JP2009231770A - Multilayer flexible printed wiring board and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer flexible printed wiring board having a stable shielding connection point, and a method for manufacturing the wiring board inexpensively and stably. <P>SOLUTION: In the multilayer flexible wiring board in which at least one cable part and at least one component mounting part are integrally formed and at least one of the cable parts has a shield layer, electric connection points 17, 36, 60 are formed from at least two layers of wiring layers to the shield layer 14, 15, 44 on the end surface of the component mounting part which makes a boudary with the cable part having the shield layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a multilayer flexible printed wiring board and a manufacturing method thereof, and more particularly to a structure of a multilayer flexible printed wiring board having a shield layer in a cable portion and a manufacturing method thereof.

  In recent years, downsizing and higher functionality of electronic devices have been promoted more and more, and therefore, there is an increasing demand for higher density of printed wiring boards. Therefore, the printed wiring board is made dense by changing the printed wiring board from a single-sided type to a double-sided type or a multilayer printed wiring board of three layers or more.

  As a part of this, it has a multilayer printed wiring board for mounting various electronic components, a separate flexible wiring board for connecting hard printed wiring boards via connectors, etc., and a flexible cable part integrated with a flexible flat cable. Multilayer flexible printed wiring boards are widespread mainly in small electronic devices such as mobile phones.

  Particularly for digital video cameras, a multilayer flexible printed wiring board having 3 layers or 4 layers or more is required. Moreover, since the cable part of the multilayer flexible printed wiring board used for a mobile phone becomes a hinge bending part, the restrictions on an external shape are large.

  The hinge bent portion is required to have high bending reliability, and the change in electrical characteristics is required to be within the standard even after several hundred thousand times of bending. The number of signal lines for small, thin, high-performance mobile phone cables is increasing, and single-layer cables cannot be used alone, and multiple layers from the inner and outer layers are required. There exists a thing as described in patent document 1 about a multilayer flexible printed wiring board.

  In addition, the multilayer flexible printed wiring board is also required to be thin. This is because with the increasing functionality of small electronic devices such as mobile phones and digital video cameras, it is necessary to reduce the size of each component. It is necessary. As a method of manufacturing a thin multilayer flexible printed wiring board, there is a method described in Patent Document 2.

  It is said that a thin four-layer flexible printed wiring board can be manufactured by sharing the cover film of the flexible printed wiring board that becomes the inner layer cable portion with the flexible insulating base material of the outer layer. However, since the formation of the outer layer cable is difficult, the above-described problem cannot be solved.

  In addition, as described in Patent Document 3, it is also known that a bent cable is a copper foil single layer with no plating, and a single-sided cable has less distortion of the conductor when bent, and has good bending characteristics. Yes. In this respect, those of Patent Documents 1 and 2 which are multi-layer types are inappropriate.

  Furthermore, in a cellular phone cable or the like, it is also necessary to form a shield layer such as a silver paste or a silver film on the outside of the cable in order to achieve both bending characteristics and noise resistance. In this respect, Patent Documents 1 and 2 are not appropriate.

  For these reasons, there has been a demand for the emergence of a method for stably and inexpensively manufacturing a thin multilayer flexible printed wiring board having a cable portion having a bending characteristic that allows drawing from a plurality of inner and outer layers.

  FIG. 8 is a cross-sectional view showing a main configuration of a conventional three-layer flexible printed wiring board (see Patent Document 1). This wiring board has a cable portion that can be pulled out from a plurality of layers including a second layer and a third layer having a shield layer.

  First, a cable lay is formed by attaching a coverlay to a flexible insulating base material 101 such as polyimide. That is, the second layer is formed by bonding a so-called cover lay 105 having an adhesive 104 on an insulating film 103 such as a polyimide film to a layer to be a cable portion of the flexible printed wiring board 102 having circuit patterns on both sides. The cable portion 106 is used.

  Similarly, a cover lay 111 is formed on a layer to be a cable portion of a flexible printed wiring board 108 having a circuit pattern including a cable portion of a third layer on one side on a flexible insulating base material 107 such as polyimide. The third layer cable portion 112 is laminated.

  The second-layer cable 106 and the third-layer cable 112 are pasted together with an adhesive 113 that has been punched in advance. Further, from the outside of each flexible insulating base material, a shield layer 114 is formed on the first layer side and a shield layer 115 is formed on the third layer side to form a cable portion having a shield layer.

