JPH11121892A - Flexible circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flexible circuit board in which short circuit is prevented by forming a dummy pattern between connection terminal patterns formed on the surface of a basic material thereby enhancing the conductivity and bonding strength even when the interval of connection terminal pattern is wide. SOLUTION: The flexible circuit board 1 has a conductor circuit pattern and connection terminal patterns 2a, 2b formed on the surface of a basic material 1a composed of a flexible insulating film. Dummy patterns 11a, 11b, 11c,... are formed between the connection terminal patterns 2a, 2b. Connection terminal patterns 4a, 4b are formed on the surface of the basic material 3a of a body to be connected, i.e., a board 3 to be connected. The flexible circuit board 1 and the board 3 to be connected are hot pressed and connected while overlapping the bonding region 6. The dummy patterns 11a, 11b, 11c,... suppress deformation of the basic material 1a to ensure an adhesive holding space 12 in a region 9 where the pattern does not exist thus suppressing flow-out of adhesive resin and enhancing the bonding strength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible circuit board for use by connecting to an electric or electronic device such as an IC chip, a liquid crystal display (LCD), or a printed wiring board, and more particularly to an anisotropic conductive adhesive. The present invention relates to a flexible circuit board which is used by being connected by (including an anisotropic conductive adhesive film).

[0002]

2. Description of the Related Art When a flexible circuit board is connected to an electric or electronic device such as a printed wiring board, such as when a driving circuit board composed of a flexible circuit board is connected to a glass substrate of an LCD. One side conductive adhesive is used. The anisotropic conductive adhesive is an adhesive in which conductive particles are dispersed in an adhesive resin. This anisotropic conductive adhesive is interposed between the connection terminals of the electric / electronic device and the flexible circuit board and is thermocompression-bonded, so that the conductive particles are crimped at the terminals where the terminals are present to secure conductivity. Since the conductive particles are dispersed in the portion where no terminal is present, the adhesion is ensured by the adhesiveness of the resin in a non-conductive state.

FIG. 4 (a) is a plan view of a connection terminal portion of a conventional flexible circuit board, and FIG. 4 (b) is an AA cross section showing an ideal state of connection to a glass substrate of an LCD to be connected. Figure,
(C) is BB sectional drawing. In FIG. 4, reference numeral 1 denotes a flexible circuit board on which connection terminal patterns 2a, 2b... Are formed on a surface of a base material 1a made of a flexible insulating film. Reference numeral 3 denotes a substrate to be connected such as a glass substrate or a printed wiring board of an LCD, and connection terminal patterns 4a, 4b... Are formed on a surface of a base material 3a made of an insulating material such as glass. Reference numeral 5 denotes an anisotropic conductive adhesive, and an adhesive resin 5
a in which conductive particles 5b are dispersed. The anisotropic conductive adhesive 5 is interposed between the flexible circuit board 1 and the connection substrate 3 in the bonding area 6 to bond the two and to conduct between the terminals 2a, 4a and between the terminals 2b, 4b. I have.

FIG. 5A shows a state before bonding.
(A) is an AA cross-sectional view, and (b) is a view showing a state during joining.
FIG. 2C is a cross-sectional view taken along line A-A of FIG. 1C, showing an actual joining state, in which 7 is a press head, and 8 is rubber for a cushion.

Since connection terminal patterns 2a, 2b... And 4a, 4b... Are formed at opposing positions on the flexible circuit board 1 and the connected board 3, respectively, FIG.
As shown in FIG. 5, an anisotropic conductive adhesive 5 is interposed between the two in the joining region 6 and the press head 7 is inserted through the rubber 8 from the flexible circuit board 1 side.
Is advanced in the direction of the arrow Y to apply pressure and heat to cure the adhesive resin 5a of the anisotropic conductive adhesive 5 and join.

