要である。
【００４７】
リフロの温度プロファイルには、１枚の基板に対して図１に示すように、最も温度の上がりやすい部品のボディ温度と、最も温度が上昇しにくい部品の端子温度との温度差が現れる。
【００４８】
このため、基板温度ばらつきΔＴ＝（部品ボディの最高温度）一（部品端子の最低温度）と定義することができる。
【００４９】
基板温度ばらつきΔＴは図２（図１の丸で囲った部分の拡大図）に示すように、部品を搭載していない生基板をリフロ炉に流した場合のピーク温度を基準として、特定の部品に見られる温度の過上昇ΔＴ_h と、大型部品の熱容量による温度低下ΔＴ_l に分けて考えることができる。
【００５０】
基板全体でΔＴの低減を考えると問題が複雑だが、個々の部品について単独でΔＴh とΔＴl を評価すれば、それぞれが最も大きい部品に着目すればよいことが分かる。
【００５１】
ΔＴ_h とΔＴ_l のうち、ΔＴ_h は他の部品温度に影響をおよぼすことはない。これに対してΔＴ_l は、部品自身の端子温度の低下のみならず、その周辺の基板温度まで影響する。そのため隣接する部品の端子温度を低下させ、はんだ付け不良を引き起こしかねない。したがって基板設計では、隣接する部品同士が互いのはんだ付け性に影響しない間隔を確保する必要がある。
【００５２】
基板全体の基板温度ばらつきΔＴを低減するには、ΔＴ_h かΔＴ_l の少なくとも一方を抑えればよいが、以上の事柄をふまえて、部品レイアウト技術ではΔＴ_l の低減を主体とする。
【００５３】
リフロ炉では、ＨＡ（ＨｏｔＡｉｒ）（熱風）とＩＲ（ＩｎｆｒａｒｅｄＲａｙ）（赤外線）などの異なる加熱原理の組み合わせで温度上昇させており、温度プロファイルは加熱条件、部品の熱容量、吸熱、伝熱、部品レイアウトなどの諸要因で相対的に決まる。
【００５４】
したがって、基板温度ばらつきΔＴもこれらの要因によって変化する。基板温度ばらつきΔＴの要因は、部品レイアウトに関するものとリフロ炉に関するものとの２つに大別できる。
【００５５】
リフロ炉に起因する項目は炉の型式や条件設定によつて大きく変わる。リフロ炉の条件は、本来最適状態に固定して用いることが理想的なので、予め汎用最適の条件を求めて固定した。
【００５６】
基板温度ばらつきΔＴを低減するには、部品の選択とレイアウトが重要である。このうち、使用部品の変更は回路の機能上困難な場合が多い。したがって、基板温度ばらつきΔＴの低減に実効的な手段は部品レイアウトである。
【００５７】
従来、部品レイアウト時にはノイズ低減や大電力部品の放熱性のほか、生産性が考慮されていたが、基板温度ばらつきΔＴは定量的に評価する手法がなく考慮されていなかった。しかしながら、基板温度ばらつきΔＴは、基板実装の高密度化やＰｄフリーはんだの導入などによって無視できない状況になっている。このため、ΔＴ_l と図３に示す部品間隔Ｄとの関係を定量的に予測評価し、設計段階でΔＴ_l を決定できる手段が必要である。なお、図３中Ａ、Ｂは部品、Ｃは基板である
【００５８】
部品には様々な種類があるため、部品を外形や構造・材質など、リフロ温度に影響する項目で数種類に分類し、図２に示すΔＴ_l が大きい部品をまず明らかにした。
【００５９】
〔表１〕に示した項目で部品を分類することで、すべての部品の影響を個別に考えるのではなく、熱的特性が近い部品の影響を一括して考える。かつ、リフロを困難にしやすい部品を重点的に検討した。
【００６０】
【表１】

【００６１】
ΔＴ_l を正確に予測するため、まずΔＴ_l をデータベース化して、予測値の妥当性が裏付けできるようにした。実際の基板上には多数の部品が実装されるが、簡単化のため２つの部品Ａ、Ｂだけを取り出して、部品間隔Ｄとリフロ温度との関係について考える。
【００６２】
リフロ加熱条件は上述の通り、あらかじめ設定した標準加熱条件（代表的部品を搭載したテスト基板で、基板温度ばらつきΔＴをよく圧縮できるＨＡとＩＲの比率や風速・コンベア速度）に固定した。
【００６３】
本発明の基板設計方法では、「部品レイアウトのΔＴへの影響は、部品同士が基板を介して温度を低下しあう現象によって現れ、温度上昇しにくい大型部品ほど周辺への影響も大きい」と考えて、部品温度そのものではなく、「部品周辺の基板温度分布」に着目した。
【００６４】
評価対象を基板温度とすることで、一度測定したデータは部品の組み合わせによらず使用できるという汎用性がある。例えば、部品Ａ周辺の基板温度分布は、部品Ａと他部品（部品Ａを含む）との部品間隔Ｄを決定するときに使用できる。また、部品周辺の基板温度は部品温度と同時に測定可能である。
【００６５】
本発明の基板設計方法では、ｋ種類の部品に対する温度測定回数はｋ×ｎ回（ _kＣ₁ ×ｎ）で済み、部品が１種類追加されても追加測定はその部品に対してのｎ回だけでよい。従来の手法と本発明の基板設計方法（本手法）とでの、部品間隔Ｄの決定に必要な測定回数の比較を〔表２〕に示す。
【００６６】
【表２】