For the connection between layers, it is essential not to apply plating to the portion corresponding to the cable portion of the third layer, but only the opening side of the so-called button plating or interlayer conduction hole where plating is applied only to the interlayer connection portion. Panel plating, single-sided plating (in this case, only the first layer is plated), and through-holes penetrating all layers or blind via-hole connections connecting adjacent layers can be selected. . Here, a combination of the through through hole 116 and button plating was selected.
Japanese Patent Publication No. 2-55958 Japanese Patent Laid-Open No. 5-90757 Japanese Unexamined Patent Publication No. 7-312469

  In such a conventional structure, the configuration of the multilayer portion 117 is complicated and thick, and thus cannot meet the above-described demand for thinning. For this reason, the level | step difference of a multilayer part and a cable part is large, and there also exists a problem that filling defect generate | occur | produces in a thin shield film etc. when forming a shield layer. In addition, when the shield electrical connection point 118 can be taken only on one surface and the above-described filling failure occurs, swelling may occur at the time of heating, which may cause a problem in adhesion.

  In particular, in a reflow process at the time of component mounting using lead-free solder in recent years, since the peak temperature is high, the heat during the reflow process may cause swelling and peeling. In addition, when drilling through holes for through holes and blind via holes, a lot of foreign matter such as chips and smears of the material of each layer accumulates in the through holes, and the desmear treatment process to remove them is complicated. Or may cause electrical connection failure due to insufficient desmear treatment. In addition, since the number of constituent materials increases, there is a problem that the material cost increases.

  The present invention has been made in consideration of the above-described points, and an object of the present invention is to provide a multilayer flexible printed wiring board having a stable shield connection point and a method for stably and inexpensively manufacturing the wiring board. .

  In order to achieve the above object, the present invention provides the following inventions.

According to the first invention,
In a multilayer flexible printed wiring board in which at least one cable portion and a component mounting portion are integrally formed, and at least one of the cable portions has a shield layer,
An electrical connection point from at least two wiring layers to the shield layer is formed on an end surface of the component mounting portion that becomes a boundary with the cable portion having the shield layer.

According to the second invention,
In the method for producing a multilayer flexible printed wiring board having a cable portion on which a shield layer is formed,
Preparing a double-sided flexible substrate having a conductive layer on both sides and a single-sided flexible substrate having a conductive layer on one side;
A mask hole is provided in one conductive layer of the double-sided flexible substrate to form a conduction hole for connecting the conductive layers on both sides, and an electrical connection point with the shield layer is provided on the other conductive layer. Forming a circuit pattern comprising:
Laminating the double-sided flexible substrate and the single-sided flexible substrate across an adhesive disposed on the inner layer side of the circuit pattern to form a multilayer circuit;
Performing the drilling of the multilayer circuit from one surface of the double-sided flexible substrate using the mask hole, and forming the conduction hole;
Removing a part of the insulating base material of the double-sided flexible substrate at an end of the circuit pattern to expose the circuit pattern;
A process of forming a via hole by plating the opening surface of the conduction hole with respect to the conduction hole and the circuit pattern, and forming an electrical connection point with the shield layer at an end of the circuit pattern When,
Forming the shield layer so as to cover the circuit pattern including at least the connection points;
It is characterized by having.

Furthermore, according to the third invention,
In the method for producing a multilayer flexible printed wiring board having a cable portion on which a shield layer is formed,
Preparing two single-sided flexible substrates (A, B);
Forming a mask hole for forming a hole for conduction in the conductive layer on one side (A) of the one-sided flexible substrate and forming a circuit pattern serving as an electrical connection point with the shield layer; ,
The two flexible circuit boards are bonded by adhering the circuit pattern on one side (A) of the single-sided flexible board and the opposite side of the conductive layer on the other side (B) of the single-sided flexible board. Laminating to form a multilayer circuit;
A hole having a diameter larger than that of the mask hole is formed at the projection position of the mask hole in the insulating base material of one side (A) of the single-sided flexible substrate, and the insulating base of the other side (B) of the single-sided flexible substrate For the material, forming the hole for conduction by drilling the multilayer circuit from the opposite surface of the conductive layer of one side (A) of the one-sided flexible substrate using the mask hole;
Removing a part of the insulating base material on one side (A) of the one-sided flexible substrate on the circuit pattern to be the connection point, and exposing the pattern to be the connection point at an end of the circuit pattern;
For the pattern to be the hole for conduction and the connection point, plating the opening surface of the hole for conduction to form a via hole, and forming the connection point at the end of the cable;
Forming a shield layer on at least the pattern to be the connection point;
It is characterized by having.

  Due to these features, the present invention has the following effects.

  According to the multilayer flexible printed wiring board of the present invention, there is little step on the cable part end face of the via hole opening face, and not only the surface layer but also the inner layer is provided with a pattern serving as an electrical connection point of the shield. Even with a shield film, etc., filling failure does not occur, and electrical connection reliability is excellent.

