JP2013149870A - Multilayer flexible wiring board and method for manufacturing multilayer flexible wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer flexible wiring board with excellent folding resistance, insulation reliability, and heat resistance.SOLUTION: A multilayer flexible wiring board (1) includes internal conductive layers (12a, 12b) and external conductive layers (14a, 14b) provided on the internal conductive layers (12a, 12b) via an adhesive resin hardener (13). The internal conductive layers (12a, 12b) and the external conductive layers (14a, 14b) are electrically connected via a blind (17). An alkali dissolution rate of the adhesive resin hardener is higher than or equal to 0.0001 μm/sec and lower than or equal to 0.01 μm/sec. A residual solvent quantity is less than or equal to 0.5 mass%. Tg (glass-transition temperature) is lower than or equal to 125°C.

Description

  The present invention relates to a multilayer flexible wiring board used for a mobile phone terminal or the like, and more particularly to a multilayer flexible wiring board having a rigid portion on which various electronic components are mounted and a flexible portion having bending or bending properties.

  In recent years, in the field of cellular phone terminals and the like, in order to improve component mounting density, finer and multilayered wiring circuits are required, and the ratio of multilayer flexible wiring boards is increasing. The multilayer flexible wiring board has a rigid part on which various electronic components are mounted, and a flexible part having bending or bending properties, and a plurality of conductive layers are respectively provided on the rigid part and the flexible part via an insulating layer. Is provided. For this reason, sufficient bendability or bendability is required in the insulating layer between the conductive layers of the flexible portion.

  As the insulating layer of the flexible portion, an epoxy material or a polyimide material can be used. In general, epoxy-based materials have a high elastic modulus and a low elongation, and thus have a problem of insufficient bendability and bendability. In addition, since the multilayer flexible wiring board is incorporated in a mobile phone terminal or the like with the flexible portion folded, it is desired to reduce the thickness of the insulating layer. For this reason, as the insulating layer of the flexible portion, a polyimide-based material having excellent insulation reliability even when the film thickness is reduced is used.

  By the way, in a multilayer flexible wiring board, via holes (plating holes) are provided between a plurality of conductive layers, and copper plating is performed in the vias to electrically connect the plurality of conductive layers. Via holes provided in the multilayer flexible wiring board are mainly through via holes provided in the double-sided flexible wiring board as the core substrate of the multilayer flexible wiring board or the rigid flexible wiring board, and mainly the double-sided flexible wiring board, the multilayer flexible wiring board, and There is a blind via hole provided between the inner conductive layer and the outer conductive layer of the rigid flexible wiring board.

  These via holes are generally provided by processing such as NC drilling, plasma etching, laser drilling, and punching. However, when a via hole is provided by these processes, there is a problem that smear occurs when the via hole is formed. When smear occurs, it causes a plating failure of a via hole, which is a serious defect of the flexible wiring board, and there is a problem that the quality of the circuit board of the flexible wiring board is deteriorated. In addition, in laser processing and drilling, since it is necessary to process each hole, continuous production of roll-to-roll is difficult, and it is a major obstacle in terms of cost reduction and productivity improvement.

  On the other hand, the via hole can be provided by chemical etching. However, in order to etch an insulating layer using a polyimide material, a strong reducing agent such as hydrazine must be used, which is an obstacle to popularization. In addition, since the etching rate is slow, it is a major obstacle in terms of cost reduction and productivity improvement.

  In order to improve chemical etching properties, a resin composition comprising an alkali-soluble resin, an oxazoline compound and a photoacid generator compound (see, for example, Patent Document 1), or an adhesive composition comprising a polyimide resin, an oxazoline compound and an epoxy resin. A thing (for example, refer patent document 2) is proposed. In order to impart alkali solubility to the insulating layer, a polyimide precursor having a polyamic acid structure in a part of the polyimide has also been proposed (Patent Document 3).

JP 2006-267145 A JP 2008-260907 A JP 2011-228493 A

  However, since the insulating layer using the resin composition described in Patent Document 1 needs to be etched with a strong alkaline solution such as tetraalkylammonium hydroxide, the mechanical strength of the thermoset of the resin composition is reduced. There is a case. Further, since the photoacid generating compound is used, the unexposed portion of the photoacid generating compound remains in the insulating layer without being decomposed, and is thermally decomposed in a thermosetting step after exposure and development. For this reason, outgas may generate | occur | produce in a thermosetting process.

  Further, when the adhesive composition described in Patent Document 2 is used, N-methylpyrrolidone needs to be used as a solvent in order to dissolve polyimide having low solvent solubility. This N-methylpyrrolidone has a problem of remaining in the insulating layer because it has low volatility and a strong hydrogen bond with polyimide. For this reason, the resin of the insulating layer is melted at the time of thermosetting, and the shape of the via hole is narrowed, or the swelling is generated at the time of solder reflow, and the insulation reliability in the heat cycle resistance may be lowered. Moreover, the epoxy resin impairs the flexibility of the polyimide when heat treatment exceeding 150 ° C. is performed for a long time, and the warpage and folding resistance may be lowered.

  In addition, since the polyimide precursor described in Patent Document 3 includes a polyamic acid structure, when used as an insulating layer, the polyamic acid structure is imidized during heat treatment and water is by-produced. For this reason, it may lead to a decrease in insulation reliability in blistering at the time of solder reflow or thermal cycle resistance.

  This invention is made | formed in view of this point, and it aims at providing the manufacturing method of a multilayer flexible wiring board excellent in bending resistance, insulation reliability, and heat resistance, and a multilayer flexible wiring board.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by using an adhesive resin cured product having predetermined physical properties, and have completed the present invention. . That is, the present invention is as follows.

  The multilayer flexible wiring board of the present invention is a multilayer flexible wiring board using a core substrate composed of a double-sided flexible substrate having at least two conductive layers, and includes an adhesive resin cured product on the conductive layer. An external conductive layer is laminated via a cured resin layer, and the conductive layer of the core substrate and the external conductive layer are electrically connected via a blind via hole provided in the adhesive resin cured layer. The cured adhesive resin has an alkali dissolution rate of 0.0001 μm / sec or more and 0.01 μm / sec or less, a residual solvent amount of 0.5 mass% or less, and a glass transition temperature (Tg). Is 125 ° C. or lower.

  In the multilayer flexible wiring board of the present invention, it is preferable that the core substrate has a through via hole, and the through via hole is filled with the cured adhesive resin.

  In the multilayer flexible wiring board of the present invention, the cured adhesive resin is subjected to thermomechanical analysis (conditions: load 0.5 μN / (μm · μm), nitrogen flow, temperature increase rate 10 ° C./min), It is preferable that the elongation from 30 ° C. to 160 ° C. is 50% or less without breaking, and the maximum thermal expansion coefficient from 30 ° C. to 180 ° C. is 5000 ppm or more.

  In the multilayer flexible wiring board of this invention, it is preferable to have a conductive particle layer on the inner wall of the blind via hole.

  In the multilayer flexible wiring board of the present invention, the cured adhesive resin preferably contains a reaction product of (A) a hydroxyl group-containing resin having a hydroxyl group and (B) a reactive compound that reacts with the hydroxyl group. .

  In the multilayer flexible wiring board of the present invention, the reactant preferably has an amide structure and an ether structure.

  In the multilayer flexible wiring board of the present invention, the hydroxyl group of the hydroxyl group-containing resin is preferably a phenolic hydroxyl group.

  In the multilayer flexible wiring board of the present invention, the hydroxyl group-containing resin is preferably alkali-soluble polyimide.

  In the multilayer flexible wiring board of the present invention, the reactive compound is preferably an oxazoline compound.

In the multilayer flexible wiring board of the present invention, the hydroxyl group-containing resin is a polyimide having a structure represented by the following general formulas (1) to (3), and the reactive compound is preferably an oxazoline compound. .

In the multilayer flexible wiring board of the present invention, the hydroxyl group-containing resin is a polyimide having a structure represented by the following general formula (4) and the following general formula (5), and the reactive compound. An oxazoline compound is preferred.

  The method for producing a multilayer flexible wiring board according to the present invention is a method for producing the above-mentioned multilayer flexible wiring board, wherein a step of providing an external conductive layer on the conductive layer of the core substrate via an uncured adhesive resin; Forming a conformal mask on the layer, forming a via heel by dissolving and removing the uncured adhesive resin with an alkaline solution through the conformal mask, and heating and curing the uncured adhesive resin And a step of plating the via hole to electrically connect the conductive layer of the core substrate and the external conductive layer, and a step of forming a wiring circuit in the external conductive layer. To do.

  In the method for producing a multilayer flexible wiring board of the present invention, in the step of providing the external conductive layer, the external conductive layer is heated in a state where a rubber base material containing a reinforcing material is applied to the main surface of the external conductive layer. It is preferable that the external conductive layer is provided via the uncured adhesive resin on the conductive layer of the core substrate by applying pressure.

  In the method for producing a multilayer flexible wiring board according to the present invention, the uncured adhesive resin has a thermogravimetric decrease at 260 ° C. of 0.5% or less by thermogravimetric analysis, and an alkali with respect to a 3 mass% NaOH aqueous solution at 50 ° C. The dissolution rate is preferably 0.3 μm / sec or more.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the multilayer flexible wiring board excellent in bending resistance, insulation reliability, and heat resistance, and a multilayer flexible wiring board is realizable.

It is a cross-sectional schematic diagram of the multilayer flexible wiring board which concerns on this Embodiment. It is a cross-sectional schematic diagram of the rigid part of the multilayer flexible wiring board which concerns on this Embodiment. It is the schematic of the manufacturing process of the multilayer flexible wiring board which concerns on this Embodiment. It is a figure which shows the other example of the manufacturing process of the multilayer flexible wiring board which concerns on this Embodiment.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic cross-sectional view of a multilayer flexible wiring board 1 according to an embodiment of the present invention. FIG. 2 is a partially enlarged view of the rigid portion 10a of the multilayer flexible wiring board shown in FIG. As shown in FIG. 1, the multilayer flexible wiring board 1 which concerns on this Embodiment is manufactured using the core board | substrate 10 which consists of a double-sided flexible wiring board. The core base material 10 includes an adhesive resin cured product layer 11 including an adhesive resin cured product, and a pair of conductive layers 12a and 12b (hereinafter referred to as “the adhesive resin cured product layer 11” provided on both main surfaces of the adhesive resin cured product layer 11). Internal conductive layers 12a and 12b "). The cured adhesive resin layer 11 functions as an interlayer insulating layer that insulates between the pair of internal conductive layers 12a and 12b, and functions as an interlayer adhesive layer that bonds between the pair of internal conductive layers 12a and 12b. A wiring circuit is formed in the internal conductive layers 12a and 12b.

