JP2011129772A - Printed wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printed wiring board capable of reducing cost. <P>SOLUTION: This printed wiring board 1 includes an insulating board 10, wires 20 laminated on the insulating board 10 and formed of copper, and a coverlay film 50 covering the wires 20, wherein each wire 20 includes a terminal part 21 exposed from the coverlay film 50. The printed wiring board further includes first coating layers 30 formed by hardening silver paste and covering the terminal parts 21, and second coating layers 40 formed by hardening carbon paste and covering all surfaces of the first coating layers 30. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a printed wiring board having terminal portions that are electrically connected to components such as contact elements and connectors.

  There is known a printed circuit board in which a gold plating film is formed on a copper pattern and a part of the gold plating film is covered with a carbon paste (see, for example, Patent Document 1).

JP 2002-280699 A

  However, the printed circuit board described above has a problem that the cost increases because it has a gold plating film, which requires management of a plating bath and a longer tact time.

  The problem to be solved by the present invention is to provide a printed wiring board capable of reducing the cost.

  The printed wiring board according to the present invention includes an insulating substrate, a wiring made of copper laminated on the insulating substrate, and a coverlay film that covers the wiring, and the wiring is exposed from the coverlay film. A printed wiring board having a terminal portion, which is formed by curing a silver paste or a gold paste, formed by curing a first covering layer that covers the terminal portion, and a carbon paste, And a second covering layer covering all surfaces.

  In the above invention, the surface resistance value of the second coating layer may be 30 Ω / square or less.

  In the above invention, the thickness of the first coating layer may be 3 μm to 35 μm.

  In the above invention, the thickness of the second coating layer may be 5 μm to 35 μm.

  In the above invention, the end portion of the second coating layer may enter the inside of the coverlay film.

  In the above invention, the first coating layer may not overlap with the coverlay film in plan view.

  According to the present invention, the first coating layer made of silver paste or gold paste and covering the terminal portion and the second coating layer made of carbon paste and covering the first coating layer are provided. The cost of the wiring board can be reduced.

FIG. 1 is a perspective view of a printed wiring board according to an embodiment of the present invention. FIG. 2 is an enlarged sectional view taken along line II-II in FIG. FIG. 3 is an enlarged cross-sectional view taken along line III-III in FIG. 4 is a plan view seen from the direction IV in FIG. FIG. 5: is sectional drawing which shows the manufacturing method of the printed wiring board in embodiment of this invention (the 1). FIG. 6: is sectional drawing which shows the manufacturing method of the printed wiring board in embodiment of this invention (the 2). FIG. 7: is sectional drawing which shows the manufacturing method of the printed wiring board in embodiment of this invention (the 3). FIG. 8 is a graph showing the results of moisture absorption tests in the examples of the present invention and comparative examples relative to the present invention. FIG. 9 is a graph showing the result of the migration test in the example of the present invention. FIG. 10 is a graph showing the result of a migration test in a comparative example for the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  1 is a perspective view of a printed wiring board in the present embodiment, FIG. 2 is an enlarged sectional view taken along line II-II in FIG. 1, FIG. 3 is an enlarged sectional view taken along line III-III in FIG. FIG. 4 is a plan view seen from the IV direction of FIG. 3.

  The printed wiring board 1 in this embodiment is a flexible printed circuit (FPC: Flexible Printed Circuit) incorporated in a TV remote control, a mobile phone, or the like. The printed wiring board 1 is electrically connected to a connecting component such as a ZIF connector (ZIF: Zero Insertion Force socket) at a terminal portion 21 of the wiring 20 described later. The printed wiring board 1 may be a rigid printed wiring board and is not particularly limited.

  As shown in FIGS. 1 and 2, the printed wiring board 1 includes an insulating substrate 10, a wiring 20, a first covering layer 30, a second covering layer 40, and a cover lay film 50. I have.

  The insulating substrate 10 is made of a sheet-like member made of, for example, polyimide.

