阅读说明：本技术 柔性印刷电路板和制造柔性印刷电路板的方法 (Flexible printed circuit board and method of manufacturing the same ) 是由 冈上润一 冈田久夫 于 2018-11-23 设计创作，主要内容包括：根据本公开的一个实施例的柔性印刷电路板设置有：基膜,其具有绝缘性能；第一导电图案,其层叠在基膜上并且覆盖有金、镍或防锈材料；以及第二导电图案,其层叠在基膜上并且覆盖有锡或焊料。(A flexible printed circuit board according to one embodiment of the present disclosure is provided with: a base film having an insulating property; a first conductive pattern laminated on the base film and covered with gold, nickel, or a rust-proof material; and a second conductive pattern laminated on the base film and covered with tin or solder.)

1. A flexible printed circuit board comprising:

an insulating base film;

a first conductive pattern laminated on the base film and coated with gold, nickel, or a rust-proof material; and

a second conductive pattern laminated on the base film and coated with tin or solder.

2. The flexible printed circuit board according to claim 1, wherein the second conductive pattern includes an IC chip mounting pad.

3. The flexible printed circuit board according to claim 1 or claim 2, wherein the first conductive pattern includes a narrow pitch connection portion at which a plurality of terminals are arranged and formed at an average width of 15 μm or less and an average interval of 15 μm or less.

4. The flexible printed circuit board according to claim 1, claim 2, or claim 3, wherein the first conductive pattern includes a wide-pitch connection portion at which a plurality of terminals are arranged and formed with an average width of 20 μm or more and with an average interval of 20 μm or more.

5. The flexible printed circuit board according to any one of claim 1 to claim 4,

wherein the second conductive pattern is coated with tin,

the tin-coated layer includes one or more first regions formed of an alloy of a metal forming the second conductive pattern and tin and one or more second regions formed of non-alloyed tin on an outer surface thereof, and

a total percentage of a footprint of the one or more first regions in the outer surface of the tin-coated layer is above 2% and below 90%.

6. The flexible printed circuit board according to claim 5, wherein an average thickness of the second region is 0.05 μm or more and 0.4 μm or less.

7. A method of manufacturing a flexible printed circuit board, comprising:

a step of forming a conductive pattern on an insulated base film;

a step of coating a part of the conductive pattern with gold, nickel, or a rust-proof material; and

a step of coating another part of the conductive pattern with tin or solder after the coating step.

8. The method of manufacturing a flexible printed circuit board according to claim 7,

wherein the coating of the gold or the nickel is performed by electroless plating, and

the coating of the tin or the solder is performed by electroless plating.

9. The method of manufacturing a flexible printed circuit board according to claim 7 or claim 8,

wherein the other part of the conductive pattern coated with tin or solder includes a pad for mounting an IC chip, and

the method further includes a step of eutectic-bonding a terminal of an IC chip to the IC chip mounting pad.

10. The method of manufacturing a flexible printed circuit board according to claim 9, wherein in the eutectic bonding step, eutectic bonding is performed by thermocompression bonding at a temperature of 250 ℃ or more and 500 ℃ or less and a pressure of 2MPaG or more and 50MPaG or less.

Technical Field

The present disclosure relates to a flexible printed circuit board and a method of manufacturing the same.

This application is based on and claims priority from japanese patent application No.2017-226635, filed on 27.11.2017, the entire contents of which are incorporated herein by reference.

Background

In an electronic apparatus having a display panel, generally, the display panel and a printed circuit board are connected together by a COF (chip on film) on which an IC chip for driving the display panel is mounted (see japanese laid-open patent application publication No. 2016-.

In COF, a copper foil laminated on a polyimide film is wet-etched to form a wiring pattern, and an IC is flip-chip mounted on the wiring pattern. Among electronic devices having a display panel, there are electronic devices that: wherein the display panel and the printed circuit board having the main circuit are connected together through a COF mounted with an IC for driving the display panel.

In the COF, such a configuration can be adopted: wherein the surface of the wiring pattern is coated with tin, and the IC chip is connected to the wiring pattern by a solder material generated by eutectic reaction of tin with a gold layer on the outer end face of the IC chip. A connection method by such eutectic reaction is called eutectic bonding, and may be performed by performing thermal compression bonding at a relatively low temperature.

[ Prior art documents ]

[ patent document ]

[ patent document 1] Japanese published patent application publication No.2016-

Disclosure of Invention

According to an aspect of the present disclosure, a flexible printed circuit board includes: an insulating base film; a first conductive pattern laminated on the base film and coated with gold, nickel, or a rust-proof material; and a second conductive pattern laminated on the base film and coated with tin or solder.

According to another aspect of the present disclosure, a method of manufacturing a flexible printed circuit board includes: a step of forming a conductive pattern on an insulated base film; a step of coating a part of the conductive pattern with gold, nickel, or a rust-proof material; and a step of coating another part of the conductive pattern with tin or solder after the coating step.

