JP2002252469A - Multilayer flexible printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer flexible printed wiring board where the yield of a boring process by drilling or die-punching is high for excellent hole-opening workability. SOLUTION: A single-sided or both-sided flexible printed wiring board and an adhesive sheet are used to form circuit layers comprising at least two layers. A Young's modulus of each adhesive is 1300 MPa or higher at the boring process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer flexible printed wiring board having excellent drilling workability in a drilling process.

[0002]

2. Description of the Related Art In recent years, the electronics field has been remarkably developed, and in particular, electronic devices for communication and consumer use have been reduced in size, weight, and density, and demands for these performances have become increasingly sophisticated. I have. In response to such demands, flexible printed wiring boards have flexibility and can withstand repeated bending, so that they can be mounted three-dimensionally and with high density in a narrow space, and can be used for wiring, cables, or connectors to electronic devices. Applications are expanding as composite parts with added functions. In particular, recently, with the miniaturization and high performance of electronic devices, there has been a tendency to increase the number of flexible printed wiring boards. This multilayer flexible printed wiring board has two or more circuit layers, and requires a drilling step by punching with a drill or a die. Therefore, defective products are more likely to appear than ordinary single-sided products. At present, the yield is lower than that of single-sided flexible printed wiring boards.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a multilayer flexible printed wiring board having a high yield in a drilling step by punching or punching a multilayer flexible printed wiring board and having excellent drilling workability. To provide.

[0004]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve such problems, and as a result, by limiting the Young's modulus of an adhesive used for a multilayer flexible printed wiring board, a drilling process is performed. It was found that the properties were improved, and the present invention was completed. That is, the present invention uses a single-sided or double-sided flexible printed wiring board and an adhesive sheet.
In a multilayer flexible printed wiring board having at least one circuit layer, the multilayer flexible printed wiring is characterized in that, at the time of drilling, the Young's modulus of the adhesive used for these is 1,300 MPa or more. It is a board.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The multilayer flexible printed wiring board (hereinafter sometimes abbreviated as multilayer FPC) in the present invention is a flexible printed wiring board having a circuit formed on a single-sided or double-sided flexible printed wiring board by a conventional method, an adhesive sheet and / or a coverlay. It is a flexible printed wiring board composed of a film and having two or more circuit layers. The flexible printed wiring board used for this multilayer flexible printed wiring board is obtained by laminating and integrating an electrically insulating base film and a metal foil via an adhesive, and a single-layer metal foil is used for one-sided flexible printing. Wiring substrates and two-layer substrates are referred to as double-sided flexible printed wiring substrates.

[0006] The cover lay film in the present invention is obtained by applying an adhesive to one surface of an electrically insulating base material film to make the semi-cured state. No, the same applies hereinafter.) In addition, the adhesive sheet is obtained by applying an adhesive to one side of the release material and bonding the release material to a semi-cured state. The flexible printed wiring board and the flexible printed wiring board are bonded to each other to perform multi-layer flexible printing. It is used as an adhesive material when manufacturing a wiring board, when bonding a flexible printed wiring board and a reinforcing board, and the like.

[0007] Examples of the electrically insulating film in the present invention include a polyimide film, a PET (polyethylene terephthalate) film, a polyester film, a polyparabanic acid film, a polyetheretherketone film, a polyphenylene sulfide film, an aramid film and the like. A polyimide film is particularly used because of its heat resistance, dimensional stability, mechanical properties, and the like. The thickness of the electrically insulating film in the present invention is usually 12.5 to
Although it is in the range of 75 μm, an appropriate thickness may be used as needed. Further, one or both surfaces of these films may be subjected to a surface treatment such as a sand blast treatment.

Examples of the metal foil in the present invention include an electrolytic copper foil, a rolled copper foil, an aluminum foil, a tungsten foil, an iron foil and the like. Generally, the metal foil is excellent in workability, flexibility, electric conductivity and the like. Electrolytic copper foil or rolled copper foil is used. The thickness of the metal foil is generally 18-70 μm,
It is determined as appropriate depending on the usage conditions and the like.

