JPH0434992A - Manufacturing method of printed wiring board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a novel printed wiring board and a method for manufacturing the same. Specifically, it is a print in which a wiring pattern made of a hardened conductive paste that is electrically connected to the pad portion of the wiring pattern is laminated via an insulating layer to a wiring pattern of an insulating substrate having a wiring pattern made of metallic copper. The present invention provides a printed wiring board with significantly reduced contact resistance between conductive layers and good solder adhesion during soldering, and a method for manufacturing the same.

[Prior art and problems to be solved by the invention] Electronic components are mounted on printed wiring boards by soldering them to pads of wiring patterns, but as wiring patterns become more complex, At the same time, it becomes difficult to set pads for the components to be mounted.

Therefore, by forming a wiring pattern on the wiring pattern that is electrically connected to the wiring pattern via an insulating layer and drawing out a pad portion at an arbitrary location, a printed wiring board with an even density of electronic components is formed. is considered.

For example, as shown in FIG. 2, such a printed wiring board is made of a hardened conductive paste on an insulating substrate 1 having a wiring pattern (A) 2 made of metallic copper. By laminating the wiring pattern (B) 4, which is electrically connected to the pad portion 6 through the connection portion 7, with the insulating layer 3 in between, the pad portion 5 made of the hardened conductive paste can be placed at any location. An example of this is a printed wiring board. In addition, in the figure, 8 is an overcoat layer.

In the above-mentioned printed wiring board, since the conductive paste is required to have adhesion to both the wiring pattern made of a metal mesh and the solder, a conductive silver paste containing silver as a conductive component is generally used.

However, printed wiring boards using the conductive silver paste described above have a problem in that a migration phenomenon occurs in which silver ions in the conductive paste migrate according to leakage current.

In order to solve this problem, it is conceivable to use a conductive copper paste containing copper powder as a conductive component.

However, with the conventionally used conductive copper paste, its cured product has poor adhesion to solder, and when a pad is formed at any location on the surface of the insulation layer using the conductive copper paste, This has the problem of causing solder defects. In order to improve this problem, when a solder adhesion improver is added to the conductive copper paste, the adhesion with the metal copper decreases, and the problem of swelling and peeling of this part due to thermal shock etc. is solved. have

[Means for Solving the Problems] As a result of repeated research to solve the above problems, the inventors of the present invention have provided a wiring pattern of an insulating substrate having a wiring pattern made of metallic copper with a pad portion of the wiring pattern. In a printed wiring board in which a wiring pattern made of a cured body of electrically connected conductive paste is laminated via an insulating layer, the cured body of the conductive paste is brought into contact with a pad portion of a wiring pattern made of metallic copper. A hardened conductive paste with high adhesiveness to the wire is present on the surface, and a hardened conductive paste with high adhesiveness to solder is present on the surface that forms the pad portion of the wiring pattern formed by the conductive paste. The present inventors have discovered that such problems can be solved by combining the above methods, and have completed the present invention.

Hereinafter, the present invention will be explained in detail with reference to the accompanying drawings. 1st
The figure is a sectional view showing a typical embodiment of the printed wiring board of the present invention. That is, in the present invention, on the surface of the insulating substrate 1,
Wiring pattern (A) made of metallic copper2. An insulating layer 3 covering the wiring pattern (A) except for the pad portion 6, and a wiring pattern (B) made of a hardened conductive copper paste.
4 are sequentially laminated, and the wiring pattern (B) 4 and the pad portion 6 of the wiring pattern (A) are electrically connected by a connecting portion 7 made of a cured body of conductive copper paste, The cured body of the conductive copper paste has an adhesion strength to metal copper of 0.5 J/m.
The wiring pattern (B
) 4, the adhesive strength of the cured conductive copper paste constituting the pad portion 5 to the solder is 0.8 kg/*m.
This is a printed wiring board characterized in that it is made of two or more conductive pastes.

In the present invention, known materials can be used for the insulating substrate 1 without any particular limitations. For example, ceramic substrates such as alumina and aluminum nitride, metal substrates whose surfaces are coated with insulating materials such as glass and resin, resins such as epoxy resins, fluorine, enol resins, and Teflon resins are lintered, paper reinforcing materials such as kraft paper, A resin substrate impregnated with a glass reinforcing material such as glass cloth is commonly used.

