JP2007150348A - Wiring substrate and electronic component mounting structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wiring substrate with high reliability which can sufficiently bear thermal stress even if long-term thermal histeresis is applied repeatedly in the wiring substrate having a through conductor with a small diameter. <P>SOLUTION: The wiring substrate has an insulating layer 1c having a through-hole 3, and a through conductor 4 which is partly formed in the through-hole 3. In the through conductor 4, a lower end closes the bottom of the through-hole 3, and a projecting part projects outwardly from the inner wall of the through-hole 3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wiring board used for mounting an electronic component such as a semiconductor element and an electronic component mounting structure using the wiring substrate.

  In general, current electronic devices are required to be small, thin, lightweight, high performance, high functionality, high quality, and high reliability, as represented by mobile communication devices. Electronic devices to be used are also required to be small and high density. Therefore, the wiring board constituting the electronic device is also required to be small, thin, and multi-terminal, and in order to realize it, the width of the wiring conductor such as the signal conductor is narrowed and the interval is narrowed. High-density wiring is achieved by increasing the number of wiring conductors.

  As a wiring board capable of such high-density wiring, a wiring board manufactured by adopting a build-up method is known. This build-up wiring board is, for example, a core insulation layer that is heat-cured by impregnating a reinforcing material such as glass cloth or aramid non-woven fabric with a thermosetting resin typified by an epoxy resin having heat resistance and chemical resistance. After the wiring conductor is formed on the surface of the substrate, a resin varnish made of a thermosetting resin such as an epoxy resin is applied and heat-cured to form an insulating layer. A through hole of about 50 to 200 μm is formed, and then the inside of the through hole and the surface of the insulating layer are chemically roughened with a roughening solution such as a potassium permanganate solution, and further, the insulating layer is formed using a semi-additive method. A conductor film made of copper plating is deposited on the surface and the inner wall of the through hole to form a wiring conductor and a through conductor, and an insulating layer, a through conductor and a wiring conductor are formed on the wiring conductor and the through conductor repeatedly. The through conductor is electrically connected to the lower wiring conductor below the through hole.

  However, when the through hole is drilled with a laser, the thermosetting resin of the insulating layer remains on the wiring conductor located under the through hole, and the inside of the through hole is roughened with a potassium permanganate solution or the like. Even if it is chemically roughened with a liquid, the thermosetting resin remaining on the wiring conductor cannot be completely removed, and the electrical connection between the through conductor and the wiring conductor is hindered. .

In order to completely remove the remaining thermosetting resin, Japanese Patent Application Laid-Open No. 2000-244127 proposes a wiring board provided with a recess by etching the surface of the wiring conductor located below the through hole. ing.
JP 2000-244127 A

However, the wiring board described in Japanese Patent Application Laid-Open No. 2000-244127 has a reduced connection area between the bottom surface of the through conductor and the wiring conductor when the small diameter through conductor has a diameter of 50 μm or less, and copper plating. The thermal expansion coefficient of the through conductor is approximately 18 × 10 ⁻⁶ / ° C, whereas the thermal expansion coefficient in the thickness direction of the insulating layer is greatly different from 80 to 200 × 10 ⁻⁶ / ° C. When the thermal history is repeatedly applied, the thermal stress due to the difference in thermal expansion between the insulating layer and the through conductor is concentrated at the connection portion between the two, causing a disconnection failure.

  The present invention has been completed in view of the problems of the prior art, and its purpose is to sufficiently withstand thermal stress even if a long-term thermal history is repeatedly applied to a wiring board having a small-diameter through conductor, and to break the wire. It is an object of the present invention to provide a wiring board with high connection reliability that does not cause the problem and an electronic component mounting structure using the wiring board.

  The wiring board of the present invention is a wiring board comprising an insulating layer having a through-hole and a through-conductor partially formed in the through-hole, the lower end of the through-conductor having the through-hole. It has a protruding portion that closes the bottom of the hole and protrudes outward from the inner wall of the through hole.

  In the wiring board of the present invention, it is preferable that the through conductor is integrally formed with the lower end portion and a portion formed in the through hole.

