JPH06350255A - Production of multilayer printed wiring board - Google Patents

Abstract

PURPOSE:To provide a method for producing a rigid flexible multilayer printed wiring board having highly reliable rigid part and flexible part. CONSTITUTION:A printed wiring board having at least one flexible layer is combined with a printed wiring board having at least one rigid layer to produce a multilayer printed wiring board wherein no adhesive is used on the circuit at the time of formation of a protective film layer in order to protect the flexible layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to improve the reliability of a rigid flexible multilayer printed wiring board having a rigid portion and a flexible portion. Rigid-flexible multilayer wiring board is capable of automatically forming a connector by processing a printed board and mounting components, and then removing a part of the rigid part and exposing a part of the flexible board coated with a layer having a flexible function. Is a feature. In this multilayer printed wiring board, the connection terminals of the connector for connecting the rigid portion and the flexible portion can be reduced, so that the mounting density of the printed wiring board can be significantly increased and the mounting density can be improved. In the future, it is expected that it can be widely applied to electronic porcelain that aims to be light, thin, short and small. Further, in the rigid flexible multilayer printed wiring board, the work of removing a part of the rigid portion is performed after mounting the components of the printed wiring board, so that the component mounting process can be simplified.

[0002]

2. Description of the Related Art Generally, as a structure of a rigid flexible multilayer printed wiring board, after forming a circuit on a flexible copper clad board, a high heat resistant resin film such as polyimide is used as an epoxy resin or an acrylic resin to protect the circuit. It is formed by adhering a thermosetting resin such as the above via an adhesive containing a plasticizer, and by stacking a rigid inner layer or outer layer printed wiring board using prepreg layers on the upper and lower sides thereof. Prior to adhering the heat resistant film, the heat resistant film with an adhesive (coverlay film) is dried at 100 to 120 ° C. for about 10 to 30 minutes in order to remove moisture absorbed by the polyimide film. . If the drying is too short, the moisture contained in the heat-resistant film will not be completely removed, and the heat resistance of the rigid-flexible multilayer printed wiring board after lamination will be deteriorated. On the contrary, if the drying is too long, the curing of the adhesive progresses, and the moldability and adhesion of the multilayer printed wiring board are impaired.

The thermal expansion coefficient of the adhesive used for adhering the heat-resistant film is larger than that of each material forming the rigid portion, so that the thermal expansion coefficient is different when a thermal cycle is applied after the through-hole plating is formed. As a result, it causes a barrel crack in the through hole plating, which causes a decrease in reliability of the through hole plating.

[0004]

DISCLOSURE OF THE INVENTION The present invention has improved the method of laminating a heat-resistant film used for circuit protection of a flexible part in the method of manufacturing a rigid flexible multilayer printed wiring board described above, and has a highly reliable multilayer structure. It relates to obtaining a printed wiring board.

[0005]

That is, the present invention has found that high reliability can be obtained by producing a rigid flexible multilayer printed wiring board without using an adhesive for bonding the heat resistant film. And
As a method therefor, it has been found that a method of using a glass cloth having a flexible function even after curing or a method of using a prepreg having a high heat resistant resin fiber as a base material is effective. As a method of using the prepreg having a flexible function even after curing, a method of using the prepreg layer itself as a circuit protective layer by sandwiching the upper and lower sides of a flexible copper clad plate on which a circuit is formed with this prepreg and laminating two By laminating the above-mentioned flexible copper clad board using this prepreg, both methods of using the base material part of the flexible copper clad board as a circuit protection layer are possible.

The structure of the present invention will be described below. The multilayer printed wiring board of the present invention is a rigid flexible multilayer printed wiring board in which at least one inner layer board or outer layer board has a flexible function, and the inner layer board or outer layer board having the flexible function is used. The general manufacturing method of a rigid multilayer printed wiring board can be used as it is, except that the circuit protection is performed. The flexible substrate layer is generally composed of an aromatic polyamideimide film or an aromatic polyimide film and a metal foil such as a copper foil which are heat-bonded with an adhesive, but the adhesive is not used. With a thermosetting resin having a flexible function even after curing by directly adding a flexibility-imparting agent such as a rubber component to the surface layer of the aromatic polyamide-imide or the aromatic polyimide precursor, the metal foil is arranged. It is also possible to use a double-sided plate or a single-sided plate in which a prepreg impregnated with a woven glass cloth or a woven cloth made of a resin such as wholly aromatic polyamide is impregnated with a varnish Conceivable.

