WO2011129127A1

WO2011129127A1 - Multi-layer flexible printed circuit board and method of manufacturing thereof

Info

Publication number: WO2011129127A1
Application number: PCT/JP2011/050818
Authority: WO
Inventors: 文彦松田
Original assignee: 日本メクトロン株式会社
Priority date: 2010-04-15
Filing date: 2011-01-19
Publication date: 2011-10-20
Also published as: JP2011228348A; CN102396300B; JP5710152B2; TWI484884B; TW201223378A; CN102396300A

Abstract

Disclosed is a method of manufacturing, inexpensively and with stability, a multi-layer flexible printed circuit board having a small-diameter step-via structure. The multi-layer flexible printed circuit board is provided with: a flexible insulation base material (11); an insulation base material (21) laminated onto the back-face of the insulation base material (11) with an adhesive layer (24) interposed therebetween; step-via holes (25) comprising upper holes (26) that penetrate through the insulation base material (11), and lower holes (27) that penetrate through the adhesive layer (24) and the flexible insulation base material (21), and that has land sections (31) exposed at the bottom face thereof; land sections (30) formed on the surface of the insulation base material (11); land sections (17b) formed on the back-face of the insulation base material (11); and step-vias (29) comprising inter-layer conductor paths (29a) that connect the land sections (30) and the land sections (17b), and inter-layer conductor paths (29b) that connect the land sections (31) and the land sections (17b). The difference in the diameters of the upper holes (26) and the lower holes (27) in the roll direction of the flexible base material, which is the starting material, is made to be greater than the difference in the diameters of the upper holes (26) and the lower holes (27) in a direction perpendicular to the roll direction.

Description

Multilayer flexible printed wiring board and manufacturing method thereof

The present invention relates to a multilayer flexible printed wiring board and a manufacturing method thereof, and more particularly to a multilayer flexible printed wiring board having a step via structure and a manufacturing method thereof.

In recent years, miniaturization and higher functionality of electronic devices are progressing more and more. Along with this, there is an increasing demand for higher density of printed wiring boards and components mounted on the printed wiring boards. In particular, for package parts used in portable devices, the number of pins is increasing and the pitch between pins is becoming narrower. On the other hand, the printed wiring board is required to be thin in consideration of wiring rules for mounting package parts and incorporation into portable devices. In order to reduce the thickness of the printed wiring board, it is conceivable to employ a flexible printed wiring board starting from a flexible insulating base material such as a polyimide film.

Also, conventionally, a build-up type multilayer flexible printed wiring board that is advantageous for mounting electronic components and the like at high density is known (see FIG. 15 of Patent Document 1). This build-up type multilayer flexible printed wiring board has a double-sided flexible printed wiring board or a multilayer flexible printed wiring board as a core substrate (inner layer), and about one or two build-up layers (outer layer) on both sides or one side of the core substrate. Thus, a high density of the flexible printed wiring board is achieved.

As described above, the build-up type multilayer flexible printed wiring board is advantageous in terms of thinning and high density of the printed wiring board. However, because of the structure, it is necessary to form a thick plating layer on the inner layer, so it is difficult to miniaturize the wiring on the outer layer. For this reason, it has been difficult to mount a multi-pin, narrow-pitch package component such as a chip size package (CSP).

In order to solve this problem, a build-up type multilayer flexible printed wiring board having a so-called step via structure is known (see FIGS. 5 and 9 of Patent Document 1). The outline of the manufacturing method of this printed wiring board is as follows. First, fine wiring is formed on a core substrate that is an inner layer, and then a buildup layer that is an outer layer is laminated on the core substrate. Then, a stepped step via hole (double hole) composed of a large-diameter upper hole and a small-diameter pilot hole is formed by laser processing (see FIG. 9 (14) of Patent Document 1). Thereafter, a step via functioning as an interlayer conductive path is formed by plating the inner wall (bottom surface and side surface) of the step via hole (see FIGS. 5 and 9 (15) of Patent Document 1). By adopting the step via structure, it is possible to miniaturize the wiring of the outer layer, so that it is possible to obtain a multilayer flexible printed wiring board that is advantageous for mounting multi-pin and narrow pitch package components.

Next, the structure and problems of a conventional build-up type multilayer flexible printed wiring board having a step via structure will be described with reference to FIG. 7 (1) is a top view of the multilayer flexible printed wiring board, FIG. 7 (2) is a cross-sectional view taken along the line AA ′ of FIG. 7 (1), and FIG. 7 (3) is FIG. FIG. 2 is a cross-sectional view taken along line BB ′ of 1).

7 (1), (2) and (3),

step vias

51A, 51B, 51C and 51D have a circular upper interlayer conductive path 51a and a circular lower interlayer conductive path 51b. The upper interlayer conductive path 51a electrically connects the land portion 52 on the surface of the multilayer flexible printed wiring board and the land portion 53 of the inner layer. On the other hand, the lower interlayer conductive path 51b electrically connects the land portion 54 on the back surface of the multilayer flexible printed wiring board and the land portion 53 of the inner layer.

In the conventional step via, upper interlayer conductive paths 51a and lower interlayer conductive paths 51b are formed concentrically like

step vias

51A, 51B, 51D shown in FIG.

The build-up type multilayer flexible printed wiring board having the above step via structure can be mounted with CSP of about 300 pins at a pitch of 500 μm, for example. However, as typified by sensor modules, for example, the number of pins on mounting parts and the narrowing of pitch are increasing, and the number of pins on mounting parts has increased from several hundred to several thousand. Yes. Since the pitch of the land portions for joining the components is the same as the pitch of the mounting pads of the mounting components, it is necessary to reduce the pitch of the land portions in accordance with the narrowing of the pitch of the mounting components. Furthermore, the multilayer flexible printed wiring board is required to electrically connect a land portion joined to a large number of pins and a predetermined connector portion. Therefore, as can be seen from FIG. 7B, a large number of

fine wirings

55, 55,... Are provided between the

step vias

51A and 51B (between the

step vias

51C and 51D).

