JP2995993B2 - Circuit connection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for electrically and mechanically connecting opposing circuits or electrodes.

[0002]

2. Description of the Related Art As electronic components have become smaller and thinner, circuits used for them have become higher in density and higher in definition. For connection of these fine circuits, for example, a method using an anisotropic conductive adhesive containing conductive particles having a particle size of about 7 to 30 μm in an amount of 1 to 10% by volume is known.

However, in the conventional method, if the conductive particles exist between adjacent circuits, a short circuit (short circuit) between the circuits occurs, and it is difficult to connect a recent high-density circuit such as 7 lines / mm or more. No longer.

Therefore, for example, Japanese Patent Application Laid-Open No. Sho 60-262430.
In the technique disclosed in Japanese Patent Application Laid-Open Publication No. H10-209, an insulative adhesive curable by ultraviolet rays (UV) or the like is interposed on a glass substrate circuit so as to face a protruding electrode on a semiconductor element, and the adhesive is cured under pressure. ing.

[0005]

However, the method disclosed in Japanese Patent Application Laid-Open No. 60-262430 does not contain conductive particles in the adhesive, so that the leakage between adjacent circuits is improved, but the connection is not improved. Unless the substrate of the circuit to be formed is limited to hard substrates such as glass and silicon, sufficient connection reliability cannot be obtained. In addition, the connection surface shape of the protruding electrode has an aspect ratio (ratio of major axis / minor axis) of 1 such as a circle or a square.
This ratio is about 3 or less even in the case of a rectangular shape or a rectangular shape.
There is a restriction on the shape of the electrode, for example, it needs to be 0 μm or less.

[0006] That is, the reason that the rigid substrates are limited to each other is that a large number of protruding electrodes have a variation in height, so that a large electrode can easily contact a circuit surface to be connected, but a small height. This is because the electrodes cannot be contacted, and it is necessary to deform the protruding electrodes between the hard substrates by the pressure at the time of connection and to connect a number of electrodes in a flattened manner. At this time, it is preferable that the electrode shape has a smaller aspect ratio. This is because the pressure can be concentrated locally and the deformation is easy, and the connection reliability can be improved by easily removing the adhesive from flowing to a portion other than the contact portion between the electrode and the circuit. .

For the above reasons, in the prior art, for example, T
AB (Tape Automated Bonding) and FPC (Flexible P
It has been extremely difficult to apply the present invention to applications in which a large number of insulated parallel electrodes (circuits) are collectively connected to other circuits, such as a rinted circuit.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has as its object the purpose of at least one of the substrates being flexible, and the projecting electrodes being extremely similar to the circuit terminal portions. An object of the present invention is to provide a method for connecting circuits using an insulating adhesive when the aspect ratio is large.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method of connecting a circuit for connecting a large number of circuits formed on an insulating substrate and opposing circuits by using an adhesive. Is formed on a flexible substrate having a circuit width of 70 μm or less, a pitch of 150 μm or less, and a breaking elongation of 10% or more. An insulating adhesive is interposed between the circuit and the opposing circuit. The circuit is aligned, and the ratio (L / W) of the connection length L to the circuit width W is 40.
As described above, a method of connecting circuits, wherein both circuits are brought into contact with each other under pressure and the adhesive is cured.

The present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view showing a circuit connection method according to the present invention. The flexible substrate 1 is a film having a breaking elongation (elongation) of 10% or more, such as polyimide, polyethylene terephthalate, and other plastic films. In particular, polyimide has a large mechanical strength and a relatively low coefficient of thermal expansion of generally 50 × 10 ⁻⁶ / ° C. or less. Therefore, a deviation from a circuit that is opposed by thermal expansion at the time of circuit connection (hereinafter referred to as a circuit deviation). Less is. The tensile modulus of these flexible substrates 1 is 1000 kg / m
m ² or less is preferred.

The reason why the elongation percentage is 10% or more is to obtain a cushion-like action for obtaining flatness among a large number of circuits by applying pressure during connection. It is preferable that the elongation percentage is large because the flexibility is high. However, when the elongation percentage is large, the above-described circuit deviation generally increases.
More preferably, it is set to 90%. Here, the elongation and the elastic modulus of the present invention are based on ASTM-D-882.

The thickness of the flexible substrate 1 is 20 to 130 μm
Is preferred in terms of strength and cost.

