JP2006013135A - Flexible circuit board and laminated body therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize sufficient incombustibility without use of a special bonding agent to which an incombustible agent is added while a polyethylene-naphtharate film is used as a base film of a flexible printed circuit board and a polyulethane system bonding agent is used for bonding between the base film and copper foil, and also to prevent peeling copper foil and conductive pattern from the base film due to deterioration in the etching resistance of the bonding agent layer and adhesive bonding of flexible printed circuit boards during storage or transportation. <P>SOLUTION: The laminated body 10 for flexible printed circuit board comprises a copper foil 1, an underlayer 2 formed of a heat resistant resin formed on one principal surface of the copper foil 1, a bonding agent layer 3 formed of polyulethane system bonding agent provided on the underlayer 2, and a base film 4 formed of polyethylenenaphtharate adhered to the copper foil 1 via the underlayer 2 and bonding agent layer 3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a laminate for a flexible printed circuit board and a flexible printed circuit board using the same.

  The flexible printed circuit board is characterized by being lightweight and capable of high-density wiring. For this reason, flexible printed circuit boards have already been used in various electronic devices, and recently, introduction into automobile electrical components has also been promoted.

  As described in Patent Document 1, a flexible printed circuit board is usually obtained by bonding a base film and a copper foil using a thermosetting adhesive and patterning the copper foil by an etching process or the like. . Moreover, the conductor pattern formed by patterning the copper foil is covered with a cover layer made of resin, if necessary.

  In general, reflow soldering is used for mounting electronic components on the flexible printed circuit board. Therefore, the flexible printed circuit board is required to have a heat resistance of 240 ° C. to 260 ° C. or higher. Therefore, many flexible printed circuit boards use a polyimide film with excellent heat resistance as the base film and cover layer, and use an epoxy adhesive with excellent heat resistance for bonding the base film and copper foil. is doing.

  However, the polyimide film has a problem that it is expensive. Therefore, it has been studied to use a cheaper film as the base film instead of the polyimide film.

  The polyethylene naphthalate film is not as heat resistant as the polyimide film, but has heat resistance enough to withstand the heat treatment performed in the reflow soldering process. Polyethylene naphthalate film is one of the cheapest films among such heat-resistant plastic films. Therefore, in some applications, a polyethylene naphthalate film has begun to be used as a base film instead of a polyimide film.

  However, the polyethylene naphthalate film is inferior in flame retardancy as compared with the polyimide film. Therefore, when polyethylene naphthalate film is used as the base film, sufficient flame retardancy, for example, UL94, which is a certification standard for flame retardancy established by an insurance laboratory (Underwriters' Laboratories) operated by the US Fire Insurance Commission In order to realize VTM-0 class flame retardancy, it is necessary to use a special adhesive to which a flame retardant is added. Use of such an adhesive hinders manufacturing cost reduction of the flexible printed circuit board.

  Moreover, although an epoxy-type adhesive is excellent in heat resistance, high temperature and long-time heat processing are required in order to complete the thermosetting. Such heat treatment is disadvantageous in terms of productivity. In addition, when a polyethylene naphthalate film is used as the base film, if an epoxy adhesive is used for bonding the base film and the copper foil, those laminates are caused by thermal stress during bonding. May cause warping and wrinkles.

  For bonding the base film and the copper foil, a polyurethane adhesive can be used instead of the epoxy adhesive. Polyurethane-based adhesives can complete thermal curing at lower temperatures and shorter times compared to epoxy-based adhesives.

  Therefore, continuous application of polyurethane adhesive dissolved in organic solvent to copper foil, drying of coating film using hot air, pasting of base film and copper foil by heating roll, and winding up of these laminates Therefore, high productivity can be realized. Moreover, since the thermal stress at the time of bonding is small compared with the case where an epoxy-type adhesive agent is used, a curvature and a wrinkle do not arise in the previous laminated body.