  The multilayer flexible wiring board 1 includes a rigid portion 10a provided at both ends where various electronic components are mounted, and a flexible portion 10b provided between the rigid portions 10a and having flexibility. The rigid portion 10a includes a pair of internal conductive layers 12a and 12b provided on both main surfaces of the adhesive resin cured product layer 11, and adhesive resin cured product layers 13a and 13b on the internal conductive layers 12a and 12b. A pair of conductive layers 14a and 14b (hereinafter referred to as “external conductive layers 14a and 14b”) and a cover coat 15 provided so as to cover a part of the pair of external conductive layers 14a and 14b. Have. The cured adhesive resin layers 13a and 13b include an insulative adhesive resin cured product and insulate between the internal conductive layer 12a and the external conductive layer 14a and between the internal conductive layer 12b and the external conductive layer 14b. In addition to functioning as an interlayer insulating layer, it functions as an interlayer adhesive layer that bonds between the internal conductive layer 12a and the external conductive layer 14a and between the internal conductive layer 12b and the external conductive layer 14b. The cured adhesive resin layer 11 and the cured adhesive resin layers 13a and 13b can be formed using the same adhesive resin. A wiring circuit is formed on the external conductive layers 14a and 14b.

  The core substrate 10 has a through via hole 16 provided so as to penetrate the internal conductive layers 12 a and 12 b and the cured adhesive resin layer 11. A pair of internal conductive layers 12 a and 12 b are electrically connected through the through via hole 16. The through via hole 16 is filled with the cured adhesive resin 13. In this way, by filling the through-hole 16 with the cured adhesive resin, the conductive layer on the through-hole wall can be fixed, and the heat resistance such as solder reflow resistance and the reliability in the cold-heat recycling test can be improved.

  Blind via holes 17 are provided between the internal conductive layer 12a and the external conductive layer 14a and between the internal conductive layer 12b and the external conductive layer 14b. Via the blind via hole 17, the internal conductive layer 12a and the external conductive layer 14a and the internal conductive layer 12b and the external conductive layer 14b are electrically connected. The blind via hole 17 may be filled with a cover coat 15.

  As shown in FIG. 2, a plating 16b is provided on the inner wall of the through via hole 16 via a conductive particle layer 16a. The conductive particle layer 16a is provided so as to cover the adhesive resin cured product layer 11 in the through via hole 16, and a part thereof is in contact with the pair of internal conductive layers 12a and 12b. A pair of internal conductive layers 12a and 12b are electrically connected via the conductive particle layer 16a. The conductive particle layer 16 a is made of, for example, carbon fine particles and has high adhesion with the adhesive resin cured product layer 11. For this reason, by providing the plating 16b through the conductive particle layer 16a, it is possible to prevent other components from being mixed between the cured adhesive resin layer 11 and the conductive particle layer 16a. Note that the conductive particle layer 16a is not necessarily provided.

  On the inner wall of the blind via hole 17, plating 17b is provided via a conductive particle layer 17a. The conductive particle layer 17a is provided so as to cover the adhesive resin cured product layers 13a and 13b in the blind via hole 17, and a part of the conductive particle layer 17a is formed of the internal conductive layer 12a and the external conductive layer 14a, or the internal conductive layer 12b and It is in contact with the external conductive layer 14b. The internal conductive layer 12a and the external conductive layer 14a, and the internal conductive layer 12b and the external conductive layer 14b are electrically connected through the conductive particle layer 17a. The conductive particle layer 17a is made of, for example, carbon fine particles and has high adhesion to the adhesive resin layers 13a and 13b. For this reason, by providing the plating 17b via the conductive particle layer 17a, it is possible to prevent other components from being mixed between the cured adhesive resin layers 13a and 13b and the conductive particle layer 17a. Note that the conductive particle layer 17a is not necessarily provided.

  The flexible portion 10b has an internal conductive layer 12a provided on one main surface of the adhesive resin cured product layer 11, and an adhesive resin cured product layer 13a provided so as to cover the internal conductive layer 12a. . The internal conductive layer 12a of the flexible portion 10b is provided so as to extend to the rigid portions 10a on both end sides, and the internal conductive layer 12b and the external conductive layer 14a of the rigid portion 10a through the through via hole 16 and / or the blind via hole 17. , 14b.

  The cured adhesive resin contained in the cured adhesive resin layers 13a and 13b has an alkali dissolution rate in the range of 0.0001 μm / sec to 0.01 μm / sec. If the alkali dissolution rate is 0.0001 μm / sec or more, it is excellent in folding resistance and cooling cycle (heat resistance), and if the alkali dissolution rate is 0.01 μm / sec or less, the insulation reliability and the remaining film during plating Excellent in properties. The alkali dissolution rate of the cured adhesive resin is preferably 0.0003 μm / sec or more and 0.008 μm / sec or less, and more preferably 0.0005 μm / sec or more and 0.005 μm / sec or less.

  In the present embodiment, the alkali dissolution rate of the cured adhesive resin is measured by removing the outer conductive layers 14a and 14b of the rigid portion 10a by router processing (outer shape processing) and then exposing the cured adhesive resin layer. It carries out with respect to 13a, 13b. In addition, the alkali dissolution rate of the adhesive cured product is such that the external conductive layers 14a and 14b are removed by etching in a state where the external conductive layers 14a and 14b are left thin, and then the adhesive cured resin cured product layers 13a and 13b are exposed. It is also possible to measure.

  Further, the cured adhesive resin has a residual solvent amount of 0.5% by mass or less. When the residual solvent amount of the cured adhesive resin is 0.5% by mass or less, the via shape and the solder reflow resistance are excellent. The amount of residual solvent in the cured adhesive resin is preferably 0.2% by mass or less, more preferably 0.1% by mass or less, and further preferably 0.05% by mass or less. Moreover, as a lower limit of the residual solvent amount of adhesive resin hardened | cured material, it is preferable that it exceeds 0 mass% from an adhesive viewpoint.

  The cured adhesive resin has a glass transition temperature (Tg) of 125 ° C. or lower. When the glass transition point is 125 ° C. or lower, the thermal cycle resistance and the insulation reliability are improved. The glass transition temperature of the cured adhesive resin is preferably 100 ° C. or less and more preferably 90 ° C. or less from the viewpoint of further improving the thermal cycle resistance and insulation reliability. Moreover, as a glass transition temperature of adhesive resin hardened | cured material, it is preferable that it is 60 degreeC or more from a heat resistant viewpoint, and it is more preferable that it is 80 degreeC or more.

  Further, the cured adhesive resin has an elongation from 30 ° C. to 160 ° C. in thermomechanical analysis (TMA) (conditions: load 0.5 μN / (μm · μm), nitrogen flow, temperature rising rate 10 ° C./min). The degree is preferably 50% or less without breaking, more preferably 45% or less, and still more preferably 40% or less. When the elongation from 30 ° C. to 160 ° C. is 50% or less without breaking, folding resistance is further improved, and heat resistance such as solder reflow resistance and thermal cycle resistance is further improved.

  Further, the maximum thermal expansion coefficient in the thermomechanical analysis of the cured adhesive resin is preferably 5000 ppm or more, more preferably 10,000 ppm or more, and the maximum thermal expansion coefficient from 30 ° C. to 180 ° C. More preferably, it is 15000 ppm or more. When the maximum thermal expansion coefficient from 30 ° C. to 180 ° C. is 5000 ppm or more, folding resistance is further improved, and heat resistance such as solder reflow resistance and thermal cycle resistance is further improved.

  Further, the tensile elastic modulus of the cured adhesive resin is within the range of 0.2 GPa or more and 3 GPa or less from the viewpoint of reducing warpage and reducing the resilience and facilitating the work of incorporating the wiring board into the device. Is preferable, and it is more preferably within a range of 0.3 GPa or more and 2 GPa or less.

  In the present embodiment, the glass transition temperature (Tg), thermomechanical analysis, and measurement of the tensile elastic modulus of the cured adhesive resin are measured by router processing (outer diameter processing). After the internal conductive layer 12a is removed, the exposed cured adhesive resin layer 13a is used. The adhesive resin cured product layer 13a was cut into a required size and measured.

Next, the manufacturing method of the multilayer flexible wiring board 1 which concerns on this Embodiment is demonstrated.
In the manufacturing method of multilayer flexible wiring board 1 according to the present embodiment, external conductive layers 14a and 14b are disposed on internal conductive layers 12a and 12b of core substrate 10 via uncured adhesive resin layers containing uncured adhesive resin. A step of forming a conformal mask on the external conductive layers 14a and 14b, a step of dissolving and removing the uncured adhesive resin layer through the conformal mask to form the blind via hole 17, and an uncured adhesion The adhesive resin cured product layers 13a and 13b are formed by heating and curing the conductive resin layer, and the inner conductive layers 12a and 12b and the outer conductive layers 14a and 14b are electrically connected by plating 17a in the blind via holes 17. And a step of forming a wiring circuit in the external conductive layers 14a and 14b.

  Hereinafter, each step will be described in detail with reference to FIG. FIG. 3 is a schematic view of a manufacturing process of the multilayer flexible wiring board 1 according to the present embodiment. In the following description, for convenience of explanation, the uncured adhesive resin layer and the cured adhesive resin layer are denoted by the same reference numerals (uncured adhesive resin layers 11 ′ and 13 ′ or cured adhesive resin). Description will be made with physical layers 11 and 13).

  The core substrate 10 is provided on both main surfaces of an uncured adhesive resin layer 11 ′ obtained by applying and drying an adhesive resin varnish, which will be described in detail later, and the uncured adhesive resin layer 11 ′. A double-sided flexible board provided with a pair of internal conductive layers 12a and 12b is used. The adhesive resin of the cured adhesive resin layer 11 includes an alkali-soluble resin. Note that the cured adhesive resin layer 11 of the core substrate 10 does not necessarily include an uncured adhesive resin. For example, as the core substrate 10, a flexible wiring board having an insulating layer formed using a conventionally known general insulating material and a pair of internal conductive layers laminated via the insulating layer may be used. Good.

  First, copper foil is laminated on both main surfaces of the uncured adhesive resin layer 11 'to provide the internal conductive layers 12a and 12b. Next, after laminating a dry film (not shown) on the internal conductive layers 12a and 12b, a part of the internal conductive layers 12a and 12b is removed by exposing and developing the dry film and etching the internal conductive layers 12a and 12b. To form a conformal mask (not shown). Next, the uncured adhesive resin layer 11 ′ exposed in the etching regions of the internal conductive layers 12 a and 12 b through the conformal mask is dissolved and removed with an alkaline solution to form the through via hole 16.

  The alkaline solution is not particularly limited as long as it can dissolve and remove the uncured adhesive resin layer 11 '. As the alkaline solution, for example, an aqueous sodium carbonate solution, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, or the like can be used. Further, in dissolving and removing the uncured adhesive resin layer 11 ′ with an alkaline solution, an alkali spray device or the like used in a general flexible wiring board manufacturing process can be used. Next, the uncured adhesive resin of the uncured adhesive resin layer 11 ′ is cured by heating at 150 ° C. to 200 ° C. for 10 minutes to 2 hours using a drying furnace.

  Next, after forming conductive particle layer 16a (not shown in FIG. 3, refer to FIG. 2) by attaching conductive fine particles (for example, carbon fine particles) to the adhesive resin cured material layer 11 in the through via hole 16, Electrolytic copper plating is performed to form a plating 16b to electrically connect the internal conductive layers 12a and 12b. Next, the double-sided flexible wiring board 10 is manufactured by forming a wiring circuit in the internal conductive layers 12a and 12b by a subtractive method or the like (see FIG. 3A). The internal conductive layers 12a and 12b may be electrically connected through blind vias.

