JP2006165231A - Multilayer flexible printed circuit board and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer flexible printed circuit board having a flexible cable section, and to provide a manufacturing method for the multilayer flexible printed circuit board. <P>SOLUTION: An internal-layer board having a cable structure is formed, a cover as a cable protective layer is formed to the internal-layer board, a first hole for a conduction is formed to the internal-layer board containing the cover, and a first through-hole is formed, by carrying out an electroless plating or/and a conductive treatment and the electroless plating to the first hole for the conduction. A previously rapped single-sided copper-clad laminated board and an adhesive are aligned and laminated to the internal-layer board, and a second hole for the conduction for forming a second through-hole will not interfere in the first through-hole and has a diameter smaller than that of the first through-hole, on the coaxis of the first through-hole. The second through-hole is formed on the coaxis of the first through-hole, by carrying out the electroless plating or/and the conductive treatment and the electroless plating to the second hole for conduction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a manufacturing method and structure of a multilayer circuit wiring board, and more particularly to a multilayer flexible circuit wiring board having a flexible 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 circuit boards. In view of this, the circuit board is made to be a multi-layer circuit board from one side to both sides or three or more layers to increase the density of the circuit board.

  As part of this, a multilayer flexible circuit with a flexible cable unit that integrates a multilayer circuit board on which various electronic components are mounted, a separate flexible wiring board that connects hard circuit boards via connectors, etc., and a flexible flat cable. Wiring boards are widespread mainly in small electronic devices such as mobile phones.

  A typical structure of a multilayer flexible circuit wiring board is such that a double-sided or single-sided flexible wiring board is used as an inner layer, and a flexible or hard base circuit board as an outer layer is laminated thereon, and through holes are connected by plating or the like. The structure is a multilayer flexible circuit wiring board having about one layer.

  However, as described in Patent Document 3 and Patent Document 4, in order to provide a flexible cable portion in the multilayer circuit wiring board, a polyimide resin cover film for the flexible cable portion and a laminate for the same There is a problem that the thermal expansion coefficient of the adhesive is high, it expands due to heat during solder reflow of about 220 to 240 ° C. during component mounting, and cracks are likely to occur in the through-hole plating layer. Since the crack can be avoided only by increasing the thickness, the conductor thickness of the surface layer becomes thick, and a multilayer flexible circuit wiring board in a form that requires high-density wiring and high-density mounting becomes a serious problem as a product.

  Patent Document 1 describes a structure in which a polyimide resin cover film of a flexible cable part is retracted outward from a through-hole conduction hole. However, when the cover film with the end face retracted is misaligned, the through-hole crack resistance is not improved, and the above problem cannot be solved. In addition, an adhesive such as a prepreg for laminating a single-sided copper-clad laminate or the like serving as an outer layer on the flexible cable part dislikes flowing out from the end face of the flexible cable part, and suppresses fluidity. For this reason, it is difficult to fill the level difference of the cover film whose end face is retracted. When the filling property of an adhesive such as a prepreg is improved, as described above, it causes a flow out from the end face of the flexible cable portion and the like, so that it is difficult to apply.

  Patent Document 2 describes a method of manufacturing a multilayer substrate by through-hole connection in which laser processing is performed so that the hole diameter of the inner layer is larger than that of the outer layer, and the through-hole plating thickness is selectively thickened only on the inner layer. ing. However, since the control of the hole diameter must be controlled by the laser processing conditions, even if the inner layer hole diameter changes due to variations in the laser processing conditions, it is necessary to determine the conditions every time the constituent material changes, There is a concern that the detection cannot be performed, and the through hole processing cannot be performed by stacking the substrates as in the conventional NC drill, and there is a disadvantage that the productivity is significantly inferior to the conventional method. In addition, regarding the control of the plating thickness, it is difficult to selectively thicken only the inner layer stably, and it is difficult to set the contrast of the plating thickness within the range described in this document. It is impossible to achieve both the through-hole reliability of the flexible circuit wiring board and the formation of fine wiring on the surface layer.

