JP2001077494A - Printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printed wiring board used for various kinds of electronic devices which is provided with a connector connecting part which produces no silver ion migration, even at narrow pitch and is superior in electrical connection stability and insertion/pulling durability. SOLUTION: The connection pattern of a connector connection part is composed of a carbon film 13, which is printed directly and formed on an insulation board 11 and of which sheet resistance is 25 Ω/sq or higher and 1 kΩ/sq or lower and pencil hardness is 2H or higher and 7H or lower. Therefore, even if the board has a narrow pitch, generation of silver ion migration can be prevented, and the sheet resistance and hardness of the carbon film 13 is set to be within a prescribed range, resulting in a connector connecting part which is superior in electrical connection stability and insertion/pulling durability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board used for various electronic devices, and more particularly, to a connector connecting portion which serves as a connecting portion with an external connector.

[0002]

2. Description of the Related Art In recent years, as electronic devices such as portable devices have been reduced in size and weight and in price, the use of narrow-pitch connectors has increased, and printed wiring boards that can be formed at low cost have been widely used. It is becoming.

[0003] The printed wiring board is a printed wiring board on which a predetermined wiring pattern is formed by printing. The wiring pattern is used to secure good electrical characteristics and strong adhesion to the insulating substrate. In most cases, it is usually constituted by a silver-based conductive film printed and formed with a silver paste, and an insulating film is often used as an insulating substrate.

The printed wiring board is usually connected to a predetermined functional part via an external connector, and a connector connection as a connection portion with the external connector is described below with reference to the drawings. explain.

FIG. 2A is a plan view of a connector connecting portion of a conventional printed wiring board, and FIG. 2B is a sectional view taken along line BB of FIG. 2A.

Reference numeral 1 denotes an insulating substrate formed of an insulating film of a predetermined shape such as polyethylene terephthalate, and a predetermined wiring pattern 2 is formed on the upper surface thereof by printing with a silver paste.

A plurality of the wiring patterns 2 are arranged in a substantially parallel positional relationship with each other in accordance with the pitch of the contact portions of an external connector (not shown). ing.

Further, the surface of the portion of the wiring pattern 2 extending to the vicinity of the outer peripheral portion of the insulating substrate 1 is covered with a carbon coating 3, and the wiring pattern 2 in this portion and the carbon coating 3 covering the same are covered with the carbon coating 3. The connection pattern 4 of the connector connection portion is configured.

The carbon coating 3 is formed by printing so as to cover the entire surface of the wiring pattern 2 in order to prevent silver ion migration, which is likely to occur when a potential difference occurs between the wiring patterns 2 made of a silver-based conductive coating. Was to be done.

For the same purpose, an intermediate portion of the wiring pattern 2 not covered with the carbon coating 3 is provided with an insulating coating 5.
Are printed on top of each other.

[0011] Even if a force is inadvertently applied to the connector connecting portion, the insulating substrate of the portion where the connecting pattern 4 is formed is formed so that the connector connecting portion is not bent and disconnection of the connecting pattern 4 does not occur. On the back of 1,
The reinforcing plate 6 is mounted.

In the conventional printed wiring board configured as described above, one corresponding to a recent narrow-pitch connector,
For example, in a printed wiring board having a connector connecting portion corresponding to a contact portion having a pitch of 0.8 mm or less, silver ion migration easily occurs because the interval between the wiring patterns 2 of the connector connecting portion becomes small. As a countermeasure, the carbon coating 3 must be formed.

[0013]

However, in recent years, as electronic devices have been further reduced in size and weight, connectors having a contact portion pitch of 0.5 mm or less have become widespread, and a printed wiring board having a connector connection portion capable of coping with the same. Demands have also become stronger, and with the configuration of the conventional printed wiring board,
When the carbon film 3 is superimposed on the wiring pattern 2, very high printing accuracy is required, and it is difficult to form the connection pattern 4 by a screen printing method usually used when forming a print film.