【００６７】
なお、従来のΔＴ評価手法では、部品のリフロ温度だけを計測評価していた。このために、部品間隔Ｄとリフロ温度の関係を得るには、部品間隔Ｄを変えてリフロ温度を測定する必要があった。例えば、部品Ａと部品Ｂについては、部品間隔Ｄを数回変えて、リフロ温度を測定するといった要領であった。また、部品Ａ同士や部品Ｂ同士についても、同様の温度測定が必要であった。
【００６８】
このような従来の手法では、ｋ種類の部品に対して _k _＋ ₁ Ｃ₂ ×ｘ×ｎ回（ｘ：部品間隔Ｄの水準数、ｎ：繰り返し数）の温度定が必要であり、部品が１種類追加されると（ｋ＋１）×ｘ×ｎ回の追加測定が必要である。このため、データベースの構築やメンテナンスが極めて困難であると考えられていた。
【００６９】
本発明の基板設計方法では、まず上述のように分類した部品の種類ごとに、部品単体での周辺の基板温度分布を測定した。その結果、部品周辺の基板温度分布は直線に近似できることがわかった。
【００７０】
例として、部品としてのＱＦＰ（ＱｕａｄＦｌａｔＰａｃｋａｇｅ）周辺の基板温度分布の様子を図４の（１）に、実測データを図４の（２）にそれぞれ示す。図４の（２）から測定データは近似直線とよく一致していることがわかる。また、ΔＴ_l の大きさから、その部品が周辺の基板温度におよぼす影響が評価できる。
【００７１】
そして、部品周辺の基板温度分布から、２つの部品Ａ、Ｂ間の基板温度分布が予測できれば、ΔＴ_l と部品間隔Ｄとの関係が定量化できる。そこで、図４の（１）、（２）に示した部品周辺の基板温度分布をもとに、２つの部品Ａ、Ｂ間の基板温度を予測できるかを検討した。
【００７２】
その結果、個々の部品によるΔＴ_l を重ね合わせることで、２つの部品Ａ、Ｂ間の基板温度を予測できることを明確にした。例として、部品間隔Ｄを変えてその中間の基板温度を測定し、個々の部品Ａ、Ｂによる影響を重ね合わせた予測値と比較した結果を図５に示す。
【００７３】
測定値と予測値との差は２〜３℃と測定誤差の範囲内であった。２つの部品Ａ、Ｂ２間の基板温度は個々の部品によるΔＴ_l を重ね合わせることで予測できることがわかる。
【００７４】
したがって、生基板温度とはんだ付け性確保に必要なΔＴ_l の許容値を設定すれば、はんだ付け不良が発生しない部品間隔Ｄが決定できる。また、ΔＴ_l の大きい部分にΔＴ_h の大きい部品を配置すればΔＴ_h が低下し、さらにΔＴを低減できる。
【００７５】
すなわち、加熱時における部品周辺の基板温度分布の様子を図６の（１）、（２）に示す。基板Ｃの上には端子部を除いた部品形状が正方形の部品Ａが一個搭載されている。
【００７６】
図６の（２）のグラフは、部品Ａの中心線３上での加熱時の基板温度分布４を表している。部品Ａの熱容量の影響によって、部品Ａの近傍での加熱時の基板温度５よりも低下し、部品Ａの中心に最も近い位置６で最低となるが、部品Ａからの距離が大きくなるにしたがって、その影響は小さくなるため、基板温度は上昇し、やがて生基板を加熱したときの温度５と等しくなる。
【００７７】
基板温度分布４は直線（線形）で近似する。また、端子部を除いた部品形状が正方形の場合は、部品周辺の基板温度は、部品Ａを中心とする同心円７状に分布する。なお、基板温度分布４は曲線で近似する場合も存在する。
【００７８】
図７の（１）、（２）は、部品間隔Ｄを決定する方法の一事例を示す模式図である。図７の（１）において、基板Ｃの上には、端子部を除いた部品形状が正方形の部品Ａと部品Ｂとが搭載されている。図７の（１）において、１０は部品Ｂの中心に最も近い位置であり、１１は部品Ｂを中心とする同心円である。
【００７９】
図７の（２）に示すように、部品Ａと部品Ｂとの間の基板温度分布１２において、部品Ａ側の温度低下量Ｈは、生基板を加熱した時の温度５からの部品Ａによる温度低下量Ｈ１と、部品Ｂによる温度低下量Ｈ２とを重ね合わせて与えられ、部品Ｂ側の温度低下量Ｉは、生基板を加熱した時の温度５からの部品Ｂによる温度低下量Ｉ１と、部品Ａによる温度低下量Ｉ２とを重ね合わせて与えられる。
【００８０】
したがって、部品Ａのはんだ接合部１３の温度は、部品Ｂの影響によって低下するし、同様に、部品Ｂのはんだ接合部１４の温度は、部品Ａの影響によって低下する。
【００８１】
部品間隔Ｄは、部品Ａのはんだ接合部１３と部品Ｂのはんだ接合部１４の温度が、それぞれ良好な接合の確保に必要な最低加熱温度１８以上になるように決定する。なお、図７中９は部品Ｂ周辺の加熱時の基板温度分布である。
【００８２】
部品周辺の基板温度分布は、部品の種類のみならず、部品サイズや基板の仕様によっても異なる。そこで、ＱＦＰなどのパッケージ部品について、数サイズの部品で温度測定を行い、部品サイズによって周辺の基板温度分布がどのように変化するかを評価した。
【００８３】
その結果、部品サイズと近似直線との関係を一般化し、部品サイズからリフロ時の基板温度分布を予測できるようにした。ＱＦＰのサイズと近似直線との関係を一般化するのに使用したデータの一部を図８に示す。
【００８４】
図８において、測定値に基づく近似直線と一般化した近似直線との誤差は３℃以下であり、一般化した近似直線はほぼ妥当な値であると言える。
【００８５】
また、端子部を除いた部品形状が正方形の部品での、ある加熱条件における部品の種類と基板温度分布との関係を示す実験データの一事例を図９に、端子部を除いた部品形状が正方形の部品での、ある加熱条件における部品のサイズと基板温度分布との関係を示す実験データの一事例を図１０に示す。
【００８６】
この実験データから部品サイズとして端子部を除いた実装面積と厚さが基板温度分布に影響すること、部品の種類で影響の程度が異なることが分かる。このことから、部品の種類毎にいくつかのサイズでデータを測定すれば、部品の種類とサイズから部品周辺の基板温度分布が予測できると言える。部品の分類は測定結果に基づいて行ってもよいが、部品の形状や内部構造、材質、はんだ接合部の位置などによって行ってもよい。
【００８７】
図１１は、端子部を除いた部品形状が正方形の部品がリフロ面にある場合の、ある加熱条件における部品周辺の基板温度分布との関係を示す実験データの一事例である。生基板の温度は約２３０℃であり、部品周辺の基板温度が低下していることと、部品周辺の基板温度分布が直線近似できることがわかる。
【００８８】
図１２は、端子部を除いた部品形状が長方形の部品が裏面にある場合の、ある加熱条件における部品周辺の基板温度分布との関係を示す実験データの一事例である。この実験データから、長さ方向と幅方向で碁板温度分布が異なるため、方向別に基板温度分布を求める必要があることが分かる。
【００８９】
また、部品サイズと同様に、基板の仕様（板厚・層数）による基板温度分布の違いをＱＦＰによる実験で確認し、データを基に基板の仕様と近似直線との関係を一般化した。
【００９０】
基板の仕様と近似直線との関係を一般化するのに使用したデータの一部を、図１３に示す。図１３において、測定値に基づく近似直線と一般化した近似直線との誤差は５℃以下であり、一般化した近似直線は図８と同様にほぼ妥当な値であると言える。
【００９１】
図１４は、ある加熱条件での基板厚と部品周辺の基板温度分布との関係を示す実験データの一事例である。基板厚が増すほどに生基板の温度が低下することが分かる。
【００９２】
図１５は、ある加熱条件での基板の層数と部品周辺の基板温度分布との関係を示す実験データの一事例である。両面基板と多層基板では部品周辺の基板温度分布の温度勾配が異なることが分かる。
【００９３】
図１６は、加熱条件の違いによる部品周辺の基板温度分布の違いを示すー事例である。同じ基板、同じ部品でも、加熱条件によって部品周辺の基板温度分布が異なることがわかる。部品の温度データを追加することで、加熱条件の違いをによる基板温度分布の違いを補正することができる。
【００９４】
図１７は、市販のパソコン用表計算ソフトウェアによって部品間隔を算出する、本発明における基板設計方法の実施手段の一事例である。
【００９５】
図１７において、１９は入力部、２０は基板温度分布の近似式表示部、２１は部品間隔表示部である。
【００９６】
そして、入力部１９に部品Ａ、Ｂの種類と、部品サイズ（長さ、幅、厚さ、リード長さ）と、基板Ｃの厚さと層数と、生基板の温度と、良好なはんだ付けを確保するための最低温度を入力することで、基板温度分布の近似式表示部２０で、２つの部品Ａ、Ｂについて周辺の基板温度分布を予測し、部品間隔表示部２１で、部品Ａ、Ｂの配置面に応じて最低必要な部品間隔Ｄを試行錯誤なく瞬時に算出することができる。ここで、基板の材質を、ガラスエポキシ基板、セラミック基板、フレキシブル基板など選択可能としてもよい。
【００９７】
このように、パソコンなどの表計算ソフトウェアを使用して加熱時における部品周辺の基板温度分布を算出するようにし、また、パソコンなどの表計算ソフトウェアを使用して加熱時における部品間隔を算出するようにしたことにより、本発明に係る基板設計方法を簡単に使えるようにツール化し、設計者自身が基板の温度低下を予測して部品をレイアウトできる。
【００９８】
なお、あらかじめ測定した温度データに基づいて基板温度への影響が小さく無視できると判断できる部品については、部品周辺の基板温度分布の予測を行わず、生基板上の任意の位置に配置することは可能であるし、また、部品周辺の基板温度分布を予測した結果、基板温度への影響が小さく無視できると判断できる部品については、生基板上の任意の位置に配置することが可能である。
【００９９】
上記した本発明に係る基板設計方法の実施形態によれば、リフロ条件を一定にした場合の基板温度ばらつきのうち、部品による基板の温度低下を予測可能とし、生基板の温度と部品による基板の温度低下の許容値から、はんだ付け温度の確保に必要な部品間隔を決定できるようになる。
【０１００】
また、温度上昇しにくい大型部品の影響による隣接部品の温度低下と、部品間隔の関係を数値化することが可能になる。このように、部品間隔を何ｍｍ以上に設定すればよいかが具体的な数値でわかるため、リフロ温度に問題がないかどうか定量的な判断が可能になる。
【０１０１】
また、本発明に係る基板設計方法の実施の形態によれば、部品が搭載されていない生基板の温度と、いくつかの部品について加熱時における、それぞれの部品周辺の基板温度の分布をあらかじめ測定しておくことで、加熱時における部品周辺の基板温度分布をモデル化し、部品の種類やサイズおよび生基板の厚さや層数などをパラメータとして部品周辺の基板温度分布を定量的に予測できるようにした。
【０１０２】
したがって、生基板の温度に対する部品の影響による基板温度の変化と、その影響が及ぶ範囲が簡単に評価できて、リフロ条件を一定にした場合の基板温度ばらつきのうち、部品による基板の温度低下を予測可能とし、生基板の温度と部品による基板の温度低下の許容値から、はんだ付け温度の確保に必要な部品間隔を決定できるようになる。
【０１０３】
また、本発明に係る基板設計方法の実施の形態によれば、部品周辺の基板温度分布の予測結果に基づいて基板温度を大きく低下させる部品を選択し、他の部品のはんだ接合部に及ぼす温度低下を計算して、それぞれの部品がはんだ付け温度を確保できる部品間隔を算出できるようにした。
【０１０４】
したがって、加熱時の基板温度をシミュレーションする方法と比較して、良好なはんだ付けが得られる加熱温度の確保に必要な部品間隔が試行錯誤なく、短時間で簡単に決定できる。
【０１０５】
図１８は、本発明における基板設計方法の実施方法として、基板設計ＣＡＤによって実施した一事例を示す慨念図である。
【０１０６】
設計画面上には部品Ａとその周辺の基板温度分布を示す同心円７および部品Ｂとその周辺の基板温度分布を示す同心円１１が表示されている。部品配置位置確定後に自動または手動でチェックを掛けることで、部品間隔Ｄが確保できているか確認できる。
【０１０７】
また、部品Ａが配置してある基板Ｃに部品Ｂを配置するときに、部品間隔Ｄが確保できない位置に配置使用とした場合に注意を表示する、あるいは、配置できないようにしてもよい。
【０１０８】
部品配置位置を確定した後には、基板全体の予想温度分布、または温度の最高部と最低部の少なくともいずれか一方を表示できるようにしてもよい。
【０１０９】
図１９は、本発明における基板設計方法を基板設計ＣＡＤによって実施した他の一事例を示す概念図である。
【０１１０】
設計画面上には部品Ａとその周辺の基板温度分布を示す同心円７、部品Ｂとその周辺の基抜温度分布を示す同心円１１、部品Ｅとその周辺の基板温度分布を示す同心円２３が表示されている。部晶Ａと部品Ｂの配置位置がすでに決定している状態で新たに部品Ｅを配置する場合で、部品Ｅの影響によって部品Ａと部品Ｂの少なくともいずれか一方のはんだ接合部が良好なはんだ付けが得られる温度に達しなくなる位置に部品Ｅを配置しようとした場合には、その旨の表示を行い、部品Ｅの影響を考慮して部品Ａと部品Ｂとの新たな部品間隔を算出して、部品Ａと部品Ｂが離れるようにする。あるいは、そのような位置に部品Ｅを配置できなくしてもよい。
【０１１１】
このように、本発明に係る基板設計方法の実施方法では、良好なはんだ付けが得られる加熱温度の確保に必要な部品間隔Ｄが適性であるか否かをチェックできる機能を有する。
【０１１２】
また、部品配置後の基板で加熱時の予想最低温度部と予想最高温度部のいずれか一方もしくは双方が表示できるようにしてもよいし、また、加熱時の基板全体の予想温度が表示できるようにしてもよいし、また、必要な部品間隔を確保できない領域に部品を配置しようとした場合にその旨を表示するか、あるいは部品が配置できない機能を有するようにしてもよい。
【０１１３】
したがって、チェック機能により、良好なはんだ付けが得られる加熱温度の確保に必要な部品間隔か否かをチェックすることができる。
【０１１４】
図２０は、基板温度が低下する部分に耐熱保証温度を超えやすい部品２４を配置した本発明における基板設計方法を用いた基板構造の実施の形態例である。
【０１１５】
この本発明に係る基板構造の実施の形態によれば、基板設計時において、あらかじめ測定した温度データに基づいて加熱時における部品周辺の基板温度分布（部品からの距離と基板温度との関係）を予測し、基板温度が低い部分に耐熱保証温度を越えやすい部品を配置するようにしてある。この場合、耐熱保証温度を越えやすい部品はアルミ電解コンデンサやＬＥＤである。
【０１１６】
したがって、部品の影響による基板温度の低下が大きい位置にアルミ電解コンデンサなど耐熱保証温度を越えやすい部品を配置することで、さらに加熱時の温度ばらつきが小さい基板を設計できる。
【０１１７】
【発明の効果】
以上説明したように、本発明に係る基板設計方法によれば、リフロ条件を一定にした場合の基板温度ばらつきのうち、部品による基板の温度低下を予測可能とし、生基板の温度と部品による基板の温度低下の許容値から、はんだ付け温度の確保に必要な部品間隔を決定できるようになる。
【０１１８】
また、本発明に係る基板設計方法の実施方法によれば、チェック機能により、良好なはんだ付けが得られる加熱温度の確保に必要な部品間隔か否かをチェックすることができる。
【０１１９】
また、本発明に係る基板構造によれば、部品の影響による基板温度の低下が大きい位置にアルミ電解コンデンサなど耐熱保証温度を越えやすい部品を配置することで、さらに加熱時の温度ばらつきが小さい基板を設計できる。
【図面の簡単な説明】
【図１】リフロ全体の温度プロファイルの説明図である。
【図２】リフロ時の基板温度のばらつきΔＴの定義の説明図である。
【図３】部品間隔Ｄを説明するための基板構造の説明図である。
【図４】（１）は部品周辺の基板温度分布の説明図である。
（２）はＱＦＰ周辺の基板温度分布の実測データのグラフ図である。
【図５】部品間隔Ｄとその中間での部品の熱容量による温度低下ΔＴ_l との関係を示すグラフ図である。
【図６】（１）は基板上における１つの部品周辺の基板温度分布の説明図である。
（２）は１つの部品周辺の基板温度分布を温度と位置とで表現したグラフ図である。
【図７】（１）は基板上における２つの部品周辺の基板温度分布の説明図である。
（２）は２つの部品周辺の基板温度分布を温度と位置とで表現したグラフ図である。
【図８】ＱＦＰ周辺の基板温度分布の実測データのグラフ図である。
【図９】端子部を除いた部品形状が正方形の部品での、ある加熱条件における部品の種類と基板温度分布との関係を示す実験データを示すグラフ図である。
【図１０】端子部を除いた部品形状が正方形の部品での、ある加熱条件における部品のサイズと基板温度分布との関係を示す実験データを示すグラフ図である。
【図１１】端子部を除いた部品形状が正方形の部品がリフロ面にある場合の、ある加熱条件における部品周辺の基板温度分布との関係を示す実験データを示すグラフ図である。
【図１２】端子部を除いた部品形状が長方形の部品が裏面にある場合の、ある加熱条件における部品周辺の基板温度分布との関係を示す実験データを示すグラフ図である。
【図１３】基板の仕様と近似直線との関係を一般化するのに使用したデータのグラフ図である。
【図１４】基板厚と生基板の温度との関係を示すグラフ図である。
【図１５】基板の層数と温度勾配との関係を示すグラフ図である。
【図１６】加熱条件の違いによる部品中心に最も近い部品端からの距離と基板温度（生基板温度）の差との関係の実測データを示すグラフ図である。
【図１７】市販のパソコン用表計算ソフトウェアによって部品間隔を算出する基板設計方法の実施手段の一事例の説明図である。
【図１８】本発明における基板設計方法を基板設計ＣＡＤによって実施した一事例を示す慨念図である。
【図１９】本発明における基板設計方法を基板設計ＣＡＤによって実施した他の事例を示す慨念図である。
【図２０】基板温度が低下する部分に耐熱保証温度を超えやすい部品を配置した基板構造の説明図である。
【符号の説明】
Ａ部品
Ｂ部品
Ｃ基板
Ｄ部品間隔
Ｅ部品
３部品の中心線
４基板温度分布
５生基板を加熱した時の温度
６部品Ａの中心に最も近い位置
７部品Ａを中心とする同心円
９部品Ｂ周辺の加熱時の基板温度分布
１０部品Ｂの中心に最も近い位置
１１部品Ｂを中心とする同心円
１２部品Ａと部品Ｂとの間の基板温度分布
１３部品Ａのはんだ接合部
１４部品Ｂのはんだ接合部
１８最低加熱温度
１９入力部
２０基板温度分布の近似式表示部
２１部品間隔表示部
２３同心円
２４耐熱保証温度を超えやすい部品[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a board design method, its implementation means, and a board structure designed by the board design method when determining the arrangement position of a surface mount component on a printed wiring board or the like.
[0002]
[Prior art]
Reflow is used as a method for soldering surface-mounted components (hereinafter, components) to a substrate. Each component on the board being reflowed varies in temperature due to differences in heat capacity and heat transfer. Large variations can cause component thermal damage and poor soldering, adversely affecting product reliability and yield.
[0003]
In particular, when Pb-free solder, which has started to be used in recent years, is used for reflow, the allowable temperature variation is reduced due to the high melting point. For this reason, even if the board can be reflowed without problems with the conventional solder, there is an increased possibility of component thermal damage and poor soldering.
[0004]
When designing a board for a new product, it is necessary to select a large, large heat capacity component or low heat resistance component in the component selection, or to redesign the substrate by trial and error. Increase the development period and development cost. In addition, thermal damage to parts is often not found by inspection, and can flow out to the market and cause failure. For this reason, it is desired to realize a substrate design that predicts temperature variations in advance and facilitates reflow.
[0005]
