JPH05327209A - Manufacture of bonding sheet for multiple layer and of multilayer substrate - Google Patents

Abstract

PURPOSE:To eliminate formation of a through hole and to attain high reliability by a method wherein one surface of a prepreg layer prepared by impregnating an inorganic or organic fiber base with thermosetting resin is coated with a flexible thermosetting bonding agent layer of a specified thickness and integrated therewith. CONSTITUTION:A double-layered bonding sheet for a multiple layer of which one layer is a prepreg layer 2a prepared by impregnating an inorganic fiber base or an organic fiber base with thermosetting resin and the other layer is a flexible thermo-setting bonding agent layer 2b is stuck on a rigid printed wiring board and a flexible printed wiring board in such a manner that the prepreg face 2a is disposed on the rigid printed wiring board side and the flexible thermosetting bonding agent layer 2b on the flexible printed wiring board side. On the occasion, bonding with a cover lay film or a base film of the flexible printed wiring board is made by the flexible thermosetting bonding agent layer 2b which is a thin film of 10 to 50mum. By using the double-layered bonding sheet for the multiple layer as a bonding layer in this way, a flex-rigid multilayer board of high reliability can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is used for a printed wiring board for electric circuits. The present invention relates to multilayer substrates. The present invention relates to a highly reliable multilayer substrate and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, electronic devices have been made smaller, lighter and faster, and there is a demand for thinner and lighter multi-layer substrates for printed wiring boards that compose the same. In order to further increase the number of layers of printed wiring boards and to omit the connectors and cables used for connecting between printed wiring boards, one flexible printed wiring board must share some layers of multiple multilayer rigid printed wiring boards. A so-called flex-rigid multi-layer board, which is integrated as a unit, has been receiving attention.

In order to manufacture a flex-rigid multilayer board, it is necessary to bond a rigid printed wiring board and a flexible printed wiring board. The surface of the flexible printed wiring board to be bonded is the base film or flexible printed wiring board. It is often the film side of the coverlay film that protects the surface. However, the film of the flexible printed wiring board has weak adhesiveness, and when the prepreg used for a rigid wiring board is usually used as the adhesive sheet at the time of bonding with the film surface, the adhesive strength was insufficient. .. Therefore, a flexible thermosetting adhesive sheet used for a flexible printed wiring board is usually used for bonding the rigid printed wiring board and the flexible printed wiring board.

Generally, a polyimide film or a polyester film is used as a cover lay film and a base film of a flexible printed wiring board. However, when a thermosetting resin such as epoxy resin, polyimide resin, and phenol resin is used, a sufficient adhesive force is obtained. I can't get it.

For this reason, a method using a flexible thermosetting adhesive sheet, which is generally used for flexible printed wiring boards, has been used for bonding the rigid printed wiring board and the flexible printed wiring board. Normally, to make a flex-rigid multilayer board, a flexible printed wiring board with conductive circuits on one or both sides is covered with a coverlay film on all or part of one or both sides to protect the circuit and enhance flexibility. Further, one or a plurality of rigid printed wiring boards having conductive circuits formed on one side or both sides, which are bonded to each other and are bonded to the upper and lower sides or one side of the rigid printed wiring boards, are bonded via an adhesive sheet to form a multilayer substrate.

FIG. 4 is a sectional view of this conventional structure.
The entire surface of the double-sided flexible printed wiring board 4 is protected by the coverlay film 3, and the coverlay film 3 side and the double-sided rigid printed wiring board 1 side are connected to each other using a flexible thermosetting adhesive sheet 5 to form a conductive circuit ( The shaded portion) is embedded and bonded.

[0007]

However, although the flexible thermosetting adhesive sheet has good adhesiveness to the film surface of the flexible printed wiring board, the flexible thermosetting adhesive sheet is tens of μm thick. When it is attempted to reduce the thickness to a thickness, if there is a conductive circuit in the portion that contacts the flexible thermosetting adhesive sheet, the conductive circuit may not be sufficiently embedded in the insulating layer. On the contrary, if the flexible thermosetting adhesive sheet has a sufficient thickness for embedding the conductive circuit, the thermosetting resin used for the flexible thermosetting adhesive sheet contains a flexible polymer component. Because it is blended,
Thermal expansion is large, and through holes are likely to occur, which causes reliability problems.

