JP2004140384A - Connection method of printed wiring board - Google Patents

Abstract

An object of the present invention is to improve connection reliability between a flexible substrate and a rigid substrate using an anisotropic conductive adhesive.
A convex insulator (4) provided between connection terminals (3) of a rigid substrate (1) is inserted into a through-hole (10) provided between connection terminals (7) of an opposing flexible substrate (5), and an anisotropic conductive adhesive (8) is provided. Then, the connection terminals 7 of the flexible substrate 5 and the connection terminals 3 of the rigid substrate 1 are electrically connected by heating and pressing.
[Selection diagram] Fig. 1

Description

The present invention relates to a method for connecting a printed wiring board, and more particularly to a method for connecting a flexible printed wiring board and a rigid printed wiring board.

In recent years, flexible printed wiring boards (hereinafter, referred to as flexible boards) having flexibility, such as polyimide films, are means for connecting the boards to each other because space can be effectively used, and in particular, rigid printed wiring that cannot be called a flexible board. It is widely used in various electronic devices as a TAB type substrate for connecting between substrates (hereinafter, referred to as rigid substrates) and for mounting a semiconductor device and connecting to a rigid substrate.

Conventionally, as a method of connecting a flexible substrate to a rigid substrate, there is a method of connecting the terminals of these two substrates with solder or a conductive paste, but these methods have recently been used for a substrate having a narrowed terminal. For the connection between the terminals, a connection method using an anisotropic conductive adhesive has been developed and used instead of these methods because the terminals are likely to be short-circuited by solder or conductive paste.

FIG. 7 shows that a flexible substrate on which a semiconductor device is mounted is connected to a glass substrate (rigid substrate) by using an anisotropic conductive adhesive disclosed in Japanese Patent Application Laid-Open No. 5-74850 (first conventional example). It is an example. As shown in FIG. 6, a lead 17 and a convex portion (insulating layer) 18 thicker than the lead are provided on a glass substrate 14 on which an electrode pattern 15 is provided and a flexible substrate 16 opposed thereto. In this configuration, the electrode patterns 15 are engaged with each other and connected using an anisotropic conductive adhesive (not shown).

FIG. 8 shows a method for connecting rigid substrates disclosed in Japanese Patent Application Laid-Open No. 5-226801 (second conventional example), which is applicable to the connection between a flexible substrate and a rigid substrate. The connection terminal 21 of the glass substrate 20 (rigid substrate) is connected to the connection terminal 25 of the circuit board 22 (rigid substrate) made of the glass substrate 23 (formed by plating or the like on the insulating film 24). This is an example in which the connection is made by using an insulating adhesive 27 in which conductive fine particles 26 are dispersed.

FIG. 9 shows that a connection terminal 31 of a glass substrate 30 (rigid substrate) of a liquid crystal display panel 29 disclosed in JP-A-7-92920 (third conventional example) is connected to a TCP (tape carrier package) 32 (flexible substrate). This is an example in which connection terminals 33 of a substrate are connected with an anisotropic conductive adhesive. As the anisotropic conductive adhesive, a material obtained by mixing conductive particles 35 and insulating particles 36 having a smaller particle size than the conductive particles 35 in a synthetic resin film 34 is used.

In the first conventional example described above, the protrusion (insulating layer) 18 is provided between the leads of the flexible substrate 16 to facilitate the alignment with the electrode pattern 15 of the glass substrate 14, but the anisotropic conductive adhesive is used. There is a possibility that an electrically short circuit may occur between the electrode patterns (leads) due to the conductive foreign matter that is mixed in when the electrode is sandwiched. In the present technology, the distance between the lead 17 of the flexible substrate 16 and the electrode pattern 15 of the glass substrate 14 is regulated by the height of the projection (insulating layer) 18, and the amount of the anisotropic conductive adhesive applied The connection resistance between the electrode pattern 15 and the lead 17 tends to vary due to the variation in the thickness of the substrate, and the mechanical connection strength between the two substrates decreases due to the small amount of the anisotropic conductive adhesive between the two substrates. There was a problem to do.

