JP5275001B2 - Manufacturing method of multilayer flexible wiring board - Google Patents

Abstract

To provide a multi-layered flexible printed wiring board and manufacturing method thereof having cables with excellent bending-tolerance for mounting thin and high-density parts correspondingly. The multi-layered flexible wiring board and manufacturing method thereof belong to the kind of multi-layered flexible wiring board having: the mounting part and the cable part formed by the internal-layer wiring bodies (111, 121, 131) of the electrically conductive pattern (6) formed on the surface of at least one site of the insulation substrates (5). It is characterized by: the said mounting part is formed in the way of coating the said electrically conductive pattern onto the composite body layer (4) of the rigid material and the adhesive resin. The said cable part has the adhesive agent layer (3) not containing the said rigid material. The surface not contacting the said composite body layer and the said electrically conductive layer of the said adhesive agent layer is coated by one continuous insulation film (2).

Description

The present invention relates to a method for manufacturing a multilayer flexible printed wiring board having a cable portion with excellent bending resistance and capable of mounting thin and high-density components.

  Mobile electronic devices represented by mobile phones, digital cameras, notebook computers, and the like are particularly strongly required to be light and thin. For this reason, in order to make mobile electronic devices lighter, thinner, and easier to use, a housing design such as a folding type or a sliding type is often used.

  In order to realize such an excellent design, a hinge structure that operates in a folding operation or a sliding operation and a wiring that can transmit an electric signal through the inside of the hinge structure are required.

  For the transmission of electrical signals inside the operating hinge, a flexible printed wiring board capable of signal transmission even in a dynamically bent state is mainly used. The flexible printed wiring board used for the hinge part is 100,000 times. It is required to endure mechanically and electrically in repeated bending operations at a level.

  On the other hand, in mobile electronic devices, the size of data to be processed, such as high-quality still image / moving image data, is rapidly increasing, and high-speed information processing is also required. On the other hand, semiconductors have been miniaturized in order to provide semiconductors with advanced functions at low cost, and semiconductor packages such as BGA and CSP have also been downsized. BGA / CSP bump pitches are also becoming smaller, such as 0.8mm, 0.5mm, 0.4mm, and 0.3mm, and the above-mentioned narrow-pitch semiconductor packages can be mounted on wiring boards including flexible printed wiring boards. Has been sought as essential.

  In addition, mobile electronic devices are strongly required to be light and thin for mobile purposes, and the substrates used are always required to be thin and light in units of 0.1 mm and 1 g.

In summary, in the present and future, the flexible printed wiring board is required to satisfy the following three conditions.
1) Have a flexible electric wiring cable part with bending resistance.
2) A high-density, narrow-pitch semiconductor package can be mounted.
3) Thin and lightweight.

  At present, the structure shown in FIG. 6 is used as the structure of a multilayer FPC for forming a flexible cable portion having bending resistance and mounting a high-density CSP.

As shown in FIG. 6, in the structure of the conventional multilayer flexible wiring board, in order to form a flexible cable portion having bending resistance, a cover film is used for the cover of the inner layer FPC that becomes the cable portion. Forming a wiring design build-up layer that enables mounting of high-density packages such as CSP, and laminating a single-sided FPC or double-sided FPC on the inner cover film described above using a laminating adhesive such as a prepreg layer, via processing It is set as the structure which performs.

However, the above conventional structure has the following problems.
(1) The build-up part, which is the mounting part, is thicker, which prevents the board from becoming lighter and thinner.
(2) When a via is formed with a laser because the build-up part is thick, not only does laser processing take time, but also the via plating takes time because the via depth increases.
(3) In addition, when the via fill is not plated, the volume of the cavity in the via increases, so in via-on-chip where the component is mounted on the via hole, the solder to be attached to the component is eaten by the via hole and soldered. Phenomenon that is not preferable in terms of mounting quality, such as non-uniformity and void remaining, are likely to occur.
Japanese Patent No. 2708980

The aforementioned Patent Document 1, the invention to the thin low-cost multi-layer flexible wiring board is shown. However, there is no mention of any compatibility between the rigidity of the mounting portion required for the thin multilayer flexible wiring board and the softness and bending resistance of the cable portion, and no solution is shown.

  The present invention has been made in view of the above points, and provides a multilayer flexible printed wiring board having a cable portion excellent in bending resistance and capable of mounting thin and high-density components and a method for manufacturing the same. With the goal.