  Further, according to the method for manufacturing a multilayer flexible wiring board of the present invention, when a hole for conduction for forming a through hole or a blind via hole is drilled, foreign materials such as chips and smears of materials of each layer are formed in the hole for conduction. The generation amount is small, and the desmear process for removing them can be processed under relatively relaxed conditions, and a larger margin for the desmear process can be secured. Further, since the number of constituent materials is reduced, the material cost can be reduced.

  Furthermore, according to the method for manufacturing a multilayer flexible wiring board of the present invention, a finer and higher-definition wiring can be formed by forming the conductor layer (first layer) on the via hole opening surface by a semi-additive method. Further, at this time, since the conductor layer on the third layer side forms a circuit by etching, it has a feature that it is possible to apply a rolled copper foil having excellent flexibility.

  As a result, it is possible to provide a method for stably and inexpensively manufacturing a flexible printed wiring board having a cable portion and having a shield layer that can be pulled out from a plurality of inner and outer layers.

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

<Example of wiring board>
FIG. 1 is a sectional view showing the structure of a three-layer flexible printed wiring board according to the present invention. In this wiring board, a cover layer 5 is bonded to a flexible insulating base material 1 such as polyimide to form a second layer cable portion 6. For this purpose, a coverlay having an adhesive 4 on an insulating film 3 such as a polyimide film is applied to a layer to be a cable portion of the flexible printed wiring board 2 having a circuit pattern including a cable portion of the second layer on both sides. 5 is formed.

  Similarly, a cover layer 11 is laminated on a flexible insulating base material 7 such as polyimide to form a third layer cable portion 12. For this purpose, a coverlay 11 having an adhesive 10 on an insulating film 9 such as a polyimide film is used for a layer to be a cable portion of the flexible printed wiring board 8 having a circuit pattern including a third layer cable portion on one side. Are bonded together to form the third-layer cable portion 12.

  This wiring board has a cable portion that is formed on a conductive layer 6 ′ as a first layer and can be pulled out from the second layer and the third conductive layer. This cable part is provided with a shield layer.

  When forming the wiring layer of the second layer cable, the connection point 6b to be connected to the shield later is formed. The second-layer cable 6 and the third-layer cable 12 are pasted together with an adhesive 13 that has been punched in advance. The connection point 6b with the shield is exposed by laser processing or the like before performing plating for interlayer connection, and thereafter, electrical connection is obtained by performing plating.

  For the connection between the layers, it is essential that no plating is applied to the portion corresponding to the cable portion of the third layer. However, after adopting button plating or single-sided plating (in this case, only the first layer is plated), through-holes penetrating all layers and blind via-hole connections for connecting adjacent layers can be made.

  Here, a combination of the through through hole 14 and button plating was selected. On the first layer surface having a large step, as shown in FIG. 1, the plating film deposited on the surface on the first layer side of the third layer cable of the step portion where the shield layer is formed includes the connection point 6b of the shield layer. You can reduce the level difference by leaving it at. As a result, electrical connection can be reliably performed, and the size of the step can be reduced, so that no filling failure occurs when the shield layer is formed.

  Further, from the outside of each flexible insulating base material, the shield layer 15 is formed on the first layer side, the shield layer 16 is formed on the third layer side, and the cable portion having the shield layer is formed. Since the shield connection point 17 on the first layer side of the third layer cable is formed in the first layer and the second layer as shown in the figure and the step can be reduced, the electrical characteristics are improved. And no filling failure occurs when the shield layer is formed.

<Example 1 of a manufacturing method>
2A to 2C are cross-sectional process diagrams illustrating Example 1 of the manufacturing method according to the present invention. This wiring board has a cable portion that can be pulled out from the second layer and the conductive layers 23 and 27 that are the third layer laminated on the conductive layer 22 as the first layer. This cable portion is provided with a shield layer.

  First, as shown in FIG. 2A (1), a conformal mask, a circuit pattern and a connection pattern with a shield layer are formed on a double-sided copper-clad laminate. That is, with respect to the double-sided copper-clad laminate 24, conformal masks 22 a and 23 a at the time of laser processing are applied to the copper foils 22 and 23 of the double-sided copper-clad laminate 24 by a photofabrication technique. An inner layer circuit pattern 23b and a second layer pattern 23c to be a connection point to the shield layer later are formed on the copper foil 23.

