WO2012124421A1

WO2012124421A1 - Flexible multilayer substrate

Info

Publication number: WO2012124421A1
Application number: PCT/JP2012/053352
Authority: WO
Inventors: 酒井　範夫; 喜人大坪
Original assignee: 株式会社村田製作所
Priority date: 2011-03-14
Filing date: 2012-02-14
Publication date: 2012-09-20
Also published as: JPWO2012124421A1; JP5715237B2

Abstract

Provided is a flexible multilayer substrate that suppresses peeling of surface conductors and resin film, has superior bond strength for the surface conductors and resin film, and suppresses occurrences of shorting defects. In this flexible multilayer substrate (1), peeling between the surface conductors (5) and the resin film (3) is suppressed and shorting defects are also suppressed by making the thickness of a resin film (3) of the outermost layer greater than the thickness of resin films (2) for inside layers and making the surface roughness of the surface of surface conductors (5) formed on the resin film (3) of the outermost layer and in contact with the resin film (3) be greater than the surface roughness of inside conductors (4).

Description

Flexible multilayer board

The present invention relates to a flexible multilayer substrate in which resin sheets made of a thermoplastic resin are laminated.

As a conventional flexible multilayer substrate, for example, a multilayer substrate described in Patent Document 1 is known. The multilayer substrate described in Patent Document 1 will be described below with reference to FIG. FIG. 4 is a cross-sectional view showing a multilayer substrate.

The multilayer substrate 101 has a conductive pattern 106 arranged in multiple layers on an insulating resin substrate 102 formed by laminating resin films 103. The conductor pattern 106 includes a surface conductor pattern 105 as a land or bottom electrode exposed on the surface of the resin substrate 102 and an internal conductor pattern 104 disposed inside the resin substrate 102. The surface conductor pattern 105 is thicker than the inner conductor pattern 104. Further, the surface roughness of the surface of the surface conductor pattern 105 in contact with the resin substrate 102 is set larger than the surface roughness of the internal conductor pattern 104. The conductor pattern 106 is appropriately electrically connected by a via hole 107.

JP 2006-344828 A

When the multilayer substrate 101 is mounted on the mother substrate or when another component is mounted on the surface conductor pattern 105 on the upper surface of the multilayer substrate 101, the surface conductor pattern 105 and the resin substrate 102 are weakly bonded. Peeling may occur between 105 and the resin substrate 102. As a means for increasing the adhesion strength between the surface conductor pattern 105 exposed on the surface and the resin substrate 102, there is a method of increasing the surface roughness of the surface of the surface conductor pattern 105 in contact with the resin substrate 102.

On the other hand, if it is attempted to reduce the height of the multilayer substrate 101 in accordance with the downsizing and thinning of electric devices such as mobile phones, it is necessary to make the resin substrate 102 thinner. In order to make the resin substrate 102 thinner, it is necessary to make the resin film 103 constituting the resin substrate 102 thinner. However, when the surface roughness of the surface conductor pattern 105 formed on the thin resin film 103 is increased, the distance between the surface conductor pattern 105 and the adjacent inner conductor pattern 104 is shortened, which may cause a short circuit failure.

In view of these circumstances, the present invention increases the surface roughness of the surface contacting the resin substrate of the surface conductor pattern formed on the top and bottom surfaces of the resin substrate, and the thickness of the resin film on the outermost layer of the resin substrate is set to the inner layer. Make it thicker than the resin film. As a result, it is an object of the present invention to provide a flexible multilayer substrate that is excellent in the adhesion strength between the surface conductor pattern and the resin substrate and in which the occurrence of short-circuit defects is suppressed.

The flexible multilayer substrate according to the present invention includes an insulating base material in which a plurality of resin films made of a thermoplastic resin are laminated, and an internal conductor formed along a part of the resin film in the insulating base material. A flexible multilayer substrate comprising a surface conductor formed on at least one of the outermost resin films among the plurality of resin films, wherein the thickness of the resin film on which the surface conductor is formed is not the outermost layer The surface roughness of the surface conductor that is thicker than the inner layer resin film and in contact with the resin film of the surface conductor is larger than the surface roughness of any surface of the inner conductor.

