JP2008098613A - Flexible print circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a single-sided flexible print circuit board with high reliability having excellent bending and sliding operations, in view of a problem that in the single-sided flexible print circuit board performing bending and sliding operations, disconnection occurs in electronic equipment having a small bend radius corresponding to more compact, more light in weight, and thinner tendency. <P>SOLUTION: There are provided a base material; a conductive circuit obtained by etching a metal foil on one surface side of the base material; a cover-lay film covering this conductive circuit, leaving a part of the conductive circuit; an electromagnetic shield layer provided on the cover-lay film, wherein a tensile elastic modulus of the base material is 4.0 GPa or more and 7.5 GPa or less, and a thickness of the base material is 5 μm or more and 22 μm or less. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a flexible printed circuit board.

  With the recent increase in functionality of electronic devices, market demands for devices having high functions are increasing due to high-density integration of substrates and components, high-density wiring, and the like. Taking a mobile phone as an example, what has traditionally been only a telephone function for calls, but in recent years, the progress of such functions as connecting to the Internet, watching TV, listening to radio, listening to music, etc. is dizzying. The demands for each component, etc., on this equipment are becoming more severe.

  On the other hand, even in the case of high-function devices in mobile devices, there is a strong demand for lighter, thinner and smaller housings for devices, and for substrates, single-sided and double-sided substrates have shifted to multilayer substrates, and passive components are becoming increasingly common. Miniaturization is progressing, and the component size is less than half of the conventional size. In addition, smaller and more functional parts typified by system in package (SIP) have been actually used.

Among them, the flexible printed circuit board is applied to wiring in a limited space part because of its flexible characteristics, and it is bent and assembled in a product, or applied to a device having a movable part and bent. It is applied to the part which operates (for example, patent document 1). Especially for mobile phones, the clamshell type (α winding) and the slide type can be cited as representatives depending on the type, but the size of the bending radius tends to become smaller due to the smaller and thinner devices. As it becomes smaller, the conventional single-sided flexible printed circuit board configuration has not been sufficient to maintain the durability required in the market.
JP-A-2005-347345

  The present invention has been made in view of the above circumstances, and in a flexible printed circuit board, even in an electronic device having a small bending radius corresponding to a reduction in size, weight and thickness, a highly reliable flexible circuit that does not cause disconnection. To provide a printed circuit board.

  A flexible printed circuit board according to the present invention comprises a base material, a conductor circuit obtained by etching a metal foil on one side of the base material, and the conductor circuit except for a part of the conductor circuit. A cover lay film for covering, and an electromagnetic wave shielding layer provided on the cover lay film, wherein the electromagnetic wave shielding layer is composed of a conductive resin layer containing conductive particles and an insulating resin layer. The conductive resin layer and the coverlay film are laminated so as to face each other, the conductive resin layer has a thickness of 1 μm or more and 20 μm or less, and the insulating resin layer has a thickness of 3 μm or more and 20 μm or less. The substrate has a tensile modulus of 4.0 GPa to 7.5 GPa and a thickness of the substrate of 5 μm to 22 μm.

  In this flexible printed circuit board, an electromagnetic wave shielding layer is provided on the coverlay film, and the thickness of the conductive resin layer constituting the electromagnetic wave shielding layer is 1 μm or more and 20 μm or less, and the thickness of the insulating resin layer. When the thickness is 3 μm or more and 20 μm or less, the tensile elastic modulus of the base material is 4.0 GPa or more and 7.5 GPa or less, and the thickness of the base material is 5 μm or more and 22 μm or less. ing. As a result, the total thickness is reduced, the bending radius accompanying the bending operation can be reduced, the stress during bending can be reduced, and a flexible printed circuit board having higher flexibility is provided. be able to.

  Further, the difference between the maximum value and the minimum value of the thickness of the conductive resin layer may be 9 μm or less. Thereby, when the difference in thickness is within this range, the bending operation can be performed smoothly, so that a flexible printed circuit board without stress concentration can be obtained.

  The cover lay film is composed of a resin film and an adhesive, and the resin film has a tensile elastic modulus of 4.0 GPa or more and 7.5 GPa or less, and glass after the adhesive is cured. The transition temperature may be 50 ° C. or higher and 160 ° C. or lower. Thereby, since the elasticity modulus of the resin film becomes high, the bending shape can be maintained in the bending operation, and the discontinuous movement of the bending portion during the bending operation can be suppressed. In addition, recent electronic devices have been remarkably reduced in size and weight, so the housing is small, the generated heat is trapped inside, and the internal temperature of the device rises, so the glass transition temperature after curing of the adhesive is reduced. By increasing the height, the shape of the bending operation can be maintained, and a flexible printed circuit board having good bending performance can be obtained.