  The double-sided copper-clad laminate 4 has copper foils 22 and 23 having a thickness of 12 μm on both surfaces of a flexible insulating base material 21 such as polyimide (here, polyimide having a thickness of 12.5 μm). The photofabrication technique for forming the conformal masks 22a and 23a, the circuit pattern 23b, and the pattern 23c is based on a series of steps such as resist layer formation, exposure, development, etching, and resist layer peeling.

  Since the alignment of both surfaces at this time is performed with respect to the solid material, the positional accuracy can be easily secured without being affected by the expansion and contraction of the material. If necessary, it is also possible to use an exposure machine capable of highly accurate alignment. Moreover, the roughening process for improving close_contact | adherence with a buildup adhesive material is performed as needed. Through the steps so far, the first and second layer circuit substrates 25 of the three-layer flexible printed wiring board are obtained.

  A single-sided copper-clad laminate 28 having a copper foil 27 (thickness 12 μm) provided on one side of a flexible insulating base material 26 (here, polyimide having a thickness of 12.5 μm) such as polyimide is prepared. The circuit base material 29 and the adhesive 30 are aligned and laminated on the copper clad laminate 8 as necessary. The adhesive 30 is previously punched so as to be laminated with the circuit base material 29.

  Next, as shown in FIG. 2A (2), the double-sided circuit base material 25 and the single-sided circuit base material 29 are aligned, and are laminated by sandwiching the adhesive 30 and using a vacuum press or the like. Up to this step, a three-layer multilayer circuit substrate 31 is obtained. The adhesive 30 is preferably a low-flow type bonding sheet or the like with little flow-out, and it is necessary to function as an adhesive for the cable portion later. Therefore, flexibility is essential. The thickness of the adhesive 30 can be selected from about 10 to 15 μm.

  Subsequently, as shown in FIG. 2B (3), laser processing is performed using the conformal masks 22a and 23a to form a conduction hole 32 for connecting the three layers and a connection point for a later shield. The two-layer pattern 23c is exposed.

  When the pattern 23c is exposed, the flexible insulating base material 21 is selectively laser processed, and the flexible insulating base material 26 is processed so as not to be processed as much as possible. The copper foil 22 is removed from the place where the process is performed.

  Further, the flexible insulating base material 21 is selectively laser processed by reducing the laser beam diameter and laser processing using the outermost part of the effective area of the beam, and the flexible insulating base material 26 is damaged as much as possible. The pattern 23c of the second layer can be exposed without providing For laser processing, a UV-YAG laser, a carbonic acid laser, an excimer laser, or the like can be selected.

  As a processing shape, for example, as shown in FIG. 2B (4), the flexible insulating base material 1 and the adhesive material 10 are processed into a so-called wave-shaped cross-sectional shape that repeats a semicircle and a plane alternately. The contact area of the plating film to be formed can be increased, and the reliability of the shield connection point can be improved.

  As shown in FIG. 2B (5), the multi-layer circuit substrate 33 having the conduction holes 32 is subjected to a conductive treatment, and electroplating of about 10 to 20 μm is performed to achieve interlayer conduction. Single-sided plating without plating was performed.

  A plating mask is formed on the copper foil surface on the third layer side, a plating film is selectively formed on the first layer, and then the plating mask is peeled off to obtain a plated multilayer circuit substrate 34. A connection point 36 is formed from the conduction hole 32 to the step via hole 35, and from the second layer pattern 23c to the shield layer, and plating deposition also occurs on the first layer side surface of the third layer cable. It is removed by etching when forming the circuit pattern of the surface layer.

  Next, as shown in FIG. 2C (6), the first layer surface with plating and the third layer surface without plating are simultaneously etched by a photofabrication technique to form circuit patterns 38 and 39.

  On the first layer surface having a large level difference, the plating film deposited on the surface on the first layer side of the third layer cable of the level difference portion where the shield layer is formed as shown in the figure is changed from the pattern 33c of the second layer to the shield layer. The level difference can be reduced by leaving the shape including the connection point. For this reason, electrical connection can be made, the level difference can be reduced, and in addition to the reduction in the material thickness, filling failure does not occur when the shield layer is formed.

  A dry film resist having a thickness of 20 μm or more is preferably applied to the first layer surface, which is the opening surface of the step via hole 35, in order to ensure tenting properties. It is not necessary to consider tenting properties, and a dry film resist for forming a fine pattern having a thickness of 10 μm or less can be applied to the thin third layer surface of the copper foil. In addition, when a liquid resist is used, it is not necessary to consider the tenting property of the step via hole 35. Therefore, the resist layers formed on the first layer surface and the third layer surface may have the same thickness.

  Next, as shown in FIG. 2C (7), a solder resist layer 40 is formed on the first layer surface, and a cover lay 43 having an adhesive 42 on an insulating film 41 such as a polyimide film is laminated on the third layer surface, A shield layer 44 such as a paste film having a predetermined opening is also formed.

