WO2013008567A1

WO2013008567A1 - Flexible printed circuit, method for manufacturing same, flexure and electronic device

Info

Publication number: WO2013008567A1
Application number: PCT/JP2012/064865
Authority: WO
Inventors: 辰珠朴; 上田　宏; 正也柿本
Original assignee: 住友電工プリントサーキット株式会社
Priority date: 2011-07-08
Filing date: 2012-06-11
Publication date: 2013-01-17
Also published as: JP2013020667A

Abstract

A cover insulating layer (4) covers the edge portion of each terminal (3) in an interconnection pad (K) and a wiring pattern (11) on the base side of the terminal together with a base insulating layer (2) therearound. The terminal is exposed only at an opening (7) which is opened at a position where the cover insulating layer faces the terminal and the bottom surface (7b) of the opening is comprised of only the upper surface (3a) of the terminal. The end face of the cover insulating layer (4) and the end face of the base insulating layer (2) are flush with each other so as to form an end face (E) of the interconnection pad.

Description

Flexible printed wiring board, manufacturing method thereof, flexure, and electronic device

The present invention relates to a flexible printed circuit (FPC), a manufacturing method thereof, a flexure, and an electronic device. More specifically, the present invention relates to a flexible printed wiring board having connection pads in which connection terminals are arranged at high density, a manufacturing method thereof, a flexure for transmitting signals of magnetic elements of a hard disk drive, and an electronic device. It is.

A lot of flexible printed wiring boards are used for electronic devices such as portable terminals, and those having characteristics suitable for the electronic devices have been developed. In particular, many developments have been made on flexures, which are flexible printed wiring boards that are used in hard disk drives (HDDs) and transmit signals from magnetic heads (for example, Patent Documents 1 to 3). The flexure is required to have not only electrical properties, but also delicate elastic properties such as mechanical properties for using an airflow flowing through a minute space between a magnetic head and a CD. In addition, with these delicate characteristics, the HDD is always required to be downsized in the electronic device. For this reason, the arrangement of magnetic heads is constantly increasing in density.

JP 2008-287835 A JP 2009-223777 A JP 2011-49316 A

The flexure is composed of a suspension metal plate that is supported with a predetermined elasticity, a base insulating layer, a conductive layer that forms wiring and terminals, and a cover insulating layer. In the flexible printed wiring board, an opening is formed in the connection pad to expose the terminal. In the opening, the terminal is exposed, and a two-layered plating layer including an Ni layer and an Au layer is formed on the exposed terminal, and is soldered to a terminal such as a head slider on which the magnetic head is disposed. It will be.
5A and 5B show a connection pad portion K of a conventional flexure, FIG. 5A is a plan view, and FIG. 5B is a cross-sectional view taken along line VB-VB. In the connection pad portion K, all the terminals 103 are exposed from the insulating cover layer 104 and extend in parallel on the metal plate 101 / base insulating layer 102 toward the terminals on the head slider side. In this structure, the cover insulating layer 104 covers only the wiring pattern 111 connected to the terminal 103 in an extreme case. The Ni / Au two-layer plating 103 a is formed on the entire terminal 103 exposed from the cover insulating layer 104.
6A to 6C show a method of manufacturing the flexure shown in FIGS. 5A and 5B. In the conventional terminal structure, as shown in FIG. 6A, the base insulating layer 102 and the cover insulating layer 104 are in contact with each other. At that location, as shown in FIG. 6B, a special technique was used to remove only the cover insulating layer 104 and leave the base insulating layer 102 to expose the terminal 103 having a certain length. That is, in the states A to C of FIG. 6, the insulating resin layer forming the cover insulating layer 104 is in a state of a chemically unstable precursor before the crosslinking is completed, while the base insulating layer 102 is Crosslinking is completed to obtain a chemically stable resin layer. Then, only the insulating cover layer 104 was removed by exposure / development to obtain the state of FIG. 6C. With this method, the structure in which each terminal 103 extends in parallel on the insulating base layer 102 so as to face a head slider (not shown) has been realized. The manufacturing method will be described later in comparison with the present invention.
However, as a result of promoting the downsizing of the HDD, the use of the connection pad portion structure in the flexure described above has resulted in a situation where insulation cannot be ensured.