  Next, on the internal conductive layers 12a and 12b of the double-sided flexible wiring board 10, an adhesive resin varnish is applied and dried to provide uncured adhesive resin layers 13a ′ and 13b ′ including the uncured adhesive resin 13 ′. . Next, a copper foil or the like is laminated on the uncured or semi-cured uncured adhesive resin layers 13a 'and 13b' to provide external conductive layers 14a and 14b (see FIG. 3B). Here, the uncured adhesive resin is filled in the through via hole 16 of the core substrate 10. A laminate (copper foil with resin) having an uncured adhesive resin layer 13a '(13b') is laminated on the internal conductive layers 12a and 12b by applying and drying an adhesive resin varnish on the copper foil. Also good. The external conductive layers 14 a and 14 b can be laminated at 50 ° C. to 140 ° C., preferably 70 ° C. to 120 ° C., more preferably 90 ° C. to 110 ° C. by using a vacuum press or a vacuum laminator.

  Next, after laminating the dry film 18 on the external conductive layers 14a and 14b, a part of the external conductive layers 14a and 14b is exposed by exposing and developing the dry film 18 (FIG. 3C). Subsequently, the external conductive layers 14a and 14b are etched to remove a part of the external conductive layers 14a and 14b to form a conformal mask, and the external conductive layer 14b in a region to be the flexible portion 10b is removed (see FIG. 3D).

  Next, the uncured adhesive resin layers 13a ′ and 13b ′ exposed to the etching regions of the external conductive layers 14a and 14b through the conformal mask are dissolved and removed with an alkaline solution to form the blind via holes 17 and the alkali The dry film 18 is peeled off with the solution. Here, the uncured adhesive resin layer 13b 'in the region to be the flexible portion 10b is also dissolved and removed (FIG. 3E). Thus, since formation of the blind via hole 17 and peeling of the dry film 18 can be performed with an alkaline solution, production efficiency can be improved and via formation cost can be reduced. As the alkaline solution, for example, a 3% by mass sodium hydroxide aqueous solution which is a dry film peeling solution can be used.

  Next, using a drying oven, the uncured adhesive resin layers 13a 'and 13b' are heated and cured to form the cured adhesive resin layers 13a and 13b. The heat curing is preferably performed at a temperature of 120 ° C. or more and 400 ° C. or less from the viewpoint of the reactivity of the uncured adhesive resin layers 13a ′ and 13b ′. More preferably, it is 150 degreeC or more and 250 degrees C or less.

  The reaction atmosphere in heat curing can be carried out in an air atmosphere or an inert gas atmosphere. In order to suppress the oxidation of a conductive layer, it is preferable that it is under nitrogen stream at high temperature. The time required for heat curing varies depending on the reaction conditions, but is usually within 24 hours, particularly preferably in the range of 0.1 to 8 hours.

  Next, after carbon fine particles are adhered to the adhesive resin cured product layers 13a and 13b in the blind via hole 17 to form a conductive particle layer (not shown in FIG. 3, refer to FIG. 2), plating 17b is performed by electrolytic copper plating. Form. Thereby, the internal conductive layer 12a and the external conductive layer 14a, and the internal conductive layer 12b and the external conductive layer 14b are electrically connected (FIG. 3F).

  Next, the external conductive layers 14a and 14b are patterned by a subtractive method to form a circuit (FIG. 3G). Next, a surface treatment such as the formation of the cover coat 15 is performed in the same manner as the conventional flexible substrate wiring board method to produce a multilayer flexible wiring board (FIG. 3H).

  As described above, in the method for manufacturing a multilayer flexible wiring board, the uncured adhesive resin layers 13a ′ and 13b ′ are dissolved and removed by an alkaline solution through a conformal mask. Generation can be suppressed. In addition, since the uncured adhesive resin layers 13a 'and 13b' and the dry film resist 18 can be dissolved and removed together with an alkaline solution, the manufacturing process of the multilayer flexible wiring board 1 can be simplified. Further, since the uncured adhesive resin layers 13a 'and 13b' have an alkali dissolution rate within a predetermined range, the uncured adhesive resin layers 13a 'and 13b' can be dissolved and removed in a short time. Furthermore, since the amount of residual solvent in the uncured adhesive resin layers 13a ′ and 13b ′ is within a predetermined range, the amount of solvent volatilization in the heating process after the formation of the blind via hole 17 can be reduced, and the multilayer flexible wiring board 1 can be swollen. Can be reduced. Thereby, it becomes possible to manufacture a multilayer flexible wiring board excellent in circuit quality with high production efficiency.

  In the manufacturing method described above, an example using the double-sided flexible wiring board 10 has been described. However, instead of the double-sided flexible wiring board 10, a single-sided flexible wiring board or a multilayer flexible wiring board is manufactured. You may use for.

  As shown in FIG. 4, the outer conductive layers 14a and 14b are heated and pressed with the rubber base material 20 having a reinforcing material so as to sandwich the outer conductive layers 14a and 14b. You may pressurize and laminate. Thereby, the flatness of the multilayer flexible wiring board 1 can be improved.

  Moreover, as uncured adhesive resin layers 13a ′ and 13b ′ in a semi-cured state before curing, the thermogravimetric decrease at 260 ° C. by thermogravimetric analysis (TG) is 0.5% or less, and 3 mass at 50 ° C. It is preferable that the alkali dissolution rate with respect to the% NaOH aqueous solution is 0.3 μm / sec or more. This facilitates dissolution and removal of the uncured adhesive resin layers 13a 'and 13b' with an alkaline solution, thereby improving the productivity of the multilayer flexible wiring board. Further, it is possible to sufficiently form a blind via with an alkaline aqueous solution. Moreover, since the residual solvent amount of the uncured adhesive resin layers 13a 'and 13b' after the alkali dissolution and removal can be reduced, the quality of the multilayer flexible wiring board can be improved. The thermogravimetric decrease at 260 ° C. by thermogravimetric analysis (TG) is preferably 0.3% by mass or less, and more preferably 0.1% by mass or less. The alkali dissolution rate with respect to the 3% NaOH aqueous solution at 50 ° C. is preferably 0.4 μm / sec or more, and more preferably 0.5 μm / sec or more.

  Next, the configuration of the adhesive resin varnish will be described in detail. The adhesive resin varnish according to the present embodiment uses (A) a hydroxyl group-containing resin containing a hydroxyl group and (B) a reactive compound that reacts with the hydroxyl group of the hydroxyl group-containing resin.

  In the present embodiment, from the viewpoint of forming a blind via by dissolving and removing the uncured adhesive resin layers 13a ′ and 13b ′ with an alkaline solution, the resin constituting the adhesive resin varnish includes an alkali-soluble functional group. An alkali-soluble resin is used. Examples of the alkali-soluble functional group include a hydroxyl group, a carboxyl group, and a sulfonic acid group. Among these, as the alkali-soluble functional group, from the viewpoint of suppressing the thermal reaction of the uncured adhesive resin layers 13a ′ and 13b ′ at the time of pressing or the like when laminating the external conductive layers 14a and 14b, Excellent hydroxyl groups are preferred. In addition, unlike a carboxyl group, a hydroxyl group does not undergo decarboxylation by heating, and therefore, outgassing due to thermal decomposition can be suppressed even when solder reflow is performed at a high temperature. For this reason, in this Embodiment, it is preferable to use (A) hydroxyl-containing resin containing a hydroxyl group as an adhesive resin varnish.

(A) Hydroxyl group-containing resin The hydroxyl group-containing resin is not particularly limited as long as it contains at least one hydroxyl group in the molecule. The hydroxyl group is not particularly limited as long as it reacts with (B) the reactive compound. Among these, a phenolic hydroxyl group is preferable from the viewpoint of excellent reactivity with the reactive compound when the uncured adhesive resin layers 13a ′ and 13b ′ are cured.

  The alkali dissolution rate of the hydroxyl group-containing resin is preferably in the range of 0.2 μm / sec to 3 μm / sec from the viewpoint of the shape of the blind via hole 17 formed using an alkaline aqueous solution. The alkali dissolution rate of the hydroxyl group-containing resin is more preferably in the range of 0.3 μm / sec to 3 μm / sec, and still more preferably in the range of 0.5 μm / sec to 3 μm / sec.

  Examples of the hydroxyl group-containing resin include polyvinyl phenol resin, novolak resin, resol resin, copolymer of acrylic acid derivative having phenolic hydroxyl group, polyvinyl acetal resin having phenolic hydroxyl group, and polyimide resin having phenolic hydroxyl group. Among these, polyvinyl phenol resin, novolak resin, and polyimide resin having a phenolic hydroxyl group are preferable.

  Examples of the polyvinylphenol resin include o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, dihydroxystyrene, trihydroxystyrene, tetrahydroxystyrene, pentahydroxystyrene, 2- (o-hydroxyphenyl) propylene, 2- Examples thereof include resins obtained by polymerizing hydroxystyrenes such as (m-hydroxyphenyl) propylene and 2- (p-hydroxyphenyl) propylene alone or in the presence of a radical polymerization initiator or a cationic polymerization initiator. .

  The polyvinyl phenol resin preferably has a polystyrene-equivalent weight average molecular weight (MW) of 500 to 100,000, more preferably 1,000 to 50,000, as measured by gel permeation chromatography.

  Examples of novolak resins include phenol, o-cresol, m-cresol, p-cresol, 2,5-xylenol, 3,5-xylenol, o-ethylphenol, m-ethylphenol, p-ethylphenol, propylphenol. , N-butylphenol, t-butylphenol, 1-naphthol, 2-naphthol, 4,4′-biphenyldiol, bisphenol-A, pyrocatechol, resorcinol, hydroquinone, pyrogallol, 1,2,4-benzenetriol, phloroglucinol At least one phenol such as formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde, furfural and the like aldehydes (in addition to formaldehyde, paraformal The hydrate, a paraldehyde instead of acetaldehyde, may be used.), Or acetone, methyl ethyl ketone, at least one and polycondensation resin obtained by ketones such as methyl isobutyl ketone. Among these, phenol as phenols, o-cresol, m-cresol, p-cresol, 2,5-xylenol, 3,5-xylenol, resorcinol and formaldehyde, acetaldehyde, propionaldehyde as aldehydes or ketones And a polycondensate are preferred. In particular, the mixing ratio of m-cresol: p-cresol: 2,5-xylenol: 3,5-xylenol: resorcinol is 40 to 100: 0 to 50: 0 to 20: 0 to 20: 0 to 20 in molar ratio. A polycondensate of mixed phenols or mixed phenols of phenol: m-cresol: p-cresol with a molar ratio of 1-100: 0 to 70: 0-60 and formaldehyde is preferable.

  From the viewpoint of lowering the melt viscosity of the uncured adhesive resin layers 13a ′ and 13b ′ and improving the embedding property, as a novolak resin, 4,4′-biphenylylene group, 2,4′-biphenylylene group, 2, It has both polymer units of a phenol resin containing a crosslinking group such as a 2′-biphenylylene group, a 1,4-xylylene group, a 1,2-xylylene group, a 1,3-xylylene group, and a phenol resin containing a methylene crosslinking group. A novolac resin is also preferred.

  The novolak resin preferably has a polystyrene-equivalent weight average molecular weight (MW) of 500 to 15,000 as measured by gel permeation chromatography, and more preferably 1,000 to 10,000.