  According to the present invention, it is possible to provide a highly reliable flexible printed circuit board that does not cause disconnection even in an electronic device having a small bending radius corresponding to a reduction in size, weight, and thickness of the flexible printed circuit board. .

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, common components are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate in the following description.

  As shown in FIG. 1, the single-sided flexible printed circuit board 100 has a structure in which a copper-clad board 10 is etched to form a circuit 13, a coverlay 20 is covered on the surface of the circuit 13, and a shield layer 40 is provided.

Next, an example of the manufacturing method of the single-sided flexible printed circuit board concerning this embodiment is explained.
As shown to Fig.1 (a), the copper clad board 10 which laminated the resin film and copper foil as a base material first is prepared. The copper-clad plate 10 is prepared by laminating a copper foil 12 on polyimide as the base material 11. At this time, the polyimide 11 and the copper foil 12 use the copper clad board 10 obtained by applying the manufacturing method of the adhesive-less two-layer material generally using the thermoplastic polyimide as an adhesive agent. Then, it is excellent in flexibility and slidability, and reliability is improved, which is preferable.

  Next, a circuit 13 is formed by etching the copper foil 12 by a subtractive method, whereby a circuit board 15 is obtained (FIG. 1B). Subsequently, a coverlay 20 for covering the circuit is prepared. The coverlay 20 is obtained by applying an epoxy adhesive layer 21 to a polyimide 22, and an opening 23 is provided in advance for electrical connection with a connection terminal portion or a shield layer ( FIG. 1 (c)). The coverlay 20 is aligned with the circuit board 15 using a heat press and bonded to obtain a flexible printed circuit board 30 (FIG. 1C).

  Next, the shield layer 40 is formed. In this case, the shield layer 41 is formed by printing a conductive metal filler-containing paste on the opening side of the cover lay of the flexible printed circuit board 30. Furthermore, in order to protect this electromagnetic wave shielding layer 40, the overcoat layer 42 is formed by printing, and the single-sided flexible printed circuit board 100 is obtained (FIG. 1 (d)).

  The resin film of the base material 11 of the copper clad plate 10 used in the present invention has a tensile elastic modulus of 4.0 GPa or more and 7.5 GPa or less, preferably 5.0 GPa or more and 7.0 GPa or less, and has excellent flexibility and slidability. When the tensile elastic modulus is 4.0 GPa or less, in the bending operation, the stress is concentrated on the copper foil, not the resin film of the base material, so that the bending and sliding properties are lowered. In addition, when the tensile elastic modulus exceeds 7.0 GPa, the assembly becomes difficult and a load is applied to the bending operation, resulting in an increase in power consumption. Furthermore, when the thickness of the resin film is 5 μm or more and 22 μm or less, preferably 9 μm or more and 20 μm, the flexibility and sliding properties are excellent. When the thickness is less than 5 μm, the handling property at the time of production is inferior, and the thickness becomes thicker than 22 μm. If the bending radius becomes smaller, the bending radius of the circuit copper foil becomes tighter and the flexibility and slidability deteriorate.

  Further, the copper foil 12 of the copper clad plate 10 is preferably a rolled foil or a highly bent electrolytic foil that is durable in bending and sliding operations, and the thickness is preferably 5 μm or more and 20 μm or less. Preferably, a thickness of 9 μm or more and 18 μm or less is excellent in flexibility and slidability, and a thickness of less than 5 μm is thin, so that the handling property of the copper-clad board 10 is inferior, the yield is lowered, and a copper foil thicker than 20 μm is used. There is a problem that high-density wiring cannot be etched.

  The highly flexible copper foil is hard enough to be easily manufactured for the production of a copper clad laminate, and uses a heat-resistant copper foil, which undergoes a heat treatment process at 300 to 450 ° C., so that the copper foil is softened and recycled. It is possible to provide a flexible copper-clad laminate that is crystallized and has excellent bending properties.

  Next, for the polyimide of the resin film that is the base material 22 of the cover lay 20, the tensile elastic modulus is 4.0 GPa to 7.5 GPa, preferably 5.0 GPa to 7.0 GPa for the same reason as that of the copper-clad plate. Excellent flexibility and slidability below. The optimum thickness of the adhesive layer 21 before molding varies depending on the thickness of the circuit, but it is preferably 8 μm or more and 25 μm or less, and the glass transition temperature after curing is 50 ° C. or more and 160 ° C. or less, preferably 60 ° C. or more and 150 or less. Excellent flexibility and slidability at temperatures below ℃. If the glass transition temperature is lower than 50 ° C., the temperature inside the device in which this flexible printed circuit board is assembled to the device is operating, so that the stress is suddenly applied to the circuit copper foil by rising from the glass transition temperature. There is a problem that breaks easily. Further, if the glass transition temperature exceeds 160 ° C., it becomes too hard, the flexibility and flexibility inherent to the flexible printed circuit board are inferior, and assembly becomes difficult.

