JP4611075B2 - 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 can reduce transmission loss with a simple layer configuration and can prevent the metal supporting board and the metal foil from peeling off and has excellent long-term reliability. There is to do.

To achieve the above object, the wiring circuit board of the present invention, the metal supporting board, a metal foil formed on the metal supporting board, a metal interposed between the metal foil and the metal supporting board thin, insulating layer formed on the metal foil, and the comprises a conductor pattern formed on the insulating layer, wherein the metal foil and the metal thin film, a through hole is formed, the The insulating layer is in contact with the metal support substrate through a through hole.
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 according to the present invention, the metal thin film is formed on a surface of the metal support substrate, and includes a first metal thin film made of a metal having high adhesion to the metal support substrate, and the first metal. It is preferable that a second metal thin film formed on the surface of the thin film and made of a metal having high adhesion to the metal foil is laminated.

  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, a metal foil is formed on a metal support substrate, and a through hole is formed in the metal foil, and the metal foil is formed on the metal foil through the through hole. The insulating layer is in contact with the metal support substrate. Therefore, the transmission loss can be reduced by a simple layer configuration, and the metal support substrate and the metal foil can be prevented from being peeled off due to the adhesion between the insulating layer and the metal support substrate. Long-term reliability can be ensured.
In addition, according to the wired circuit board of the present invention, the metal thin film having a through hole is interposed between the metal support substrate and the metal foil, so that the adhesion between the metal support substrate 2 and the metal foil 4 is increased. Can be further improved.

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, this wired circuit board 1 is a suspension board with circuit, and a metal foil 4 having a through hole 3 is formed on a metal support board 2 extending in the longitudinal direction. A base insulating layer 5 as an insulating layer is formed, a conductor pattern 6 is formed on the base insulating layer 5, and a cover insulating layer 7 is formed on the conductor pattern 6 as necessary. ing.

The metal support substrate 2 is made of a flat metal foil or a metal thin plate. 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 15-76 micrometers, for example, Preferably, it is 18-25 micrometers.
Further, the metal foil 4 is formed as a pattern on the surface of the metal support substrate 2 so as to include a portion facing the portion where the conductor pattern 6 is formed and the through hole 3 is formed. Copper is preferably used as the metal forming the metal foil 4. Moreover, the thickness is 2-5 micrometers, for example.

A plurality of through holes 3 are formed in the metal foil 4. The plurality of through holes 3 are spaced apart from each other, and each through hole 3 is formed so as to penetrate the thickness direction of the metal foil 4. The through-hole 3 has an opening cross section formed in an appropriate shape such as a circle or a rectangle. The size of the through hole 3 is, for example, a circle having a diameter of 15 to 1000 μm. The length is 15 to 1000 μm. Further, the number of the through holes 3 is not particularly limited, and is, for example, 1 to 200 per 1 mm ^{2 of} the metal foil. Although not particularly limited, the through holes 3 are provided in an aligned arrangement such as a staggered pattern or a mesh pattern. .

Moreover, for further improving the adhesion between the metal supporting board 2 and the metal foil 4, Ru is interposed a thin metal film 9 between the metal supporting board 2 and the metal foil 4. A through-hole 3 communicating with the metal foil 4 is formed in the metal thin film 9. As the metal forming the metal thin film 9, for example, chromium, gold, silver, platinum, nickel, titanium, silicon, manganese, zirconium, and alloys thereof, or oxides thereof are used. Moreover, the thickness is 0.01-1.5 micrometers, for example, Preferably, it is 0.1-1.5 micrometers. In addition, the metal thin film 9 takes into consideration the adhesion between the metal support substrate 2 and the metal foil 4. After the metal thin film 9 is formed, the second metal thin film 9 made of a metal having high adhesion to the metal foil 4 can be laminated on the surface of the first metal thin film 9 to form a multilayer.

  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 8-12 micrometers.

The insulating base layer 5 covers the metal foil 4 and is filled in the through holes 3 formed in the metal foil 4, and adheres to the surface of the metal support substrate 2 in the through holes 3. ing.
The conductor pattern 6 is formed on the surface of the base insulating layer 5 as a wiring circuit pattern including 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 wiring circuit board, are used, for example. Of these, copper is preferably used. Moreover, the thickness is 5-20 micrometers, for example, Preferably, it is 7-17 micrometers, The width | variety of each wiring is 15-50 micrometers, for example, Preferably it is 20-30 micrometers, The space | interval between each wiring is, for example, It is 15-50 micrometers, Preferably, it is 20-30 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 2-8 micrometers, for example, Preferably, it is 3-5 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 the resist 8 is reversed on the surface of the metal support substrate 2 with the pattern of the metal foil 4 described above (a pattern including the through holes 3). Form with a pattern. For example, the resist 8 is formed by a known method in which exposure and development are performed using a dry film resist.
Then, as shown in FIG. 2B, the resist 8 is used as a plating resist, and the surface of the metal supporting substrate 2 exposed from the resist 8 is subjected to electrolytic plating or electroless plating, preferably electrolytic plating, and more preferably, Metal foil 4 is formed by electrolytic copper plating.

Next, as shown in FIG. 2C, the resist 8 is removed by a known etching method such as chemical etching (wet etching) or peeling. Thereby, the through hole 3 is formed in the metal foil 4.
In this manner, if the resist 8 is plated as the plating resist and then removed, the through hole 3 can be formed in the metal foil 4 simultaneously with the formation of the metal foil 4.