As a conventional substrate design method for determining the placement position of the surface mount component, for example, an MPU (miniature arithmetic processing unit) and a memory (storage device) are used to suppress signal delay time and reduce electrical noise. Can be placed as close as possible.
[0006]
In addition, as another conventional substrate design method for arranging surface mount components, a method of determining the component interval by sequentially simulating the substrate temperature during heating and evaluating the temperature variation from the simulation result (Disclosed in Japanese Patent Laid-Open No. 11-201647).
[0007]
[Problems to be solved by the invention]
However, in the former conventional board design method described above, when heating the board to solder the component, the temperature variation on the board surface caused by the difference in the heat capacity of the part is unknown, and the temperature There is a problem that some parts may be thermally damaged due to excessive rise in temperature, or there is a risk that the temperature rise locally is insufficient and soldering failure occurs.
[0008]
In addition, in the latter latter board design method, it takes time to create an analysis model, and the temperature variation on the board surface during heating can be evaluated for the first time after simulation of heating. The decision has a problem that trial and error by simulation is necessary.
[0009]
The present invention has been made paying attention to the above-mentioned problems, and the first object thereof is based on temperature data measured in advance, the distance from the component during heating, the substrate temperature, and the like. A board design method that can predict the relationship between the parts (hereinafter referred to as the board temperature distribution around the parts) quantitatively and calculate the part spacing required to ensure the soldering temperature between the parts with a simple method during board design. Is to provide.
[0010]
In addition, the second object of the present invention is to provide a method for carrying out a board design method capable of checking whether or not a component interval necessary for securing a heating temperature at which good soldering is obtained is appropriate. Is to provide.
[0011]
In addition, the third object of the present invention is to design a board with a smaller temperature variation during heating by arranging parts that are likely to exceed the heat resistance guarantee temperature at a position where the substrate temperature is greatly lowered due to the influence of the parts. It is to provide a substrate structure that can be used.
[0012]
[Means for Solving the Problems]
In order to achieve the first object described above, a substrate design method according to the present invention provides a substrate temperature distribution (distance from a component and a substrate) around a component during heating based on temperature data measured in advance during the substrate design. Component spacing required to ensure a good soldering temperature by predicting the temperature) and calculating the temperature change that the component exerts on the solder joints of other components through the board I decided to decide.
[0013]
Then, the raw substrate temperature and the substrate temperature distribution around the component may be used as the temperature data, and the temperature data may be measured by limiting the raw substrate and the component.
[0014]
Here, the component is an electronic component to be mounted on the substrate, such as a package component such as QFP or BGA. The raw board is a board on which no component is mounted. The component interval is, for example, an interval between opposing side end portions of two components or an interval between centers of two components.
[0015]
Therefore, it is possible to predict the temperature drop of the board due to the part among the board temperature variation when the reflow condition is fixed, and it is necessary to secure the soldering temperature from the raw board temperature and the allowable value of the temperature drop of the board due to the part It becomes possible to determine a proper part interval.
[0016]
In addition, it is possible to quantify the relationship between the temperature drop of adjacent parts due to the influence of a large part that does not easily rise in temperature and the part spacing. In this way, since it can be understood by a specific numerical value how many mm the part interval should be set, it is possible to quantitatively determine whether there is a problem in the reflow temperature.
[0017]
Further, the board design method according to the present invention is the above-described board design method according to the present invention, in which the temperature of the raw board on which no component is mounted and the substrate temperature around each component when several components are heated. By measuring the distribution of the substrate in advance, the substrate temperature distribution around the component during heating can be calculated using the heat capacity, specific heat, heat conduction, heat transfer, heat, etc. Factors that affect copying are formulated as parameters, so that the substrate temperature distribution around the parts can be predicted quantitatively.
[0018]
Therefore, it is possible to easily evaluate the change in the substrate temperature due to the effect of the component on the temperature of the raw substrate and the range of the influence, and the substrate temperature variation due to the component among the substrate temperature variation when the reflow condition is constant Predictability is possible, and the part interval necessary for securing the soldering temperature can be determined from the temperature of the raw board and the allowable value of the temperature drop of the board due to the parts.
[0019]
When the substrate temperature distribution around the component is predicted using the component type as a parameter, the component classification may be based on the difference in the measured substrate temperature distribution around the component.
[0020]
In addition, the shape of the part may be used for classifying the part, the internal structure of the part may be used for classifying the part, and the material of the part may be used for classifying the part. Alternatively, the position of the solder joint may be used for component classification.
[0021]
Further, when the substrate temperature distribution around the component is predicted using the component size as a parameter, the length and width of the component may be used as the component size. At this time, the length and width of the component may be the size excluding the terminal portion.
[0022]
The substrate temperature distribution around the component may be predicted separately in the length direction and the width direction of the component. Also, the thickness of the part may be used as the part size. At this time, the thickness of the component may be a size excluding the terminal portion.
[0023]
Further, when the substrate temperature distribution around the component is predicted using the number of layers of the raw substrate as a parameter, the presence or absence of the inner layer may be focused on as the number of layers of the raw substrate.
[0024]
Further, the board design method according to the present invention is the above-described board design method according to the present invention, wherein a component that greatly reduces the substrate temperature is selected based on a prediction result of the substrate temperature distribution around the component, and the solder of other components The temperature drop exerted on the joint was calculated so that the component spacing at which each component can secure the soldering temperature can be calculated.
[0025]
Therefore, compared with the method of simulating the substrate temperature during heating, the component spacing necessary for ensuring the heating temperature at which good soldering can be obtained can be easily determined in a short time without trial and error.
[0026]
The board design method according to the present invention is the board design method according to the present invention described above, wherein the substrate temperature distribution around the component may be obtained based on the center of the component, or the substrate temperature distribution around the component. May be determined based on the end of the part closest to the center of the part.
[0027]
Further, it is preferable that the substrate temperature distribution around the component approximates linearly. Alternatively, the substrate temperature distribution around the component is preferably approximated to a curve. In this case, the linear is a straight line, for example. The curve may be, for example, a multi-order expression such as quadratic or cubic, or a logarithmic function.
[0028]
In addition, for parts that can be judged to be negligible and have little influence on the substrate temperature based on the temperature data measured in advance, the peripheral substrate temperature distribution is not predicted, and it is arranged at any position on the raw substrate. Alternatively, as a result of predicting the substrate temperature distribution around the component, components that have a small influence on the substrate temperature and can be determined to be negligible may be arranged at arbitrary positions on the raw substrate. The fact that the influence on the substrate temperature is small and can be ignored is determined in consideration of measurement errors and furnace temperature changes.