An object of the present invention is to eliminate the above-mentioned drawbacks, and to provide a multilayer substrate having excellent adhesion between layers, eliminating the occurrence of through holes, and having excellent reliability, and a manufacturing method thereof. is there.

[0009]

The two-layered multilayer adhesive sheet of the present invention is a state in which an inorganic fiber base material or an organic fiber base material is impregnated with a thermosetting resin, dried, and heat-curable. One side of the prepreg layer of flexible thermosetting adhesive layer 10
It is characterized in that it is covered with a thickness of 50 μm and is integrated.

Further, the multilayer substrate of the present invention is a multilayer substrate including a rigid printed wiring board, a flexible printed wiring board, and an adhesive layer for adhering both of these wiring boards, wherein the two-layered multilayer is used as the adhesive layer. An adhesive sheet for use is used.

In the multilayer substrate of the present invention, the prepreg layer of the double-layered multilayer adhesive sheet is adhered to the rigid printed wiring board side, and the flexible thermosetting adhesive layer is the flexible printed wiring board. It is preferable that the structure is adhered to the side.

Further, the method for producing a multilayer board according to the present invention is the method for producing a multilayer printed board in which a rigid printed wiring board and a flexible printed wiring board are produced by using the multilayer adhesive sheet, Using a double-layered multilayer adhesive sheet, the prepreg layer is arranged on the side of the rigid printed wiring board, and the flexible thermosetting adhesive layer is arranged on the side of the flexible printed wiring board. Including the step of laminating.

At this time, depending on the required thickness or structure of the multilayer board, the rigid printed wiring board and the flexible printed wiring board may be bonded together by using a plurality of the same or various multilayer adhesive sheets. In some cases, at least, using the two-layered multilayer adhesive sheet for adhesion in contact with the flexible printed wiring board,
Arranging the flexible thermosetting adhesive layer of the two-layered multilayer adhesive sheet toward the flexible printed wiring board side,
Good to stick together.

The substrate used for the prepreg layer of the double-layered multilayer adhesive sheet is an inorganic fiber substrate such as glass cloth or glass mat and / or an aromatic polyamide fiber,
One or more organic fibers such as cellulose fibers and polyester fibers can be used, and the material thereof is not particularly limited.

The thermosetting resin used to impregnate the base material used for the prepreg layer of the double-layered multilayer adhesive sheet includes epoxy resin, polyimide resin, bismaleimide triazine resin, phenol resin and the like, and is not particularly limited. The prepreg layer needs to have a thickness sufficient to embed the conductive circuit of the rigid printed wiring board in contact therewith, and it is suitable that the finished thickness after lamination is 0.05 mm to 0.25 mm.

The flexible thermosetting adhesive layer of the double-layered multilayer adhesive sheet is an adhesive in which a flexible polymer is modified with a thermosetting resin to enable thermosetting, and an inorganic filler is added if necessary. Is a sheet. Flexible polymers used for the flexible thermosetting adhesive layer include elastomers such as nitrile rubber, acrylic rubber, urethane rubber, and silicone rubber, and thermoplastic resins such as polyamide resin, polyester resin, and acrylic resin. There is no particular limitation.

The thermosetting resin used for the flexible thermosetting adhesive layer may be an epoxy resin, a polyimide resin, a bismaleimide triazine resin, a phenol resin or the like, and is not particularly limited.

Since the flexible thermosetting adhesive layer has a large thermal expansion, it is preferable to make the adhesiveness to the film surface of the flexible printed wiring board as thin as possible, and a thickness of 10 μm to 50 μm is tested. Was found to be suitable.

The double-layered multi-layered adhesive sheet can be prepared by applying a flexible thermosetting adhesive varnish on one surface of the prepreg layer, drying the varnish, and integrating the prepreg layer into a double-layered structure.

The double-layered multi-layered adhesive sheet can be prepared by forming a double layer by thermocompressing a flexible thermosetting adhesive sheet on one surface of the prepreg layer and integrating them.