Drawings

Fig. 1 is a schematic plan view of a flexible printed circuit board according to one embodiment of the present disclosure;

fig. 2 is a schematic cross-sectional view of the flexible printed circuit board of fig. 1;

FIG. 3 is a schematic plan view of a tin coating;

FIG. 4 is a schematic cross-sectional view of a tin coating;

fig. 5 is a schematic cross-sectional view of a display device using the flexible printed circuit board of fig. 1;

FIG. 6 is a schematic plan view of a flexible printed circuit board according to an embodiment of the present disclosure that differs from FIG. 1; and is

Fig. 7 is a schematic sectional view of the flexible printed circuit board of fig. 6.

Detailed Description

[ problems to be solved by the invention ]

In the COF for the display panel, since an IC chip for driving the display panel is mounted on the same surface as a surface on which terminals connected to the display panel and terminals connected to the printed circuit board are arranged, the arrangement in the electronic device is limited. In addition, COFs are inferior in flexibility and are prone to breaking (disconnection) as compared with general flexible printed wiring boards.

In view of the above circumstances, an object of the present disclosure is to provide a flexible printed circuit board capable of mounting an IC chip and capable of being directly connected to a terminal of another device, a circuit, or the like, and a method of manufacturing the flexible printed circuit board.

[ Effect of the present disclosure ]

The flexible printed circuit board according to one aspect of the present disclosure and the flexible printed circuit board obtained by the method of manufacturing the flexible printed circuit board according to another aspect of the present disclosure enable an IC chip to be mounted and to be directly connected to a terminal of another device, a circuit board, or the like.

[ description of various embodiments of the present disclosure ]

According to an aspect of the present disclosure, a flexible printed circuit board includes: an insulating base film; a first conductive pattern laminated on the base film and coated with gold, nickel, or a rust-proof material; and a second conductive pattern laminated on the base film and coated with tin or solder.

In the flexible printed circuit board, since the first conductive pattern is coated with gold, nickel, or a rust-proof material, the conductive connectivity of the first conductive pattern with other circuits is not easily lowered. Therefore, the flexible printed circuit board can be reliably connected to a terminal of another device or a circuit board. In addition, in the flexible printed circuit board, since the second conductive pattern is coated with tin or solder, the IC chip can be easily and reliably mounted on the second conductive pattern by eutectic reaction.

In the flexible printed circuit board, the second conductive pattern may include a pad for mounting an IC chip. In this way, by the second conductive pattern including the pad for mounting the IC chip, the IC chip can be mounted on the second conductive pattern more easily and more reliably by the eutectic reaction.

In the flexible printed circuit board, the first conductive pattern may include a narrow pitch connection portion at which the plurality of terminals are arranged and formed at an average width of 15 μm or less and an average interval of 15 μm or less. In this way, the first conductive pattern including the narrow pitch connection portion enables direct connection with the terminal at a relatively small line pitch.

In the flexible printed circuit board, the first conductive pattern may include a wide pitch connection portion at which the plurality of terminals are arranged and formed at an average width of 20 μm or more and an average interval of 20 μm or more. In this way, the flexible printed circuit board can be used to connect a display panel or the like to another printed circuit board or the like by the first conductive pattern including the wide-pitch connection portion.

In the flexible printed circuit board, the second conductive pattern may be coated with tin, the tin-coated layer may include one or more first regions and one or more second regions on an outer surface thereof, the one or more first regions are formed of an alloy of a metal forming the second conductive pattern and tin, the one or more second regions are formed of non-alloy tin, and a total occupied area percentage of the one or more first regions in the outer surface of the tin-coated layer is 2% or more and 90% or less. In this way, by making the total occupied area percentage of the one or more first regions in the outer surface of the tin-coated layer be 2% or more and 90% or less, the amount of the brazing material formed by the eutectic reaction when bonding with the terminal of the IC chip can be made appropriate, short circuits between adjacent circuits of the second conductive pattern can be prevented, and bonding with the terminal of the IC chip can be made more reliable.

In the flexible printed circuit board, the average thickness of the second region may be 0.05 μm or more and 0.4 μm or less. By setting the average thickness of the second region to 0.05 μm or more and 0.4 μm or less in this way, the amount of solder formed by eutectic reaction at the time of bonding with the terminal of the IC chip can be made appropriate, short-circuiting between adjacent circuits of the second conductive pattern can be prevented, and bonding with the terminal of the IC chip can be made more reliable.

According to another aspect of the present disclosure, a method of manufacturing a flexible printed circuit board includes: a step of forming a conductive pattern on an insulated base film; a step of coating a part of the conductive pattern with gold, nickel, or a rust-proof material; and a step of coating the other part of the conductive pattern with tin or solder after the coating step.

Since the manufacturing method of the flexible printed circuit board performs the coating of tin or solder after the coating of gold, nickel or rust-preventive material, the coating layer of gold, nickel or rust-preventive material and the coating layer of tin or solder can be appropriately formed. Therefore, according to the method of manufacturing a flexible printed circuit board, a printed circuit board capable of mounting an IC chip and directly connectable to a terminal of another device, a circuit, or the like can be obtained.

