Manufacturing method of flexible printed wiring board

Abstract

The manufacturing method of the flexible printed wiring board relating to an embodiment includes a step of preparing a metal foil clad laminate 1 including an insulating substrate 2 and metal foil 3 and metal foil 4 provided on main surfaces of the substrate 2, a step of forming a circuit pattern 5 by patterning the metal foil 3, a step of forming a peelable printing plate layer 6 on the substrate 2 so as to embed the pattern 5, a step of forming blind holes 7a and 7b where the pattern 5 is exposed inside by partially removing the printing plate layer 6, a step of printing conductive paste with the printing plate layer 6 as a printing mask, and filling the conductive paste 8 inside the blind holes, and a step of peeling off the printing plate layer 6 from the metal foil clad laminate 1.

Claims

1. A manufacturing method of a flexible printed wiring board comprising: a step of preparing a metal foil clad laminate including an insulating substrate and metal foil provided on at least one of main surfaces of the insulating substrate; a step of forming a circuit pattern by patterning the metal foil; a step of forming a peelable printing plate layer on the insulating substrate so as to embed the circuit pattern; a step of forming a blind hole where the circuit pattern is exposed inside by partially removing the printing plate layer; a step of printing conductive paste with the printing plate layer as a printing mask, and filling the conductive paste inside the blind hole; and a step of peeling off the printing plate layer from the metal foil clad laminate; wherein the metal foil clad laminate is a double-sided metal foil clad laminate provided with first metal foil and second metal foil respectively on a front surface and a back surface of the insulating substrate, and the circuit pattern includes a conformal mask, and wherein, in the step of forming the blind hole, by irradiating the printing plate layer with a laser beam and partially removing the printing plate layer and the insulating substrate, a bottomed step via hole where the first metal foil is exposed in the middle and the second metal foil is exposed at a bottom surface is formed as the blind hole.

2. The manufacturing method of the flexible printed wiring board according to claim 1, wherein the printing plate layer is formed by sticking a film with a slightly adhesive material to the metal foil clad laminate.

3. The manufacturing method of the flexible printed wiring board according to claim 1, wherein the printing plate layer is formed by sticking a UV curing type adhesive film to the metal foil clad laminate, adhesiveness is extinguished by irradiating the UV curing type adhesive film with UV light after the conductive paste is printed, and the UV curing type adhesive film is peeled off from the metal foil clad laminate.

4. The manufacturing method of the flexible printed wiring board according to claim 1, wherein, in the step of preparing the metal foil clad laminate, a roll metal foil clad laminate is prepared as the metal foil clad laminate, and the steps from the step of forming the circuit pattern to at least the step of printing the conductive paste are carried out by a roll-to-roll method.

5. The manufacturing method of the flexible printed wiring board according to claim 4, further comprising a step of thermally curing the conductive paste and forming an insulating protective layer at a predetermined part of the metal foil clad laminate, wherein the steps from the step of forming the circuit pattern to the step of forming the insulating protective layer are carried out by the roll-to-roll method.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 consists of FIGS. 1.1-1.4 and show a process sectional view for illustrating a manufacturing method of a flexible printed wiring board relating to a first embodiment.

(2) FIG. 2 consists of FIGS. 2.1-2.4 and show a process sectional view for illustrating the manufacturing method of the flexible printed wiring board relating to the first embodiment, following FIG. 1.

(3) FIG. 3 is a perspective view illustrating manufacture of a plurality of kinds of flexible printed wiring boards by a roll-to-roll method.

(4) FIG. 4 consists of FIG. 4A and 4B and FIG. 4A is a plan view for illustrating the manufacturing method of the flexible printed wiring board relating to a second embodiment, and FIG. 4B is a sectional view along an A-A line in FIG. 4A.

(5) FIG. 5 consists of FIGS. 5.1 and 5.2 and show a process sectional view for illustrating the manufacturing method of the flexible printed wiring board relating to the second embodiment, following FIG. 4.