For the adhesive in the present invention, either a thermoplastic resin or a thermosetting resin which is already known may be used as a raw material. Examples of the thermoplastic adhesive include polyimide, polyamide and modified resins thereof,
Nylon / epoxy, NB as thermosetting adhesive
R / phenol type, NBR / epoxy type, polyester / epoxy type, imide / epoxy type and the like can be mentioned. The thickness of the adhesive layer varies depending on the application, and is generally 10 to 20 μm for a flexible printed wiring board, 15 to 50 μm for a coverlay film, and 15 to 50 μm for an adhesive sheet. In the present invention, it is necessary that the Young's modulus of the adhesive after curing is 1,300 MPa or more at the time of performing the boring process, and more preferably, 1,400 MPa.
a or more and 3,000 or less. If the Young's modulus of the adhesive after curing is less than 1,300 MPa, adhesive scum adheres to the inside of the drill hole, and there is a high possibility that plating failure (continuity failure) occurs during through-hole plating, so that multilayer flexible printed wiring is required. Plate yield and reliability are reduced. Factors that determine the Young's modulus of the cured adhesive are the type, composition,
The conditions include the curing conditions of the adhesive, and the mixing ratio of the condensation resin having two or more functional groups. Since the relationship between these factors and the Young's modulus is not directly related to the present invention, a detailed description is omitted.

Drilling and die punching are examples of drilling processes for the multilayer flexible printed wiring board. The multilayer flexible printed wiring board of the present invention is preferably drilled. Furthermore, in the present invention, using a single-sided or double-sided flexible printed wiring board and an adhesive sheet, the multi-layer flexible printed wiring board in which two or more circuit layers are formed is excellent in drilling workability, In the drilling of a multilayer flexible printed wiring board in which four or more circuit layers are formed using a single-sided or double-sided flexible printed wiring board and an adhesive sheet, more excellent drilling workability can be obtained.

[0011]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

<< Various Substrates >> Sources and specifications of various substrates used in Examples are shown. 1. CCL (Flexible Printed Wiring Board) ・ RAS32S57 (Shin-Etsu Chemical Co., Ltd. single-sided CCL trade name) polyimide film 1 mil / adhesive 13 μm / rolled copper foil 1/2 oz ・ RAS32S27 (Shin-Etsu Chemical Co., Ltd. single-sided CCL trade name) polyimide film 1. mil / adhesive 13 μm / rolled copper foil 1/2 oz · RAS32D57 (Shin-Etsu Chemical Co., Ltd. double-sided CCL trade name) polyimide film 1 mil / adhesive 13 μm / rolled copper foil 1/2 oz 2. Coverlay film CA333 (Shin-Etsu Chemical Co., Ltd. CL trade name) polyimide film 1 mil / adhesive 25 μm CA323 (Shin-Etsu Chemical Co. Ltd. CL trade name) polyimide film 1 mil / adhesive 25 μm Adhesive sheet E33 (BS trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) 25 μm adhesive (RAS32S57 and RAS32S27 are single-sided CCL
Therefore, the types of the adhesives are different from each other. The former has a larger Young's modulus than the latter. RAS32D57 is double-sided C
The adhesive used in CL is the same as that used for RAS32S57. CA333 and CA323 differ in the type of adhesive used. The former has a larger Young's modulus than the latter. )

<< Physical Property Evaluation Method >> The physical properties of the multilayer FPC of the present invention were measured by the following methods. 1. Measurement of Young's modulus According to ASTM B882. Cut the sample into 1/2 inch x 5 inch shape
/ Min was measured at a speed of / min, and the Young's modulus was determined from the obtained SS curve. As a sample, an uncured adhesive sheet was prepared, and a heat sheet up to the point when drilling in each processing step was added thereto was used. That is,
Table 1 shows the measured values for the flexible printed wiring board (electrically insulating film, adhesive layer, laminate made of copper foil), adhesive sheet, and coverlay film adhesive layer.
It described in. 2. Evaluation of drill workability PS100 manufactured by Sumitomo Electric (diameter: 1.00 mm / length: 8.0)
mm), rotation speed 90,000 rpm, INFEDED
336 holes each having a diameter of 1 mm were opened at 2.4 m / min, and the appearances of these holes were observed with a 60-fold magnifying glass, and evaluated based on the following criteria (see the explanatory diagram of FIG. 4). A: Drill scum adheres inside the hole B: Drill scum of 200 μm or more adheres inside the hole C: Drill scum less than 200 μm adheres inside the hole D: No drill scum adheres

(Embodiment 1) RAS32S5 with single-sided CCL
7 and the adhesive sheet E33 were used to fabricate a multilayer FPC having a structure as shown in FIG. 1 (press conditions: 180 ° C.,
4.9 MPa, 90 minutes). The drill workability was evaluated for this, and the results are shown in Table 1 together with the Young's modulus measured by the above method.