In the method of manufacturing the flexible printed circuit board, the coating of gold or nickel may be performed by electroless plating, and the coating of tin or solder may be performed by electroless plating. In this way, by performing the coating of gold or nickel by electroless plating, and performing the coating of tin or solder by electroless plating, it is possible to prevent the connectivity of the coating of gold or nickel and the coating of tin or solder from being impaired. In addition, by performing electroless plating to coat gold or nickel, and coating tin or solder, a flexible printed circuit board capable of connecting terminals of an IC chip more easily and reliably can be obtained.

In the method of manufacturing a flexible printed circuit board, the portion of the conductive pattern coated with tin or solder may include a pad for IC chip mounting, and the method may further include the step of eutectic-bonding a terminal of the IC chip to the pad for IC chip mounting. In this way, by coating the conductive pattern with tin or solder, the portion including the pad for IC chip mounting, and by including the step of eutectic-bonding the terminal of the IC chip to the pad for IC chip mounting, a flexible printed circuit board capable of more reliably mounting the IC chip by eutectic bonding can be obtained.

In the method of manufacturing a flexible printed circuit board, in the step of eutectic bonding, eutectic bonding may be performed by thermocompression bonding at a temperature of 250 ℃ or more and 500 ℃ or less and a pressure of 2MPaG or more and 50MPaG or less. In this way, by performing eutectic bonding by thermocompression bonding at a temperature of 250 ℃ to 500 ℃ and under a pressure of 2MPaG to 50MPaG, it is possible to prevent deterioration of the flexible printed wiring board and further improve the bonding strength between the terminal of the IC chip and the IC chip mounting pad.

Note that the "rust preventive material" is a concept that: which includes an organic material forming a coating layer on a surface of a material forming the first conductive pattern, and includes a material (including a bonded material) chemically bonded with the material forming the first conductive pattern to form passivation.

[ details of embodiments of the present disclosure ]

Hereinafter, embodiments of a flexible printed circuit board according to the present disclosure will be described in detail with reference to the accompanying drawings.

[ first embodiment ]

Fig. 1 and 2 show a flexible printed circuit board 1 according to an embodiment of the present invention. The flexible printed circuit board 1 further includes an insulating base film 2, a front surface conductive pattern 3 laminated on the front surface of the base film 2, a rear surface conductive pattern 4 laminated on the rear surface of the base film 2, a front surface protective layer 5 partially covering the front surface conductive pattern 3, and a rear surface protective layer 6 partially covering the rear surface conductive pattern 4.

The front side conductive pattern 3 comprises a front side first conductive pattern 8 coated with a gold coating 7 and comprises a second conductive pattern 10 coated with a tin coating 9. The front side first conductive pattern 8 and the second conductive pattern 10 are present at the portion exposed from the front side protective layer 5, in other words, the gold coat 7 or the tin coat 9 is laminated at the portion exposed from the front side protective layer 5 of the front side conductive pattern 3. On the other hand, at the portion of the front conductive pattern 3 coated with the front protective layer 5, the gold coating layer 7 and the tin coating layer 9 may not be laminated.

The rear conductive pattern 4 includes the rear first conductive pattern 12 coated with the gold coating 11, but does not include the conductive pattern coated with tin. The rear surface first conductive pattern 12 exists at a portion exposed from the rear surface protective layer 6.

The front surface conductive pattern 3 and the rear surface conductive pattern 4 are connected by a through hole 13 formed through the base film 2.

In addition, the IC chip 14 is mounted on the front surface conductive pattern 3 of the flexible printed circuit board 1.

< basic film >

The base film 2 is formed of a material having a synthetic resin as a main component and has flexibility. Examples of the main component of the base film 2 include soft materials such as polyimide, liquid crystal polyester, polyethylene terephthalate, polyethylene naphthalate, fluorine resin, and the like. Among them, polyimide having excellent insulation properties, flexibility, heat resistance, and the like is preferable. In addition, the base film 2 may be porous, and may contain fillers, additives, and the like.

The lower limit of the average thickness of the base film 2 is not particularly limited, but is preferably 5 μm, and more preferably 12 μm. On the other hand, the upper limit of the average thickness of the base film 2 is preferably 2mm, and more preferably 1.6 mm. In the case where the average thickness of the base film 2 is less than the lower limit, the strength of the base film 2 or the base material for a printed circuit board may be insufficient. In contrast, in the case where the average thickness of the base film 2 exceeds the upper limit, the flexibility of the flexible printed circuit board 1 may be insufficient.

< conductive Pattern >

The front surface conductive pattern 3 and the back surface conductive pattern 4 may be formed by patterning a layer of the layered conductor of the base film 2.

Examples of the material of the conductors forming the front surface conductive pattern 3 and the rear surface conductive pattern 4 include metals such as copper, silver, platinum, nickel, and the like. Among them, as the material of the front surface conductive pattern 3 and the back surface conductive pattern 4, copper which is low in cost and excellent in conductivity is preferable.