  In addition, as the hydroxyl group-containing resin, a polyimide having a phenolic hydroxyl group is particularly preferable from the viewpoint of excellent folding resistance and insulation reliability.

  Examples of the polyimide resin having a phenolic hydroxyl group include a polyimide resin having a phenolic hydroxyl group in the main chain and / or a polyimide resin having a terminal. Among these, it is preferable that at least the main chain has a phenolic hydroxyl group.

  Hereinafter, a polyimide having a phenolic hydroxyl group used as a hydroxyl group-containing resin will be described in detail. Examples of the polyimide having a phenolic hydroxyl group include those shown in the following embodiments.

(First embodiment)
The polyimide having a phenolic hydroxyl group according to the first embodiment is an alkali-soluble siloxane polyimide having a structure represented by the following general formula (1) to the following general formula (3). In this alkali-soluble siloxane polyimide, the residue from which the carboxyl group anhydride is removed is represented by the following general formula (2), and the residue from which the amino group is removed is represented by the following general formula (3). It is obtained by reacting the diamine represented.

(Second Embodiment)
The polyimide according to the second embodiment is an alkali-soluble polyimide including a structure represented by the following general formula (4) and the following general formula (5). This alkali-soluble polyimide is obtained by reacting a tetracarboxylic dianhydride represented by the following general formula (6) with a diamine in which the residue from which the amino group has been removed is represented by the following general formula (5). can get.

Examples of the tetracarboxylic dianhydride used for synthesis of the alkali-soluble polyimide according to the first embodiment, in the general formula (2), R ₁ is independently from each other, the number 1 to number 30 carbon atoms It is a monovalent hydrocarbon group. Examples of R ₁ include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, and hexyl groups; cycloalkyl groups such as cyclopentyl and cyclohexyl groups; aryl groups such as phenyl groups; benzyl groups, Examples include aralkyl groups such as phenethyl group; alkenyl groups such as vinyl group, allyl group, propenyl group, isopropenyl group, and butenyl group. Among these, from the viewpoint of easy availability of raw materials, R ₁ is preferably a methyl group, an ethyl group, a phenyl group, or a vinyl group.

Examples of R ₂ include a residue obtained by removing a carboxyl group anhydride from an alkyl succinic anhydride such as propyl succinic anhydride, norbornyl anhydride, propyl nadic acid anhydride, and the like. Among these, a residue obtained by removing a carboxyl group anhydride from propyl succinic anhydride, norbornyl anhydride, or propyl nadic acid anhydride is preferable. n is an integer of 1 to 50, preferably 3 to 30, and more preferably 5 to 15. n may be the same or different. Examples of such tetracarboxylic dianhydrides include tetracarboxylic dianhydrides having a silicone chain represented by the following formula group (7).

  As content of the component derived from the tetracarboxylic dianhydride which has a silicone chain in the polyimide which has a phenolic hydroxyl group, it is preferable that it is 40 mass% or more, and it is more preferable that it is 60 mass% or more.

  A polyimide having a phenolic hydroxyl group obtained by using a tetracarboxylic dianhydride having a silicone chain is excellent in alkali dissolution rate and low warpage. In addition, since tetracarboxylic dianhydride having a silicone chain is excellent in solubility in a solvent, for example, it is possible to obtain a polyimide having a phenolic hydroxyl group without using a polymerization solvent having an amide structure such as NMP. . Thereby, since the polymerization solvent excellent in drying property can be used, the residual solvent amount of the adhesive resin cured product layers 13a and 13b can be reduced.

  Examples of the diamine in which the residue from which the amino group has been removed are represented by the above general formula (3) include 4,4′-diaminobiphenyl-3,3′-diol, 2,2′-bis (3-amino-4- Hydroxyphenyl) hexafluoropropane. Among these, 2,2'-bis (3-amino-4-hydroxyphenyl) hexafluoropropane is particularly preferable.

  Examples of the tetracarboxylic dianhydride represented by the general formula (6) used for the synthesis of the alkali-soluble polyimide according to the second embodiment include 3,3 ′, 4,4′-biphenyltetracarboxylic acid dihydrate. Anhydride, 2,3,3 ′, 4′-biphenyltetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenone Tetracarboxylic dianhydride, 2,2 ′, 3,3′-benzophenonetetracarboxylic dianhydride, 3,3′-oxydiphthalic dianhydride, 4,4′-oxydiphthalic dianhydride, bis (3 , 4-dicarboxyphenyl) sulfone dianhydride, polydimethylsiloxane-containing acid dianhydride, and the like. These tetracarboxylic dianhydrides may be used alone or in combination of two or more.

  Examples of the diamine in which the residue from which the amine group has been removed are represented by the above general formula (5) include 4,4′-diaminobiphenyl-3,3′-diol and 3,3′-diaminobiphenyl-4,4′-. Diol, 4,3′-diaminobiphenyl-3,4′-diol, 4,4′-diaminobiphenyl-3,3 ′, 5,5′-tetraol, 3,3′-diaminobiphenyl-4,4 ′ , 5,5′-tetraol, 2,2′-bis (3-amino-4-hydroxyphenyl) hexafluoropropane, 2,2′-bis (3-amino-2,4-dihydroxyphenyl) hexafluoropropane 2,2′-bis (4-amino-3,5-dihydroxyphenyl) hexafluoropropane and the like. These diamines may be used alone or in combination of two or more. Among these diamines, 4,4′-diaminobiphenyl-3,3′-diol, 2,2′-bis (3-amino-), from the viewpoints of solubility, insulation reliability, polymerization rate, and availability of polyimide. 4-Hydroxyphenyl) hexafluoropropane is preferred.

  As content of the diamine represented by the said General formula (5), it is preferable that it is 5 mol%-30 mol% with respect to all the diamine, and it is more preferable that it is 10 mol%-25 mol%. If the content of the diamine represented by the general formula (5) is 5 mol% or more, the alkali solubility is improved, and if it is 30 mol% or less, the solvent solubility is improved.

  In addition to the tetracarboxylic dianhydride, a conventionally known tetracarboxylic dianhydride may be used in combination as long as the effects of the present invention are achieved. Examples of such tetracarboxylic dianhydrides include pyromellitic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3- Dicarboxyphenyl) propane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, bis (3 , 4-Dicarboxyphenyl) methane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, 2,2-bis (4- (4-aminophenoxy) phenyl) propane, 1,3-dihydro -1,3-dioxo-5-isobenzofurancarboxylic acid-1,4-phenylene ester, 4- (2,5-dioxotetrahydrofuran-3-yl) -1,2,3,4-tetrahydrona Talen-1,2-dicarboxylic anhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 2,3,5,6 -Pyridinetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride, 2,2- Bis (4- (3,4-dicarboxyphenoxy) phenyl) hexafluoropropane dianhydride, 2,2-bis (4- (3,4-dicarboxybenzoyloxy) phenyl) hexafluoropropane dianhydride, 2 , 2′-bis (trifluoromethyl) -4,4′-bis (3,4-dicarboxyphenoxy) biphenyl dianhydride and the like, and cyclobutanthate Carboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 2,3,5,6-cyclohexanetetracarboxylic dianhydride, 5- (2,5-dioxotetrahydro- 3-furanyl) -3-methyl-3-cyclohexene-1,2-dicarboxylic dianhydride, bicyclo [2,2,2] oct-7-ene-2,3,5,6 tetracarboxylic dianhydride And aliphatic tetracarboxylic dianhydrides such as 1,2,3,4-butanetetracarboxylic dianhydride. These tetracarboxylic dianhydrides may be used alone or in combination of two or more. Among these tetracarboxylic dianhydrides, 4,4'-oxydiphthalic dianhydride is preferably used from the viewpoint of flexibility, solubility, insulation reliability and polymerization rate of polyimide.

  Moreover, conventionally well-known diamino can be used together with the said diamine in the range with the effect of this invention. Examples of such diamines include 3,3′-diaminobenzophenone, 4,4′-diaminobenzophenone, 3,3′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether, 1,3-bis (3-amino Phenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, bis (3- (3-aminophenoxy) phenyl) ether, bis (4- (4-aminophenoxy) phenyl) ether, 1,3-bis (3- (3-aminophenoxy) phenoxy) benzene, 1,4-bis (4- (4-aminophenoxy) phenoxy) benzene, bis (3- (3- (3-aminophenoxy) phenoxy) phenyl) ether, Bis (4- (4- (4-aminophenoxy) phenoxy) phenyl) ether, 1,3-bis ( -(3- (3-aminophenoxy) phenoxy) phenoxy) benzene, 1,4-bis (4- (4- (4-aminophenoxy) phenoxy) phenoxy) benzene, 4,4'-bis (3-aminophenoxy) ) Biphenyl, 4,4′-bis (4-aminophenoxy) biphenyl, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl ] Propane, 2,2-bis [4- (3-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2-bis [4- (4-aminophenoxy) Phenyl] -1,1,1,3,3,3-hexafluoropropane, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, bis (3-amino Phenyl) sulfide, bis (4-aminophenyl) sulfide, bis (3-aminophenyl) sulfoxide, bis (4-aminophenyl) sulfoxide, bis (3-aminophenyl) sulfone, bis (4-aminophenyl) sulfone, 2 , 2-bis [4- (3-aminophenoxy) phenyl] butane, α, ω-bis (2-aminoethyl) polydimethylsiloxane, α, ω-bis (3-aminopropyl) polydimethylsiloxane, α, ω -Bis (4-aminobutyl) polydimethylsiloxane, α, ω-bis (4-aminophenyl) polydimethylsiloxane, α, ω-bis (3-aminopropyl) polydiphenylsiloxane, and the like.

  Among these diamines, polyoxyethylene diamine, polyoxypropylene diamine, and other polyoxyalkylene diamines containing oxyalkylene groups having different numbers of carbon chains are preferably used in order to reduce the elastic modulus of polyimide. Examples of polyoxyalkylene diamines include polyoxyethylene diamines such as Jeffamine ED-600, ED-900, ED-2003, EDR-148, and HK-511 manufactured by Huntsman, Jeffamine D-230, D-400, Polyoxypropylene diamines such as D-2000, D-4000, polyetheramine D-230, D-400, D-2000 manufactured by BASF, and poly, such as Jeffamine XTJ-542, XTJ-533, XTJ-536 Examples thereof include a diamine having a tetramethyleneethylene group. Furthermore, in order to improve the solubility of polyimide, α, ω-bis (2-aminoethyl) polydimethylsiloxane, α, ω-bis (3-aminopropyl) polydimethylsiloxane, α, ω-bis (4 -Aminobutyl) polydimethylsiloxane, α, ω-bis (4-aminophenyl) polydimethylsiloxane, α, ω-bis (3-aminopropyl) polydiphenylsiloxane, α- (2-aminopropyl) -ω-aminopoly (Oxypropylene) and the like can be used.

  As content of the said diamine, it is preferable that it is 25 mol%-65 mol% with respect to all the diamine, and it is more preferable that it is 40 mol%-65 mol%. The elastic modulus of a polyimide becomes a suitable range because content of the said diamine is 25 mol%-65 mol%. Moreover, if content of the said diamine is 25 mol% or more, a softness | flexibility and solvent solubility will improve, and if it is 65 mol% or less, alkali solubility will improve.

