JP2007109716A - Process for producing printed board having cable portion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for integrally forming a multilayer substrate having a cable portion becoming a hollow structure by leading out the cable portion from the outer layer portion of the multilayer substrate. <P>SOLUTION: (1) For the copper foil of a one side copper clad laminate which is laminated on an inner layer core substrate, a flexible cable portion circuit pattern is formed and a connection pad portion is formed at the distal end on the component mounting portion side of the flexible cable portion circuit pattern. (2) A surface protection insulating film is formed excepting a part of the circuit pattern and the connection pad portion formed in the process (1). (3) On at least one side of the inner layer core substrate, a laminate is formed by laminating the one side copper clad laminate formed in the processes (1, 2) such that the copper foil is directed toward the outer surface. (4) An outer layer circuit pattern is formed by etching on the copper foil of the one side copper clad laminate formed in the process (3). (5) A surface protection insulating film having an opening at a required position is formed on the outer layer circuit pattern including the connection pad portion. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a printed circuit board used in an electronic apparatus, and more particularly to a multilayer flexible printed circuit board formed by connecting a plurality of component mounting parts with a cable part protruding from the component mounting part.

  A printed circuit board is mounted on a device by mounting electronic components, but in many cases, three-dimensional component mounting is required to realize a compact device. For this purpose, a method of bending the printed circuit board is required.

  Thus, a multilayer flexible printed circuit board is provided in which a component mounting portion (portion requiring a thickness) and a flexible portion (cable portion) for connecting the component mounting portions are integrally formed. By using such a printed circuit board, the space can be effectively utilized by bending the flexible portion after component mounting and placing it in a three-dimensional arrangement, thereby achieving compactness.

  In recent years, such a printed circuit board has been widely used in a part having a hinge structure such as a notebook personal computer and a folding mobile phone, which is frequently opened and closed. In this case, the cable part is housed by being spirally wound in the hinge part (Patent Document 1). Recently, a hinge structure corresponding to more complicated movement has also been shown (Patent Document 2). For this reason, a more flexible cable part structure is required. Usually, the force required for bending is smaller when the single-sided material is the cable part than the double-sided material.

  For this reason, when the wiring density is high, the bending stress of the cable portion is relieved by forming a double-sided single-sided material with better flexibility and making the space between them (Patent Document 3). This method shows a two-layer substrate in which two single-sided flexible substrates are stacked. However, there is an example in which a multilayer substrate is formed by stacking outer layer materials using this structure as a core (Patent Literature). 4). In the example of Patent Document 4, the cable portion is drawn from the inner layers (second and third layers) of the four-layer board.

  Conventionally, as described above, a cable part structure is used in which a cable part is drawn from a two-layer board in which two single-sided flexible boards are stacked, or an inner layer of a multilayer board, and a single-sided material is a two-piece structure. . When the cable portion is pulled out from the inner layer of the multilayer substrate, the inner layer material on which the circuit pattern has been previously formed is laminated, so that there is no particular problem with the circuit pattern formation.

  However, the cable portion cannot be drawn from the first and fourth layers of the four-layer board as shown in FIG. That is, in the case of a two-layer substrate in which two single-sided flexible substrates are stacked, a pattern is formed after the substrate materials are bonded together, but there is a step between a hollow portion and a portion that is not. If this level difference is large, a gap is generated between the material and the exposure mask in the photolithography process, and the exposure image is blurred by so-called out-of-focus, so-called exposure blur causes circuit pattern width widening or short-circuit.

  Normally, such exposure blur can be avoided if the distance between the material and the exposure mask is 50 μm or less. In the case of a two-layer substrate in which two single-sided flexible substrates are stacked, the laminating adhesive or prepreg is more than 50 μm. If a thin material is used, a circuit pattern can be formed.

  However, for example, in the case of a substrate having a structure as shown in FIG. 7A, bending occurs as shown in FIG. 7B. That is, as shown in FIG. 7A, a single-sided copper-clad laminate 71 for outer layers is laminated on the outer side of an inner layer core substrate in which two inner layer substrates 73 are laminated via a laminating adhesive (or prepreg) 72. Then, as shown in FIG.7 (b), a bending will arise in a cable part.