[0029]
Further, the substrate temperature at an arbitrary position may be predicted by superimposing the decrease in the substrate temperature due to a plurality of components, and the interval between the components necessary for ensuring the heating temperature at which good soldering can be obtained may be determined.
[0030]
In addition, the effect of the component on the substrate temperature during heating is evaluated by the difference between the substrate temperature around the component and the temperature of the raw substrate, and the effects of individual components are superimposed to predict the soldering temperature of the component Thus, the interval between parts necessary for ensuring the heating temperature at which good soldering can be obtained may be determined.
[0031]
Further, the substrate temperature around the component at the time of heating under a certain heating condition may be predicted.
[0032]
Further, the average value may be predicted by comprehensively including the substrate temperature around the component during heating under a plurality of heating conditions.
[0033]
Further, the difference in the substrate temperature around the component during heating depending on the heating condition may be corrected by correcting the mathematical formula by adding measurement data.
[0034]
In addition, the substrate design method according to the present invention calculates the substrate temperature distribution around the component during heating using spreadsheet software such as a personal computer in the above-described substrate design method according to the present invention.
[0035]
Then, the part interval during heating is calculated using spreadsheet software such as a personal computer.
[0036]
Therefore, in order to easily use the board design method according to the present invention, it is possible to use a personal computer spreadsheet software as a tool, and the designer can predict the temperature drop of the board and lay out the components.
[0037]
In order to achieve the second object, the substrate design method according to the present invention includes a substrate temperature distribution (components) around a component during heating based on temperature data measured in advance during the substrate design. Between the distance from the board and the board temperature), and by calculating the temperature change that the part exerts on the solder joints of other parts through the board, it is possible to secure a heating temperature that can achieve good soldering It is possible to determine a part interval necessary for checking and check whether or not the part interval is appropriate.
[0038]
Here, the raw substrate temperature and the substrate temperature distribution around the component may be used as temperature data measured in advance, and the temperature data may be measured by limiting the raw substrate and components.
[0039]
In addition, one or both of the expected minimum temperature part and the expected maximum temperature part at the time of heating may be displayed on the board after the components are arranged, and the expected temperature of the entire board at the time of heating can be displayed. It may be.
[0040]
In addition, when a component is to be arranged in an area where a necessary component interval cannot be secured, a message to that effect may be displayed, or a function in which the component cannot be arranged may be provided.
[0041]
Therefore, it is possible to check whether or not the distance between the components is necessary for ensuring a heating temperature at which good soldering can be obtained.
[0042]
In order to achieve the above third object, the circuit board structure according to the present invention has a substrate temperature distribution (distance from the component) around the component during heating based on temperature data measured in advance at the time of designing the substrate. The relationship between the temperature and the substrate temperature was predicted, and components that would easily exceed the heat-resistant guaranteed temperature were placed in areas where the substrate temperature was low.
[0043]
And it is preferable that the component which is easy to exceed the heat-resistant guarantee temperature is an aluminum electrolytic capacitor. Moreover, it is preferable that the component which is easy to exceed heat-resistant guarantee temperature is LED.
[0044]
Therefore, by disposing a component that easily exceeds the guaranteed heat resistance temperature, such as an aluminum electrolytic capacitor, at a position where the substrate temperature is greatly lowered due to the influence of the component, it is possible to design a substrate with a smaller temperature variation during heating.
[0045]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0046]
Problems caused by board temperature variations during reflow are thermal damage to components and poor soldering. In order to prevent these problems from occurring, it is necessary that the body temperature of the component is equal to or lower than the heat resistance temperature (which varies depending on the component), and the terminal temperature is equal to or higher than the melting point of the solder.
[0047]
In the reflow temperature profile, as shown in FIG. 1 for one substrate, a temperature difference between the body temperature of a component whose temperature is most likely to rise and the terminal temperature of a component whose temperature is most difficult to rise appears.
[0048]
For this reason, it can be defined as substrate temperature variation ΔT = (maximum component body temperature) one (minimum component terminal temperature).
[0049]
As shown in FIG. 2 (enlarged view of the circled portion in FIG. 1), the substrate temperature variation ΔT is a specific component based on the peak temperature when a raw substrate on which no component is mounted is passed through a reflow furnace. Temperature rise ΔT seen in_h And the temperature drop ΔT due to the heat capacity of large parts_l It can be divided into two.
[0050]
Considering the reduction of ΔT for the entire substrate, the problem is complicated. However, if ΔTh and ΔTl are evaluated for each individual component, it can be seen that it is only necessary to focus on the largest component.
[0051]
ΔT_h And ΔT_l ΔT_h Does not affect the temperature of other components. In contrast, ΔT_l This affects not only a decrease in the terminal temperature of the component itself, but also the temperature of the surrounding substrate. As a result, the terminal temperature of adjacent components can be lowered, leading to poor soldering. Therefore, in the board design, it is necessary to secure an interval in which adjacent components do not affect each other's solderability.
[0052]
In order to reduce the substrate temperature variation ΔT of the entire substrate, ΔT_h Or ΔT_l Although it is sufficient to suppress at least one of the_l Mainly to reduce
[0053]
In the reflow furnace, the temperature is raised by a combination of different heating principles such as HA (Hot Air) (hot air) and IR (Infrared Ray) (infrared rays), and the temperature profile is the heating conditions, heat capacity of the parts, heat absorption, heat transfer, Relatively determined by various factors such as component layout.
[0054]
Accordingly, the substrate temperature variation ΔT also varies depending on these factors. The factors of the substrate temperature variation ΔT can be broadly classified into two types, those related to the component layout and those related to the reflow furnace.
[0055]
Items resulting from reflow furnaces vary greatly depending on the furnace type and condition settings. Since it is ideal that the conditions of the reflow furnace are originally fixed and used in an optimal state, general-purpose optimal conditions were obtained and fixed in advance.
[0056]
In order to reduce the substrate temperature variation ΔT, the selection and layout of components are important. Of these, changing the parts used is often difficult due to the function of the circuit. Therefore, an effective means for reducing the substrate temperature variation ΔT is the component layout.
[0057]
Conventionally, productivity has been considered in addition to noise reduction and heat dissipation of high-power components during component layout, but substrate temperature variation ΔT has not been considered because there is no quantitative evaluation method. However, the substrate temperature variation ΔT cannot be ignored due to the high density of the substrate mounting or the introduction of Pd-free solder. For this reason, ΔT_l 3 is quantitatively predicted and evaluated at the design stage._l A means is needed to determine In FIG. 3, A and B are components, and C is a substrate.
[0058]
Since there are various types of parts, the parts are classified into several types according to items that affect the reflow temperature, such as the outer shape, structure and material, and ΔT shown in FIG._l First revealed the big parts.
[0059]
By classifying parts according to the items shown in [Table 1], the influences of parts with similar thermal characteristics are considered together rather than considering the influence of all parts individually. In addition, we focused on parts that make reflow difficult.
[0060]
[Table 1]

