JPH11121931A - Printed wiring board and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent electrical connection failure due to air accumulation, abnormal deposition, or the like from occurring, by making laser irradiate a wider area than a thin-layer part, forming a hole to get to a lower-layer conductor layer at a thin-layer part and an insulation resin layer, and then electrically connecting an upper layer metal foil and a lower layer conductor layer via the hole. SOLUTION: A dry film is laminated on an upper-layer copper foil 3 of a laminated resin body with a copper foil, a pattern is exposed to a position where a via hole is preferably formed by UV irradiation, and development and half etching are made, thus forming a thin-layer part 8. Then, a carbon dioxide gas laser device is positioned and set, laser 4 with a diameter W1 that is larger than a dimension W2 of the thin-layer part 8 is applied, the thin-layer part 8 and an epoxy resin 1 are melted, vaporized, and dissolved for forming a hole 5, and a dry film is peeled. Then, the inside of the hole 5 is subjected to smearing treatment, and a copper plating for electrically connecting an upper layer copper foil 3 and a lower layer copper foil 2 via the hole 5 is performed, thus forming a via hole 6 and hence achieving reliable electrical connection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, as electronic devices have become smaller, there has been a demand for smaller, higher density, lighter weight, higher reliability printed circuit boards. For these requirements, in addition to the printed wiring board material itself, miniaturization, miniaturization, reliability, and the like of the conductor width, conductor gap, through hole, via hole, and the like are required. Among them, the via hole is the inner via hole,
For the blind via hole, miniaturization, miniaturization, reliability of electrical connection, and the like are required. Conventionally, drilling and laser drilling have been proposed as via hole forming methods. For example, JP-A-58-64097 and JP-A-61-95792 disclose laser drilling.

Japanese Unexamined Patent Application Publication No. 58-64097 discloses that a hole (slightly smaller than the laser beam diameter) is formed in a conductor layer above the lowermost layer of a conductor layer to be electrically connected by etching in advance. ), A laser is irradiated from above through the holes (substrate surface is scanned), and the resin layer between the conductor layers from the uppermost layer to the lowermost layer is removed. It has been disclosed.

Japanese Patent Application Laid-Open No. 61-95792 discloses a printed wiring board in which holes are made by a laser beam having a light irradiation area which covers a metal foil removed portion (the laser light irradiation area is made larger than the metal foil removed portion). Is disclosed.

[0005]

As described in the above publications, a hole is previously formed in a conductor layer, and a laser is irradiated to an area larger than the hole or a laser is scanned over a wider area than the hole. In this method, the holes in the conductor layer serve as a mask for laser beam irradiation, and have an effect of removing the resin layer.
However, in the step of previously drilling holes in the conductor layer, there is a problem that the accuracy of the hole diameter is not good. In the laser drilling step, the irradiated laser is reflected by the lower conductor layer and the resin layer is further removed to make the hole in the resin layer larger. Further, the laser beam reflected by the lower conductor layer is reflected by the back surface of the upper conductor layer to remove the resin layer, thereby making the hole in the resin layer near the back surface of the upper conductor layer larger and wider.
The hole in the resin layer near the back surface of the upper conductor layer becomes larger than the hole in the upper conductor layer, and there is a serious problem that air is trapped in the electric connection process of the via hole and an electric connection failure occurs due to abnormal deposition or the like.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a printed wiring board for forming a circuit pattern on a substrate on which a metal foil and an insulating resin layer are laminated, and a method for manufacturing the same. Forming a layer portion, forming a hole in the thin layer portion and the insulating resin layer by irradiating a laser to an area larger than the thin layer portion and reaching the lower conductive layer, the upper metal foil through the hole, Electrically connecting the lower conductor layer;
Forming a circuit pattern on the upper metal foil by a subtractive method. A thin layer portion 8 of the upper metal foil 3 having a dimension W2 smaller than the thickness of the upper metal foil.
Is formed in the step of forming the thin layer portion, and the size of the dimension W2 of the thin layer portion is reduced in comparison with forming the entire thickness of the upper metal foil by forming the thin layer portion. It can be formed accurately and uniformly. Further, in the step of forming a hole by irradiating a laser, melting and vaporization start from a substantially central portion of the thin layer portion 8 by laser energy to form a hole, and a hole is formed at a substantially central portion of the thin layer portion. In the process of forming holes by melting, vaporizing, and decomposing the insulating resin layer 1, the thin layer portion becomes a mask for a laser beam, drilling is started from a diameter smaller than the diameter of laser irradiation, and the holes 5 reach the lower conductor layer 2. When the thin layer is melted and vaporized almost entirely, no large holes are formed in the vicinity of the upper metal foil. It is an object of the present invention to provide an accurate and highly reliable printed wiring board that has solved the problems such as no printed wiring board and a method for manufacturing the same.