In electronic devices, there is always a demand for downsizing the connection structure of the flexible printed wiring board, and it is important to ensure insulation between the wirings in the connection pad portion, not limited to the above flexure. That is, generally, a flexible printed wiring board is required to have a structure that can reliably maintain insulation between terminals of the connection pad portion.

The present invention provides a flexible printed wiring board, a manufacturing method thereof, a flexure, and an electronic device that can ensure insulation between terminals in a connection pad portion in which a plurality of terminals are arranged at high density. Objective.

The flexible printed wiring board of the present invention includes a connection pad portion. The flexible printed wiring board includes a metal plate, a base insulating layer, a wiring pattern for forming a wiring or the like in contact with the base insulating layer, and a cover insulating layer covering the wiring pattern. A plurality of terminals extending from the wiring pattern and terminating on the base insulating layer are arranged. In each terminal, the insulating cover layer covers the terminal end of the terminal and the wiring pattern on the base side of the terminal together with the surrounding insulating base layer, and the insulating cover layer corresponds to the terminal. The terminal is exposed only in the opening that is opened at, and the bottom surface of the opening is constituted only by the upper surface of the terminal. Further, the end face of the insulating cover layer and the end face of the insulating base layer are aligned to form the end face of the connection pad portion.

According to said structure, there is no common opening part in a connection pad part, and an opening part (window) is provided for every terminal. For this reason, one terminal is located in one opening, and the upper surface of the one terminal forms the bottom of the opening. The connection partner is soldered to the bottom surface of the opening for each electrode, for example. Therefore, in the connection pad part, the opening part provided in one terminal is located in a line.
As a result, even if the distance between the terminals is reduced to form a high-density array, it is possible to prevent a short circuit from occurring between adjacent terminals. Moreover, the durability of the entire connection pad portion can be improved.
In addition, the insulating cover layer is different from the insulating base layer in the cross-linked state (polymerization progress state), for example, so that it is not necessary to pattern only the insulating cover layer by development. That is, the insulating base layer need not be a removal (development) stopper for the removal (patterning) of the insulating cover layer. In the present invention, the end of the connection pad portion may be removed by etching the cover insulating layer and the base insulating layer together. For this reason, it is not necessary to use photosensitive polyimide or a special developer for patterning the insulating cover layer, and the cost of the material can be reduced. A great man-hour reduction can be obtained in terms of man-hours.

At the end of the connection pad portion, the end of the metal plate is preferably located away from the end surface of the connection pad portion, and the back surface of the base insulating layer is exposed at the end of the back surface of the connection pad portion.
As a result, when the connection partner is connected with solder or the like, it is possible to avoid a situation in which the metal plate and the terminal or the like are conductively connected with the solder even if a solder control failure occurs.

The openings may have an arrangement pitch of 150 μm or less and a length along the extending direction of the wiring of the openings of 75 μm or less.
Reflecting the recent increase in the density of signal wiring, the terminal arrangement of the connection pad portion is also increased in density, and the terminals are also miniaturized. In such a high-density arrangement of minute terminals, a flexible printed wiring board including the connection pad portion having the above-described structure is extremely effective in securing insulation between terminals. That is, in the case of the connection pads having the above arrangement pitch and terminal length, good insulation is secured in the flexible printed wiring board of the present invention, which is preferably applied.

The main component of the resin layer forming the cover insulating layer can be a non-photosensitive resin.
According to the structure of the connection pad portion, it is not necessary to use the insulating base layer as a stopper for removing the insulating cover layer with a developer in patterning the insulating cover layer. Thereby, it is not necessary to use a photosensitive resin for the cover insulating layer. The cover insulating layer and the base insulating layer can be patterned by etching in a simple and clear process using a non-photosensitive resin for the cover insulating layer. As a result, it is not necessary to use an expensive photosensitive resin or a developer thereof, and the manufacturing process can be simplified, so that material costs, man-hours, and manufacturing time can be reduced.