  As for the shield layer 41, a layer serving as an electromagnetic wave shield is formed on a flexible printed circuit board using a conductive paste containing a metal filler by a method such as screen printing. As the metal filler, a metal such as gold, silver, copper, or aluminum, or an alloy is used singly or as a mixture of plural kinds. The size of the filler is not particularly limited, but a filler of several nm to several μm is used. The constituent component of the paste is used by mixing this metal filler with a thermosetting epoxy resin or the like. The thickness of the shield layer 41 is not less than 1 μm and not more than 20 μm, preferably not less than 3 μm and not more than 18 μm. If the thickness is less than 1 μm, there are problems that the printing technique becomes difficult and the shielding effect is not stable. If the thickness exceeds 20 μm, the bending radius on the circuit side becomes smaller when the shield layer 41 is placed outside due to its thickness. It becomes easy to apply stress to the circuit and breaks easily. In addition, the thickness variation due to the printing of the shield layer 41 is likely to generate a part that is momentarily stressed in the bending operation and sliding operation, so the difference between the minimum thickness and the maximum thickness is 9 μm or less. It is desirable. Since the thickness variation is reduced by reducing the thickness variation, the flexibility and slidability are improved by printing thinner. The shield layer 41 may be formed on the coverlay side, the base material side, one side, or both sides of the flexible printed circuit board.

  The organic coating layer is formed for the purpose of covering and protecting the surface of the shield layer 41, but this component is not a problem as long as it is a general thermosetting resin, and the thickness is 3 μm or more and 20 μm or less. If formed, there is little influence on both flexibility and slidability, and these characteristics tend to be further improved by making the thickness thinner, and the variation in thickness is also small for the same reason as the shield layer 41. Is better in both flexibility and slidability.

  Moreover, as the electromagnetic wave shielding layer 40, a metal film deposited on a resin film such as PPS and bonded to a flexible printed circuit board with a conductive adhesive may be used. In this case, an alternative to the organic coating is a resin film.

  By using the above flexible printed circuit board, the total thickness is reduced, the bending radius accompanying the bending operation can be reduced, the stress during bending can be reduced, and the conductive resin layer can be reduced. When the difference between the maximum value and the minimum value of the thickness is 9 μm or less, the bending operation can be performed smoothly, so that a flexible printed circuit board without stress concentration can be obtained. Furthermore, since the elastic modulus of the resin film is high, the bent shape can be maintained in the bending operation, and the discontinuous movement of the bending portion during the bending operation can be suppressed. In addition, recent electronic devices are remarkably advanced in size and weight, so the housing is small and the generated heat is trapped inside, so the internal temperature of the device rises and the glass transition temperature after curing of the adhesive By increasing the height, the shape of the bending operation can be maintained, and a flexible printed circuit board having good bending performance can be obtained.

EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example and a comparative example, this invention is not limited to this.
(Example 1)
Using a copper-clad plate with a tensile modulus of 6.8 GPa with a substrate thickness of 15 μm and a copper foil thickness of 18 μm (rolled) as the copper-clad plate, a circuit with L / S = 75/75 m was formed by etching. Apply adhesive (glass transition temperature after curing 107 ° C (TMA measurement)) to polyimide (thickness 12.5μm, tensile elastic modulus 4.1GPa Apical NPI, manufactured by Kaneka), and punch openings etc. in advance The wet material was bonded to a copper-clad plate with a vacuum press, and a silver paste (SW1000 manufactured by Asahi Chemical Research Laboratory) was printed on the coverlay side by screen printing to a thickness of 10 μm, and the finish was 6 to 14 μm. Further, the organic coating film (CR18KT1) was similarly printed on the silver paste by screen printing, and the finish was 10 ± 5 μm. A single-sided flexible printed circuit board was produced as a test pattern for bending evaluation. The thickness of the silver paste and the organic coating was measured using a test coupon.

  As an evaluation method, the obtained single-sided flexible printed circuit board is set in a one-turn winding jig housing (inner diameter φ5 mm), both ends are fixed, and a clamshell type opening / closing operation (FIG. 2) of a mobile phone is performed 1 One cycle was operated per second, and the number of times until disconnection was measured.

  Also, set a single-sided flexible printed circuit board in the same form as the IPC test, set the bending radius to 1 mm, fix both ends, set the operating length to 30 mm, operate horizontally for one cycle per second (Fig. 3), and disconnect The number of times until was measured.

Evaluation criteria:
In the open / close operation, 300,000 times or more, and in the IPC bending test type, the number of horizontal operations is 300,000 times or more, ◯. Measurements were made up to 500,000 times or more, and those that passed both tests were marked as ◎.