  However, the polyurethane-based adhesive is inferior in resistance to the etching process performed for patterning the copper foil, as compared with the epoxy-based adhesive. Therefore, the conductor pattern formed by patterning the copper foil may be peeled off from the base film in the etching process or the reflow soldering process. That is, since the polyurethane-based adhesive has insufficient etching resistance, it is difficult to achieve a sufficient yield in the etching process and the reflow soldering process.

  Furthermore, when a polyurethane adhesive is used for bonding the base film and the copper foil, if a part of the adhesive layer is exposed along with the patterning of the copper foil, the flexible printed circuit boards are stacked or stored. When transported, they may be in close contact (adhesive adhesion).

Thus, from the viewpoint of production cost, it is desirable to use a polyethylene naphthalate film as the base film and use a polyurethane adhesive for bonding the base film and the copper foil. However, in this case, a special adhesive added with a flame retardant must be used to achieve sufficient flame retardancy, and the conductive layer is inferior in etching resistance. Is easy to peel off from the base film. Furthermore, there is also a problem that the flexible printed circuit boards adhere to each other during storage or transportation.
JP 2003-174260 A

  The object of the present invention is to use a special adhesive that uses a polyethylene naphthalate film as a base film of a flexible printed circuit board and uses a polyurethane adhesive to bond the base film and the copper foil, but adds a flame retardant. It is possible to realize sufficient flame retardancy without using the adhesive, peel off the conductive pattern from the base film due to the poor adhesive resistance of the adhesive layer, and adhesion between the flexible printed circuit boards during storage or transportation It is to prevent adhesion.

  According to the first aspect of the present invention, a copper foil, a base layer made of a heat-resistant resin formed on one main surface of the copper foil, and an adhesive layer made of a polyurethane-based adhesive provided on the base layer And a base film made of polyethylene naphthalate bonded to the copper foil through the base layer and the adhesive layer, to provide a flexible printed circuit board laminate.

  According to a second aspect of the present invention, there is provided a flexible printed circuit board manufactured using the flexible printed circuit board laminate according to the first aspect, wherein the copper foil is patterned into a conductor pattern. A flexible printed circuit board is provided.

In the first and second side surfaces, the heat-resistant resin may be a polyamideimide resin or a polyimide resin. The dry basis weight of the underlayer may be in the range of 10 g / m ^{2 to} 40 g / m ² . The dry basis weight of the adhesive layer may be in the range of 5 g / m ^{2 to} 15 g / m ² .

  According to the present invention, a special adhesive containing a flame retardant is used while using a polyethylene naphthalate film as a base film of a flexible printed circuit board and using a polyurethane-based adhesive for bonding the base film and the copper foil. Delivers sufficient flame resistance without using, and peels the conductor pattern from the base film due to poor etching resistance of the adhesive layer, and adhesive adhesion between flexible printed circuit boards during storage or transportation Can be prevented.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same referential mark is attached | subjected to the same or similar component, and the overlapping description is abbreviate | omitted.

  FIG. 1 is a cross-sectional view schematically showing a flexible printed circuit board laminate according to one embodiment of the present invention.

  A flexible printed circuit board laminate 10 shown in FIG. 1 includes a copper foil 1. On one main surface of the copper foil 1, a base layer 2 made of a heat-resistant resin is formed. An adhesive layer 3 made of a polyurethane adhesive is provided on the base layer 2. A polyethylene naphthalate film is bonded as a base film 4 to the copper foil 1 through the base layer 2 and the adhesive layer 3.

  As the copper foil 1, for example, a rolled copper foil or an electrolytic copper foil can be used. For applications where high flexibility is not required, a cheaper electrolytic copper foil is usually used.

  The thickness of the copper foil 1 is appropriately set according to the use of the flexible printed circuit board manufactured using the laminate 10 and the target manufacturing cost. The thickness of the copper foil 1 is, for example, in the range of 9 μm to 70 μm.

