JP2006202788A - Method for manufacturing multilayer polyimide flexible circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a void-free multilayer polyimide flexible circuit board. <P>SOLUTION: In a method for manufacturing the multilayer polyimide flexible circuit board, the conductor foil surface of a conductive foil application substrate with a polyimide resin as a base and the polyimide layer of another similar conductive foil application substrate are overlapped so that they are in contact each other via a precured polyimide film, and are cured at high temperature in a pressurized state. In this case, conductor foil that becomes an inner layer is coated with polyimide 230, which is soft-baked at 100-150°C for 20-90 minutes, and is precured for 20-90 minutes at 170-250°C. The conductor foil having the precured imide layer and the imide layer of another conductor foil-spread substrate are overlapped so that they are in contact each other, and are cured at a high temperature of 250-350°C for 20-240 minutes in a pressurized state. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a multilayer polyimide flexible circuit board, and more specifically, a multilayer polyimide flexible film having no insulating layer other than polyimide, having almost no voids, and having excellent through-hole reliability, heat resistance, and quality stability. The present invention relates to a method for manufacturing a circuit board.

  A conventional multilayer polyimide flexible printed circuit board is manufactured by inserting an acrylic or epoxy-modified polyimide film adhesive between the polyimide film and conductor layer bonded with an adhesive and thermocompression bonding. Was.

  However, these multilayer substrates are notable for various chemical properties and heat resistance properties of the epoxy and acrylic adhesive layers used compared to the polyimide layers used for insulating layers other than the adhesive layers. Because it is inferior, when forming a through hole, it has a problem of smear caused by heat during drilling and a problem of swelling during desmear treatment with potassium permanganate, resulting in poor product yield and low reliability around the through hole. The problem was.

As a proposal to solve such a problem, polyimide varnish is applied to at least one of the opposing surfaces of the metal foil, dried, and these metal foils are stacked and pressed and bonded together by a pressing roller rotating in a hot air drying furnace, or In addition, there is a proposal for a method for producing a multilayer polyimide flexible printed circuit board in which a polyimide film is sandwiched between a plurality of metal foils to be superposed, and these are crimped and bonded together by a pressure roller rotating in a hot air drying furnace (for example, patent literature) 1). The pressure bonding with this roller is performed by heating and pressure bonding at 245 ° C. and 75 kgf / cm ² (7355 kPa) for 30 minutes.

JP-A-5-299848

  However, the polyimide varnish conventionally used is a polyamic acid solution, and the one obtained by applying this polyamic acid and then imidizing it by completely removing the solvent has poor adhesiveness. Bonding is carried out with the remaining part, and complete imidization is performed by post-cure after bonding. For this reason, the by-product residue accompanying imidization and the presence of voids due to solvent evaporation are unavoidable in the adhesive layer of the resulting laminate, and there is a decrease in quality due to voids and variations in lot-to-lot quality. It was rare.

  In view of such a situation, the inventors of the present invention have reached the present invention as a result of intensive studies on a void-free multilayer polyimide flexible circuit board.

  That is, the method for producing a multilayer polyimide flexible circuit board according to the present invention comprises a polyimide film in which a conductor foil surface of a polyimide-based conductor foil-clad substrate and a polyimide layer of another similar conductor foil-clad substrate are precured. Is a method for producing a multilayer polyimide flexible circuit board, which is superposed so as to be in contact with each other and cured at a high temperature in a pressurized state, wherein polyimide is applied on the conductor foil as the inner layer, and soft baking is performed at 100 to 150 ° C. for 20 to 90 minutes. After that, it is precured at 170 to 250 ° C. for 20 to 90 minutes, and the conductor foil having this precured imide layer and the imide layer of another conductor foil-clad substrate are stacked so as to contact each other, and in a pressurized state, 250 to 350 ° C. And high temperature curing for 20 to 240 minutes.

  According to the method of the present invention, since the resin layer is entirely made of polyimide, there is no problem of chemical resistance and heat resistance due to the conventional adhesive layer, and since there is no void in the adhesive layer, electrical characteristics due to the void are present. There is no degradation of quality, etc., and the stability of quality is excellent.

