JP2007096186A - Circuit board and its production process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance adhesion between an insulation layer and a conductor portion of a circuit board. <P>SOLUTION: The circuit board comprises a plurality of wiring layers, an insulation layer 20 having a fibrous filler and a resin 24 and insulating the plurality of wiring layers, and a conductor portion 41 formed on the sidewall 30a of a via 30 penetrating the insulation layer 20. The fibrous filler projecting from the sidewall 30a and contained in the conductor portion 41 has a length X longer than the film thickness Z of the conductor portion 41. Consequently, adhesion between the insulation layer and the conductor portion can be enhanced and a highly reliable circuit board can be provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique of a circuit board having an insulating layer containing a fibrous filler. More specifically, the present invention relates to a technique for a circuit board having excellent adhesion of a conductor portion such as a metal to an insulating layer.

  In recent years, the power consumption of LSIs has been increasing as LSIs have further improved performance and functions. Further, as electronic devices are downsized, mounting substrates are also required to be downsized, high density, and multi-layered. For this reason, the power consumption (heat density) per volume of the circuit board is increased, and the necessity for heat radiation countermeasures is increasing.

  For this reason, in a multilayer board | substrate, the structure provided with the via | veer for ensuring conduction | electrical_connection of each layer of a multilayer board | substrate, or suppressing a temperature rise is known. In addition, an insulating layer in which glass fibers are mixed into a resin is also used to improve strength and functionality.

Patent Document 1 discloses a printed wiring board in which an organic resin substrate is subjected to counterbore processing and a large number of beard-like fibers exposed on the side walls of the formed recesses are covered with a through-hole plating layer.
Japanese Patent Laid-Open No. 5-55401

  However, the length of the fiber exposed vertically from the side wall of the recess is allowed only to the extent that it can be covered with the through-hole plating layer, and depends on the thickness of the copper plating. Therefore, there is a possibility that the copper plating is peeled off from the insulating resin when the heat load is high.

  This invention is made | formed in view of such a subject, The objective is to provide the technique which improves the adhesiveness of the insulating layer and conductor part in a circuit board.

  One embodiment of the present invention is a circuit board. The circuit board includes a plurality of wiring layers, an insulating layer having a fibrous filler and a resin, and insulating the plurality of wiring layers, and a conductor portion formed on a side wall of a through-hole penetrating the insulating layer. The length of the fibrous filler that protrudes from the side wall and is included in the conductor portion is larger than the film thickness of the conductor portion. Here, as the fibrous filler, glass fiber is suitable from the viewpoint of heat dissipation and strength.

  According to this aspect, the length of the fibrous filler included in the conductor portion is larger than the film thickness of the conductor portion, thereby improving the adhesion between the insulating layer and the conductor portion due to the anchor effect. it can. In addition, it is not necessary for all the fibrous fillers to be longer than the film thickness of the conductor portion, and the above-described effects can be obtained if at least one fibrous filler is long.

  Here, the conductor portion includes not only the case of functioning as an electrical conduction portion that is connected to a plurality of wiring layers to form a multilayer wiring, but also the case of functioning as a heat transfer path during heat dissipation. As a conductor part, the metal which can be formed by a plating process is preferable, for example, you may form by copper plating.

  Moreover, when a conductor part is copper plating, the thermal expansion coefficient of glass and copper is compounded and the thermal expansion coefficient of copper plating reduces by making glass fiber with a small thermal expansion coefficient bite into copper plating. As a result, the expansion of copper plating during a thermal load is reduced, and the generation of cracks in the vicinity of the boundary between the resin and copper plating can be suppressed.

  In the above aspect, the through hole is preferably formed by drilling. According to this, the glass fiber protruding from the side wall tends to be inclined with respect to the side wall due to rotation during drilling, and the length of the protruding glass fiber tends to be larger than the film thickness of the conductor portion.

  Another embodiment of the present invention is a method for manufacturing a circuit board. The circuit board manufacturing method includes a step of forming a through hole by drilling in an insulating layer having a fibrous filler and a resin to insulate a plurality of wiring layers, and a resin portion of the side wall of the through hole. And a step of forming a conductor portion by plating on the side wall where the resin portion is dissolved.

  According to this aspect, the resin portion of the sidewall is melted before the plating treatment. Therefore, since the resin portion of the side wall is dissolved, the fibrous filler contained in the insulating layer can be more exposed, and the fibrous filler protruding longer than the film thickness of the conductor portion is formed. be able to. Here, as the fibrous filler, glass fiber is suitable from the viewpoint of heat dissipation and strength.

  A combination of the above-described elements as appropriate can also be included in the scope of the invention for which patent protection is sought by this patent application.