Preferably, the front surface conductive pattern 3 and the rear surface conductive pattern 4 are formed with a substantially constant thickness. The lower limit of the average thickness of the front surface conductive pattern 3 and the back surface conductive pattern 4 is preferably 2 μm, and more preferably 5 μm. On the other hand, the upper limit of the average thickness of the front surface conductive pattern 3 and the back surface conductive pattern 4 is preferably 50 μm, and more preferably 40 μm. In the case where the average thickness of the front surface conductive patterns 3 and the rear surface conductive patterns 4 is less than the lower limit, breakage of the front surface conductive patterns 3 and the rear surface conductive patterns 4 may occur. On the other hand, in the case where the average thickness of the front surface conductive patterns 3 and the rear surface conductive patterns 4 exceeds the upper limit, the flexibility of the printed circuit board 1 may be unnecessarily reduced.

(first conductive pattern)

The front-surface first conductive pattern 8 includes narrow-pitch connection portions 15, and a plurality of terminals are arranged at a constant pitch (center interval) at the narrow-pitch connection portions 15. For example, the narrow pitch connection portion 15 is connected to a terminal of another device such as a display panel.

For example, the connection of the terminals to the narrow pitch connection portions 15 can be achieved by using a surface mounting technique using steps such as reflow soldering, thermosetting of a conductive adhesive, and thermocompression bonding using an anisotropic conductive sheet.

The lower limit of the average width of each terminal of the narrow-pitch connection portion 15 is preferably 3 μm, and more preferably 5 μm. On the other hand, the upper limit of the average width of each terminal of the narrow-pitch connection portion 15 is preferably 15 μm, and more preferably 10 μm. In the case where the average width of each terminal of the narrow-pitch connection portion 15 is less than the lower limit, the electrical connection of the narrow-pitch connection portion 15 to other terminals may be unreliable. In contrast, in the case where the average width of each terminal of the narrow-pitch connection portion 15 exceeds the upper limit, a device or a circuit such as a display panel which can be connected to the flexible printed circuit board 1 may be limited.

The lower limit of the average interval of the terminals of the narrow-pitch connection portion 15 is preferably 3 μm, and more preferably 5 μm. On the other hand, the upper limit of the average interval of the terminals of the narrow-pitch connection portion 15 is preferably 15 μm, and more preferably 10 μm. In the case where the average interval of the terminals of the narrow-pitch connection portion 15 is smaller than the above-described lower limit, a short circuit may occur between the terminals of the narrow-pitch connection portion 15. In contrast, in the case where the average interval of the terminals of the narrow pitch connection 15 exceeds the upper limit, a device that can be connected to the flexible printed circuit board 1 may be limited.

The rear surface first conductive pattern 12 includes a wide pitch connection portion 16, at which a plurality of linear or rectangular shaped terminals are arranged at a constant pitch so as to be connected to terminals provided on another printed circuit board or the like at the wide pitch connection portion 16.

Similarly to the narrow-pitch connection portions 15, the connection of the terminals to the wide-pitch connection portions 16 can be achieved by using a surface mounting technique using steps such as reflow soldering, thermosetting of a conductive adhesive, and thermocompression bonding using an anisotropic conductive sheet, for example.

The lower limit of the average width of each terminal of the wide-pitch connection portion 16 is preferably 20 μm, and more preferably 25 μm. On the other hand, the upper limit of the average width of each terminal of the wide pitch connection portion 16 is preferably 1.0mm, and more preferably 0.4 mm. In the case where the average width of the respective terminals of the wide-pitch connection portion 16 is less than the lower limit, the circuit connected to the wide-pitch connection portion 16 may become expensive. In contrast, in the case where the average width of the respective terminals of the wide pitch connection portion 16 exceeds the upper limit, the size of the flexible printed circuit board 1 or the electronic device using the flexible printed circuit board 1 may become excessively large.

The lower limit of the average interval of the terminals of the wide-pitch connection portion 16 is preferably 20 μm, and more preferably 25 μm. On the other hand, the upper limit of the average interval of the terminals of the wide pitch connection portion 16 is preferably 1.0mm, and more preferably 0.4 mm. In the case where the average interval of the terminals of the wide-pitch connection portion 16 is less than the lower limit, a short circuit may occur between the terminals of the wide-pitch connection portion 16. In contrast, in the case where the average interval of the terminals of the wide pitch connection portion 16 exceeds the upper limit, the size of the flexible printed circuit board 1 or the electronic device using the flexible printed circuit board 1 may become excessively large.

The gold coating 7 coated on the front side first conductive pattern 8 and the gold coating 11 coated on the rear side first conductive pattern 12 protect the front side first conductive pattern 8 to reduce the resistance of the outer surface. The lower limit of the average thickness of the gold coating 7 and the gold coating 11 is preferably 0.03 μm, and more preferably 0.09 μm. On the other hand, the upper limit of the average thickness of the gold coating layer 7 and the gold coating layer 11 is preferably 0.9 μm, and more preferably 0.4 μm. In the case where the average thickness of the gold coating layer 7 and the gold coating layer 11 is less than the lower limit, the front surface first conductive pattern 8 may not be sufficiently protected. In contrast, in the case where the average thickness of the gold coating layer 7 and the gold coating layer 11 exceeds the upper limit, the flexible printed circuit board 1 may become expensive.