Moreover, the Ru is interposed a thin metal film 9 between the metal supporting board 2 and the metal foil 4 first resist a metal thin film 9 was formed on the entire surface of the metal supporting board 2, the surface of the metal thin film 9 8 Form. In order to form the metal thin film 9 on the entire surface of the metal supporting substrate 2, sputtering or electrolytic plating is used. Next, after the metal foil 4 is formed using the resist 8 as a plating resist, the resist 8 is removed, and then the metal thin film 9 where the resist 8 has been formed is known, for example, by chemical etching (wet etching) or the like. It is removed by etching or peeling.

  And as shown in FIG.2 (d), 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. In forming the base insulating layer 5, when a synthetic resin solution is applied to the surface of the metal foil 4, the through hole 3 formed in the metal foil 4 is filled with the synthetic resin solution. By drying and further curing the synthetic resin solution, the base insulating layer 5 is formed in the through hole 3 so as to be in close contact with the surface of the metal support substrate.

Next, as shown in FIG. 2E, 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 (f), 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 a synthetic resin is formed by heating, and thereby the printed circuit board 1 is obtained. 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.
Furthermore, although not shown, the metal supporting board 2 may be cut out into a desired shape by etching as necessary.

  In the printed circuit board 1 obtained in this way, as shown in FIG. 1, the metal foil 4 is formed on the metal supporting board 2 so as to include a portion facing the portion where the conductor pattern 6 is formed. Has been. 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. By doing so, the transmission loss of the conductor pattern 6 can be reduced. Also, the metal foil 4 formed on the metal support substrate 2 has a through hole 3, and the base insulating layer 5 is in close contact with the metal support substrate 2 through the through hole 3. The adhesion between the base insulating layer 5 and the metal support substrate 2 can prevent the metal support substrate 2 and the metal foil 4 from being peeled off, and can ensure excellent long-term reliability.

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 metal support substrate made of stainless steel having a thickness of 25 μm was prepared, and a chromium thin film having a thickness of 0.3 μm and a copper thin film having a thickness of 0.8 μm were sequentially formed on the entire surface of the metal support substrate by sputtering. Next, a plating resist having a pattern reverse to the pattern of the metal foil in which three through-holes having a side length of 15 μm are formed on the surface of the metal thin film per 1 mm ² of the metal foil is formed. The film was formed using a dry film resist (see FIG. 2A). Then, a copper foil having a thickness of 5 μm was formed as a metal foil on the entire surface of the metal thin film exposed from the plating resist by electrolytic copper plating (see FIG. 2B). Then, the plating resist was removed by chemical etching, and the portion of the metal thin film where the plating resist was formed was removed by chemical etching to form a through hole in the metal foil and the metal thin film (FIG. 2C). reference). Then, a varnish of a photosensitive polyamic acid resin is applied to the surface of the metal foil and the metal support substrate so that the varnish is filled in the through holes formed in the metal foil, and then exposed and developed, and further heated. By curing, a base insulating layer made of a polyimide resin having a thickness of 10 μm covers the entire surface of the metal foil, and is also filled into the through holes formed in the metal foil, and the surface of the metal support substrate in the through holes (See FIG. 2D). 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). Furthermore, after coating a varnish of a photosensitive polyamic acid resin so as to cover the conductor pattern, exposure and development, and further heat-curing, a cover insulating layer made of polyimide resin having a thickness of 5 μm is formed on the surface of the conductor pattern. The pattern was formed so as to cover the entire surface (excluding terminals) (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 opening cross section of the through hole formed in the metal foil was changed to a square having a side length of 20 μm.
Comparative Example 1
A suspension board with circuit was obtained in the same manner as in Example 1 except that the through hole was not formed in the metal foil.

Comparative Example 2
A suspension board with circuit was obtained in the same manner as in Example 1 except that the metal foil was not formed.
Evaluation (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 input of the output signal strength is expressed by the following equation (1). The transmission efficiency was evaluated as a ratio to the 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, Comprising: (a) is a pattern reverse to a metal foil pattern (pattern containing a through-hole) on a metal support substrate, (B) is a step of forming a metal foil on the metal supporting substrate exposed from the resist by plating, (c) is a step of removing the resist, and (d) is a metal foil. Forming an insulating base layer on the metal supporting substrate; (e) forming a conductive pattern on the insulating base layer; (f) insulating the base layer so as to cover the conductive pattern; A process of forming a cover insulating layer on the substrate is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wiring circuit board 2 Metal support board 3 Through-hole 4 Metal foil 5 Base insulating layer 6 Conductor pattern

Claims (4)

Metal supporting board, the metal metal foil formed on the supporting substrate, a metal thin film to be interposed between the metal supporting board and the metal foil, an insulating layer formed on the metal foil, and, comprising a conductor pattern formed on said insulating layer,
A through-hole is formed in the metal foil and the metal thin film , and the insulating layer is in contact with the metal support substrate through the through-hole.   The wired circuit board according to claim 1, wherein the metal supporting board is made of stainless steel and the metal foil is made of copper. The metal thin film is formed on a surface of the metal support substrate, and is formed on a surface of the first metal thin film made of a metal having high adhesion to the metal support substrate, and the metal foil. The printed circuit board according to claim 1, wherein a second metal thin film made of a metal having a high adhesive strength is laminated. The wiring circuit board, characterized in that it is a suspension board with circuit, printed circuit board according to any one of claims 1 to 3.

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