  In the wiring board of the present invention, preferably, the insulating layer is a resin.

  In the wiring board of the present invention, preferably, the through conductor is formed by plating.

  Preferably, the wiring board of the present invention further includes a wiring conductor connected so as to cover the lower end portion from below.

  In the wiring board of the present invention, preferably, the wiring conductor has a connection portion with the lower end portion thinner than the remaining portion.

  In the wiring board of the present invention, preferably, the wiring conductor has a concave portion formed on a surface thereof, and the lower end portion is disposed in the concave portion.

  The wiring board according to the present invention is preferably characterized in that the upper surface of the protruding portion and the upper surface of the wiring conductor are located on the same plane.

  The electronic component mounting structure of the present invention is characterized in that the electronic component is mounted on the wiring board of the present invention.

  According to the present invention, even when a mounting component such as a semiconductor element is mounted on a wiring board, even if a long-term thermal history is repeatedly applied, it can withstand longitudinal tensile stress resulting from thermal stress, and disconnection does not occur. It can be highly reliable.

  Next, the wiring board of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view showing an example of an embodiment when the wiring board of the present invention is applied to a build-up wiring board, and FIG. 2 is an enlarged cross-sectional view of the main part of FIG.

  In these drawings, 1 is an insulating layer, 2 is a wiring conductor, 3 is a through-hole, 4 is a through-conductor, and 5 is a recess formed in a region located below the through-hole 3. A wiring board is configured. In this example, the first insulating layer 1b and the second insulating layer 1c are laminated on the upper and lower surfaces of the core insulating layer 1a serving as the core, respectively.

  The core insulating layer 1a has a function as a support for the first and second insulating layers 1b and 1c and has a function of imparting strength to the wiring board, and is a plate having a thickness of about 0.3 to 1.5 mm. is there. Such a core insulating layer 1a is formed, for example, by impregnating a glass cloth in which glass fibers are woven vertically and horizontally with a thermosetting resin such as an epoxy resin or a bismaleimide triazine resin, and has a diameter of 0.1 to 1.0 from the upper surface to the lower surface. It has a plurality of through holes 11 of about mm. The wiring conductor 2 is attached to the upper and lower surfaces, and the through-hole conductor 12 is attached to the inner wall of each through-hole 11. The through-holes are formed on the inner wall of the through-hole 11. It is electrically connected through the conductor 12.

  In such a core insulating layer 1a, a copper foil having a thickness of 3 to 50 μm is applied to the entire upper and lower surfaces of a sheet for an uncured core insulating layer, and this copper foil is etched after the sheet is cured. The wiring conductor 2 is formed in a predetermined pattern, and after the sheet is thermally cured, the through hole 11 is further plated on the inner wall of the through hole 11 by drilling from the upper surface to the lower surface. Through-hole conductors 12 are formed by depositing and depositing copper plating having a thickness of about 3 to 50 μm by the method. The wiring conductor 2 may be formed integrally with the through-hole conductor 12 by plating when the through-hole conductor 12 is deposited on the inner wall of the through-hole 11.

  Furthermore, the core insulating layer 1a is filled with resin pillars 13 made of a thermosetting resin such as an epoxy resin or a bismaleimide triazine resin in the through hole 11. The resin pillar 13 is used to form the first and second insulating layers 1b and 1c immediately above and below the through hole 11 by closing the through hole 11, and is an uncured paste-like thermosetting The resin is filled in the through-hole 11 by screen printing, thermally cured, and then the upper and lower surfaces thereof are polished to be substantially flat. Insulating layers 1b and 1c are laminated on the upper and lower surfaces of the core insulating layer 1a including the resin pillars 13.

  Each of the first and second insulating layers 1b and 1c has a thickness of about 20 to 60 μm, a thermosetting resin such as an epoxy resin or a modified polyphenylene ether resin, and a particle size of 0.01 to 2 μm and a content of 10 to 50. It consists of inorganic insulating fillers such as silica and alumina / aluminum nitride.