(6) FIG. 6 consists of FIG. 6A and FIG. 6B, FIG. 6A is a plan view for illustrating the manufacturing method of the flexible printed wiring board relating to the second embodiment, following FIG. 5, and FIG. 6B is a sectional view along the A-A line in FIG. 6k

(7) FIG. 7 consists of FIG. 7A and FIG. 7B, FIG. 7A is a plan view for illustrating the manufacturing method of the flexible printed wiring board relating to the second embodiment, following FIG. 6, and FIG. 7B is a sectional view along the A-A line in FIG. 7A.

(8) FIG. 8 consists of FIG. 8A and FIG. 8B, FIG. 8A is a plan view for illustrating the manufacturing method of the flexible printed wiring board relating to the second embodiment, following FIG. 7, and FIG. 8B is a sectional view along the A-A line in FIG. 8A.

(9) FIG. 9 is a sectional view of the flexible printed wiring board relating to a modification of the second embodiment.

DESCRIPTION OF EMBODIMENTS

(10) Hereinafter, with reference to the drawings, a manufacturing method of a flexible printed wiring board relating to embodiments of the present invention will be described. Further, same signs are attached to components having equal functions in respective figures, and detailed description of the components of the same sign is not repeated.

(11) (First Embodiment)

(12) The manufacturing method of the flexible printed wiring board relating to the first embodiment of the present invention will be described with reference to FIG. 1 and FIG. 2. The flexible printed wiring board manufactured by the manufacturing method relating to the present embodiment includes an interlayer connecting path formed of conductive paste.

(13) First, as illustrated in FIG. 1.1, a metal foil clad laminate 1 is prepared. The metal foil clad laminate 1 is a double-sided metal foil clad laminate including an insulating substrate 2, and metal foil 3 and metal foil 4 provided respectively on a front surface (upper surface) and a back surface (lower surface) of the insulating substrate 2. The insulating substrate 2 is a flexible insulating film (25 m thick, for instance) composed of polyimide, polyethylene-terephthalate (PET), a liquid crystal polymer (LCP) or the like, and the metal foil 3 and the metal foil 4 are copper foil (12 m thick, for example). Further, the metal foil 3 and the metal foil 4 may be constituted of a metal (silver, aluminum or the like) other than copper. Also, for manufacture by a roll-to-roll method, in this process, a roll-like metal foil clad laminate may be prepared as the metal foil clad laminate 1.

(14) Next, as illustrated in FIG. 1.2, a circuit pattern 5 is formed by patterning the metal foil 3 of the metal foil clad laminate 1. Similarly, the metal foil 4 is processed into a predetermined circuit pattern. The metal foil 3 and the metal foil 4 are patterned by etching using a known photofabrication method, for example. In addition, it is preferable to expose etching resist by direct exposure. By this, the need of a photomask is eliminated, and by switching an exposure pattern for each required quantity, the manufacture of many kinds of flexible printed wiring boards in small quantities can be coped with.

(15) The circuit pattern 5 formed in this process includes a conformal mask 5a for forming a conduction hole by laser processing, and wiring 5b extending in a predetermined direction (a direction orthogonal to a paper surface in FIG. 1). Further, the conformal mask 5a may also serve as a land. For example, the conformal mask 5a is in a doughnut shape whose inner diameter is 150 m and outer diameter (land diameter) is 250 m.

(16) Next, as illustrated in FIG. 1.3, a peelable printing plate layer 6 is formed on the insulating substrate 2 so as to embed the circuit pattern 5. In more detail, the printing plate layer 6 is formed by sticking a film with a slightly adhesive material to the metal foil clad laminate 1 using a laminator device or the like. The film with the slightly adhesive material includes an insulating film and a slightly adhesive material layer provided on the insulating film.

(17) The printing plate layer 6 formed in this process needs to have resistance against heating treatment and chemical treatment in processes described later. As the printing plate layer 6, preferably, a PET film with a slightly adhesive material (for example, SOMATAC CR 1155 manufactured by SOMAR Corporation) is used.

(18) Further, the printing plate layer 6 may be formed by sticking a UV curing type adhesive film that has adhesiveness in an initial state and loses the adhesiveness by being irradiated with UV light to the metal foil clad laminate 1. Also, the printing plate layer 6 may be formed by coating a resin that loses the adhesiveness by heat treatment such as heating on the insulating substrate 2.