Hereinafter, a printed wiring board according to the present invention and a method for manufacturing the same will be described in detail. 1 (a) and 1 (b)
1 is a cross-sectional view of one embodiment showing a printed wiring board according to the present invention and a method for manufacturing the same. FIG. 2 is a sectional view showing a conventional embodiment.

In a printed wiring board and a method of manufacturing the same according to the present invention, a thin layer portion is generally formed by selectively removing an upper metal foil at a desired position for forming a hole on a substrate on which a metal foil and an insulating resin layer are laminated. And irradiating a laser to an area larger than the thin layer portion to form a hole in the thin layer portion and the insulating resin layer to form a hole reaching the lower conductor layer, and the upper metal foil through the hole. And a circuit pattern formed on a metal foil by a subtractive method by electrically connecting the lower conductor layer. In addition, a coating film for protecting the surface is formed as necessary.

Further, the printed wiring board and the method of manufacturing the same according to the present invention do not necessarily need to adopt the structure shown in FIG. 1, and the printed wiring board may have any number of layers as needed, [Sulholes (two-layer through holes, multi-layer through holes, etc.) and via holes (two-layer via holes, multi-layer via holes, blind via holes, inner via holes, etc.)] may be formed at desired positions. It may be formed by an additive method.

[0010] The insulating resin layer of the printed wiring board and the method of manufacturing the same according to the present invention is not particularly limited. A resin mainly used for a printed wiring board may be used as a main component, a resin impregnated in a nonwoven fabric or a woven fabric may be used, or a resin filled with an organic or inorganic filler may be used. Further, these may be combined.

The printed wiring board according to the present invention and the metal foil used in the method for manufacturing the same are not particularly limited. A foil such as copper, stainless steel, nichrome, tungsten, and aluminum generally used for a printed wiring board may be used. Preferably, it is a copper foil. Moreover, the thickness of the metal foil is 7 to 50μ.
m is preferred. More preferably, it is 7 to 40 μm.
Particularly preferably, it is 7 to 25 μm. The metal foil having such a thickness is easy to manufacture and handle, and is easily available.

The method of forming the thin layer portion by partially removing the upper metal foil of the printed wiring board and the method of manufacturing the same according to the present invention is not particularly limited. A layer serving as an etching mask is formed on the surface of the metal foil, the etching mask at a desired position for forming a hole is removed, and the metal foil at a portion where the etching mask is removed is etched with an etching solution to form a thin layer portion. To form Examples of the etching mask include an etching resist by a screen printing method, a photographic method, or the like, or a metal layer etching resist by solder, Ni-Au, or the like. The remaining thickness of the metal foil in the thin layer portion is preferably 5 to 50% of the original metal foil. More preferably, it is 5 to 40%. With such a thickness, the hole in the metal foil by the laser is sharp. Further, compared to etching the entire thickness of the original metal foil, the etching diameter is accurate because it is stopped halfway and a thin layer portion is formed.

The method of forming holes in the printed wiring board and the method of manufacturing the same according to the present invention is a method using a laser, and the type of the laser is not particularly limited. Examples thereof include a high energy carbon dioxide laser, an ultraviolet laser, a Xe laser, an excimer laser, a YAG laser, and an Ar laser.
Preferably, a carbon dioxide laser and an ultraviolet laser are used. More preferably, it is an ultraviolet laser in which the resin is decomposed and perforated without carbonization. By using such a laser, holes of smaller diameter can be quickly and accurately drilled. Further, a thin layer portion is formed by etching, and the surface of the thin layer portion becomes uneven, which has an effect of well absorbing laser energy. The laser is reflected and hardly melted on the surface of the metal foil other than the thin layer, and the laser is melted and vaporized by absorbing energy in the uneven state of the thin layer. That is, holes are formed using the metal foil other than the thin layer portion as a mask.

The method for electrically connecting via the holes in the printed wiring board and the method for manufacturing the same according to the present invention is not particularly limited. Preferably, a method of electrically connecting the upper metal foil and the lower conductor layer by metal plating, or applying and filling a conductive substance (a resin or an adhesive mixed with a metal filler, a conductive resin, etc.) to the holes to make the electrical connection. And how to do it. More preferably, a method of electrical connection by metal plating is used.

The method of forming a circuit pattern in the printed wiring board and the method of manufacturing the same according to the present invention is a subtractive method, and the steps are not particularly limited. As the etchant, cupric chloride, ferric chloride and the like are preferable. More preferably, ferric chloride has a large etching factor (aspect ratio).