The insulating cover layer contains a non-photosensitive polyimide precursor ink as a non-photosensitive resin liquid. The insulating cover layer contains 3,3 ′, 4,4′-biphenyltetracarboxylic anhydride (BPDA) as a main component, pyromellitic dianhydride (PMDA) as an acid component. The insulating cover layer has p-phenylenediamine (PDA), 2,2′-dimethyl-4,4′-diaminobiphenyl (mTBHG), and 2,2′-bis (trifluoromethyl) -4, as diamine components. 4'-diaminobiphenyl (TFMB) can be included.
This makes it possible to impart good etching properties essential in the present manufacturing method by using a flexible polyimide resin and setting the thermal expansion coefficient within a predetermined range (15 ppm / ° C. to 20 ppm / ° C.). Any property is a property of the polyimide resin after the curing treatment. Etchability is very important because, at the same etching opportunity, an opening is provided in the insulating cover layer and the end face of the insulating cover layer / base insulating layer is formed. In particular, the opening can be formed on the terminal with high accuracy by ensuring good etching properties by the monomer composition and an etching stopper by metal (terminal).

The non-photosensitive polyimide precursor ink can include 1,3-bis (3-aminopropyl) tetramethyldisiloxane (APDS).
As a result, the adhesive force can be increased, and the opening can be prevented from being displaced and contributed to a highly accurate opening.

The flexure of the present invention is any one of the above-described flexible printed wiring boards, and is characterized in that it is connected to a magnetic head of a hard disk drive (HDD) at a connection pad portion.
With the above configuration, in order to reduce the size of the magnetic head and increase the signal density, etc., the connection pads of the magnetic head and the connection pads of the flexure that are arranged in a high density are connected to each other by the corresponding terminals. It can be connected while securing. Moreover, it can be set as the flexure excellent in economical efficiency.

An electronic apparatus according to the present invention includes any one of the flexible printed wiring boards described above.
By using any of the flexible printed wiring boards described above, good durability can be obtained while maintaining insulation between terminals arranged at high density. Moreover, since the structure of the connection pad portion itself and the manufacturing process are simplified, high economic efficiency can be obtained.

The method for producing a printed wiring board of the present invention produces a flexible printed wiring board having a connection pad portion. The manufacturing method includes a step of preparing a base sheet having a base insulating layer on a metal plate, a step of forming a wiring pattern including a terminal in contact with the base insulating layer, and a cover insulation covering the wiring pattern including the terminal. Forming a layer, applying a non-photosensitive resin liquid so as to overlap the base insulating layer, drying the coated non-photosensitive resin liquid, and then thermally curing the base insulating layer and Etching the heat-cured insulating cover layer. In the etching step, an opening is formed in the insulating cover layer so that the terminal serves as an etching stopper, the terminal forms the bottom surface of the opening, and the end surface of the insulating cover layer and the end surface of the insulating base layer are aligned. Thus, the cover insulating layer and the base insulating layer are etched so that the metal plate serves as an etching stopper so as to form the end face of the connection pad portion.

In the above manufacturing method, the opening on the terminal with respect to the insulating cover layer and the patterning of the insulating base layer / cover insulating layer are performed by etching in parallel. The opening etching stopper is in charge of the terminal, and the base insulating layer / cover insulating layer etching stopper is in charge of the metal plate. Since these stoppers are made of metal and the etching metal / resin selectivity is high, the base insulating layer and the cover insulating layer can be patterned with high accuracy. For this reason, it becomes possible to carry out fine processing (fine patterning) for forming an opening in the insulating cover layer for each terminal with high accuracy. In the case of the connection pad portion having an arrangement pitch of 200 μm or less and each terminal length of 75 μm or less as described above, the desired connection pad portion is obtained unless patterning is performed using such an etching method having high metal / resin selectivity. It ’s difficult.
When the above etching method is used, it is not necessary to pattern only the cover insulating layer in a region where the base insulating layer and the cover insulating layer are in contact with each other as in the conventional case. That is, the insulating cover layer is formed of a photosensitive resin to be a precursor that is not completely polymerized, the insulating base layer is kept in a stable state after completion of the polymerization, and it is not necessary to pattern only the insulating cover layer by development. At this time, the base insulating layer functions as a development stopper. In this conventional manufacturing method, photosensitive resin such as photosensitive polyimide is expensive, and the developer is also expensive. Also in the manufacturing process, since the insulating cover layer is developed at the precursor stage, the time restriction of the process is strong and the number of processes increases. As a result, the conventional flexible printed wiring board having the structure of the connection pad portion has to be expensive. As described above, by using etching with high metal / resin selectivity, it is possible to reduce the material cost, the manufacturing cost, the manufacturing period, and the like while accurately forming the fine and high-density array of openings.