(19) Next, as illustrated in FIG. 1.4, the printing plate layer 6 is partially removed and blind holes 7a and 7b where the circuit pattern 5 is exposed inside and which do not pass through the metal foil clad laminate 1 are formed. In more detail, the blind hole 7a is formed by emitting a laser beam to the printing plate layer 6 aiming at the almost center of the conformal mask 5a and partially removing the printing plate layer 6 and the insulating substrate 2. The blind hole 7a is a bottomed step via hole where the metal foil 3 is exposed in the middle and the metal foil 4 is exposed at a bottom surface.

(20) Similarly, the blind hole 7b is formed by emitting the laser beam to the printing plate layer 6 aiming at the wiring 5b and partially removing the printing plate layer 6. At the bottom surface of the blind hole 7b, the wiring 5b is exposed.

(21) In addition, as a laser for forming the blind holes 7a and 7b, a carbon dioxide laser is used for example, however, other lasers may be used.

(22) Also, when irradiating the conformal mask 5a with the laser beam, it is preferable to adjust a beam diameter of the laser beam to be an intermediate value (for example, 200 m) of the inner diameter and the outer diameter of the conformal mask 5a by an aperture or the like. By narrowing an alignment area in this way, laser processing position accuracy can be improved, and the diameter of the land can be further reduced. Further, in the case that the beam diameter is 200 m, the conformal mask 5a is exposed in the doughnut shape of about 25 m width inside the blind hole 7a.

(23) Also, formation of the blind holes 7a and 7b is not limited to the laser processing. For example, in the case that the printing plate layer 6 is formed of a photosensitive resin, the blind holes 7a and 7b may be formed by etching the printing plate layer 6 by direct exposure or the like.

(24) After forming the blind holes 7a and 7b, desmear treatment is performed. The desmear treatment is performed by plasma treatment which is dry treatment, permanganic acid treatment which is wet treatment, or the like alone, or a combination thereof.

(25) Next, as illustrated in FIG. 2.1, conductive paste is printed with the printing plate layer 6 as a printing mask, and conductive pastes 8a and 8b are filled inside the blind holes 7a and 7b. For example, the conductive paste is printed by a squeegee of a screen printer or the like.

(26) By turning the laser-processed printing plate layer 6 to the printing mask in this way, the need of positioning a screen plate and the circuit pattern is eliminated, and the conductive paste can be highly accurately printed on the circuit pattern 5. Also, since a screen printer not having a highly accurate positioning mechanism can be used, a density of the flexible printed wiring board can be increased at a low cost.

(27) Next, as illustrated in FIG. 2.2, the printing plate layer 6 is peeled off from the metal foil clad laminate 1. For example, by a roll-to-roll process, the printing plate layer 6 is continuously peeled off from the metal foil clad laminate 1.

(28) Additionally, in the case that the printing plate layer 6 is formed of the UV curing type adhesive film, after printing the conductive paste, the adhesiveness is extinguished by irradiating the UV curing type adhesive film with the UV light, and the UV curing type adhesive film is peeled off from the metal foil clad laminate 1 thereafter.

(29) Next, as illustrated in FIG. 2.3, the conductive pastes 8a and 8b are thermally cured. The conductive pastes 8a and 8b are cured, and become cured conductive pastes 9a and 9b respectively.

(30) Next, as illustrated in FIG. 2.4, using a vacuum press or a vacuum laminator or the like, a cover lay (insulating protective layer) 10 is formed at a predetermined part of the metal foil clad laminate 1. For the cover lay 10, on an insulating film 10a such as a polyimide film, an adhesive layer 10b formed of an acrylic-based or epoxy-based adhesive is formed. After sticking the cover lay 10 to the metal foil clad laminate 1, surface treatment such as gold plating and outline machining to the circuit pattern 5 are performed as needed.