For example, when the step via pitch is 400 μm and the distance between the land portions in the layer (inner layer) where the fine wiring is formed is 200 μm, as shown in FIG. When the wiring 55 is arranged, the wiring pitch of the wiring 55 is about 30 μm. As described above, the region in which the

wirings

55, 55,... Are provided is a region requiring the smallest pitch among the multilayer flexible printed wiring boards. In order to provide fine wiring between step vias, it is necessary to reduce not only the land portion but also the diameter of the step via hole to about 50 to 100 μm.

Conventionally, when trying to reduce the diameter of a step via hole, it is difficult to align the upper hole and the lower hole of the step via hole due to the use of a roll-shaped flexible base material. There was a problem in that the plating around the pilot hole deteriorated. Next, these problems will be described in detail.

First, the problem of misalignment between the upper and lower holes of the step via hole will be explained. When manufacturing a multilayer flexible printed wiring board, a flexible copper-clad laminate in which a copper foil is provided on one or both sides of a flexible insulating base material is used as a starting material. This copper-clad laminate is long and wound up in a roll. While this long copper-clad laminate is unwound by an unwinding roll, a process such as exposure is performed for each predetermined area called a sheet area. Then, when the process is finished for a certain sheet area, the copper-clad laminate is conveyed in the roll direction (conveyance direction), and the next sheet area is processed. This process is repeated to finish the process for all the sheet regions on the surface of the copper clad laminate, and then the copper clad laminate is turned over, and the back surface is similarly treated in sheet region units. Thus, in the manufacture of a multilayer flexible printed wiring board, a flexible copper-clad laminate is used while being unwound and wound. For this reason, expansion and contraction of the copper-clad laminate occurs in the roll direction, and alignment during exposure is difficult.

More specific description will be given with reference to FIG. As shown in FIGS. 8A and 8B, the long double-sided copper-clad laminate 61 is wound around one end by an unwinding roll 62 and wound at the other end by a winding roll 63. Processing such as exposure is performed with the sheet region 64 of the double-sided copper clad laminate 61 as a unit. When the process is completed for a certain sheet area 64, the unwinding roll 62 and the take-up roll 63 rotate to convey the sheet area 64 in the roll direction, and process the next adjacent sheet area. As can be seen from this, the double-sided copper-clad laminate 61 unwound from the unwinding roll 62 tends to expand and contract in the roll direction. As a process in which this expansion and contraction becomes a problem, consider a case where a conformal mask is formed on the front and back surfaces of the double-sided copper-clad laminate 61 by a photofabrication technique. This conformal mask is used to form a step via hole using a conformal laser processing method. As shown in FIG. 8B, after a resist layer (not shown) is formed on the surface of the sheet region 64, the alignment mark M1 on the sheet region 64 and the alignment mark M2 formed on the glass mask for exposure are used. Use to align. After this alignment, exposure and development are performed to form a resist layer processed into a predetermined pattern. However, even if the alignment marks M1 and M2 are precisely aligned using an apparatus capable of high-accuracy alignment, misalignment caused by expansion and contraction of the double-sided copper-clad laminate 61 in the roll direction will not occur. It is difficult to prevent it sufficiently. When forming a resist layer on both sides of the double-sided copper-clad laminate 61 in order to form a conformal mask for forming a step via hole, it is particularly difficult to avoid misalignment. This is because, in order to form a resist layer processed into a predetermined pattern on both sides of the double-sided copper-clad laminate 61, first, a resist layer is first formed sequentially on a plurality of sheet regions on the surface of the double-sided copper-clad laminate 61. Thereafter, the double-sided copper-clad laminate 61 wound up on the winding roll is turned over, and the back surface is exposed sequentially for each sheet region using another glass mask to form a resist layer in the sheet region on the back surface. . At this time, it is practically very difficult to completely match the expansion / contraction degree of the double-sided copper-clad laminate 61 when exposing the front surface with the expansion / contraction degree of the double-sided copper-clad laminate 61 when exposing the back surface.

Further, in the above exposure process, as can be seen from FIG. 8A, the length in the roll direction of the exposure area 66 on the double-sided copper-clad laminate 61 exposed by one exposure is the double-sided copper-clad laminate. For example, the width of the plate 61 is preferably about 1.5 to 2 times. Thereby, the number of products (multilayer flexible printed wiring boards) 65 that can be taken from one sheet region 64 can be increased, and productivity can be improved. However, as the exposure area 66 is increased in the roll direction of the double-sided copper-clad laminate 61, it becomes difficult to ensure the parallelism of the exposure light, and as the exposure area 66 goes to the left and right ends in FIG. The positional deviation accompanying expansion and contraction of the double-sided copper-clad laminate 61 increases. That is, if the exposure area 66 is expanded with respect to the roll direction of the double-sided copper-clad laminate 61 in order to improve productivity, the influence of expansion and contraction of the double-sided copper-clad laminate 61 on the alignment accuracy increases.

For the above reasons, the lower interlayer conductive path 51b of the step via 51C shown in FIGS. 7 (1) and 7 (3) has a positional shift greater than the allowable amount with respect to the roll direction (vertical direction in the figure). When such a large misalignment occurs, the conformal mask does not function properly when forming the step via hole, and a minute dent, burring or the like occurs on the inner wall of the step via hole. For this reason, when forming the plating layer on the inner wall of the step via hole, the plating layer is not formed in the recessed portion of the inner wall because the renewability of the plating solution or the like is poor. As a result, the void as shown in FIG. 56 is generated. When such a void 56 is generated, the plating layer is easily broken, and the reliability of the step via as the interlayer conductive path may be lowered.

In FIG. 7 (1), the positional deviation occurs only in the step via 51C. However, in actuality, when the step via hole is formed using a conformal laser processing method or the like, the flexible base material is in the roll direction. By expanding or contracting, the possibility of positional deviation also occurring in step vias near the step via 51C (for example,

step vias

51A, 51B, 51D) is high.

In order to support high-density mounting, the diameter of the step via hole needs to be 100 μm or less as described above. However, if the diameter of the step via hole is reduced to this extent, a position deviation of only about 20 to 30 μm is generated and the state becomes like the step via 51C in FIG.