Further, in the present invention, the wiring pattern (A) 2 formed on the surface of the insulating substrate 1 is intended to be a wiring pattern made of metal copper. Such a wiring pattern (A) can generally be formed by laminating a layer of metallic copper on the surface of an insulating substrate and etching this. Specifically, the common method is to laminate copper foil on the surface of an insulating substrate, wire plating, evaporate copper, etc., and then etch this to form a wiring pattern. It is. The wiring pattern (A) has a pad portion. In the present invention, the term "pad section" refers to a connection section for connecting the wiring pattern to another wiring or a lead of a component, and includes a land section.

In the present invention, the insulating layer 3 is provided to cover the wiring pattern (A) except for the wiring pattern (A) 2. For the insulating layer 3, any known insulating material can be used without particular limitation as long as it has electrical insulation properties. In general, an insulating material whose range for forming an insulating layer can be easily set is preferable. For example, a known resist ink that is cured by light or heat is preferable. Such resist ink can be applied to the surface of the wiring pattern (A) except for the pad portions by means such as printing, and by curing it, it is easy to form an insulating layer. . As the resist ink, a curable composition having a known composition such as an epoxy resin curable composition, an acrylic resin curable composition, or an epoxy resin/acrylic resin mixed curable composition is used.

The thickness of the insulating layer 3 is not particularly limited, but is generally 30 mm.
~50 μm is suitable.

In the present invention, the wiring pattern (B) 4 is a wiring pattern formed of a cured body of conductive copper paste, and is composed of the pad portion 6 of the wiring pattern (A) and the hardened body of conductive copper paste. The insulating layer 3 has a pad portion 5 on the surface of the insulating layer 3 for electrical connection via a connecting portion 7 and for soldering.

The greatest feature of the present invention is that as a cured body of conductive copper paste constituting the wiring pattern (B) 4 and the connection part 7,
The hardened conductive copper paste in contact with the pad portion 6 of the wiring pattern (A) 2 has an adhesion strength of 0.5 to metal copper.
A hardened conductive paste having a conductive paste of 1/mm2 or more is used, and a hardened conductive mesh paste constituting the pad part 5 in the wiring pattern (B) 4 is made of a conductive paste with an adhesion strength of 0.8 to 711112 or more. The purpose is to use a hardened paste.

In the present invention, the adhesion strength of the cured body of the conductive paste to the surface to be coated is 21! after the conductive paste is applied onto the surface to be coated and cured. The pad part of a tin-plated copper wire having an m square pad at the tip was firmly attached by soldering or adhesive, and the conductor was pulled perpendicularly to the cured surface using a tensile tester to measure its tensile strength. It is a value.

The printed wiring board of the present invention includes a cured body of at least two types of conductive copper pastes in the connecting portion 7 and the wiring pattern (
By using it as a conductor constituting the wiring pattern (B), it is possible to extremely effectively prevent an increase in resistance between the pad part of the wiring pattern (A) and the pad part of the wiring pattern (B). Soldering on the pad portion 5 can improve properties. Furthermore, since the conductive component of the conductive paste is copper powder, there is no migration phenomenon of metal ions, which occurs when the conductive silver paste described above is used, and the conductive paste has stable performance.

The hardened conductive mesh paste that contacts the pad portion of the wiring pattern (A) has an adhesion strength of 0 to metal copper,
There is no particular restriction as long as it has an adhesion of 5 kg/mm2 or more. To give an example of a typical cured product, the main components are copper powder as a conductive component, a binder component such as a resol type phenolic resin, and a reducing agent such as an unsaturated fatty acid such as oleic acid or a salt thereof. Examples include hardened conductive copper paste (hereinafter also referred to as copper-adhesive steel paste).

The cured conductive copper and paste constituting the pad portion 5 in the wiring pattern (B) 4 may have an adhesion strength to solder of 0.8 kg/layer 2 or more, ', -. There are no particular restrictions. Typical cured products include copper powder as a conductive component, a binder component such as a resol type phenolic resin, a reducing agent such as an unsaturated fatty acid such as oleic acid, or a salt thereof, and a soldering accelerator. Examples include cured conductive copper paste (hereinafter also referred to as solder adhesive paste) made of a metal chelate forming agent such as triethanolamine.

Further, in the present invention, as long as the copper adhesive copper paste and the solder adhesive copper paste are respectively present on the above contact surface, the characteristics of the cured body of the conductive copper paste in other parts are not particularly limited. In general, in order to reduce the contact resistance between the cured bodies as much as possible, it is preferable to use a cured body of the above-mentioned two types of conductive copper pastes. Further, it is preferable in terms of the manufacturing process that the hardened body of the copper adhesive paste has the connecting portion 7, and the hardened body of the solder adhesive steel paste has the pattern (B). Further, the contact surface between the cured body of the copper-adhesive copper paste and the hardened body of the solder-adhesive steel paste is preferably formed so that the contact resistance is 10 ohms or less.