  For this reason, when pulling out the cable part from the single-sided copper clad laminate 71 for the outer layer, it is impossible to set the step between the hollow part and the part that is not so within 50 μm, no matter how thin the material is selected. As a result, a gap is generated between the material and the exposure mask in the photolithography process, and it is impossible to avoid problems such as circuit pattern width widening and short circuit due to exposure blur. For example, as shown in FIG. 7C, even when the cable portion is pulled out from the single-sided copper-clad laminate 71 for the outer layer on one side, bending occurs similarly, and exposure is caused by the gap generated between the material and the exposure mask in the photolithography process. Blur occurs.

In addition, when manufacturing by the subtractive method, the plating layer at the time of forming the interlayer conductive part such as the through hole is also placed on the circuit pattern of the cable part that is required to be flexible, and it is bent more than when there is no plating layer. Results in inferiority.
JP-A-6-31216 JP 2003-133664 A Japanese Patent Laid-Open No. 7-312469 JP 2003-133733 A Japanese Utility Model Publication No. 2-65377 JP-A-61-58294

  Conventionally, in the case of a structure in which the cable portion is pulled out from such an outer layer, for example, a structure in which a flexible substrate is bonded to a rigid base material as in Patent Document 5 or a rigid base material shown in a conventional example in Patent Document 6 is a flexible substrate. There is only a method of connecting with, and cannot be integrally formed.

  The present invention has been made in consideration of the above-described points, and provides a method for integrally forming a multilayer board that pulls out a cable part from an outer layer part on at least one side of the multilayer board and connects a component mounting part. Objective.

In order to achieve the above object, according to the present invention, an outer layer cable portion circuit pattern, which is difficult to form after forming a multilayer substrate, is formed before lamination. That is,
(1) The flexible cable portion circuit pattern and the component mounting portion side base of the flexible cable portion circuit pattern are etched by etching on the copper foil of the single-sided copper clad laminate laminated on the inner core substrate. A connection pad portion is formed at the end.
(2) The flexible cable portion circuit pattern formed in the step (1) and the connection pad portion formed on the component mounting portion side base end portion of the circuit pattern, the component mounting portion of the connection pad portion A surface protective insulating film is formed except for a part of the side tip.
(3) The single-sided copper-clad laminate produced in the steps (1) and (2) is attached to at least one side of the inner-layer core substrate by an adhesive member excluding a portion corresponding to the flexible cable portion. A laminated body is formed so that the foil faces the outer surface, and an interlayer conductive portion is formed at a required position of the component mounting portion.
(4) Forming on the flexible cable part circuit pattern and the component mounting part side base end part of the flexible cable part circuit pattern of the copper foil of the single-sided copper clad laminate formed and laminated in the step (3) An outer layer circuit pattern is formed by an etching method for the portions other than the connection pad portion thus formed.
(5) A surface protective insulating film having an opening at a required position is formed on the outer layer circuit pattern including the connection pad portion.

  A flexible cable portion for connecting a plurality of component mounting portions is formed by a single-sided copper-clad laminate laminated on at least one side of the inner-layer core substrate, which is characterized by undergoing the steps (1) to (5). Further, it is a method for manufacturing a multilayer flexible printed circuit board.

  In the present invention, in the method for producing a multilayer flexible printed board formed by laminating a single-sided copper-clad laminate for forming not only a component mounting part but also a flexible cable part on at least one side of the inner layer core board, A technique can be established in which circuit pattern formation of the outer cable portion, which has been difficult in the past, is formed before lamination.

  In addition, since the miniaturization of the flexible cable portion circuit pattern, which was difficult when forming the interlayer conductive portion such as a through hole by panel plating, the fine circuit pattern is formed first in the method of the present invention, Only the copper foil thickness of the copper clad laminate material can be etched, which is an effective means for miniaturization.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

Embodiment 1

  FIG. 1 shows the flow of the entire process of the method of the present invention, and FIGS. 2 to 6 show the process of forming an outer layer circuit pattern during the process.

  In the method of the present invention, a printed circuit board is manufactured through each process as shown in FIG. That is, an outer layer substrate is formed in steps S1 to S3, an inner layer substrate is formed in step S4, and both substrates are stacked in step S5 to form a multilayer substrate. Then, the multilayered substrate is processed in steps S6 to S10 to form an outer flexible printed circuit board.