According to the flexible printed wiring board or the like of the present invention, it is possible to ensure insulation between terminals in a connection pad portion in which a plurality of terminals are arranged with high density. Further, the material cost and the manufacturing cost can be reduced, and the manufacturing period can be shortened.

It is a top view which shows the flexure in embodiment of this invention. FIG. 2 is a plan view showing a connection pad portion on the head slider side of the flexure of FIG. 1. FIG. 2 is a cross-sectional view taken along the line IIB-IIB, showing a connection pad portion on the head slider side of the flexure of FIG. It is a perspective view showing the connection pads of the head slider and the flexure, and showing the positional relationship of the connection pads of the head slider and the flexure. It is sectional drawing which shows the connection pad of a head slider and a flexure, and shows the state electrically connected by dripping a solder drop. 1 shows a flexure manufacturing method of the present embodiment, in which A is a cross-sectional view showing a state in which a wiring pattern is formed on a metal plate / base insulating layer, and B is a non-photosensitive polyimide ink for forming a cover insulating layer. Sectional drawing which shows the processed state, C is sectional drawing which shows the state which patterned the cover insulating layer and the base insulating layer from the same etching process, D is sectional drawing which shows the state which etched the metal plate. It is a top view which shows the connection pad part of the conventional flexure. FIG. 10 is a cross-sectional view taken along line VB-VB, showing a connection pad portion of a conventional flexure. A conventional manufacturing method is shown, A is a cross-sectional view showing a state where a photosensitive polyimide ink for forming a cover insulating layer is applied, B is a cross-sectional view showing a state where the cover insulating layer is patterned by exposure and development, C FIG. 3 is a cross-sectional view showing a state where a base insulating layer is patterned by etching.

1 metal plate, 1e end face of metal plate, 2 base insulating layer, 3 terminal, 3a terminal upper surface (or Ni / Au plating layer), 4 cover insulating layer, 7 opening, 7b opening bottom, 10 flexure, 11 Wiring pattern, 19 Carriage arm, 20 Head slider, 20k Head slider connection pad, 23 Head slider terminal, 25 Solder, 50 Head suspension assembly, E Terminal plane, K Connection pad, P terminal pitch, 101 Metal plate , 102 Base insulating layer, 103 terminals, 104 cover insulating layer, 111 wiring pattern.

FIG. 1 is a diagram showing a flexure 10 and a head suspension assembly 50 including the flexure according to an embodiment of the present invention. A head suspension assembly 50 is attached to a carriage arm 19 that rotates the magnetic head along a track of the HDD. The flexure 10 that is a flexible printed wiring board is used to transmit a signal that is input and electromagnetically converted by a magnetic head. For this reason, the flexure 10 is provided from the head slider 20 on which the magnetic head is disposed to the outer peripheral surface of the support shaft at the base of the carriage arm (not shown), and is disposed over the connection substrate unit for connection to the outside. A metal plate 1 having a certain spring elasticity is used for the flexure 10, and a wiring pattern 11 for signal transmission described above is included in an insulating layer. The flexure 10 and other components of the head suspension assembly 50 are provided with a metal material having a certain elasticity so that the head slider 20 floats stably at a predetermined height when a magnetic disk (not shown) rotates and an air current flows. Yes. The flexure 10 includes a connection pad portion K for connecting to an electrode in the magnetic head at an end facing the head slider 20. The feature of this embodiment is the structure and manufacturing method of the connection pad portion K on the magnetic head side of the flexure 10.