  ADVANTAGE OF THE INVENTION According to this invention, the adhesiveness of the insulating layer and conductor part in a circuit board can be improved, and a highly reliable circuit board can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the structure described below is an illustration and does not limit the scope of the present invention at all.

(Structure of circuit board)
FIG. 2 is a cross-sectional view showing the structure of the multilayer circuit board 10 according to the present embodiment. The circuit board 10 includes a plurality of insulating layers 20, 21, 22, vias 30 formed so as to penetrate the insulating layer 20, and a plurality of layers formed between the plurality of insulating layers 20 or on the surface of the insulating layer 20. Wiring layers 40, and via plugs 50 that connect each wiring layer 40 in the vertical direction of the circuit board 10.

  The insulating layer 20 is a material obtained by impregnating a glass cloth with an insulating resin 24. Examples of the resin include epoxy resin, melamine derivatives such as BT resin, liquid crystal polymer, PPE resin, polyimide resin, fluororesin, phenol resin, An organic resin such as polyamide bismaleimide is preferably used. It is preferable that the glass cloth has three layers in the epoxy resin. Here, one layer means a state in which glass fibers extending in different directions intersect each other, and three layers means a state in which three layers are stacked in the vertical direction with this state as a unit.

  In this embodiment, an epoxy resin copper-clad laminate (for example, FR-4) made of a flame-retardant glass cloth base material was used. Here, the thermal conductivity of FR-4 is 0.33 W / mK, and the withstand voltage is 29 MV / mm (when the frequency of the applied voltage is 50 Hz).

  The via 30 functions as a thermal via that releases heat generated by the heating element, for example, the LSI chip 60, disposed on the surface of the circuit board 10 to the back surface of the circuit board 10.

  For the wiring layer 40, for example, copper wiring by plating is preferably used. In addition, the via plug 50 can achieve good conduction at the boundary surface by using copper which is the same material as the wiring layer 40.

  A circuit device having excellent thermal conductivity by mounting a semiconductor element such as an LSI chip 60 or a passive element such as a capacitor or resistor on the circuit board 10 according to the present embodiment and electrically connecting to the wiring layer 40. Is obtained.

(Via fabrication method)
Next, a method for manufacturing the via 30 in the circuit board 10 will be described with reference to FIG. 3A is a cross-sectional view schematically showing an insulating layer including a glass cloth, FIG. 3B is a cross-sectional view in which a via is formed in the insulating layer shown in FIG. 3A by a drill, and FIG. ) Is a cross-sectional view showing a state in which the vicinity of the via shown in (b) is melt-treated, and FIG. 3D is a cross-sectional view showing a state in which the melt-treated via shown in (c) is plated.

  As shown in FIG. 3A, the insulating layer 20 according to the present embodiment includes glass fibers 23a extending in the horizontal direction on the paper surface and glass fibers 23b extending in the vertical direction on the paper surface (hereinafter referred to as glass fibers 23a). 23b are collectively referred to as glass fiber 23).

  When the via 30 is formed at a desired position of the insulating layer 20 by drilling, a part of the glass fiber 23 is cut (see FIG. 3B). In this embodiment, the glass fiber protruding from the side wall tends to be inclined with respect to the side wall due to rotation during drilling, and the length of the glass fiber tends to be larger than the film thickness of the conductor portion.

  In this state, desmear treatment with a chemical solution (for example, a permanganate solution) that dissolves only the insulating resin 24 without dissolving the glass fiber 23 is performed. By this process, the resin residue generated at the time of via formation by drilling and the resin on the via sidewall surface are removed. However, the inorganic material filled in the insulating layer 20 for the purpose of enhancing the heat dissipation property, in this embodiment, the glass fiber 23 remains undissolved. Therefore, the glass fiber contained in the insulating layer can be exposed more, and a glass fiber longer than the film thickness of the conductor portion can be formed.

  As a result, as shown in FIG. 3C, a part of the glass fiber 23 included in the insulating layer 20 protrudes from the side wall of the via 30.

  Next, a copper thin film of several hundred nanometers is deposited on the via 30 side wall surface by electroless copper plating using palladium as a catalyst. Thereafter, the conductor portion 41 is formed by electrolytic plating using a copper sulfate solution as a plating solution (see FIG. 3D). The thickness of the copper plating is preferably about several tens of μm, more preferably about 10 to 30 μm. In this embodiment, the film thickness is about 15 μm.

  Thus, by performing the copper plating process with the glass fiber 23 protruding from the via side wall, the protruding glass fiber 23 is taken into the copper plating, and is formed by the resin and plating contained in the insulating layer 20. Adhesion with the conductor part 41 can be improved. As a result, it is possible to suppress the peeling of the metal film that is the conductor portion from the resin and the occurrence of cracks, thereby improving the reliability of the circuit board.