FIG. 3 shows another conventional method.
As shown in the plan view of FIG. 3A and the cross-sectional view of FIG. 3B, a portion of the wiring pattern 2 extending to the vicinity of the outer peripheral portion of the insulating substrate 1 is covered with a water-repellent insulating film 7 such as a fluororesin. However, in the above-described configuration, it is necessary to immerse the connector connection portion in a water-repellent treatment solution containing a fluororesin or the like as a main component and then dry and volatilize the solvent. Processing time is required, productivity is low, it is difficult to make the thickness of the insulating film 7 uniform, and furthermore, the contact portion of the external connector has to be cut into the insulating film 7 to conduct with the wiring pattern 2. At this time, there is a problem that a pinhole is generated in the wiring pattern 2 and the connection becomes unstable, or the insulating property is deteriorated due to shaving powder of the wiring pattern 2.

The present invention solves such a conventional problem. Even if the pitch is narrow, silver ion migration does not occur, and electrical connection stability and insertion / extraction durability are excellent. An object of the present invention is to provide a printed wiring board having a connector connection portion at low cost.

[0016]

In order to achieve the above-mentioned object, a printed wiring board according to the present invention is characterized in that a connection pattern of a connector connecting portion is formed by directly printing on an insulating substrate a sheet resistance value of 25 Ω / sq or more and 1 kΩ. / Sq or less and a carbon coating having a pencil hardness of 2H or more and 7H or less.

Accordingly, since the connection pattern is made of carbon, it is possible to prevent the occurrence of silver ion migration even when the connection pattern is of a narrow pitch, and to further reduce the sheet resistance and hardness of the carbon coating within a predetermined range. With this setting, a printed wiring board having a connector connection portion having excellent electrical connection stability and insertion / extraction durability can be obtained at low cost.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to a first aspect of the present invention is directed to a printed wiring board on which a predetermined wiring pattern is formed by printing on an insulating substrate. The connection pattern has a sheet resistance value of 25 Ω / sq or more and 1 kΩ / sq or less and a pencil hardness of 2
A printed wiring board made of a carbon coating directly formed on the insulating substrate of not less than H and not more than 7H, wherein the pitch of the connection pattern of the connector connection portion is, for example, 0.8 mm pitch or 0.5 mm pitch or less. Even in the case of a pitch, since the connection pattern is composed of only the carbon film, the occurrence of silver ion migration can be eliminated irrespective of the pitch, and the connection pattern can be easily formed by a screen printing method or the like. The sheet resistance of the coating is 25Ω
/ Sq or more and 1 kΩ / sq or less, the electric signal of the circuit in the usual electronic equipment can be conducted without any trouble, and the pencil hardness of the carbon coating is 2H or more and 7H or less. Even if it is repeatedly inserted and removed about 20 times, a printed wiring board having a connection pattern in which the carbon film is hardly scraped and pinholes and the like are hardly generated, and a connection failure due to this is hardly generated easily and inexpensively. It has the effect that it can be obtained.

According to a second aspect of the present invention, in the first aspect, the carbon film contains a polyester resin having a glass transition temperature of 40 ° C. or more and 80 ° C. or less as a binder resin. Since the carbon coating contains, as a binder resin, a highly flexible polyester resin having a relatively high glass transition temperature of 40 ° C. or more and 80 ° C. or less, it is particularly excellent in bendability and is made of polyethylene terephthalate or the like. Since it has excellent hardness and excellent adhesion properties to the insulating film, it has an effect of easily providing a connection pattern having excellent durability against insertion and removal with an external connector.

According to a third aspect of the present invention, in the first aspect, the carbon coating contains a phenol resin as a binder resin and has a pencil hardness of 4H or more and 7% or more.
H or less, and the carbon coating is
As the binder resin contains a phenol resin with appropriate hardness and toughness, the hardness can be easily increased to 4H or more and 7H or less in pencil hardness, and a connection pattern that is extremely excellent in the durability of insertion and removal with external connectors can be obtained. It has the effect that the one provided can be easily obtained.