In order to achieve the above object, in the present invention,
A conductive layer on one surface of the insulating film, and a peelable cover that covers the conductive layer, and a prepreg layer that is a composite of a glass cloth and an adhesive resin as a rigid material on the other surface , and the rigidity Prepare an outer layer laminated material in which an adhesive layer made of the adhesive resin not containing a material is formed,
Providing a inner wiring body conductive pattern is formed on both surfaces of the insulating base member,
To both sides of the inner layer wiring body, the laminated wiring board formed by laminating the outer layer laminate in contact with the surface having the composite layer and the adhesive layer,
Forming at least one of a via and a through hole in the laminated wiring board;
Forming a plating layer necessary for the laminated wiring board,
Forming a dry film on the plating layer;
A method for manufacturing a multilayer flexible wiring board having a mounting portion and a cable portion, which are formed by removing a plating layer corresponding to the portion where the adhesive layer is formed by etching, and forming a cable portion,
Is to provide.

  As described above, the present invention can reduce the number of layers of the insulating film and the adhesive that constitute the mounting portion, and can easily reduce the thickness of the substrate. As a result, it is possible to reduce the processing time and cost for laser drilling, via plating, and via fill plating for via processing for interlayer conduction.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 2 show two structural examples of a multilayer flexible wiring board according to the present invention. 3 to 6 show four examples of manufacturing methods related to the present invention.

(First structural example)
FIG. 1 shows a cross-sectional structure of a multilayer flexible printed wiring board having a four-layer structure, which is one of the basic structures of the present invention.

(Second structural example)
FIG. 2 shows a cross-sectional structure of a multilayer flexible printed wiring board having a six-layer structure, which is another basic structure of the present invention.

(Production method)
3 to 6 show a method for manufacturing a multilayer flexible printed wiring board according to the present invention.

(Manufacturing method 1)
FIG. 3 shows a basic example of the manufacturing method according to the present invention. This basic example includes the following steps (1) to (5).
(1) A conductive metal foil 1 is formed on one side of the insulating film 2, and at least a component that is a component of the mounting portion on the surface opposite to the conductive metal foil 1 across the insulating film 2 is used as a rigid material. A prepreg layer 4 having a glass cloth and an adhesive resin as constituent elements is formed, and an outer layer laminated material 111 in which an organic adhesive 3 that does not include glass cloth as a constituent element is formed in a portion to be a constituent element of the cable portion. Prepare.
As a material of the insulating film 2, an insulating film used for a flexible printed circuit board such as polyimide, polyamide, LCP (liquid crystal polymer), PEN (polyethylene naphthalate), or the like can be used. As a material of the conductive metal foil 1, various rolled copper foils and electrolytic copper foils are possible.
As the material of the adhesive 3, it is possible to use an adhesive that does not include a glass cloth and has excellent bending resistance, such as an adhesive for a cover film used when manufacturing a single-sided FPC or a double-sided FPC. As the prepreg layer 4, prepregs such as epoxy, imide, and BT resin (registered trademark) containing glass cloth can be used.
(2) An inner layer wiring body 112 in which the conductive pattern 6 is formed on the insulating base material 5 is prepared.
(3) Overlay the conductive pattern surface of the inner-layer wiring body 112 and the inner-layer wiring body 112 so that the adhesive surface from which the release of the outer-layer laminated material 111 formed in the step (1) is peeled faces each other. A laminated wiring board 100 is formed by laminating the outer layer laminated material 111 with a vacuum laminating press.
(4) The conductive layer 1, the insulating film 2 and the prepreg layer 4 are partially removed with a CO2 laser or the like from the surface where the conductive layer 1 of the laminated wiring board 100 produced in the above step (3) is present, and the inner layer wiring body 112 The surface of the conductive pattern 6 formed thereon is exposed.
Next, a pilot hole 7 serving as a via is formed through a necessary cleaning process such as a desmear process. Before and after the laser processing, it is also possible to perform processing and desmear processing of the pilot hole 7 of the through hole by drilling.
(5) After the step (4), the exposed surface of the laminated wiring board 100 is subjected to conductive treatment, electrolytic copper plating, and the like to form the plating layer 8. This plating layer 8 provides interlayer conduction between vias and through holes. By using a filled plating technique such as via fill plating or through hole fill plating as the plating, it is also possible to fill the via hole and the through hole hole with a conductive metal.

  A dry film for etching (not shown) is formed on the plating layer 8 corresponding to the cable portion of the laminated wiring board 100 in the step (5), and unnecessary metal portions are removed by etching to remove the conductive layer 8. Form.