(31) Through the above-described processes, a flexible printed wiring board 100 illustrated in FIG. 2.4 is obtained. In the flexible printed wiring board 100, the circuit patterns formed on both surfaces of the insulating substrate 2 are electrically connected by the cured conductive paste 9a. Also, a thickness of the wiring 5b is increased by the cured conductive paste 9b. Thus, without thickening a wiring width, a current capacity of the wiring can be increased.

(32) As described above, in the manufacturing method of the flexible printed wiring board relating to the first embodiment, the printing plate layer 6 is formed so as to embed the circuit pattern 5. Then, after forming the blind holes 7a and 7b by partially removing the printing plate layer 6, the conductive paste is printed with the printing plate layer 6 as the printing mask, and the conductive pastes 8a and 8b are filled inside the blind holes 7a and 7b. Therefore, it is not needed to position the circuit pattern 5 and the screen plate in the present embodiment, and the conductive paste can be accurately printed to a fine circuit pattern.

(33) Since the conductive paste can be accurately printed, the refinement of the circuit pattern of the flexible printed wiring board can be advanced. For example, since the conductive paste can be accurately filled in a conduction hole of a small diameter, the diameter of the conformal mask 5a (land) can be reduced. Also, since the conductive paste can be accurately printed and formed on the wiring, the wiring width can be narrowed while securing a required current capacity.

(34) Also, in the manufacturing method of the flexible printed wiring board relating to the present embodiment, since the conductive paste is printed by the printing plate layer 6, there is no need of preparing or exchanging an exclusive screen plate for each product. Therefore, as illustrated in FIG. 3, different products (a product A, a product B, and a product C) can be easily manufactured for each sheet. It is also easy to manufacture different numbers of sheets (manufacture amounts) for the respective products like the product A for five sheets, the product B for three sheets, and the product C for ten sheets or the like. Therefore, according to the present embodiment, many kinds of flexible printed wiring boards in small quantities can be stably manufactured with high productivity.

(35) Further, since the need of arranging and exchanging work or the like of the screen plate is eliminated, according to the first embodiment, by preparing a roll-like metal foil clad laminate 1 in the process of preparing the metal foil clad laminate 1, the processes from the process of forming the circuit pattern 5 to the process of thermally curing the conductive pastes 8a and 8b can be performed by the roll-to-roll method.

(36) In the case that sheet lengths of the individual products are the same, the roll-to-roll method is possible up to the process of forming the cover lay 10. Even in the case that the sheet lengths of the individual products are different, since there is no need of using an exclusive tool (an exposure mask or a printing plate or the like) for each product, the roll-to-roll process is possible to the process before the process of forming the cover lay 10. In the case of using a photosensitive cover instead of the cover lay, even when the sheet lengths of the individual products are different, the roll-to-roll method is possible to the process of forming the cover.

(37) As described above, the processes from the process of forming the circuit pattern 5 to the process of forming the cover lay 10 may be performed by the roll-to-roll method. Further, it is preferable to perform the processes from the process of forming the circuit pattern 5 to at least the process of printing the conductive paste by the roll-to-roll method. By continuously making the process flow by the roll-to-roll method, manufacturing efficiency of the flexible printed wiring board can be substantially improved.

(38) In addition, in the description of the first embodiment, the double-sided metal foil clad laminate is used as the metal foil clad laminate 1, however, it is possible to apply the manufacturing method of the present embodiment even to a single-sided metal foil clad laminate. For example, the conductive paste may be formed by printing using the printing plate layer on the circuit pattern formed by patterning the metal foil of the single-sided metal foil clad laminate.

(39) (Second Embodiment)

(40) Next, the manufacturing method of the flexible printed wiring board relating to the second embodiment of the present invention will be described with reference to FIG. 4 to FIG. 8. The flexible printed wiring board manufactured by the manufacturing method relating to the present embodiment includes a jumper connecting path formed of the conductive paste.

(41) First, as a starting material, a metal foil clad laminate 1A is prepared. The metal foil clad laminate 1A is a single-sided metal foil clad laminate including the insulating substrate 2 and the metal foil 3 provided on the front surface (upper surface) of the insulating substrate 2. Further, the metal foil clad laminate 1A may be a double-sided metal foil clad laminate.