Next, a description will be given of the deterioration of the surrounding shape with plating when the diameter of the step via hole is reduced. When plating the inner wall of the step via hole to form a step via which is an interlayer conductive path, if the diameter of the upper hole of the step via hole is small (for example, φ100 μm or less), The renewability of the plating solution is poor. As a result, as shown in the lower interlayer conductive path 51b of the step via 51A in FIGS. 7 (2) and 7 (3), a plating contact failure may occur. More specifically, when the design lower limit value of the thickness of the plating layer formed on the inner wall of the step via hole is 10 μm, there may be a portion where the thickness is 1/2 or less of the lower limit value. In such a case, the plating layer may be broken by a thermal shock such as a temperature cycle, and the reliability of the step via as an interlayer conductive path cannot be ensured.

Conventionally, blind via holes and through holes having a non-circular shape such as an oval shape are known for interlayer connection portions that electrically connect two layers (see

Patent Documents

2, 3, and 4). However, none of these documents is directed to the step via structure, and the problem of a decrease in alignment accuracy due to expansion and contraction of the flexible base material when forming a small diameter step via hole and this No solution is disclosed.

JP 2007-128970 A JP 2000-151111 A JP 2002-064274 A Japanese Patent Application Laid-Open No. 11-274677

An object of the present invention is to provide a method for stably and inexpensively manufacturing a multilayer flexible printed wiring board having a small diameter step via structure.

According to one aspect of the present invention, there is provided a multilayer flexible printed wiring board starting from a roll-shaped flexible base material, wherein the first flexible insulating base is a part of the flexible base material. And a second flexible member having first and second surfaces opposite to each other, wherein the first surface is laminated on the back surface of the first flexible insulating base material via an adhesive layer. A conductive insulating base material, an upper hole penetrating the first flexible insulating base material in a thickness direction, a diameter smaller than the upper hole, communicating with the upper hole, and the adhesive layer and the first 2 is a pilot hole that penetrates the flexible insulating base material 2 in the thickness direction and exposes the first outer layer land portion provided on the second surface of the second flexible insulating base material on the bottom surface. And a step via hole having a surface of the first flexible insulating base material around the upper hole. A second outer layer land portion formed on the back surface of the first flexible insulating base material, an inner layer land portion formed around the pilot hole, and an inner wall of the upper hole. An upper interlayer conductive path that electrically connects the outer land portion and the inner land portion, and a lower interlayer that is formed on the inner wall of the pilot hole and electrically connects the first outer land portion and the inner land portion. A first via which is a difference between the diameter of the upper hole and the diameter of the lower hole with respect to the roll direction of the roll-shaped flexible base material. A multilayer flexible printed wiring board is provided that is larger than a second difference that is a difference between the diameter of the upper hole and the diameter of the lower hole in a direction perpendicular to the vertical direction.

According to another aspect of the present invention, a roll having a first flexible insulating base material and a first copper foil and a second copper foil on the front surface and the back surface, respectively, and wound on an unwinding roll A double-sided copper-clad laminate in the form of a roll, one end of the double-sided copper-clad laminate in the form of a roll is pulled out from the take-up roll in the roll direction, Forming a first conductive pattern layer having an opening for an upper hole and a second conductive pattern layer having an opening for a lower hole; a second flexible insulating base material; A single-sided copper-clad laminate having a copper foil, and laminating and adhering the single-sided copper-clad laminate to the back surface of the double-sided copper-clad laminate via an adhesive layer, A laser beam is irradiated from the side, and the upper hole opening and the lower hole opening are formed as a conformal mask. By performing laser processing, an upper hole penetrating the first flexible insulating base material in the thickness direction, and communicating with the upper hole, the adhesive layer and the second flexible insulating base Forming a step via hole that penetrates the material in the thickness direction and has a pilot hole in which the third copper foil is exposed on the bottom surface, and subjecting the inner wall of the step via hole to an electrolytic copper plating treatment, Forming a step via for electrically connecting the conductive pattern layer, the second conductive pattern layer, and the third copper foil, the method for manufacturing a multilayer flexible printed wiring board, wherein The first difference that is the difference between the diameter of the hole opening and the diameter of the lower hole opening is that the diameter of the upper hole opening and the diameter of the lower hole opening with respect to the direction perpendicular to the roll direction. This is greater than the second difference, which is the difference in diameter. Method for manufacturing a multilayer flexible printed wiring board, wherein is provided.

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

According to the present invention, the difference between the diameters of the upper hole (upper hole opening) and the lower hole (lower hole opening) in the roll direction of the flexible insulating base material is the upper hole in the direction perpendicular to the roll direction. It is larger than the difference between the diameter of the (upper hole opening) and the diameter of the lower hole (lower hole opening). For this reason, the positional deviation allowable amount of the pilot hole (the pilot hole opening) with respect to the roll direction can be made larger than the positional deviation allowable amount in the direction perpendicular to the roll direction. As a result, a normal step via hole can be obtained even when the flexible insulating base material expands and contracts in the roll direction.

Furthermore, according to the present invention, since the opening area of the upper hole of the step via hole is increased, when forming a plating layer on the inner wall of the step via hole, the renewability of the plating solution and the like is improved. Can be a good step via.

Therefore, according to the present invention, a multilayer flexible printed wiring board having a small-diameter step via with high reliability as an interlayer conductive path can be obtained inexpensively and stably.

It is a figure for demonstrating the manufacturing method of the multilayer flexible printed wiring board which has the step-via structure concerning embodiment of this invention. (1), (2) and (3) are process sectional views, and (4) is a top view corresponding to (3). It is process sectional drawing for demonstrating the manufacturing method of the multilayer flexible printed wiring board which has the step via structure which concerns on embodiment of this invention following FIG. It is a figure for demonstrating the structure of the multilayer flexible printed wiring board which has a step-via structure concerning embodiment of this invention. (1) is a top view of the multilayer flexible printed wiring board, (2) is a cross-sectional view taken along the line AA ′ in (1), and (3) is a line BB ′ in (1). It is sectional drawing which follows a line. FIG. 4 is a cross-sectional view taken along line C-C ′ of FIG. It is a top view which shows the modification of the step via hole which concerns on embodiment of this invention. It is a figure which shows the example of mounting of the components to the multilayer flexible printed wiring board which concerns on this embodiment. (1) is a top view of a multilayer flexible printed wiring board on which components are mounted, and (2) is a cross-sectional view taken along line A-A ′ of (1). It is a figure for demonstrating the structure of the buildup type multilayer flexible printed wiring board which has the conventional step-via structure. (1) is a top view of the multilayer flexible printed wiring board, (2) is a cross-sectional view taken along the line AA ′ in (1), and (3) is a line BB ′ in (1). It is sectional drawing which follows a line. It is a figure for demonstrating the process with respect to a roll-shaped double-sided copper clad laminated board. (1) is a top view of a double-sided copper-clad laminate, and (2) is a side view of the double-sided copper-clad laminate and a glass mask for exposure.

