JP2846145B2 - Circuit board 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 connecting circuit boards, and more particularly, to a display such as a liquid crystal display panel (LCD), a plasma display (PDP), or an electroluminescence (EL) having a fine pitch connection electrode with a low pitch. The present invention relates to a method for connecting a circuit board such as a flexible circuit board (FPC) and a rigid circuit board (PCB).

[0002]

2. Description of the Related Art Conventionally, an anisotropic conductive adhesive in which conductive particles are dispersed in an insulating resin has been used for connection of a circuit board. Due to the lower pitch, the electrical connection tends to be unstable. For this reason, attempts have been made to solve this disadvantage by making the particle size uniform and using resin particles coated with a noble metal such as Au having a small contact resistance as the conductive particles.

[0003]

However, in connection of a circuit board with an anisotropic conductive film of a type in which conductive particles are dispersed, the lower the pitch, the poorer the dispersion of the conductive particles,
There is an increased risk of short-circuiting due to accidental or static electricity or other series of conductive particles.In addition, precious metals are used to reduce contact resistance, and the yield of conductive particles deteriorates due to extremely uniform particle size. There was a problem that it became expensive.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art. Even if the pitch of the connection electrodes becomes small, there is little danger of short-circuiting between adjacent electrodes, and the contact resistance is low. It is an object of the present invention to provide an inexpensive circuit board connection method, in which both circuit boards having a sum of steps of 5 μm or more with respect to an insulating plate of a connection electrode of each circuit board have a volume resistivity of 10 ^7. A circuit characterized in that a connection is made by applying heat and pressure to a hot-adhesive adhesive having a ripened component and a minimum melt viscosity at the time of thermocompression bonding of 1 × 10 ⁷ poise or less at 〜１０10 ¹⁸ Ω · cm. The gist is a method of connecting the substrates.

[0005] The adhesive used in the present invention desirably solidifies during heating and pressurizing. Therefore, the adhesive should contain a thermosetting component. As the thermosetting component, an epoxy resin type, a urethane type, an acrylic type, Silicone, chloroprene,
Examples thereof include nitrile-based synthetic rubber and the like. In order to improve peel strength, resistance to temperature change, and flexibility for the purpose of improving reliability, it is effective to blend a thermoplastic resin with them.

Examples of the thermoplastic resin include polyamide, polyester, ionomer, ethylene-vinyl acetate copolymer (EVA), ethylene-acrylic acid copolymer (EAA), and ethylene-methacrylic acid copolymer (EM).
A), Ethylene-ethyl acrylate copolymer (EEA)
And various synthetic rubbers such as nitrile rubber (NBR), styrene-butadiene rubber (SBR), styrene-ethylene-butylene-styrene copolymer (SEBS), and modified products and composites thereof. Is raised. The most effective ones in terms of peel strength and reaction temperature are NBR and S having carboxylated terminal or side chain.
One-part heat-curable epoxy resin is blended with 10 to 1,000 parts by weight, preferably 20 to 200 parts by weight, based on 100 parts by weight of a synthetic rubber such as BR or SEBS. In any case, these include a curing agent, a vulcanizing agent, a control agent, a deterioration inhibitor, a heat-resistant additive, a heat conduction improver, a tackifier, a softener, a coloring agent, various coupling agents, and a metal deactivator. And the like are suitably added.

When bonding by heating and pressing, melting → gelation →
Although it goes through a process of curing, the adhesive must flow to the extent that it melts and the adhesive flows, and the connection electrode having a step must be electrically connected. Therefore, the melt viscosity of the adhesive in this case is 1 × 10 ^7. It must be less than poise, preferably less than 5 × 10 ⁶ poise. The facing connection electrode to be connected must have a step into the insulating plate, that is, between the electrode portion and the non-electrode portion, into which the adhesive of the electrode portion flows. The sum of the steps of the facing electrode to the insulating plate is 5 μm. When the step is too large, the adhesive is not filled and sufficient adhesive strength cannot be obtained. Therefore, the thickness is preferably 100 μm or less.

The electrode to be connected may have a roughened surface or be provided with protrusions to improve connection reliability, but is not an essential requirement. The adhesive between the facing electrodes to be connected flows by heating and pressurizing and is removed from between the electrodes, but in some parts it remains between the electrodes although it is very small, and in some parts the electrodes are directly Contact. At this time, in order to obtain a low-resistance electrical connection, the circuit board must have a volume resistivity of 10 ¹⁸ Ω · cm or less at 60 ° C. to 100 ° C. as a condition of actual use. However, the adjacent connection electrodes of each circuit board must maintain insulation so as not to hinder the driving of the circuit board. For this purpose, the volume resistivity is 10 ⁷ under the conditions of actual use of the circuit board.
Ω · cm or more is required.

According to the method of connecting circuit boards of the present invention, as described above, the above-mentioned adhesive formed in a film shape between the electrodes to be connected is placed, and heated and pressed under appropriate conditions. Although this condition can be obtained, these conditions may be determined depending on the adhesive used for connection.