[0006] The connection terminal pattern 2a,
4a and between 2b and 4b, the adhesive resin 5a flows out and the conductive particles 5b are connected to the connection terminal patterns 2a and 4a or 2b.
And 4b to ensure conductivity. In the region 9 where the connection terminal patterns 2a, 2b and 4a, 4b are not present, that is, between the terminal patterns 2a or 4a and 2b or 4b, the conductive particles 5b are dispersed in the adhesive resin 5a and the anisotropic conductive adhesive 5 Is cured and fixed between the substrates 1 and 3,
Secure adhesive strength in non-conductive state.

However, the state shown in FIG. 4 (b) is an ideal state. When the distance between the connection terminal patterns 2a or 4a and 2b or 4b is small, the state is close to this, and the conductivity and the adhesiveness are improved. However, when the distance is large, it is difficult to secure the adhesiveness due to the outflow of the adhesive.

FIG. 5B shows a state during bonding in such a case. In a region 9 where no pattern exists, the elasticity of the rubber 8 and the flexibility of the connected substrate 3 cause the connected substrate 3 to be bonded.
Is deformed and the anisotropic conductive adhesive 5 easily flows out from the ends 10a and 10b shown in FIG. For this reason, as shown in FIG. 5C, there is a problem in that the amount of the adhesive in the region 9 where no pattern exists after bonding decreases, and the bonding strength may decrease.

Further, the anisotropic conductive adhesive 5 is applied to the ends 10a, 1
0b, the conductive particles 5b are crosslinked and aggregated near the ends 10a and 10b, and only the adhesive resin 5a may flow out. When the conductive particles 5b aggregate, the connection terminal pattern 2a There is a problem that a short circuit may occur between (4a) and 2b (4b), and the reliability may be reduced.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a flexible circuit board which can increase the conductivity and the adhesive strength even when the interval between the connection terminal patterns is wide and does not cause a short circuit. That is.

[0011]

The present invention is the following flexible circuit board. (1) A flexible circuit board connected to an electric / electronic device with an anisotropic conductive adhesive, which corresponds to a base made of a flexible insulating film and connection terminals formed on the electric / electronic device. A flexible circuit board having connection terminal patterns formed at intervals on the surface of the base material and dummy patterns formed between the connection terminal patterns. (2) The flexible circuit board according to the above (1), wherein the connection terminal pattern has an adhesive accommodating recess. (3) The flexible circuit board according to the above (1) or (2), wherein an interval formed between the connection terminal pattern and the dummy pattern is 0.3 mm or less.

The electric / electronic device to be connected may be one having connection terminals formed at an interval.
A printed board such as a CD glass substrate or a printed wiring board is generally used, but an element such as an IC chip or a holder for holding the element may be used. The connection terminals formed on such electric / electronic devices are connection terminal patterns in the case of a printed circuit board, but leads are directly used as connection terminals in the case of elements, holders and the like.

As a flexible circuit board connected to such an electric / electronic device, there is a flexible circuit board in which an accessory circuit of an electric / electronic device such as a drive circuit of an LCD is formed as a conductor circuit pattern. It is used by connecting to electrical and electronic equipment. In such a flexible circuit board, connection terminal patterns are formed on the surface of a base made of a flexible insulating film at intervals corresponding to connection terminals of electric / electronic devices.

The flexible insulating film serving as the substrate is a film having flexibility and insulating properties, and is preferably a film of polyimide, polyester, aramid, polycarbonate or the like, but may be a film made of other plastics or other materials. . The substrate is 10 to 100 μm, preferably 15
Thicknesses of ~ 75 [mu] m are preferred.

A conductor circuit pattern is formed on at least one surface of such a base material, and connection terminal patterns of the circuit pattern are formed at positions corresponding to connection terminals of electric / electronic equipment as a connection object. . Regarding the connection terminals of electric / electronic devices, the intervals between the terminals are not constant from the viewpoint of the shape and structure of the devices or the design of the circuit board, and terminals with a wide interval are also formed. Accordingly, the connection terminals formed on the flexible circuit board are also formed with correspondingly wide intervals. The width of the connection terminal is 0.02 to 1 mm, preferably 0.1 to 1 mm.
When the width is more than 0.3 mm, it is preferable to form an adhesive accommodating recess as described later.

