JP2004128362A

JP2004128362A - Printed-circuit board

Info

Publication number: JP2004128362A
Application number: JP2002293145A
Authority: JP
Inventors: Yukihiro Shibata; 柴田　行裕; Ryoji Kuwano; 桑野　亮司; Kenichi Maehara; 前原　謙一
Original assignee: AKITA SHINDENGEN KK; Shindengen Electric Manufacturing Co Ltd; Akita Shindengen Co Ltd
Current assignee: AKITA SHINDENGEN KK; Shindengen Electric Manufacturing Co Ltd; Akita Shindengen Co Ltd
Priority date: 2002-10-07
Filing date: 2002-10-07
Publication date: 2004-04-22

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printed-circuit board capable of preventing such an insulation deterioration as a migration. <P>SOLUTION: An electronic printed-circuit board has circuit patterns on a base material, and the circuit patterns and base material are coated with an insulation layer to form a component land, as well as the circuit patterns or the component lands coated with soldering pastes containing flux, and loaded with electronic components to be soldered. In the electronic printed-circuit board, before the soldering paste is formed, one or more locations of the insulation layers are removed that are positioned in arbitrary portions between the patterns, between the component lands, and between the component lands and the patterns, thereby preventing the flux from being connected at the arbitrary portions. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【産業上の利用分野】本発明は、電子部品等が搭載されるプリント基板に係り、近接する電極間で生ずるマイグレーション等の絶縁劣化を防止するプリント基板の構造に関するものである。
【０００２】
【従来の技術】プリント基板は半田付け時に生ずる半田ブリッジの防止または配線パターン保護のため、エポキシ樹脂等の半田レジストでコーティングされている。プリント基板の近接した電極間に電位差があると、正電極を構成する銀、銅、半田等の金属が水分の作用によりイオン化して、プリント基板の表面に沿って対向する負電極に移動して析出する所謂マイグレーションと呼ばれる現象が発生する。
このような状態が長期間続くと、その析出した金属で電極間の抵抗値が急激に低下して、電圧の印加された電極間に異常電流が流れ電子回路を損傷する。マイグレーションはプリント基板自体の特性（素材の吸湿性）の他、電極材料、電極間隔、電子部品の半田付け時のフラックス残査、使用環境（特に、高温多湿、又は多湿で温度変化が大きい時に生ずる結露状態）等の影響を受ける。
【０００３】図２は従来のプリント基板の構造を示す。この構造では、特にフラックス残さが多く、フラックスが回路パターン間でつながっている場合は特に、マイグレーション等の絶縁劣化が発生しやすかった。
【０００４】これを解決するために、発明者らは図３のように回路パターンの間にはじめシルク印刷をして、パターンの間に山を作ることにより、マイグレーション等の絶縁劣化を防止しようとし、実験してみたが、あまり効果はなかった。
はんだを少なくする方法もとったが別の問題が発生し産業上利用可能性が低かった。電位差を小さくする方法も考えたが、現実的ではなかった。
特許文献１の方法は、通常の状態では効果が得られるが、フラックスが回路パターン間でつながってしまうと、マイグレーション等の絶縁劣化を防ぐことは不可能であった。
特許文献２の方法は、絶縁層の山を作っているが、特殊な絶縁層を必要とするため、製造コストが上がり、適用困難であった。
特許文献３の方法は、特殊な追加工を必要とするため、製造コストが上がり、適用困難であった。
特許文献４は、電位差のあるパターン間に、電気的に接続されない遮蔽パターンを設ける方法である。この方法は通常の状態では最も製造コストも安く、マイグレーション等絶縁劣化防止には効果が得られるが、フラックスが回路パターン間でつながってしまうと、パターンが絶縁層で被われているのにも関わらず、電気的に接続されていない遮蔽パターンが反応し、イオン化した電極材料が電極間を移動してしまい、マイグレーション等の絶縁劣化を防ぐことは不可能であった。
特許文献５の方法は、特殊な絶縁層を必要とするため製造コストが上がり、適用困難であった。
また、マイグレーション等の絶縁劣化を防ぐためには、はんだづけ後、基板を洗浄するのが効果的であるが、コストの問題、環境への影響等から避けたかった。
【０００５】
【特許文献１】特開昭６１−２６８０９０　第１図
【特許文献２】特開平８−１０７２６５　図１、図２
【特許文献３】特開平９−１４８６９０　図１〜図７
【特許文献４】特開２０００−２５２５９７図２、図３
【特許文献５】特開２００２−１８５１２９　図１〜図６
【０００６】
【発明が解決しようとする課題】
本発明は、簡単な構造で製造コストを抑えつつ、イオン化した電極材料が電極間を移動するのを阻止して、マイグレーション等の絶縁劣化を防止するプリント基板を提供することを目的とする。
【０００７】
【課題を解決するための手段】上記課題を解決するために本発明は、基板のパターン、あるいは部品ランドの間の絶縁層を簡単な手法で除去することにより、製造コストを抑えつつ、フラックスが回路パターン間でつながるのを防ぐものである。
【０００８】また、そのときの絶縁層を除去する個所はパターンあるいは部品ランドから５ミリ以内とし、基板の大型化を防ぎながらもマイグレーション等の絶縁劣化を防ぐものである。
【０００９】はんだ量が多く、フラックス量が多くなる個所は、絶縁層を複数個所除去し、また、切削加工により、確実にフラックスが回路パターン間でつながるのを防ぐようにした。
【００１０】更に、絶縁層を除去する個所は、電位差の大きいところがマイグレーション等の絶縁劣化が発生しやすいため、その個所だけを選択的に除去できるようにした。
【００１１】
【発明実施の形態】
図１は本発明の一実施例断面図である。今回はガラスエポキシプリント基板を例に挙げる。基板を設計する段階で、あらかじめマイグレーション等の絶縁劣化をおこしやすい個所のソルダーレジストを除去するようにし、後は通常と同じ工程でプリント基板を製造すればよい。特別な工程は一切不要である。単に部分部分でソルダーレジストのない基板を使用するだけである。また、応用例として、ドリルで基板に穴加工を施したり、Ｖカットを入れる等機械的にソルダーレジストを切除する方法もある。後は通常と同じように、
１　はんだペースト形成
２　電子部品を搭載
３　熱を加えてはんだをとかす
といった通常の工程で電子回路プリント基板を製造すれば良い。また、応用例として、ドリルで基板に穴加工を施したり、Ｖカットを入れる等機械的に絶縁層を切除して、フラックスが回路パターン間でつながるのを防止することができる。
【発明の効果】以上詳細に説明したように、本発明によれば、絶縁層を除去した個所でフラックスがとまるので、フラックスが回路パターン間でつながるのを防ぎ、イオンの移動が阻止でき、マイグレーション等の絶縁劣化を防ぐことが出来る。その結果、プリント基板に搭載された電子部品及び電子回路は保護される。
【図面の簡単な説明】
【図１】本発明一実施例のプリント基板断面図　ペースト形成前
【図２】本発明一実施例のプリント基板断面図　熱を加えた後
【図３】従来のプリント基板断面図　ペースト形成前
【図４】従来のプリント基板断面図　熱を加えた後
【図５】従来のプリント基板断面図の２　ペースト形成前
【図６】従来のプリント基板断面図の２　熱を加えた後
【符号の説明】
１　はんだ
２　フラックス
３　絶縁層
４　基材
５　回路パターン
６　シルク印刷[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed circuit board on which electronic parts and the like are mounted, and more particularly to a structure of a printed circuit board which prevents insulation deterioration such as migration between adjacent electrodes.
[0002]