  The first and second insulating layers 1b and 1c are provided to provide an insulation interval for wiring the wiring conductors 2 at high density, and the upper and lower wiring conductors 2 are covered on the inner wall of the through hole 3. High density wiring can be formed in three dimensions by electrical connection through the formed through conductors 4. The first and second insulating layers 1b and 1c are formed by sequentially laminating films made of uncured thermosetting resin and inorganic insulating filler on the upper and lower surfaces of the core insulating layer 1a, respectively, and thermosetting them. It is formed by doing. In addition, after forming the first insulating layer 1b, the wiring conductor 2 is formed on the surface thereof with a copper plating film having a thickness of about 3 to 50 μm in a predetermined pattern by a conventionally known semi-additive method or subtractive pattern formation method. It is formed by depositing.

  A through hole 3 is formed in the second insulating layer 1c on the wiring conductor 2 formed on the first insulating layer 1b. The through hole 3 has an opening diameter of about 20 to 100 μm, and is formed by stacking the second insulating layer 1c and then processing it using a conventionally known carbon dioxide laser, UV-YAG laser, excimer laser, or the like. .

  The wiring conductor 2 has a function as a conductive path for connecting each electrode of an electronic component (not shown) such as a semiconductor element to be mounted to an external electric circuit board (not shown). The thickness of 2 is preferably about 3 to 50 μm, and 3 μm or more from the viewpoint of transmitting a high-speed signal is to prevent peeling due to a difference in thermal expansion between the wiring conductor 2 and the insulating layers 1b and 1c. From the viewpoint, it is preferably 50 μm or less.

  In the wiring board of the present invention, the concave portion 5 having a diameter larger than that of the through hole 3 is formed on the upper surface immediately below the through hole 3 of the wiring conductor 2 so that the through hole 3 is located inside thereof. The inside of the recess 5 is filled with copper plating. This is important in the wiring board of the present invention.

  According to the present invention, the concave portion 5 having a diameter larger than that of the through hole 3 is formed on the upper surface immediately below the through hole 3 of the wiring conductor 2 so that the through hole 3 is located inside the concave portion 5. Since the filling is performed by plating, the portion formed in the concave portion 5 of the copper plating becomes a wedge, and the through conductor 4 and the wiring conductor 2 can be firmly connected. Therefore, even when a long-term thermal history is applied repeatedly in the state of an electronic component mounting structure in which electronic components such as semiconductor elements are mounted on a wiring board, it withstands longitudinal tensile stress resulting from thermal stress and disconnection occurs. There can be no connection reliability.

  Such wiring conductor 2 / through hole 3 and through conductor 4 are formed by the following method. First, the second insulating layer 1c is deposited on the first insulating layer 1b having the wiring conductor 2 deposited on the surface, and the through-hole 3 is formed in the second insulating layer 1c on the wiring conductor 2 by laser. A part of the wiring conductor 2 is exposed. Next, the surface of the second insulating layer 1c, the inner wall of the through-hole 3, and the wiring conductor 2 exposed inside the through-hole 3 are immersed in a roughening solution such as a permanganate aqueous solution at 60 ° C. for about 15 minutes. After that, it is immersed in an etching solution made of sulfuric acid / hydrogen peroxide solution at 25 ° C. for several minutes, and the wiring conductor 2 exposed inside the through hole 3 is etched to form a through hole at a portion exposed in the through hole 3. A recess 5 having a diameter larger than 3 is formed. Next, it is immersed in an electroless copper plating solution composed of copper sulfate, rossel salt, formalin, EDTA sodium salt, stabilizer, etc. at 40 ° C. for about 30 minutes, and the surface of the insulating layer 1c, the inner wall of the through hole 3, and the entire surface of the recess 5 1 to 2 μm of electroless copper plating is deposited. Furthermore, a plating-resistant resin layer having a wiring pattern-shaped opening is deposited on the electroless copper plating layer, and immersed in an electrolytic copper plating solution composed of sulfuric acid, sulfuric acid pentahydrate, chlorine, and brightener for about 1 hour. After the electrolytic copper plating is applied to the opening of the plating resistant resin layer, the plating resistant resin layer is peeled off and etched to form the wiring conductor 2 and the through conductor 4.