  In Patent Document 5 and Patent Document 6, through-hole plating is performed on the inner layer circuit in advance, and the outer layer is laminated. Then, a conduction hole is formed coaxially with the through-hole, and further through-hole plating is performed. A method for providing a contrast of the plating thickness is described. However, since these methods simplify the inner layer desmear process, it is difficult to apply to a multilayer flexible circuit wiring board in which the inner layer circuit desmear process having a cable is essential. In addition, in order to prevent cracks in the polyimide resin cover film layer and adhesive layer in the vicinity of the flexible cable portion having a high thermal expansion coefficient unique to the multilayer flexible circuit wiring board, these It is necessary to increase the thickness of the through-hole plating of the layer, but in the range described in Patent Document 5 and Patent Document 6, since only the through-hole plating thickness up to the interlayer connection portion of the inner layer circuit is increased, the problem cannot be solved. Absent.

  For these reasons, there has been a demand for a method of effectively preventing through-hole cracks in a multilayer flexible circuit wiring board by a method with good productivity without increasing the surface conductor thickness.

  8 to 10 are sectional process diagrams showing a conventional method for manufacturing a double-sided circuit wiring board. First, as shown in FIG. 8 (1), a flexible insulating base material 61 such as polyimide is used. A so-called double-sided copper-clad laminate 64 having conductive layers 62 and 63 such as copper foil on both sides is prepared.

  Next, as shown in FIG. 2B, a circuit pattern 65 such as a cable is formed on the copper foil layers 62 and 63 of the double-sided copper-clad laminate 64 by using an etching method based on a normal photofabrication method. To form an inner layer circuit 66.

  Next, as shown in FIG. 3 (3), a cover is formed by bonding a polyimide film 67 to a circuit pattern 65 such as a cable via an adhesive 68, and a cable portion 70 is formed.

  Next, as shown in FIG. 4 (4), a so-called single-sided copper-clad laminate 73 having a conductive layer 72 such as a copper foil on one side of an insulating base material 71 and this is punched into a desired shape by a mold or the like. An adhesive 74 is prepared for bonding to the processed cable portion 70 of FIG. The thickness of the conductive layer 72 at this time is 50 μm or less, and particularly preferably 35 μm or less.

  Next, as shown in FIG. 5 (5), the single-sided copper-clad laminate 73 and the adhesive 74 are bonded together and punched into a desired shape using a mold or the like.

  Next, as shown in (1) of FIG. 9, the single-sided copper-clad laminate 75 of FIG. 5 (5) is laminated on the cable part 70 of FIG.

  Next, as shown in FIG. 2B, a conduction hole 76 is formed by an NC drill or the like.

  Next, as shown in (1) of FIG. 10, the through hole 77 is formed by electroplating after the electroconductive plating 76 is subjected to electroless plating or conductive treatment. In this case, the plating thickness of the through hole 77 is preferably about 30 to 50 μm in order to ensure reliability.

Next, as shown in FIG. 2B, a circuit pattern 78 is formed on the through-hole surface by using an etching method based on a normal photofabrication method. Thereafter, a surface treatment such as formation of a photo solder resist layer, solder plating, nickel plating, gold plating, or the like is performed on the substrate surface as necessary, and outer shape processing is performed to obtain the multilayer flexible circuit wiring board 79.
JP-A-6-21653 JP 2001-210953 A Japanese Patent No. 2631287 Japanese Patent No. 3427011 JP-A-62-190797 JP-A-8-264952

  It is an object of the present invention to provide a multilayer flexible circuit wiring board and a method for manufacturing the multilayer flexible circuit wiring board capable of ensuring both through-hole connection reliability and forming a fine pattern on the surface layer in the production of the multilayer flexible circuit wiring board.

  According to the present invention for solving the above problems, in the multilayer flexible circuit wiring board having through-hole connection, the outer periphery of the conduction hole of the cover serving as the cable protection layer of the inner layer board having the cable structure is the first through-hole plating film And a multilayer flexible circuit wiring board characterized in that the inner periphery is reinforced with a second plating film continuous with the through-hole plating of the outer layer.