Since the surface roughness of the surface of the surface conductor in contact with the resin film increases, the adhesion strength between the surface conductor and the outermost resin film increases. As a result, the connection reliability between the flexible multilayer substrate and the mother substrate and between the flexible multilayer substrate and another component is improved.

In addition, since the thickness of the resin film on which the surface conductor is formed is thicker than the thickness of the inner resin film, the required distance between the surface conductor and the adjacent internal conductor is maintained even if the surface roughness of the surface conductor is increased. It is. As a result, the occurrence of short-circuit defects can be suppressed.

The flexible multilayer board according to the present invention is preferably characterized in that the inner conductor and the surface conductor have substantially the same thickness.

In this case, it is not necessary to prepare multiple types of materials having different thicknesses as the material for the inner conductor and the surface conductor.

According to the present invention, since the surface roughness of the surface conductor in contact with the resin film is increased, the adhesion strength between the surface conductor and the outermost resin film is increased. As a result, the connection reliability between the flexible multilayer substrate and the mother substrate and between the flexible multilayer substrate and another component is improved. In addition, since the thickness of the resin film on which the surface conductor is formed is thicker than the thickness of the inner resin film, even if the surface roughness of the surface conductor is increased, the necessary distance between the surface conductor and the adjacent internal conductor is small. Kept. As a result, the occurrence of short-circuit defects can be suppressed.

It is sectional drawing of the flexible multilayer substrate which concerns on embodiment of this invention. It is sectional drawing which shows the manufacturing process of the flexible multilayer substrate which concerns on embodiment of this invention. FIG. 3 is a cross-sectional view showing a manufacturing step that follows FIG. 2. It is sectional drawing which shows the cross-sectional state of the conventional multilayer substrate.

Hereinafter, a flexible multilayer substrate according to an embodiment of the present invention will be described with reference to FIG.

The flexible multilayer substrate 1 includes an insulating base material 10, an inner conductor 4, a surface conductor 5, and a via conductor 6.

The insulating substrate 10 is formed by laminating a resin film 2 and a resin film 3 made of a thermoplastic resin. The resin film 2 is disposed on the inner layer portion of the insulating base material 10, and the resin film 3 is disposed on the outermost layer of the insulating base material 10. The thickness of the resin film 3 is larger than the thickness of the resin film 2, and the thickness of the resin film 3 exemplified in this embodiment is a film of 50 μm. On the other hand, the thickness of the resin film 2 is 25 μm. That is, the insulating base material 10 is configured to sandwich the resin film 2 arranged in the inner layer with the resin film 3 having a thickness larger than that of the resin film 2.

The inner conductor 4 is a conductor formed along the resin film 2 inside the insulating base material 10. The surface conductor 5 is formed on the surface and the bottom surface of the insulating substrate 10, and the surface conductor 5 formed on the surface is formed on the bottom surface as a land or the like for mounting other components such as a chip capacitor and an IC chip. The surface conductor 5 is a conductor that serves as a bottom electrode or the like for surface mounting on the mother board. Here, both the land and the bottom electrode will be described as the surface conductor 5. The inner conductor 4 and the surface conductor 5 have the same thickness. Here, an example having a thickness of 12 μm is illustrated.

The surface roughness of the surface conductor 5 in contact with the resin film 3 is larger than the surface roughness of the internal conductor 4. Here, the surface conductor 5 has a surface roughness Ra = 3 μm and Rz = 15 μm, and the inner conductor 4 has a surface roughness Ra = 1 μm and Rz = 5 μm. The surface roughness was measured using a contact type surface roughness meter. The surface roughness Ra and Rz are defined in JIS B 0601-2001 “Definition and display of surface roughness”, Ra is “arithmetic mean roughness”, and Rz is “maximum height”.

The inner conductor 4 and the surface conductor 5 are formed by processing a copper foil bonded to one side of the resin film 2 and the resin film 3. The size of the surface roughness of the inner conductor 4 and the surface conductor 5 can be made different by changing the roughening plating process conditions applied to the copper foil. For example, the difference in surface roughness can be obtained by selecting a plating solution to be used when copper plating is performed after foil formation or by changing the time for immersing the copper foil in the plating solution.

