JP4640853B2 - Printed circuit board - Google Patents

Description

  The present invention relates to a wired circuit board, and more particularly to a wired circuit board such as a suspension board with circuit.

Conventionally, a suspension board with circuit is known in which an insulating layer made of resin and a conductor pattern made of copper are sequentially formed on a metal supporting board made of stainless steel.
In such a suspension board with circuit, since the metal support board is made of stainless steel, transmission loss increases in the conductor pattern.
Therefore, in order to reduce transmission loss, a lower conductor made of copper or a copper alloy containing copper as a main component is formed on a suspension made of stainless steel, and an insulating layer, a recording-side conductor, and a lower conductor are formed on the lower conductor. It has been proposed to sequentially form the reproduction-side conductor (for example, see Patent Document 1).
JP 2005-11387 A

However, in the above proposal, the adhesion between the suspension and the lower conductor is insufficient, and it is difficult to ensure long-term reliability.
An object of the present invention is to provide a printed circuit board that is capable of reducing transmission loss with a simple layer structure, and that improves the adhesion between a metal supporting board and a metal foil and is excellent in long-term reliability. is there.

In order to achieve the above object, a wired circuit board according to the present invention includes a metal support substrate, a metal thin film formed on the metal support substrate, a metal foil formed on the metal thin film, and the metal An insulating layer formed on the foil; and a wiring formed on the insulating layer. The metal supporting substrate has an opening facing the metal foil, and an end of the metal thin film It is characterized by being formed so as to be covered with a metal support substrate.
The wired circuit board of the present invention is formed on a metal support substrate, a metal thin film formed on the metal support substrate, a metal foil formed on the metal thin film, and the metal foil. The metal support substrate has an opening facing the metal foil, and a portion of the metal thin film facing the wiring in the thickness direction. The metal support substrate is formed so as to be exposed from the metal support substrate and covered at both ends in the width direction perpendicular to the longitudinal direction of the wiring in the metal thin film.
In the wired circuit board of the present invention, it is preferable that the opening is formed by etching.
In the wired circuit board of the present invention, it is preferable that the metal supporting board is made of stainless steel and the metal foil is made of copper.

In the wired circuit board of the present invention, it is preferable that the metal thin film is formed by sputtering or electrolytic plating, and the metal foil is formed by electrolytic plating.
In the wired circuit board of the present invention, it is preferable that the wired circuit board is a suspension board with circuit.

According to the wired circuit board of the present invention, since the metal thin film is formed between the metal support substrate and the metal foil, transmission loss can be reduced by a simple layer configuration, and the metal support substrate and the metal foil can be reduced. Adhesion with the foil can be sufficiently achieved, and excellent long-term reliability can be ensured.
According to the wired circuit board of the present invention, the metal thin film is formed on the metal support substrate, and the metal foil is formed on the metal thin film. Therefore, the portion of the metal support substrate facing the metal foil In addition, when the opening is formed by etching so that the end of the metal thin film is covered with the metal support substrate, the metal thin film becomes a barrier layer, and the metal foil can be prevented from being etched. .

FIG. 1 is a cross-sectional view of an essential part showing an embodiment of a printed circuit board according to the present invention.
In FIG. 1, a wired circuit board 1 is a suspension board with circuit mounted on a hard disk drive, and a metal thin film 3 is formed on a metal supporting board 2 extending in the longitudinal direction. In addition, a metal foil 4 is formed, and a base insulating layer 5 as an insulating layer is formed on the metal foil 4, and a conductor pattern 6 is formed on the base insulating layer 5. Accordingly, a cover insulating layer 7 is formed on the conductor pattern 6.

The metal support substrate 2 is made of a flat metal foil or a metal thin plate. In the metal support substrate 2, an opening 9 facing the metal foil 4 is formed so that the end of the metal thin film 3 described in detail below is covered with the metal support substrate 2. Further, the opening 9 has both ends of the metal thin film 3 facing the wiring (described later) in the thickness direction exposed from the metal support substrate 2 and both ends of the metal thin film 3 in the width direction (direction perpendicular to the longitudinal direction of the wiring) The part is formed so as to be covered with the metal support substrate 2.
As the metal forming the metal support substrate 2, for example, stainless steel, 42 alloy, or the like is used, and stainless steel is preferably used. Moreover, the thickness is 15-30 micrometers, for example, Preferably, it is 20-25 micrometers.
Further, the metal thin film 3 is formed in a pattern in which the end portion is covered with the metal support substrate 2 so as to face the portion where the metal foil 4 is formed on the surface of the metal support substrate 2. More specifically, in the metal thin film 3, a portion facing the wiring in the thickness direction is exposed from the metal support substrate 2, and both end portions in the width direction of the metal thin film 3 are covered with the metal support substrate 2.
Examples of the metal that forms the metal thin film 3 include chromium, gold, silver, platinum, nickel, titanium, silicon, manganese, zirconium, and alloys thereof, or oxides thereof. Moreover, the thickness is 0.01-1 micrometer, for example, Preferably, it is 0.1-1 micrometer.