  Next, a method for producing polyimide will be described. As a method for producing polyimide, all methods for producing polyimide including known methods can be applied. Among these, it is preferable to perform the reaction in an organic solvent. Examples of the solvent used for the synthesis of polyimide include N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, γ-butyrolactone, triglyme, 1,2-dimethoxyethane, tetrahydrofuran, 1 , 3-dioxane, 1,4-dioxane, dimethyl sulfoxide, benzene, toluene, xylene, mesitylene, phenol, cresol, methyl benzoate, ethyl benzoate and the like. These may be used alone or in combination of two or more.

  From the viewpoint of making the residual solvent amount of the adhesive resin cured product layers 13a and 13b within a preferable range, a solvent having excellent drying property is preferable as a solvent used for polymerization of polyimide. Examples of the solvent having excellent drying properties include solvents that do not contain an amide structure. Among these, γ-butyrolactone, triglyme, 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxane, 1,4-dioxane, dimethyl sulfoxide, benzene, toluene, xylene, mesitylene, phenol, cresol, excellent in volatility, Methyl benzoate, ethyl benzoate and the like are preferable.

  When a polyimide having a amide structure such as N, N-dimethylformamide, N, N-dimethylacetamide, or N-methyl-2-pyrrolidone is used in the synthesis of polyimide, the polyimide and amide structure are also used under reduced pressure conditions. It is difficult to reduce the residual amount of the solvent to 0.5% or less due to hydrogen bonding between the solvent and the solvent. When a polyimide is polymerized using a solvent having an amide structure, a poor solvent is added after the polymerization to precipitate the polymer, the precipitated polymer is collected and dried, and then dissolved again in a solvent with good volatility. It is preferable to use it.

  As a density | concentration of the reaction raw material in the synthesis | combination of a polyimide, it is preferable that it is 2 mass%-80 mass%, and it is more preferable that it is 20 mass%-50 mass%.

  The molar ratio of tetracarboxylic dianhydride and diamine used for the synthesis of polyimide is preferably in the range of 0.8 to 1.2. Within this range, the molecular weight of the polyimide can be increased, and the elongation and the like are also improved. The molar ratio of tetracarboxylic dianhydride and diamine is more preferably 0.9 to 1.1, and still more preferably 0.92 to 1.07.

  The weight average molecular weight of the polyimide is preferably 5000 or more and 100,000 or less. Here, the weight average molecular weight refers to a molecular weight measured by gel permeation chromatography using polystyrene having a known number average molecular weight as a standard. The weight average molecular weight is more preferably from 10,000 to 60,000, and even more preferably from 15,000 to 50,000. When the weight average molecular weight is from 5,000 to 100,000, the elongation of the cured adhesive resin layers 13a and 13b obtained using the adhesive resin varnish is improved, and the mechanical properties are improved. Further, it can be applied without bleeding to a desired film thickness when the uncured adhesive resin layers 13a 'and 13b' are applied.

  Specifically, the polyimide is synthesized by the following method. First, the polyimide precursor which consists of a polyamic acid structure is manufactured by carrying out the polycondensation reaction of the reaction raw material within the range of room temperature to 80 degreeC. Next, the polyimide precursor is preferably heated to 100 ° C. to 400 ° C. to imidize, or chemically imidized using an imidizing agent such as acetic anhydride, thereby repeating unit structure corresponding to polyamic acid. Is obtained. In the case of imidization by heating, in order to remove by-product water, dehydration is carried out under reflux using a Dean-Stark type dehydrator in the presence of an azeotropic agent (preferably toluene or xylene). Is also preferable.

  Moreover, it is also preferable to obtain a polyimide by carrying out the reaction at 80 ° C. to 220 ° C. to advance both the generation of the polyimide precursor and the thermal imidization reaction. That is, a diamine component and an acid dianhydride component are suspended or dissolved in an organic solvent, and reacted under heating at 80 ° C. to 220 ° C. to cause both generation of a polyimide precursor and dehydration imidization. It is also preferable to obtain polyimide.

  Moreover, the terminal of the polymer main chain of the polyimide precursor can be end-capped with a terminal capping agent made of a monoamine derivative or a carboxylic acid derivative. By sealing the terminal of the polymer main chain of polyimide, the storage stability derived from the terminal functional group is excellent.

  Examples of the end capping agent comprising a monoamine derivative include aniline, o-toluidine, m-toluidine, p-toluidine, 2,3-xylidine, 2,6-xylidine, 3,4-xylidine, and 3,5-xylidine. O-chloroaniline, m-chloroaniline, p-chloroaniline, o-bromoaniline, m-bromoaniline, p-bromoaniline, o-nitroaniline, p-nitroaniline, m-nitroaniline, o-aminophenol P-aminophenol, m-aminophenol, o-anisidine, m-anisidine, p-anisidine, o-phenetidine, m-phenetidine, p-phenetidine, o-aminobenzaldehyde, p-aminobenzaldehyde, m-aminobenzaldehyde, o-aminobenzonitrile, p-aminobenzonitrile Ryl, m-aminobenzonitrile, 2-aminobiphenyl, 3-aminobiphenyl, 4-aminobiphenyl, 2-aminophenylphenyl ether, 3-aminophenylphenyl ether, 4-aminophenylphenyl ether, 2-aminobenzophenone, 3 -Aminobenzophenone, 4-aminobenzophenone, 2-aminophenyl phenyl sulfide, 3-aminophenyl phenyl sulfide, 4-aminophenyl phenyl sulfide, 2-aminophenyl phenyl sulfone, 3-aminophenyl phenyl sulfone, 4-aminophenyl phenyl sulfone , Α-naphthylamine, β-naphthylamine, 1-amino-2-naphthol, 5-amino-1-naphthol, 2-amino-1-naphthol, 4-amino-1-naphthol, 5-amino Aromatic monoamines such as 2-naphthol, 7-amino-2-naphthol, 8-amino-1-naphthol, 8-amino-2-naphthol, 1-aminoanthracene, 2-aminoanthracene, 9-aminoanthracene Of these, derivatives of aniline are preferably used. These may be used alone or in combination of two or more.

  Examples of the terminal blocking agent made of a carboxylic acid derivative mainly include carboxylic anhydride derivatives. Examples of the terminal blocking agent comprising a carboxylic acid derivative include phthalic anhydride, 2,3-benzophenone dicarboxylic acid anhydride, 3,4-benzophenone dicarboxylic acid anhydride, 2,3-dicarboxyphenyl phenyl ether anhydride, 3,4-dicarboxyphenyl phenyl ether anhydride, 2,3-biphenyl dicarboxylic acid anhydride, 3,4-biphenyl dicarboxylic acid anhydride, 2,3-dicarboxyphenyl phenyl sulfone anhydride, 3,4-dicarboxy Phenylphenyl sulfone anhydride, 2,3-dicarboxyphenyl phenyl sulfide anhydride, 3,4-dicarboxyphenyl phenyl sulfide anhydride, 1,2-naphthalenedicarboxylic acid anhydride, 2,3-naphthalenedicarboxylic acid anhydride, 1,8-naphthalenedicarboxylic anhydride, 1,2-a Tiger Sen dicarboxylic acid anhydride, 2,3-anthracene dicarboxylic acid anhydride, 1,9-aromatic dicarboxylic acid anhydrides such as anthracene dicarboxylic acid anhydride. Of these aromatic dicarboxylic acid anhydrides, phthalic anhydride is preferably used. These may be used alone or in combination of two or more.

  You may use the polyimide solution obtained by superposition | polymerization as it is, without removing a solvent. Moreover, it can also be set as an adhesive resin varnish by adding a required solvent, an additive, etc.

(B) Reactive compound A reactive compound reacts with the hydroxyl group of the alkali-soluble hydroxyl group-containing resin described above. When the reactive compound reacts with the hydroxyl group of the hydroxyl group-containing compound, the uncured adhesive resin layers 13a ′ and 13b ′ are heated and cured, and the alkali resistance of the cured adhesive resin layers 13a and 13b is expressed. In the present embodiment, the reactive compound has at least one reactive functional group that reacts with the hydroxyl group of the hydroxyl group-containing resin in the molecule. Examples of the reactive functional group include an oxazoline group, an oxazine group, an epoxy group, and an oxetane group.

  In the method for manufacturing a multilayer flexible wiring board according to the present embodiment, the uncured adhesive resin layers 13a ′ and 13b ′ are dissolved and removed through a conformal mask formed on the external conductive layers 14a and 14b, and the blind via hole 17 is removed. Form. Then, after forming the blind via hole 17, the uncured adhesive resin layers 13a 'and 13b' are cured by heating. For this reason, in the uncured adhesive resin layers 13a and 13b ′, sufficient alkali solubility is required before heating, and the alkali solubility of the adhesive resin cured product layers 13a and 13b is lowered after heat curing. It is necessary to let Therefore, in the present embodiment, the reactive compound is 100 ° C. or less, preferably 120 ° C. or less, and the reaction of the hydroxyl group-containing resin with the hydroxyl group proceeds slowly, and the reaction is performed at 170 ° C. or more, preferably 150 ° C. or more. Is used so that the uncured adhesive resin layers 13a ′ and 13b ′ are sufficiently cured.

  Examples of the reactive compound include an oxazoline compound, a benzoxazine compound, an epoxy compound, an oxetane compound, and the like. Among these, an oxazoline compound, a benzoxazine compound, and an oxetane compound are preferable, and an oxazoline compound that does not by-produce water by reaction with a hydroxyl group of a hydroxyl group-containing resin is particularly preferable. Here, the oxazoline compound is a compound having at least one oxazoline group in the molecule. Moreover, as an oxazoline compound, what has two or more oxazoline groups in a molecule | numerator from a viewpoint of sealing the hydroxyl group of a hydroxyl-containing compound and forming bridge | crosslinking between hydroxyl-containing compounds is preferable.

  In the present embodiment, an appropriate amount of a reactive compound (for example, an oxazoline compound) is added to a hydroxyl group-containing resin (for example, polyimide) having a hydroxyl group, and dried at an appropriate temperature. Thereby, the uncured adhesive resin layers 13a ′ and 13b ′ are dissolved and removed by a 3% by mass aqueous sodium hydroxide solution at a predetermined temperature (for example, 48 ° C.) to form through vias, blind vias, or through holes. It becomes possible. In addition, the hydroxyl group of the hydroxyl group-containing resin reacts with the reactive compound (for example, the oxazoline group of the oxazoline compound) by a heat treatment for 1 hour at a predetermined temperature (for example, 180 ° C.), and can exhibit resistance to an aqueous alkali solution. . Further, when a reaction compound containing a plurality of oxazoline groups is used, cross-linking is formed between the molecules of the hydroxyl group-containing compound (for example, polyimide).

  Examples of the oxazoline compound include 1,3-bis (4,5-dihydro-2-oxazolyl) benzene, K-2010E, K-2020E, K-2030E, 2,6-bis (4- Isopropyl-2-oxazolin-2-yl) pyridine, 2,6-bis (4-phenyl-2-oxazolin-2-yl) pyridine, 2,2′-isopropylidenebis (4-phenyl-2-oxazoline), 2,2'-isopropylidenebis (4-tertiarybutyl-2-oxazoline) and the like can be mentioned. These oxazoline compounds may be used alone or in combination of two or more.