  In order to embody the present invention to solve the above problems, as a first manufacturing method, in the manufacturing method of a multilayer flexible circuit wiring board, an inner layer substrate having a cable structure is formed, and a cover serving as a cable protection layer is formed on the inner layer substrate. Forming a first conduction hole in the inner substrate including the cover, and subjecting the first conduction hole to electroless plating or / and conductive treatment and electrolytic plating to form a first through hole. A first through-hole that is formed and laminated with a single-sided copper-clad laminate and an adhesive that have been pre-punched and aligned with the inner-layer substrate so as not to interfere with the first through-hole on the same axis as the first through-hole. Forming a second through hole for forming a second through hole having a smaller diameter, and electroless plating or / and conducting treatment and electrolytic plating on the second through hole Method for manufacturing a multilayer flexible circuit wiring board and forming a second through hole coaxially of the first through-hole is employed by applying.

  In order to embody the present invention that solves the above problems, as a second manufacturing method, in the manufacturing method of a multilayer flexible circuit wiring board, an inner layer substrate having a cable structure is formed, and a cover that serves as a cable protection layer is formed on the inner layer substrate. Forming a first conduction hole in the inner substrate including the cover, and subjecting the first conduction hole to electroless plating or / and conductive treatment and electrolytic plating to form a first through hole. Formation of a second conduction hole for forming a second through hole having a diameter larger than that of the first through hole, which is formed in advance and does not interfere with the first through hole on the same axis as the first through hole. Then, a die-cut single-sided copper-clad laminate and an adhesive are aligned and laminated on the inner layer substrate, and the second conductive hole is electrolessly plated or / and electrically conductive and electroplated. Method for manufacturing a multilayer flexible circuit wiring board and forming a second through hole coaxially of the first through-hole is employed by the applying.

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

  In the multilayer flexible circuit wiring board having through-hole connection according to the present invention, the outer periphery of the conduction hole of the cover, which is the cable protection layer of the inner layer board having the cable structure, is formed of the first through-hole plating film, and the inner circumference is the outer layer. Since the multilayer flexible circuit wiring board is reinforced by the second plating film continuous with the through-hole plating, the inner layer board is compared with the multilayer flexible circuit wiring board having the through-hole connection by the conventional method. Although the through-hole plating thickness of the surface layer can be reduced while increasing the through-hole plating thickness, it is possible to form a fine pattern on the surface layer while ensuring reliability. In addition, since the plating thickness of the surface layer can be reduced, the flatness of the surface layer caused by variations in the plating thickness is also improved and the mountability is improved. It can be provided inexpensively and stably.

  Hereinafter, the present invention will be further described with reference to the illustrated embodiments.

  1 to 4 are process diagrams showing a method of manufacturing a multilayer flexible circuit wiring board according to an embodiment of the present invention. First, as shown in FIG. A so-called double-sided copper-clad laminate 4 having conductive layers 2 and 3 such as copper foil on both sides of the base material 1 is prepared.

  Next, as shown in FIG. 2 (2), a circuit pattern 5 such as a cable is formed on the copper foil layers 2 and 3 of the double-sided copper-clad laminate 4 by using an etching method based on a normal photofabrication method. To form an inner layer circuit 6.

  Next, as shown in FIG. 3 (3), the cover 9 is formed by bonding the polyimide film 7 to the circuit pattern such as the cable of the inner layer circuit 6 through the adhesive 8, and the cable portion 10 is formed.

  Next, as shown in FIG. 4 (4), the conduction hole 11 is formed with an NC drill or the like. As the diameter of the conduction hole 11, for example, a diameter of 500 μm is applicable.

  Next, as shown in (1) of FIG. 2, the through hole 12 is formed by electroplating after conducting the electroless plating or conductive treatment on the conduction hole 11. In this case, the plating thickness of the through hole 12 is preferably about 30 to 50 μm in order to ensure reliability.

  Next, as shown in FIG. 2 (2), through-hole lands 13 are formed on the through-hole surface by an etching method using a normal photofabrication method, and an inner layer circuit 14 including a cable portion is obtained. .