In addition, the metal thin film 3 takes into account the adhesion between the metal support substrate 2 and the metal foil 4. For example, the metal thin film 3 is formed on the surface of the metal support substrate 2 with a first metal made of metal having high adhesion to the metal support substrate 2. After the metal thin film 3 is formed, the second metal thin film 3 made of a metal having high adhesion to the metal foil 4 may be laminated on the surface of the first metal thin film 3 to form a multilayer.
The metal foil 4 is formed as a pattern on the surface of the metal thin film 3 so as to face at least a portion where the conductor pattern 6 is formed. Copper is preferably used as the metal forming the metal foil 4. Moreover, the thickness is 2-5 micrometers, for example, Preferably, it is 2-4 micrometers.

  The base insulating layer 5 is formed on the surface of the metal support substrate 2 so as to cover the metal foil 4. As the insulator for forming the base insulating layer 5, a synthetic resin such as polyimide, polyether nitrile, polyether sulfone, polyethylene terephthalate, polyethylene naphthalate, or polyvinyl chloride, which is usually used as an insulator of a printed circuit board, is used. Used. Of these, a photosensitive synthetic resin is preferably used, and a photosensitive polyimide is more preferably used. Moreover, the thickness is 5-15 micrometers, for example, Preferably, it is 8-10 micrometers.

  The conductor pattern 6 is formed on the surface of the base insulating layer 5 as a wiring circuit pattern composed of a plurality of (for example, four) wirings arranged in parallel along the longitudinal direction at intervals. . As a conductor which forms the conductor pattern 6, metals, such as copper, nickel, gold | metal | money, solder, or those alloys normally used as a conductor of a printed circuit board, are used, for example. Of these, copper is preferably used. Moreover, the thickness is 5-20 micrometers, for example, Preferably, it is 7-15 micrometers, The width | variety of each wiring is 15-100 micrometers, for example, Preferably it is 20-50 micrometers, The space | interval between each wiring is, for example, It is 15-100 micrometers, Preferably it is 20-50 micrometers.

The insulating cover layer 7 is formed on the surface of the insulating base layer 5 so as to cover the conductor pattern 6. As an insulator that forms the insulating cover layer 7, the same insulator as the above-described insulating base layer 5 is used. Moreover, the thickness is 3-10 micrometers, for example, Preferably, it is 4-5 micrometers.
Such a printed circuit board 1 can be manufactured, for example, by the method shown in FIG.

First, as shown in FIG. 2A, a metal support substrate 2 is prepared, and a metal thin film 3 is formed on the entire surface of the metal support substrate 2 by sputtering or electrolytic plating.
And as shown in FIG.2 (b), the resist 8 is formed in the pattern reverse to the pattern of the metal foil 4 mentioned above. For example, the resist 8 is formed by a known method in which exposure and development are performed using a dry film resist.

Next, as shown in FIG. 2C, the metal foil 4 is formed on the entire surface of the metal thin film 3 exposed from the resist 8 by electrolytic plating, preferably electrolytic copper plating, using the resist 8 as a plating resist. .
Then, as shown in FIG. 2D, the resist 8 and the metal thin film 3 where the resist 8 is formed are removed by a known etching method such as chemical etching (wet etching) or peeling.

  And as shown in FIG.2 (e), after apply | coating the solution (varnish) of the above-mentioned synthetic resin uniformly, for example on the surface of the metal foil 4 and the metal support substrate 2, it dries, and then, as needed Then, the base insulating layer 5 made of synthetic resin is formed by curing by heating. The base insulating layer 5 can also be formed as a pattern by exposing and developing a photosensitive synthetic resin. Furthermore, the formation of the insulating base layer 5 is not particularly limited to the above method. For example, a synthetic resin is formed in advance on a film, and the film is attached to the surfaces of the metal foil 4 and the metal support substrate 2 by a known adhesion. It can also be stuck through the agent layer.