  In the first layer surface having a large level difference shown in FIG. 2C (6), the level difference can be reduced by the connection point with the shield layer, so that no filling failure occurs when the shield layer is formed. Furthermore, since the electrical connection area between the shield layer and the circuit pattern is increased, the connection reliability between the shield layer and the circuit pattern is also improved. On the third layer surface with only the thickness difference of the circuit pattern, there is no problem in the filling property of the shield layer and the connection reliability between the shield layer and the circuit pattern.

  Before and after this process, two-layer extraction from the second layer and the third layer having the shield layer is performed by subjecting the substrate surface to surface treatment such as solder plating, nickel plating, and gold plating as necessary, and performing external processing. A three-layer flexible printed wiring board 45 having a cable portion that can be obtained is obtained.

  Further, as shown in FIG. 2C (8), the shield connection point 36 can be extended to form a flat portion on the first layer surface side of the third layer cable. In this case, electroless nickel gold plating or the like is preferably performed on the exposed shield connection point 36 for the purpose of preventing oxidation.

  FIG. 3 shows the single-sided plating method in FIG. 2 (5). A set of two multilayer circuit base materials 33 each having a conduction hole 32, and a distance G between the circuit base materials 33 of 15 mm or less. Electrolytic copper plating is performed at a predetermined interval. Thereby, each becomes a shielding board with respect to a mutual 3rd layer, and a plating film can be selectively deposited from the mutual 1st layer side.

  If the distance between the base materials 33 is closer than 5 mm, the base material 33 has flexibility, so that it becomes difficult to contact the paired substrates during plating or to renew the liquid on the third layer side. There is a risk that it will not be washed.

  On the other hand, when the distance between the base materials 33 is longer than 15 mm, the mutual shielding effect is weakened, and plating may be deposited on the periphery of the base material, particularly the base material, and may also be deposited on the cable surface.

  FIGS. 4A and 4B are shown in more detail. As shown in FIG. 4A, the periphery of the circuit substrate 33 is clamped and set on the plating rack 37. FIG. When viewed from the A-A ′ cross-sectional direction, as shown in FIG. 4B, two circuit base materials 33 are set in one plating rack 37.

  When the plating rack 37 side is used as a cathode during electrolytic copper plating, and anodes are arranged on both sides of the plating layer, the plating rack is preferably positioned at the approximate center of a set of anodes. Thereby, a copper plating film is deposited with a thickness substantially equal to the first layer of the two circuit substrates 33.

<Example 2 of a manufacturing method>
5A and 5B are sectional process diagrams showing Example 2 of the method for manufacturing a three-layer flexible printed wiring board of the present invention. This wiring board has a cable portion that can be drawn out of the second layer and the third conductive layer, and a shield layer is provided on the cable portion. The conductive layer as the first layer is formed later.

  First, as shown in FIG. 5A (1), a second layer serving as a connection point of a conformal mask 52a, an inner layer circuit pattern 52b, and a later shield on the copper foil 52 of the single-sided copper-clad laminate 53. Pattern 52c is formed.

  This is because, for example, a circuit pattern on one side of a single-sided copper clad laminate 53 having a 12 μm-thick copper foil 52 on one side of a flexible insulating base material 51 such as polyimide (here, polyimide having a thickness of 12.5 μm). Is performed by a series of steps of forming by photofabrication technique.

  If necessary, a roughening treatment is performed to improve adhesion with the build-up adhesive. Through the steps so far, the circuit substrate 54 on which the inner layer circuit pattern of the second layer of the three-layer flexible printed wiring board is formed is obtained (the first layer will be formed later).

  Then, a single-sided copper-clad laminate 28 in which a copper foil 27 having a thickness of 12 μm is formed on one side of a flexible insulating base material 26 such as polyimide (here, polyimide having a thickness of 12.5 μm) is aligned as necessary. The circuit base material 29 from which the guides and the like have been die-cut and the adhesive 30 that has been die-cut in advance for laminating the circuit base material 29 are aligned and laminated.

  Next, as shown in FIG. 5A (2), the circuit substrate 54 on which the second-layer inner layer circuit pattern is formed and the single-sided circuit substrate 29 are laminated by a vacuum press or the like with the adhesive 30 interposed therebetween. Through the steps so far, a multilayer circuit substrate 55 having two conductor layers out of the three layers is obtained.

  The adhesive 30 is preferably a low-flow type bonding sheet or the like with little flow-out, and it is necessary to function as an adhesive for the cable portion later. Therefore, flexibility is essential. The thickness of the adhesive 30 can be selected from about 10 to 15 μm.