According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the insulating substrate is formed of an insulating film, and a portion of the connector connecting portion where a connection pattern is formed is formed. A reinforcing plate is attached to the back surface of the insulating film, and a flexible printed wiring board having flexibility with a connector connection portion having appropriate rigidity can be easily configured. In this connector connection portion, ,
When inserting and connecting to the external connector, the strength of the reinforcing plate can prevent bending and other deformations and reduce the occurrence of breaks in the connection pattern due to this, thus maintaining stable electrical connection with the external connector Has the effect of being able to.

Hereinafter, an embodiment of the present invention will be described.

FIG. 1A is a plan view of a connector connecting portion of a printed wiring board according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along line AA of FIG. As shown in the figure, a wiring pattern 12 made of a silver-based conductive film is printed and formed with a silver paste on an upper surface of an insulating substrate 11 made of an insulating film of a predetermined shape such as polyethylene terephthalate. It is the same as the technology, but as shown in FIG.
Are formed only up to a position at a predetermined distance from the outer peripheral portion of the insulating substrate 11.

Reference numeral 13 denotes a plurality of carbon coatings directly formed on the insulating substrate 11 by printing.
A is electrically connected to each of the wiring patterns 12, the intermediate portion 13B is arranged in a substantially parallel positional relationship with the pitch of the contact portion of the external connector (not shown), and the other end 13C is insulated. It extends to the vicinity of the outer peripheral portion of the substrate 11.

That is, in the printed wiring board according to the present invention, the carbon coating 13 between the intermediate portion 13B and the other end 13C is formed by the connection pattern 14 of the connector connection portion.
It has become.

Above the connection between the wiring pattern 12 and the one end 13A of the carbon coating 13 connected to the wiring pattern 12, there is a purpose of preventing silver ion migration between the wiring patterns 12 made of the silver-based conductive coating. The fact that the insulating film 15 is provided and that the reinforcing plate 16 is mounted on the back surface of the insulating substrate 11 at the portion where the connection pattern 14 is formed are the same as those in the prior art.

Next, a brief description will be given of a method of forming the printed wiring board having the above-described structure. First, a silver paste is printed and formed on the insulating substrate 11 in a predetermined pattern by a screen printing method or the like, and hot air circulation combined with far infrared rays is performed. The wiring pattern 12 is formed by heating and curing in a furnace at 150 ° C. for about 5 minutes.

Subsequently, a carbon paste is printed by a screen printing method or the like so that the carbon coating 13 has the above-described arrangement state, and the printed carbon paste is heated at 150 ° C. for about 5 minutes in a hot air circulating furnace combined with far infrared rays. A carbon film 13 is formed by heating and curing, and thereafter, an insulating film 15 is formed by printing so as to cover the wiring pattern 12 and one end 13A of the carbon film 13 connected thereto,
Finally, the reinforcing plate 16 is attached.

After the carbon film 13 is first formed by printing, it is connected to one end 13A to form the wiring pattern 12
May be formed by printing.

As described above, since the connection pattern 14 of the connector connection portion of the printed wiring board according to the present invention is composed of only the carbon coating 13, the pitch is, for example, 0.5 mm.
Even if the pitch is less than or equal to the pitch, it can be easily and inexpensively formed by the screen printing method, and the silver ion migration does not occur.