In the above-mentioned second conventional example, there is a problem that an electric short circuit occurs between the connection terminals due to conductive foreign substances mixed when the anisotropic conductive adhesive 28 is sandwiched, and a problem that a misalignment between the two substrates increases. Was.

Further, in the third conventional example described above, by adding insulating particles 36 smaller than the conductive particles 35 to the synthetic resin film 34 of the anisotropic conductive adhesive, the conductive particles 35 contact each other between adjacent terminals and leak ( Although electric leakage due to short circuit is prevented, the anisotropic conductive adhesive is used for the liquid crystal display panel in the same manner as the problem of misalignment between the TCP 32 and the liquid crystal panel 29 and the technique of the above two publications. There is a possibility that an electrically short-circuit may occur between adjacent connection terminals due to a conductive foreign substance mixed when sandwiched between the terminal and the TCP.

In addition, the above technology has other common problems as follows.
(1) Since the connection terminals are not visible due to the base material of the flexible substrate, it is necessary to provide an alignment mark individually when aligning each connection terminal. Also, it was difficult to visually confirm the workmanship.
(2) The rigid board and the flexible board have a large coefficient of thermal expansion, each of which thermally expands and contracts during thermocompression bonding, resulting in displacement of connection terminals. At this time, since there is nothing to control the displacement, the anisotropic conductive adhesive is thermally cured in the displaced state, causing electrical open / short.

An object of the present invention is to provide a method for connecting a flexible substrate and a rigid substrate, which solves the problems of the substrate connection technology using the anisotropic conductive adhesive as described above.

The present invention provides a method for connecting a printed wiring board in which connection terminals of a flexible board and connection terminals of a rigid board are opposed to each other and are electrically connected by an anisotropic conductive adhesive, provided between the connection terminals of the rigid board. The convex insulator is inserted into a through hole provided between the connection terminals of the flexible substrate facing the connection terminals of the flexible substrate with the anisotropic conductive adhesive and the rigid substrate facing the connection terminals. The configuration is characterized in that the connection terminals are electrically connected.

The thickness of the convex insulator is greater than the thickness of the connection terminal of the rigid board and the thickness of the connection terminal of the flexible board, and is greater than the thickness of the connection terminal of the rigid board and the thickness of the flexible board. By making it thinner, the contact area between the anisotropic conductive adhesive and the substrate is increased to improve the mechanical connection strength between the two substrates, and conductive foreign substances adhered to the surface of the anisotropic conductive adhesive, etc. Can be isolated from the surfaces of the connection terminals of the two substrates, and a short circuit between the connection terminals due to conductive foreign matter can be prevented.

The convex insulator is provided between the connection terminals of the rigid board, and is inserted into a through hole provided between the connection terminals of the flexible board to connect the two boards with the anisotropic conductive adhesive. By doing so, it is possible to reduce the misalignment of the corresponding terminals of both substrates.

As described above, according to the present invention, the following effects can be obtained.
(1) Since the through-holes are provided in the flexible substrate, positioning by alignment before thermocompression bonding and workability confirmation after thermocompression bonding become easy.
(2) By inserting the convex insulator of the printed board into the through hole of the flexible board during thermocompression, terminal displacement of each board due to thermal expansion and contraction at the time of thermocompression is regulated, and electrical opening due to terminal displacement is caused. -The occurrence of short circuits can be prevented.
(3) By inserting the convex insulator of the printed board into the through-hole of the flexible board at the time of thermocompression bonding, conductive foreign substances mixed when sandwiching the anisotropic conductive adhesive can be pushed out from between adjacent terminals, The occurrence of an electrical short can be prevented.
(4) Since the anisotropic conductive adhesive adheres to the side surface of the through hole of the flexible substrate and the periphery of the convex insulator of the printed circuit board during thermocompression bonding, the area of the anisotropic conductive adhesive bonded to the substrate increases. The mechanical connection strength between the two substrates and the anisotropic conductive adhesive can be improved.

A connection method for connecting the flexible board and the rigid board according to the first embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is an enlarged sectional view showing a substrate connection structure between a flexible substrate and a rigid substrate according to the first embodiment of the present invention. In the drawing, reference numeral 1 denotes a rigid substrate, and 2 denotes a base material of the rigid substrate. Reference numeral 3 denotes a connection terminal formed on the surface of the rigid substrate, and reference numeral 4 denotes a convex insulator formed between the connection terminals of the rigid substrate 1.