  As the addition amount of the oxazoline compound, the molar ratio of the hydroxyl group of the hydroxyl group-containing compound to the oxazoline group of the oxazoline compound is preferably hydroxyl group / oxazoline group = 0.5-4, and preferably 0.7-3. More preferred. If the hydroxyl group / oxazoline group = 0.5 or more, the flexibility and heat resistance of the cured adhesive resin layers 13a and 13b are improved. If the hydroxyl group / oxazoline group = 4 or less, the uncured adhesive resin layer 13a. The alkali processability of “, 13b” is improved.

  From the viewpoint of sufficiently removing volatile components such as a solvent and residual monomer and making it soluble in an alkaline aqueous solution, the uncured adhesive resin layers 13a ′ and 13b ′ are: It is preferable to heat at 50 to 140 ° C. for 1 to 60 minutes by a vacuum drying method or the like. The uncured adhesive resin layers 13a ′ and 13b ′ heated at 50 to 140 ° C. for 1 to 60 minutes are soluble in an alkaline aqueous solution, so that there is no need for laser drilling or the like used in the production of flexible printed wiring boards. And can be used as uncured adhesive resin layers 13a ′ and 13b ′ that can process blind vias with an alkaline aqueous solution.

  After the blind via is formed with an alkaline aqueous solution, the remaining uncured adhesive resin layers 13a ′ and 13b ′ are heated at a higher temperature (for example, 160 ° C. to 200 ° C.), so that the hydroxyl group-containing compound and the reactive compound are heated. In this case, a crosslinking reaction mainly occurs and becomes insoluble in an alkaline aqueous solution. Specifically, depending on the film thickness of the uncured adhesive resin layers 13a ′ and 13b ′ to be formed, the maximum temperature is set in a range of 150 ° C. to 220 ° C. in an oven or a hot plate, and air is applied for 5 minutes to 100 minutes. Alternatively, the crosslinking reaction proceeds by heating in an inert atmosphere such as nitrogen. The heating temperature may be constant over the entire processing time or may be gradually raised.

  When an oxazoline compound is used as the reactive compound, the cured adhesive resin cured product layers 13a and 13b of the multilayer flexible wiring board 1 obtained through the cross-linking reaction are substantially free from free components. The adhesive resin cured products 13a and 13b include a reaction product having an amide structure and an ether structure. The amide structure and ether structure of this reaction product can be analyzed by microinfrared spectroscopy.

(C) Flame retardant The adhesive resin varnish according to the present embodiment can also be used by containing a flame retardant from the viewpoint of improving flame retardancy. Although it does not restrict | limit especially as a flame retardant, A halogen-containing compound, a phosphorus-containing compound, an inorganic flame retardant, etc. are mentioned. These flame retardants may be used alone or in combination of two or more.

  Examples of the halogen-containing compound include an organic compound containing chlorine and an organic compound containing bromine. Examples of the halogen-containing compound include pentabromodiphenyl ether, octabromodiphenyl ether, decabromodiphenyl ether, tetrabromobisphenol A, hexabromocyclododecane tetrabromobisphenol A, and the like.

  Examples of the phosphorus-containing compound include phosphorus compounds such as phosphazene, phosphine, phosphine oxide, phosphate ester, and phosphite ester. In particular, when polyimide is used as the hydroxyl group-containing compound, it is preferable to use phosphazene, phosphioxide or phosphate ester from the viewpoint of compatibility with polyimide.

  As the phosphazene, a cyclic phosphazene having a phenoxy group is preferable, and a cyclic phosphazene having a cyano group or a hydroxyl group in addition to the phenoxy group is more preferable. The cyclic phosphazene having a hydroxyl group and a phenoxy group is alkalinized by reacting the hydroxyl group of the cyclic phosphazene with a reactive compound (for example, the oxazoline group of the oxazoline compound) when the uncured adhesive resin layers 13a ′ and 13b ′ are heated and cured. Since solubility can be reduced, it is preferable. In particular, it is preferable to use a mixture of a cyclic phosphazene having a cyano group in the phenoxy group and a cyclic phosphazene having a hydroxyl group in the phenoxy group.

  Examples of inorganic flame retardants include antimony compounds and metal hydroxides. Examples of the antimony compound include antimony trioxide and antimony pentoxide. By using the antimony compound and the halogen-containing compound in combination, the antimony compound pulls out the halogen atom from the halogen-containing compound at a predetermined temperature (for example, the thermal decomposition temperature range of the plastic) to generate antimony halide. The flame retardancy can be increased. Examples of the metal hydroxide include aluminum hydroxide and magnesium hydroxide.

  Since an inorganic flame retardant does not dissolve in an organic solvent, it is preferable to use a powder having a particle size of 100 μm or less. If the particle size of the powder is 100 μm or less, it is preferable because it is easy to be mixed into the uncured adhesive resin layers 13a ′ and 13b ′ and the transparency of the cured cured adhesive resin is not impaired. In order to further increase the flame retardancy, the particle size of the powder is preferably 50 μm or less, and more preferably 10 μm or less.

  The addition amount of the flame retardant is not particularly limited and is appropriately selected depending on the type of the flame retardant used. Generally, it is used in the range of 5% by mass to 50% based on the content of the hydroxyl group-containing compound.

  When the uncured adhesive resin layers 13a 'and 13b' are formed into a coating film using an adhesive resin varnish, the viscosity and thixotropy are adjusted according to the coating method. If necessary, a filler or a thixotropic agent can be added and used. It is also possible to add additives such as known antifoaming agents, leveling agents and pigments.

(D) Adhesive Material The adhesive resin varnish according to the present embodiment is used by including an adhesive material from the viewpoint of improving the adhesion between the internal conductive layers 12a and 12b and the external conductive layers 14a and 14b. You can also. Although it does not restrict | limit especially as an adhesive material, A phenol compound, a nitrogen-containing organic compound, an acetylacetone metal complex etc. are mentioned. Among these, a phenol compound is particularly preferable.

  The adhesive resin varnish may contain an organic solvent in addition to a hydroxyl group-containing compound and a reactive compound. By making it the state melt | dissolved in the organic solvent, it can be preferably used as a varnish.

  Examples of such organic solvents include amide solvents such as N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dimethylformamide, N, N-diethylformamide, N-methyl-2-pyrrolidone, γ -Lactone solvents such as butyrolactone and γ-valerolactone, sulfur-containing solvents such as dimethyl sulfoxide, diethyl sulfoxide and hexamethyl sulfoxide, phenol solvents such as cresol and phenol, diethylene glycol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme) And ether solvents such as tetraglyme, dioxane, tetrahydrofuran, butyl benzoate, ethyl benzoate, and methyl benzoate. These organic solvents may be used alone or in combination.

  In the present embodiment, in order to develop the formation property of the blind via and the heat resistance of the solder reflow and the thermal cycle test of the multilayer board, the solvent is added while suppressing the reaction between the hydroxyl group-containing compound and the reactive compound. It is necessary to volatilize. When an amide solvent is used, the hydrogen bond between the hydroxyl group of the hydroxyl group-containing compound (for example, polyimide) and the amide solvent is strong, and the amide solvent is less likely to volatilize. Therefore, as a solvent for the adhesive resin varnish, γ-butyrolactone, triglyme, 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxane, 1,4, which does not contain an amide structure and has excellent volatility. -Solvents such as dioxane, dimethyl sulfoxide, benzene, toluene, xylene, mesitylene, phenol, cresol, methyl benzoate, ethyl benzoate are preferably used. Since these solvents can reduce the amount of residual solvent by drying under normal pressure, they are excellent in productivity.

  The adhesive resin varnish may contain a crosslinkable compound having a thermally crosslinkable functional group. The heat crosslinkable compound is not particularly limited as long as it forms a crosslink via a heat crosslinkable functional group, and examples thereof include triazine compounds and benzoxazine compounds.

  As the triazine compound, melamines and cyanuric acid melamines are preferable. Examples of melamines include melamine derivatives, compounds having a structure similar to melamine, and melamine condensates. Specific examples of melamines include, for example, methylolated melamine, ammelide, ammelin, formoguanamine, guanylmelamine, cyanomelamine, arylguanamine, melam, melem, melon and the like.

  Examples of melamine cyanurates include equimolar reaction products of cyanuric acid and melamines. Moreover, some of the amino groups or hydroxyl groups in the melamine cyanurates may be substituted with other substituents. Among these, melamine cyanurate can be obtained, for example, by mixing an aqueous solution of cyanuric acid and an aqueous solution of melamine, reacting at 90 ° C. to 100 ° C. with stirring, and filtering the generated precipitate, Yes, a commercially available product can be used as it is or after being pulverized into a fine powder.

  The benzoxazine compound may be composed only of monomers, or several molecules may be polymerized into an oligomer state. Moreover, you may use the benzoxazine compound which has a different structure simultaneously. Specifically, bisphenol benzoxazine is preferably used.

  Further, the uncured adhesive resin layers 13a 'and 13b' according to the present embodiment can be used as a resin-coated metal foil by applying an adhesive resin varnish on the metal foil and drying it. In this case, there is no particular limitation on the method of applying and drying the adhesive resin varnish for forming the uncured adhesive resin layers 13a 'and 13b' on the surface of the copper foil. For example, the adhesive resin varnish is coated on the surface of the copper foil using an edge coater, gravure coater, spin coater, etc., and dried in a heating furnace to be semi-cured uncured adhesive resin layer on the copper foil. 13a 'and 13b' are formed to obtain a resin-coated copper foil. The film thickness obtained after drying is an average thickness of 5 μm to 50 μm. In order to reduce the solvent in the uncured adhesive resin layers 13a 'and 13b', it is preferable to heat at 50 ° C to 140 ° C for 1 minute to 60 minutes at normal pressure or reduced pressure.

  Moreover, the adhesive resin hardened | cured material 13 which concerns on this Embodiment protects the wiring pattern of a wiring board by providing adhesive resin hardened | cured material layer 13a, 13b so that the wiring pattern formed on the base material may be covered. It can be suitably used as a film.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples made to clarify the effects of the present invention, but the present invention is not limited to these examples.

<Reagent>
In the examples and comparative examples, the reagents used are as follows.
Polyimide component: BPDA (Mitsui Chemicals), 1,3-bis (3-aminophenoxy) benzene (APB-N) (Mitsui Chemicals), 4,4'-oxydiphthalic dianhydride (ODPA) (Manac Co., Ltd.), polyalkyl ether diamine Baxodur (TM) EC302 (manufactured by BASF), 2,2′-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (6FAP) (CHANGE ZHOU SUNLIGHT MEDICAL RAW MATERIAL CO.,) LTD.).
Oxazoline compound: 1,3-bis (4,5-dihydro-2-oxazolyl) benzene (PBO) (manufactured by Mikuni Pharmaceutical Co., Ltd.).
Phosphazene compounds: (trade name) FP-300, FP-400 (Fushimi Pharmaceutical Co., Ltd.).
Solvent: 1,3-dimethyl-2-imidazolidinone (DMI) (manufactured by Neos).
Others: Toluene, γ-butyrolactone, triethylene glycol dimethyl ether, dimethyl sulfoxide, phenol, 4,4'-di (chloromethyl) biphenyl, formalin aqueous solution, methanol, caustic soda are specially purified reagents manufactured by Wako Pure Chemical Industries, Ltd. Was used without performing.