[0061]
ΔT_l First, ΔT_l Was made into a database so that the validity of the predicted values could be confirmed. A large number of components are mounted on an actual substrate, but for simplification, only two components A and B are taken out and the relationship between the component interval D and the reflow temperature is considered.
[0062]
As described above, the reflow heating conditions were fixed to standard heating conditions set in advance (the ratio of HA to IR and the wind speed / conveyor speed that can compress the substrate temperature variation ΔT on a test board on which representative components are mounted).
[0063]
According to the board design method of the present invention, “the influence of the component layout on ΔT appears due to a phenomenon in which the temperatures of the parts are lowered through the board, and the larger the parts that are less likely to rise in temperature, the greater the influence on the periphery”. Therefore, we focused on the “substrate temperature distribution around the component”, not the component temperature itself.
[0064]
By setting the evaluation target as the substrate temperature, data once measured can be used regardless of the combination of components. For example, the substrate temperature distribution around the component A can be used when determining the component interval D between the component A and other components (including the component A). The substrate temperature around the component can be measured simultaneously with the component temperature.
[0065]
In the board design method of the present invention, the number of temperature measurements for k types of components is k × n times (_kC₁ Xn), and even if one kind of part is added, additional measurement may be performed only n times for the part. [Table 2] shows a comparison of the number of measurements required for determining the component interval D between the conventional method and the board design method (this method) of the present invention.
[0066]
[Table 2]