In the present invention, an overcoat layer 8 may be provided on the wiring pattern (B) if necessary. As such an overcoat layer, the materials of the insulating layer described above can be used without particular limitation.

Although the method for manufacturing the printed wiring board of the present invention is not particularly limited, a method that reduces the contact resistance between the copper adhesive copper paste and the solder adhesive copper paste as much as possible is recommended. That is, when two types of cured conductive copper pastes having different compositions are laminated, a problem arises in that the contact resistance increases significantly.

The present inventors have repeatedly conducted research to reduce the contact resistance between cured bodies of such pastes in the method of manufacturing printed wiring boards, and have found that after applying a copper-adhesive copper paste, # present on the surface of the paste. l In the absence of a powder oxide layer,
It has been found that by applying solder-adhesive copper pastes, the contact resistance between cured bodies of these pastes can be significantly reduced.

The present invention involves forming a wiring pattern (A) made of metal copper on the surface of a JIJI substrate, covering the wiring pattern (A) with an insulating layer except for the pad portion, and then applying a layer to the pad portion that adheres to the metal copper. After applying a conductive copper paste that forms a hardened conductive paste with a strength of 0.5 kg/mm2 or more, the copper powder on the surface of the conductive copper paste is coated with solder without an oxide layer. A conductive copper paste forming a cured conductive paste having an adhesion strength of 0.8 kHz/mu2 or more is continuously applied to the surface, and a wiring pattern (B) is formed on the surface of the insulating layer. A method for manufacturing a printed wiring board with features is provided.

In the method of the present invention, the method for forming the wiring pattern (A) made of copper metal on the surface of the insulating substrate is not particularly limited, but the method described above is preferred.

That is, after a layer made of metallic copper is laminated on the surface of an insulating substrate by a method such as laminating copper foil, copper plating, or vapor depositing copper, this is etched to form a wiring pattern ( The method of forming A) is common.

Furthermore, the method of laminating the insulating layer except for the pad portion of the wiring pattern (A) is not particularly limited, but generally, as described above, a pattern is formed by applying a known resist ink by a method such as printing. However, a method of curing this is recommended.

Wiring pattern exposed after formation of the above insulating layer (A)
The above-described copper-adhesive steel paste is applied to the pad portion. The application of the copper-adhesive copper paste is applied to the wiring pattern (A
), but in general, it is preferable to apply the paste so that the thickness is approximately the same as that of the insulating layer so that the cured paste forms a connection part. As the method for applying the copper paste, any known method such as screen printing may be used without particular limitation.

In the method of the present invention, an important requirement is that after applying the copper-adhesive steel paste, the solder-adhesive steel paste is applied in a state where no oxide layer exists on the copper powder present on the surface of the paste, A wiring pattern with a pad part on an insulating layer (
B). That is, with these seven configurations, it is possible to extremely effectively prevent an increase in contact resistance when laminating copper pastes having different compositions.

The method of forming a wiring pattern (B) on an insulating layer by applying a solder-adhesive copper paste in a state where there is substantially no oxide layer on the copper powder present on the surface of the copper-adhesive copper paste is particularly Not limited. Here is an example of a typical method.

(A) Copper adhesion While the copper paste is uncured, solder adhesion steel paste is applied onto the uncured copper paste and the paste is cured to form connections and wiring patterns (
Method (B) of forming the solder adhesive copper paste, after hardening the solder adhesive copper paste and soft etching its surface, applying the solder adhesive copper paste to the cured surface to form the connection part and the wiring pattern (B). (C) Conductive copper paste After curing the paste in a substantially non-oxidizing atmosphere, a solder adhesive copper paste is applied to the cured surface to form connections and wiring patterns (B) A method of forming a is suitable. In particular, method (A) is recommended because it is excellent in reducing contact resistance and curing.

In the method (A) above, the uncured state of the adhesive mesh paste is a general term for the state in which the rope paste has not completely hardened, but especially the state in which the rope paste is tack-free. It is preferable that the state is hardened to the state of tf
In addition, such curing may be carried out under heating conditions that do not oxidize the copper powder.

Further, as the soft etching conditions in the above method (B), known etching conditions that substantially remove the oxide layer present on the surface of metal copper can be used without any particular restriction. For example, use an etching solution such as an aqueous solution of sodium sulfate or a mixture of sulfuric acid and hydrogen peroxide at 25 to 40°C.
Conditions for etching for 0 to 30 seconds are suitable.