(42) Next, as illustrated in FIG. 4A and FIG. 4B, a circuit pattern 11 is formed by patterning the metal foil 3. In addition, the metal foil 3 is patterned by etching using the known photofabrication method, for example.

(43) The circuit pattern 11 formed in this process includes wiring 11a that extends in a predetermined direction, a receiving land 11b and a receiving land 11c. The receiving land 11b and the receiving land 11c are arranged respectively on both sides of the wiring 11a so as hold the wiring 11a therebetween. In more detail, wiring is connected respectively to the receiving land 11b and the receiving land 11c in a circular shape, and the wiring 11a is arranged so as to pass through between a pattern having the receiving land 11b at an end and a pattern having the receiving land 11c at an end.

(44) Next, as illustrated in FIG. 5.1, a cover lay (insulating protective layer) 12 is formed so as to embed the circuit pattern 11 at a predetermined part of the metal foil clad laminate 1A. For the cover lay 12, similarly to the cover lay 10 described in the first embodiment, an adhesive layer 12b is formed on an insulating film 12a.

(45) Then, as illustrated in FIG. 5.2, a peelable printing plate layer 13 is formed on the cover lay 12. Since the printing plate layer 13 is similar to the printing plate layer 6 described in the first embodiment, detailed description will be omitted.

(46) Next, as illustrated in FIG. 6A and FIG. 6B, a jumper opening 20 including a blind hole 14 where the receiving land 11b is exposed inside, a blind hole 15 where the receiving land 11c is exposed inside, and a connecting groove part 16 where the cover lay 12 is exposed at a bottom surface and which connects the blind hole 14 and the blind hole 15 is formed. In more detail, first, the printing plate layer 13 and the cover lay 12 are partially removed and the blind hole 14 and the blind hole 15 are formed. The receiving land 11b is exposed at the bottom surface for the blind hole 14, and the receiving land 11c is exposed at the bottom surface for the blind hole 15. For example, the blind hole 14 (15) is formed by emitting a laser beam to the printing plate layer 13 aiming at the almost center of the receiving land 11b (11c) and partially removing the printing plate layer 13 and the cover lay 12.

(47) After forming the blind holes 14 and 15, the printing plate layer 13 is partially removed, and the connecting groove part 16 is formed. The connecting groove part 16 has the cover lay 12 (insulating film 12a) exposed at the bottom surface, and connects the blind hole 14 and the blind hole 15.

(48) The connecting groove part 16 is formed by irradiating the printing plate layer 13 between the blind hole 14 and the blind hole 15 with the laser beam and partially removing the printing plate layer 13, for example. At the time, output of a laser device (a carbon dioxide laser, for example) is adjusted so as to remove only the printing plate layer 13, and the laser beam is emitted to the printing plate layer 13 while being linearly scanned. Further, in order to improve selective processability of the printing plate layer 13 and the cover lay 12, a UV-YAG laser of a short wavelength, an excimer laser, or the like may be used.

(49) By forming the blind holes 14 and 15 and the connecting groove part 16 as described above, the jumper opening 20 is formed. After forming the jumper opening 20, the desmear treatment is performed.

(50) In addition, in the process of forming the jumper opening 20, a forming order of the blind hole 14, the blind hole 15 and the connecting groove part 16 is arbitrary. For example, the blind holes 14 and 15 may be formed after forming the connecting groove part 16, or they may be formed in the order of the blind hole 14, the connecting groove part 16 and the blind hole 15.

(51) Next, as illustrated in FIG. 7A and FIG. 7B, the conductive paste is printed with the printing plate layer 13 and the cover lay 12 as the printing mask, and conductive paste 17 is filled inside the jumper opening 20. Thus, the conductive paste 17 is filled inside the blind holes 14 and 15 and the connecting groove part 16. Printing in this process is performed using a squeegee of a screen printer or the like, for example.