Next, as shown in FIG. 2F, the conductor pattern 6 is formed in the above-described wiring circuit pattern by a known patterning method such as an additive method or a subtractive method.
For example, in the case of patterning by the additive method, first, a conductive thin film is formed on the entire surface of the base insulating layer 5 by, for example, a vacuum film forming method or a sputtering method, and the surface of the conductive thin film Then, exposure and development are performed using a dry film resist or the like to form a plating resist having a pattern that is reverse to the wiring circuit pattern. Next, the conductive pattern 6 is formed as a wiring circuit pattern on the surface of the conductive thin film exposed from the plating resist by plating, and the plating thin film and the portion of the conductive thin film on which the plating resist has been formed are removed by etching or the like. The plating may be either electrolytic plating or electroless plating, but electrolytic plating is preferably used, and among them, electrolytic copper plating is preferably used.

  For example, when patterning is performed by the subtractive method, first, a conductor layer is formed on the entire surface of the base insulating layer 5. The formation of the conductor layer is not particularly limited, and for example, the conductor layer is attached to the entire surface of the base insulating layer 5 via a known adhesive layer. Next, the conductive layer is exposed and developed using a dry film resist or the like to form an etching resist having the same pattern as the wiring circuit pattern. Thereafter, the conductive layer exposed from the etching resist is etched (wet etching), and then the etching resist is removed.

  Next, as shown in FIG. 2 (g), for example, the above-mentioned synthetic resin solution is uniformly applied to the surface of the base insulating layer 5 so as to cover the conductor pattern 6, and then dried, and then necessary. Accordingly, the cover insulating layer 7 made of synthetic resin is formed by curing by heating. The insulating cover layer 7 can also be formed as a pattern by exposing and developing a photosensitive synthetic resin. Further, the formation of the insulating cover layer 7 is not particularly limited to the above method. For example, the surface of the insulating base layer 5 is formed such that a synthetic resin is previously formed on a film and the film is covered with the conductive pattern 6. Moreover, it can also stick through a well-known adhesive bond layer.

Although not shown, the insulating cover layer 7 is formed so as to expose a portion to be a terminal portion of the conductor pattern 6. In order to expose the portion to be the terminal portion of the conductor pattern 6, it is formed into a pattern using the above-described photosensitive synthetic resin, or drilled with a laser or a punch.
Thereafter, in order to adjust the characteristic impedance, the printed circuit board 1 has a portion facing the metal foil 4 in the metal support substrate 2 (a portion facing the wiring in the thickness direction) as shown by a dotted line in FIG. ) Are removed by etching, and the opening 9 is formed so that the end portions (both ends in the width direction) of the metal thin film 3 are covered with the metal support substrate 2. Thereby, the printed circuit board 1 is obtained.
In the printed circuit board 1 obtained in this way, as shown in FIG. 1, a metal foil 4 is laminated on a metal supporting board 2 via a metal thin film 3. Therefore, the transmission loss of the conductor pattern 6 facing the metal support substrate 2 increases only with the metal support substrate 2, whereas the metal foil 4 is interposed between the metal support substrate 2 and the conductor pattern 6 in this way. Thereby, the transmission loss of the conductor pattern 6 can be reduced. In addition, by interposing the metal thin film 3 between the metal support substrate 2 and the metal foil 4, the adhesion between the metal support substrate 2 and the metal foil 4 can be sufficiently achieved with a simple layer configuration, and is excellent. Long-term reliability can be ensured.

  In addition, when the opening 9 is formed in the metal support substrate 2 by etching as described above, the metal wiring 4 is directly laminated on the metal support substrate 2 in the conventional wired circuit board. The foil 4 is also etched.

  However, in this wired circuit board 1, the metal thin film 3 is laminated on the metal support substrate 2, and the metal foil 4 is laminated on the metal thin film 3. When the opening 9 is formed so that the end portion of the metal thin film 3 is covered with the metal support substrate 2, the metal thin film 3 becomes a barrier layer and the metal foil 4 can be prevented from being etched. it can.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the examples and comparative examples.
Example 1
A 0.03 μm-thick chromium thin film and a 0.07 μm-thick copper thin film were sequentially formed as a metal thin film on a metal support substrate made of stainless steel having a thickness of 25 μm (see FIG. 2A). And the plating resist of the pattern reversed with the pattern of metal foil was formed using the dry film resist (refer FIG.2 (b)). Next, a copper foil having a thickness of 4.0 μm was formed by electrolytic copper plating on the entire surface of the metal thin film exposed from the plating resist (see FIG. 2C). Then, after removing the plating resist and the metal thin film where the plating resist was formed by chemical etching (see FIG. 2 (d)), the surface of the metal foil and the metal supporting substrate is coated with a varnish of photosensitive polyamic acid resin. After coating, the base insulating layer made of polyimide resin having a thickness of 10 μm was formed as a pattern covering the entire surface of the metal foil by exposure and development, and further heat curing (see FIG. 2 (e)). . Next, a conductive pattern having a thickness of 10 μm was formed as a wiring circuit pattern on the surface of the base insulating layer by an additive method (see FIG. 2F). Further, after applying a photosensitive polyamic acid resin varnish so as to cover the conductor pattern, exposure and development, and further heat-curing, the cover insulating layer made of polyimide resin having a thickness of 5 μm is formed on the entire surface of the conductor pattern. It was formed as a pattern covering (excluding the terminal portion) (see FIG. 2G). Thereafter, gold plating was applied to the terminal portion, and the metal support substrate was cut into a desired shape by etching to obtain a suspension board with circuit.