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the printed wiring board according to the present invention and a method for manufacturing the same will be described below. The printed wiring board and the method for manufacturing the same according to the present invention are not limited to the following embodiments.

(Example 1) First, a circuit pattern is formed by a subtractive method on a copper-clad double-sided slab in which a copper foil of 18 μm thickness is laminated on both sides of an epoxy resin, the copper foil is blackened, and a chemical reduction is performed. Processed.

Next, a resin body with copper foil (about 18 μm thick copper foil 3 (upper layer metal foil) having an insulating resin layer 1 (epoxy resin) of about 50 μm adhered) is placed on the copper-clad double-sided plate. The alignment was performed and the layers were stacked. (Pressure 25 kg, temperature 180
Degree, time 120 minutes)

Next, the upper copper foil 3 of the laminated resin body with copper foil
Laminate a dry film on the (upper layer metal foil), expose the pattern at the desired position for forming a via hole by irradiating ultraviolet rays, develop, and half-etch with ferric chloride to form a thin layer portion 8 (diameter of about 0.2 mm, copper foil) Of about 5 μm). The surface of the thin layer portion 8 was uneven and rough, and was in a state of high absorption of laser energy.

Next, it is positioned and set on a processing table of a carbon dioxide laser device, and W2 (diameter of about 0.2 m) of the thin layer portion 8 is set.
m (thin layer) with a diameter larger than the laser (dimension W1 is about 0.3 mm).
The thin film 8 and the epoxy resin 1 were melted, vaporized, and decomposed to form a hole 5 by irradiating the thin film 8 with a beam diameter of 3 mm, and the dry film was peeled off. This peeling process may be performed after the thin layer portion 8 is formed, but if the peeling process is performed after all the holes are formed, the scattered matter during the laser processing rides on the dry film and the peeling of the dry film occurs. Can be removed. (Similarly, the thin layer portion 8 was irradiated with a laser, the laser was stopped halfway, and the thin layer portion was observed. When the thin layer portion was observed, a hole was opened in the center of the thin layer portion and the periphery was in a molten state. The energy of the beam is high in the center,
It is conceivable that the heat conduction of the thin layer portion thinner than the surroundings is small. )

Next, the inside of the hole 5 is subjected to a smearing treatment by the potassium permanganate method, and the upper copper foil 3 is passed through the hole.
Then, copper plating (electroless copper plating + electrolytic copper plating) for electrically connecting the lower copper foil 2 (lower conductor layer 2) was performed to form a via hole 6.

Next, the dry film is laminated, the pattern is baked, developed, and the copper foil is etched with ferric chloride, peeled off to form a circuit pattern, and a resist for protecting the copper foil on the surface is soldered. A printed wiring board with via holes was formed except for the attachment area.

In the printed wiring board manufactured as described above, the holes were not larger than the dimension W2 of the thin layer portion, and the upper copper foil and the lower copper foil were electrically connected to each other by the via holes with high reliability.

[0024]

According to the printed wiring board and the method of manufacturing the same of the present invention, in the step of selectively removing the upper layer metal foil to form a thin layer portion, compared with the hole forming for removing the entire thickness. The holes formed in the thin layer are thus accurate. In addition, the surface of the thin layer portion is in an uneven state and the laser energy absorption is good. Further, by irradiating a laser having a dimension W1 having a larger area than the thin layer portion formed with the dimension W2, melting and vaporization start from the center of the thin layer portion, and the insulating resin layer also melts, vaporizes and decomposes from the central portion. When the starting dimension W2 is reached, a hole reaching the lower conductor layer is formed, and an electrical connection is good, accurate, and highly reliable without forming an abnormal hole near the upper metal foil. The manufacturing method can be provided.

[0025]

[Brief description of the drawings]

FIG. 1 is a sectional view of one embodiment showing a printed wiring board according to the present invention and a method for manufacturing the same. FIG. 1A is a sectional view of a mode of laser irradiation, and FIG. 1B is a sectional view of a mode of via hole formation. FIG. 2 is a sectional view showing a conventional embodiment.

[0026]

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating resin layer 2 Lower conductor layer 3 Upper metal foil 4 Laser 5 Hole 6 Via hole 7 Window 8 Thin layer part

Claims (1)

[Claims] 1. A printed wiring board for forming a circuit pattern on a substrate on which a metal foil and an insulating resin layer are laminated, and a method for manufacturing the same, wherein a thin layer portion is formed by selectively removing an upper metal foil partially. Forming a hole in the thin layer portion and the insulating resin layer by irradiating a laser to an area larger than the thin layer portion in the thin layer portion and the insulating resin layer, and electrically connecting the upper metal foil and the lower conductor layer through the hole; And a step of forming a circuit pattern on the upper metal foil by a subtractive method.