JPH0685335B2 - Thermocompression bonding member and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a liquid crystal display (L
CD), electroluminescence (EL), light emitting diode (LED), electrochromic display (ECD), plasma display, and the like, and connection terminals of a display board and connection terminals of a circuit board on which the driving part is mounted, or various electric circuit boards. The present invention relates to a thermocompression bonding connection member used for connecting between connection terminals and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, thermocompression bonding members are LC
Connection of a display device such as D, EL, LED, ECD, or plasma display with a hard printed wiring board (PCB) or a flexible printed circuit board (FPC), or a PCB,
It is used for connection between FPCs. In recent years, the number of circuits of various electric circuit boards has increased with the increase in size, color, and miniaturization of displays, and the shape of the circuit pattern on the thermocompression-bonding connection member for connecting these has become more complicated.

As a result, the width of the conductive lines forming the circuit pattern has been reduced to 0.07 to 0.20 mm. In addition, the circuit pattern may not be composed of only straight conductive lines, but may have a part that is bent at a right angle or an acute angle in the middle, or that curves and curves. Not only the gap becomes smaller, but when screen-printing the conductive line, the angle of the squeegee made of synthetic rubber or the like that agitates on the screen plate with respect to the conductive line changes, which reduces the pressure of the conductive paste passing through the screen plate. Since the conductive line is constricted or broken, it is very difficult to form the circuit pattern by screen printing.

Therefore, conventionally, the production of the thermocompression-bonding connecting member having a complicated circuit pattern by screen printing has a poor yield and is limited in pitch, bending angle, bending angle, etc. Can no longer meet the design requirements. Conventionally, the conductive line that constitutes the circuit pattern of the thermocompression-bonding connection member is formed by screen-printing a conductive paste in which conductive particles are mixed and dispersed in an organic binder solution, and the conductive paste has a wire diameter of 10 to 30 μm.
After being separated by about m screen wire rods and the intersections of these wire rods and filled in the screen openings, they are transferred onto the substrate and connected to each other along the screen openings to form the desired conductive lines.

Next, as shown in FIG. 4, the screen plate 1
When is separated from the base material 2, a shear stress is generated between the edge of the screen opening 3 and the conductive paste, and the viscosity of the conductive paste in the portion in contact with the edge is reduced. A sag 5 of about 30 to 50 μm tends to occur from the width of the portion 3. As a result, the conductive lines are short-circuited, or the width between the conductive lines is narrowed even if a short circuit does not occur. A short circuit easily occurs between the conductive lines, and the function as a connecting member cannot be achieved.

Therefore, in order to obtain a fine circuit pattern,
Although the device has been devised to increase the viscosity and fluctuation of the conductive paste and suppress the flow, if the viscosity of the conductive paste is increased, the broken lines of the circuit pattern and the conductive lines of the curved parts will be blurred and the conductive line will be disconnected. Therefore, there is a limit to the increase in viscosity. Therefore, a method is adopted in which the width of the screen opening is corrected to be narrowed by about 30 to 50 μm and a desired conductive line width is obtained by using a conductive paste having a relatively low viscosity. However, when the distance between the adjacent conductive lines is reduced to 0.15 to 0.40 mm, the width of the opening is also narrowed, the ratio of the correction is relatively large, and the ratio of the area divided by the screen wire is also large. Since the screen plate passability also deteriorates, it becomes difficult to obtain a stable conductive line, and there has been a limit to the circuit pattern shape that can be handled by screen printing. Furthermore, as will be described later, as a method of imparting anisotropic conductivity to the thermocompression-bonding connection member, when the conductive particles larger than the original conductive particles in the conductive paste are mixed, the correction of the opening is not performed. The passability of the conductive paste on the screen plate is significantly hindered, and the limit of the circuit pattern shape that can be handled by screen printing is further lowered.

[0007]

Therefore, in the method of manufacturing the thermocompression-bondable connecting member, the finer or more complicated the circuit pattern, the worse the screen printability of the conductive paste. There was a fatal defect that the conductive line was constricted, faint or broken.