[0021]

The multilayer adhesive sheet is an adhesive sheet for adhering a flexible printed wiring board and a rigid printed wiring board, and one layer is a prepreg layer obtained by impregnating an inorganic fiber base material or an organic fiber base material with a thermosetting resin. Is a flexible thermosetting adhesive layer, which is a double-layered multilayer adhesive sheet, with the prepreg surface on the rigid printed wiring board side and the flexible thermosetting adhesive layer on the flexible printed wiring board side. By laying out and adhering to each other, the conductive circuit on the side of the rigid printed wiring board that is in contact with the double-layered multilayer adhesive sheet is sufficiently embedded, and the adhesiveness with the rigid printed wiring board is strengthened, and at the same time the flexible printed wiring board is formed. The adhesiveness of can also be made strong.

In addition, since the double-layered multilayer adhesive sheet is adhered to the cover lay film or the base film of the flexible printed wiring board by the flexible thermosetting adhesive layer which is a thin film of several tens of μm, the through-hole adhesive sheet High reliability can be secured without any occurrence.

[0023]

Embodiments of the multilayer substrate of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view showing an embodiment of the multi-layer substrate of the present invention, showing a six-layer multi-layer substrate. FIG. 2 is a schematic cross-sectional view showing an example of the double-layered multilayer adhesive sheet 2.

The multilayer board of this embodiment comprises a double-sided rigid printed wiring board 1, a double-sided flexible printed wiring board 4 whose upper and lower surfaces are covered with a coverlay film 3, and an adhesive layer for adhering these both wiring boards. In the multi-layer substrate including, the adhesive layer, which is a feature of the present invention, is composed of two layers of a prepreg layer 2a in which a base material is impregnated with a thermosetting resin, and a flexible thermosetting adhesive layer 2b. It is a double-layered, multilayer adhesive sheet 2. In the double-layered multilayer adhesive sheet 2, the prepreg layer 2a is bonded to the double-sided rigid printed wiring board 1 side, and the flexible thermosetting adhesive layer 2b is bonded to the double-sided flexible printed wiring board 4 side. ing.

FIG. 3 is a schematic sectional view showing another example of the double-layered multilayer adhesive sheet according to the present invention. This double-layered multilayer adhesive sheet 2 is obtained by sticking a release film 2c on the flexible thermosetting adhesive layer 2b side of the double-layered multilayer adhesive sheet 2 of FIG.

(Example) (Preparation of prepreg layer) As shown in Table 1, each thermosetting resin was dissolved in an organic solvent and the compounded thermosetting resin varnish was impregnated into each fiber base material, Dry and prepreg 1
4 prepreg layers were prepared.

[0028]

[Table 1] (Preparation of Flexible Thermosetting Resin Varnish) As shown in Table 2, each flexible polymer and each thermosetting resin were dissolved in an organic solvent and blended to prepare a flexible thermosetting adhesive varnish.

[0029]

[Table 2] (Preparation of double-layered multilayer adhesive sheet and six-layer flex-rigid multilayer board) Examples 1 to 10 were combined with the previously prepared prepregs and flexible thermosetting adhesive varnishes to form a double-layered multilayer adhesive. A sheet was prepared, and a method for preparing a six-layer flex-rigid multilayer board using the double-layered multilayer adhesive sheet was shown.

Further, Comparative Examples 1 to 3 show a method for producing a six-layer flex-rigid multilayer board using a prepreg or a flexible thermosetting adhesive sheet made of a flexible thermosetting adhesive varnish. ..

Table 3 shows combinations of the prepreg and the flexible thermosetting adhesive varnish in the double-layered multilayer adhesive sheets of Examples 1 to 10, and the prepregs or the flexible sheets used in the adhesive sheets of Comparative Examples 1 to 3. 1 shows a thermosetting adhesive varnish.

[0032]

[Table 3] (Examples 1 to 6) Polypropylene film (60 μm
Thickness), a flexible thermosetting adhesive varnish is applied with a reverse coater and dried at 130 ° C. for 5 minutes to obtain a flexible thermosetting adhesive with a release film having a thickness of 30 μm and a flexible thermosetting adhesive sheet. did.