2A and 2B show the connection pad portion K of the flexure 10 in the present embodiment, FIG. 2A is a plan view, and FIG. 2B is a cross-sectional view taken along the line IIB-IIB. The connection pad portion K is covered with the insulating cover layer 4 except for the opening 7. That is, except for the small window 7, it is covered with the insulating cover layer 4. A terminal 3 having an enlarged width is located at the tip of the wiring 11. Although one terminal 3 has one opening (window) 7, the entire area of the opening 7 is set within the area of the terminal 3 in plan view. This is because the terminal 3 is used as an etching stopper when the cover insulating layer 4 is etched, as will be described later in the manufacturing method. Two plating layers of Ni / Au are provided on the upper surface 3 a of the terminal 3 exposed in the opening 7. In the description of the present invention, the upper surface 3a of the terminal 3 and the plating layer formed on the surface are specified as the upper surface 3a or the plating layer 3a without distinction unless otherwise specified.
The size in the connection pad part K is illustrated as follows. This is just an example. A higher density array may be used.
(1) Pitch P between terminals 3: 150 μm or less, for example, about 100 μm. This is required from the HDD design side. As shown in FIG. 3A and FIG. 3B, it naturally matches the terminal arrangement of the head slider 20.
(2) Pitch of the openings 7: The same pitch as the terminals, 150 μm or less, for example, about 100 μm.
(3) Terminal 3: The length in the longitudinal (extending) direction, which is a direction orthogonal to the pitch direction, is, for example, about 100 μm and the width is about 50 μm.
(4) Opening 7: The length in the longitudinal direction is about 50 μm, and the length in the width direction is 40 μm.
The arrangement of the terminals 3 and the openings 7 with a pitch of 150 μm or less is very high density, and is rare as a connection between connection pads of an electronic device that is conductively connected with solder.
As can be seen from FIG. 2A, since the terminals 3 are exposed only at the openings 7, the insulation between the terminals 3 can be enhanced regardless of the high-density arrangement. Further, when conducting conductive connection with the head slider 20, it is possible to make it difficult to cause a short circuit between adjacent terminals, for example. Further, the durability of the connection pad portion K itself can be significantly improved as compared with the conventional connection pad portion shown in FIG.

The following features can be seen from the cross-sectional view of FIG. 2B.
(F1) When the opening 7 is opened in the insulating cover layer 4, the terminal 3 of the conductive layer made of metal can be used as an etching stopper by etching. In general, since metal / resin can be etched with high selectivity in etching, highly accurate etching can be performed.
(F2) At the end surface E of the connection pad portion K, the end surfaces of the cover insulating layer 4 and the base insulating layer 2 are aligned. Although the metal plate 1 is in a position retracted inward from the end surface E in the final stage of being a product, it should have been extended before the end surface E during manufacture. Accordingly, the end surface E can also be made the end surface E by aligning the end surfaces of the cover insulating layer 4 and the base insulating layer 2 by etching using the metal plate 1 as an etching stopper.
The formation of the end surface E and the formation of the opening 7 can be performed simultaneously in the same etching opportunity. This etching process will be described in detail later.
(F3) As shown in FIG. 2B, the Ni / Au two-layer plating is limited to the bottom surface 7 b of the opening 7. For this reason, the material cost of expensive gold plating can be reduced significantly.
In addition to the above, the flexure 10 of the present embodiment has many advantages as a manufacturing method including the above (F1) to (F3).

3A and 3B are diagrams for explaining an example of conductive connection between the connection pad portion K of the flexure 10 and the connection pad 20k of the head slider 20. FIG. FIG. 3A is a perspective view showing the relationship between the position and posture of the connection pad 20k of the head slider 20 and the connection pad portion K of the flexure 10, and FIG. 3B is a conductive connection between the

terminals

3 and 23 by solder 25. It is sectional drawing of the state which carried out. There are many forms of connection between the head slider 20 and the flexure 10, and FIGS. 3A and 3B show an example only.
As shown in FIG. 3A, the connection pad 20 k of the head slider 20 in the present embodiment is provided on a side surface facing the connection pad portion K of the flexure 10. The terminal 23 of the connection pad 20k of the head slider 20 and the bottom surface 7b of the opening 7 of the flexure 10 or the terminal 3 (3a) are preferably arranged so as to form an intersection angle close to a right angle. As shown in FIG. 3B, when the solder droplets are dropped, the corner concave portion forming the crossing angle is set to the top side, and the molten solder droplet is dropped into the corner concave portion, so that the terminal 3 (3a) and the head slider are dropped. The terminals 23 of the 20 connection pads 20k are conductively connected. When a solder drop is dropped on the corner recess, a funnel-shaped dropping tool that concentrates on the terminal to be dropped, or a blocking wall is inserted between the opening 7 and partially in the adjacent opening. However, it is better to use a jig with no room for solder drops.