Furthermore, it is complicated to adjust the viscosity of the conductive paste, change the setting of printing conditions, etc., and the manufacturing conditions are unstable and the viscosity of the conductive paste and the printing conditions do not match. When the paste is supplied, the conductive lines become thick, bleed, sag, and the insulation between the conductive lines cannot be maintained, which lowers production efficiency and reduces the production efficiency. When the distance is 0.40 mm or less, printing cannot be performed at all, resulting in many restrictions on the design.

[0009]

DISCLOSURE OF THE INVENTION The present inventors have found that the relationship between the amount and viscosity of a solvent contained in a conductive paste used for screen printing during the production of a thermocompression-bonding connecting member and the conductive paste extruded from a screen opening. Paying attention to the behavior over time of, the conductive paste is printed on the base material and at the same time, the solvent is removed from the conductive paste within 1 second to increase the viscosity,
By controlling the leveling of the conductive paste and forming a conductive line having a line width approximately the same as the width of the screen opening, screen printing of complicated parts of the circuit pattern is facilitated, and conventional screen printing is not industrially compatible. The present inventors have succeeded in providing a thermocompression-bondable connecting member having a complicated and fine circuit pattern, which is possible and has a broken line portion or a curved portion having an interval between adjacent conductive lines of 0.4 mm or less.

That is, the first aspect of the present invention has anisotropic conductive means at least at the joint with the circuit board to be connected on the circuit pattern consisting of conductive lines formed by screen-printing a conductive paste on the surface of the base material. In the thermocompression-bonding connecting member, a circuit pattern having a bent line portion or a curved portion in which the distance between adjacent conductive lines is 0.4 mm or less is printed on the surface of the base material through a layer that absorbs the solvent contained in the conductive paste. A thermocompression-bonding connecting member, which is characterized in that the second invention is
The method for manufacturing a thermocompression-bondable connecting member according to claim 1, wherein an absorbent of a solvent contained in the conductive paste is applied to the surface of the base material, and the conductive paste is screen-printed thereon to form a space between adjacent conductive lines. The present invention is directed to a method of manufacturing a thermocompression-bondable connecting member, which is characterized in that a circuit pattern having a bent line portion or a curved portion of 0.4 mm or less is formed. According to such a method of the present invention, the conductive paste retains a low viscosity with good printability until it passes through the screen plate, and then the viscosity increases instantly when it is adhered to the substrate to be printed. Since the sagging of the conductive paste in the width direction is suppressed, it is possible to easily obtain a thermocompression-bonding connecting member having a circuit pattern of a fine shape.

The present invention will be described with reference to FIG.
Is a plan view of a thermocompression-bonding connecting member in which conductive lines 7 having bent line portions 6 are gathered together to form a circuit pattern, and 8 is a joint portion with a circuit board to be connected (not shown). (B)
(A) is an enlarged sectional view taken along line XX of (a), and (c) is an example in which an anisotropic conductive means different from that of (b) is provided. To screen-print such a thermocompression-bondable connecting member, (d)
As shown in FIG. 1, a layer (hereinafter referred to as an absorption layer) 9 that absorbs a solvent contained in the conductive paste is formed on the base material 2 by coating or the like, and the conductive paste is printed on the screen plate 1 by the screen plate 1. When released, conductive lines 7 are formed on the base material 1. However, since the solvent contained in the conductive paste is quickly absorbed by the absorption layer 9, the viscosity does not rise and sagging does not occur. (E) shows the case where the thermocompression-bondable connection board (a) is superposed on the connection electrode 11 of the circuit board 10 to be connected via the anisotropic conductive connection means 14 containing the conductive particles 12 in the insulating adhesive 13. 2 shows a cross section of the connection portion of the thermocompression-bondable connection substrate, which includes the conductive line 7 and the connection electrode 11.
Are aligned and face each other and thermocompression bonded.

The base material of the thermocompression-bonding connecting member to which the present invention is applied is not particularly limited, but a heat-resistant polymer film such as polyimide, polyethylene terephthalate, or polycarbonate having a thickness of 10 to 10 is used. It is selected from a 50 μm film.