<Weight average molecular weight measurement>
Gel permeation chromatography (GPC), which is a method for measuring the weight average molecular weight, was measured under the following conditions. Using N, N-dimethylformamide (manufactured by Wako Pure Chemical Industries, Ltd., for high performance liquid chromatograph) as a solvent, 24.8 mmol / L lithium bromide monohydrate (manufactured by Wako Pure Chemical Industries, Ltd., purity before measurement) 99.5%) and 63.2 mmol / L phosphoric acid (manufactured by Wako Pure Chemical Industries, Ltd., for high performance liquid chromatograph) were used.
Column: Shodex KD-806M (manufactured by Showa Denko KK)
Flow rate: 1.0 mL / min Column temperature: 40 ° C
Pump: PU-2080 Plus (manufactured by JASCO)
Detector: UV-2075 Plus (UV-VIS: UV-Visible Absorber, manufactured by JASCO)
A calibration curve for calculating the weight average molecular weight was prepared using standard polystyrene (manufactured by Tosoh Corporation).

<Measurement of alkali dissolution rate of cured adhesive resin>
The alkali dissolution rate of the cured adhesive resin is determined by the adhesive adhesion after the outer conductive layer of the rigid part of the multilayer flexible printed wiring board produced by router processing (outer shape processing) remains thin and the external conductive layer is removed by etching. It measured with respect to the surface of a resin cured material layer. The surface of the cured adhesive resin was sprayed with a 3% sodium hydroxide solution at 48 ° C. for 5 to 60 minutes, washed with water, and dried at 50 ° C. for 5 hours. The film thickness remaining at room temperature was measured and the dissolved film thickness was divided by the time taken for dissolution to determine the film reduction rate.

<Measurement of residual solvent amount of cured adhesive resin>
The measurement of the amount of residual solvent in the cured adhesive resin was measured after leaving the outer conductive layer of the rigid part of the multilayer flexible printed wiring board produced by router processing (outer shape processing) thin, removing the external conductive layer by etching, and then exposing it. It implemented using the adhesive resin hardened | cured material. The cured adhesive resin was finely cut, immersed in a solvent DMF, and heated at about 60 ° C. overnight to extract the remaining solvent. Using a # 007-17 (ID-0.32 mm, film thickness 0.50 μm, length 30 m) column manufactured by Quadrex, gas chromatography (GC analysis) was performed to determine the amount of residual solvent.

<Measurement of glass transition temperature, elongation, thermal expansion coefficient, elastic modulus of cured adhesive resin>
The glass transition temperature (Tg), thermomechanical analysis, and measurement of tensile elastic modulus of the cured adhesive resin were carried out using the adhesive cured product layer obtained as follows. First, the adhesive resin cured product layer of the flexible part is removed by router processing (outer diameter processing), and after leaving the inner conductive layer thin, the inner conductive layer is removed by etching, and the cured adhesive resin product is obtained. Get a layer. Next, after the adhesive resin cured product layer was washed with water, the cured adhesive resin cured product was used at 50 ° C. for 5 hours. A sample was prepared so that the film thickness of the cured adhesive resin layer was 30 μm.

  The glass transition temperature (Tg), elongation, and thermal expansion coefficient (CTE) were measured by setting the sample in a TMA tester (EXSTAR6000 / Seiko Instruments). Measurement was performed under a load of 1.25 mN / μm, under nitrogen at a rate of temperature increase of 10 ° C./min, and the temperature was raised from room temperature to 220 ° C. to determine the glass transition temperature and elongation. As the maximum thermal expansion coefficient, the maximum value was used in the thermal expansion coefficient obtained by the tangent of the slope of the elongation-temperature curve obtained by raising the temperature from 30 ° C. to 180 ° C. The elastic modulus (tensile elastic modulus) was measured according to JIS C 2318.

<Measurement of via shape>
The produced multilayer flexible wiring board was embedded with an epoxy resin, then subjected to cross-section polishing, and the shape of the blind via was observed with an optical microscope. The case where no resin residue was observed on the wall surface or bottom of the blind via was marked as ◯, and the case where resin residue was observed on the wall surface or bottom of the blind via was marked as x.

<Haze folding test>
Folding resistance was evaluated by a goby folding test. Resin on comb substrate of wiring surface (line and space is 20 μm / 20 μm, base film thickness is 20 μm) after copper etch-out using ESPANEX MC-12-20-00CEM (manufactured by Nippon Steel Chemical Co., Ltd.) After laminating the copper foil and performing predetermined drying and curing, the copper layer of the resin-coated copper foil portion was removed by etching. Next, a sample was prepared by drying at 50 ° C., and 180 ° goby folding (counting once with one reciprocation) was performed using the prepared sample. Observe the folded part with an optical microscope (ECLIPS LV100 made by Nikon Co., Ltd.), ◎ if the resin layer and the copper layer are not cracked more than twice, and ◯ if the crack is in the second time, The case where cracks occurred at the first time was marked with x.

<Solder reflow resistance test>
In accordance with the JPCA-BM02 standard, the solder reflow resistance test was performed by laminating a copper foil with a resin on a copper foil, performing predetermined drying and curing, and then cutting the sample cut to 3 cm × 3 cm in a solder bath at 260 ° C. for 60 seconds. Dipping was carried out. The surface was observed with a 500-fold optical microscope, and when there was no abnormality such as blistering or scorching on the film surface, it was rated as ◯, and when abnormality was observed, it was marked as x. In addition, the swelling here indicates that the surface of the cured film had a bulge of 5 μm or more after the immersion in the solder bath, and the burning indicates that the area of 1% or more was discolored.

<Cooling cycle resistance (cooling shock test)>
In the thermal shock test, the produced four-layer wiring board was evaluated at −40 ° C., 120 ° C., and 1000 cycles according to the JPCA-HD01-2003 standard. The case where the fluctuation of the connection resistance during the cycle was within 10% was marked with ◯, and the case where it exceeded 10% was marked with x.

<Insulation reliability test (85 ° C, 85% humidity)>
The insulation reliability test was performed as follows. Espanex M (manufactured by Nippon Steel Chemical Co., Ltd.) (insulating layer thickness 25 μm, conductor layer copper foil F2-WS (18 μm)) is used as the base material of the flexible printed circuit board. Line / space: 50 μm / 50 μm A comb-shaped wiring board was created. On this circuit board, a copper foil with resin (film thickness after drying of the resin part is 15 microns) was laminated, dried and cured, and then the copper foil of the copper foil with resin layer was removed by etching. The resistance is measured while standing for 8 hours under the conditions of DC 50 V, 85 ° C., and humidity 85%. The case where the insulation resistance is 10 9 Ω or more is ◎, the case of 10 8 Ω is ◎, 10 The case where it did not reach the 8th power of Ω was taken as x.

<Insulation reliability test (HAST resistance)>
The insulation reliability test was performed as follows. An adhesive resin varnish was applied onto a comb-type substrate having a line and space of 20 μm / 20 μm, dried, and baked at 180 ° C. for 1 hour. The migration tester cable was soldered, and the insulation resistance value was measured under the following conditions.
Insulation degradation evaluation system: SIR-12 (Enomoto Kasei Co., Ltd.)
HAST chamber: EHS-211M (Espec Corp.)
Temperature: 110 ° C
Humidity: 85%
Applied voltage: 2V
Application time: 528 hours Insulation resistance value: The case where the insulation resistance is 10 8 Ω or more, ◎, the case of 10 7 Ω range is ◯, and the case where it does not reach 10 7 Ω is ×.

<Appearance (Dendrite)>
The comb substrate after the above insulation reliability test was observed with an optical microscope (ECLIPS LV100, manufactured by Nikon Corporation) under the conditions of transmitted light and 200 times. It was.

[Preparation Example 1]
A three-necked separable flask was equipped with a nitrogen condenser, a thermometer, and a ball condenser equipped with a moisture separation trap. At oil bath room temperature, triethylene glycol dimethyl ether (22.5 g), γ-butyrolactone (52.5 g), toluene (20.0 g), 4,4′-oxydiphthalic dianhydride (ODPA) 1.00 g, both ends Acid dianhydride-modified silicone (acid anhydride equivalent = about 500 g / mol) (see the above formula group (7): X-22-2290AS, manufactured by Shin-Etsu Chemical Co., Ltd.) 35.00 g was added and stirred until uniform. Furthermore, after adding 14.2Og of 2,2'-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (6FAP) little by little, it heated up to 180 degreeC and heated for 2 hours. During the reaction, by-product water was azeotroped with toluene and dehydrated under reflux using a ball-mounted condenser equipped with a water separation trap. After draining by-product water, the reflux was stopped, toluene was removed, and the mixture was cooled to room temperature. Next, polyimide A varnish was obtained by carrying out pressure filtration of the product with a 5 micrometers filter. The weight average molecular weight was 27000.

  Polyimide A in the resin composition was 69% by mass, 1,3-bis (4,5-dihydro-2-oxazolyl) benzene (PBO) as an oxazoline compound was 6% by mass, and a flame retardant manufactured by Fushimi Pharmaceutical Co., Ltd. An adhesive resin varnish was prepared so that the FP300 was 25% by mass. Metal foil with resin was created and evaluated.

[Preparation Example 2]
A three-necked separable flask was equipped with a nitrogen condenser, a thermometer, and a ball condenser equipped with a moisture separation trap. In an oil bath room temperature, 344 g of 1,3-dimethyl-2-imidazolidinone (DMI), 90 g of toluene, 78.4 g of dimethyl sulfoxide, 2,2′-bis (3-amino-4-hydroxyphenyl) hexafluoropropane ( (6FAP) 48.8 g and polyalkyl ether diamine Baxxodur (registered trademark) EC302 (manufactured by BASF) 112.8 g were added and stirred until uniform. Further, 120 g of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) was added little by little, and then the temperature was raised to 180 ° C. and heated for 3 hours. During the reaction, by-product water was azeotroped with toluene and dehydrated under reflux using a ball-mounted condenser equipped with a water separation trap. After draining by-product water, the reflux was stopped, toluene was removed, and the mixture was cooled to room temperature. Next, polyimide B varnish was obtained by pressure-filtering the product with a 5 μm filter. The weight average molecular weight was 28000.

  Subsequently, methanol was added to the polymerization solution to precipitate a polymer, and the recovered polymer was dried at 50 ° C. under vacuum for 24 hours. Thereafter, using a mixed solvent of γ-butyrolactone / dimethyl sulfoxide (80/20 mass ratio), polyimide B in the resin composition was 60 mass%, and 1,3-bis (4,5-dihydro- as an oxazoline compound. 2-oxazolyl) benzene (PBO) is 15% by mass, FP300 and FP400 made by Fushimi Pharmaceutical Co., Ltd. as flame retardants are 6% by mass and 18% by mass, respectively, and Irganox 245 (IRG245, manufactured by BASF) is used as an antioxidant. An adhesive resin varnish was prepared so as to be 1% by mass.

[Preparation Example 3]
4,4′-oxydiphthalic dianhydride (ODPA) 7.50 g, acid dianhydride modified silicone at both ends (acid anhydride equivalent = about 500 g / mol) (see formula group (7) above: X-22-2290AS) (Shin-Etsu Chemical Co., Ltd.) 25.00 g and 2,2′-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (6FAP) 17.50 g. It was.