Hereinafter, a multilayer flexible printed wiring board according to an embodiment of the present invention will be described with reference to the drawings.

In addition, in each figure, the same code | symbol is attached | subjected to the component which has an equivalent function, and the detailed description of the component of the same code | symbol is not repeated. Further, the drawings are schematic and show mainly the characteristic portions according to the embodiment, and the relationship between the thickness and the planar dimension, the ratio of the thickness of each layer, and the like are different from the actual ones.

First, with reference to FIG. 1 thru | or FIG. 3, the manufacturing method of the multilayer flexible printed wiring board which has the step-via structure which concerns on this embodiment is demonstrated.

(1) First, a double-sided copper clad laminate 14 having a copper foil 12 and a copper foil 13 each having a thickness of 1 μm is prepared on both sides of a flexible insulating base material 11 (for example, a polyimide film having a thickness of 25 μm). This double-sided copper-clad laminate 14 is in the form of a roll wound around an unwinding roll. 1 (1) is a cross-sectional view showing a part of a double-sided copper-clad laminate 14 in which one end of a roll-shaped double-sided copper-clad laminate 14 is drawn out from a roll in the roll direction. is there. In FIG. 1 (1), the roll direction is the direction perpendicular to the paper surface, and the horizontal direction is the width direction of the roll material.

(2) Next, a resist layer (not shown) is formed in the sheet region on the copper foil 12 of the double-sided copper clad laminate 14. The thickness of the resist layer is preferably about 1.2 to 2 times the thickness of the wiring layer to be formed. Because, when the thickness of the resist layer is thinner than 1.2 times the thickness of the wiring layer, when plating is performed by the semi-additive method, the plating film grows beyond the thickness of the resist layer due to variations in the plating thickness, As a result, wiring failure may occur. On the other hand, when the thickness of the resist layer is thicker than twice the thickness of the wiring layer, it becomes difficult to form fine wiring, which may result in poor wiring. Therefore, here, the thickness of the designed wiring is 10 μm, and the thickness of the resist layer is 15 μm.

(3) Next, the resist layer on the copper foil 12 formed in the previous step is exposed and developed to pattern the resist layer into a predetermined pattern. Thereby, as shown in FIG. 1 (1), the plating resist layer 15A is formed on the copper foil 12 of the double-sided copper clad laminate 14. As will be described later, the plating resist layer 15A is used for forming a desired conductive pattern layer by a semi-additive method.

Thereafter, while carrying the double-sided copper-clad laminate 14 in the roll direction, the above process is performed for each sheet region to form the plating resist layer 15A. After forming the plating resist layer 15A for all the sheet regions on the surface of the double-sided copper-clad laminate 14, the double-sided copper-clad laminate 14 wound around the take-up roll is turned over, and then one end is unwound, Process the back side as follows.

(4) Next, a resist layer (not shown) is formed in the sheet region on the copper foil 13 of the double-sided copper clad laminate 14. The thickness of this resist layer was 15 μm for the same reason as in the case of the resist layer on the copper foil 12.

(5) Next, the resist layer on the copper foil 13 formed in the previous step is exposed and developed to pattern the resist layer into a predetermined pattern. Thereby, as shown in FIG. 1 (2), a plating resist layer 15 B is formed on the copper foil 13 of the double-sided copper-clad laminate 14. This plating resist layer 15B is used for forming a desired conductive pattern layer by a semi-additive method, similarly to the above-described plating resist layer 15A.

(6) Next, as can be seen from FIG. 1 (3), electrolytic copper plating is performed on both surfaces of the double-sided copper clad laminate 14 on which the plating resist

layers

15A and 15B are formed. Thereby, the electrolytic copper plating layers 16 and 17 are formed on the copper foil 12 and the copper foil 13 exposed in the openings of the plating resist

layers

15A and 15B, respectively. Here, the thickness of the electrolytic copper plating layers 16 and 17 was 10 μm.

(7) Next, as shown in FIG. 1 (3), after peeling the plating resist

layers

15A and 15B, the copper foil 12 and the copper foil 13 not covered with the electrolytic copper plating layers 16 and 17 are formed by flash etching. Remove. In this flash etching, an etchant having selectivity for the metal contained in the seed layer (copper foil 12 and copper foil 13) is used. For example, when the seed layer contains nickel, a mixed solution of nitric acid and hydrochloric acid can be used as the etchant.

Through the steps so far, as shown in FIGS. 1 (3) and (4), the conductive pattern layer composed of the copper foil 12 (13) and the electrolytic copper plating layer 16 (17) is formed into a flexible insulating base material. 11 is obtained. FIG. 1 (4) shows a top view of the double-sided circuit substrate 18. As can be seen from FIGS. 1 (3) and (4), the conductive pattern layer has an opening at a predetermined position. A conformal mask 19 (upper hole opening) that is an opening of the conductive pattern layer formed on the surface of the double-sided circuit substrate 18 functions to form an upper hole of a step via hole. On the other hand, the conformal mask 20 (opening for pilot holes) that is an opening of the conductive pattern layer formed on the back surface of the double-sided circuit substrate 18 functions to form pilot holes for step via holes. In this step, if the position of the conformal mask 20 is shifted with respect to the conformal mask 19, the prepared hole of the step via hole is displaced from the upper hole. As a result, as described above, the reliability of the step via is lowered due to the generation of voids and the deterioration of the surrounding shape with plating. However, in this embodiment, as shown in FIG. 1 (4), the conformal mask 19 is formed in an oval shape, and the major axis of this oval is parallel to the roll direction. For this reason, even if the conformal mask 18 is displaced in the roll direction with respect to the conformal mask 19 by the expansion and contraction of the flexible insulating base material 11 (double-sided copper clad laminate 14) in the roll direction, Since the positional deviation tolerance in the roll direction is large, a normal step via hole can be formed.