(second conductive pattern)

The second conductive pattern 10 includes IC chip mounting pads 17 having a planar shape and arrangement corresponding to the terminals of the IC chip 14. The IC chip 14 is connected to the circuit of the flexible printed circuit board 1 by connecting the terminals of the IC chip 14 to the IC chip mounting pads 17.

The tin coating 9 coated on the second conductive pattern 10 can easily and reliably mount the IC chip to the IC chip mounting pad 17 of the second conductive pattern by causing eutectic reaction with the gold layer on the terminal outer surface of the IC chip 14.

The lower limit of the average thickness of the tin coating 9 is preferably 0.1 μm, and more preferably 0.2 μm. On the other hand, the upper limit of the average thickness of the tin coating layer 9 is preferably 1.0 μm, and more preferably 0.5 μm. In the case where the average thickness of the tin coating layer 9 is less than the lower limit, the amount of tin available for eutectic reaction may be insufficient, and the IC chip 14 may not be reliably connected to the IC chip mounting pad 17. In contrast, in the case where the average thickness of the tin coating 9 exceeds the upper limit, the tin coating 9 may fluidize at the time of eutectic reaction, thereby causing short circuits between the circuits of the second conductive pattern 10. It should be noted that the average thickness of the tin coating 9 can be measured using, for example, an X-ray fluorescence spectrometer.

As shown in fig. 3 and 4, on the outer surface of the tin coating layer 9, one or more first regions 18 and one or more second regions 19 may be formed, the one or more first regions 18 being formed of an alloy of the metal forming the second conductive pattern 10 and tin, and the one or more second regions 19 being formed of non-alloyed tin. In the present embodiment, a sea-island like structure is formed on the outer surface of the tin coating layer 9 so that a plurality of first regions 18 are dispersed in the second regions 19. In addition, it is preferable that the plurality of first regions 18 are arranged in the second region 19 at substantially equal density. For example, the first region 18 is formed by alloying tin contained in the tin coating layer 9 with a metal such as copper constituting the second conductive pattern 10 by heat treatment in the manufacturing process of the flexible printed circuit board 1.

The lower limit of the total percentage of the occupied area of the one or more first regions 18 in the outer surface of the tin coating 9 is preferably 2%, and more preferably 10%. On the other hand, the upper limit of the total occupied area percentage of the one or more first regions 18 in the outer surface of the tin coating 9 is preferably 90%, more preferably 80%, and still more preferably 70%. In the case where the total occupied area percentage of the one or more first regions 18 in the outer surface of the tin coating layer 9 is less than the lower limit, the amount of the brazing material formed by the eutectic reaction when bonding with the terminal of the IC chip increases, and thus a short circuit may occur between adjacent circuits of the second conductive pattern 10. In contrast, in the case where the total occupied area percentage of the one or more first regions 18 in the outer surface of the tin coating layer 9 exceeds the upper limit, the amount of the brazing material formed by the eutectic reaction becomes insufficient, and the bonding with the terminal of the IC chip may become insufficient. It should be noted that the total percentage of the occupied area of the first region 18 may be measured, for example, by: the outer surface of the tin coating layer 9 was imaged at 5000 times magnification using an energy dispersive X-ray (EDX) analyzer to measure the total percent occupied area of the plurality of first regions in the outer surface of the tin coating layer 9.

The lower limit of the average thickness of the second regions 19 (the average of the thicknesses of all the second regions 19 formed on the outer surface of the tin coating layer 9) is preferably 0.05 μm, and more preferably 0.10 μm. On the other hand, the upper limit of the average thickness of the second region 19 is preferably 0.4 μm, and more preferably 0.3 μm. In the case where the average thickness of the second region 19 is less than the lower limit, the amount of the brazing material formed by the eutectic reaction becomes insufficient, and the bonding with the terminal of the IC chip may become insufficient. On the other hand, in the case where the average thickness of the second region 19 exceeds the upper limit, the amount of the brazing material formed at the time of bonding with the terminal of the IC chip increases, and thus a short circuit may occur between the circuits of the second conductive pattern 10. It should be noted that the average thickness of the second region 19 may be measured using, for example, an electrolyte membrane thickness meter.

(protective layer)

The front surface protective layer 5 and the back surface protective layer 6 have openings that expose the narrow-pitch connection portions 15, the wide-pitch connection portions 16, and the pads 17 for IC chip mounting, and mainly protect the portions of the front surface conductive patterns 3 and the back surface conductive patterns 4 that are not covered with the gold coat 7 and the gold coat 11, and the tin coat 9.

As the front surface protective layer 5 and the back surface protective layer 6, for example, a coating layer, a solder resist, or the like can be used.

The coatings used as the front surface protective layer 5 and the back surface protective layer 6 may be configured to include a protective film and an adhesive layer.

The protective film of the coating is preferably flexible and insulating. Examples of the main component of the protective film include polyimide, epoxy resin, phenol resin, acrylic resin, polyester, thermoplastic polyimide, polyethylene terephthalate, fluorine resin, liquid crystal polymer, and the like. In particular, polyimide is preferable in terms of heat resistance. It should be noted that the protective film may contain other resins, weather-resistant agents, antistatic agents, etc., in addition to the main components.