  The above phenomenon will be described in more detail with reference to FIG. Fig.1 (a) is a schematic diagram at the time of seeing the state which formed the via | veer in the insulating layer by drilling from upper direction. FIG.1 (b) is a schematic diagram when the state which plated the via | veer shown to (a) is seen from upper direction.

  As shown in FIG. 1A, when the via 30 is formed in the insulating layer 20 by drilling, a number of glass fibers 23 protrude from the via sidewall 30a. In particular, since the via 30 is formed by a rotating drill, some of the protruding glass fibers 23 protrude spirally along the via sidewall 30a.

  If only the resin is dissolved in this state, the resin portion of the side wall 30a is retracted, and the glass fiber 23 is exposed longer. Therefore, when the plating process is performed, glass fibers having a length X larger than the plating film thickness Z are encapsulated in the conductor portion 41 as shown in FIG. Here, the length X of the glass fiber included in the conductor portion is, for example, a length along the glass fiber 23c protruding from the side wall 30a, as shown in FIG. Moreover, the plating film thickness Z is the thickness which goes to the normal line direction of the side wall 30a. In this embodiment, the film thickness Z is about 15 μm, and in that case, glass fibers having a length X of about 15 to 30 μm may be present in the conductor portion 41.

  Therefore, according to this embodiment, the glass fiber 23 in which the length X of the glass fiber> the plating film thickness Z> is easily present in the conductor portion 41 by the drilling process and the resin melting treatment, and the length X of the glass fiber <Compared with the case where only the glass fiber having the plating film thickness Z is present, the adhesion between the resin and the conductor part such as wiring can be further improved, and peeling of the metal such as wiring can be suppressed.

  The present invention is not limited to the above-described embodiments, and various modifications such as design changes can be added based on the knowledge of those skilled in the art. The form can also be included in the scope of the present invention.

  In the above-described embodiment, the case of a thermal via (through hole) penetrating the insulating layer is described as an example, but the present invention is not limited to this. The same effect can be obtained even if the recess is provided in the insulating layer.

  In the above-described embodiment, the plating film thickness Z does not necessarily have to be uniform. When the plating film thickness Z varies depending on the location, the length X of the glass fiber included in the conductor portion from the thinnest film thickness Z1. Should be large.

  In the above-described embodiment, the wiring layers are formed on both surfaces of the insulating layer, but the structure of the wiring layers is not limited to this. For example, the wiring layer may be provided only on one side of the insulating layer. A plurality of wiring layers may be stacked via a plurality of insulating layers.

  In the above-described embodiment, the insulating resin layer is a multilayer, but may be a single layer structure.

Fig.1 (a) is a schematic diagram at the time of seeing the state which formed the via | veer in the insulating layer by drilling from upper direction. FIG.1 (b) is a schematic diagram when the state which plated the via | veer shown to (a) is seen from upper direction. It is sectional drawing which shows the structure of the multilayer circuit board which concerns on embodiment. 3A is a cross-sectional view schematically showing an insulating layer including a glass cloth, FIG. 3B is a cross-sectional view in which a via is formed in the insulating layer shown in FIG. 3A by a drill, and FIG. ) Is a cross-sectional view showing a state in which the vicinity of the via shown in (b) is melt-processed, and FIG. 3D is a cross-sectional view showing a state in which the melt-processed via shown in (c) is plated.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Circuit board, 20, 21, 22 Insulating layer, 23 Glass fiber, 24 Resin, 30 Via, 30a Side wall, 40 Wiring layer, 41 Conductor part, 50 Via plug, 60 LSI chip.

Claims (6)

Multiple wiring layers;
An insulating layer having a fibrous filler and a resin to insulate the plurality of wiring layers;
A conductor formed on a side wall of a through hole penetrating the insulating layer;
With
A circuit board characterized in that the length of the fibrous filler protruding from the side wall and encapsulated in the conductor is larger than the film thickness of the conductor.   The circuit board according to claim 1, wherein the fibrous filler is a glass fiber.   The circuit board according to claim 1, wherein the plurality of wiring layers and the conductor are electrically connected.   The circuit board according to claim 1, wherein the through hole is formed by drilling.   5. The circuit board according to claim 1, wherein the fibrous filler has a direction protruding from the side wall oblique to a normal direction of the side wall. Forming a through hole by drilling in an insulating layer having a fibrous filler and a resin to insulate a plurality of wiring layers;
A step of dissolving the resin portion of the side wall of the through hole; and
Forming a conductor portion by plating on the side wall where the resin portion is dissolved;
A method of manufacturing a circuit board, comprising:

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