  The underlayer 2 made of a heat resistant resin imparts flame retardancy to the laminate 10. In addition, the base layer 2 is such that the adhesive layer 3 is exposed to an etchant when the copper foil 1 is patterned by an etching process, and the adhesive layer 3 is partially exposed by the etching process. To prevent.

  The material used for the underlayer 2 is not particularly limited as long as it is a heat-resistant resin having adhesion to the copper foil 1 and the adhesive layer 3. However, since the polyamide-imide resin or the polyimide-based resin has self-digestibility, when these resins are used as a heat-resistant resin, particularly excellent flame retardancy can be imparted to the laminate 10.

  The underlayer 2 can be formed, for example, by applying a coating liquid obtained by dissolving a heat-resistant resin in an organic solvent on one main surface of the copper foil 1 and drying and curing the coating film. For application of this coating liquid, for example, a gravure printing method or the like can be used.

The dry basis weight of the underlayer 2 is, for example, 10 g / m ² or more. When the dry basis weight of the underlayer 2 is too small, it is difficult to obtain sufficient flame retardancy. Moreover, when the dry basic weight of the base layer 2 is too small, the adhesive bond layer 3 will be partially exposed by the etching process of the copper foil 1, and as a result, the conductor pattern formed by patterning the copper foil 1 becomes the base film 4. The effect of preventing peeling from the film and the effect of preventing the flexible printed circuit boards from adhering to each other at the time of storage or transportation do not remarkably appear.

The dry basis weight of the underlayer 2 is, for example, 40 g / m ² or less. If the drying basis weight of the underlayer 2 is too large, drying defects such as defective defoaming may occur in the drying process of the previous coating film due to the difference in the drying state between the surface layer part and the deep part. . Further, as the dry basis weight of the underlayer 2 is increased, the manufacturing cost increases.

  In order to form the adhesive layer 3 made of a polyurethane-based adhesive, for example, a coating solution obtained by dissolving a polyurethane-based adhesive in an organic solvent is applied on the base layer 2, and the resulting coating is heated with hot air. Dry by spraying. Thereafter, the polyurethane adhesive is heat-cured in a state where the base film 4 is adhered to the coating film by using a heating roll. Thereby, the adhesive bond layer 3 which consists of a polyurethane-type adhesive agent is obtained.

  In addition, application | coating to the copper foil 1 of this coating liquid, drying of the coating film using a hot air, bonding of the base film 4 and copper foil with a heating roll, and winding of the laminated body 10 obtained by it are continuous. Can be done automatically. That is, dry lamination of the copper foil 1 and the base film 4 can be performed continuously.

The dry basis weight of the adhesive layer 3 is, for example, 5 g / m ² or more. When the dry basis weight of the adhesive layer 3 is too small, the adhesive force between the copper foil 1 or a conductor pattern obtained by patterning the copper foil 1 and the base film 4 may be insufficient.

The dry basis weight of the adhesive layer 3 is, for example, 15 g / m ² or less. When the dry basis weight of the adhesive layer 3 is too large, it is difficult to employ high-speed bonding using a dry laminator. For this reason, manufacturing cost rises.

  The thickness of the base film 4 is appropriately set according to, for example, the thickness of the copper foil 1. The thickness of the base film 4 is, for example, in the range of 25 μm to 75 μm.

  FIG. 2 is a cross-sectional view schematically showing an example of a flexible printed circuit board that can be manufactured using the laminate 1 of FIG.

  In the flexible printed circuit board 100 shown in FIG. 2, the copper foil 1 of the laminate 10 shown in FIG. 1 is patterned to form a conductor pattern 1 '.

  This flexible printed circuit board 100 has the simplest structure among flexible printed circuit boards that can be manufactured using the laminate 1 of FIG. If the laminated body 1 of FIG. 1 is used, it is also possible to manufacture the flexible printed circuit board of another structure.

  For example, a metal bump for electrically connecting an electronic component to be mounted on the flexible printed circuit board 100 and the conductor pattern 1 ′ may be disposed on the conductor pattern 1 ′. As this metal bump, for example, a solder bump may be formed.