The lower limit of the average thickness of the protective film is not particularly limited, but is preferably 3 μm, and more preferably 10 μm. In addition, the upper limit of the average thickness of the protective film is not particularly limited, but is preferably 500 μm, and more preferably 150 μm. In the case where the average thickness of the protective film is less than the lower limit, breakage may easily occur, particularly during the manufacturing process. In contrast, in the case where the average thickness of the protective film exceeds the upper limit, the thickness of the flexible printed circuit board may be unnecessarily increased.

The adhesive constituting the adhesive layer is not particularly limited, but is preferably an adhesive having excellent flexibility and heat resistance. Examples of such adhesives include various resin-based adhesives such as epoxy, polyimide, polyester, phenolic, polyurethane, acrylic, melamine, and polyamideimide, and the like.

The lower limit of the average thickness of the adhesive layer is preferably 5 μm, and more preferably 10 μm. On the other hand, the upper limit of the average thickness of the adhesive layer is preferably 50 μm, and more preferably 40 μm. In the case where the average thickness of the adhesive layer is less than the lower limit, the adhesive strength of the front surface protective layer 5 and the back surface protective layer 6 may become insufficient. On the other hand, in the case where the average thickness of the adhesive layer exceeds the upper limit, the flexible printed circuit board may become excessively thick.

As the solder resist for the front surface protective layer 5 and the back surface protective layer 6, a single layer structure such as a photosensitive solder resist or a thermosetting solder resist may be used, or a dry film solder resist including a base film and a resist layer may be used.

Examples of the main component of the solder resist (in the case of a dry film solder resist, the main component of the resist layer) include epoxy resin, polyimide, and silicone resin. Among them, epoxy resins, particularly epoxy acrylate resins are preferably used. As the base film of the dry film solder resist, for example, polyimide or the like can be used.

The lower limit of the average thickness of the solder resist on the front surface conductive pattern 3 and the back surface conductive pattern 4 is preferably 3 μm, and more preferably 5 μm. On the other hand, the upper limit of the average thickness of the solder resist on the front surface conductive pattern 3 and the back surface conductive pattern 4 is not particularly limited, but is preferably 100 μm, and more preferably 50 μm. In the case where the average thickness of the solder resist on the front surface conductive pattern 3 and the back surface conductive pattern 4 is less than the lower limit, the protection of the front surface conductive pattern 3 and the back surface conductive pattern 4 may become insufficient. In contrast, in the case where the average thickness of the solder resist on the front surface conductive pattern 3 and the back surface conductive pattern 4 exceeds the upper limit, the flexibility of the printed circuit board may become insufficient.

< IC chip >

Examples of the IC chip 14 include an IC chip constituting a part of a circuit formed at least partially by the flexible printed circuit board 1, and include an IC chip controlling a display panel or the like connected to the narrow pitch connection portion 15.

The IC chip 14 includes terminals having at least an outer surface formed of gold, and these terminals are connected to the IC chip mounting pads 17 of the second conductive patterns 10 by eutectic bonding.

< advantages >

As described above, since the front side first conductive pattern 8 is coated with the gold coating layer 7 and the rear side first conductive pattern 12 is coated with the gold coating layer 11, the flexible printed circuit board 1 can be electrically connected to another device or circuit easily and reliably by ensuring the conductivity of the outer surfaces of the front side first conductive pattern 8 and the rear side first conductive pattern 12.

In addition, in the flexible printed circuit board 1, since the second conductive pattern 10 is coated with the tin coating layer 9, the terminal of the IC chip 14 can be easily and reliably mounted by the eutectic reaction.

Therefore, as shown in fig. 5, in the flexible printed circuit board 1, in a state where an IC for driving the display panel is mounted as the IC chip 14 on the IC chip mounting pad 17 of the second conductive pattern 10, the narrow-pitch connection portion 15 of the front surface first conductive pattern 8 can be easily, reliably and directly connected to the terminal of the display panel DP as another device, and the wide-pitch connection portion 16 of the rear surface first conductive pattern 12 can be easily, reliably and directly connected to the terminal of the main printed circuit board MPC where the main circuit of the electronic device is formed.

In the flexible printed circuit board 1, the IC chip 14 is mounted on the IC chip mounting pad 17 of the second conductive pattern 10 in advance. For example, with the tin coating 9 of the second conductive pattern 10, when heat is applied when connecting a terminal of another circuit or the like to the narrow-pitch connection portion 15 or the wide-pitch connection portion 16, tin may form an alloy with copper forming the second conductive pattern 10, and connectivity may be reduced. However, by mounting the IC chip 14 on the IC chip mounting pad 17 in advance, connection failure of the IC chip 14 can be prevented.

[ method of manufacturing Flexible printed Circuit Board ]

The flexible printed circuit board 1 of fig. 1 may be manufactured by a method of manufacturing a flexible printed circuit board according to one embodiment of the present disclosure.