The adhesive 2 is used for bonding the flexible substrate 1 and the circuit 3 and is discarded as required. If the adhesive 2 is provided, it is preferable because the circuit can be easily flattened at the time of connection, as in the case of the flexible substrate 1. If the adhesive 2 is not provided, it is possible to increase the density of the circuit and improve the heat resistance. Becomes

The material of the circuit 3 is not particularly limited, but Cu is preferable in terms of economy. In addition, the surface of the circuit has a roughness of 0.1 to 10 due to the formation of irregularities due to surface roughening or the like, or the presence of a coating layer such as a coating layer of Sn, Zn, Au, solder, or the like.
It is preferable to make the surface uneven to about 10 μm because the contact with another circuit to be connected becomes easy.

The method of manufacturing the circuit 3 is not particularly limited, but the electrolytic method is easy to obtain the above-described surface roughening, and the rolling method and the additive method are easy to obtain a high-definition circuit.

The height H of the circuit 3 is determined by the thickness T of the flexible substrate 1.
It is preferable to set the following. This ratio (H / T) can be reduced as the elongation percentage of the flexible substrate 1 increases,
0.9, and more preferably 0.3 to 0.8 is preferable because both circuit deviation and height flatness at the time of connection can be achieved.

Assuming that P is the circuit pitch and W is the width of the top of the circuit, the present invention can apply W = 70 μm or less, P = 150 μm or less, more preferably W = 45 μm or less, and P = 90 μm.

Although not shown in FIG. 1, the present invention can be practiced even when the width of the top of the circuit is equal to the width of the bottom on the substrate side, or when the width of the top is larger than the width of the bottom.

When W is larger than 70 μm, the excess adhesive is not sufficiently removed at the time of connection, and when P is larger than 150 μm, the adhesiveness in the space becomes insufficient.

The present invention is characterized in that it can be applied even if these values become smaller.

The length L of the connecting portion is, as schematically shown in FIG. 2, the distance over which the adhesive is formed in the length direction of the circuit. That is, it is the length of the adhesive 4 formed before the connection, or the distance of the circuit after the connection after the connection, and if both are different, the shorter distance is adopted. Here, the ratio to the circuit width, that is, (L / W) is 40 or more,
Preferably, it is set to 60 or more, because the number of contact points at the connection portion increases.

Although it is preferable that (L / W) is large, the upper limit is about 300 because the mounting area increases.
This ratio is preferably from 60 to 200, and more preferably from 65 to 150.

The insulating adhesive 4 may be applied to one of the circuits 3 and 6, or may be applied to either of the circuits 3 and 6. In the case of a film, it is also possible to connect both circuits at once while positioning them without attaching them to the circuits 3 and 6 as shown in FIG.

As described above, the insulating adhesive 4 may be liquid or solid, but when it is in the form of a film, an application step is not required as compared with the case of a liquid, and it is necessary to obtain a continuous tape having a constant thickness. Since it is possible, it is preferable because the manufacturing process can be easily automated.

As the material of the insulating adhesive 4, a thermoplastic material used for an adhesive sheet or the like, or a material which is curable by heat or light can be widely applied. The use of a curable material is preferred because of its excellent heat resistance and moisture resistance after connection. Among them, an epoxy adhesive can be preferably applied because it can be cured in a short time, has good connection workability, and has excellent molecular structure and excellent adhesiveness.

The epoxy-based adhesive mainly comprises, for example, a high-molecular-weight epoxy resin, a solid epoxy resin and a liquid epoxy resin, and an epoxy resin modified with urethane, polyester, NBR, or the like. In general, the system comprises a system to which various modifiers such as an agent and another polymer, a catalyst and the like are added. If these adhesives have tackiness at around room temperature, temporary fixing after circuit alignment is simple and preferable.

The thickness is determined so that the space between the circuits can be filled after the connection in consideration of the height of the circuit to be connected, and is generally 5 to 40 μm.

The epoxy resin referred to in the present invention is a compound having two or more epoxy groups in one molecule, and various materials can be applied.

The latent curing agent refers to a latent curing agent having a shelf life of at least one month at 30 ° C. or lower in the coexistence of an epoxy resin and rapidly curing under heating.

The means for latentization is not particularly limited. For example, it does not dissolve in an epoxy resin at room temperature, but dissolves and rapidly reacts when heated to around the melting point. For example, boron acetate, hydrazide, tertiary amine, imidazole , Dicyandiamide and the like, derivatives thereof, thermal decomposition type curing agents such as amine imide, molecular sieve encapsulation type and microcapsule type. These can be used alone or in combination of two or more.