When the external connector has a pitch of 0.5 mm, the dimension between the connection patterns 14 of the connector connection part (indicated by the dimension D in FIG. 1B) is determined by the printing accuracy by the screen printing method. Considering the fitting accuracy to the external connector, etc., it is in the range of 0.1 to 0.25 mm, preferably 0.15 mm
It is desirable to set to about
If the thickness of the carbon coating 13 constituting the layer No. 4 (indicated by the dimension E in FIG. 1 (b)) is less than 5 μm, the sheet resistance becomes high and the insertion / extraction durability is poor. Since it may occur, it is preferable that the thickness is 5 μm or more.
It is desirable to form it with a thickness of m. The carbon coating 13 formed by printing with the carbon paste is composed of a binder resin and conductive materials such as carbon and graphite. In general, the ratio of the binder resin to the conductive material in the carbon coating 13 is small. Then, the sheet resistance value decreases, but, for example, if the sheet resistance value is less than 25 Ω / sq, the adhesion to the insulating substrate 11 deteriorates, and the coating hardness decreases to 1H or less in pencil hardness. When the insertion and removal of the carbon coating 13 are repeated, the carbon coating 13 tends to be easily scraped.

On the other hand, when the ratio of the binder resin to the conductive material in the carbon coating 13 increases, the sheet resistance increases, the adhesion to the insulating substrate 11 improves, and the coating hardness also increases with the pencil hardness. 4H or higher, the durability against insertion and withdrawal from the external connector is improved. For example, when the sheet resistance exceeds 1 kΩ / sq, the carbon coating 13 has a pencil hardness of 8H or higher. Therefore, the durability of insertion and removal with the external connector is further improved, but the carbon coating 13 is liable to be warped or cracked, and the high sheet resistance increases the resistance of circuit wiring of the electronic device. Inconveniences such as low transmission accuracy of electric signals are likely to occur.

In consideration of the above, the carbon coating 1
By adjusting the ratio of the binder resin to the conductive material of No. 3, the sheet resistance is desirably in the range of 25 Ω / sq to 1 kΩ / sq, preferably in the range of 50 Ω / sq to 600 Ω / sq. .

In this case, as the binder resin, a phenol resin, an epoxy resin, a phenoxy resin,
Polyester resin, polyurethane resin, acrylic resin,
And modified resins thereof.On the other hand, examples of the conductive material include various carbon blacks and graphites, and the ratio of the binder resin to the conductive material is appropriately set according to the combination of the respective materials to meet the above conditions. You have to get what you want.

The binder resin of the carbon film 13 will be described in more detail. A thermosetting polyester resin having a glass transition temperature of about 70 ° C. is used as the binder resin, and carbon black and graphite are mixed and dispersed therein. Screen printing of carbon paste
When formed by baking, a carbon coating 13 having a sheet resistance value of about 100 Ω / sq and a pencil hardness of 3H can be formed.
4 with the connector connection to the external connector
When the surface of the carbon coating 13 is checked afterwards, there is no scraping of the carbon coating 13 and no generation of pinholes, and good electrical connection stability can be obtained.

Similarly, when a thermosetting polyester resin having a glass transition temperature of about 10 ° C. is used as a binder resin and a carbon paste in which carbon black and graphite are intermixed and dispersed is used, The sheet resistance of the carbon coating 13 is about 100Ω.
/ Sq and a pencil hardness of 1H, which means that the carbon coating 13 was shaved when it was inserted into and removed from the external connector two or three times.

As described above, when the carbon coating 13 constituting the connection pattern 14 of the connector connection portion contains a thermosetting polyester resin having a glass transition temperature of about 70 ° C. as a binder resin. In addition, the connection pattern 14 having both bending resistance, which is a characteristic of the polyester resin, adhesion to an insulating film such as polyethylene terephthalate, and insertion / extraction durability can be formed.

Although the above description has been made on the case where the polyester resin as the binder resin has a glass transition temperature of about 70 ° C., the same applies to those having a glass transition temperature in the range of 40 ° C. or more and 80 ° C. or less. A product having excellent insertion / extraction durability is obtained.

In particular, in the case of those having a glass transition temperature of 60 ° C. or more and 80 ° C. or less, the coating hardness is 3H in pencil hardness.
Since the carbon coating 13 can be formed on the carbon coating 13, a more excellent one can be easily obtained in the insertion and removal durability.