2. Description of the Related Art A printed circuit board is coated with a solder resist such as an epoxy resin in order to prevent a solder bridge generated at the time of soldering or to protect a wiring pattern. If there is a potential difference between the adjacent electrodes on the printed circuit board, metals such as silver, copper, and solder constituting the positive electrode are ionized by the action of moisture and move to the opposite negative electrode along the surface of the printed circuit board. A phenomenon called so-called migration that occurs is generated.
If such a state continues for a long time, the resistance value between the electrodes is rapidly reduced by the deposited metal, and an abnormal current flows between the electrodes to which a voltage is applied, thereby damaging the electronic circuit. Migration occurs in addition to the characteristics of the printed circuit board itself (hygroscopicity of the material), electrode material, electrode spacing, flux residue during soldering of electronic components, and usage environment (especially when the temperature changes greatly due to high temperature and humidity or high humidity). (Dew condensation).
FIG. 2 shows the structure of a conventional printed circuit board. In this structure, the flux residue is particularly large, and particularly when the flux is connected between circuit patterns, insulation deterioration such as migration is likely to occur.
In order to solve this problem, the inventors tried to prevent insulation deterioration such as migration by performing silk printing at the beginning between circuit patterns as shown in FIG. 3 and forming peaks between the patterns. I experimented, but it was not so effective.
Although a method for reducing the amount of solder was used, another problem occurred, and its industrial applicability was low. A method of reducing the potential difference was also considered, but was not realistic.
Although the method of Patent Document 1 can provide an effect in a normal state, it is impossible to prevent insulation deterioration such as migration when a flux is connected between circuit patterns.
Although the method of Patent Document 2 forms a mountain of insulating layers, it requires a special insulating layer, which increases the manufacturing cost and is difficult to apply.
The method of Patent Document 3 requires special additional processing, so that the manufacturing cost increases and it is difficult to apply.
Patent Document 4 discloses a method of providing a shielding pattern that is not electrically connected between patterns having a potential difference. This method has the lowest manufacturing cost under normal conditions, and is effective in preventing insulation deterioration such as migration.However, when flux is connected between circuit patterns, it is possible to prevent the pattern from being covered with an insulating layer. However, a shield pattern that is not electrically connected reacts, ionized electrode material moves between the electrodes, and it is impossible to prevent insulation deterioration such as migration.
The method of Patent Document 5 requires a special insulating layer, which increases the manufacturing cost and is difficult to apply.
Further, in order to prevent insulation deterioration such as migration, it is effective to wash the substrate after soldering. However, it was desired to avoid the problem of cost, influence on the environment, and the like.
[0005]
[Patent Document 1] Japanese Patent Application Laid-Open No. 61-268090 FIG. 1 [Patent Document 2] Japanese Patent Application Laid-Open No. 8-107265
[Patent Document 3] Japanese Patent Application Laid-Open No. 9-148690 FIGS.
[Patent Document 4] JP-A-2000-252597 FIGS. 2 and 3
[Patent Document 5] JP-A-2002-185129 FIGS.
[0006]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a printed circuit board that has a simple structure, suppresses manufacturing costs, prevents ionized electrode material from moving between electrodes, and prevents insulation deterioration such as migration.
[0007]
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention removes an insulating layer between substrate patterns or component lands by a simple method, thereby reducing the manufacturing cost and reducing the flux. This prevents connection between circuit patterns.