  The outermost conductive layer 8 is formed by forming a reverse pattern with a semi-additive plating resist after the previous step (4), and simultaneously forming a conductive pattern and an interlayer conduction path by electrolytic copper plating. It is also possible to remove the metal layer 1 by soft etching.

  Thereafter, a solder resist is formed on the conductive layer 8 of the mounting portion, and after performing necessary surface treatment such as gold plating or solder plating, the components are mounted.

(Effect of Manufacturing Method 1)
Due to these characteristics, the manufacturing method 1 has the following effects.

  First, it is possible to reduce the number of material constituent layers of the insulating material in the build-up part that becomes the mounting part, and it becomes easy to reduce the thickness of the substrate.

  In addition, the thinner build-up portion insulating material enables laser drilling for via processing for interlayer conduction, processing time and cost for via plating and via fill plating to be reduced.

  In addition, when via fill plating or hole filling is not performed, the volume of the cavity in the via can be reduced, and when via-on-chip mounting a component on the via hole, the solder to be attached to the component is eaten into the via hole. As a result, it is possible to expect an effect of reducing phenomena that are undesirable in terms of mounting quality, such as a phenomenon in which the solder connection is uneven and a void remaining.

  Furthermore, in this manufacturing method, by optimizing the thickness and application location of the highly rigid prepreg layer including the glass cloth, the manufacturing process of the multilayer flexible substrate can be made roll-to-roll, and the manufacturing of the multilayer flexible wiring board is possible. Process automation, yield improvement, and cost reduction are possible.

(Manufacturing method 2)
FIG. 4 shows a second embodiment of the manufacturing method according to the present invention. The second embodiment includes the following steps (1a) to (6).
(1a) An outer layer laminated material 121 in which a metal foil as the conductive pattern 1 is formed on one side of the insulating film 2 is prepared. As a material of the insulating film 2, an insulating film material used for flexible printed wiring boards such as polyimide, polyamide, LCP, and PEN can be used. As a material of the conductive metal foil 1, various rolled copper foils and electrolytic copper foils are possible.
(2a) A prepreg layer 4 comprising a glass cloth as a rigid material and an adhesive resin as constituent elements is formed at least on a portion to be a mounting portion of the conductive pattern surface of the inner layer wiring body 122 on which the conductive pattern 1 is formed. The inner-layer wiring body 122 is prepared in which the adhesive resin 3 that does not include glass cloth as a constituent element is formed at least in a portion that becomes a constituent element of the cable portion.
(3) The outer layer laminated material 121 is laminated on the inner layer wiring body 122 by vacuum hot pressing or the like.
(4) The conductive layer (metal foil) 1, the insulating film 2 and the adhesive layer 3 are partially removed from the surface of the outermost conductive layer 1 of the outer layer laminate 122 in the step (3) with a CO2 laser or the like. Then, the surface of the conductive pattern 6 formed in the inner layer wiring body 122 is exposed, and a pilot hole 7 serving as a via is formed. Before and after laser processing, it is also possible to drill through holes for drilling through holes.
(5) After the above step (4), after carrying out necessary cleaning steps such as desmear treatment, conductive treatment and electrolytic copper plating are further performed to form a plating layer 8, and vias and throughs that are interlayer conductive structures A hole is formed. By using a filled plating technique such as so-called via fill plating or through hole fill plating as the plating method, it is possible to fill the via hole and the through hole hole with a conductive metal.
(6) An etching dry film is formed on the plating layer 8 of the laminated wiring board 100 in the above step (5), and unnecessary metal portions are removed by etching to form a conductive pattern 8.

(Effect of Manufacturing Method 2)
After that, a solder resist is formed on the conductive pattern 8 of the component mounting portion, and after the surface treatment necessary for gold plating, solder plating or the like is performed, the component can be mounted. Due to these characteristics, the manufacturing method 1 described in FIG. 3 has the same effect.

(Manufacturing method 3)
FIG. 5 shows Reference Example 1 of the manufacturing method according to the present invention. The reference example 1 includes the following steps.

In the reference example 1 shown in FIG. 5, a so-called peelable (called “peelable”) metal foil is used instead of the conductive pattern 1 used in the step (1) of FIG. In order to improve the handling of thin conductive metal foil, this metal foil is laminated with a thin metal foil and a thick metal foil as its cover, and a multilayer structure that can easily peel and remove the thick metal foil as needed It is configured as a metal foil.