FIG. 4 is a diagram showing a method of manufacturing the flexure of the present embodiment, particularly a method of forming the connection pad portion K. First, a laminate in which the base insulating layer 2 is disposed on the metal plate 1 is prepared, and a wiring pattern layer including the terminals 3 is formed on the base insulating layer 2.
For the metal plate 1, a metal foil or a metal thin plate is used, for example, stainless steel, 42 alloy (Fe—Ni alloy) is preferably used. The thickness of the metal plate 1 is preferably, for example, 10 μm to 60 μm, particularly 15 μm to 30 μm.
For the base insulating layer 2, it is preferable to use a polyimide resin such as polyimide or polyamideimide, or a polyamide resin in consideration of flexibility, thermal expansion coefficient, and the like. The insulating base layer 2 has a thickness of, for example, 2 μm to 30 μm, preferably 5 μm to 20 μm.
For example, copper, nickel (Ni), gold, solder, or an alloy thereof is used as the conductor layer for forming the wiring pattern layer including the terminals 3, and copper is preferably used. In order to form the wiring pattern of the copper layer, either a subtractive method or an additive method may be used, but in order to form a fine pattern with high accuracy, it is preferable to form by an additive method. In the additive method, a seed film (seed film) made of a conductive thin film (not shown) is formed on the base insulating film 2 by a sputtering method or the like. The seed film is preferably made of chromium or copper. In particular, a chromium thin film and a copper thin film are preferably laminated sequentially by sputtering. Here, the thickness of the chromium thin film is preferably about 10 to 60 nm, for example, and the thickness of the copper thin film is preferably about 50 to 200 nm, for example.
A resist pattern for plating having a pattern opposite to the wiring pattern is formed on the seed film. The plating resist is formed as a resist pattern by a known method using, for example, a dry film resist. Next, a wiring pattern including the terminals 3 is formed by plating in a region where the plating resist is not formed. The plating may be electrolytic plating or electroless plating, but electrolytic plating is preferable, and electrolytic copper plating is particularly preferable. The thickness of the wiring pattern layer including the terminal by plating, that is, the copper layer is, for example, 2 μm to 25 μm, preferably 5 μm to 20 μm. The width of the wiring is, for example, 10 μm to 500 μm, preferably 30 μm to 300 μm. The gap between the wirings is, for example, 10 μm to 1000 μm, preferably 10 μm to 500 μm.
The conventional flexure manufacturing method shown in FIG. 6 is the same as the manufacturing method of the present embodiment until this stage.

After the plating resist is removed by a known etching method, a cover insulating layer 4 for covering the wiring pattern layer is formed. Conventionally, photosensitive polyimide has been used for the cover insulating layer 4. However, in this embodiment, non-photosensitive polyimide is used for the cover insulating layer 4. First, the non-photosensitive polyimide ink is applied to the wiring pattern including the terminals 3 and the base insulating layer (polyimide layer) 2. A polyimide layer (cover insulating layer 4) formed from this non-photosensitive polyimide ink through a drying and curing (heating) process has the following characteristics.
(A1) Coefficient of thermal expansion (CTE): 15 ppm / ° C. to 20 ppm / ° C.
(A2) Good etching property and adhesion The above thermal expansion coefficient and good etching property are realized.
In order to obtain the above (A1) and (A2), the following polyimide monomer composition was synthesized to prepare a polyimide ink.
<Monomer composition>:
(1) Acid component: BPDA (3,3 ', 4,4'-biphenyltetracarboxylic anhydride) is added with PMDA (pyromellitic dianhydride) as the main component.
(2) Diamine component: PDA (p-phenylenediamine) and mTBHG (2,2'-dimethyl-4,4'-diaminobiphenyl), TFMB (2,2'-bis (trifluoromethyl) -4,4 ' -Diaminobiphenyl).
(3) Component for improving adhesion: APDS (1,3-bis (3-aminopropyl) tetramethyldisiloxane) was added.
As shown in FIG. 4B, the polyimide ink is coated and then dried and subjected to a thermosetting treatment. The thermal effect treatment is performed by heating to 250 ° C. or higher, for example, heating to 350 ° C. Thereafter, by using the dry film resist, the opening 7 is opened by the same etching, and the end surface E of the connection pad portion K is formed. In this etching, plasma etching, RIE (Reactive Ion Etching), dry etching such as sputtering, wet etching using a chemical solution, and laser processing can be used.