The method of manufacturing a flexible printed circuit board includes: a step of forming conductive patterns (a front surface conductive pattern 3 and a back surface conductive pattern 4) on the insulating base film 2 (a conductive pattern forming step); a step of coating a part of the front surface conductive pattern 3 and the back surface conductive pattern 4 with gold by electroless plating (electroless gold plating step); a step of coating different portions of the front surface conductor pattern 3 and the back surface conductor pattern 4 with tin by electroless plating after the electroless gold plating step (electroless tin plating step); a step of laminating a front surface protective layer 5 and a back surface protective layer 6 on portions of the front surface conductive patterns 3 and the back surface conductive patterns 4 which are not covered with gold or tin after the electroless tin plating step (protective layer laminating step); and a step of eutectic-bonding the terminals of the IC chip 14 to the front surface conductive pattern 3 coated with tin (eutectic bonding step).

(conductive pattern formation step)

In the conductive pattern forming step, for example, the front surface conductive patterns 3 and the back surface conductive patterns 4 are formed on the front surface and the back surface of the base film 1 by a known method such as a subtractive method or a semi-additive method.

In a typical subtractive method, a metal layer is laminated on the front and back surfaces of the base film 2 by, for example, adhesion of a metal foil, deposition of a metal, sintering of fine metal particles, metal plating, or the like, and a resist pattern is formed at portions of the metal layer corresponding to the desired front conductive patterns 3 and the desired back conductive patterns 4, and is etched to form the front conductive patterns 3 and the back conductive patterns 4. In addition, in the semi-additive method, thin seed layers are formed on the front and back surfaces of the base film 2 by, for example, vapor deposition of a metal, sintering of fine metal particles, electroless plating of a metal, or the like, resist patterns having openings corresponding to the desired front surface conductive patterns 3 and the desired back surface conductive patterns 4 are formed on the surfaces of the seed layers, and the front surface conductive patterns 3 and the back surface conductive patterns 4 are formed by electroplating the seed layers exposed in the openings of the resist patterns.

(electroless gold plating step)

The electroless gold plating step may include a step of forming a resist pattern covering portions of the front surface conductive pattern 3 and the back surface conductive pattern 4 other than the portions to be coated with the gold coat layer 7 and the gold coat layer 11, a step of dipping an intermediate product of the flexible printed circuit board having the resist pattern formed thereon in an electroless gold plating solution, and a step of peeling off the resist pattern.

(electroless tin plating step)

The electroless tin plating step may include a step of forming a resist pattern covering portions of the front surface conductive pattern 3 and the back surface conductive pattern 4 other than the portion to be coated with the tin coating 9, a step of dipping the intermediate product of the flexible printed circuit board 1 having the resist pattern formed thereon in an electroless tin plating solution, and a step of peeling off the resist pattern. In addition, the electroless tin plating step may include a step of heat-treating the intermediate product of the flexible printed circuit board 1 to suppress whisker generation in the tin coating 9.

The heat treatment temperature of the heat treatment step may be, for example, 100 ℃ or more and 140 ℃ or less. The heat treatment time in the heat treatment step may be, for example, one hour or more and three hours or less. It should be noted that in the case where the heat treatment is performed under the above-described heat treatment conditions, the average thickness of the one or more second regions 19 decreases in a range of about 0.1 μm or more and 0.4 μm or less from the outer surface of the tin coating layer 9. Therefore, in the step of immersion in electroless tin plating solution, the immersion time is adjusted so as to form the tin plating layer 9 having a thickness in which the reduction amount is previously considered.

(protective layer lamination step)

The protective layer laminating step performs lamination using a known method such as a coating layer, a solder resist, or the like.

(eutectic bonding step)

In the eutectic bonding step, the terminals of the IC chip 14 and the IC chip mounting pads 17 of the second conductive patterns 10 are connected by eutectic bonding. The eutectic bonding may be achieved by thermocompression bonding.

The lower limit of the temperature of the thermal compression bonding is preferably 250 ℃ and more preferably 270 ℃. On the other hand, the upper limit of the temperature of the thermal compression bonding is preferably 500 ℃ and more preferably 470 ℃. In the case where the temperature of the thermocompression bonding is lower than the lower limit, the bonding strength of the terminals of the IC chip 14 and the IC chip mounting pads 17 may be insufficient. In contrast, in the case where the temperature of the thermal compression bonding exceeds the upper limit, the flexible printed circuit board 1 may be deteriorated by heating.

The lower limit of the pressure of the thermocompression bonding is preferably 2MPaG, and more preferably 5 MPaG. On the other hand, the upper limit of the pressure of the thermocompression bonding is preferably 50MPaG, and more preferably 30 MPaG. In the case where the pressure of the thermocompression bonding is less than the lower limit, the bonding strength of the terminals of the IC chip 14 and the IC chip mounting pads 17 may be insufficient. In contrast, in the case where the pressure of the thermal compression bonding exceeds the upper limit, the flexible printed circuit board 1 may deteriorate.