中 In the figure, reference numeral 5 denotes a flexible substrate, 6 denotes its base material, and 7 denotes connection terminals for connecting the flexible substrate 5 to the rigid substrate 1. Reference numeral 8 denotes an anisotropic conductive adhesive for electrically connecting the terminals of both substrates, reference numeral 10 denotes a through hole of the flexible substrate 5, and a base material between the connection terminals 7 of the flexible substrate 5. 6 is provided.

As shown in FIG. 1, in the first embodiment of the present invention, the convex insulator 4 provided between the connection terminals 3 of the rigid board 1 is inserted into the through-hole 10 from the connection terminal 7 side of the flexible board 5, The anisotropic conductive adhesive 8 is hot-melt-infiltrated into the through-hole 10 from the surface opposite to the connection terminals 7 of the flexible substrate 5, sandwiched between the connection terminals 3, 7 of both substrates and thermocompression-bonded, so that the terminals of both substrates are different. It is characterized in that it is electrically connected via an isotropic conductive adhesive 8.

FIG. 2 is a schematic view showing the structure of the rigid substrate 1 of FIG. 1, (a) is a plan view, and (b) is a cross-sectional view taken along line AA of (a). As the base material of the rigid substrate 1, an epoxy resin, a polyimide resin, a transparent glass substrate, or the like reinforced with glass fiber can be used. The connection terminals 3 are formed by patterning a copper foil by etching, and the surfaces of the connection terminals 3 are nickel-plated and gold-plated. What has been subjected to is used.

The convex insulator 4 provided between the connection terminals 3 of the rigid substrate 1 is formed by patterning a photosensitive resist by photolithography or finely processing a thermosetting resist by laser light, and can be inserted into the through hole 10 of the flexible substrate 5. It has a rectangular or truncated pyramid shape in size. At this time, the thickness of the convex insulator 4 is thicker than the sum of the thickness of the connection terminals 3 of the rigid substrate 1 and the thickness of the connection terminals 7 of the flexible substrate 5 (see FIG. 3). It is necessary to make the thickness smaller than the sum of the thickness of the terminal 3 and the thickness of the flexible substrate 5 (terminal + base). The thickness of the convex insulator 4 is greater than the thickness of the connection terminals of the rigid substrate plus the thickness of the connection terminals of the flexible substrate, and the thickness of the connection terminals of the rigid substrate plus the thickness of the connection terminals of the flexible substrate If the thickness is smaller than that, a short circuit between the terminals is likely to occur due to the conductive foreign matter pushed onto the surface of the convex insulator. When the thickness of the convex insulator 4 is larger than the sum of the thickness of the connection terminals of the rigid substrate and the thickness of the flexible substrate (terminal + base material), the conductive particles of the anisotropic conductive adhesive between the two substrates can be provided. It is not preferable because the pressing force required to crush the slab is insufficient.

Note that an epoxy resin-based resist can be used as the photosensitive resist or the thermosetting resist for forming the convex insulator 4.

A resist 9 is coated on both sides of the connection terminal 3 in order to protect wiring and the like connected to the connection terminal 3. The resist 9 may be a photosensitive resist or a thermosetting resist for forming the convex insulator 4. Can be used.

FIG. 3 is a schematic view showing the structure of the flexible substrate 5 of FIG. 1, (a) is a plan view, and (b) is a cross-sectional view taken along line AA of (a). A flexible polyimide resin or the like is used for the base material of the flexible substrate 5. The connection terminal 7 is obtained by patterning a copper foil by etching and subjecting its surface to nickel plating, gold plating, or the like. The through-hole 10 is formed by a punching process or the like to a size that allows the convex insulator 4 of the rigid substrate 1 of FIG. 2 to be inserted between the connection terminals 7. If the flexible substrate 5 has a comb-like shape, the connection portion may be deformed due to its flexibility. Therefore, the configuration is such that only a through hole is provided in the base material.

FIG. 4 is a schematic cross-sectional view for explaining a method for forming the substrate connection structure of the first embodiment of the present invention in FIG.