In this embodiment, the length of the major axis of the ellipse of the conformal mask 19 is twice the length of the minor axis. That is, the length of the major axis was 160 μm, and the length of the minor axis was 80 μm. On the other hand, as can be seen from FIG. 1 (4), the conformal mask 20 was formed in a perfect circular shape (diameter 60 μm). In this case, the positional deviation allowable amount with respect to the direction intersecting with the roll direction at 90 ° (that is, the width direction of the double-sided copper-clad laminate 14) is within ± 10 μm. On the other hand, the positional deviation tolerance in the roll direction is within ± 50 μm, and the positional deviation tolerance in the direction in which expansion and contraction occurs can be greatly increased.

(8) Next, as shown in FIG. 2 (1), on the back surface of the double-sided circuit substrate 18 (the lower side in FIG. 2 (1)), an adhesive layer 24 (for example, 15 μm thick) is provided on one side. The copper-clad laminate 23 is laminated and bonded. This single-sided copper-clad laminate 23 has, for example, a copper foil 22 having a thickness of 12 μm on one side of a flexible insulating base material 21 (for example, a polyimide film having a thickness of 25 μm). The single-sided copper-clad laminate 23 is laminated on the back surface of the double-sided circuit substrate 18 so that the flexible insulating base material 21 is in contact with the adhesive layer 24. Note that the adhesive layer 24 is preferably formed using a low-flow type prepreg or an adhesive with a low flow-out such as a bonding sheet.
(9) Next, as shown in FIG. 2 (2), the conformal mask 19 is irradiated with laser light from the side of the conformal mask 19 (the upper side in FIG. 2 (2)), and the

conformal lasers

19 and 20 are used. Processing. Thereby, a step via hole (conduction hole) 25 having an upper hole 26 and a lower hole 27 is formed. The upper hole 26 penetrates the flexible insulating base material 11, and the electrolytic copper plating layer 17 is exposed on the bottom surface. The lower hole 27 communicates with the upper hole 26 and penetrates the adhesive layer 24 and the flexible insulating base material 21. The lower hole 27 has a smaller diameter than the upper hole 26, and the copper foil 22 is exposed on the bottom surface of the lower hole 27. As described above, when performing laser processing in this step, the conformal mask 19 functions as a mask for forming the upper hole 26, and the conformal mask 20 functions as a mask for forming the lower hole 27. In the laser processing for forming the step via hole 25, it is possible to use laser light such as UV-YAG laser, carbonic acid laser, and excimer laser.

Here, the details of the laser processing in this step will be described. As the processing laser, a carbon dioxide gas laser (manufactured by Mitsubishi Electric Corporation, ML605GTXIII-5100U2) having a high processing speed and excellent productivity was used. After adjusting the laser beam diameter to 200 μm with an aperture or the like, 5 shots of a laser pulse with a pulse width of 10 μSec and a pulse energy of 5 mJ were irradiated to form a step via hole 25. The diameter of the laser beam is adjusted to be larger than the length of the major axis of the elliptical conformal mask 19, and a laser pulse is irradiated toward the center of the ellipse of the conformal mask 19. 26 and a perfect circular pilot hole 27 can be suitably formed. If the laser beam diameter cannot be adjusted larger than the length of the major axis of the conformal mask 19, the irradiation target position is divided into, for example, three or four points on the major axis, and the laser pulse is shifted in the major axis direction. You may make it irradiate, carrying out. By oscillating the galvanometer mirror, the irradiation target position of the laser beam can be moved in a wider range than the length of the long axis. Therefore, even if the irradiation target position is divided, laser processing can be performed without affecting the productivity. Under the above laser conditions, it is possible to form the step via hole 25 having the oval upper hole 26 in the same manner as the conventional concentric step via hole.

(10) Next, plasma processing and wet etching are performed as a desmear process for removing the resin residue in the step via hole 25. By this etching, the copper foil 13 in the step via hole 25 is removed as shown in FIG.

(11) Next, a conductive treatment and a subsequent electrolytic copper plating treatment are performed on the electrolytic copper plating layer 16 and the inner wall of the step via hole 25. Thereby, as shown in FIG. 2 (3), the electrolytic copper plating layer 28 is formed on the inner wall (side surface and bottom surface) of the step via hole 25 and the electrolytic copper plating layer 16. In order to ensure interlayer conduction, the thickness of the electrolytic copper plating layer 28 is, for example, 15 to 20 μm. Thereby, the step via 29 having the upper interlayer conductive path 29a and the lower interlayer conductive path 29b is formed. The upper interlayer conductive path 29a of the step via 29 is to electrically connect the land portion 30 on the front surface side and the land portion 17b on the inner layer, and the lower interlayer conductive path 29b is connected to the land portion 17b on the inner layer and the land portion on the back surface side. 31 is electrically connected.

The plating process in this step is so-called single-sided plating in which the opening surface of the step via hole 25 is only on one side (upper side in the drawing), and thus the plating process is performed only on the opening surface side of the step via hole 25. For this reason, the electrolytic copper plating layer 28 is not formed on the copper foil 22 on the back surface. The single-sided plating may be realized by performing a plating process after forming a plating mask so as to cover the copper foil 22 on the back side, or after a shielding plate is provided on a plating apparatus or a plating jig or the like. It may be realized by performing. Thus, by using single-sided plating instead of double-sided plating, an excess copper plating film is not formed on the copper foil 22, and the thickness of the copper foil 22 can be prevented from becoming thick. By keeping the copper foil 22 thin, it is possible to process the copper foil 22 with high accuracy and form a fine pattern such as a land portion.

(12) Next, as shown in FIG. 2 (4), the land portion 30 is formed by processing the electrolytic copper plating layer 28 into a predetermined pattern using a photofabrication method. Similarly, the land portion 31 is formed on the back surface by processing the copper foil 22 into a predetermined pattern using a photofabrication method.