(Example 2)
A single-sided flexible printed circuit board was prepared and evaluated in the same manner as in Example 1 except that a copper-clad plate having a substrate thickness of 14 μm and a copper foil thickness of 18 μm (rolled) was used and the tensile modulus of the copper-clad plate was set to 5.5 GPa. did.
(Example 3)
A single-sided flexible printed circuit board was prepared and evaluated in the same manner as in Example 1 except that the silver paste was printed to a thickness of 15 μm by screen printing, and the finish was 11 to 19 μm.
Example 4
A single-sided flexible printed circuit board was prepared and evaluated in the same manner as in Example 1 except that the thickness of the organic coating film was changed to 15 ± 5 μm.
(Example 5)
A single-sided flexible printed circuit board is prepared in the same manner as in Example 1 except that the silver paste is printed to a thickness of 15 μm by screen printing, the finish is 10 to 20 μm, and the thickness of the organic coating film is 15 ± 5 μm. And evaluated.
(Example 6)
Single-sided flexible as in Example 1 using a highly flexible electrolytic foil having a base material thickness of 15 μm, an elongation of 15% and a copper foil thickness of 18 μm, and using a copper-clad plate having a tensile elastic modulus of 6.8 GPa. A printed circuit board was created and evaluated.
(Example 7)
A single-sided flexible printed circuit board was prepared and evaluated in the same manner as in Example 1 except that a coverlay polyimide film was used and a modulus of elasticity of 6.9 GPa (thickness: 12.5 μm, manufactured by Ube Industries, Upilex) was used.
(Comparative Example 1)
A single-sided flexible printed circuit board was prepared and evaluated in the same manner as in Example 1 except that the thickness of the silver paste was 25 ± 5 μm, which was aimed at 25 μm.
(Comparative Example 2)
A single-sided flexible printed circuit board was prepared and evaluated in the same manner as in Example 1 except that the thickness of the silver paste was 10 ± 8 μm with a target of 10 μm and the thickness of the substrate was 25 μm.

It is process sectional drawing of the flexible printed circuit board which concerns on embodiment of this invention. It is the schematic which shows the motion in the portable apparatus used for the flexible printed circuit board which concerns on embodiment of this invention. It is the schematic which shows the other motion in the portable apparatus used for the flexible printed circuit board which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Copper-clad board 11 Base material 12 Copper foil 13 Circuit 15 Circuit board 20 Coverlay 21 Adhesive 22 Film 30 Flexible printed circuit board 40 Electromagnetic wave shielding layer 41 Shield layer 42 Overcoat 50 Hinge part 60 Bending part 100 Single-sided flexible printed circuit board

Claims (10)

A substrate;
A conductor circuit obtained by etching a metal foil on one side of the substrate;
A coverlay film covering the conductor circuit leaving a part of the conductor circuit;
An electromagnetic wave shielding layer provided on the coverlay film,
The electromagnetic wave shielding layer is composed of a conductive resin layer containing conductive particles and an insulating resin layer, and the conductive resin layer and the coverlay film are laminated so as to face each other. The thickness of the conductive resin layer is 1 μm or more and 20 μm or less, the thickness of the insulating resin layer is 3 μm or more and 20 μm or less, and the tensile modulus of the base material is 4.0 GPa or more and 7.5 GPa A flexible printed circuit board having a thickness of 5 μm or more and 22 μm or less.   The flexible printed circuit board according to claim 1, wherein a difference between a maximum value and a minimum value of the thickness of the conductive resin layer is 9 μm or less.   The flexible printed circuit board according to claim 1, further comprising a metal thin film layer between the conductive resin layer containing the conductive particles and the insulating resin layer.   The flexible printed circuit board according to claim 1, wherein the metal foil is a rolled copper foil.   The flexible printed circuit board according to claim 4, wherein the rolled copper foil has a thickness of 5 μm or more and 22 μm or less.   The flexible printed circuit board according to claim 1, wherein the metal foil is a highly bent electrolytic foil.   The flexible printed circuit board according to claim 6, wherein the thickness of the highly bent electrolytic foil is 5 μm or more and 22 μm or less.   The flexible printed circuit board according to claim 6 or 7, wherein an elongation percentage of the highly bent electrolytic foil is 8% or more and 20% or less after heat treatment at 180 ° C for 1 hour.   The flexible printed circuit board according to any one of claims 6 to 8, wherein the tensile strength of the highly bent electrolytic foil is 125 MPa or more and 300 MPa or less. The coverlay film is composed of a resin film and an adhesive,
The tensile modulus of the resin film is 4.0 GPa or more and 7.5 GPa or less, and the glass transition temperature after curing of the adhesive is 50 ° C or more and 160 ° C or less. The flexible printed circuit board in any one.

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