(4) A method for forming a substrate connection structure according to the first embodiment will be described in detail with reference to FIG. First, a 30 to 50 μm thick film-like anisotropic conductive adhesive 8 is set on the rigid substrate 1 having the structure shown in FIG.

Next, after the flexible substrate having the structure shown in FIG. 3 and the cushion material 12 are sequentially set on the anisotropic conductive adhesive 8, the anisotropic conductive adhesive 8 is re-melted from the surface of the cushion material 12 by the heat tool 11. The substrate is heated under pressure at a curing temperature for a predetermined time, and the terminals of both substrates are electrically connected with the anisotropic conductive adhesive 8. With this method, the substrate connection structure of FIG. 1 can be obtained. The binder resin of the anisotropic conductive adhesive 8 can be a thermosetting epoxy resin or urethane resin, and the conductive particles of the anisotropic conductive adhesive 8 include metal particles such as nickel or acrylic resin. Particles having a diameter of 4 to 8 μm, which are obtained by subjecting a sphere to nickel or gold plating or further insulatingly coating these are used.

FIG. 5 is an enlarged cross-sectional view of a main part of a substrate comparing a conventional substrate connection structure with the substrate connection structure of the present invention. As can be seen from FIG. 5, in the present invention (see FIG. 5B), the following excellent effects can be obtained as compared with the conventional substrate connection structure (see FIG. 5A).
(1) The convex insulator of the rigid board and the through-hole of the flexible board can be used for regulating displacement, and electrical open / short due to the displacement is eliminated.
(2) The conductive foreign matter 13 between the adjacent connection terminals is pushed away from between the terminals by the convex insulator 4, so that an electric short circuit can be prevented.
(3) The area of the anisotropic conductive adhesive 8 in contact with the flexible substrate 5 and the rigid substrate 1 is greatly increased as compared with the conventional configuration, so that mechanical connection strength can be maintained.
(4) The through-holes 10 in the flexible substrate 5 facilitate positioning and visual confirmation between the flexible substrate and the connection terminals 7 of the rigid substrate 1 by alignment.

Next, a substrate connection method according to the second embodiment of the present invention will be described with reference to FIG. In the embodiment of the present invention, in the case where the shape of the convex insulator 4 provided between the connection terminals 3 of the rigid substrate 1 in the above-described first embodiment is formed so that the cross-sectional shape becomes a step shape. In this case, the connection structure is formed in the same process as in the first embodiment.

The convex insulator 4 provided between the connection terminals 3 of the rigid substrate 1 is formed by patterning of an epoxy resin-based photosensitive resist by photolithography or fine processing by laser processing of a cured resin film of a thermosetting epoxy resin, and is flexible. It has a rectangular or square truncated pyramid shape with a size that can be inserted into the through hole 10 of the substrate 5. At this time, the entire thickness of the convex insulator 4 is equal to the thickness of the connection terminal 3 of the rigid substrate 1 in the same manner as in the first embodiment, and the thickness of the connection terminal 7 of the flexible substrate 5 (see FIG. 5). And the thickness of the connection terminals 3 of the rigid board 1 and the thickness of the flexible board 5 (terminal + base) need to be smaller. The thickness of the convex insulator 4 is greater than the thickness of the connection terminals of the rigid substrate plus the thickness of the connection terminals of the flexible substrate, and the thickness of the connection terminals of the rigid substrate plus the thickness of the connection terminals of the flexible substrate If the thickness is smaller than that, a short circuit between the terminals is likely to occur due to the conductive foreign matter pushed onto the surface of the convex insulator. When the thickness of the convex insulator 4 is larger than the sum of the thickness of the connection terminals of the rigid substrate and the thickness of the flexible substrate (terminal + base material), the conductive particles of the anisotropic conductive adhesive between the two substrates can be provided. This is not preferable because the pressing force necessary for crushing is insufficient.

In the present embodiment, the shape of the convex insulator 4 is formed so that its cross-sectional shape becomes a step-like shape, so that the contact area with the anisotropic conductive adhesive is smaller than that of the first embodiment. And the mechanical connection strength can be improved.