  The recess 5 has a polygonal shape such as a rectangle or trapezoid, a semicircular shape, etc., and the diameter of the opening is preferably about 5 to 20% larger than the diameter of the bottom. If the diameter of the recess 5 is less than 5% larger than the diameter of the bottom of the through-hole 3, there is little wedge-like biting and the wiring conductor 2 and the through-conductor 4 cannot be firmly connected, and a long-term thermal history can be applied repeatedly. Then, there is a tendency to break, and if it exceeds 20%, the copper plating solution cannot sufficiently penetrate into the recess 5 and the penetrating conductor 4 having a good shape cannot be formed. Therefore, the diameter of the recess 5 is preferably about 5 to 20% larger than the diameter of the bottom of the through hole 3.

  The depth of the recess 5 is preferably about 5 to 50% with respect to the thickness of the wiring conductor 2. If the depth is less than 5% of the thickness of the wiring conductor 2, the thermosetting resin remaining on the wiring conductor 2 cannot be completely removed, and the electrical connection between the through conductor 4 and the wiring conductor 2 is hindered. If the depth exceeds 50%, the wiring conductor 2 becomes thin and the electric resistance tends to increase. Therefore, the depth of the recess 5 is preferably about 5 to 50% with respect to the thickness of the wiring conductor 2.

  Thus, according to the wiring board of the present invention, the concave portion 5 having a diameter larger than the diameter of the through hole 3 is formed in the region located below the through hole 3 of the wiring conductor 2, and the concave portion 5 is filled with copper plating. As a result, the copper plating can be wedged into the portion located below the through conductor 4 of the wiring conductor 2 to form a strong connection portion, so that mounting parts such as semiconductor elements are mounted on the wiring board. Thus, it is possible to provide a wiring board with high connection reliability that can sufficiently withstand the tensile stress in the vertical direction caused by thermal stress when a long-term thermal history is repeatedly applied, and that is free from disconnection.

  The present invention is not limited to one example of the above-described embodiment, and various modifications can be made without departing from the gist of the present invention. For example, in the above-described embodiment, the first embodiment Although the example in which the through conductor 4 is formed in the insulating layer 1c is shown, the through conductor 4 may be formed in the second insulating layer 1b. Furthermore, a solder-resistant resin layer 6 may be deposited on the surface of the outermost insulating layer 1c in order to improve heat resistance during solder reflow.

It is sectional drawing which shows an example of embodiment of the wiring board of this invention. It is a principal part expanded sectional view of the wiring board of FIG.

Explanation of symbols

1. Insulating layer 1a ... Core insulating layer 1b ... First insulating layer 1c ... .... Second insulation layer 2 ... Wiring conductor 3 ... Through hole 4 ... Through conductor 5 ... .... Recess

Claims (9)

A wiring board comprising an insulating layer having a through hole, and a through conductor partially formed in the through hole,
The wiring board according to claim 1, wherein the through conductor has a projecting portion whose lower end portion closes a bottom portion of the through hole and projects outward from an inner wall of the through hole.   The wiring substrate according to claim 1, wherein the through conductor is integrally formed with the lower end portion and a portion formed in the through hole.   The wiring board according to claim 1, wherein the insulating layer is a resin.   The wiring substrate according to claim 1, wherein the through conductor is formed by plating.   The wiring board according to claim 1, further comprising a wiring conductor connected so as to cover the lower end portion from below.   The wiring board according to claim 5, wherein the wiring conductor has a connection portion with the lower end portion thinner than the remaining portion.   The wiring board according to claim 5, wherein a concave portion is formed on a surface of the wiring conductor, and the lower end portion is disposed in the concave portion.   The wiring board according to claim 5, wherein an upper surface of the protruding portion and an upper surface of the wiring conductor are located on the same plane.   An electronic component mounting structure formed by mounting an electronic component on the wiring board according to claim 1.

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