(52) In this way, in the second embodiment, by turning the laser-processed printing plate layer 13 and cover lay 12 to the printing mask, the conductive paste can be highly accurately printed on the circuit pattern 11. Also, the need of an exclusive screen plate is eliminated, and the need of positioning between the screen plate and the circuit pattern 11 is also eliminated.

(53) Next, the printing plate layer 13 is peeled off from the metal foil clad laminate 1A (cover lay 12). For example, by the roll-to-roll process, the printing plate layer 13 is continuously peeled off from the metal foil clad laminate 1A.

(54) Then, as illustrated in FIG. 8A and FIG. 8B, the conductive paste 17 printed in accordance with a shape of the jumper opening 20 is thermally cured, and turned to cured conductive paste 18 that functions as a jumper wire.

(55) Thereafter, for insulation property reservation and physical protection of the cured conductive paste 18, the jumper wire is coated with various kinds of resist, cover lay or overcoat materials or the like, as needed.

(56) Through the processes described above, the flexible printed wiring board having a configuration that the receiving land 11b and the receiving land 11c are electrically connected by the jumper wire formed of the cured conductive paste 18 is obtained.

(57) Further, for the second embodiment as well, similarly to the first embodiment, the individual processes can be performed by the roll-to-roll process.

(58) Also, in the above description, the number of the receiving lands is two, however, it is not limited thereto. Three or more receiving lands may be formed and the jumper wire that electrically connects the receiving lands may be formed.

(59) Also, a planar shape of the jumper wire is not limited to a straight line shape, and can be an arbitrary shape such as a curve.

(60) Also, in the description of the second embodiment, the single-sided metal foil clad laminate is used as the metal foil clad laminate 1A, however, as illustrated in the following modification, the manufacturing method of the second embodiment is applicable to the double-sided metal foil clad laminated as well.

(61) <Modification of second embodiment>

(62) In this modification, as illustrated in FIG. 9, as a starting material, the metal foil clad laminate 1 which is the double-sided metal foil clad laminate is used. Then, similarly to the first embodiment, the metal foil 3 is patterned, and the circuit pattern including the wiring 11a, the receiving land 11b and the receiving land 11c is formed. Here, the receiving land 11b is formed into the doughnut shape for example, and turned to a conformal mask. Further, the receiving land 11c may be also turned to the conformal mask.

(63) Next, in the process of forming the blind hole 14 described above, a bottomed step via hole where the metal foil 3 is exposed in the middle and the metal foil 4 is exposed at the bottom surface is formed. Thereafter, similarly to the processes described above, the conductive paste is filled in the jumper opening, the printing plate layer is peeled off, and the filled conductive paste is cured and turned to the cured conductive paste 18. The cured conductive paste 18 formed in this way, as illustrated in FIG. 9, functions as the jumper wire, and also functions as an interlayer connecting path that electrically connects the circuit patterns formed on both surfaces of the insulating substrate 2.

(64) On the basis of the above description, those skilled in the art may conceive additional effects and various modifications of the present invention. However, aspects of the present invention are not limited to the embodiments described above. Various additions, modifications and partial deletion are possible without departing from the conceptual spirit and meaning of the present invention derived from contents defined in the scope of claims and the equivalency thereof.

REFERENCE SIGNS LIST

(65) 1, 1A metal foil clad laminate

(66) 2 insulating substrate

(67) 3, 4 metal foil

(68) 5 circuit pattern

(69) 5a conformal mask

(70) 5b wiring

(71) 6 printing plate layer

(72) 7a, 7b blind hole

(73) 8a, 8b conductive paste (before being cured)

(74) 9a, 9b cured conductive paste

(75) 10 cover lay (insulating protective layer)

(76) 10a insulating film

(77) 10b adhesive layer

(78) 11 circuit pattern

(79) 11a wiring

(80) 11b, 11c receiving land

(81) 12 cover lay (insulating protective layer)

(82) 12a insulating film

(83) 12b adhesive layer

(84) 13 printing plate layer

(85) 14, 15 blind hole

(86) 16 connecting groove part

(87) 17 conductive paste (before being cured)

(88) 18 cured conductive paste

(89) 20 jumper opening

(90) 100 flexible printed wiring board