  Next, as shown in FIG. 5A (3), using a conformal mask 52a formed by directly processing a flexible insulating base material 51 such as polyimide with a laser, an adhesive located on the opening surface of the conformal mask. 30 and the flexible insulating base material 26 are subjected to laser processing to form a conduction hole 56 for connecting the three layers, and the second layer pattern 52c to be a connection point of a later shield is exposed.

  When the pattern 52c is exposed, only the flexible insulating base material 51 is laser processed. Since the flexible insulating base material 26 needs to be processed as little as possible, the flexible insulating base material 51 is selectively formed by reducing the laser beam diameter and laser processing using the pattern 52c as a metal mask. Laser processing is performed to expose the pattern 52c of the second layer. For laser processing, a UV-YAG laser, a carbonic acid laser, an excimer laser, or the like can be selected.

  As shown in FIG. 5B (4), the multi-layer circuit substrate 57 having the conduction holes 56 is subjected to a conductive treatment, and an electrolytic plating of about 10 to 20 μm is performed to obtain interlayer conduction, but the third layer is plated. Single-sided plating is essential. For this reason, a plating mask is formed on the copper foil surface on the third layer side, a plating film is selectively formed on the first layer side, and then the plating mask is peeled and removed, whereby the plated multilayer circuit substrate 58 is obtained.

  A step via hole 59 is formed from the conduction hole 56, a connection point 60 of the shield layer is formed from the second layer pattern 53c, and plating deposition also occurs on the first layer side surface of the third layer cable. It is removed by etching when forming a circuit pattern on the surface layer later.

  Next, as shown in FIG. 5B (5), the first layer surface formed by plating and the third layer surface not plated are simultaneously etched by a photofabrication method to form circuit patterns 61 and 39. .

  At this time, a dry film resist having a thickness of 20 μm or more is preferably applied to the first layer surface, which is the opening surface of the step via hole 59, in order to ensure tenting properties. A dry film resist for forming a fine pattern having a thickness of 10 μm or less can be applied to the thin third layer surface of the copper foil that does not require consideration of tenting properties. In addition, when a liquid resist is used, it is not necessary to consider the tenting property of the step via hole 59, so that the resist layers formed on the first layer surface and the third layer surface may have the same thickness.

  Next, a solder resist layer 40 is formed on the first layer surface, a cover lay 43 having an adhesive 42 is laminated on an insulating film 41 such as a polyimide film on the third layer surface, and a paste film or the like provided with a predetermined opening The shield layer 44 is also formed.

  On the first layer surface having a large level difference, the level difference can be reduced by the shield connection point, so that no filling failure occurs when the shield layer is formed. Furthermore, since the electrical connection area between the shield layer and the circuit pattern is increased, the connection reliability between the shield layer and the circuit pattern is also improved. On the third layer surface with only the thickness difference of the circuit pattern, there is no problem in the filling property of the shield layer and the connection reliability between the shield layer and the circuit pattern.

  Two layers from the second layer and the third layer having a shield layer are formed by subjecting the substrate surface to a surface treatment such as solder plating, nickel plating, gold plating or the like before and after this step to perform external processing. A three-layer flexible printed wiring board 62 having a cable portion that can be pulled out is obtained.

  Thus, since the conductor layer on the via hole opening surface can be formed only by the plating layer and can be formed thin, finer wiring can be formed as compared with the first embodiment.

<Example 3>
FIG. 6 is a sectional process diagram showing Example 3 of the method for manufacturing a wiring board according to the present invention. This wiring board can be pulled out from the second layer and the third layer having the shield layer, and the steps up to (3) in FIG. 2B are the same as those in the first embodiment.

  As shown in FIG. 5A (1), the multi-layer circuit substrate 57 having the conduction holes 56 is subjected to a conductive treatment, and electroplating of about 10 to 20 μm is performed to obtain interlayer conduction, but the third layer is plated. Single-sided plating is essential.

  At this time, on the first layer side, a plating resist 71 for forming a circuit by a semi-additive method is formed, and a resist layer 72 serving as an etching resist is also formed on the copper foil surface on the third layer side. The layer and the third layer are exposed simultaneously.

  In FIG. 5A, reference numeral 72a represents an imaging pattern after exposure, and an etching resist pattern is obtained by developing later. Thereafter, on the third layer side only, a plating mask 73 such as a slightly adhesive film is further developed on the etching resist 72 which has been subjected to exposure, and developed.