As described above, when the surface conductor 5 is used as a land or bottom electrode by making the surface roughness of the surface conductor 5 in contact with the resin film 3 larger than the surface roughness of the internal conductor 4, the surface conductor 5 and the resin film are used. The adhesion force of 3 is increased, and the fixing strength is improved. As a result, peeling between the surface conductor 5 and the resin film 3 is suppressed, and the connection reliability with the electronic component mounted on the surface conductor 5 and the mother board is improved. A conductor having a large surface roughness has poor electrical characteristics. However, since the surface conductor 5 is used as a land or a bottom electrode, there is little need to consider the influence on the electrical characteristics. On the other hand, since the internal conductor 4 is required to have good electrical characteristics, the surface roughness is preferably small. Further, since the inner conductor 4 is disposed in the insulating base material 10 and the possibility of peeling from the resin film is low, it is not considered to improve the adhesive strength with the resin film by increasing the surface roughness. May be.

However, when the surface roughness of the surface conductor 5 is increased, when the resin film 3 is thin, the distance between the surface conductor 5 and the adjacent internal conductor 4 is shortened, which may cause a short circuit failure.
Therefore, by making the thickness of the resin film 3 larger than the thickness of the resin film 2, a necessary distance is maintained between the surface conductor 5 formed on the resin film 3 and the adjacent inner conductor 4. As a result, occurrence of a short circuit can be suppressed.

As described above, the thicknesses of the inner conductor 4 and the surface conductor 5 are substantially the same. By making the thicknesses of the inner conductor 4 and the surface conductor 5 the same, it is not necessary to prepare a plurality of materials having different thicknesses.

Further, when the surface conductor 5 is made thicker than the inner conductor 4 as in the prior art, a thick conductor and a thin conductor are mixed in the flexible multilayer substrate 1, and the inner conductor 4 thinner than the surface conductor 5 when the flexible multilayer substrate 1 is bent. Bending stress concentrates on As a result, disconnection or peeling may occur in the inner conductor 4 where bending stress is concentrated. However, since the thicknesses of the surface conductor 5 and the inner conductor 4 are the same in the present invention, bending stress does not concentrate on the inner conductor 4 when the flexible multilayer substrate 1 is bent, and disconnection and peeling can be suppressed.

Further, in order to form the inner conductor 4 and the surface conductor 5, a process of applying a photoresist on the copper foil, exposing, developing, and etching is required. When the copper foil thickness is different, the thickness of the photoresist, the exposure and development conditions, the etching conditions, and the like are different. Therefore, the thickness of the internal conductor 4 and the surface conductor 5 may be the same from the viewpoint of ease of setting process conditions. It is advantageous.

Next, a method for manufacturing a flexible multilayer substrate according to an embodiment of the present invention will be described with reference to FIGS.

First, a resin film 2 made of LCP (liquid crystal polymer) which is a thermoplastic resin is prepared. As a constituent material of the resin film 2, PEEK (polyetheretherketone), PEI (polyetherimide), PPS (poniphenylenesulfide), PI (polyimide) and the like are used in addition to LCP. In this embodiment, the resin film 2 having a thickness of 25 μm is used. This resin film 2 has a copper foil with a thickness of 12 μm on one side. The surface roughness of this copper foil is Ra = 1 μm and Rz = 5 μm. In addition, although copper foil is illustrated here, it can replace with other metal foil which consists of Ag, Al, SUS, Ni, Au, its alloy, etc. (FIG. 2 (a)).

Next, a via hole 6a is formed by irradiating a carbon dioxide laser on the resin film side of the predetermined film of the resin film 2 (the back side of the surface having the copper foil). Thereafter, the smear (resin residue) in the via hole 6a is removed. (FIG. 2 (b)).

Next, a resist 9 corresponding to a desired internal conductor pattern is formed on the copper foil 4a of the resin film 2 by general-purpose photolithography. (FIG. 2 (c)).