  The wiring 20 is a line made of copper and is laminated on the insulating substrate 10. As shown in FIGS. 1 and 2, the end face 22 of the wiring 20 is located on the inner side of the outer edge of the insulating substrate 10, and the terminal portion 21 described later includes the first and second coating layers 30. , 40 covers the end face 22.

Moreover, the printed wiring board 1 in this embodiment is provided with the six wiring 20 as shown in FIG. As shown in FIG. 3, these wirings 20 are arranged so that the pitch is P, and the respective wirings 20 are insulated from each other. In addition, the width of the wiring 20 has a _{w 1.} The number of wirings 20 is not particularly limited, and may be one or six or more.

  This wiring 20 has the terminal part 21 exposed from the coverlay film 50 (after-mentioned), as shown in FIG.2 and FIG.4. The terminal portion 21 is covered with first and second coating layers 30 and 40, which will be described later, and the connection parts are electrically connected.

  The first covering layer 30 is laminated between the terminal portion 21 and the second covering layer 40 (described later), and is generated between the terminal portion 21 (copper) and the second covering layer 40 (carbon). Suppresses galvanic corrosion. The first coating layer 30 is formed by screen-printing a silver paste on the terminal portion 21 and curing it. In addition, you may form the 1st coating layer 30 by screen-printing and hardening a gold paste.

  Here, the standard electrode potential of silver (Ag) in the silver paste is about 0.8 (V), and the difference from the standard electrode potential (0.34 (V)) of copper (Cu) constituting the wiring 20 Is relatively small. Also for the gold paste, the standard electrode potential of gold (Au) is about 1.5 (v), and the difference from the standard electrode potential of copper (0.34 (V)) constituting the terminal portion 21 is different. It is relatively small. In this way, galvanic corrosion is unlikely to occur between silver and gold and copper, and can be brought into direct contact with copper.

As shown in FIG. 2, the thickness of the first coating layer 30 is t _1, and this t ₁ is preferably in the range of 3 μm to 35 μm (3 μm ≦ t ₁ ≦ 35 μm). By setting the thickness t ₁ of the first coating layer 30 to 3 μm or more, “pinholes” and “blurs” during screen printing can be suppressed, and between the terminal portion 21 and the second coating layer 40. The first coating layer 30 can be reliably interposed.

On the other hand, the cohesive failure of the silver paste (gold paste) can be suppressed by setting the thickness t ₁ of the first coating layer 30 to 35 μm or less.

Thus, by setting the thickness t ₁ of the first coating layer 30 within the above range, galvanic corrosion can be suppressed while maintaining the mechanical strength.

Moreover, as shown in FIG. 3, the width w ₂ of the first coating layer 30 is relatively larger than the width w ₁ of the terminal portion 21 (wiring 20) (w ₂ > w ₁ ). In the X direction in the figure, the terminal portion 21 is completely covered.

  As shown in FIGS. 2 to 4, the second coating layer 40 covers the entire surface of the first coating layer 30, and electrochemical migration (hereinafter simply referred to as “first coating layer 30”) is exposed. , Referred to as migration). Further, the upper surface of the second coating layer 40 is a contact point with the connection component. The second coating layer 40 is formed by screen printing carbon paste on the first coating layer 30 and curing.

As shown in FIG. 2, the thickness of the second coating layer 40 is t _2, and this t ₂ is preferably in the range of 5 μm to 35 μm (5 μm ≦ t ₂ ≦ 35 μm). By setting the thickness t ₂ of the second coating layer 40 to 5 μm or more, it is possible to suppress the second coating layer 40 from being peeled by contact with the connecting component and exposing the first coating layer 30. Yes. On the other hand, by setting the thickness t2 of the _second coating layer 40 to 35 μm or less, cohesive failure of the carbon paste is suppressed and mechanical strength is maintained. Thus, the thickness t _2, With the above-mentioned range, while maintaining the mechanical strength, can be effectively suppressed migration due to the first coating layer 30 is exposed.

  As shown in FIG. 3, the second coating layers 40 are insulated from each other, and the distance L between the adjacent second coating layers 40 is 100 μm or more.