  Next, as shown in FIG. 3 (3), a so-called single-sided copper-clad laminate 17 having a conductive layer 16 such as a copper foil on one side of an insulating base material 15 and this is punched into a desired shape by a mold or the like. An adhesive 18 for bonding to the processed inner layer circuit 14 including the cable portion of FIG.

  Next, as shown in FIG. 4 (4), the single-sided copper-clad laminate 17 and the adhesive 18 are bonded together and punched into a desired shape with a mold or the like to obtain a single-sided copper-clad laminate 19.

  Next, as shown in FIG. 3 (1), the single-sided copper-clad laminate 19 of FIG. 2 (4) is punched into the inner layer circuit 14 including the cable portion of FIG. 2 (2) via an adhesive 18. Are laminated.

  Next, as shown in FIG. 2B, the conduction hole 20 is formed by an NC drill or the like. As the diameter of the conduction hole 20, a diameter that does not interfere with the through hole 12, for example, a diameter of 150 to 300 μm can be selected. If the hole diameter is too small, the drill blade is likely to be broken, which may lead to a decrease in yield or deterioration of the contact with the through-hole plating. If the hole diameter is large, the through hole 12 may be damaged when the conduction hole 20 is formed due to problems such as alignment.

  Next, as shown in FIG. 4 (1), the excess adhesive 18 in the conduction hole 20 after drilling is removed by desmearing as necessary.

  Next, as shown in FIG. 2 (2), after conducting the conductive treatment to the conduction hole 20, a through hole 21 is formed by electroplating. The plating thickness of the through hole 21 at this time may be relatively thin, and for example, connection reliability can be ensured at about 15 μm.

  Next, as shown in FIG. 3C, a circuit pattern 22 is formed on the through-hole surface by using an etching method using a normal photofabrication method. Thereafter, surface treatment such as formation of a photo solder resist layer, solder plating, nickel plating, and gold plating is performed on the substrate surface as necessary, and outer shape processing is performed to obtain the multilayer flexible circuit wiring board 23.

  5 to 7 are process diagrams showing a method of manufacturing a multilayer flexible circuit wiring board according to another embodiment of the present invention. First, as shown in FIG. A so-called double-sided copper-clad laminate 34 having conductive layers 32 and 33 such as copper foil on both surfaces of the insulating base material 31 is prepared.

  Next, as shown in FIG. 2B, a circuit pattern 35 such as a cable is formed on the copper foil layers 32 and 33 of the double-sided copper-clad laminate 34 by using an etching method based on a normal photofabrication method. To form the inner layer circuit 36.

  Next, as shown in FIG. 3 (3), a cover 39 is formed by bonding a polyimide film 37 with an adhesive 38 to a circuit pattern 35 such as a cable of the inner layer circuit 36 to form a cable portion 40.

  Next, as shown in FIG. 4 (4), a conduction hole 41 is formed by an NC drill or the like. As the diameter of the hole 41 for conduction, for example, a diameter of 300 μm is applicable.

  Next, as shown in (1) of FIG. 6, after conducting the electroless plating or the conductive treatment on the hole 41 for conduction, the conductive hole is formed, and then the through hole 42 is formed by electroplating. In this case, the plating thickness of the through hole 42 is preferably about 30 to 50 μm in order to ensure reliability.

  Next, as shown in FIG. 2 (2), through-hole lands 43 are formed on the through-hole surface by using an etching method based on a normal photofabrication method to obtain an inner layer circuit 44 including a cable portion. .

  Next, as shown in FIG. 3 (3), a so-called single-sided copper-clad laminate 47 having a conductive layer 46 such as a copper foil on one side of an insulating base material 45, and this is punched into a desired shape by a mold or the like. An adhesive 48 is prepared for bonding to the processed inner layer circuit 44 including the cable portion shown in (2) of FIG.

  Next, as shown in FIG. 4 (4), the single-sided copper-clad laminate 47 and the adhesive material 48 are bonded together and punched into a desired shape with a mold or the like, and the conduction hole 50 is formed with an NC drill or the like. A single-sided copper-clad laminate 49 is obtained by forming. As the diameter of the conduction hole 50, a diameter that does not interfere with the through hole 42, for example, a diameter of 500 μm can be selected.