Next, when a modified phenol resin is used as a binder resin for the carbon coating 13, a phenol resin having an appropriate hardness and toughness causes a three-dimensional cross-linking reaction during thermosetting, and a pencil having similar characteristics is obtained. A carbon coating 13 having a hardness of 4H or more and 7H or less can be formed. In this carbon coating 13, even if the insertion and removal with an external connector is performed 30 times or more, the carbon coating 13 is scraped,
There is no pinhole or the like, and good electrical connection stability is obtained.

On the other hand, with respect to the carbon coating 13 having a pencil hardness of 8H or more when the content of the modified phenol resin is large, the durability against insertion and withdrawal with an external connector can be guaranteed 50 times or more. Warpage and cracking are likely to occur, and the sheet resistance value is 10 kΩ / s.
As described above, it is not practical because a problem such as exceeding q occurs.

In the printed wiring board according to the present invention, if the insulating substrate 11 is an insulating film, other than polyethylene terephthalate, polyimide, polyethylene naphthalate, polyether imide, polyphenyl sulfone, polyether sulfone, polyether ether ketone may be used. The same effect can be obtained when an insulating substrate having rigidity is used without using an insulating film.

[0043]

As described above, according to the present invention, the connection pattern of the connector connection portion, which is a portion to be connected to the external connector, has a sheet resistance value of 25 Ω / sq or more and 1 kΩ / sq.
In addition, since a carbon coating having a pencil hardness of 2H or more and 7H or less is directly formed on the insulating substrate by printing, it can be easily formed by a screen printing method regardless of the pitch of the connection pattern. An advantageous effect is obtained that a printed wiring board having a connector connection portion that does not generate ion migration and has excellent electrical connection stability with an external connector and excellent insertion / extraction durability can be realized at low cost.

[Brief description of the drawings]

FIG. 1A is a plan view of a connector connecting portion of a printed wiring board according to an embodiment of the present invention. FIG. 1B is a cross-sectional view taken along line AA in FIG.

FIG. 2A is a plan view of a connector connecting portion of a conventional printed wiring board. FIG. 2B is a cross-sectional view taken along line BB of FIG. 2A.

3A is a plan view of a connector connecting portion of another conventional printed wiring board, and FIG. 3B is a cross-sectional view taken along line CC in FIG. 3A.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Insulating substrate 12 Wiring pattern 13 Carbon coating 13A One end 13B Intermediate part 13C Other end 14 Connection pattern 15 Insulating coating 16 Reinforcement plate

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinji Okawa 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F term (reference) 4E351 AA01 BB01 BB31 CC11 CC22 CC31 DD05 DD29 DD41 EE03 EE11 GG02 GG12 5E317 AA07 BB01 BB11 BB14 CC22 CC52 CD21 GG14 GG17 5E338 AA01 AA12 AA16 BB72 BB75 CC01 CD13 CD32 EE26

Claims (4)

[Claims] In a printed wiring board on which a predetermined wiring pattern is formed by printing on an insulating substrate, a connection pattern of a connector connecting portion, which is a portion connected to an external connector, has a sheet resistance value of 25 Ω / sq or more and 1 kΩ /. A printed wiring board comprising a carbon coating directly formed on the insulating substrate having a sq or less and a pencil hardness of 2H or more and 7H or less. 2. The printed wiring board according to claim 1, wherein the carbon coating contains a polyester resin having a glass transition temperature of 40 ° C. or more and 80 ° C. or less as a binder resin. 3. The carbon coating contains a phenol resin as a binder resin, and has a pencil hardness of 4H or more and 7H or more.
The printed wiring board according to claim 1, wherein: 4. The insulating substrate according to claim 1, wherein the insulating substrate is formed of an insulating film, and a reinforcing plate is mounted on a back surface of the insulating film in a portion where the connection pattern of the connector connection portion is formed. Printed wiring board.