[0067]
In the conventional ΔT evaluation method, only the reflow temperature of the component is measured and evaluated. For this reason, in order to obtain the relationship between the component interval D and the reflow temperature, it is necessary to change the component interval D and measure the reflow temperature. For example, for the parts A and B, the reflow temperature is measured by changing the part interval D several times. Further, the same temperature measurement is necessary for the parts A and B.
[0068]
In such a conventional method, for k types of parts,_k ₊ ₁ C₂ Xxx x n times (x: number of parts interval D level, n: number of repetitions) is required. When one kind of part is added, (k + 1) x xx n additional measurements are required. is there. For this reason, it was thought that construction and maintenance of a database were very difficult.
[0069]
In the substrate design method of the present invention, first, the peripheral substrate temperature distribution of a single component was measured for each type of component classified as described above. As a result, it was found that the substrate temperature distribution around the component can be approximated to a straight line.
[0070]
As an example, the state of substrate temperature distribution around a QFP (Quad Flat Package) as a part is shown in FIG. 4 (1), and the measured data is shown in FIG. 4 (2). It can be seen from (2) of FIG. 4 that the measurement data agrees well with the approximate straight line. ΔT_l From this size, the influence of the component on the peripheral substrate temperature can be evaluated.
[0071]
If the substrate temperature distribution between the two components A and B can be predicted from the substrate temperature distribution around the component, ΔT_l And the part interval D can be quantified. Therefore, it was examined whether the substrate temperature between the two components A and B could be predicted based on the substrate temperature distribution around the components shown in (1) and (2) of FIG.
[0072]
As a result, ΔT due to individual parts_l It was clarified that the substrate temperature between the two parts A and B can be predicted by superimposing. As an example, FIG. 5 shows a result obtained by measuring the intermediate substrate temperature while changing the component interval D and comparing the predicted values obtained by superimposing the influences of the individual components A and B.
[0073]
The difference between the measured value and the predicted value was in the range of 2 to 3 ° C. and measurement error. The substrate temperature between the two parts A and B2 is ΔT due to the individual parts._l It can be seen that it can be predicted by overlaying.
[0074]
Therefore, ΔT necessary to secure the raw board temperature and solderability_l If the allowable value is set, the component interval D at which no soldering failure occurs can be determined. ΔT_l ΔT in the larger part of_h If a large part is placed, ΔT_h And ΔT can be further reduced.
[0075]
That is, the state of the substrate temperature distribution around the component during heating is shown in (1) and (2) of FIG. On the substrate C, one component A having a square component shape excluding the terminal portion is mounted.
[0076]
The graph (2) in FIG. 6 represents the substrate temperature distribution 4 during heating on the center line 3 of the component A. Due to the influence of the heat capacity of the component A, the temperature is lower than the substrate temperature 5 at the time of heating in the vicinity of the component A and becomes the lowest at the position 6 closest to the center of the component A, but as the distance from the component A increases. Since the influence becomes small, the substrate temperature rises and eventually becomes equal to the temperature 5 when the raw substrate is heated.
[0077]
The substrate temperature distribution 4 is approximated by a straight line (linear). When the component shape excluding the terminal portion is square, the substrate temperature around the component is distributed in a concentric circle 7 centered on the component A. The substrate temperature distribution 4 may be approximated by a curve.
[0078]
(1) and (2) in FIG. 7 are schematic views showing an example of a method for determining the component interval D. FIG. In (1) of FIG. 7, a component A and a component B having a square component shape excluding the terminal portion are mounted on the substrate C. In (1) of FIG. 7, 10 is the position closest to the center of the part B, and 11 is a concentric circle with the part B as the center.
[0079]
As shown in (2) of FIG. 7, in the substrate temperature distribution 12 between the component A and the component B, the temperature drop amount H on the component A side is due to the component A from the temperature 5 when the raw substrate is heated. The temperature decrease amount H1 and the temperature decrease amount H2 due to the component B are given in an overlapping manner, and the temperature decrease amount I on the component B side is the temperature decrease amount I1 due to the component B from the temperature 5 when the raw substrate is heated. The temperature drop amount I2 due to the part A is given in an overlapping manner.
[0080]
Therefore, the temperature of the solder joint portion 13 of the component A is lowered due to the influence of the component B, and similarly, the temperature of the solder joint portion 14 of the component B is lowered due to the influence of the component A.
[0081]
The part interval D is determined so that the temperatures of the solder joint part 13 of the part A and the solder joint part 14 of the part B are equal to or higher than the minimum heating temperature 18 necessary for ensuring a good joint. Note that 9 in FIG. 7 is a substrate temperature distribution during heating around the component B.
[0082]
The substrate temperature distribution around the component differs depending not only on the type of component, but also on the component size and board specifications. Therefore, for package parts such as QFP, temperature measurement was performed with several parts, and it was evaluated how the peripheral substrate temperature distribution changes depending on the part size.
[0083]
As a result, the relationship between the component size and the approximate line is generalized so that the substrate temperature distribution during reflow can be predicted from the component size. FIG. 8 shows a part of data used to generalize the relationship between the QFP size and the approximate line.
[0084]
In FIG. 8, the error between the approximate straight line based on the measured values and the generalized approximate straight line is 3 ° C. or less, and it can be said that the generalized approximate straight line is a reasonable value.
[0085]
In addition, FIG. 9 shows an example of experimental data indicating the relationship between the type of component under a certain heating condition and the substrate temperature distribution in a component having a square shape excluding the terminal portion. FIG. 10 shows an example of experimental data showing the relationship between the component size and the substrate temperature distribution under a certain heating condition in a square component.
[0086]
From this experimental data, it can be seen that the mounting area and thickness excluding the terminal portion as the component size affect the substrate temperature distribution, and the degree of influence varies depending on the type of component. From this, it can be said that the substrate temperature distribution around the component can be predicted from the type and size of the component if data is measured at several sizes for each type of component. The classification of the parts may be performed based on the measurement result, but may be performed according to the shape of the part, the internal structure, the material, the position of the solder joint portion, or the like.
[0087]
FIG. 11 is an example of experimental data showing a relationship with a substrate temperature distribution around a component under a certain heating condition when a component having a square shape excluding the terminal portion is on the reflow surface. It can be seen that the temperature of the raw substrate is about 230 ° C., the substrate temperature around the component is lowered, and the substrate temperature distribution around the component can be linearly approximated.
[0088]
FIG. 12 is an example of experimental data showing a relationship with a substrate temperature distribution around a component under a certain heating condition when a component having a rectangular shape excluding the terminal portion is on the back surface. From this experimental data, it can be seen that the substrate temperature distribution needs to be obtained for each direction because the board temperature distribution differs between the length direction and the width direction.
[0089]
Similarly to the component size, the difference in the substrate temperature distribution depending on the substrate specifications (plate thickness and number of layers) was confirmed by an experiment using QFP, and the relationship between the substrate specifications and the approximate line was generalized based on the data.
[0090]
FIG. 13 shows a part of data used to generalize the relationship between the board specification and the approximate line. In FIG. 13, the error between the approximate straight line based on the measured values and the generalized approximate straight line is 5 ° C. or less, and it can be said that the generalized approximate straight line is a substantially reasonable value as in FIG.
[0091]
FIG. 14 is an example of experimental data showing the relationship between the substrate thickness under a certain heating condition and the substrate temperature distribution around the component. It can be seen that the temperature of the raw substrate decreases as the substrate thickness increases.
[0092]
FIG. 15 is an example of experimental data showing the relationship between the number of substrate layers under a certain heating condition and the substrate temperature distribution around the component. It can be seen that the temperature gradient of the substrate temperature distribution around the component differs between the double-sided board and the multilayer board.
[0093]
FIG. 16 shows an example of the difference in substrate temperature distribution around the component due to the difference in heating conditions. It can be seen that the substrate temperature distribution around the component varies depending on the heating conditions even for the same substrate and the same component. By adding the component temperature data, the difference in substrate temperature distribution due to the difference in heating conditions can be corrected.
[0094]
FIG. 17 shows an example of means for implementing the board design method according to the present invention, in which the component spacing is calculated using commercially available personal computer spreadsheet software.
[0095]
In FIG. 17, 19 is an input unit, 20 is an approximate expression display unit for substrate temperature distribution, and 21 is a component interval display unit.
[0096]
And, in the input unit 19, the types of components A and B, the component size (length, width, thickness, lead length), the thickness and number of layers of the substrate C, the temperature of the raw substrate, and good soldering By inputting the minimum temperature for ensuring the above, the approximate expression display unit 20 for the substrate temperature distribution predicts the peripheral substrate temperature distribution for the two components A and B, and the component interval display unit 21 displays the component A, The minimum required component interval D can be calculated instantaneously without trial and error in accordance with the arrangement plane of B. Here, the material of the substrate may be selectable such as a glass epoxy substrate, a ceramic substrate, and a flexible substrate.
[0097]
In this way, use a spreadsheet software such as a personal computer to calculate the substrate temperature distribution around the part during heating, and use a spreadsheet software such as a personal computer to calculate the part interval during heating. As a result, the board design method according to the present invention is made into a tool so that it can be used easily, and the designer can predict the temperature drop of the board and lay out the components.
[0098]
For parts that can be judged to be negligible and have little influence on the board temperature based on the temperature data measured in advance, it is not possible to place the board temperature distribution around the part in any position on the raw board. Further, as a result of predicting the substrate temperature distribution around the component, it is possible to place a component that can be determined to be negligible with little influence on the substrate temperature and placed at any position on the raw substrate.