Furthermore, in the above method (C), as a method of curing the copper paste in a substantially non-oxidizing atmosphere, the copper paste may be cured by vapor of an inert liquid such as a fluorine-based inert liquid, nitrogen,
A method of curing in an inert gas such as argon is preferred.

Furthermore, in the method of the present invention, any known method may be employed without particular limitation as the method for forming the wiring pattern (B) by applying the solder adhesive steel paste. Generally, printing methods such as screen printing are suitable.

[Effects] As can be understood from the above explanation, the printed wiring board of the present invention has a connection portion that contacts the pad portion of the wiring pattern (A) and a conductive copper that forms the pad portion of the wiring pattern (B). By laminating and using a hardened copper-adhesive paste and a hardened solder-adhesive steel paste as the hardened paste, the connection portion with the connection portion of the pad portion of the wiring pattern (A), and the above wiring pattern (B)
At the connection part of the pad part with the solder, it exhibits stable electrical characteristics over a long period of time, and is characterized in that the deterioration of the characteristics due to physical shocks such as thermal shock and impact is extremely small.

Further, the printed wiring board obtained by the method of the present invention has the above-mentioned characteristics and can effectively reduce the increase in contact resistance between the hardened material of the steel adhesive paste and the hardened material of the solder adhesive steel paste. It is possible to prevent this, and the electrical resistance of the resulting printed wiring board can be made extremely small. It is presumed that the above-mentioned effect of preventing an increase in contact resistance is due to the fact that the formation of an oxide film on the surface of the wire contained in the copper-adhesive steel paste is suppressed by this method when the solder-adhesive steel paste is laminated. Ru.

[Examples] Examples are shown below to specifically explain the present invention, but the present invention is not limited to these Examples.

In addition, in the Examples, various tests were conducted by the following methods.

(a) Solder dip method test The printed wiring board was immersed in a rosin-based or organic acid-based blank, and then immersed in a solder bath at 240 to 260°C for 5 seconds. After repeating this operation 5 times for each of the 10 samples, observe the swelling and peeling of the hardened conductive copper paste at the connection pad part of the wiring pattern (A),
0 if there is no blistering or peeling at all, Δ if there is some blistering or peeling, and × if there is a lot of blistering or peeling.
The adhesion of the cured product was evaluated as follows.

In addition, the soldering properties were evaluated as 0 for good and X for poor.

(b) Reflow method test Print cream solder on the pad part of the printed wiring board,
Preheating was performed for 30 seconds at 150°C in a far-infrared reflow oven, and then the cream solder was reflowed at a peak temperature of 260°C. After repeating this operation 5 times for each of the 10 samples, observe the blistering or peeling of the hardened conductive copper paste at the connection pad part of the wiring pattern (A), and check if there is no blistering or peeling at all. The adhesion of the cured product was evaluated, with Δ indicating slight swelling or peeling, and X indicating considerable swelling or peeling. In addition, the soldering quality was evaluated as good when it was good and as poor when O1 was bad.

Example 1 (a) Paper phenol copper-clad laminate (rTLC-321J
An etching resist was coated on the substrate (trade name, manufactured by Toho Chemical ■) and etched using a ferric chloride solution to form a wiring pattern (A) made of metallic copper. Next, for soldering of the wiring pattern (A), an insulating resist (rUVR-1500, TS-35J: trade name, manufactured by Taiyo Ink Manufacturing Co., Ltd. ) was applied and cured by irradiation with ultraviolet light. Furthermore, in order to improve the insulation properties, the above-mentioned operation for forming the insulating layer was performed once again.

(b) Next, the adhesion strength to metal copper is 0.8/
Copper-adhesive copper paste (rNF-2000J: trade name, manufactured by Tuck Electric Wire M) of 2 mm2 was applied to the connection pad portion of the wiring pattern and heated at 80° C. for 10 minutes.

Temporarily cured.

(c) Furthermore, the adhesion strength to solder J is 1.2 J/mm.
2 solder tll copper pe-X) (rSP-1920J:
(trade name, manufactured by Tack Electric Wire ■) was screen printed on the insulating substrate, including the above-mentioned steel adhesive copper paste, and heated at 160°C for 30 minutes to harden. The wiring pattern including the pad section (
B) was formed.

(d) Finally, screen print a solder resist (rS-222J: trade name, manufactured by Taiyo Ink Seisakusho) on all soldering parts except for the pads and harden it to form an overcoat layer of solder resist. did.