  In the step (1b), a thin metal foil serving as the conductive pattern 1 and a thick metal foil serving as the cover 9 are laminated on one surface of the insulating film 2, and at least a portion serving as a component of the mounting portion on the other surface. A prepreg layer 4 having a glass cloth as a rigid material and an adhesive resin as a constituent element is formed, and an organic adhesive 3 that does not include the glass cloth as a rigid material as a constituent element is formed in a portion that is a constituent element of the cable portion. A formed outer layer laminated material 131 is prepared.

  Step (2) is a step of forming the inner-layer wiring body 132 and is the same as step (2) in the manufacturing method 1.

  Steps (3-1) and (3-2) correspond to step (3) in production method 1 and 2 but use a peelable material as outer layer laminated material 131 to show before and after peeling. Illustrated as two steps.

  Steps (4) and subsequent steps in FIG. 5 are the same as steps (4) and subsequent steps in FIGS.

(Effect of manufacturing method 3)
In manufacturing method 3, since the thickness of the outermost copper foil before plating that can be formed by handling in the manufacturing process can be reduced compared to manufacturing method 1, by reducing the load of laser processing and reducing the total conductor thickness after plating By improving the workability of the fine pattern by the subtractive method and using the copper foil before plating as the seed layer for the semi-additive method, the micro-wiring and vias are simultaneously plated by the semi-additive method. Soft etching removal can be performed more efficiently.

FIG. 6 shows Reference Example 2 of the manufacturing method according to the present invention. This reference example 2 is constituted by the following steps.

  In step (1), the same outer layer laminated material 141 as in step (1) of manufacturing method 1 is prepared.

  In step (2b), instead of the inner layer wiring body 112 of the manufacturing method 1 shown in FIG. 3, an inner layer wiring body 142 in which interlayer conduction is formed by through holes is prepared.

  In the step (3), the outer layer laminated material 141 and the inner layer wiring body 142 are laminated in the same manner as in the step 3 of the manufacturing method 1 to form the laminated wiring board 100.

  In the step (4b), the pilot hole 7 for interlayer conduction is formed in the outer layer laminated material 141 in accordance with the center position of the through hole of the inner layer wiring body 142 constituting the laminated wiring board 100, and the step of the manufacturing method 1 shown in FIG. In the same manner as in No. 4, it is formed by laser processing.

  Step (5) and subsequent steps are the same as step (5) and subsequent steps in FIGS.

(Effect of Manufacturing Method 4)
In the manufacturing method 4, a so-called through-hole structure prepared hole that conducts the outermost layer through a through-hole as an interlayer conduction structure can be formed by laser machining instead of drilling. As a result, a design in which vias and through-through holes are mixed is possible, and the degree of freedom in wiring board design can be increased.

Sectional drawing which shows the structure of the 1st Example of the multilayer flexible wiring board which concerns on this invention. Sectional drawing which shows the structure of the 2nd Example of the multilayer flexible wiring board which concerns on this invention. Process drawing which shows the basic example of the manufacturing method which concerns on this invention. Process drawing which shows the Example of the manufacturing method which concerns on this invention. Process drawing which shows the reference example 1 of the manufacturing method which concerns on this invention. Process drawing which shows the reference example 2 of the manufacturing method which concerns on this invention. The cross-sectional block diagram which shows the conventional structure.

Explanation of symbols

1 conductive pattern (conductive foil), 2 insulating film, 3 adhesive layer, 4 prepreg layer,
5 Insulating base material, 6 Conductive pattern, 7 Via pilot hole, 8 Conductive pattern, 9 Conductive pattern,
100 laminated wiring board, 111, 121, 131, 141 outer layer laminated material,
112,122,132,142 Inner layer wiring body.

Claims (1)

A conductive layer on one surface of the insulating film, and a peelable cover that covers the conductive layer, and a prepreg layer that is a composite of a glass cloth and an adhesive resin as a rigid material on the other surface , and the rigidity Prepare an outer layer laminated material in which an adhesive layer made of the adhesive resin not containing a material is formed,
Providing a inner wiring body conductive pattern is formed on both surfaces of the insulating base member,
To both sides of the inner layer wiring body, the laminated wiring board formed by laminating the outer layer laminate in contact with the surface having the composite layer and the adhesive layer,
Forming at least one of a via and a through hole in the laminated wiring board;
Forming a plating layer necessary for the laminated wiring board,
Forming a dry film on the plating layer;
A method of manufacturing a multilayer flexible wiring board having a mounting portion and a cable portion, wherein a portion of the plating layer corresponding to the portion where the adhesive layer is formed is removed by etching to form a cable portion.

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