[0099]
According to the embodiment of the substrate design method according to the present invention described above, among the substrate temperature variations when the reflow conditions are made constant, it is possible to predict the temperature decrease of the substrate due to the component, and the temperature of the raw substrate and the substrate due to the component can be predicted. From the allowable value of the temperature drop, it becomes possible to determine the part interval necessary for securing the soldering temperature.
[0100]
In addition, it is possible to quantify the relationship between the temperature drop of adjacent parts due to the influence of a large part that does not easily rise in temperature and the part spacing. In this way, since it can be understood by a specific numerical value how many mm the part interval should be set, it is possible to quantitatively determine whether there is a problem in the reflow temperature.
[0101]
Further, according to the embodiment of the board design method according to the present invention, the temperature of the raw board on which no part is mounted and the distribution of the board temperature around each part when several parts are heated are measured in advance. By modeling, the substrate temperature distribution around the component during heating can be modeled, and the substrate temperature distribution around the component can be quantitatively predicted using parameters such as the type and size of the component and the thickness and number of layers of the raw substrate. did.
[0102]
Therefore, it is possible to easily evaluate the change in the substrate temperature due to the effect of the component on the temperature of the raw substrate and the range of the influence, and the substrate temperature variation due to the component among the substrate temperature variation when the reflow condition is constant Predictability is possible, and the part interval necessary for securing the soldering temperature can be determined from the temperature of the raw board and the allowable value of the temperature drop of the board due to the parts.
[0103]
In addition, according to the embodiment of the board design method according to the present invention, the part that greatly reduces the board temperature is selected based on the prediction result of the board temperature distribution around the part, and the temperature exerted on the solder joint of other parts By calculating the drop, it was possible to calculate the distance between parts that could ensure the soldering temperature of each part.
[0104]
Therefore, compared with the method of simulating the substrate temperature during heating, the component spacing necessary for ensuring the heating temperature at which good soldering can be obtained can be easily determined in a short time without trial and error.
[0105]
FIG. 18 is a conceptual diagram showing an example implemented by the board design CAD as an implementation method of the board design method of the present invention.
[0106]
On the design screen, a concentric circle 7 indicating the substrate temperature distribution around the component A and its periphery and a concentric circle 11 indicating the substrate temperature distribution around the component B and its periphery are displayed. By checking automatically or manually after the part placement position is determined, it can be confirmed whether the part interval D is secured.
[0107]
Further, when the component B is arranged on the board C on which the component A is arranged, a caution may be displayed or may not be arranged when the component is used at a position where the component interval D cannot be secured.
[0108]
After the component placement position is determined, the predicted temperature distribution of the entire board or at least one of the highest and lowest temperature portions may be displayed.
[0109]
FIG. 19 is a conceptual diagram showing another example in which the board design method according to the present invention is implemented by board design CAD.
[0110]
On the design screen, a concentric circle 7 indicating the substrate temperature distribution of the component A and its surroundings, a concentric circle 11 indicating the basic temperature distribution of the component B and its surroundings, and a concentric circle 23 indicating the substrate temperature distribution of the component E and its surroundings are displayed. ing. In the case where the part E is newly arranged in a state where the arrangement positions of the part crystal A and the part B have already been determined, the solder joint of at least one of the part A and the part B is good due to the influence of the part E. If the part E is to be arranged at a position where the temperature cannot be reached, a display to that effect is displayed, and a new part interval between the part A and the part B is calculated in consideration of the influence of the part E. Thus, the parts A and B are separated. Alternatively, the part E may not be arranged at such a position.
[0111]
As described above, the method for carrying out the board designing method according to the present invention has a function of checking whether or not the component interval D necessary for securing the heating temperature at which good soldering is obtained is appropriate.
[0112]
In addition, one or both of the expected minimum temperature part and the expected maximum temperature part at the time of heating may be displayed on the board after the components are arranged, and the expected temperature of the entire board at the time of heating can be displayed. Alternatively, when a component is to be arranged in an area where a necessary component interval cannot be secured, a message to that effect may be displayed, or a function may not be provided.
[0113]
Therefore, it is possible to check whether or not the distance between the components is necessary for ensuring a heating temperature at which good soldering can be obtained.
[0114]
FIG. 20 shows an embodiment of a substrate structure using the substrate design method according to the present invention in which a component 24 that easily exceeds the guaranteed heat resistance temperature is arranged in a portion where the substrate temperature decreases.
[0115]
According to the embodiment of the substrate structure according to the present invention, the substrate temperature distribution around the component during heating (the relationship between the distance from the component and the substrate temperature) is calculated based on the temperature data measured in advance at the time of designing the substrate. In anticipation, parts that are likely to exceed the heat resistance guarantee temperature are arranged in the part where the substrate temperature is low. In this case, parts that easily exceed the heat-resistant guaranteed temperature are aluminum electrolytic capacitors and LEDs.
[0116]
Therefore, by disposing a component that easily exceeds the guaranteed heat resistance temperature, such as an aluminum electrolytic capacitor, at a position where the substrate temperature is greatly lowered due to the influence of the component, it is possible to design a substrate with a smaller temperature variation during heating.
[0117]
【The invention's effect】
As described above, according to the board design method according to the present invention, it is possible to predict the temperature drop of the board due to the part among the board temperature variations when the reflow conditions are constant, and the temperature of the raw board and the board due to the part From the permissible value of the temperature drop, it is possible to determine the component interval necessary for securing the soldering temperature.
[0118]
Further, according to the method for carrying out the board designing method according to the present invention, it is possible to check whether or not the distance between the components is necessary for securing the heating temperature at which good soldering can be obtained by the check function.
[0119]
In addition, according to the substrate structure of the present invention, by placing a component that easily exceeds the guaranteed heat resistance temperature, such as an aluminum electrolytic capacitor, at a position where the decrease in the substrate temperature due to the effect of the component is large, the substrate is further reduced in temperature variation during heating. Can be designed.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a temperature profile of an entire reflow.
FIG. 2 is an explanatory diagram of a definition of a substrate temperature variation ΔT during reflow.
FIG. 3 is an explanatory diagram of a board structure for explaining a component interval D;
4A is an explanatory diagram of a substrate temperature distribution around a component. FIG.
(2) is a graph of measured data of substrate temperature distribution around the QFP.
FIG. 5 shows a temperature drop ΔT due to the heat capacity of a part interval D and the part in between._l It is a graph which shows the relationship.
FIG. 6A is an explanatory diagram of a substrate temperature distribution around one component on a substrate.
(2) is a graph representing the substrate temperature distribution around one component in terms of temperature and position.
FIG. 7 is an explanatory diagram of a substrate temperature distribution around two components on a substrate.
(2) is a graph representing the substrate temperature distribution around two components in terms of temperature and position.
FIG. 8 is a graph of measured data of the substrate temperature distribution around the QFP.
FIG. 9 is a graph showing experimental data showing the relationship between the type of component and the substrate temperature distribution under a certain heating condition in a component having a square shape excluding the terminal portion.
FIG. 10 is a graph showing experimental data showing the relationship between the component size and the substrate temperature distribution under a certain heating condition in a component having a square shape excluding the terminal portion.
FIG. 11 is a graph showing experimental data showing a relationship with a substrate temperature distribution around a component under a certain heating condition when a component having a square shape excluding the terminal portion is on the reflow surface.
FIG. 12 is a graph showing experimental data showing a relationship with a substrate temperature distribution around a component under a certain heating condition when a component having a rectangular shape excluding the terminal portion is on the back surface.
FIG. 13 is a graph of data used to generalize the relationship between substrate specifications and approximate lines.
FIG. 14 is a graph showing the relationship between substrate thickness and raw substrate temperature.
FIG. 15 is a graph showing the relationship between the number of layers of a substrate and a temperature gradient.
FIG. 16 is a graph showing measured data of the relationship between the distance from the component end closest to the component center and the difference in substrate temperature (raw substrate temperature) due to the difference in heating conditions.
FIG. 17 is an explanatory diagram of an example of means for implementing a board design method for calculating a component interval by using commercially available personal computer spreadsheet software.
FIG. 18 is a conceptual diagram showing an example in which the substrate design method according to the present invention is implemented by substrate design CAD.
FIG. 19 is a conceptual diagram illustrating another example in which the substrate design method according to the present invention is implemented by substrate design CAD.
FIG. 20 is an explanatory diagram of a board structure in which components that easily exceed the heat resistance guarantee temperature are arranged in a portion where the board temperature decreases.
[Explanation of symbols]
A parts
B parts
C substrate
D Parts spacing
E parts
3 Centerline of parts
4 Substrate temperature distribution
5 Temperature when the raw substrate is heated
6 Position closest to the center of part A
7 Concentric circles centering on part A
9 Substrate temperature distribution during heating around component B
10 Position closest to the center of part B
11 Concentric circles centering on part B
12 Substrate temperature distribution between component A and component B
13 Solder joint of component A
14 Solder joint of component B
18 Minimum heating temperature
19 Input section
20 Substrate temperature distribution approximate expression display
21 Parts spacing display
23 Concentric circles
24 Parts that easily exceed the heat-resistant guaranteed temperature