  As a result, a plating resist 71 is formed, and electrolytic plating is performed through the conductive film to form a plating pattern 74 only on the first layer side. At this time, the shield connection point 60 is also formed. Thereafter, the plating resist 71 on the first layer side is removed, and the conductive film is removed by etching.

  Next, FIG. 5A (2) is a cross-sectional view taken along line A-A ′ of FIG. 5A (1). An etching resist 72 on the third layer side is formed on the inside of the substrate about several millimeters from the outer shape of the substrate, and a plating mask 73 is formed on the entire surface of the third layer side substrate including the exposed substrate 75 of several millimeters.

  Next, in FIG. 5A (3), the first layer surface formed by plating is protected with a slightly adhesive film or the like, and the circuit layer 39 is formed on the third layer surface not plated by etching by a photofabrication technique. .

  Since the first layer surface and the third layer surface are simultaneously exposed, high positional accuracy can be ensured. A dry film resist for forming a fine pattern having a thickness of 10 μm or less can be applied to the thin third layer surface of the copper foil.

  Subsequent steps are the same as those in FIG. 2, so that the cable portion has fine wiring from the first layer to the third layer and can be drawn out from the second layer and the third layer having the shield layer. A three-layer flexible printed wiring board 76 having is obtained.

  Thus, by forming the conductor layer (first layer) on the opening surface of the via hole by a semi-additive method, it is possible to form a finer and higher-definition wiring than in the second embodiment. At this time, since the conductor layer on the third layer side forms a circuit by etching, a rolled copper foil having excellent flexibility can be applied.

The conceptual cross-sectional block diagram of the structure of the three-layer flexible printed wiring board which has a shield layer concerning this invention. BRIEF DESCRIPTION OF THE DRAWINGS The conceptual cross-sectional block diagram which shows the one part manufacturing process of the 3 layer flexible printed wiring board which concerns on Example 1 of this invention. BRIEF DESCRIPTION OF THE DRAWINGS The conceptual cross-sectional block diagram containing the perspective view which shows the partial manufacturing process of the three-layer flexible printed wiring board which concerns on Example 1 of this invention. BRIEF DESCRIPTION OF THE DRAWINGS The conceptual cross-sectional block diagram which shows the one part manufacturing process of the 3 layer flexible printed wiring board which concerns on Example 1 of this invention. BRIEF DESCRIPTION OF THE DRAWINGS The conceptual cross-sectional block diagram which shows the structure of the three-layer flexible printed wiring board concerning Example 1 of this invention. BRIEF DESCRIPTION OF THE DRAWINGS The conceptual cross-sectional block diagram which shows the structure of the three-layer flexible printed wiring board concerning Example 1 of this invention. The conceptual cross-sectional block diagram which shows the one part manufacturing process of the three-layer flexible printed wiring board which concerns on Example 2 of this invention. The conceptual cross-sectional block diagram which shows the one part manufacturing process of the three-layer flexible printed wiring board which concerns on Example 2 of this invention. The conceptual cross-section block diagram which shows the structure of the three-layer flexible printed wiring board concerning Example 3 of this invention. 7A and 7B are a plan view showing a state of the plating pattern after the treatment shown in FIG. 6 and a cross-sectional view taken along the line A-A ′. The conceptual cross-sectional block diagram of the structure of the conventional 3 layer flexible printed wiring board.

Explanation of symbols

1 flexible insulating base material, 2 double-sided flexible printed wiring board, 3 insulating film,
4 Adhesive, 5 Coverlay, 6 Cable part of the second layer, 7 Flexible insulating base material,
8 single-sided flexible printed wiring board, 9 insulating film, 10 adhesive, 11 coverlay,
12 cable part of the third layer, 13 adhesive, 14, 15 shield layer,
16 through hole, 17 electrical connection point with shield layer, 21 flexible insulating base material,
22 copper foil, 22a, 23a conformal mask, 23 copper foil, 23b circuit pattern,
23c Second layer pattern to be a shield connection point, 24 double-sided copper-clad laminate,
25 1st and 2nd layer circuit substrates, 26 flexible insulating base material, 27 copper foil,
28 single-sided copper-clad laminate, 29 third layer circuit substrate, 30 adhesive,
31 3 layer multilayer circuit substrate, 32 hole for conduction, 33 multilayer circuit substrate having hole for conduction,
34 plated multilayer circuit substrate, 35 step via hole, 36 shield connection point,
37 plating rack, 38 outer layer circuit pattern of the first layer,
39 third layer outer layer circuit pattern, 40 solder resist, 41 insulating film,
42 Adhesive, 43 Coverlay, 44 Shield layer,
45 Three-layer flexible printed wiring board according to the present invention, 51 Flexible insulating base material,
52 copper foil, 52a conformal mask, 52b circuit pattern,
52c Second layer pattern to be the connection point of shield, 53 Single-sided copper-clad laminate,
54 a second layer circuit substrate, 55 a three layer multilayer circuit substrate, 56 conduction holes,
57 multilayer circuit substrate having holes for conduction, 58 plated multilayer circuit substrate,
59 step via hole, 60 shield connection point, 61 first layer outer layer circuit pattern,
62 three-layer flexible printed wiring board according to the present invention, 71 plating resist,
72 etching resist, 72a exposure imaging pattern on the etching resist,
73 plating mask, 74 plating pattern, 75 third layer side substrate surface,
76 Three-layer flexible printed wiring board according to the present invention, 101 flexible insulating base material,
102 double-sided flexible printed wiring board, 103 insulating film, 104 adhesive,
105 coverlay, 106 second layer cable part, 107 flexible insulating base material,
108 single-sided flexible printed wiring board, 109 insulating film, 110 adhesive,
111 Coverlay, 112 Third layer cable part, 113 Adhesive,
114, 115 shield layer, 116 through hole, 117 multilayer part,
118 Electrical connection point with shield layer.