As the absorbent applied to form the absorption layer on the above-mentioned substrate, it is necessary that the conductive paste has the ability to instantly absorb the solvent before it reaches the substrate through the screen opening and flows. , Organic polymer substances having solubility parameters similar to those of various solvents used for preparing conductive paste described later, for example, vinyl chloride resin, vinyl acetate resin, copolymers thereof, styrene resin, acrylic resin, thermoplastic polyester , Thermoplastic polyurethane, polybutadiene, polyvinyl alcohol, polyvinyl butyral, polycarbonate resin, polyamide resin, polyimide resin, epoxy resin, alkyd resin, phenol resin, unsaturated polyester resin, isoprene rubber, butadiene rubber, butyl rubber, styrene butadiene rubber,
Examples thereof include butadiene acrylonitrile rubber and other synthetic rubbers, styrene-based, polyester-based, urethane-based thermoplastic elastomers and the like.

These polymer substances may be either thermoplastic or thermosetting, but the adhesion to the substrate, the thermocompression bonding property required for the connecting member, flexibility, curing of the conductive paste, and drying Vinyl chloride / vinyl acetate copolymer is required because it must have heat resistance that does not cause deformation, cracking, slack, etc. due to the heat of about 100 to 150 ° C and solvent resistance that does not cause deformation or dissolution by the absorbed solvent. , Acrylic resins, thermoplastic polyesters, thermoplastic polyurethanes, and epoxy resins are preferable. If necessary, isocyanates, amines, acid anhydrides, and aldehydes may be added as a curing agent for crosslinking the polymer substance. . A known curing accelerator such as a tertiary amine compound or an organometallic compound may be added optionally, but it is desirable to avoid a hygroscopic or ionic substance that promotes migration of metal powder in the conductive paste.

The absorption of the solvent contained in the conductive paste is
In addition to the affinity with the above-mentioned polymer substances, it is preferable that the solvent has a molecular weight of 2,000- It should have a low molecular weight of 30,000, preferably 5,000 to 30,000. In this case, from the viewpoint of heat resistance and surface tackiness, it is desirable to add 0.1 to 10 wt% of a reinforcing filler such as dry silica, wet silica, silicate and activated calcium carbonate. This is because when the screen plate separation is bad in the printing performed in the next step, the conductive paste may bleed or sag, so that the tackiness of the surface is suppressed and the apparent heat resistance is increased. Although heat resistance can be increased by three-dimensional crosslinking, the molecular weight between crosslinking points is 2,000 or more, preferably 20,000.
The above is necessary for the above reason. Therefore, thermoplastic polyester and thermoplastic polyurethane are most preferable as the polymer substance.

The application of the absorbent may be carried out by a conventionally known method, and it is not necessary to particularly limit the solvent having the ability to dissolve the above-mentioned polymer substance, but it is used, for example, for preparing a conductive paste described later. It may be selected from various solvents, dissolved and made into a solution, and then applied using a printing method such as a screen printing method or a gravure printing method, or roll coating, bar coating, knife coating,
A coating method such as spray coating, spin coating, or dipping may be used. Further, the coated material is dried or cured and dried to obtain a substrate having a solid absorption layer.

The location where the absorption layer is provided so as to easily absorb the solvent contained in the conductive paste on the substrate may be limited to the printed portion where the circuit pattern is to be formed,
It may be the entire printed surface on the substrate. Coating thickness is 0.1 to 50
μm, preferably 1.0 to 20 μm, and below this,
There is not enough capacity to absorb the solvent in the conductive paste, and if it is more than this, the surface condition such as mottled spots and stripes on the coating film caused by convection of the components of the absorption layer that occurs during the drying process of the absorption layer will be minute. This is because it is unsuitable for providing a circuit pattern and loses flexibility as a thermocompression-bonding connecting member.