Example 2 Double-sided CCL RAS32D5
7, two adhesive sheets E33 and coverlay film C
A multi-layer FP having a structure as shown in FIG.
C was prepared (press conditions: 160 ° C., 4.9 MPa,
30 minutes). After performing a heat treatment at 160 ° C. for 5 hours, drill workability was evaluated. The results are shown in Table 1 together with the Young's modulus measured by the above method.

Example 3 Double-sided CCL RAS32D5
7 and a 25 μm-thick thermoplastic polyimide resin-based adhesive sheet to prepare a multilayer FPC having a structure as shown in FIG. 3 (press conditions: 200 ° C., 4.9 MPa, 10 μm).
Minutes). The drill workability was evaluated for this, and the results are shown in Table 1 together with the Young's modulus measured by the following method.

Comparative Example 1 Single-sided CCL RAS32S5
7 and the adhesive sheet E33 were used to fabricate a multilayer FPC having a structure as shown in FIG. 1 (press conditions: 160 ° C.,
4.9 MPa, 30 minutes). After heat treatment at 160 ° C. for 1 hour, drill workability was evaluated. The results are shown in Table 1 together with the Young's modulus measured by the above method.

(Comparative Example 2) RAS32S2 of single-sided CCL
7 and the adhesive sheet E33 were used to fabricate a multilayer FPC having a structure as shown in FIG. 1 (press conditions: 160 ° C.,
4.9 MPa, 30 minutes). After performing a heat treatment at 160 ° C. for 5 hours, drill workability was evaluated. The results are shown in Table 1 together with the Young's modulus measured by the above method.

Comparative Example 3 Double-sided CCL RAS32D5
2 was used, and a multilayer FPC having a structure as shown in FIG. 2 was prepared using two sheets of a thermoplastic polyimide resin-based adhesive sheet having a thickness of 25 μm and a coverlay film CA333 (press conditions: 160 ° C., 4.9 MPa, 30 minutes). The drill workability was evaluated for this, and the results are shown in Table 1 together with the Young's modulus measured by the above method.

Comparative Example 4 Double-sided CCL RAS32D5
7, two adhesive sheets E33 and coverlay film C
Multi-layer FP using two A323s and having a structure as shown in FIG.
C was prepared (press conditions: 160 ° C., 4.9 MPa,
30 minutes). After heat treatment at 160 ° C. for 3 hours, drill workability was evaluated, and the results are shown in Table 1 together with the Young's modulus measured by the above method.

[0021]

[Table 1]

(Summary of Examples) In Examples 1 to 3, the Young's modulus of all the adhesives involved in the copper-clad laminate, the adhesive sheet, and the coverlay film is 1,300 or more, and the drillability is C. , D. This proved a clear correlation between the Young's modulus of 1,300 or more and the excellent drill workability. On the other hand, in Comparative Examples 1 to 4, the adhesive (layer) involved in the copper-clad laminate, the adhesive sheet, and the coverlay film
If one of the Young's moduli is less than 1,300,
The drill workability was concentrated on A and B, which proved to be impractical.

[0023]

According to the present invention, it is possible to provide a multilayer flexible printed wiring board having excellent drilling workability, thereby increasing the yield and reliability of the flexible printed wiring board. Its utility is high.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a cross section of an example of a multilayer flexible printed wiring board according to the present invention.

FIG. 2 is an explanatory diagram of a cross section of another example of the multilayer flexible printed wiring board according to the present invention.

FIG. 3 is an explanatory diagram of another example of the multilayer flexible printed wiring board according to the present invention.

FIG. 4 is an explanatory diagram showing a state of attachment of drill scum inside a drill hole in a drill workability test of an example.

[Explanation of symbols]

 1 rolled copper foil, 2 adhesive (coverlay film), 3 adhesive layer, 4 adhesive sheet, 5 polyimide film.

Claims (1)

[Claims] 1. An adhesive used in a single-sided or double-sided flexible printed wiring board and a multilayer flexible printed wiring board in which two or more circuit layers are formed using an adhesive sheet at the time of forming a hole. Wherein the Young's modulus of the multilayer flexible printed wiring board is 1,300 MPa or more.