An intermediate layer having a flexible function,
Alternatively, as a prepreg having a flexible function even after curing for forming a circuit protective layer provided on the outer layer circuit surface, a glass woven fabric or a whole woven fabric can be used in a varnish of a thermosetting resin to which a flexibility-imparting agent such as a rubber component is added. A prepreg impregnated with a woven fabric made of a super heat-resistant resin such as aromatic polyamide is used.

[0008]

The present invention will be described with reference to the following examples. Example 1 Insulating layer thickness of 0.025 mm and copper foil thickness of 35 μm made of polyimide flexible double-sided copper clad board (Nippon Steel Chemical Co., Ltd., trade name Espanex) of 2500 pieces arranged on a basic lattice (2.54 mm pitch). A flexible inner layer board having an inner layer pattern of 6 mmφ lands was dried at 120 ° C. for 1 hour, and 20 parts by weight of acrylonitrile butadiene rubber was added to the resin, and 100 parts by weight of brominated bisphenol A type epoxy was used as a main component and dicyandiamide. 4 parts by weight and 0.2 parts by weight of 2 methyl 4 ethyl imidazole are used as a curing agent and a curing catalyst, respectively, and methyl ethyl ketone 80
Parts by weight and 14 parts by weight of dimethylformamide mixed with a mixed varnish impregnated with 10801 type glass cloth having a thickness of 0.051 mm and dried, and scissors with a flexibility-imparting prepreg (resin amount 70%). A 0.6mmt outer layer glass epoxy single-sided copper clad plate for outer layer (outer layer copper foil thickness 18 μm) is laminated one by one, and laminated at a molding temperature of 175 ° C., a molding pressure of 30 kg · f / cm ^{2 and a} molding time of 2 hours. By pressing, a flexible rigid multilayer copper clad plate having the layer structure shown in FIG. 1 was obtained.

A 0.35 mmφ hole was drilled in the obtained flexible rigid multilayer copper clad plate, 2500 holes were made in the land position of the inner layer at a drill rotation speed of 80 krpm and a feed rate of 1.6 m / min. Through-hole plating having a thickness of 25 μm was formed by plating and copper sulfate plating. An outer layer pattern was formed by a tenting method to connect adjacent through holes having lands in series at the positions of the through holes of the copper clad plate on which the above through hole plating was formed to obtain a printed wiring board for temperature cycle test.

The above-mentioned printed circuit board for temperature cycle test is put in a temperature cycle test tank and MIL-STD202FM.
ETHOD 102A temperature cycle test condition C (-65
C. and 125.degree. C.), and the change in through-hole conduction resistance was measured for each cycle. The results are shown in Table-1. Also, a sample obtained by removing the outer layer copper foil of the flexible rigid multilayer copper clad plate without forming the multilayer circuit by etching method was cut into 10 cm × 10 cm, boiled in boiling water for 2 hours, and then in a solder bath at 260 ° C. To 20
Second dipping was performed to investigate heat resistance after moisture absorption. The results are shown in Table-2.
It was shown to.

Example 2 Two flexible double-sided copper clad plates used in Example 1 were prepared, and one side of the copper foil was removed by etching to remove the copper foil. An inner layer circuit similar to that of Example 1 was formed on one side of the copper foil at 120 ° C. After drying for 1 hour, it was sandwiched between the flexibility-imparting prepregs used in Example 1, and 0.1 mmt glass epoxy prepregs were placed on the upper and lower sides thereof, respectively. Laminating presses were performed under the same conditions as in Example 1 with a structure in which clad plates (outer layer copper foil thickness 18 μm) were stacked one by one to obtain a flexible rigid multilayer copper clad plate having a layer structure shown in FIG.

The obtained flexible rigid multilayer copper clad plate was processed in the same manner as in Example 1 and subjected to a temperature cycle test and a moisture absorption heat resistance test. The results are shown in Tables 1 and 2.

Example 3 Flexibility-imparting prepreg 25 parts acrylonitrile butadiene rubber 20 parts triazine prepolymer 20 parts brominated bisphenol A type epoxy 50 parts methyl ethyl ketone 50 parts dimethylformamide 20 parts 1 in a mixed varnish
Example 2 except that a flexibility-imparting prepreg produced by impregnating 080 type glass cloth with a resin amount of 70% was used.
The flexible rigid multilayer board manufactured under the same conditions as in Example 1 was processed by the same method as in Example 1 and subjected to a temperature cycle test and a moisture absorption heat resistance test. The results are shown in Tables 1 and 2.