It is desirable that the surface state of the absorbing layer is a fine hole or satin that does not hinder the formation of a fine circuit pattern because it promotes absorption, but an average roughness of 10 μm or less, preferably 3 μm or less, and a substrate It is necessary to be careful because contamination that impairs absorption, adhesion of water, etc., and adsorption may occur on the surface.

The organic binder which is a solvent contained in the conductive paste is generally vinyl chloride resin, vinyl acetate resin,
These copolymers, acrylic resins, thermoplastic polyesters, thermoplastic polyurethanes, polybutadienes, polyimide resins, epoxy resins, alkyd resins, phenol resins and the like, and, if necessary, curing agents such as isocyanates, amines and acid anhydrides. Examples of the solvent that has been used to dissolve it include ester-based, ketone-based, ether ester-based, chlorine-based, ether-based, alcohol-based, and hydrocarbon-based solvents such as methyl acetate, ethyl acetate, and isopropyl acetate. However, ester-based, ketone-based, and ether-ester-based are frequently used, and the viscosity of the conductive paste is adjusted to 50 to 1,000 poise and the degree of thixotropy is adjusted to 2 to 15. The ratio of the solvent component in the conductive paste is 80% by weight or less, preferably 50% by weight or less, in consideration of the capacity of the absorbing layer, the molecular weight and the like.

The fine powder to be conductive particles has an outer diameter of 0.1 to 1
00μm granular, scale-like, plate-like, dendritic, dice-like silver, silver-plated copper, copper, gold, nickel, palladium and alloys thereof, resin powder plated with one or more of these metals , One kind or two or more kinds of graphite powder, carbon black such as furnace black, channel black, etc. are mixed and dispersed in the organic binder in an amount of 10 to 90% by weight, and if necessary, a suitable curing accelerator, leveling agent, dispersion stabilizing Additives such as agents, defoamers, thixotropic agents, metal deactivators, etc. are added.

As the screen wire used for forming the circuit pattern, a plain weave or twill weave of an iron alloy such as stainless steel having a wire diameter of 10 to 40 μm, or an electroformed plate formed in a grid pattern by nickel plating or the like is used as a rigid frame. Generally, a stretched material is used, and when forming a fine circuit pattern,
It is necessary to make the wire material thin so that the opening of the mask material such as acrylic resin, that is, the opening substantially equal to the shape of the desired circuit pattern is not blocked by the wire or the intersection of the wire, and the thickness of the wire is inevitable. The ratio of aperture ratio / thickness is preferably 0.8 or more, more preferably 1.5 or more from the viewpoint of the permeability of the conductive paste, but it is better to increase the strength of the wire material without decreasing the strength of the gauze or plate. It is necessary to reduce the diameter, and it is desirable that the aperture ratio is 30% or more, preferably 60% or more.

Further, the adhesive used in the joint portion with the circuit board to be connected of the present invention is not limited to this, and may be thermoplastic or thermosetting as long as it exhibits adhesiveness by heating. It may be present, but thermoplastics can be bonded by heating at a relatively low temperature for a short time, have a long pot life, and thermosetting ones have large adhesive strength and excellent heat resistance, so they are suitable for the intended use. It may be selected as appropriate.

As the solvent for dissolving the adhesive, ester-based, ketone-based, ether ester-based, chlorine-based, ether-based, alcohol-based, hydrocarbon-based, etc., such as methyl acetate, ethyl acetate, isopropyl acetate, etc. Examples thereof include ester type, ketone type and ether ester type.

The conductive particles for imparting anisotropic conductivity to the anisotropic conductive means used at the joint with the circuit board to be connected are gold, silver, copper, nickel, palladium, stainless steel,
Metal particles such as brass and solder, ceramic particles such as tungsten carbide and silica carbide, carbon particles, plastic particles whose surface is coated with metal, and the like are used. It is determined in consideration of the stability and reliability of the connection, the allowable limit of the peel strength, etc. in consideration of the distance between the adjacent conductive lines, etc., but normally the one of 5 to 150 μm is used. Further, this shape is not particularly limited, and may be spherical, needle-like, scale-like, plate-like, dendritic, dice-like, protuberant spherical,
An indefinite shape or the like is used, and the optimum one is selected in consideration of the stability and reliability of the connection.