The performance of the printed wiring board obtained by the above method was as shown in Table 1.

Table 1 Example 2 A printed wiring board was obtained in the same manner as in Example 1 except that step (b) was performed in the following manner.

(b) Coating the same copper-adhesive copper paste as that used in Example 1 to the connection groove part of the wiring pattern (A),
It was heated at 160° C. for 30 minutes to completely cure it. Furthermore,
The surface was coated with an aqueous solution of sodium persulfate for 20 minutes at 35°C.
Etching was performed for seconds. After that, wash with water and heat at 80℃ for 1
Drying was performed for 0 minutes.

Table 12 shows the results of various tests on the printed wiring board obtained.

Table 2 A printed wiring board was obtained in the same manner except for the following steps.

(b) Apply a copper-adhesive copper paste similar to that used in Example 1 to the connection pad portion of the wiring pattern (A), and apply a fluorine-based inert liquid (rIL-270J: trade name, Tokuyama Soda ■). It was completely cured by immersing it in steam (boiling point = 177°C) for 10 minutes.

Table 3 shows the results of various tests on the printed wiring board obtained.

Table 3 Example 3 A comparative example in which step (b) in Example 1 was performed in the following manner.
1 A printed wiring board was obtained in the same manner as in Example 1, except that step (b) and step (c) were carried out in the following manner. That is, copper adhesive copper paste (rNF-200
0J: Product name, manufactured by Tack Electric Wire ■) was screen printed on an insulating substrate including the connection pad part of the wiring pattern and the pad part, and heated at 160°C for 30 minutes to harden it to form a solder-adhesive copper paste. Soldering with the cured product formed a wiring pattern (B) including a pad portion.

Table 4 shows the results of various tests on the printed wiring board obtained.

Comparative Example 2 A printed wiring board was obtained in the same manner as in Example 1, except that step (b) and step (C) were carried out in the following manner. That is, solder adhesive copper paste (rSP-19
20J: Product name, manufactured by Tack Electric Wire ■) was screen printed on an insulating substrate including the connection pad part of the wiring pattern and the pad part, and heated at 160°C for 30 minutes to harden it to form a solder-adhesive copper paste. Soldering with the cured product formed a wiring pattern (B) including a pad portion.

Table 5 shows the results of various tests on the printed wiring board obtained.

Table 5

[Brief explanation of drawings]

FIG. 1 is a new view showing a typical structure of the printed wiring board of the present invention. FIG. 2 is a sectional view showing the structure of a conventional printed wiring board. In the figure, 1 is an insulating substrate, 2 is a wiring pattern (A)
, 3 is an insulating layer, 4 is a wiring pattern (B), 5 and 6 are pad portions, 7 is a connection portion, and 8 is an overcoat layer.

Claims (1)

[Claims] 1) A wiring pattern made of metallic copper (
A), an insulating layer covering the wiring pattern (A) except for the pad portion, and a wiring pattern (B) made of a hardened conductive copper paste are sequentially laminated, and the wiring pattern (B) and the wiring pattern (A) are laminated in sequence. ) is electrically connected to the pad portion of wiring pattern A) by a connecting portion made of a hardened conductive copper paste, the hardened conductive copper paste being in contact with the pad portion of wiring pattern A). The adhesion strength of the cured conductive copper paste to metallic copper is 0.5 kg/mm^
The adhesion strength of the hardened conductive copper paste constituting the pad portion of the wiring pattern (B) to the solder is 0.8 kg/mm^ by the hardened body of two or more conductive pastes.
A printed wiring board comprising a cured body of two or more conductive pastes. 2) The contact resistance between a cured conductive paste with an adhesion strength of 0.5 kg/mm^2 or more to metal copper and a cured conductive paste with an adhesion strength of 0.8 kg/mm^2 or more to solder is 10 mΩ. The printed wiring board according to claim 1, which is as follows. 3) Wiring pattern (A) made of metallic copper on the surface of the insulating substrate
), the wiring pattern (A) except the pad portion is covered with an insulating layer, and then a conductive paste having an adhesion strength to metal copper of 0.5 kg/mm^2 or more is applied to the pad portion. After applying a conductive copper paste that forms a cured product, the adhesion strength to solder is 0.8 in the absence of an oxide layer on the copper powder present on the surface of the conductive copper paste.
A print characterized in that a conductive copper paste forming a hardened conductive paste of kg/mm^2 or more is continuously applied to the surface, and a wiring pattern (B) is formed on the surface of the insulating layer. Method of manufacturing wiring boards.