Among the above, a microcapsule type curing agent can be preferably applied. The microcapsule type curing agent is
Substantially all surfaces of the core material made of the curing agent are covered with the coating layer. The hardening agent which is the core material of the microcapsule type hardening agent includes aliphatic amine, aromatic amine, carboxylic anhydride, thiol, alcohol, phenol, isocyanate, tertiary amine, boron complex salt, inorganic acid, hydrazide compound and imidazole Compounds and the like and modified products thereof can be employed.

Of these, tertiary amines, boron complex salts, which can be cured quickly and are excellent in bonding workability, and which can act as a catalyst in an ionic polymerization type so that their chemical equivalents can be reduced.
Hydrazide compounds and imidazole compounds are preferred,
Among them, an imidazole compound whose activation temperature is easily controlled in a wide range depending on the type of the derivative and a modified product thereof are more preferably used. These are used alone or as a mixture of two or more.

The insulating adhesive 4 is preferably a material which is curable at a low temperature as much as possible. At this time, ultraviolet rays (UV) can be used together.

The elongation percentage of the cured adhesive is 10% or less,
More preferably, the content is set to 1 to 5%, because peeling due to deformation of the flexible substrate 1 after connection can be prevented.

The insulative adhesive 4 may contain a small amount of conductive particles as required, which does not impair the insulation with the adjacent circuit.

At this time, the maximum particle size of the conductive particles must be smaller than the gap between the adjacent circuits, and the average particle size is preferably 10 μm or less, more preferably 0.5 to 7 μm. If it is less than 0.5 μm, the dispersibility is reduced and leakage is likely to occur. If it is less than 10 μm, the distance between the electrodes of the connection part increases, and the reliability tends to decrease.

The amount added to the adhesive is 0.01 to 1.0% by volume, preferably 0.8% by volume or less, more preferably 0.1% by volume or less.

The reason why the average particle diameter and the amount of addition are smaller and smaller than those frequently used in conventional anisotropic conductive adhesives is that the conductive particles of the present invention are used as auxiliary materials for forming unevenness of a circuit. This is because, if the addition amount is small, the dispersibility of the particles in the adhesive is also improved, and insulation between adjacent circuits is easily obtained.

The substrate 5 may be a flexible substrate similar to the above-described flexible substrate 1. However, if the substrate 5 is more rigid than the flexible substrate 1, the connection structure obtained according to the present invention is hardly deformed and rigid. Is preferable. Examples of the substrate 5 include glass, ceramic, resin, and a composite thereof.

The circuit 6 is the same as the circuit 3 or ITO, Ni, Cr, Au, T
Various materials such as a and solder can be applied.

Next, a connection method will be described.

For example, as shown in FIG. 1, an insulating adhesive 4 is interposed between the circuits 3 and 6, and the circuits 3 and 6 are aligned.
The flexible substrate 1 and the substrate 5 are heated and pressed. At this time, the temperature is about 50 to 200 ° C., and the pressure is about 5 to 100 kgf / cm ² . Due to the heating and pressurization, the viscosity of the insulating adhesive 5 is remarkably reduced, and a part or all of the circuits 3 and 6 come into contact with each other, so that the circuits 3 and 6 can be conducted. Therefore, at this time, the inspection of the conduction state can be performed in a state where the adhesive is not cured.

Due to the pressurization, the surplus insulating adhesive 5 passes through the space between the circuits and protrudes outside the length L of the connection portion.

As the heating is continued, the insulating adhesive 5 is cured, and the circuits 3 and 6 can be firmly connected.

The adhesive that has protruded to the ends acts as reinforcement for bonding and as a moisture-proof material for the connection portion, and may be removed as necessary.

FIG. 3 shows a schematic sectional view of the structure obtained as described above.

[0048]

According to the present invention, variations in the circuit height can be achieved by setting the elongation percentage of the flexible substrate to 10% or more, the circuit width to 70 μm or less, and the height to the thickness of the flexible substrate or less. Absorption can be achieved by deformation of the flexible substrate, and reliability at the time of connection is improved.