Claims

At the time of board design, based on the temperature data measured in advance, the substrate temperature distribution around the part at the time of heating (the relationship between the distance from the part and the board temperature) is predicted, and the part passes through the board to the other parts. A board design method characterized in that a component interval necessary for ensuring a heating temperature at which good soldering is obtained is determined by calculating a temperature change exerted on a solder joint.

By measuring in advance the temperature of the raw board on which the component is not mounted and the substrate temperature distribution around each of the components at the time of heating for some of the components, the temperature around the components at the time of heating is measured. 2. The substrate temperature distribution is expressed in terms of parameters such as the type and size of the component and the thickness, the number of layers, and the material of the raw substrate so that the substrate temperature distribution around the component can be quantitatively predicted. The substrate design method described.

Based on the prediction result of the substrate temperature distribution around the component, select the component that greatly reduces the substrate temperature, calculate the temperature drop on the solder joint of the other component, and solder each component The board design method according to claim 1, wherein the component interval capable of securing temperature can be calculated.

4. The substrate design method according to claim 1, wherein a raw substrate temperature and the substrate temperature distribution around the component are used as the temperature data.

4. The substrate design method according to claim 1, wherein the temperature data is measured by limiting the raw substrate and the component.

4. The substrate design method according to claim 1, wherein the time of heating is a time when the highest temperature is being heated.

4. The substrate design method according to claim 1, wherein the substrate temperature distribution around the component is obtained based on a center of the component.

The substrate design method according to claim 1, wherein the substrate temperature distribution around the component is obtained based on a component end closest to the component center.

4. The substrate design method according to claim 1, wherein the substrate temperature distribution around the component is approximated linearly.

The substrate design method according to claim 1, wherein the substrate temperature distribution around the component is approximated to a curve.

For the part that can be judged to be negligible with little influence on the substrate temperature based on the temperature data measured in advance, the substrate temperature distribution around the component is not predicted, and the component is placed at an arbitrary position on the raw substrate. The substrate design method according to claim 1, wherein the substrate design method is arranged.

As a result of predicting the substrate temperature distribution around the component, the component that can be judged to have a small influence on the substrate temperature and can be ignored is arranged at an arbitrary position on the raw substrate. Item 4. The substrate design method according to any one of Items 3 to 3.

3. When predicting the substrate temperature distribution around the component using the type of the component as the parameter, the classification of the component is based on a difference in the measured substrate temperature distribution around the component. PCB design method.

The board design method according to claim 13, wherein the shape of the component is used for classification of the component.

The board design method according to claim 13, wherein an internal structure of the component is used for classification of the component.

The board design method according to claim 13, wherein a material of the component is used for classification of the component.

The board design method according to claim 13, wherein the position of the solder joint is used for classification of the component.

3. The board design according to claim 2, wherein when the substrate temperature distribution around the component is predicted using the size of the component as the parameter, the length and width of the component are used as the component size. Method.

The substrate design method according to claim 18, wherein the substrate temperature distribution around the component is predicted by dividing the component in a length direction and a width direction.

19. The board design method according to claim 18, wherein the thickness of the component is used as the component size.

3. The board design according to claim 2, wherein when the substrate temperature distribution around the component is predicted using the number of layers of the raw substrate as the parameter, the presence or absence of an inner layer is focused on as the number of layers of the substrate. Method.

Claims wherein the substrate temperature at an arbitrary position is predicted by superimposing the influence of the plurality of components on the substrate temperature, and the component interval necessary for securing a heating temperature at which good soldering is obtained is determined. The substrate design method according to claim 1.

The influence of the component on the substrate temperature at the time of heating is expressed by the difference between the substrate temperature around the component and the temperature of the raw substrate, and the influence of the individual components is superimposed to be the temperature of the solder joint portion of the component The board design method according to claim 1, wherein the component interval necessary for securing a heating temperature at which good soldering is obtained is determined by predicting the above.

The substrate design method according to claim 1, wherein the substrate temperature around the component at the time of heating under a certain heating condition is predicted.

The substrate design method according to claim 1, wherein an average value is predicted by comprehensively including the substrate temperature around the component at the time of heating under a plurality of heating conditions.

The substrate design method according to claim 1, wherein a difference in the substrate temperature around the component during heating according to a heating condition can be corrected.

27. The board design method according to claim 26, wherein a difference in the board temperature around the component is corrected by adding measurement data.

4. The substrate design method according to claim 1, wherein the substrate temperature distribution around the component during heating is calculated using spreadsheet software such as a personal computer.

The board design method according to claim 1, wherein the part interval during heating is calculated using spreadsheet software such as a personal computer.

At the time of board design, based on the temperature data measured in advance, the substrate temperature distribution around the part at the time of heating (the relationship between the distance from the part and the board temperature) is predicted, and the part passes through the board to the other parts. By calculating the temperature change on the solder joint, it is possible to determine the component spacing necessary to secure the heating temperature to obtain good soldering and to check whether this component spacing is appropriate. An implementation method of a substrate design method, comprising:

31. The method for implementing a board design method according to claim 30, wherein one or both of an expected lowest temperature part and an expected highest temperature part during heating can be displayed on the board after the component placement.

32. The method for implementing a substrate design method according to claim 31, wherein an expected temperature of the entire substrate during heating can be displayed.

31. The method for implementing a board design method according to claim 30, further comprising a function of displaying the fact when the component is to be arranged in an area where the necessary interval between the components cannot be secured, or having the function that the component cannot be arranged.

When designing a board, predict the board temperature distribution around the part during heating (the relationship between the distance from the part and the board temperature) based on the temperature data measured in advance, and easily exceed the heat-resistant guaranteed temperature at the part where the board temperature is low A circuit board structure in which components are arranged.

35. The circuit board structure according to claim 34, wherein the component that easily exceeds the guaranteed heat resistance temperature is an aluminum electrolytic capacitor or LED.