Claims (4)

In a multilayer flexible printed wiring board in which at least one cable portion and a component mounting portion are integrally formed, and at least one of the cable portions has a shield layer,
An electrical connection point from at least two wiring layers to the shield layer is formed on an end surface of the component mounting portion that becomes a boundary with the cable portion having the shield layer. A multilayer flexible printed wiring board having a shield layer in the part. In the method for producing a multilayer flexible printed wiring board having a cable portion on which a shield layer is formed,
Preparing a double-sided flexible substrate having a conductive layer on both sides and a single-sided flexible substrate having a conductive layer on one side;
A mask hole is provided in one conductive layer of the double-sided flexible substrate to form a conduction hole for connecting the conductive layers on both sides, and an electrical connection point with the shield layer is provided on the other conductive layer. Forming a circuit pattern comprising:
Laminating the double-sided flexible substrate and the single-sided flexible substrate across an adhesive disposed on the inner layer side of the circuit pattern to form a multilayer circuit;
Performing the drilling of the multilayer circuit from one surface of the double-sided flexible substrate using the mask hole, and forming the conduction hole;
Removing a part of the insulating base material of the double-sided flexible substrate at an end of the circuit pattern to expose the circuit pattern;
A process of forming a via hole by plating the opening surface of the conduction hole with respect to the conduction hole and the circuit pattern, and forming an electrical connection point with the shield layer at an end of the circuit pattern When,
Forming the shield layer so as to cover the circuit pattern including at least the connection points;
A method for producing a multilayer flexible printed wiring board, comprising: In the method for producing a multilayer flexible printed wiring board having a cable portion on which a shield layer is formed,
Preparing two single-sided flexible substrates (A, B);
Forming a mask hole for forming a hole for conduction in the conductive layer on one side (A) of the one-sided flexible substrate and forming a circuit pattern serving as an electrical connection point with the shield layer; ,
The two flexible substrates are laminated by adhering the circuit pattern on one side (A) of the single-sided flexible substrate and the opposite surface of the conductive layer on the other side (B) of the single-sided flexible substrate. And forming a multilayer circuit;
A hole having a diameter larger than that of the mask hole is formed at the projection position of the mask hole in the insulating base material of one side (A) of the single-sided flexible substrate, and the insulating base of the other side (B) of the single-sided flexible substrate For the material, forming the hole for conduction by drilling the multilayer circuit from the opposite surface of the conductive layer of one side (A) of the one-sided flexible substrate using the mask hole;
Removing a part of the insulating base material on one side (A) of the one-sided flexible substrate on the circuit pattern to be the connection point, and exposing the pattern to be the connection point at an end of the circuit pattern;
For the pattern to be the hole for conduction and the connection point, plating the opening surface of the hole for conduction to form a via hole, and forming the connection point at the end of the cable;
Forming a shield layer on at least the pattern to be the connection point;
A method for producing a multilayer flexible printed wiring board, comprising: In the manufacturing method of the multilayer flexible printed wiring board of Claim 3,
A first resist layer for forming a pattern by a semi-additive method on the opening surface of the hole for conduction when plating the opening surface of the hole for conduction with respect to the hole for conduction, and the opposite surface Simultaneously exposing the second resist layer for forming a pattern by an etching technique on the conductive layer of the single-sided flexible substrate B,
Further forming a plating mask on the second resist layer, developing the first resist layer, forming a via hole by plating the opening surface of the hole for conduction,
A method for producing a multilayer flexible printed wiring board, comprising:

Images