FIG. 2 is an enlarged cross-sectional view illustrating the board connection structure according to the first embodiment of the present invention. FIG. 2 is a structural sectional view of a rigid substrate used for the substrate connection structure according to the first embodiment of the present invention. FIG. 2 is a structural sectional view of a flexible substrate used for the substrate connection structure according to the first embodiment of the present invention. FIG. 3 is a schematic cross-sectional view for explaining the method for forming the substrate connection structure according to the first embodiment of the present invention. FIG. 5 is an enlarged cross-sectional view of a main part of a substrate comparing a conventional substrate connection structure with a substrate connection structure of the present invention. FIG. 4 is an enlarged cross-sectional view illustrating a substrate connection structure according to a second embodiment of the present invention. FIG. 11 is an enlarged cross-sectional view showing a first example of a conventional substrate connection structure. It is a sectional enlarged view showing the example of the 2nd conventional board connection structure. FIG. 11 is an enlarged cross-sectional view illustrating a third conventional substrate connection structure example.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Rigid board 2,6 Base material 3,7,21,25,31,33 Connection terminal 4 Convex insulator 5,16 Flexible board 8,28 Anisotropic conductive adhesive 9 Resist 10 Through hole 11 Heat tool 12 Cushion DESCRIPTION OF SYMBOLS 13 Conductive foreign substance 14, 20, 23, 30 Glass substrate 15 Electrode pattern 17 Lead 18 Convex part (insulating layer)
19, 29 Liquid crystal display panel 22 Circuit board 24 Insulating film 26 Conductive fine particles 27 Insulating adhesive 32 TCP
34 synthetic resin film 35 conductive particles 36 insulating particles

Claims (10)

Providing a flat rigid board having a first connection terminal arranged and having a convex insulator disposed between the first connection terminals;
Providing a flexible substrate having a second connection terminal corresponding to the first connection terminal, and having a through hole provided between the second connection terminals;
Placing an anisotropic conductive adhesive film on the rigid substrate, and placing the flexible substrate on the anisotropic conductive adhesive film so that the first connection terminals correspond to the second connection terminals;
The convex insulator is inserted into the through hole, the anisotropic conductive adhesive film is re-melted, and the connection terminal of the flexible substrate and the connection terminal of the rigid substrate opposed thereto are connected to the anisotropic conductive adhesive. Pressurizing and heating the flexible substrate and the anisotropic conductive adhesive film to the rigid substrate so as to be electrically connected by an agent. The thickness of the convex insulator is greater than the sum of the thickness of the connection terminal of the rigid board and the thickness of the connection terminal of the flexible board, and the thickness of the connection terminal of the rigid board; 2. The method for connecting a printed wiring board according to claim 1, wherein the thickness of the connection terminal is smaller than the sum of the thickness of the flexible board and the thickness of the flexible board. 2. The method for connecting a printed wiring board according to claim 1, wherein the shape of the convex insulator is a rectangular shape, a truncated pyramid shape, or a stepped shape thereof. Providing the rigid substrate,
The method for connecting a printed wiring board according to any one of claims 1 to 3, further comprising forming the convex insulator by patterning a photosensitive resist by photolithography or laser processing a thermosetting resist. The method according to claim 4, wherein the photosensitive resist is an epoxy resin-based resist. The method according to claim 4, wherein the thermosetting resist is an epoxy resin-based resist. The method according to claim 1, wherein the first connection terminal of the rigid board and the second connection terminal of the flexible board are formed by sequentially coating nickel plating and gold plating on a copper foil. Connection method of printed wiring board. The length of the through-hole of the flexible board is the same as the length of the connection terminal of the flexible board, and the width of the through-hole is larger than the width of the convex insulator of the rigid board. 8. The method for connecting a printed wiring board according to any one of 7. The anisotropic conductive adhesive is provided on the surface of the convex insulator, between the second connection terminal of the flexible board and the first connection terminal of the rigid board facing the second connection terminal, the through-hole wall, and the flexible board. The method for connecting a printed wiring board according to claim 1, wherein the first connection terminal side surface and the first connection terminal side surface of the rigid board are covered. The method according to any one of claims 1 to 9, wherein the binder resin of the anisotropic conductive adhesive is a thermosetting epoxy resin or a urethane resin.

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