In the conventional flexure manufacturing method, in the process corresponding to FIG. 4B of the present embodiment, as shown in FIG. 6A, a photosensitive polyimide ink is applied and dried to form the cover insulating layer 104. . In drying, depending on the positive type and the negative type, heating is performed at about 130 ° C. to 150 ° C. so that polyimide crosslinking (polymerization) is not completed in a predetermined region to be removed. In the next exposure and development process, the region to be removed is removed and the cover insulating layer 104 is patterned (B in FIG. 6). By this exposure / development, the cover insulating layer 104 is almost removed except for the wiring pattern 111 as shown in FIG. 5A. All of the terminals 103 are exposed. As the developer, it is preferable to use an organic one and adjust the blending so that the sharpness of patterning becomes high.
In the patterning of the insulating cover layer 104 by the above development, the insulating base layer 102 is a stable polyimide layer that has been polymerized, whereas the insulating cover layer 104 is an unstable precursor, Pattern. At this time, the selectivity of the insulating base layer 102 functioning as a development stopper and the insulating cover layer 104 to be removed is not sufficiently high as the etching selectivity between the metal and the resin. As a result, a sufficiently high dimensional accuracy could not be pursued in patterning. In other words, it has been difficult to cope with the recent trend of high-density terminal arrangement by this conventional method.
Further, the photosensitive polyimide ink and the developer are considerably more expensive than the non-photosensitive polyimide ink and the etching liquid in the present embodiment, and in the method of the present embodiment, the material cost is in the cover insulating layer and the like. If limited, it can be reduced to about a fraction of the conventional material cost.

In the conventional manufacturing method, thereafter, as shown in FIG. 6C, the base insulating layer 102 is patterned by etching using the metal plate 101 as an etching stopper. The patterning of the base insulating layer 102 using the metal plate 101 as an etching stopper is the same as the patterning of the base insulating layer 2 in the present embodiment. Conventionally, patterning of the insulating cover layer 104 by exposure / development and patterning of the insulating base layer 102 by etching are performed in two stages. However, in the present embodiment, the base insulating layer 2 is also etched at the same etching opportunity as the patterning of the cover insulating layer 4 for forming the opening 7 to form the end surface E.
Therefore, according to the present embodiment, not only the material cost but also the manufacturing process can be reduced and the manufacturing period can be shortened.

<Insulating layer etching accuracy>
As described above, the etching stopper of the opening 7 is the terminal 3 formed of a metal layer such as a copper layer, and the etching stopper of the end surface E is the metal plate 1 made of stainless steel or the like. Since the etching selectivity between the metal and the resin is high, the etching can be performed with high accuracy.
Referring to FIG. 2A, in the present embodiment, opening (window) 7 is formed by opening, for example, an opening (window) 7 having a width of 40 μm on terminal 3 having a width of 50 μm. That is, even if the opening 7 is opened without error, the allowable deviation in the width direction is only 5 μm. Such high-accuracy patterning of the insulating cover layer 4 is impossible by conventional development using a base insulating layer as a stopper. This is possible only by etching using a metal as an etching stopper.

After the insulating cover layer 4 and the insulating base layer 2 are etched to form the end surface E, the excessively extending metal plate 1 is removed by etching. By this etching, the end surface 1 e of the metal plate 1 is positioned closer to the opening 7 than the end surface E of the base insulating layer 2 and the cover insulating layer 4. As a result, it is possible to easily avoid problems such as short circuits when soldering to the head slider.