In addition, the portion where the insulating layer is removed at this time is set to be within 5 mm from the pattern or the component land, so as to prevent the deterioration of the insulation such as migration while preventing the substrate from being enlarged.
At locations where the amount of solder is large and the amount of flux is large, a plurality of insulating layers are removed, and cutting is surely prevented from connecting the flux between circuit patterns.
Furthermore, where the insulating layer is removed, where there is a large potential difference, insulation degradation such as migration is likely to occur, so that only that portion can be selectively removed.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a sectional view of one embodiment of the present invention. This time, the glass epoxy printed circuit board is taken as an example. At the stage of designing the board, the solder resist at a portion where insulation deterioration such as migration is likely to occur is removed in advance, and the printed board may be manufactured in the same process as usual. No special steps are required. Simply use a substrate without solder resist in some parts. Further, as an application example, there is a method of mechanically removing a solder resist such as making a hole in a substrate with a drill or making a V cut. After that, as usual,
1 Solder paste formation 2 Mounting of electronic components 3 Electronic circuit printed circuit board may be manufactured by a normal process of melting solder by applying heat. Further, as an application example, it is possible to prevent the flux from being connected between the circuit patterns by mechanically cutting off the insulating layer such as making a hole in the substrate with a drill or making a V-cut.
As described above in detail, according to the present invention, the flux stops at the portion where the insulating layer is removed, so that the flux is prevented from being connected between the circuit patterns, the movement of ions can be prevented, and the migration can be prevented. Etc. can be prevented. As a result, the electronic components and electronic circuits mounted on the printed circuit board are protected.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a printed circuit board according to one embodiment of the present invention before paste formation. FIG. 2 is a cross-sectional view of a printed circuit board according to one embodiment of the present invention after heat is applied. FIG. 3 is a cross-sectional view of a conventional printed circuit board before paste formation. FIG. 4 is a cross-sectional view of a conventional printed circuit board. After heat is applied. FIG. 5 is a cross-sectional view of a conventional printed circuit board before formation of a paste. FIG. 6 is a cross-sectional view of a conventional printed circuit board after applying heat. ]
DESCRIPTION OF SYMBOLS 1 Solder 2 Flux 3 Insulating layer 4 Base material 5 Circuit pattern 6 Silk printing

Claims

Forming a circuit pattern on the substrate, forming a component land by applying an insulating layer on the circuit pattern and the substrate, forming a solder paste containing a flux on the circuit pattern or the component land, An electronic component is mounted on the circuit pattern or the component land on which is formed and soldered, in an electronic circuit printed board, between the pattern and the pattern, between the component land and the component land, between the component land and the pattern, A printed circuit board, wherein one or a plurality of the insulating layers are removed before the formation of the solder paste so that the flux is not connected at the arbitrary places.

2. The printed circuit board according to claim 1, wherein the portion to be removed is provided within 5 mm from a pattern or a component land.

3. The printed circuit board according to claim 1, wherein the width of the insulating layer at the portion to be removed is 50 microns or more.

The printed circuit board according to claim 1, wherein the arbitrary portion is formed by not applying the insulating layer in advance.

The printed circuit board according to claim 1, wherein the arbitrary portion is formed by cutting by cutting.

The printed circuit board according to claim 1, wherein the arbitrary portion is a pattern having a large potential difference or between component lands.