  As a conductive foil-clad substrate based on a polyimide resin in the present invention, a manufacturing method is prepared by a casting method if it is composed of a polyimide and a conductive foil layer without a normal acrylic or epoxy adhesive layer. Or manufactured by a plating method. A pattern-processed flexible printed circuit board can be obtained by subjecting the substrate to circuit processing by an ordinary method. As the conductor constituting the conductor foil, any conductor that is usually used for a circuit board can be used, and specific examples include copper foil, aluminum foil, nickel foil, SUS foil, and the like.

  A polyimide resin is a polymer containing a cyclic imide group, and is usually obtained by reacting a diamine with an acid anhydride and then heating or chemically imidizing. Generally, diamines include phenylenediamine, diaminodiphenylmethane, and diamino. Diphenyl sulfone, diaminodiphenyl ether, etc. are used as acid anhydrides, such as trimellitic acid anhydride, pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, etc. However, the polyimide resin used in the production method of the present invention is preferably one that can be attached even in a state where no polyamic acid is left, and examples of such a polyimide resin include a polyamideimide resin. .

  Among these polyamide-imide resins, it has excellent heat resistance, insulation and electrical properties, excellent chemical resistance (plating resistance), low thermal shrinkage at cure, good stability over time, and storage at room temperature Therefore, a polyimide resin having a repeating unit shown below is preferable.

  An example of such a polyimide resin is Durimide D10A (trade name, manufactured by Fuji Film Electronics Materials Co., Ltd.).

In the following, the manufacturing method of the present invention will be described with reference to FIG. 1, taking as an example a case where a copper-clad polyimide substrate is used as the conductive foil-clad substrate.
First, a copper-clad substrate (A), in the present invention, a liquid polyimide 230 is applied on a copper foil 210 of one copper-clad substrate (B) 200 as shown in FIG. When this liquid polyimide is cured, it is preferably the same as the polyimides 120 and 220 constituting the copper-clad substrate.
Of course, the copper foil of the copper-clad substrate (B) 200 may have a circuit pattern formed by a circuit formation process.
The thickness of the polyimide 230 applied is preferably 1 to 10 μm after curing. If the coating thickness exceeds 10 μm, voids are likely to occur, which is not preferable. If the coating thickness is less than 1 μm, the adhesive strength between the layers of the multilayer substrate may be insufficient.

  Next, the applied polyimide is soft-baked at 100 to 150 ° C. for 20 to 90 minutes, preferably under a reduced pressure of several hundred torr (several hundred × 133.3 Pa), for example, 200 to 500 torr (26700 to 66700 Pa). This soft baking removes most of the solvent contained in the liquid polyimide. Thereby, even if pre-curing is performed in the next step, voids due to solvent volatilization are not generated.

  Next, the soft-baked imide layer 232 is preferably precured at 170 to 250 ° C. for 20 to 90 minutes under a reduced pressure of several hundred torr (several 100 × 133.3 Pa). At this stage, almost all of the solvent contained in the liquid polyimide is removed, but the polyimide 120 can be bonded by high-temperature curing under pressure.

Next, as shown in FIG. 1E, the polyimide layer of the other copper-clad substrate (A) 100 is placed on the pre-cured polyimide layer 234 of the copper-clad substrate (B) 200 on which the precured polyimide 234 is laminated. 120, contact with each other, align as necessary with pins, eyelets, etc., as required, press at a high temperature such as a vacuum press at 250-350 ° C under a reduced pressure atmosphere at a temperature higher than the pre-curing temperature 300, high temperature curing is performed at 35-80 kg / cm ² for 20-240 minutes. Thereby, a void-free two-layer polyimide flexible circuit board is obtained. By repeating this process, a multilayer polyimide flexible circuit board having an arbitrary number of layers can be obtained.

  Patterning is performed by adding a circuit formation process of the desired shape before and after the stacking, and if necessary, through holes (Through Hole TH), inner buyer holes (Inner Via Hole IVH), blind buyer holes (Blind Via Hole) BVH) etc. can also be provided.