Example 2
A suspension board with circuit was obtained in the same manner as in Example 1 except that the metal thin film was changed to a nickel chromium alloy thin film having a thickness of 0.03 μm.
Example 3
A suspension board with circuit was obtained in the same manner as in Example 1 except that the metal thin film was changed to an electrolytic gold plating film (formed by electrolytic gold plating) having a thickness of 1 μm.

Comparative Example 1
A suspension board with circuit was obtained in the same manner as in Example 1 except that a copper foil was directly formed by electrolytic copper plating on a metal supporting board without forming a metal thin film.
Comparative Example 2
A suspension board with circuit was obtained in the same manner as in Example 1 except that the metal thin film and the metal foil were not formed.

Evaluation (Copper foil etching evaluation)
In order to adjust the characteristic impedance, the metal support substrate of the suspension board with circuit obtained in each example and each comparative example is etched to provide an opening facing the metal foil, and the end of the metal thin film is the metal support substrate. In Examples 1 to 3, it was confirmed that the metal thin film became a barrier layer and the copper foil as the metal foil was not etched. On the other hand, in Comparative Example 1, it was confirmed that the copper foil as the metal foil was etched.
(Transmission efficiency evaluation)
In the suspension board with circuit obtained in each example and each comparative example, the output signal strength (P _OUT ) and the input signal strength (P _IN ) are measured, and the output signal strength is expressed by the following equation (1). The transmission efficiency was evaluated as a ratio to the input signal strength. The results are shown in Table 1.

Transmission efficiency (%) = P _OUT / P _IN (1)
(Adhesion evaluation)
The suspension board with circuit obtained in each example and each comparative example was left under the condition of a temperature of −40 ° C. and then left under the condition of a temperature of 120 ° C. About the suspension board with attachment, the adhesive force between a metal support substrate and metal foil was evaluated by tape peeling. The results are shown in Table 1.

It is principal part sectional drawing which shows one Embodiment of the wired circuit board of this invention. It is a manufacturing process figure which shows the manufacturing method of the printed circuit board shown in FIG. 1, (a) is the process of forming a metal thin film on a metal support substrate by sputtering or electrolytic plating, (b) is a metal A step of forming a resist on the thin film in a pattern reverse to the pattern of the metal foil, (c) forming a metal foil by electrolytic plating on the metal thin film exposed from the resist, (d) (A) forming a base insulating layer on a metal supporting substrate including a metal foil; (f) removing the resist and the metal thin film in a portion where the resist has been formed; (G) shows the process of forming a cover insulating layer on a base insulating layer so that a conductor pattern may be coat | covered.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wiring circuit board 2 Metal support board 3 Metal thin film 4 Metal foil 5 Base insulating layer 6 Conductor pattern 9 Opening

Claims (6)

A metal support substrate; a metal thin film formed on the metal support substrate; a metal foil formed on the metal thin film; an insulating layer formed on the metal foil; And wiring formed on,
The printed circuit board according to claim 1, wherein an opening facing the metal foil is formed in the metal support substrate such that an end of the metal thin film is covered with the metal support substrate. A metal support substrate; a metal thin film formed on the metal support substrate; a metal foil formed on the metal thin film; an insulating layer formed on the metal foil; And wiring formed on,
The metal support substrate has an opening facing the metal foil, a portion of the metal thin film facing the wiring in the thickness direction is exposed from the metal support substrate, and a longitudinal direction of the wiring in the metal thin film The printed circuit board is formed so that both ends in the width direction orthogonal to the metal support board are covered with the metal support board.   The printed circuit board according to claim 1, wherein the opening is formed by etching. The metal support substrate is made of stainless steel, and the metal foil is made of copper,
The printed circuit board according to claim 1. The printed circuit board according to claim 1, wherein the metal thin film is formed by sputtering or electrolytic plating, and the metal foil is formed by electrolytic plating. The wired circuit board is a suspension board with circuit.
The wired circuit board according to any one of 5.

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