The distance between the connection terminals is wide, for example, 0.3 mm
In the case of exceeding, the anisotropic conductive adhesive flows out at the time of bonding as described above, and the bonding strength is reduced. Therefore, in the present invention, a dummy pattern is formed between connection terminal patterns having a large space. The dummy pattern is formed in substantially the same shape as the connection terminal pattern. However, the dummy pattern is formed only at or near the connection terminal portion independently of the conductor circuit pattern, and is not involved in electrical connection.

The shape, width and the like of the dummy pattern can be arbitrarily set. However, in order to secure the bonding strength, it is preferable that the shape and size of the dummy pattern are substantially equal to those of the connection terminal. It is preferable that the distance between the connection terminal pattern and the dummy pattern and the distance between the connection terminals or the dummy pattern be 0.3 mm or less. By forming a dummy pattern between the connection terminals, the width of the dummy pattern can be reduced when the distance between the connection terminal and the dummy pattern becomes too narrow, but when the distance is wide, a plurality of dummy patterns are formed. Is preferred. Dummy pattern width is 0.02-0.8
mm, preferably 0.04 to 0.5 mm.

The dummy pattern is formed of the same material as the circuit pattern and the connection terminal at the same time. That is, the conductor circuit pattern formed on the base material is formed into a plurality of strips on at least one surface of the base material so as to have a connection terminal pattern at an end portion. At this time, a dummy pattern is formed between the connection terminals. I do. These conductor patterns are preferably formed by etching a conductor layer formed by metallizing and plating.

Metallization for forming a conductor layer is a method of forming a metal thin film having a thickness of 0.1 to 0.5 μm on the surface of a substrate, such as vacuum evaporation, sputtering, or ion plating. A conductor layer is formed by electrodepositing a metal to a thickness of 1 to 10 μm on the thin film thus formed by electrolytic plating. Copper is generally used as the conductor, but other conductors such as copper alloy, silver, and aluminum may be used.

In the etching for forming a conductor pattern such as a conductor circuit pattern, a connection terminal pattern and a dummy pattern on the conductor layer, first, an etching resist having a shape corresponding to the conductor pattern is formed on the conductor layer, and an excess is formed by an etching solution. Dissolve the conductor layer. The etching resist can be formed by any method such as a printing method and a photographic method. In the etching, an excess conductor layer is removed by immersing the substrate on which the etching resist is formed in an etching solution, and a conductor circuit pattern having a shape corresponding to the etching resist is formed. After that, when the etching resist is removed by contact with a solvent or a strong alkaline solution, the conductor pattern is exposed.

The conductor circuit pattern and the connection terminal pattern can be provided with a metal coating by subjecting the surface to electrolytic solder plating, electrolytic tin plating, or nickel plating, and then further to gold plating or the like. The durability is further improved. It is not necessary to perform such processing on the dummy pattern, but it may be formed. It is preferable to form a protective layer on the substrate on which the conductive circuit pattern is formed in such a manner as to cover the conductive circuit pattern in a portion other than the connection terminal portion.

The anisotropic conductive adhesive is an adhesive in which conductive particles are dispersed in an adhesive resin, preferably a thermosetting resin,
Generally, it is used in the form of an anisotropic conductive adhesive film formed in a film shape. Such an anisotropic conductive adhesive does not have conductivity before thermocompression bonding, but thermosetting in a state where conductive particles are crimped between connection terminals by thermocompression bonding and conductive particles are dispersed in other parts A resin that cures and provides conductivity and adhesion is used.

The adhesive resin is preferably a thermosetting resin such as an epoxy resin, a phenol resin, a hydroxyl-containing polyester resin, or a hydroxyl-containing acrylic resin, but may be a thermoplastic resin. When a thermosetting resin is used, production and storage at room temperature and relatively low temperature (40 to 100 ° C)
The curing is preferably carried out with a heat-active latent curing agent which does not cause a curing reaction at the time of drying and causes a curing reaction by heating and pressurizing (thermocompression bonding) at a curing temperature.