Comparative Example 1 A flexible inner layer plate on which a circuit was formed by the same method as in Example 1 was dried under the conditions of 120 ° C. for 1 hour, and a thickness of 2
A coverlay film (DuPont, trade name Pyralux) in which an acrylic adhesive is coated on one side of a 5 μm polyimide film to a thickness of 50 μm,
What was dried under the condition of 20 minutes was laminated with the adhesive layer on the inner copper foil side, and 0.1mmt glass epoxy prepreg was placed on each of the upper and lower sides, and 0.5mm was placed on the upper and lower sides.
A flexible rigid multi-layered copper clad having a layer structure shown in FIG. 3 in which the glass epoxy single-sided copper clad boards for outer layers (outer layer copper foil thickness 18 μm) are stacked one by one under the same conditions as in Example 1. I got a plate. The plexiable rigid multilayer copper clad plate thus obtained was processed in the same manner as in Example 1 and subjected to a temperature cycle test and a moisture absorption heat resistance test. The results are shown in Tables 1 and 2.

[0015]

[Table 1] Through-hole resistance value after temperature cycle test of each printed wiring board Number of cycles Initial value 5 cycles 25 cycles 50 cycles 100 cycles Example 1 10.0Ω 10.5Ω 10.5Ω 10.4Ω 11.3Ω Example 2 11.0Ω 11.2Ω 10.9Ω 11.0Ω 10.7Ω Example 3 10.4Ω 10.6Ω 10.5Ω 10.4Ω 10.7Ω Comparative Example 1 10.9Ω 10.9Ω 10.3Ω Open Open

[0016]

[Table 2] Moisture absorption heat resistance test result of each printed wiring board Abnormality etc. Example 1 No delamination after soldering Example 2 Same as above Example 3 Same as above Comparative Example 1 Coverlay film after soldering There is the occurrence of delamination between the glass epoxy prepreg

[0017]

As is clear from the detailed description of the invention and the examples, the flexible rigid multilayer printed wiring board according to the present invention has excellent through-hole reliability and moisture absorption / heat resistance. It is possible to manufacture a flexible rigid multilayer printed wiring board with high performance, and its industrial significance is high.

[0018]

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing a laminated structure of a flexible rigid multilayer copper clad plate.

FIG. 2 is a sectional view schematically showing a laminated structure of a flexible rigid multilayer copper clad plate.

FIG. 3 is a cross-sectional view showing a schematic laminated structure of a flexible rigid multilayer copper clad plate.

[Explanation of symbols]

 The symbols in FIGS. 1 to 3 indicate the following, respectively. A: Flexible inner layer board with insulation layer thickness of 0.025 mm B: Flexible prepreg with thickness of 0.07 mm B ': Glass epoxy prepreg with thickness of 0.1 mm C: Glass epoxy single-sided copper clad board with insulation layer thickness of 0.5 mm C': Insulation Glass-epoxy single-sided copper clad board with a layer thickness of 0.4 mm D: Coverlay film with a thickness of 0.025 mm

Front page continuation (72) Inventor Koichi Nakano 6-1, 1-1 Shinjuku, Katsushika-ku, Tokyo Mitsubishi Gas Chemical Co., Ltd. Tokyo factory

Claims (4)

[Claims] 1. A multilayer printed wiring board in which a printed wiring board having at least one layer of a flexible function and a printed wiring board having at least one layer of a rigid function are combined to protect a circuit of a flexible layer. A method for manufacturing a multilayer printed wiring board characterized by not using an adhesive when forming a protective film layer on a circuit 2. The method for producing a multilayer printed wiring board according to claim 1, wherein a glass cloth or a highly heat resistant resin fiber having a flexible function after curing is used as a base material for sticking a protective film of a flexible circuit. For manufacturing a multilayer printed wiring board characterized by using a prepreg 3. The method for manufacturing a multilayer printed wiring board according to claim 2, wherein the multilayer printed wiring board is formed by heating and pressing a prepreg having a flexible function even after curing to protect the flexible circuit in the multilayer printed wiring board. 4. The method for manufacturing a multilayer printed wiring board according to claim 2, wherein the flexible copper clad board on which two or more circuits are formed is multilayered by using a prepreg having a flexible function even after curing. Characteristic multi-layer printed wiring board manufacturing method