When the conductive particles are dispersed in an adhesive and used in an excessively small amount, the particles do not exist on the connecting electrode to be connected, resulting in disconnection and high resistance.
If it is too large, the anisotropic conductivity will be stochastically connected in the planar direction, so 0.1 or more per 100 parts by volume of the adhesive component.
It may be in the range of 30 parts by volume, but is preferably 1 to 15 parts by volume. When this adhesive is applied on the absorption layer, it is desirable to select an adhesive component that does not cause erosion due to deformation, dissolution or the like in the absorption layer, or conversely, the absorption layer is used as the adhesive layer. It is preferable that the substance is not attacked by the components.

When the conductive particles are fixed on the conductive line, the conductive particles are mixed in the conductive paste to form a circuit pattern. However, in order to obtain a stable connection, the area of the conductive line at the joint is increased. The conductive particles may be mixed so that the number of particles per 1 mm ² is 20 or more, preferably 50 or more, but as described above, there may be a problem in printability during formation of the circuit pattern. So
It is necessary to determine the particle size in consideration of both the stability of connection and the printability of the circuit pattern by the printing plate. That is, the width of the opening, or the uneven length (l) of the lattice-shaped opening formed by the gauze and the plate forming the printing plate, the particle size (r) of the conductive particles, and the thickness of the conductive line ( Since the relation between w) is not printable when r> l and the connection is not stable when r << w, it is necessary that r <l and r ≧ (1/5) w.

Further, if the previous absorption layer is a member exhibiting adhesiveness by thermocompression bonding, it is possible not to apply an adhesive thereto, in which case the conductive line is directly connected to the connection terminal of the circuit board to be connected. To achieve continuity.
In this way, the anisotropically conductive adhesive is applied to at least the joint with the circuit board to be connected, but if the adhesive is applied only to the joint, it may be applied to other parts as necessary. A known insulating resist layer may be provided.

[0028]

In the method of manufacturing a thermocompression-bonding connecting member according to the present invention, an absorbing layer that easily absorbs the solvent contained in the conductive paste is first formed on the surface of the base material, and the conductive paste is screen-printed thereon. Since it forms a conductive line,
The conductive paste is printed on the absorption layer through the gaps between the screen wire rods, and the conductive paste spreads and connects immediately below each thin screen wire rod to form one conductive line. However, at the edge of the screen opening, the solvent contained in the conductive paste is rapidly absorbed by the absorbing layer within, for example, one second, so that the conductive paste increases in viscosity and does not cause sagging or bleeding as in the conventional case. Absent. As a result, it is possible to reliably screen print even a circuit pattern which cannot be formed in the related art such that the interval between the adjacent conductive lines is 0.4 mm or less.

[0029]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited thereto. A 25 μm thick polyethylene terephthalate film (Lumirror S-10, manufactured by Toray Industries, Inc.) is used as a base material, and terephthalic acid, isophthalic acid, sebacic acid, ethylene glycol, neopentyl glycol are used as raw materials on one side of the film as an absorption layer. Synthesized molecular weight 20,000 to 25,000, glass transition point
Dissolve 100 parts by weight of a saturated copolyester resin having a hydroxyl value of 6.0 KOHmg / g, an acid value of 1.0 KOHmg / g and a solubility parameter of 9.2 in toluene at 45 ° C. and block the hexamethylene diisocyanate biuret trimer with methyl ethyl ketoxime. The solid isocyanate content of 85% and the isocyanate content of 12% by weight were added to 10 parts by weight of the blocked isocyanate compound and dissolved and mixed uniformly. The mixture obtained in (1) was applied to the entire surface by a gravure coater so that the thickness of the coating film after drying was 2 μm, and dried by an infrared (IR) dryer.