The conductive particles include graphite powder, copper, silver,
Any conductive powder such as a metal powder such as nickel, tin, palladium, and solder, a resin plated with nickel, gold, and the like, a metal, and other powders can be used. The conductive particles having a particle size of 1 to 50 μm, preferably 3 to 20 μm can be used. The anisotropic conductive adhesive is often formed into a film and used in the form of an anisotropic conductive adhesive film. These adhesive resin and conductive particles are dispersed or dissolved in an appropriate solvent to form an anisotropic conductive adhesive. The anisotropic conductive adhesive is often formed into a film and used in the form of an anisotropic conductive adhesive film.

In the flexible circuit board according to the present invention, the connection regions are overlapped and bonded by thermocompression so that the connection terminal patterns face the connection terminals of the electric / electronic equipment to be connected. At this time, the resin flowed out between the connection terminal of the connected object and the connection terminal pattern of the flexible circuit board, and the conductive particles were pressed to secure the connectivity, and the conductive particles were dispersed in the region without the pattern. In this state, the resin cures and maintains adhesiveness.

In this case, since a dummy pattern is formed in a portion where the distance between the connection terminal patterns is wide, when the pressure is applied by a press head through rubber, the dummy pattern suppresses the deformation of the base material, and the connection terminal pattern and the connection terminal pattern are deformed. The adhesive holding space can be maintained between them, and the adhesive strength can be increased. Although the gap between the connected body and the flexible circuit board is reduced by the absence of the connection terminal of the connected body, the adhesive holding space can be formed and the bonding strength is increased.

In the above-mentioned flexible circuit board, the adhesive strength tends to decrease when the width of the connection terminal pattern is widened. However, when the adhesive accommodating recess is formed in the connection terminal pattern, the adhesive is held to increase the adhesive strength. be able to. The adhesive containing recess may have any shape such as a groove, a circle, and a square.

[0028]

According to the present invention, since the dummy pattern is formed between the connection terminals, the conductivity and the adhesive strength can be increased even when the interval between the connection terminal patterns is wide.
A flexible circuit board which does not cause a short circuit is obtained.

[0029]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is a plan view of a connection terminal portion of a flexible circuit board according to an embodiment, and FIG.
CC sectional view showing a state connected to the glass substrate of
(C) is a DD sectional view, and the same reference numerals as those in FIGS. 4 and 5 indicate the same or corresponding parts.

In FIG. 1, a flexible circuit board 1 has a conductive circuit pattern (not shown) and connection terminal patterns 2a and 2b connected thereto formed on a surface of a base material 1a made of a flexible insulating film. I have. And, between the connection terminal patterns 2a and 2b, dummy patterns 11a and 11b,
11c are formed. Dummy patterns 11a, 1
Are formed at the same time by etching using the same material as the conductor circuit pattern and the connection terminal patterns 2a and 2b, but are formed independently so as not to be electrically connected to these.

As shown in FIG. 1, the connection substrate 3 as a connection body has connection terminal patterns 4a and 4b formed on the surface of a base material 3a made of an insulating base material such as a glass substrate. The anisotropic conductive adhesive 5 is obtained by dispersing conductive particles 5b in an adhesive resin 5a. An anisotropic conductive adhesive 5 is interposed between the flexible circuit board 1 and the connected substrate 3 in the bonding area 6 to bond the two, and to connect the terminals 2a, 4a and 2b, 4b.
b is electrically connected.

The above-mentioned flexible circuit board 1 is shown in FIG.
As in the case of (b), the bonding region 6 is formed on the connected substrate 3.
And pressurized and heated by a press head 7 via a cushion rubber 8 for thermocompression bonding and connection. In this case, the connecting terminal patterns 2a, 2b... And 4a, 4b
Are formed, an anisotropic conductive connecting agent 5 is interposed between the two in the joining region 6 in a state where they are opposed to each other, and a press head 7 is provided from the flexible circuit board 1 side via a rubber 8. Is advanced in the direction of the arrow Y and pressurized and heated to cure and bond the adhesive resin 5a of the anisotropic conductive adhesive 5.