In the above embodiment, only the flexure is exemplified as the flexible printed wiring board. However, the present invention is not limited to a flexure as long as it has constituent requirements, and may be any other flexible printed wiring board.

Although the embodiments and examples of the present invention have been described above, the embodiments and examples of the present invention disclosed above are merely examples, and the scope of the present invention is the implementation of these inventions. It is not limited to the form. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

According to the flexible printed wiring board and the like of the present invention, it is possible to secure insulation between the terminals and enhance the durability of the connection pad part itself in the connection pad part in which a plurality of terminals are arranged with high density. In addition, since a normal non-photosensitive polyimide or etching method is used without using photosensitive polyimide or a corresponding developer, the material cost can be greatly reduced. In addition, since the manufacturing process can be omitted, the manufacturing cost can be reduced and the manufacturing period can be shortened.

Claims

A flexible printed wiring board having a connection pad portion,
A metal plate, a base insulating layer, and a wiring pattern for forming a wiring in contact with the base insulating layer;
A cover insulating layer covering the wiring pattern;
In the connection pad portion, a plurality of terminals extending from the wiring pattern and terminating on the insulating base layer are arranged,
In each terminal, the insulating cover layer covers the terminal portion of the terminal and the wiring pattern on the base side of the terminal together with the insulating base layer around the terminal, and the insulating cover layer corresponds to the terminal. The terminal is exposed only at the opening that opens at a position where the bottom surface of the opening is composed only of the upper surface of the terminal,
An end face of the insulating cover layer and an end face of the insulating base layer are aligned to form an end face of the connection pad portion.
At the end of the connection pad portion, the end of the metal plate is located away from the end surface of the connection pad portion, and the back surface of the base insulating layer is exposed at the end of the back surface of the connection pad portion. The flexible printed wiring board according to claim 1, wherein the flexible printed wiring board is characterized.
3. The flexible printed wiring board according to claim 1, wherein the openings have an arrangement pitch of 150 μm or less and a length of the openings in a direction orthogonal to the arrangement pitch direction is 75 μm or less. 4. .
The flexible printed wiring board according to any one of claims 1 to 3, wherein a main component of the resin layer forming the cover insulating layer is a non-photosensitive resin.
The cover insulating layer contains a non-photosensitive polyimide precursor ink as a non-photosensitive resin liquid, and has 3,3 ′, 4,4′- as a main component of pyromellitic dianhydride (PMDA) as an acid component. Biphenyltetracarboxylic anhydride (BPDA) is included, and p-phenylenediamine (PDA), 2,2′-dimethyl-4,4′-diaminobiphenyl (mTBHG), and 2,2′-bis are used as the diamine component. The flexible printed wiring board according to claim 4, comprising (trifluoromethyl) -4,4′-diaminobiphenyl (TFMB).
6. The flexible printed wiring board according to claim 5, wherein the non-photosensitive polyimide precursor ink contains 1,3-bis (3-aminopropyl) tetramethyldisiloxane (APDS).
7. The flexible printed wiring board according to claim 1, wherein the flexure is connected to a magnetic head of a hard disk drive (HDD) at the connection pad portion.
An electronic apparatus comprising the flexible printed wiring board according to any one of claims 1 to 6.
A method for producing a flexible printed wiring board comprising a connection pad portion,
Preparing a base sheet comprising a base insulating layer on a metal plate;
Forming a wiring pattern including terminals in contact with the base insulating layer;
Applying a non-photosensitive resin liquid so as to overlap the base insulating layer in order to form a cover insulating layer covering the wiring pattern including the terminals;
Drying the coated non-photosensitive resin liquid, and then thermosetting;
Etching the base insulating layer and the heat-cured cover insulating layer,
In the etching step, an opening is formed in the insulating cover layer so that the terminal serves as an etching stopper, the terminal forms a bottom surface of the opening, and an end face of the insulating cover layer and an end face of the base insulating layer And the insulating cover layer and the insulating base layer are etched so that the metal plate serves as an etching stopper so as to form an end face of the connection pad portion. .