  Alternatively, a cover layer may be bonded and the conductor pattern 1 ′ may be covered with this cover layer. For example, a polyethylene naphthalate film may be used as the cover layer. The cover layer and the flexible printed circuit board 100 may be bonded using, for example, a polyurethane adhesive.

  Furthermore, a plurality of flexible printed circuit boards 100 shown in FIG. 2 may be stacked. That is, you may manufacture a multilayer substrate as a flexible printed circuit board using the laminated body 1 of FIG. In this case, the flexible printed circuit boards 100 may be bonded together using, for example, a polyurethane-based adhesive.

  When manufacturing a multilayer substrate as a flexible printed circuit board, interlayer connection may be performed. For example, by providing through holes in the base film 4, the adhesive layer 3, the base layer 2, etc. at the position of the conductor pattern 1 ′, and burying these through holes with a connecting conductor, the conductor patterns 1 ′ are electrically connected to each other. May be.

  An electronic component can be mounted on the flexible printed circuit board 100 described above using, for example, reflow soldering. That is, the flexible printed circuit board 100 can be used as a tape carrier or the like.

  In addition, the flexible printed circuit board 100 may not include electronic components. That is, the flexible printed circuit board 100 may be a flexible flat cable.

  Examples of the present invention will be described below. In addition, the following examples are described in order to help understanding of the present invention, and the present invention should not be limited to these examples.

Example 1
3 to 7 are cross-sectional views schematically illustrating a method for manufacturing a flexible printed circuit board according to an embodiment of the present invention. In this example, as described below, a flexible printed circuit board was manufactured according to the method shown in FIGS.

First, as shown in FIG. 1, a base layer 2 made of polyamideimide was formed on one main surface of the copper foil 1. The underlayer 2 is formed on one main surface of a copper foil having a thickness of 35 μm (F3-WS, manufactured by Furukawa Circuit Foil Co., Ltd.) 1 and polyamideimide insulating varnish (manufactured by Dainichi Seika Kogyo Co., Ltd., Bridinol AI-03). Was applied by a gravure printing method, and the coating film obtained thereby was heated at 200 ° C. for 60 seconds to be dried and cured, thereby obtaining an underlayer ² having a dry basis weight of 15 g / m ² . . Moreover, the gravure printing of the polyamideimide insulating varnish was performed by a rotogravure printing method, and a Roll to Roll method was adopted for a series of processes for forming the underlayer 2.

  Here, the Roll-to-Roll system is a thin film-like or thin-plate-like material wound around a winding core such as a steel tube or a paper tube, and while winding this around another winding core, A method of continuously performing one or more treatments. A process adopting the Roll to Roll method is excellent in productivity, and has a large cost merit when a large number of the same structure is manufactured.

Next, as shown in FIG. 4, a polyethylene naphthalate film as a base film 4 was bonded to the copper foil 1 provided with the base layer 2 by dry lamination using a polyurethane-based adhesive. More specifically, first, a polyurethane-based adhesive (manufactured by Toyo Morton Co., Ltd., Adcoat 76P1) is applied on the base layer 2 so that an adhesive layer 3 having a dry basis weight of 9 g / m ² is obtained. The coating film was dried. Thereafter, a polyethylene naphthalate film having a thickness of 50 μm (Teonex Q83, manufactured by Teijin DuPont Films Ltd.) was stacked on the adhesive layer 3 and passed between heating rolls. The Roll to Roll method was adopted for a series of processes for bonding the copper foil 1 and the base film 4 together. As described above, a flexible printed circuit board laminate 10 was obtained.

  Next, as shown in FIGS. 5 and 6, a resist pattern 5 having a shape corresponding to the conductor pattern 1 ′ to be formed was formed on the copper foil 1. More specifically, thermosetting etching resist ink (manufactured by Toyobo Co., Ltd., ER-304N) is applied only to the position corresponding to the conductor pattern 1 ′ to be formed on the surface of the copper foil 1 by the rotary gravure printing method. Was applied. Further, a Roll to Roll method was adopted as a process for forming the resist pattern 5.