Through the above steps, the multilayer flexible printed wiring board 32 having the step via structure according to the present embodiment is obtained. Thereafter, if necessary, a protective photo solder resist layer is formed on a portion where soldering is unnecessary, and the surface of the land portion or the like is subjected to surface treatment such as solder plating, nickel plating, or gold plating. Thereafter, the roll material on which the plurality of multilayer flexible printed

wiring boards

32, 32,... Are manufactured is cut for each sheet region. Finally, the outer shape is processed by punching with a mold. The roll material can be cut in any step as long as it is after the formation of the plating resist

layers

15A and 15B and before the outer shape processing.

Next, the structure of the multilayer flexible printed wiring board according to this embodiment will be described in detail with reference to FIG.

FIG. 3 is a top view and a sectional view of the multilayer flexible printed wiring board 32 having the long hole step via structure according to the present embodiment. FIG. 3A is a top view of the multilayer flexible printed wiring board 32. 3 (2) is a cross-sectional view taken along the line A-A 'of FIG. 3 (1), and FIG. 3 (3) is a cross-sectional view taken along the line B-B' of FIG. 3 (1).

As can be seen from FIGS. 3 (1), (2) and (3), the step via 29 formed in the multilayer flexible printed wiring board 32 has an oval upper interlayer conductive path 29a and a regular circular lower interlayer conductive path 29b. Have

The land portion 30 is provided on the front surface of the multilayer flexible printed wiring board 32, and the land portion 31 is provided on the back surface. The land portion 31 has good flatness since there is no step via opening surface, and is therefore suitable as a land for mounting components.

Inner layer wiring 17a and land portion 17b are formed by processing electrolytic copper plating layer 17 in the above-described manufacturing process. The wiring 17a electrically connects the land portion 17b of the multilayer flexible printed wiring board 32 and the connector portion with the outside. The land portion 17 b is electrically connected to the land portion 30 and the land portion 31 by the step via 29.

The wiring 17a and the land portion 17b will be described in detail with reference to FIG. FIG. 4 is a cross-sectional view taken along the line C-C ′ of FIG. As can be seen from FIG. 4, the wiring 17 a is disposed between the

step vias

29 and 29 so as to run in parallel with the major axis direction of the upper interlayer conductive path 29 a (upper hole 26). By arranging the wiring 17a in this way, the opening area of the step via 29 (upper hole 26) can be increased without reducing the wiring density of the wiring 17a.

Next, the relationship between the size of the upper hole (conformal mask 19) and the lower hole (conformal mask 20) of the step via hole and the positional deviation allowable amount will be specifically described using numerical values.

Table 1 shows the ratio of the major axis to the minor axis of the positional deviation allowance for each of the case where the conventional upper hole and the lower hole are both circular, and the upper hole of the present embodiment is an oval and the lower hole is a perfect circle. It is a summary. Here, the “major axis / minor axis ratio of allowable positional deviation” means the ratio (x / y) of the allowable positional deviation (x) in the major axis direction and the allowable positional deviation (y) in the minor axis direction. To do.

Table 1 shows three examples in which the length of the major axis of the upper hole is different. That is, the length of the major axis of the upper hole is 120 μm in Example 1, 160 μm in Example 2, and 240 μm in Example 3. In all cases, the length of the short axis is 80 μm. Thus, the length of the major axis of the upper hole (conformal mask 19) is preferably about 1.5 to 3 times the length of the minor axis. If it is smaller than 1.5 times, there is a possibility that the positional deviation allowable amount is not sufficient. On the other hand, if it is larger than three times, the positional displacement tolerance increases, but the time required to form the above-described step via hole 25 by laser processing increases, and as a result, the productivity may decrease.

As shown in Table 1, the ratio of the length of the major axis to the length of the minor axis is 1.5 times, 2 times and 3 times in Example 1, Example 2 and Example 3, respectively. When the ratio of the length of the major axis to the length of the minor axis is converted into the “major axis / minor axis ratio of the allowable positional deviation”, the ratio becomes three times, five times and nine times. As described above, according to the present embodiment, the positional deviation allowable amount in the major axis direction is significantly increased to 3 to 9 times the positional deviation allowable amount in the short axis direction (that is, the conventional positional deviation allowable amount). Can be increased.

As described above, in this embodiment, the upper hole 26 of the step via hole 25 is an oval and the lower hole 27 is a regular circle. Thereby, the tolerance | permissible_quantity with respect to the position shift of the major axis direction of the conformal mask 20 for the pilot holes 27 can be increased significantly conventionally. For this reason, even when the flexible insulating base material 11 expands and contracts in the roll direction (conveying direction) during the manufacturing process of the multilayer flexible printed wiring board, the normal step via hole 25 can be formed. As a result, according to the present embodiment, a multilayer flexible printed wiring board having the highly reliable step via 29 as an interlayer conductive path can be obtained.

Furthermore, since the upper hole 26 of the step via hole 25 is larger than in the conventional case, the renewability of the plating solution and the like when the plating process is performed on the inner wall of the step via hole is improved. For this reason, the stable step via around plating can be formed. As a result, according to the present embodiment, the reliability of the step via as the interlayer conductive path can be further improved.

Next, a modified example of the step via hole according to the present embodiment will be described with reference to FIG. FIGS. 5 (1) to 5 (4) all show a top view of a step via hole that can increase the positional displacement tolerance with respect to the roll direction (vertical direction in the figure).

In the step via hole 101 shown in FIG. 5 (1), not only the upper hole 101a but also the lower hole 101b are formed in an oval shape. Even in the case of such a shape, it is possible to increase the positional displacement tolerance with respect to the major axis direction as compared with the conventional concentric step via hole. In the case of this modification, the opening area of the pilot hole 101b is also larger than that of a conventional regular circle, so that the renewability of the plating solution and the like can be further improved.

The step via hole 102 shown in FIG. 5 (2) has an oval upper hole 102a and an elliptical lower hole 102b. Since the pilot hole 102b is elliptical, it is possible to improve the renewability of the plating solution and the like, and it is possible to increase the positional deviation margin in the rotation direction (the direction of the arrow in FIG. 5 (2)). That is, when the resist layer is exposed to form the plating resist layer 15B described above, the corner of the pilot hole 102b is rounder than the oval in the rotation direction as compared with the step via hole 101 in FIG. The allowable amount of positional deviation can be increased.