Further, by miniaturizing the circuit width to 70 μm or less, it is possible to promote the outflow of the adhesive to portions other than the circuit contact portion at the time of connection, thereby obtaining good contact of the connection circuit. At this time, since the aspect ratio of the circuit is as large as 40 or more, the contact probability in the length direction of the circuit is increased, and the connection reliability is improved.

Further, in the present invention, it is possible to add a very small amount of conductive particles to the adhesive so as not to impair the insulating property with respect to the adjacent circuit. Because it acts as a forming material, the contact probability is improved,
Further, good circuit contact can be made by, for example, destroying a contaminated layer on the circuit surface, so that connection reliability can be further improved.

Further, since the adhesive is in the form of a film containing an ethoxy resin and a latent curing agent as necessary components, long-term storage until use and curing in a short time can be achieved at the same time, and the strength and resistance of the minute connection portion can be improved. The environment is improved.

Further, the adhesive which has protruded out of the connection portion and hardened acts as a mechanical reinforcing and moisture-proof layer.

[0053]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples, but the present invention is not limited to these examples. [Examples 1 to 3 and Comparative Example 1] The height of UPILEX S (polyimide film manufactured by Ube Industries, Ltd., thickness 25 μm, elongation 30%, tensile modulus 900 kg / cm ² ) via an adhesive layer 18 μm Cu circuit (W = 30 μm, P = 70
FPC with 0.5 μm Sn plating on the surface
Then, a glass substrate (thickness: 1.1 mm) on which an ITO circuit having a thickness of 2000 A facing the circuit was formed was prepared.

Bisphenol A type solid epoxy resin (epoxy equivalent: 4.000) / liquid epoxy novolak resin (epoxy equivalent: 178) / microcapsule type curing agent (HX-3721: manufactured by Asahi Kasei Kogyo Co., Ltd.) Nickel 287 (manufactured by International Nickel Co., Ltd., average) in an insulating adhesive having a ratio of 30/50/20, a masterbatch in which a curing agent having a surface coated with a polyurethane material dispersed in a liquid bisphenol epoxy. Content (particle size of 2 to 4 μm) is 0 (Example 1), 0.09% by volume (Example 2), 0.4% by volume.
(Example 3) and 2.0% by volume (Comparative Example 1) were changed to release-treated polyethylene terephthalate (PE).
T) An adhesive film having a thickness of 15 μm formed on the film was prepared.

Curing of the adhesive film (200 ° C.-10
Min), the elongation percentage was 2.6 to 3.5%.

The above adhesive film was placed on a glass substrate with a width of 2.
The film was provisionally adhered so as to be orthogonal to the circuit in mm, the PET film was removed, and then the FPC circuit and the glass circuit were aligned under a microscope. Temporary fixation after alignment was easy due to the tackiness of the adhesive film.

Thereafter, both circuits were connected to each other with a connection length of 2 mm by heating and pressing at 170 ° C., 30 kgf / cm ² for 30 seconds, and the resistance of the connection after the thermal shock test was evaluated.

The results are shown in Table 1. The connection resistance was measured by a multimeter under heating at 60 ° C. using the glass substrate circuit of the connection body as a common terminal and the circuit of the flexible substrate as another terminal. If there are more than 3 kΩ (including wiring resistance) among 200 electrodes in one connection, it is regarded as open (x),
Less than 3 kΩ was regarded as good (○).

The insulation resistance between adjacent circuits was measured with a high-megohm meter, and less than 10 MΩ was indicated by (x) as a short circuit, and 10 MΩ or more was indicated by (○).

As shown in the table, each of the examples exhibited good connection resistance and insulation even after the reliability test.

However, in Comparative Example 1, a short circuit occurred between the circuits due to the connection using the conventional anisotropic conductive film.

[0062]

[Table 1] [Examples 4 to 6] The FPC of Example 1 was manufactured using Kapton K (manufactured by Torre Dupont, polyimide film, thickness 7).
5 μm, elongation 85%, elongation modulus 400 kg / mm ² )
And a 25 μm-high Cu circuit (W =
30 μm, P = 90 μm, and a Zn-based rust preventive treatment) was formed on the surface. 1.1m thick as facing circuit
A circuit board was prepared in which a Cr substrate was formed on a m glass substrate and an ITO circuit was formed thereon.

The same evaluation as in Examples 1 to 3 was performed, and the results are shown in Table 1.