  Thereafter, as shown in FIG. 6, the copper foil 1 was etched using the resist pattern 5 as an etching mask to form a conductor pattern 1 '. Here, a ferric chloride aqueous solution was used as an etchant. Further, as shown in FIG. 7, the resist pattern 5 was peeled off from the conductor pattern 1 'using a sodium hydroxide aqueous solution. Subsequently, this was thoroughly washed with water and dried. A Roll to Roll method was adopted for a series of processes for etching, peeling, washing with water, and drying. As described above, a flexible printed circuit board 100 wound up in a roll shape was obtained.

(Example 2)
Polyimide insulating varnish (manufactured by Ube Industries, Ltd., U- Varnish A) except that drying basis weight using the formed the undercoat layer 2 of 13 g / m ² is by the same method as that described in Example 1, A flexible printed circuit board 100 wound up in a roll shape was obtained.

Example 3
A flexible printed circuit board 100 wound up in a roll shape was obtained in the same manner as described in Example 1, except that a polyethylene naphthalate film having a thickness of 75 μm was used as the base film 4.

Example 4
Polyamideimide insulating varnish (Dainichiseika Color & Chemicals Mfg. Co., Burijinoru AI-03) except that drying basis weight using the formed the undercoat layer 2 of 7 g / m ^2, similar to that described in Example 1 By the method, the flexible printed circuit board 100 wound up in a roll shape was obtained.

(Example 5)
Except that the adhesive layer 3 having a dry basis weight of 3 g / m ² was formed using a polyurethane adhesive (manufactured by Toyo Morton Co., Ltd., Adcoat 76P1), the same method as described in Example 1 was used. A flexible printed circuit board 100 wound up in a roll shape was obtained.

(Comparative Example 1)
A flexible printed circuit board 100 wound up in a roll shape was obtained by the same method as described in Example 1 except that the base layer 2 was not formed.

(Example 6)
Epoxy coatings (Tanaka Chemical Co., AON427) except that drying basis weight using the formed the undercoat layer 2 of 15 g / m ^2, by the same method as described in Example 1, into a roll The wound flexible printed circuit board 100 was obtained.

(Comparative Example 2)
A flexible printed circuit board wound up into a roll by the same method as described in Example 1 except that a polyethylene terephthalate film (Lumirror, manufactured by Toray Industries, Inc.) having a thickness of 50 μm was used as the base film 4. 100 was obtained.

(Comparative Example 3)
A flexible printed circuit board 100 wound up in a roll shape was obtained by the same method as described in Example 5 except that the base layer 2 was not formed.

(Comparative Example 4)
In the same manner as described in Example 5, except that the base layer 4 was not used and a polyethylene terephthalate film (Lumirror, manufactured by Toray Industries, Inc.) having a thickness of 50 μm was used as the base film 4, A flexible printed circuit board 100 wound up was obtained.

  About each flexible printed circuit board 100 obtained by the said Examples 1 thru | or 6 and the comparative examples 1 thru | or 4, by each test shown below, copper foil peeling strength, a flame retardance, the adhesiveness after an etching, and heat resistance Evaluated. The results are summarized in Table 1.

(1) Copper foil peel strength A test was conducted in accordance with JIS C 5016.

(2) Flame retardancy A test was conducted in accordance with UL94.

(3) Adhesiveness after etching The flexible printed circuit board 100 wound up in a roll shape is maintained at a temperature of 50 ° C. for 120 hours, and then the flexible printed circuit boards 100 do not adhere to each other when the flexible printed circuit board 100 is drawn out. It was evaluated whether or not it could be peeled.