The lower limit of the time of the thermal compression bonding is preferably 0.2 seconds, and more preferably 0.4 seconds. On the other hand, the upper limit of the time of the thermal compression bonding is preferably 20 seconds, and more preferably 10 seconds. In the case where the time for the thermal compression bonding is less than the lower limit, the bonding strength of the terminals of the IC chip 14 and the IC chip mounting pads 17 may be insufficient. In contrast, in the case where the time of the thermal compression bonding exceeds the upper limit, the production efficiency of the flexible printed circuit board 1 may be lowered, or the flexible printed circuit board 1 may be deteriorated due to heating.

According to the method of manufacturing the flexible printed circuit board 1, as described above, the flexible printed circuit board 1 capable of being electrically connected to another circuit or an IC chip easily and reliably can be manufactured.

[ second embodiment ]

Fig. 6 and 7 show a flexible printed circuit board 1a according to an embodiment of the present invention different from that of fig. 1. The flexible printed circuit board 1a further includes an insulating base film 2a, front surface conductive patterns 3a laminated on the front surface of the base film 2a, and a front surface protective layer 5a partially covering the front surface conductive patterns 3 a.

The configurations of the base film 2a, the front surface conductive patterns 3a, and the front surface protective layer 5a in the flexible printed circuit board 1a of fig. 6 may be similar to those of the base film 2, the front surface conductive patterns 3, and the front surface protective layer 5 in the flexible printed circuit board 1 of fig. 1 except for the planar shapes. Therefore, with the flexible printed circuit board 1a in fig. 6, the same components as those of the flexible printed circuit board 1 in fig. 1 are denoted by the same reference numerals, and the duplicated description is omitted.

The front side conductive pattern 3a includes a front side first conductive pattern 8a coated with a gold coating layer 7, and includes a second conductive pattern 10 coated with a tin coating layer 9.

The front surface first conductive pattern 8a and the second conductive pattern 10 are present at the portion exposed from the front surface protective layer 5 a. In other words, the gold coat layer 7 or the tin coat layer 9 is laminated on the portion of the front surface conductive pattern 3a exposed from the front surface protective layer 5 a. On the other hand, at the portion of the front surface conductive pattern 3a coated with the front surface protective layer 5a, the gold coat layer 7 and the tin coat layer 9 may not be laminated.

In addition, the flexible printed circuit board 1a includes the IC chip 14 and the electronic component 20 mounted on the front surface conductive pattern 3 a.

(first conductive pattern)

The front surface first conductive pattern 8a includes a narrow pitch connection portion 15 at which a plurality of terminals are arranged at a constant pitch, and electronic component mounting pads 21 having a planar shape and an arrangement corresponding to the terminals of the electronic component 20.

For example, the narrow pitch connection portion 15 is connected to a terminal of another device such as a display panel. In addition, the flexible printed circuit board 1a constitutes a main circuit that controls another device such as a display panel by connecting the terminals of the electronic component 20 to the pads for electronic component mounting, the other device being connected to the narrow-pitch connection portion 15.

(second conductive pattern)

The second conductive pattern 10 includes IC chip mounting pads 17 having a planar shape and arrangement corresponding to the terminals of the IC chip 14. The IC chip 14 is connected to the circuit of the flexible printed circuit board 1a by connecting the terminals of the IC chip 14 to the IC chip mounting pads 17.

[ other examples ]

The embodiments disclosed above should be considered in all respects as illustrative and not restrictive. The scope of the invention is not limited to the configurations of the above-described embodiments but is indicated by the claims, and all changes within the meaning and range equivalent to the claims are intended to be embraced therein.

In the flexible printed circuit board, the first conductive pattern may be coated with nickel or a rust-proof material (coated with a nickel coating or a rust-proof coating) instead of gold. It should be noted that the rust inhibitive coating can be formed by coating a commercially available rust inhibitive material.

In the flexible printed circuit board, the second conductive pattern may be coated with solder (coated with a solder coating) instead of tin.

In the flexible printed circuit board, the second conductive patterns may be formed on both front and back sides of the base film. In addition, the second conductive pattern may include a wide pitch connection portion. In this case, the IC chip is connected to the second conductive pattern by solder.

The flexible printed circuit board may be a single-sided circuit board without the second conductive pattern, or may be a multi-layered circuit board including a plurality of base films and additional conductive patterns laminated between the base films.

On the flexible printed circuit board, the IC chip may not be mounted on the IC chip mounting pad.

For a flexible printed circuit board, a surface protective layer and a back surface protective layer are not necessary.

In the method of manufacturing the flexible printed circuit board, the gold coating (or nickel coating) and the tin coating (or solder coating) may be formed by electrolytic plating (electroplating) or other methods.

Description of the reference numerals

1. 1 a: flexible printed circuit board

2. 2 a: base film

3. 3 a: front side conductive pattern

4: back side conductive pattern

5. 5 a: front protective layer

6: back protective layer

7: gold coating

8: front first conductive pattern

8 a: first conductive pattern

9: tin coating

10: second conductive pattern

11: gold coating

12: back first conductive pattern

13: through hole

14: IC chip

15: narrow-pitch joint

16: wide-pitch joint

17: pad for mounting IC chip

18: first region

19: second region

20: electronic component

21: pad for mounting electronic component

DP: display panel

MPC: main printed circuit board