The prepreg 1 is placed on the flexible thermosetting adhesive side of the flexible thermosetting adhesive sheet with release film,
Fluororesin release roll and heating roll (surface temperature 120
Temperature of 60 kgf with the glass epoxy prepreg surface on the fluororesin release roll side and the polypropylene film surface of the flexible thermosetting adhesive on the heating roll side.
The pressure-sensitive adhesive sheet was attached at a pressure of / 500 mm and laminated to obtain a double-layered multilayer adhesive sheet 2 with a release film. A double-sided flexible printed circuit board (polyimide film base, conductor layer 35 μm copper foil) is used to form the circuits of the third and fourth layers and the cable part, cut into the required shape, and protect the entire surface. Two cut coverlay films (polyimide film thickness 25μm, adhesive thickness 35μ
m) 3 respectively, and further polyethylene films (100 μm thick) are placed on each outside, fixed, sandwiched between stainless steel mirror surface plates, temperature 160 ° C., pressure 30 kg
It was heated at / cm ² for 1 hour and laminated by pressure, taken out from the stainless mirror face plate, and made into a double-sided flexible printed wiring board 4.

A second layer of circuit is formed on one side of a glass epoxy double-sided board, and the other side is entirely copper foil.
A double-layer double-sided rigid printed wiring board 1 was prepared. A fifth-layer circuit was formed on one side of a glass epoxy double-sided board, and one side was entirely copper foil to obtain a five- and six-layer double-sided rigid printed wiring board 1.

On each of the multi-layered adhesive surfaces on both sides of the double-sided flexible printed wiring board 4 provided with the coverlay film 3,
The double-layered multilayer adhesive sheet 2 with a release film cut into a required shape is peeled off from the polypropylene film, which is a release film, and the flexible thermosetting adhesive surface is directed toward the cover lay film 3 side. A release film (polyethylene 120 μm) for thickness adjustment was placed on the double-sided flexible printed wiring board 4 of the cable portion, which was placed at a predetermined position on the adhesive surface and where the double-layered multilayer adhesive sheet 2 was not placed.

On the third layer circuit side of the double-sided flexible printed wiring board 4 on which the double-layered multilayer adhesive sheet 2 and the thickness adjusting release film are placed, two layers of the double-sided rigid printed wiring board 1 for one and two layers are provided. The second circuit side of the double-sided flexible printed wiring board 4 on which the double-layered multilayer adhesive sheet 2 and the thickness-adjusting release film are placed. The fifth-layer circuit surface of the double-sided rigid printed wiring board 1 for 6 layers is aligned and positioned so that the whole is fixed, sandwiched between stainless steel mirror plates, and heated for 1 hour at a temperature of 160 ° C and a pressure of 30 kg / cm ² , The sheets were laminated by pressure, taken out from the stainless mirror plate, and used as a six-layer substrate.

Next, after drilling and plating the six-layer board, circuits on the first and sixth layers on both surfaces are formed, and unnecessary portions other than the multilayer portion of the double-sided rigid printed wiring board are cut and removed. The cable part was exposed by removing the release film to obtain a six-layer flex-rigid multilayer board having a thickness of 1.6 mm.

(Examples 7 to 9) A flexible thermosetting adhesive varnish was applied to a prepreg with a reverse coater, and 13
It was dried at 0 ° C. for 5 minutes to form a flexible thermosetting adhesive layer 2b having a thickness of 20 μm. Next, since the tackiness remains on the surface of the flexible thermosetting adhesive as it is, a polypropylene film (60 μm thick) is stacked as a release film, and a prepreg surface is provided between the silicone rubber roll and the metal roll on the silicone rubber roll side. Line pressure 60kg with the polyethylene film side of the flexible thermosetting adhesive on the metal roll side
A polyethylene film was pressure-bonded and laminated at f / 500 mm to obtain a two-layered multilayer adhesive sheet 2 with a release film.

Thereafter, the same procedure as in (Examples 1 to 6) is performed,
A six-layer flex-rigid multilayer board having a thickness of 1.6 mm was prepared.
(Example 10) A flexible thermosetting adhesive varnish was applied to a prepreg by a reverse coater and dried at 130 ° C for 5 minutes to form a 30 µm thick flexible thermosetting adhesive layer to form a two-layer structure. The multilayer adhesive sheet 2 was used.

Thereafter, the same procedure as in (Examples 1 to 6) is performed,
A six-layer flex-rigid multilayer board having a thickness of 1.6 mm was prepared.

