JP2012079934A - Flexible printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flexible printed circuit board in which connection strength of an anisotropic conductive material can be stably ensured.SOLUTION: In the flexible printed circuit board, organic layers having a circuit formed therebetween are bonded together with the anisotropic conductive material. The organic layers are made of polyimide, and a surface roughness of surfaces to be bonded of the polyimide is 8 nm or more.

Description

  The present invention relates to a flexible printed circuit board, and more particularly to a flexible printed circuit board in which organic layers on which circuits are formed are bonded with an anisotropic conductive material.

  Conventionally, flexible printed circuit board connection structures using an anisotropic conductive film (ACF) are disclosed in, for example, Japanese Patent Application Laid-Open Nos. 11-121899 (Patent Document 1), Japanese Patent Application Laid-Open No. 4-352486 (Patent Document 2), and Japanese Patent Application Laid-Open No. 2008-. No. 166401 (Patent Document 3) and Japanese Patent Application Laid-Open No. 2003-46231 (Patent Document 4).

Japanese Patent Laid-Open No. 11-121892 JP-A-4-352486 JP 2008-166401 A JP 2003-46231 A

  Patent Document 1 discloses a terminal structure that improves the connection strength of an anisotropic conductive adhesive. An adhesive accommodating recess is provided in the terminal pattern.

  Patent Document 2 discloses a connection structure using an anisotropic conductive film of FPC (flexible printed circuit) with high connection reliability.

  Patent Document 3 discloses that a groove portion is provided on the terminal surface as a structure of a terminal that improves the adhesion strength by the anisotropic conductive adhesive.

  Patent Document 4 discloses a connection structure of anisotropic conductive layers that can be thinned, and discloses that an anisotropic conductive layer is connected after a resin exposed portion between terminals is dug down by etching or the like.

  The technique described in the above document has a problem that the required adhesive strength by the anisotropic conductive layer cannot be secured stably.

  Accordingly, the present invention has been made to solve the above-described problems, and provides a flexible printed board capable of stably securing the connection strength by an anisotropic conductive material.

  A flexible printed circuit board according to the present invention is a flexible printed circuit board in which an organic material layer on which a circuit is formed is bonded with an anisotropic conductive material, and the organic material layer is made of polyimide, and the surface roughness of the adherend surface of the polyimide is The thickness is 8 nm or more, and preferably 8 nm or more and 30 nm or less. The present inventor has found that the adhesive strength required by the anisotropic conductive material cannot be stably secured unless the surface roughness of the organic layer is 8 nm or more. If the surface roughness becomes too large, the ion migration property will be reduced, and the unevenness of the circuit surface related to the surface roughness of the organic layer will affect the bending resistance, wiring adhesion, etc., so the surface roughness of the organic layer Is preferably 30 nm or less.

  The peel strength with respect to the organic layer is, for example, 4 N / cm or more, preferably 4 N / cm or more and 20 N / cm or less.

  According to this invention, it is possible to provide a connection structure of anisotropic conductive layers capable of improving the bonding strength.

It is sectional drawing which shows the connection structure of the multilayer flexible printed circuit board according to Embodiment 1 of this invention. It is sectional drawing which shows the structure for obtaining the electrical connection in the anisotropic conductive layer formed of the anisotropic conductive material in detail, and is sectional drawing of the part enclosed by II in FIG. It is a figure which shows an example of the wiring pattern of the flexible printed circuit board according to this invention. It is a graph which shows the relationship between the surface roughness and peel strength in the to-be-adhered surface of a polyimide at the time of using CP8016 (brand name) by Sony Chemical Information Device company as an anisotropic conductive layer, and using a polyimide as an organic substance layer. It is a figure which shows the cantilever used in the process of measuring peel strength with the method according to this invention. It is a perspective view which expands and shows only the front-end | tip part of the cantilever shown in FIG.

  Embodiments of the present invention will be described below with reference to the drawings. In the following embodiments, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

(Embodiment 1)
1 is a sectional view showing a connection structure of a multilayer flexible printed circuit board according to Embodiment 1 of the present invention. Referring to FIG. 1, in anisotropic conductive layer connection structure 5 according to the first embodiment of the present invention, interlayer adhesive layer 20 is provided on organic material layer 10. The organic layer 10 is made of polyimide. The interlayer adhesive layer 20 is connected to the organic material layer 10. An organic layer 40 is provided on the interlayer adhesive layer 20. A conductive layer 30 is provided in the interlayer adhesive layer 20 so as to be in contact with the organic material layer 40. The conductive layer 30 is a wiring layer made of copper.

  An organic layer 40 is provided on the interlayer adhesive layer 20. An anisotropic conductive layer 50 is disposed on the organic material layer 40. A conductive layer 60 is disposed in the anisotropic conductive layer 50 so as to be in contact with the organic material layer 40. A conductive layer 70 is provided in the anisotropic conductive layer 50 on the side opposite to the conductive layer 60. The anisotropic conductive layer 50 is in contact with the organic material layer 80. The organic layer 80 is connected to the interlayer adhesive layer 110 made of polyimide by the interlayer adhesive layer 90. The organic layer 100 includes an interlayer adhesive layer 110 and a conductive layer 120 provided in the interlayer adhesive layer 110 and in contact with the organic layer 100. An organic layer 130 is disposed on the interlayer adhesive layer 110.