[0010]

The connection method of the present invention is constituted as described above. The sum of the steps of the electrodes to be connected is 5 μm or more, and the melt viscosity at the time of heating of the adhesive connecting the electrodes is 10 ⁷ poise or less. Although the adhesive flows from between the electrodes and remains between the trace electrodes, the volume resistivity is 10 ¹⁸ Ω · cm or less, so that a low-resistance electrical connection can be obtained and the volume resistivity can be reduced to 10 ¹⁸ Ω · cm. ^By setting the resistance to ⁷ Ω · cm or more, insulation from the adjacent electrode is substantially maintained, and since the adhesive has thermosetting properties, springback is prevented and electrical connection is maintained. Also, unlike the type in which conductive particles are dispersed,
There is almost no danger of a short circuit, and an inexpensive connection structure can be obtained because expensive conductive particles are not used.

[0011]

Next, an embodiment will be described with reference to the drawings. Embodiment 1 As shown in FIG. 1, one circuit board is provided with an electrode pitch of 0.2 mm, a copper foil thickness of 35 μm, and a Sn-plated connection electrode 2 on an insulating plate 1 having a polyimide (PI) thickness of 75 μm. The other circuit board used was an LCD in which a glass electrode 3 of a transparent tin oxide electrode (ITO) having an electrode pitch of 0.2 mm was provided on a glass insulating plate 4. Next, based on 100 parts by weight of terminal carboxylated NBR, 100 parts by weight of a one-part heat-curable epoxy adhesive using a microencapsulated imidazole-modified epoxy as a curing agent, 20 parts by weight of a tackifier, γ-mercaptotrimethoxysilane 1 part by weight of 1 part by weight of 1 part by weight of trimethoxysilane was dissolved in a mixed solvent of toluene: MEK = 8: 2, and the mixed adhesive 5 was coated on the other circuit board. The thickness was set to 30 μm. The adhesive 5 has a volume resistivity at 25 ° C. of 10 ¹³ Ω · cm, 17
The melt viscosity before curing at 0 ° C. was 3 × 10 ⁵ poise. One of the circuit boards is stacked with the adhesive 5 interposed therebetween,
When heat-sealed at 170 ° C., 40 kg / cm ² and 30 sec, the connection resistance was 0.5Ω or less. In addition, when the test was performed on 150 pin × 10 circuit boards, there was no short circuit and the 90 ° peel strength was 800 g /
cm or more.

(Embodiment 2) As shown in FIG.
Using the adhesive 5 used in the above, the other circuit board provided with the projections 6 of 5 μm on the connection electrode 3 and the connection electrode 2 of one circuit board are overlapped, and heated at 170 ° C., 40 kg / cm ² , 30 sec. Sealed connection. When the connection resistance was measured, the initial value was 0.5Ω as the maximum value,
The maximum value was 0.8Ω after being left at 95 ° C. and 95% RH for 1000 hrs.

[0013]

As described above, according to the present invention, a short circuit due to a chain of conductive particles between adjacent connection electrodes can be prevented even when a circuit board having a connection electrode with a low pitch is connected by using no conductive particles. It is possible to provide an inexpensive circuit board connection method without worrying about occurrence. Further, the connection reliability of the connection electrode can be further improved by roughening the connection surface of the connection electrode or providing the projection.

[Brief description of the drawings]

FIG. 1A is a plan view of a connection portion of a circuit board according to the present invention,
(B) is a longitudinal sectional view taken along line XX of (a), and (c) is a longitudinal sectional view taken along line YY of (a).

FIG. 2 is a cross-sectional view taken along line XX of FIG.
It is a longitudinal cross-sectional view of the same location as a line.

[Explanation of symbols]

 1, 4 Insulating plate 2, 3 Connection electrode 5 Adhesive 6 Projection 7 Upper glass substrate 8 Sealing material 9 Liquid crystal

Continuation of front page (56) References JP-A-1-124976 (JP, A) JP-A-60-154480 (JP, A) JP-A-61-260562 (JP, A) JP-A-3-95520 (JP) JP-A-63-250626 (JP, A) JP-A-4-6771 (JP, A) JP-A-64-50307 (JP, A) JP-A-2-33032 (JP, U) (58) Field surveyed (Int.Cl. ⁶ , DB name) H01R 11/01 G02F 1/1345 H01B 5/16

Claims (3)

(57) [Claims] 1. A thermocompression bonding method in which both circuit boards each having a sum of steps of 5 μm or more with respect to an insulating plate of a connection electrode of each circuit board have a volume resistivity of 10 ⁷ to 10 ¹⁸ Ω · cm, contain a hardened component, A method for connecting circuit boards, wherein the connection is performed by applying heat and pressure using a heat-adhesive adhesive having a minimum melt viscosity of 1 × 10 ⁷ poise or less. 2. The method according to claim 1, wherein the heat-adhesive adhesive is a thermoplastic resin.
The connection method according to claim 1, wherein the thermosetting component contains at least 10 to 1000 parts by weight of an epoxy resin based on parts by weight. 3. The connection method according to claim 1, wherein the sum of the steps of the connection electrode is 5 to 100 μm.