[Preparation Example 4]
In a glass reaction kettle equipped with a stirrer, a condenser, and a nitrogen gas introduction tube, phenol 404.2 g (4.30 mol), 4,4′-di (chloromethyl) biphenyl 150.70 g (0.6 mol) Were added and reacted at 100 ° C. for 3 hours, followed by addition of 28.57 g (0.4 mol) of 42% formalin aqueous solution, and then reacted at 100 ° C. for 3 hours. Meanwhile, the methanol produced was distilled off. After completion of the reaction, the obtained reaction solution was cooled and washed with water three times. The oil layer was separated, and unreacted phenol was removed by distillation under reduced pressure to obtain 251 g of phenol novolac resin D.

  10 g of the obtained phenol novolac resin, 2 g of 1,3-bis (4,5-dihydro-2-oxazolyl) benzene (PBO) as an oxazoline compound, 4 g of FP300 manufactured by Fushimi Pharmaceutical Co., Ltd. as a flame retardant, and N as a solvent -An adhesive resin varnish was prepared using 40 g of methylpyrrolidone.

[Example 1]
As the core substrate, a double-sided flexible wiring board (Espanex M, manufactured by Nippon Steel Chemical Co., Ltd., copper foil thickness 12 μm, insulating resin layer thickness 20 μm) was used. A through via hole having a diameter of 100 μm was formed on the double-sided flexible wiring board by drilling and copper plating. Further, a copper wiring circuit (28 μm thickness) having a minimum pitch of 130 μm was formed.

  As the copper foil with resin (laminated body), the adhesive resin varnish obtained from Preparation Example 1 was applied onto a 12 μm thick electrolytic copper foil (F2-WS, manufactured by Furukawa Electric) using a bar coater, and then 90 ° C. And dried for 30 minutes in a heated oven. This copper foil with resin was placed on the upper and lower surfaces of the core substrate, and further sandwiched from both sides with a release film.

  As the vacuum laminating apparatus, a vacuum press (manufactured by Kitagawa Seiki Co., Ltd.) was used in which a heat-resistant silicon rubber having a hardness of 50% and containing glass cloth inside was bonded to the entire surface of the upper and lower surface plates. The silicon rubber was a 50 cm square size. As a laminating method, the above-mentioned laminated body was put in a state where the silicon rubber surface temperature was preliminarily heated to 100 ° C., evacuation was performed without pressurizing for 2 minutes, and then pressurization was performed at a pressure of 1 MPa for 2 minutes for lamination.

  Next, for connection between the copper foil of the core substrate and the copper foil of the laminated body, after laminating a dry film on the copper foil of the laminated body, the copper foil at a predetermined position by exposure / development and etching And a conformal mask with a diameter of 100 μmφ was formed at a site where a blind via was necessary.

  Next, a 3% sodium hydroxide aqueous solution heated to 48 ° C. is sprayed on the exposed uncured adhesive resin layer for about 30 seconds on the exposed uncured adhesive resin layer to remove the resin layer. The blind via hole was formed.

  Next, the uncured adhesive resin layer in a semi-cured state was cured by heating at 180 ° C. for 1 hour using a curing and drying furnace to obtain a cured adhesive resin layer. Resin residues were not observed on the wall surface and bottom of the obtained blind via, the formation of the blind via hole was good, and the desmear process with an aqueous potassium permanganate solution or the like was unnecessary.

  Next, in order to make an electrical connection with the inner layer core substrate, a plating process for blind via holes was performed. First, carbon fine particles were attached to the cured adhesive resin layer on the inner wall of the hole to form a conductive particle layer. As a forming method, after dipping in a carbon black dispersion, the dispersion wrinkles were removed with an acid-based aqueous solution. Thereafter, electrolytic copper plating was applied to complete electrical connection on both sides.

  Next, the circuit formation process similar to the conventional multilayer flexible wiring board was performed. The subsequent steps were performed in the same manner as in the conventional method for manufacturing a multilayer flexible wiring board.

  Regarding the embedding property of the adhesive resin cured product into the core substrate of the multilayer flexible wiring board thus produced and the surface smoothness in the copper wiring circuit, the cross-section polishing is performed after embedding with an epoxy resin, and the optical microscope is used. Observations were made. When the adhesive resin cured material was embedded in the through via hole, no voids due to poor embedding were confirmed. Regarding the surface smoothness, the difference in the substrate thickness between the copper wiring and the wiring was within 3 μm. The evaluation results are shown in Table 2 below.

  As described above, the multilayer flexible substrate produced in Example 1 can be drilled instantaneously through an exposure / development process, unlike a manufacturing method using a conventional laser processing machine, and can be a simple lamination method. A continuous production process with resin embedding and surface smoothness has become possible.

  The alkali dissolution rate, residual solvent amount, Tg (° C.), elongation (%), maximum coefficient of thermal expansion (CTE, ppm), and elastic modulus of the cured adhesive resin of Example 1 are shown in Table 1 below. The multilayer flexible wiring board of Example 1 was excellent in the shape of via holes, folding resistance, solder reflow resistance, thermal cycle resistance, and insulation reliability.

[Examples 2 to 7 and Comparative Examples 1 to 5]
The multilayer flexible wiring board produced by changing the composition of the resin composition varnish was evaluated. The conditions and results of Examples 2 to 7 are shown in Table 1 and Table 2 below. The conditions and results of Comparative Examples 1 to 5 are shown in Table 3 and Table 4 below. In Example 2, the copper foil with resin was dried at 90 ° C. for 15 minutes under reduced pressure. In Examples 4 to 7 and Comparative Examples 3 and 4, as described in Preparation Example 2, the polymer was precipitated by adding it to a poor solvent, and after collecting and drying, a composition was prepared. Tables 1 and 3 show the drying conditions and heat curing conditions of Examples 1 to 7 and Comparative Examples 1 to 5.

  As can be seen from Table 1 and Table 2, in the multilayer flexible wiring board according to the present embodiment, the alkali dissolution rate of the cured adhesive resin is set within a predetermined range, and the residual solvent amount is set to a predetermined value or less. It can be seen that a multilayer flexible wiring board having excellent folding resistance and insulation reliability and excellent heat resistance can be realized.

  As can be seen from Table 3 and Table 4, in the multilayer flexible wiring board according to the comparative example, at least one of the alkali dissolution rate, the residual solvent amount, and the glass transition temperature of the cured adhesive resin is outside the predetermined range. It can be seen that at least one of folding resistance, insulation reliability, and heat resistance is inferior.

  INDUSTRIAL APPLICABILITY The present invention has an effect that a multilayer flexible wiring board excellent in folding resistance, insulation reliability, and heat resistance can be realized, and in particular, a multilayer flexible wiring for a rigid flexible wiring board used for a mobile phone terminal or the like. It can be suitably used as a plate. Moreover, the manufacturing method of the multilayer flexible wiring board which can reduce via formation cost and is excellent in production efficiency is realizable.

DESCRIPTION OF SYMBOLS 1 Multilayer flexible wiring board 10a Rigid part 10b Flexible part 11 Adhesive resin cured material layer 12a, 12b Internal conductive layer 13 Adhesive resin cured material 13 'Uncured adhesive resin 13a, 13b Adhesive resin cured material layer 13a', 13b 'Uncured adhesive resin layer 14a, 14b External conductive layer 15 Cover coat 16 Through-via hole 16a, 17a Conductive particle layer 16b, 17b Plating 17 Blind via hole 18 Dry film

Claims (14)

  A multilayer flexible wiring board using a core substrate composed of a double-sided flexible substrate having at least two conductive layers, wherein external conductive material is passed through an adhesive resin cured material layer containing an adhesive resin cured material on the conductive layer. Layers are laminated, and the conductive layer of the core substrate and the external conductive layer are electrically connected via a blind via hole provided in the cured adhesive resin layer, and the cured adhesive resin product Has an alkali dissolution rate of 0.0001 μm / sec or more and 0.01 μm / sec or less, a residual solvent amount of 0.5 mass% or less, and a glass transition temperature (Tg) of 125 ° C. or less. A multilayer flexible wiring board.   The multilayer flexible wiring board according to claim 1, wherein the core substrate has through via holes, and the through via holes are filled with the cured adhesive resin.   The cured adhesive resin has an elongation from 30 ° C. to 160 ° C. by thermomechanical analysis (conditions: load 0.5 μN / (μm · μm), nitrogen flow, temperature increase rate 10 ° C./min). 3. The multilayer flexible wiring board according to claim 1, wherein the multilayer flexible wiring board is 50% or less without breaking and has a maximum coefficient of thermal expansion from 30 ° C. to 180 ° C. of 5000 ppm or more.   The multilayer flexible wiring board according to any one of claims 1 to 3, further comprising a conductive particle layer on an inner wall of the blind via hole.   The adhesive resin cured product contains a reaction product of (A) a hydroxyl group-containing resin having a hydroxyl group and (B) a reactive compound that reacts with the hydroxyl group. The multilayer flexible wiring board in any one.   6. The multilayer flexible wiring board according to claim 5, wherein the reactant has an amide structure and an ether structure.   6. The multilayer flexible wiring board according to claim 5, wherein the hydroxyl group of the hydroxyl group-containing resin is a phenolic hydroxyl group.   The multilayer flexible wiring board according to claim 5, wherein the hydroxyl group-containing resin is an alkali-soluble polyimide.   The multilayer flexible wiring board according to any one of claims 5 to 8, wherein the reactive compound is an oxazoline compound. The hydroxyl group-containing resin is a polyimide having a structure represented by the following general formulas (1) to (3), and the reactive compound is an oxazoline compound. The multilayer flexible wiring board in any one.

The hydroxyl group-containing resin is a polyimide having a structure represented by the following general formula (4) and the following general formula (5), and the reactive compound. The multilayer flexible wiring board according to any one of claims 5 to 9, wherein the multilayer flexible wiring board is an oxazoline compound.

  A method for manufacturing a multilayer flexible wiring board according to any one of claims 1 to 11, wherein an external conductive layer is provided on a conductive layer of a core substrate via an uncured adhesive resin, and the external conductive layer is formed. Forming a conformal mask on the layer, forming a via heel by dissolving and removing the uncured adhesive resin with an alkaline solution through the conformal mask, and heating and curing the uncured adhesive resin And a step of plating the via hole to electrically connect the conductive layer of the core substrate and the external conductive layer, and a step of forming a wiring circuit in the external conductive layer. A method for manufacturing a multilayer flexible wiring board.   In the step of providing the external conductive layer, in a state where a rubber base material containing a reinforcing material is applied to the main surface of the external conductive layer, the external conductive layer is heated and pressed to form the core on the conductive layer of the core substrate. The method for producing a multilayer flexible wiring board according to claim 12, wherein the external conductive layer is provided via an uncured adhesive resin.   The uncured adhesive resin has a thermogravimetric decrease at 260 ° C. of 0.5% or less by thermogravimetric analysis, and an alkali dissolution rate in a 3 mass% NaOH aqueous solution at 50 ° C. of 0.3 μm / sec or more. The method for producing a multilayer flexible wiring board according to claim 12 or 13,

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