  Next, as shown in FIG. 7 (1), the single-sided copper-clad laminate obtained by punching the inner layer circuit 44 including the cable portion shown in FIG. 6 (2) through the adhesive 48 (4) shown in FIG. 49 are stacked.

  Next, as shown in FIG. 2B, the conduction hole 50 is subjected to a conductive treatment, and then a through hole 51 is formed by electroplating. The plating thickness of the through hole 51 at this time may be relatively thin, and for example, connection reliability can be ensured at about 15 μm.

  Next, as shown in FIG. 3C, a circuit pattern 52 is formed on the through-hole surface by using an etching method based on a normal photofabrication method. Thereafter, surface treatment such as formation of a photo solder resist layer, solder plating, nickel plating, gold plating or the like is performed on the substrate surface as necessary, and external processing is performed to obtain the multilayer flexible circuit wiring board 53.

The manufacturing process figure which shows the manufacturing method of the multilayer flexible circuit wiring board by one Example of this invention. The manufacturing process figure following FIG. The manufacturing process figure following FIG. Manufacturing process figure following FIG. The manufacturing process figure which shows the manufacturing method of the multilayer flexible circuit wiring board by the other Example of this invention. Manufacturing process figure following FIG. Manufacturing process figure following FIG. The manufacturing process figure which shows the manufacturing method of the multilayer flexible circuit wiring board by the conventional method. The manufacturing process figure following FIG. Manufacturing process figure following FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Flexible insulating base material 2 Copper foil layer 3 Copper foil layer 4 Double-sided copper clad laminated board 5 Circuit pattern 6 Inner layer circuit 7 Polyimide film 8 Adhesive 9 Cover 10 Cable part 11 Conductive hole 12 Through hole 13 Through hole land 14 Inner layer circuit including cable portion 15 Flexible insulating base material 16 Copper foil layer 17 Single-sided copper-clad laminate 18 Adhesive 19 Die-cut single-sided copper-clad laminate 20 Conductive hole 21 Through hole 22 Circuit pattern 23 Multilayer flexible circuit Wiring board

Claims (3)

  In a multilayer flexible circuit wiring board having through-hole connection, the outer periphery of the conduction hole of the cover, which is the cable protection layer of the inner-layer board having the cable structure, is formed of the first through-hole plating film, and the inner circumference is the outer-layer plating. A multilayer flexible circuit wiring board characterized by being reinforced with a continuous second plating film.   In the method for manufacturing a multilayer flexible circuit wiring board, an inner layer substrate having a cable structure is formed, a cover serving as a cable protection layer is formed on the inner layer substrate, and a first conduction hole is formed on the inner layer substrate including the cover. The first through hole is formed on the first conductive hole by electroless plating and / or conductive treatment and electrolytic plating, and a single-sided copper-clad laminate and an adhesive previously punched are used as the inner layer substrate. The second conductor is formed to form a second through hole having a diameter smaller than that of the first through hole, which is aligned and stacked on the first through hole and does not interfere with the first through hole. A through hole is formed, and the second through hole is formed coaxially with the first through hole by performing electroless plating or / and conducting treatment and electrolytic plating on the second conductive hole. Method for manufacturing a multilayer flexible circuit wiring board, characterized by.   In the method for manufacturing a multilayer flexible circuit wiring board, an inner layer substrate having a cable structure is formed, a cover serving as a cable protection layer is formed on the inner layer substrate, and a first conduction hole is formed on the inner layer substrate including the cover. The first through hole is formed on the first through hole by electroless plating or / and conducting treatment and electrolytic plating, and the first through hole is coaxially formed in advance on the first through hole. Form the second through hole for forming the second through hole having a diameter larger than the first through hole without interference, and align the die-cut single-sided copper-clad laminate and adhesive with the inner layer substrate The second through hole is placed on the same axis as the first through hole by applying electroless plating or / and conducting treatment and electrolytic plating to the second conduction hole. Method for manufacturing a multilayer flexible circuit wiring board, which comprises forming.

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