Further, the width w ₃ of the second coating layer 40 is relatively larger than the width w _{2 of} the first coating layer 30 (w ₃ > w ₂ ), as shown in FIG. In the X direction, the entire surface of the first coating layer 30 is completely covered. The second width _{w 3} of the covering layer 40, by increasing or 50 [mu] m than the width _{w 2} of the first coating layer _{30 (w 3> w 2 +} 50μm), in the screen printing, the first coating layer All 30 surfaces can be reliably covered.

  The surface resistance value of the second coating layer 40 (carbon paste) is 30 Ω / square or less, and current loss is suppressed in the electrical connection between the terminal portion 21 and the connection component.

  Furthermore, in this embodiment, the 2nd edge part 41 of this 2nd coating layer 40 has entered the inside of the cover-lay film 50 mentioned later, as shown in FIG.2 and FIG.4. Thereby, the terminal part 21 is not exposed to the outside at all, and corrosion of the terminal part 21 is effectively suppressed.

  As shown in FIG. 1, the coverlay film 50 covers the portion of the printed wiring board 1 excluding the terminal portion 21 and protects the wiring 20. In addition, in the terminal part 21 of the wiring 20, the coverlay film 50 is not laminated | stacked for the electrical connection with a connection component.

  Although not specifically shown, the coverlay film 50 includes an insulating film and an adhesive layer that bonds the insulating film and the wiring 20. The insulating film is made of polyimide, for example. The adhesive layer is made of an adhesive made of an epoxy resin, for example.

  Here, as shown in FIGS. 2 and 4, the third end portion 51 of the cover lay film 50 includes the first end portion 31 of the first covering layer 30 and the second end portion of the second covering layer 40. It is located between the end portions 41. That is, the cover lay film 50 covers the second coating layer 40 in addition to the wiring 20 as described above in the plan view shown in FIG. 4, but does not overlap with the first coating layer 30. Yes. Thus, corrosion of the wiring 20 is suppressed, and the printed wiring board 1 is suppressed from becoming thick at the edge (third end portion 51) of the coverlay film 50.

  As described above, in the printed wiring board 1 according to the present embodiment, the first coating layer 30 made of silver paste is interposed between the terminal portion 21 (copper) and the second coating layer 40 (carbon). . Thereby, generation | occurrence | production of the galvanic corrosion between the 2nd coating layer 40 and the terminal part 21 is suppressed.

  Here, as shown in FIGS. 2 and 4, in the portion A between the first end portion 31 of the first covering layer 30 and the coverlay film 50, the second covering layer 40 and the terminal portion 21 are directly connected. In contact. However, this portion A forms a parallel circuit with the portion B (the portion where the second covering layer 40 is connected to the terminal portion 21 via the first covering layer 30), and the reliability of the electrical connection Sex is preserved.

  Moreover, since all the surfaces of the 1st coating layer 30 which consists of silver paste are covered with the 2nd coating layer 40, the migration by a silver paste is suppressed.

  Thus, in the printed wiring board 1 according to the present embodiment, the terminal portion 21 made of copper is covered with the first coating layer 30 made of silver paste (gold paste), and the entire surface of the first coating layer 30 is further covered. Is covered with the second coating layer 40 made of carbon paste, the reliability of the electrical connection with the connection component is improved.

  Here, if the first coating layer 30 is formed by plating, the tact time becomes long and the management of the plating bath is required. For this reason, the printed wiring board 1 in which the first coating layer 30 is formed by screen printing is lower in cost than the printed wiring board in which the first coating layer is formed by plating.

  Moreover, in order to form the 1st coating layer 30 by plating, it is necessary to provide the lead wire connected to the terminal part 21. This lead wire occupies a large area in the printed wiring board. On the other hand, in screen printing, it is not necessary to provide such lead wires, and the printed wiring board 1 can be reduced in size by forming the first coating layer 30 by screen printing.

  In the printed wiring board 1 according to the present embodiment, the first and second coating layers 30 and 40 are laminated on the terminal portion 21 that is electrically connected to a connection component such as a ZIF connector, but the invention is not particularly limited. For example, in a printed wiring board incorporated in a cellular phone, an electrode portion electrically connected to a metal dome that is a contact element (switch component) is made of copper, and the electrode portion is made of a silver paste or a gold paste. One coating layer may be laminated, and a second coating layer made of carbon paste may be laminated on the first coating layer.