The connection terminal patterns 2a,
4a and between 2b and 4b, the adhesive resin 5a flows out and the conductive particles 5b are connected to the connection terminal patterns 2a and 4a or 2b.
And 4b to ensure conductivity. Region 9 where connection terminal patterns 2a, 2b and 4a, 4b do not exist, ie, connection terminal patterns 2a or 4a and 2b or 4b
In between, the conductive particles 5b are dispersed in the adhesive resin 5a and the anisotropic conductive adhesive 5 is cured and fixed between the substrates 1 and 3, and the adhesive force is secured in a non-conductive state.

In this case, since the dummy patterns 11a, 11b and 11c are formed between the connection terminal patterns 2a and 2b, the dummy patterns 11a, 11b and 11c suppress the deformation of the base material 1a, and the area 9 where no pattern exists exists. The adhesive holding space 12 is secured in the adhesive resin 5a.
And the adhesive strength can be increased.
Since the connection terminal patterns 4a and 4b do not exist in the portions of the connected substrate 3 facing the dummy patterns 11a, 11b and 11c, the base material 1a is deformed by that amount, but is maintained in the necessary adhesive holding space. It is possible.

If a film such as a preservation film is formed on the dummy patterns 11a, 11b and 11c, the thickness of the dummy pattern is increased, and the adhesive holding space 12 is enlarged to increase the bonding strength. .

Also, the formation of the adhesive holding space 12 reduces the outflow of the adhesive, so that the aggregation of the conductive particles 5b at the ends 10a and 10b as shown in FIG. Is prevented.

FIG. 2A is a plan view of a flexible circuit board according to another embodiment, and FIG. 2B is a cross-sectional view taken along the line E-E showing a joined state. In this embodiment, adhesive connection recesses 13a and 13b are formed in the connection terminal patterns 2a and 2b of the flexible circuit board 1 in the joint region 6. The adhesive accommodating recesses 13a and 13b have a shape in which the connection terminal patterns 2a and 2b are divided at the joint region 6, but may have a circular or square or other concave shape.

The above-mentioned flexible circuit board 1 is also joined to the connection board 3 in the same manner as in FIG.
Since the a and 13b are formed, the anisotropic conductive adhesive 5 is held at these portions, and the bonding strength can be increased even when the width of the connection terminal patterns 4a and 4b is wide.

[0039]

EXAMPLES Examples of the present invention and comparative examples will be described below. Example 1 As a flexible circuit board 1 shown in FIG. 1, a thickness of 8 μm was formed on both upper and lower surfaces of a polyimide base material 1 a having a thickness of 25 μm.
A copper pattern of m was formed, and nickel-gold plating was performed thereon to form a conductor circuit pattern, a connection terminal pattern, and a dummy pattern. A substrate in which an ITO pattern was formed as connection terminal patterns 4a and 4b on a glass substrate 3a for LCD as a substrate to be connected 3 was used, and the above-mentioned flexible circuit board 1 was connected. As the anisotropic conductive adhesive, a thermosetting adhesive in which nickel-gold plated resin particles (5 μm in diameter) were dispersed as conductive particles in an epoxy resin was used.

The width of the connection terminal patterns 2a, 2b, 4a and 4b of the flexible circuit board 1 and the connection substrate 3 is 0.45 mm, and the interval between these terminal patterns is 0.4.
A dummy pattern 11a, 11b, 11c having a width of 0.15 mm is formed at the center of the above-mentioned space of the flexible circuit board 1 with a width of 5 mm (that is, a pattern pitch of 0.9 mm).
Use silicone rubber as 180 ℃ -30kgf
/ Cm ² -10 seconds.

Connection strength immediately after crimping and 60 ° C.-90% RH
Table 1 shows the results of measuring the adhesive strength after aging and the number of occurrences of short circuits after −500 hours. The adhesive strength was determined by converting the strength at the time of pulling the connection portion in the direction of 90 ° at a pulling speed of 50 mm / min into a value per 1 cm width. The occurrence of short-circuit was represented by the fraction of the number of short-circuited portions between adjacent patterns in 100 patterns.