Then, on this, the polygonal line portion 6 shown in FIG.
A circuit pattern having a curved portion 15 shown in FIG. 3 was applied to a screen plate (screen wire diameter 20 μm, mesh thickness 20 μm, aperture ratio 34%).
Nickel electroforming plate) was used to synthesize terephthalic acid, sebacic acid, ethylene glycol and neopentyl glycol as raw materials.
Dissolve 100 parts by weight of a saturated copolyester resin having a hydroxyl value of 6.0 KOHmg / g, an acid value of 1.0 KOHmg / g and a solubility parameter of 9.2 in toluene at 45 ° C. and block the hexamethylene diisocyanate biuret trimer with methyl ethyl ketoxime. A solid paste containing 85% solid content and 12% by weight isocyanate content as a binder, ethyl carbitol acetate as a solvent, and a conductive paste containing scaly silver powder having a particle size of 1 to 3 μm as conductive particles. Table 1 shows the printing yield (100 sheets printed) when printed.

[0031]

[Table 1]

Further, as a comparative example, polyethylene terephthalate having no absorption layer (Lumirror S-1 manufactured by Toray Industries, Inc.)
The printing yield when the base material of 0) is used is shown in the same table.

[0033]

The thermocompression-bonding connecting member and the method for producing the same according to the present invention are characterized in that a base material coated with an absorbent having a thickness of 0.1 to 50 μm capable of easily absorbing the solvent contained in the conductive paste is electrically conductive. The paste is screen-printed to reduce the viscosity of the conductive paste and improve the printability, while suppressing the sagging of the conductive paste, thereby reducing the adjacent conductive line of 0.4 mm or less. Not only is it possible to form circuit patterns with sharp breaks and large bend angles with intervals, but conventionally, the opening of the printing plate was corrected to be smaller than the conductive line width assuming the sagging of the conductive paste. Can be expanded according to the width of the conductive line, further improving the printability, greatly improving the printing yield, and the fine circuit pattern that was previously impossible. One for thermocompression bonding connection member is provided in easily and highly reproducible, it is of an effect such as obtained for complex designs of recent thermocompression bonding connection member.

[Brief description of drawings]

FIG. 1 is an example of a thermocompression-bonding connection member of the present invention, (a) is a plan view, (b) is a longitudinal sectional view taken along line XX of (a),
(C) is a vertical cross-sectional view of an example in which an anisotropic conductive means different from (b) is provided, (d) is a vertical cross-sectional view schematically showing a conductive line printing, and (e) is a circuit board to be connected according to the present invention. FIG. 6 is a vertical cross-sectional view of a joint portion when the thermocompression-bonding connection member of FIG.

FIG. 2 is a circuit pattern diagram on a screen plate used for printing in Examples.

FIG. 3 is another circuit pattern diagram on the screen plate used for printing in the example.

FIG. 4 is a vertical cross-sectional view schematically showing printing of conductive lines by a conventional method for manufacturing a thermocompression-bondable connecting member.

[Explanation of symbols]

1 ... Screen version 8 ... Joined part 15 ...
Curved portion 2 ... Base material 9 ... Absorption layer 3 ... Opening portion 10 ... Connected circuit board 4 ... Conductive line 11 ... Connection electrode 5 ... Dull 12 ... Conductive particles 6 ... Broken line portion 13 ... Insulating adhesive 7 ... Conductive line 14 ... Anisotropic conductive means

Claims (2)

[Claims] 1. A thermocompression-bonding connection member having anisotropic conductive means at least at a joint with a circuit board to be connected on a circuit pattern formed of a conductive line formed by screen-printing a conductive paste on the surface of a base material. , A heat treatment characterized in that a circuit pattern having a broken line portion or a curved portion with a space between adjacent conductive lines of 0.4 mm or less is printed on the surface of the substrate through a layer that absorbs the solvent contained in the conductive paste. Crimping connection member. 2. The method for producing a thermocompression-bondable connecting member according to claim 1, wherein an absorbent of a solvent contained in the conductive paste is applied to the surface of the base material, and the conductive paste is screen-printed thereon. A method for manufacturing a thermocompression-bonding connecting member, which comprises forming a circuit pattern having a bent line portion or a curved portion in which adjacent intervals of conductive lines are 0.4 mm or less.