(4) Heat resistance (appearance after heat treatment)
A thermosetting solder resist ink (manufactured by Taiyo Ink Manufacturing Co., Ltd., TF-200FR1 / MK-20S) was screen printed on the flexible printed circuit board 100. Subsequently, this coating film was dried and cured by heating at 150 ° C. for 30 minutes to form a resist pattern.

  Next, this sample was cut into a size of 50 mm × 50 mm. The cut sample piece is attached to an aluminum plate (1N30-H18, thickness 0.2 mm) using a heat-resistant double-sided adhesive tape, and the maximum surface temperature of the sample piece is maintained at 240 ° C. for 5 seconds using an infrared heating device. Heated to be.

  Then, the sample piece was peeled from the aluminum plate and the state was observed visually. Specifically, it was examined whether or not a shape change such as warpage occurred in the sample piece peeled from the aluminum plate. Thereby, the heat resistance of the flexible printed circuit board 100 was evaluated.

  As shown in Table 1, the flexible printed circuit boards 100 of Examples 1 to 6 were excellent in adhesion and heat resistance after etching. In particular, the flexible printed circuit boards 100 of Examples 1 to 3 were excellent in all of the copper foil peel strength, flame retardancy, adhesion after etching, and heat resistance. In addition, the flexible printed circuit boards 100 of Examples 1 to 3 and 6 were superior in copper foil peel strength as compared to the flexible printed circuit boards 100 of Examples 4 and 5. In addition, the flexible printed circuit boards 100 of Examples 1 to 3 and 5 were superior in flame retardancy compared to the flexible printed circuit boards 100 of Examples 4 and 6.

  On the other hand, the flexible printed circuit boards 100 of Comparative Examples 1, 3, and 4 were in close contact with each other, and as a result, the flexible printed circuit boards 100 were damaged when rolled out from the roll-up state. Moreover, the flexible printed circuit board 100 of the comparative examples 2 and 4 produced the curvature by heat processing. Furthermore, the flexible printed circuit boards 100 of Comparative Examples 1, 3, and 4 were inferior in copper foil peel strength and flame retardancy.

Sectional drawing which shows schematically the laminated body for flexible printed circuit boards which concerns on 1 aspect of this invention. Sectional drawing which shows schematically an example of the flexible printed circuit board which can be manufactured using the laminated body of FIG. Sectional drawing which shows schematically the manufacturing method of the flexible printed circuit board based on the Example of this invention. Sectional drawing which shows schematically the manufacturing method of the flexible printed circuit board based on the Example of this invention. Sectional drawing which shows schematically the manufacturing method of the flexible printed circuit board based on the Example of this invention. Sectional drawing which shows schematically the manufacturing method of the flexible printed circuit board based on the Example of this invention. Sectional drawing which shows schematically the manufacturing method of the flexible printed circuit board based on the Example of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Copper foil, 1 '... Conductor pattern, 2 ... Base layer, 3 ... Adhesive layer, 4 ... Base film, 5 ... Resist pattern, 10 ... Laminated body for flexible printed circuit boards, 100 ... Flexible printed circuit board.

Claims (4)

  Copper foil, base layer made of heat-resistant resin formed on one main surface of the copper foil, adhesive layer made of polyurethane adhesive provided on the base layer, the base layer and the adhesive A laminate for a flexible printed circuit board, comprising: a base film made of polyethylene naphthalate bonded to the copper foil via a layer. ^2. The flexible print according to claim 1, wherein the heat-resistant resin is a polyamide-imide resin or a polyimide-based resin, and a dry basis weight of the base layer is in a range of 10 g / m ^{2 to} 40 g / m ^2. Laminate for circuit board. The laminate for a flexible printed circuit board according to claim 1 or 2, wherein the dry basis weight of the adhesive layer is in the range of 5 g / m ^{2 to} 15 g / m ² .   It is a flexible printed circuit board manufactured using the laminated body for flexible printed circuit boards of any one of Claim 1 thru | or 3, Comprising: The said copper foil is patterned into the conductor pattern, It is characterized by the above-mentioned. Flexible printed circuit board.

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