Embodiment 2 In Embodiment 1, as shown in FIG. 2, a width of 0.15 mm is set at the center of the connection terminal patterns 2a and 2b of the flexible circuit board 1.
The recesses 13a and 13b of the adhesive accommodating portions are formed, and the results of the same measurement are shown in Table 1.

Comparative Example 1 Table 1 shows the results of the same measurement in Example 1 where no dummy pattern was formed.

Comparative Example 2 Table 1 shows the results of the same measurement in Example 2 except that no dummy pattern was formed.

[0045]

[Table 1]

Embodiment 3 In the same manner as in Embodiment 1, except that a 35 μm thick copper pattern is formed on both sides of a glass fiber reinforced epoxy resin substrate having a thickness of 1 mm as a substrate 3 to be connected, and a nickel-gold plated substrate is used. Tested. A dummy pattern having a width of 0.6 mm and a spacing of 0.6 mm (that is, a pattern pitch of 1.2 mm) of the connection terminal pattern of the flexible circuit board 1 and the connection-target board 3 and a width of 0.2 mm at the center of the spacing. Are formed, and the results of similar measurements are shown in Table 2.

Example 4 In Example 3, an adhesive receiving recess having a width of 0.2 mm was formed at the center of the connection terminal pattern of the flexible circuit board 1.
Table 2 shows the measurement results.

Comparative Example 3 Table 2 shows the results of the measurement in Example 3 in which no dummy pattern was formed.

Comparative Example 4 Table 2 shows the results of a similar measurement in Example 4 where no dummy pattern was formed.

[0050]

[Table 2]

From the results of Tables 1 and 2, it can be seen that the formation of the dummy pattern increases the initial and aging bond strengths, and the formation of the adhesive holding space increases the tendency. It can be seen that no short circuit occurred.

Reference Example 1 FIG. 3 shows a change in the adhesive strength (peel strength) when the interval between the patterns was changed in Comparative Example 1. From FIG. 3, it can be seen that in order to obtain an adhesive strength of 800 gf / cm, the interval between the patterns should be 0.3 mm or less.

[Brief description of the drawings]

FIG. 1A is a plan view of a flexible circuit board according to an embodiment,
(B) is a CC sectional view showing the connection state, (c) is a DD
It is sectional drawing.

FIG. 2A is a plan view of a flexible circuit board according to another embodiment, and FIG. 2B is an EE cross-sectional view showing a connection state.

FIG. 3 is a graph showing test results of Reference Example 1.

FIG. 4A is a plan view of a conventional flexible circuit board,
(B) is an AA sectional view showing an ideal connection state, (c)
Is a CC sectional view.

FIG. 5 (a) shows a state before joining, and FIG.
A sectional view, (b) is an AA sectional view showing a state during joining,
(C) is an AA sectional view showing an actual joining state.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flexible circuit board 1a Base material 2a, 2b, 4a, 4b Connection terminal pattern 3 Connected substrate 3a Base material 5 Anisotropic conductive adhesive 5a Adhesive resin 5b Conductive particles 6 Joining area 7 Press head 8 Rubber 9 Area where no pattern exists 10a, 10b End 11a, 11b, 11c Dummy pattern 12 Adhesive holding space 13a, 13b Adhesive accommodating recess

Claims (3)

[Claims] 1. A flexible circuit board connected to an electric / electronic device by an anisotropic conductive adhesive, comprising: a base made of a flexible insulating film; and a connection terminal formed on the electric / electronic device. A flexible circuit board having connection terminal patterns formed at intervals on the surface of a base material and dummy patterns formed between the connection terminal patterns. 2. The flexible circuit board according to claim 1, wherein an adhesive accommodating recess is formed in the connection terminal pattern. 3. The gap formed between the connection terminal pattern and the dummy pattern is 0.3 mm or less.
Or the flexible circuit board according to 2.