  First, a single-sided copper clad laminate is prepared (Step S1), and a circuit pattern is formed only around the cable portion (Step S2). Thereafter, a surface protective insulating film is formed only around the cable portion (step S3). On the other hand, an inner layer core substrate is formed separately (step S4), and in step S5, the outer layer substrate and the inner layer substrate are laminated by an adhesive member excluding a portion corresponding to the cable portion to form a multilayer substrate.

  Next, an interlayer conductive portion for interlayer connection is formed on the multilayer substrate (step S6), an outer layer circuit pattern is formed (step S7), and a surface protective insulating film is formed (step S8). Thereafter, external processing is performed (step S9), and a multilayer flexible printed board is completed (step S10).

  Next, each step will be described with reference to FIGS.

  First, as shown in FIG. 2, a single-sided copper-clad laminate having a component mounting part 100 and a cable part 200 is provided with a cable part circuit pattern 1 and an outer layer circuit pattern of the component-mounting part later. It forms by etching with respect to copper foil. At this time, the connection pad part 2 for connecting the cable part circuit pattern 1 and the outer layer circuit pattern of the component mounting part is formed. A broken line portion in FIG.

  The width 2a of the connection pad 2 is preferably set to be 0.05 mm or more wider than the cable portion circuit pattern width 1a in consideration of the amount of exposure deviation when forming the outer layer circuit pattern of the component mounting portion in a subsequent process. . In addition, the length 2b of the connection pad 2 is determined so that the outer layer circuit pattern of the component mounting portion is obtained as described later in order to obtain an exposure shift amount when forming the outer layer circuit pattern of the component mounting portion and more connection reliability. It is preferable that the exposure is performed in an overlapping manner, and it is preferably 0.5 mm or more in consideration of a shift in forming a surface protective insulating film described later.

  At this stage, a circuit pattern is formed on the copper foil layer of a single-sided copper-clad laminate without a plating layer, so the copper foil layer that is thinner than the copper foil layer on which the plating layer is formed is etched. A pattern can be formed. The circuit pattern may be formed by a normal etching process.

  Next, as shown in FIG. 3A, the surface protective insulating film 3 and a flexible insulating resin film such as a polyimide film are adhesively laminated to the portion where the circuit pattern is formed in FIG. At this time, if the surface protective insulating film 3 is displaced and rides on the portion where the copper foil on the component mounting portion 100 side of the connection pad portion 2 is left, an outer layer circuit pattern of the component mounting portion 100 is formed in a subsequent process. Since there is a possibility of short-circuiting later, the adhesive laminate of the flexible insulating resin film is fastened to the front of the etched portion.

  Accordingly, the A1-A1 cross-sectional shape of the portion including the connection pad 2 at this time is as shown in FIG. 3B, and the A2-A2 cross-sectional shape not including the connection pad 2 portion is FIG. As shown in c). Here, 11 is a copper foil material for the outer layer copper clad laminate, and 4 is an insulating base material.

  The distance g between the etched portion and the portion where the coverlay 3 is laminated is preferably set to 0.1 to 0.3 mm in consideration of a shift during lamination.

  Next, a single-sided copper-clad laminate obtained by forming the above-described circuit pattern and connection pads on the previously formed inner layer core substrate and laminating the surface protective insulating film 3 is laminated to form a multilayer substrate After that, interlayer conductive parts such as through holes and via holes are formed. The process so far is performed by a conventional method. Here, the formation method of the interlayer conduction | electrical_connection part by subtractive method and panel plating is assumed.

  FIG. 4A shows a state in which image exposure and development are performed using the dry film 5 after panel plating. A portion where the surface protective insulating film 3 is laminated in the previous step is a region 31. The cable part circuit pattern 1 is also hidden from the panel-plated copper foil 12 and cannot be seen, but is shown for convenience. The shape of the A3-A3 cross section including the connection pad 2 portion at this time is as shown in FIG.

  In FIG. 4B, the dry film 5 is overlapped with the portion covered with the cover lay 3 by the length p at the portion of the connection pad 2, and this overlap causes the subsequent etching. Further, the connection pad 2 is prevented from being disconnected. The overlap length p is preferably 0.07 mm or more in consideration of side etching during etching.

  FIG. 5A shows a state in which an outer layer circuit pattern other than the connection pad portion 2 formed at the mounting portion side base end portion of the cable portion circuit pattern 1 and the cable portion circuit pattern 1 is formed by etching thereafter. Yes. The cross-sectional shape along the line A4-A4 including the connection pad 2 at this time is as shown in FIG. By the overlap length p, the circuit pattern 1 formed before lamination and the circuit pattern 13 formed thereafter are reliably connected.