Next, the portion of the copper foil 4a that is not coated with the resist 9 is etched. Thereafter, the resist 9 is removed to form the inner conductor 4. (FIG. 2D), (FIG. 2E).

Next, the via hole 6a is filled with a conductive paste by screen printing or the like to form the via conductor 6. The conductive paste to be filled contains Cu as a main component. In addition to Cu, this conductive paste is, for example, a conductive paste containing Sn—Ag alloy powder, or at least one selected from the group consisting of Bi, Cu, Ag, Zn, Sn, In, Sb and Ni. You may use the electrically conductive paste containing the alloy powder containing a metal. (FIG. 3 (f)). Further, as a means for connecting the interlayer of the resin film 2 and the interlayer of the

resin films

2 and 3, other methods such as applying a conductor to the via hole 6 by plating may be used.

The process of forming the surface conductor 5 on the resin film 3 is the same as the process of forming the inner conductor 4 on the resin film 2 (the process diagram for forming the surface conductor 5 on the resin film is omitted). In this embodiment, the resin film 3 having a thickness of 50 μm is used. Further, a copper foil having a thickness of 12 μm is used. The surface roughness of the copper foil is Ra = 3 μm and Rz = 15 μm. Further, a via conductor is also formed in the resin film 3 as necessary.

Next, a predetermined number of the resin film 2 on which the internal conductor 4 is formed and the resin film 3 on which the surface conductor 5 is formed are prepared and laminated. In the present embodiment, first, the resin film 3 is arranged so that the surface conductor 5 is arranged on the bottom surface of the insulating base material 10. Next, the resin film 2 is disposed on the resin film 3 so that the inner conductor 4 is on the bottom. On top of that, two resin films 2 are arranged so that the internal conductor 4 is arranged on the top. Next, the resin film 3 is disposed so that the surface conductor 5 is disposed on the upper surface of the insulating base material 10. Thereafter, the resin film 2 and the resin film 3 are thermocompression bonded at 250 to 300 ° C. for 20 to 30 minutes. The thickness of the resin film 2 and the resin film 3 after the thermocompression bonding is in a state of being contracted at substantially the same rate as that before the thermocompression bonding. (FIG. 2 (g)).

Next, after the chip capacitor 7 is disposed so that the external electrode of the chip capacitor 7 at least partially overlaps the surface conductor 5, the chip capacitor 7 is mounted with the solder 8. (FIG. 2 (h)).

In this embodiment, three resin films 2 are laminated. However, the number of resin films 2 can be changed as appropriate. Moreover, if it is not necessary to mount other components on the flexible multilayer substrate 1, the resin film 3 may be the outermost layer without arranging the resin film 3 on the upper surface side of the insulating base 10. The same applies to the case where the flexible multilayer substrate 1 is not surface-mounted on the mother substrate. In this case, the resin film 3 may not be disposed on the bottom surface side of the insulating base material 10.

1: Flexible multilayer substrate 2: Resin film 3: Resin film 4: Internal conductor 4a: Copper foil 5: Surface conductor 6: Via conductor 6a: Hole for via 7: Chip capacitor 8: Solder 9: Resist 10: Insulating substrate 101: Multilayer substrate 102: Resin substrate 103: Resin film 104: Internal conductor pattern 105: Surface conductor pattern 106: Conductor pattern 107: Via hole (via conductor)

Claims

An insulating base material in which a plurality of resin films made of thermoplastic resin are laminated;
An inner conductor formed along a part of the resin film in the insulating substrate;
Among the plurality of resin films, a surface conductor formed on at least one of the outermost resin films,
A flexible multilayer substrate comprising:
The thickness of the resin film on which the surface conductor is formed is thicker than the thickness of the inner layer resin film that is not the outermost layer,
The flexible multilayer substrate, wherein the surface roughness of the surface conductor in contact with the resin film is larger than the surface roughness of any surface of the inner conductor.
The flexible multilayer substrate according to claim 1, wherein the inner conductor and the surface conductor have substantially the same thickness.
The inner conductor and the surface conductor are made of metal foil,
The flexible multilayer substrate according to claim 1 or 2.