Example 1
Using polyimide D10A (trade name, manufactured by Fuji Film Electronics Materials Co., Ltd.) as a polyimide, a copper-clad substrate having a 10 μm thick cured polyimide layer formed on a copper foil is prepared, and predetermined circuit processing is performed on the copper foil surface. The flexible circuit board was obtained.
A 65 wt% N-methylpyrrolidone (NMP) solution of polyimide D10A was applied onto the copper foil of this substrate so that the film thickness after imidization was 3 μm. The substrate (B) was placed under a reduced pressure of about 100 torr (13300 Pa), and soft-baked at 100 to 150 ° C. for about 1 hour to skip low boiling point components.

  The substrate was then precured at about 220 ° C. for about 90 minutes under the same vacuum to skip NMP.

The circuit board and a copper-clad board in which a cured polyimide layer having a thickness of 10 μm is formed on the same copper foil are brought into contact with the imide layer of the circuit board and the imide layer of the copper-clad board under the same reduced pressure. The temperature was gradually raised to 350 ° C. under a pressure of 70 kgf / cm ² (6865 kPa) using a press, and high temperature curing was performed at 350 ° C. for 1 hour. This substrate was further subjected to drilling, through-hole plating, and pattern formation to obtain a two-layer polyimide flexible circuit board. Even if this substrate was drilled for through holes, the finished state was good and there was almost no smear, so desmear treatment was not necessary. Further, as a treatment corresponding to the desmear treatment, even when the potassium permanganate treatment was performed, the chemical resistance was extremely excellent, so that the insulating layer was not eluted. Moreover, when this circuit board was cut and a 3 μm thick precured and high temperature cured polyimide layer was observed, no voids were observed.

  In this embodiment, an example of two layers is shown, but a multilayer circuit board having an arbitrary number of layers can be obtained by repeating this operation.

(Comparative Example 1)
Using a coating machine, the polyamic acid solution was uniformly and continuously cast onto a commercially available copper foil having a thickness of 18 μm, and dried with hot air at 150 ° C. to obtain a polyamideimide-coated metal foil. It was wound up into two coils. The thickness of this polyamideimide coated metal foil was 28 μm.

Using these two polyimide-coated metal foil coils, the respective polyimide layers were in contact with each other, laminated under the conditions of a temperature of 220 ° C. and a linear pressure of 20 kgf / cm (1960 N / cm), and 245 ° C. and 75 kgf / cm ^2. It pressed for 1 hour on conditions (7355kPa), and obtained the metal foil polyimide laminated board. When this laminate was cut and the laminate portion was observed, a large number of voids were observed.

  INDUSTRIAL APPLICABILITY According to the present invention, a multilayer polyimide flexible circuit board having excellent heat resistance and no voids can be obtained, and is useful as a substrate for various electronic components that require heat resistance and high-density mounting. .

It is the schematic which shows the manufacturing process of a multilayer flexible circuit board.

Explanation of symbols

100: Copper-clad substrate (A), 200: Copper-clad substrate (B)
110, 210: Copper foil, 120, 220: Polyimide layer 230: Applied liquid polyimide, 232: Soft baked polyimide 234: Precured polyimide 130: High temperature cured polyimide and polyimide 120 integrated layer

Claims (4)

  Multilayer that superimposes the conductor foil surface of a polyimide-based conductor foil-clad substrate and the polyimide layer of another similar conductor foil-clad substrate via a precured polyimide film, and cures at high temperature under pressure It is a manufacturing method of a polyimide flexible circuit board, and after applying polyimide on a conductor foil which becomes an inner layer, soft baking at 100 to 150 ° C. for 20 to 90 minutes, precuring at 170 to 250 ° C. for 20 to 90 minutes, The multilayer polyimide is characterized in that the conductor foil having the precured imide layer and the imide layer of another conductor foil-clad substrate are stacked so as to be in contact with each other and cured under high pressure at 250 to 350 ° C. for 20 to 240 minutes. A method of manufacturing a flexible circuit board.   2. The method for producing a multilayer polyimide flexible circuit board according to claim 1, wherein each of soft baking, pre-curing, and high-temperature curing is performed under a reduced pressure atmosphere.   The method for producing a multilayer polyimide flexible circuit board according to claim 1, wherein the coating thickness of the liquid polyimide film is 1 to 10 μm. The method for producing a multilayer polyimide flexible circuit board according to any one of claims 1 to 3, wherein the polyimide is a polyimide having a repeating unit shown below.

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