  The connection pad portion 2 is in a state in which the circuit pattern is a protrusion as shown in FIG. 5B, and is easily subjected to external impact. For this reason, as shown in FIG. 6 (a) and FIG. 6 (b) showing a cut surface along the line A5-A5, the surface protective insulating film 6 is formed by adhesion of a flexible insulating film or printing formation of a solder resist. It is preferable to cover the connection pad portion 2 with. A region 61 in FIG. 6A is a region covered with these surface protective insulating films 6.

Application examples

  In the step (5) in the embodiment, it is possible to build up and laminate an outer layer forming material instead of the surface protective insulating film. In this case, the substrate obtained in steps (1) to (4) in the example becomes a new inner layer core substrate.

Explanatory drawing which shows a series of processes of this invention method. The top view which shows the connection part of the component mounting part and cable part of a printed circuit board to which this invention is applied. 3A is an explanatory view showing a connection pad used in the present invention, FIG. 3B is a cross-sectional view taken along line A1-A1 in FIG. 3A, and FIG. 3C is FIG. Sectional drawing cut | disconnected in the position which follows the A2-A2 line | wire in a). FIG. 4A is an explanatory diagram showing circuit patterns of a component mounting portion and a cable portion connected by a connection pad constructed according to the present invention, and FIG. 4B is a cross section taken along line A3-A3 in FIG. Figure. FIG. 5A is an explanatory view showing circuit patterns of a component mounting portion and a cable portion connected by a connection pad constructed according to the present invention, and FIG. 5B is a cross section taken along line A4-A4 in FIG. Figure. FIG. 6A is an explanatory diagram showing circuit patterns of a component mounting portion and a cable portion connected by a connection pad constructed according to the present invention, and FIG. 6B is a cross section taken along line A5-A5 in FIG. 6A. Figure. FIGS. 7A, 7B, and 7C are explanatory views showing the configuration of the conventional example and the bending caused thereby.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cable part circuit pattern 11 Material of outer layer copper clad laminate Copper foil 12 Panel plating copper foil 2 Connection pad 3 Surface protection insulating film 31 Area where surface protection insulation film was laminated 4 Insulation base material 5 of outer layer copper clad laminate Rear dry film 6 Surface protective insulating film 61 Area 71 covered with surface protective insulating film Single-sided copper-clad laminate 72 Adhesive member 73 Inner layer board a Cable part b Component mounting part g Distance p Overlap length

Claims (2)

A multilayer flexible printed circuit board in which a single-sided copper-clad laminate is laminated on at least one side of the inner layer core board, and a plurality of component mounting parts are electrically connected by a flexible cable part extending from the component mounting part In the manufacturing method of the multilayer flexible printed circuit board formed, it forms through the following processes in order, The manufacturing method of the multilayer flexible printed circuit board characterized by the above-mentioned.
(1) The flexible cable portion circuit pattern and the component mounting portion side base of the flexible cable portion circuit pattern are etched by etching on the copper foil of the single-sided copper clad laminate laminated on the inner core substrate. A connection pad portion is formed at the end.
(2) The flexible cable portion circuit pattern formed in the step (1) and the connection pad portion formed on the component mounting portion side base end portion of the circuit pattern, the component mounting portion of the connection pad portion A surface protective insulating film is formed except for a part of the side tip.
(3) The single-sided copper-clad laminate produced in the steps (1) and (2) is attached to at least one side of the inner-layer core substrate by an adhesive member excluding a portion corresponding to the flexible cable portion. A laminated body is formed so that the foil faces the outer surface, and an interlayer conductive portion is formed at a required position of the component mounting portion.
(4) Forming on the flexible cable part circuit pattern and the component mounting part side base end part of the flexible cable part circuit pattern of the copper foil of the single-sided copper clad laminate formed and laminated in the step (3) An outer layer circuit pattern is formed by an etching method for the portions other than the connection pad portion thus formed.
(5) A surface protective insulating film having an opening at a required position is formed on the outer layer circuit pattern including the connection pad portion. In the manufacturing method of the printed circuit board of Claim 1,
In the step (5), a multilayer flexible printed circuit board manufacturing method, wherein an outer layer forming material is built up and laminated instead of the surface protective insulating film.

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