The step via hole 103 shown in FIG. 5 (3) has a regular circular upper hole 103a and an oval lower hole 103b. As shown in FIG. 5 (3), although the oval pilot hole 103b is provided in a direction perpendicular to the roll direction, the upper hole 103a is a perfect circle, so that the rotation direction (FIG. 5 (3) It is possible to increase the positional displacement tolerance with respect to (in the direction of arrow).

The step via hole 104 shown in FIG. 5 (4) has a substantially square upper hole 104a and a substantially rectangular lower hole 104b. The substantially rectangular pilot hole 104b is provided in a direction perpendicular to the roll direction, but the upper hole 104a is substantially square, so that the rotation direction (the direction of the arrow in FIG. 5 (4)) is relative to the rotation direction. It is possible to increase the positional displacement tolerance.

Not limited to the above-described modifications, the upper hole and the lower hole in each example can be combined. For example, a step via hole in which both the upper hole and the lower hole are elliptical may be used. The direction of the major axis of the pilot hole is parallel to the direction of the major axis of the upper hole. Further, it may be a step via hole constituted by a regular circular upper hole and a substantially rectangular lower hole. The direction of the long side of the pilot hole is a direction perpendicular to the roll direction.

In addition, the upper hole may be an ellipse having a major axis parallel to the roll direction, and the pilot hole may be a perfect circle or an ellipse having a major axis in the same direction as the upper hole.

Next, an example of mounting components on the multilayer flexible printed wiring board according to this embodiment will be described with reference to FIG. FIG. 6A is a top view showing a state in which the component 44 is mounted on the multilayer flexible printed wiring board according to the present embodiment. FIG. 6B is a cross-sectional view taken along the line A-A ′ of FIG. As can be seen from FIG. 6 (1), the component 44 is mounted in the component mounting area 41.

As can be seen from FIG. 6 (2), the component 44 is mounted on the land portion 31 on the back surface of the multilayer flexible printed wiring board 32 via bumps 45. As a result, the component 44 can be mounted with a higher flatness than when mounted on the land portion 30. As a result, there is no possibility that voids or the like are generated in the joint portion, and a highly reliable joint can be obtained.

As can be seen from FIG. 6A, the wiring 17a provided in the inner layer of the multilayer flexible printed wiring board 32 passes from the component mounting area 41A (41B) to the connector section 43A (43B) through the wiring area 42A (42B). The land portion 31 of the component mounting area 41 is electrically connected to the

connector portions

43A and 43B. More specifically, the wiring 17a that electrically connects the land portion 31 of the component mounting region 41A, which is the upper half region of the component mounting region 41, and the connector portion 43A extends from the land portion 31 arranged in the component mounting region 41A. It is routed to the connector portion 43A through the wiring area 42A. Similarly, the wiring 17a that electrically connects the land portion 31 of the component mounting region 41B, which is the lower half region of the component mounting region 41, and the connector portion 43B is connected to the wiring region from the land portion 31 arranged in the component mounting region 41B. 42B is routed to the connector portion 43B.

The mounted component 44 is, for example, a sensor module having a very large number of pins, and the direction in which the fine wiring 17a is drawn is limited to approximately one direction. In such a case, by providing the wiring 17a so as to run in the major axis direction of the step via 29, it is possible to increase the area of the opening of the step via 29 without impairing the wiring density of the wiring 17a. is there.

As described above, in this embodiment, the upper hole of the step via hole is formed into an oval shape, and the major axis direction thereof is parallel to the roll direction of the roll material of the flexible printed wiring board. Thereby, in the exposure process for forming a conformal mask for a step via hole, a normal step via hole can be formed even when the flexible base material expands and contracts in the roll direction. As a result, according to the present embodiment, a multilayer flexible printed wiring board having a highly reliable step via as an interlayer conductive path can be obtained.

Furthermore, in this embodiment, since the upper hole is larger than the conventional step via hole, the renewability of the plating solution and the like when the plating layer is formed on the inner wall of the step via hole is improved. For this reason, it is possible to form a step via with a good surrounding shape with plating. That is, according to the present embodiment, a multilayer flexible printed wiring board having step vias with higher reliability as interlayer conductive paths can be obtained.

In addition, according to the present embodiment, the exposure area can be expanded in the roll direction and the area of one sheet region can be expanded by increasing the positional deviation allowable amount. Thereby, the number of the multilayer flexible printed wiring boards which can be taken from one sheet area | region can be increased, and productivity can be improved.

As is apparent from the effects of the present embodiment described above, according to the present invention, a multi-layer flexible printed wiring board having a small-diameter step via structure stably and inexpensively without introducing a new process or apparatus. Can be manufactured.

In addition, the shape of the upper hole and the lower hole of the step via hole according to the present invention is not limited to the above-described embodiment and modification. More generally, the difference between the diameter of the conformal mask 19 (the upper hole 26) and the diameter of the conformal mask 20 (the lower hole 27) with respect to the roll direction of the flexible base material is a direction perpendicular to the roll direction. The difference between the diameter of the conformal mask 19 (the upper hole 26) and the diameter of the conformal mask 20 (the lower hole 27) may be larger. By doing in this way, it becomes possible to increase the positional shift allowable amount with respect to the roll direction.

Based on the above description, those skilled in the art may be able to conceive additional effects and various modifications of the present invention, but the aspects of the present invention are not limited to the above-described embodiments. Various additions, modifications, and partial deletions can be made without departing from the concept and spirit of the present invention derived from the contents defined in the claims and equivalents thereof.