(Comparative Example 1) A six-layer flex-rigid multilayer board having a thickness of 1.6 mm was prepared in the same manner as in Example except that prepreg 1 was used as the adhesive sheet.

Comparative Example 2 A polypropylene film (60 μm thick) was coated with varnish 2 as an adhesive sheet 13
Dry at 0 ° C for 5 minutes, flexible thermosetting adhesive thickness 20μm
Using a flexible thermosetting adhesive sheet with a release film,
Conducted except that the flexible thermosetting adhesive was transferred to a predetermined position on the cover lay film surface of the double-sided flexible printed wiring board 4 with a heat roll, and the thickness of the release film for thickness adjustment was set to 20 μm. A six-layer flex-rigid multilayer board having a thickness of 1.4 mm was prepared in the same manner as in the example.

Comparative Example 3 A polypropylene film (60 μm thick) was coated with varnish 3 as an adhesive sheet, and 13
Dry at 0 ° C for 5 minutes, flexible thermosetting adhesive thickness 70μm
Using a flexible thermosetting adhesive sheet with a release film,
Conducted except that the flexible thermosetting adhesive was transferred to a predetermined position on the cover lay film surface of the double-sided flexible printed wiring board 4 with a heat roll and the thickness of the release film for thickness adjustment was 70 μm. A six-layer flex-rigid multilayer board having a thickness of 1.5 mm was prepared in the same manner as in the example.

The characteristics of the six-layer flex-rigid multilayer boards of Examples 1 to 10 and Comparative Examples 1 to 3 are shown in Table 4.

[0045]

[Table 4] Table 4 shows each item of the interlayer adhesion on the coverlay film surface, the through hole reliability by the silicon oil dip cooling / heating cycle test, and the circuit embedding property.

In Table 4, the interlayer adhesion is the adhesion on the cover lay film surface or the flexible printed wiring board surface. Through hole reliability is a thermal cycle test in which it is dipped in silicone oil, and 20 ℃ and 260 ℃ each
After adding 50 cycles every 0 seconds, an electrical continuity test was conducted between the front and back conductors.

As can be seen from Table 4, Examples 1-10
Shows the satisfactory results for all items,
On the other hand, Comparative Example 1 is inferior in interlayer adhesion, Comparative Example 2 is inferior in circuit embedding property, and Comparative Example 3 is inferior in through hole reliability.

[0048]

As described above, according to the multilayer substrate and the method of manufacturing the same of the present invention, a highly reliable flex-rigid multilayer plate is obtained by using the double-layered multilayer adhesive sheet as the adhesive layer. Can be done, and the effect is great.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a multilayer substrate according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a double-layered multilayer adhesive sheet according to an example of the present invention.

FIG. 3 is a schematic cross-sectional view of a double-layered multilayer adhesive sheet according to an example of the present invention.

FIG. 4 is a schematic cross-sectional view showing the structure of a conventional multi-layer substrate.

[Explanation of symbols]

 1 Double-sided rigid printed wiring board 2 Double-layered multilayer adhesive sheet 2a Prepreg layer 2b Flexible thermosetting adhesive layer 2c Release film 3 Coverlay film 4 Double-sided flexible printed wiring board 5 Flexible thermosetting adhesive sheet

Claims (3)

[Claims] 1. A flexible thermosetting adhesive layer having a thickness of 10 to 50 μm is coated on one surface of a prepreg layer in which a fibrous base material is impregnated with a thermosetting resin and is dried and thermosetting is possible. , A double-layered multilayer adhesive sheet characterized by being integrated. 2. A multi-layer substrate including a rigid printed wiring board, a flexible printed wiring board, and an adhesive layer for adhering the two wiring boards to each other, wherein the adhesive layer is a two-layered multilayered structure. A multi-layer substrate, which is an adhesive sheet for use. 3. The double-layered multilayer according to claim 1, wherein the rigid printed wiring board and the flexible printed wiring board are bonded to each other by using a multilayer adhesive sheet, and the multilayer adhesive sheet is used as the multilayer adhesive sheet. Using the adhesive sheet for use, the prepreg layer is arranged on the rigid printed wiring board side, and the flexible thermosetting adhesive layer is arranged on the flexible printed wiring board side. A method for manufacturing a multi-layer substrate, which comprises a step.