Also in this example, a good connection was obtained. [Examples 7 to 9] The FPC base material of Example 1 was replaced with MCF-5.
000I (manufactured by Hitachi Chemical Co., Ltd., polyimide / Cu two-layer structure, polyimide elongation 20%, tensile modulus 8)
(00 kg / mm ² , thickness 25 μm, Cu height 18 μm), and other configurations and evaluations were the same as in Examples 4 to 6. Good connection characteristics were also exhibited in the case of a so-called two-layer FPC having no adhesive between the flexible substrate and Cu. Example 10 Upilex R (a polyimide film manufactured by Ube Industries, Ltd., thickness 25 μm, elongation 130%, tensile modulus 380 kg / mm ² ) was used as a flexible substrate, and the Cu height was 18 μm via an adhesive layer. Circuit (W = 60 μm, P
= 140 μm). As an adhesive film, an epoxy resin (epoxy equivalent 470) and a polyvinyl butyral resin (vinyl acetate component 2.0% by weight, average polymerization degree 50)
0) and HX-3721 (supra) at a ratio of 60: 2
At 0:20, an adhesive film having a thickness of 20 μm was formed on the polytetrafluoroethylene substrate. The elongation of this film after curing (200 ° C. for 10 minutes) was 4.5%. The circuits facing each other were made of ITO on a glass substrate, and connection and evaluation of the circuits were performed in the same manner as in Example 1 except that the connection width was 3 mm. The results are shown in Table 1. Each of the examples had good connection characteristics. [Comparative Example 2] The circuit of Example 10 was replaced with W = 90 μm, P = 2
The same connection and evaluation as in Example 10 were performed, except that the thickness was changed to 00 μm. The results are shown in Table 1. In this example, since the circuit width was large and the adhesive was not sufficiently removed except for the contact portion of the circuit, the adhesive was thermally expanded by heating at the time of evaluation, and the circuit was opened. Example 11 The connection of the flexible substrates of Example 10 was evaluated in the same manner as in Example 10. As shown in Table 1, good connection characteristics were obtained between the flexible substrates.

[0065]

As described in detail above, it is possible to connect an ultrafine circuit for connecting a large number of insulated parallel circuits to other circuits at once.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a circuit connection method according to the present invention.

FIG. 2 is a schematic plan perspective view showing a circuit connection method according to the present invention.

FIG. 3 is a schematic cross-sectional view of a structure obtained by a circuit connection method according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flexible board 2 Adhesive 3 Circuit 4 Insulating adhesive 5 Substrate 6 Circuit

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor, Kyohisa Ota, 1500, Oji, Oji, Shimodate-shi, Ibaraki Hitachi Chemical Co., Ltd. (72) Inventor: Tatsuo Ito, 1150 Goshomiya, Oaza, Shimodate, Ibaraki Pref. Hitachi Chemical Co., Ltd., Goshomiya Plant (56) References JP-A-53-57481 (JP, A) 51-119732 (JP, A) JP-A-62-22383 (JP, A) JP-A-60-35595 (JP, A) JP-A-61-161793 (JP, A) JP-A-4-109569 (JP, A A) JP-A-62-254372 (JP, A) JP-A-4-163992 (JP, A) JP-A-6-85422 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) ) H01R 43/00 H01R 43/02 H01R 9/09 H01R 4/00- 4/22 H05K 3/36

Claims (4)

(57) [Claims] 1. A method for connecting a plurality of circuits formed on an insulating substrate and an opposing circuit by an adhesive, wherein at least one of the circuits has a circuit width of 70 μm or less, a pitch of 150 μm or less, and an elongation at break. Is formed on a flexible substrate of 10% or more, and the two circuits are aligned by interposing an insulating adhesive between the circuit and the opposing circuit, and the length L of the connection portion and the circuit width W Ratio (L / W) to 40
As described above, a method of connecting circuits, wherein both circuits are brought into contact with each other under pressure and the adhesive is cured. 2. The method according to claim 1, wherein the height of the circuit formed on the flexible substrate is equal to or less than the thickness of the flexible substrate. 3. The circuit connecting method according to claim 1, wherein the insulating adhesive is a film containing an epoxy resin and a latent curing agent as main components. 4. The method according to claim 1, wherein the insulating adhesive comprises an epoxy resin and a latent curing agent as main components, and further comprises conductive particles of 0.01 to
3. The circuit connecting method according to claim 1, wherein the circuit is in the form of a film containing 1.0% by volume.