  Moreover, the terminal part in this invention means the electrical contact with other components, and is a concept also including the above electrode parts.

  Next, the manufacturing method of the printed wiring board in this embodiment is demonstrated.

  5-7 is sectional drawing which shows the manufacturing method of the printed wiring board in this embodiment.

  First, as shown in FIG. 5, the wiring 20 is formed (wiring forming step). In the wiring formation step, for example, a photosensitive resist film is laminated on the copper foil laminated on the insulating substrate 10 and patterned by a photolithography technique. Next, the wiring 20 is formed by etching with a chemical having metal corrosivity.

  Next, as shown in FIG. 6, a first coating layer 30 made of silver paste is formed (first coating step). In the first covering step, a silver paste is screen-printed on a portion that becomes the terminal portion 21 in the wiring 20. Here, in the screen printing, by setting the mesh count within the range of 150 to 400, it is possible to suppress problems such as “blur” and “smudge”, and silver paste is also printed on the wiring 20 having a narrow pitch P. Can do.

  Next, as shown in FIG. 7, a second coating layer 40 made of carbon paste is formed (second coating step). In the second coating step, a carbon paste is screen printed on the first coating layer 30. Here, in the screen printing, by setting the mesh count within the range of 150 to 400, it is possible to suppress problems such as “blur” and “smudge”, and to print the carbon paste on the wiring 20 with a narrow pitch P. Can do.

  Next, the coverlay film 50 is laminated on the wiring 20 (coverlay lamination step). In this cover lay stacking step, as shown in FIGS. 2 and 4, the third end 51 of the cover lay film 50 is replaced with the first end 31 of the first covering layer 30 and the second covering layer 40. The cover lay film 50 is affixed to the wiring 20 so as to be positioned between the second end 41 and the portion where the first and second coating layers 30 and 40 are laminated is covered with the cover lay film 50. Try to expose

  Next, the cover lay film 50 is pressed and heated to be fixed to the wiring 20.

  In this embodiment, the cover lay stacking step is performed after the second covering step, but is not particularly limited. For example, the cover lay lamination step may be performed after the wiring formation step, and then the first and second covering steps may be performed.

  The embodiment described above is described for facilitating the understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

  FIG. 8 is a graph showing the results of the moisture absorption test in Examples and Comparative Examples, FIG. 9 is a graph showing the results of migration tests in Examples, and FIG. 10 is a graph showing the results of migration tests in Comparative Examples.

  Below, the effect of the present invention was confirmed by examples and comparative examples that further embody the present invention. The following examples and comparative examples are for confirming the effect on the reliability of the electrical connection of the printed wiring board of the embodiment described above.

<Example 1>
In Example 1, a printed wiring board having the same structure as that of the above-described embodiment was produced. In the sample of Example 1 (the number of samples is 10 in each of the following moisture absorption test and migration test), the wiring is made of copper, the first coating layer is made of silver paste, and the second The coating layer was composed of carbon paste. The wiring pitch P is 500 μm, the wiring width w ₁ is 100 μm, the thickness t ₁ of the first coating layer is 20 μm, the width w ₂ of the first coating layer is 200 μm, and the second coating The layer thickness t ₂ was 20 μm, and the width w ₃ of the second coating layer was 400 μm.

  The sample of Example 1 was subjected to a moisture absorption test and a migration test.

  In the moisture absorption test, the temperature is set to 85 ° C., the relative humidity is set to 85% RH, and the electrical resistance value between two terminal portions located at both ends of the wiring (for example, the terminal portion 21a and the terminal portion 21b in FIG. 1) is measured. did. The results of the moisture absorption test of Example 1 are shown in FIG. In FIG. 8, the horizontal axis is the test time, the vertical axis is the electrical resistance value between the terminal portions, and the change over time of the electrical resistance value (average value of 10 samples) of Example 1 is shown (Comparative Example). The same applies to 1.)