11, 21 Flexible insulating

base material

12, 13, 22 Copper foil 14 Double-sided copper clad

laminate

15A, 15B Plating resist

layer

16, 17, 28 Electrolytic

copper plating layer

17a, 55

Wiring

17b, 30, 31, 52, 53 , 54 Land 18 Double-sided

circuit base material

19, 20 Conformal mask 23 Single-sided copper-clad laminate 24

Adhesive layer

25, 101, 102, 103, 104 Step via

hole

26, 101a, 102a, 103a,

104a Upper hole

27, 101b , 102b, 103b,

104b Pilot holes

29, 51A, 51B, 51C,

51D Step vias

29a, 51a Upper interlayer

conductive paths

29b, 51b Lower interlayer conductive paths 32 Multilayer flexible printed

wiring boards

41, 41A, 41B

Component mounting areas

42A,

42B Wiring area

43A, 43B Connector portion 44 Component 45 Bump 56 Id 61 (roll) roll 63 winding unwinding double-sided copper-clad laminate 62 roll 64 seat area 65 product (multilayer flexible printed wiring board)
66 Exposure area

Claims

A multilayer flexible printed wiring board starting from a rolled flexible base material,
A first flexible insulating base material that is part of the flexible base material;
A second flexible insulating base having first and second surfaces facing each other, wherein the first surface is laminated on the back surface of the first flexible insulating base material via an adhesive layer Material,
An upper hole penetrating the first flexible insulating base material in a thickness direction, a diameter smaller than the upper hole, communicating with the upper hole, the adhesive layer and the second flexible insulation A step via hole penetrating through the base material in a thickness direction and having a bottom hole in which a first outer layer land portion provided on the second surface of the second flexible insulating base material is exposed on a bottom surface When,
A second outer layer land portion formed around the upper hole on the surface of the first flexible insulating base material;
An inner land land portion formed around the pilot hole on the back surface of the first flexible insulating base material;
An upper interlayer conductive path formed on the inner wall of the upper hole and electrically connecting the second outer layer land portion and the inner layer land portion, and formed on the inner wall of the lower hole, the first outer layer land portion, A step via having a lower interlayer conductive path electrically connecting the inner layer land portion,
With
The first difference that is the difference between the diameter of the upper hole and the diameter of the pilot hole with respect to the roll direction of the roll-shaped flexible base material is the diameter of the upper hole with respect to the direction perpendicular to the roll direction. A multilayer flexible printed wiring board characterized by being larger than a second difference which is a difference in diameter of the pilot hole.
The upper hole of the step via hole is an ellipse or an ellipse having a major axis in a direction parallel to the roll direction, and the lower hole is a regular circle or elongated in a direction parallel to the major axis of the upper hole. The multilayer flexible printed wiring board according to claim 1, wherein the multilayer flexible printed wiring board is an ellipse or an ellipse having an axis.
3. The multilayer flexible printed wiring board according to claim 2, wherein the first difference is in a range of 3 to 9 times the second difference.
The multilayer flexible printed wiring board according to claim 2, further comprising a component mounted on the first outer layer land portion.
3. The wiring according to claim 2, further comprising a wiring having one end electrically connected to the inner layer land portion, the other end electrically connected to a predetermined connector portion, and running in a direction parallel to the roll direction. Multilayer flexible printed wiring board.
The multilayer flexible printed wiring board according to claim 1, wherein the first difference is in a range of 3 to 9 times the second difference.
The multilayer flexible printed wiring board according to claim 6, further comprising a component mounted on the first outer layer land portion.
7. The wiring according to claim 6, further comprising a wiring having one end electrically connected to the inner layer land portion and the other end electrically connected to a predetermined connector portion, and running in a direction parallel to the roll direction. Multilayer flexible printed wiring board.
The multilayer flexible printed wiring board according to claim 1, further comprising a component mounted on the first outer layer land portion.
10. The wiring according to claim 9, further comprising a wiring that has one end electrically connected to the inner layer land portion, the other end electrically connected to a predetermined connector portion, and running in a direction parallel to the roll direction. Multilayer flexible printed wiring board.
2. The wiring according to claim 1, further comprising a wiring having one end electrically connected to the inner land portion and the other end electrically connected to a predetermined connector portion, and running in a direction parallel to the roll direction. Multilayer flexible printed wiring board.
A roll-shaped double-sided copper-clad laminate having a first flexible insulating base material and a first copper foil and a second copper foil on its front and back surfaces, respectively, wound around an unwinding roll is prepared. And
One end of the roll-shaped double-sided copper-clad laminate is drawn out from the winding roll in the roll direction,
Forming a first conductive pattern layer having an opening for an upper hole and a second conductive pattern layer having an opening for a lower hole, respectively, on the front surface and the back surface of the first flexible insulating base material;
Preparing a single-sided copper-clad laminate having a second flexible insulating base material and a third copper foil on one side;
The single-sided copper-clad laminate is laminated and bonded to the back surface of the double-sided copper-clad laminate via an adhesive layer,
The first flexible insulating base is formed by irradiating a laser beam from the upper hole opening side and performing laser processing using the upper hole opening and the lower hole opening as a conformal mask. An upper hole penetrating the material in the thickness direction, communicating with the upper hole, penetrating the adhesive layer and the second flexible insulating base material in the thickness direction, and the third copper foil on the bottom surface Forming a step via hole having an exposed pilot hole, and
A multilayer that forms a step via that electrically connects the first conductive pattern layer, the second conductive pattern layer, and the third copper foil by performing electrolytic copper plating on the inner wall of the step via hole A method for manufacturing a flexible printed wiring board, comprising:
The first difference that is the difference between the diameter of the upper hole opening and the diameter of the lower hole opening with respect to the roll direction is the diameter of the upper hole opening with respect to the direction perpendicular to the roll direction. A method for producing a multilayer flexible printed wiring board, wherein the method is larger than a second difference that is a difference in diameter of the opening for the pilot hole.
The opening for the upper hole of the first conductive pattern layer is an oval or an ellipse having a major axis in a direction parallel to the roll direction, and the opening for the pilot hole of the second conductive pattern layer The method for producing a multilayer flexible printed wiring board according to claim 12, which is a regular circle or an oval or an ellipse having a major axis in a direction parallel to the roll direction.
14. The method for manufacturing a multilayer flexible printed wiring board according to claim 13, wherein the first difference is in a range of 3 to 9 times the second difference.
13. The method for manufacturing a multilayer flexible printed wiring board according to claim 12, wherein the first difference is in a range of 3 to 9 times the second difference.