  At the interface 41 between the organic material layer 40 and the anisotropic conductive layer 50, the surface roughness of the organic material layer 40 is 8 nm or more and 30 nm or less.

  Also at the interface 81 between the anisotropic conductive layer 50 and the organic material layer 80, the surface roughness of the surface of the organic material layer 80 is 8 nm or more and 30 nm or less.

The organic layers 40 and 80 are made of polyimide.
FIG. 2 is a cross-sectional view showing in detail a configuration for obtaining electrical connection in the anisotropic conductive layer, and is a cross-sectional view of a portion surrounded by II in FIG. Referring to FIG. 2, nickel particles 51 are interposed between conductive layer 60 and conductive layer 70. Conduction between the conductive layer 60 and the conductive layer 70 is achieved by the nickel particles 51.

  The entire nickel particles 51 do not have to be nickel, and the central portion is made of resin, and a nickel layer may be provided on the outer periphery thereof.

Furthermore, the nickel layer surface may be covered with another conductive material.
FIG. 3 is a view showing a flexible printed board in which the connection structure of anisotropic conductive layers according to the present invention is used. With reference to FIG. 3, the flexible printed circuit board 1 is provided with a plurality of wirings 2. Each wiring 2 is composed of conductive layers 30, 60, 70 and 120 in the cross section of FIG. In a region where these wirings overlap in the thickness direction, an anisotropic conductive layer is disposed between the wirings as shown in FIG. Then, when some force is applied to the wiring, conduction between the wiring is achieved.

  FIG. 4 shows the surface roughness of polyimide and the peel strength of the anisotropic conductive layer when CP-8016K (trade name) manufactured by Sony Chemical Information Device Co. is used as the anisotropic conductive layer and polyimide is used as the organic layer. It is a graph which shows the relationship. FIG. 4 shows the initial peel strength when the anisotropic conductive layer and the organic layer are brought into contact with each other, and corresponds to the unused state.

  FIG. 4 shows that the peel strength is preferable when the average surface roughness is 8 nm or more and 30 nm or less.

The preferable peel strength is 4 N / cm or more and 20 Ncm or less.
The “average surface roughness” refers to the average surface roughness (Ra) in a region having one side of 1 μm × 1 μm, and is defined by JIS B 0601. Specifically, the average roughness Ra on the diagonal line of a square region having one side of 1 μm was defined as “average surface roughness”.

This peel strength was measured by the following method.
FIG. 5 is a view showing a cantilever used in a process of measuring peel strength by the method according to the present invention. 6 is an enlarged perspective view showing only the tip portion of the cantilever shown in FIG. Referring to FIGS. 5 and 6, cantilever 200 includes a main body part 210, an arm part 220 connected to main body part 210, and a needle part 230 attached to arm part 220. In the cantilever 200, the tip radius R is 10 nm or more and 30 nm or less. The tip shape of the tip is processed with a focused ion beam. By setting the tip radius R to 10 nm or more and 30 nm or less, the tip can be processed with a focused ion beam and the tip can be confirmed with an electron microscope.

  The needle height D is preferably 5 μm or more and 10 μm or less. In the cantilever, when the unevenness of the polyimide surface is examined, the polyimide surface may have large unevenness, and the minimum height is set to 5 μm in order to cope with the large unevenness. If the height D is too high, the mechanical strength decreases, so the upper limit is set to 10 μm.

  The lever width W is preferably 20 μm or more and 50 μm or less, and the lever length L is preferably 100 μm or more and 250 μm or less.

  For the measurement of peel strength, a sample including an interface between the organic layer 40 and the anisotropic conductive layer 50 is obtained by pasting ACF on a copper-etched polyimide film constituting the organic layer and cutting out to a size of 5 mm × 10 mm. It was. The sample was pressure-bonded to glass, and the cantilever 200 was used to peel the polyimide organic material layer 40 from the end of the short side, and the stress was measured. The pressure bonding time was 10 seconds, the pressure was 10 MPa, and the pressure bonding temperature was from room temperature to 180 ° C. The peeling angle was 90 ° and the peeling speed was 50 mm / min.

  The organic layers 40 and 80 may be polyethylene terephthalate (PET) and liquid crystal polymer (LCP).

  As the anisotropic conductive layer, not only CP-8016K manufactured by Sony Chemical Information Device Corporation, but also MF-504 (trade name) manufactured by Hitachi Chemical Co., Ltd. can be used.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention can be used in the field of substrates having an anisotropic conductive layer.

Claims (3)

A flexible printed circuit board that adheres an organic material layer on which a circuit is formed with an anisotropic conductive material,
The said organic substance layer consists of polyimides, The surface roughness of the to-be-adhered surface of this polyimide is a flexible printed circuit board which is 8 nm or more.   The flexible printed circuit board according to claim 1, wherein a surface roughness of the adherend surface of the polyimide is 8 nm or more and 30 nm or less.   The flexible printed circuit board according to claim 1, wherein a peel strength with respect to the organic material layer is 4 N / cm or more.