In the migration test, the temperature was set to 85 ° C., the relative humidity was set to 85% RH, a voltage of 50 V was applied between adjacent terminal portions (for example, the terminal portion 21a and the terminal portion 21c in FIG. 1) for 1000 hours, The electrical resistance value between the terminal portions was measured. The result of the migration test of Example 1 is shown in FIG. In FIG. 9, the horizontal axis represents time, the vertical axis represents the electrical resistance value between the terminal portions, and the change over time in the electrical resistance value between the adjacent terminal portions is shown (the same applies to FIG. 10). In the numerical values on the horizontal axis in FIG. 9, “mE + n” means “m × 10 ^{+ n} ” (the same applies to FIG. 10).

<Comparative Example 1>
In Comparative Example 1, ten samples of the printed wiring board having the same structure as Example 1 were produced except that the first coating layer was not laminated. A moisture absorption test was performed on the sample of Comparative Example 1. The result of the moisture absorption test of Comparative Example 1 is shown in FIG.

<Comparative Example 2>
In Comparative Example 2, ten samples of the printed wiring board having the same structure as Example 1 were produced except that the second coating layer was not laminated. A migration test was performed on the sample of Comparative Example 2. The result of the migration test of Comparative Example 2 is shown in FIG.

<Discussion>
In Comparative Example 1 in the moisture absorption test, as shown in FIG. 8, the electrical resistance value increased at 100 hours after the start of the test, and after 1000 hours, the electrical resistance value exceeded 3Ω. It is considered that galvanic corrosion occurred at the interface of the terminal portion and copper oxide was generated, thereby increasing the electrical resistance value.

  On the other hand, in Example 1 in the moisture absorption test, no significant change in the electrical resistance value occurred even after 1000 hours had elapsed after the start of the test.

  Therefore, an increase in electrical resistance is suppressed by interposing the first coating layer made of silver paste between the wiring (terminal portion) made of copper and the second coating layer made of carbon paste. It can be seen that the reliability of the electrical connection is improved.

  In Comparative Example 2 in the migration test, as shown in FIG. 10, the electric resistance value sharply decreases when 200 hours have elapsed after the start of the test. It is considered that migration is caused by the silver paste being exposed, and adjacent terminal portions are short-circuited.

  On the other hand, in Example 1 in the migration test, as shown in FIG. 9, even after 1000 hours passed from the start of the test, the electrical resistance value did not rapidly decrease.

From this, it turns out that the short circuit of the adjacent terminal parts can be suppressed and the reliability of electrical connection improves because the 2nd coating layer covers all the surfaces of the 1st coating layer.

DESCRIPTION OF SYMBOLS 1 ... Printed wiring board 10 ... Insulating board 20 ... Wiring 21 ... Terminal part 30 ... 1st coating layer 31 ... 1st edge part 40 ... 2nd coating layer 41 ... 2nd edge part 50 ... Cover-lay film 51. Third end

Claims (6)

An insulating substrate;
Laminated on the insulating substrate and made of copper,
A cover lay film covering the wiring,
The wiring is a printed wiring board having a terminal portion exposed from the coverlay film,
A first coating layer formed by curing a silver paste or a gold paste, and covering the terminal portion;
A printed wiring board, comprising: a second coating layer formed by curing a carbon paste and covering all surfaces of the first coating layer. The printed wiring board according to claim 1,
The printed wiring board, wherein the surface resistance value of the second coating layer is 30 Ω / square or less. The printed wiring board according to claim 1 or 2,
The printed wiring board, wherein the first covering layer has a thickness of 3 μm to 35 μm. The printed wiring board according to any one of claims 1 to 3,
The printed wiring board, wherein the thickness of the second coating layer is 5 μm to 35 μm. The printed wiring board according to any one of claims 1 to 4,
The printed wiring board according to claim 1, wherein an end portion of the second coating layer enters an inner side of the coverlay film. The printed wiring board according to claim 5,
The printed wiring board, wherein the first covering layer does not overlap with the coverlay film in plan view.

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