JP2006216674A - Printed circuit with improved heat dissipation performance and circuit module comprising the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an improved printed circuit board whose heat dissipation is improved, in which high density mounting is achieved and a circuit pattern is easily made into multiple layers. <P>SOLUTION: The circuit board is provided with a circuit upper face pattern layer 2a and an intermediate pattern layer 3 which are arranged by intervening a first insulating layer 5, and a circuit lower face pattern layer 4 which is disposed on an opposite side of the intermediate pattern layer 3 by intervening a second insulating layer 6. A first back facing hole 9 formed from a surface toward an inner part is formed at least in the first insulating layer 5 or the second insulating layer 6. The circuit upper face pattern layer 2a or the circuit lower face pattern layer 4 and the intermediate pattern layer 3 are connected by a conductor film 2b with thermal conductivity of 50 W/(m K) or above, which is continuously formed on an inner wall face of the first back facing hole 9. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a printed circuit board, and more specifically, an improved printed circuit board that has improved heat dissipation, can be mounted at high density, and can easily make multiple circuit patterns. About. The present invention also relates to a circuit module using such a printed circuit board.

  In recent years, communication devices and information devices have greatly shifted to “palm” type products represented by mobile phones. Under such circumstances, higher-density mounting of components has been made more than ever. On the other hand, the function of a mobile phone as a communication device or an information device is also improved, and it cannot be expected that the power consumption will greatly decrease in the future. Therefore, power consumption per unit volume is increasing.

  In particular, in a communication device equipped with a light emitting element such as a semiconductor laser or a light emitting diode, the current-light conversion efficiency is directly affected by temperature. In addition, since the operation such as light emission / detection is analog, the temperature change may directly affect not only power consumption but also performance such as a reduction in communication distance.

  An example of the configuration of a printed circuit board with improved heat dissipation is disclosed in Patent Document 1, for example. A typical configuration is shown in FIG.

  Referring to FIG. 9, a circuit pattern 2 and an inner wiring pattern 31 are provided with an insulating layer (glass epoxy substrate) 5 containing an inorganic filler interposed. Circuit components 8 a and 8 b are connected to the circuit pattern 2. A heat radiator 12 is provided on the back surface of the insulating layer 5 with an insulating layer (glass epoxy substrate) 6 interposed therebetween. A counterbore 9 is provided on the upper surface of the insulating layer 5. The circuit pattern 2 is formed to extend to the inner wall surface of the counterbore hole 9. A light emitting diode 1 that is a heat generating circuit component is connected to the circuit pattern 2 formed on the bottom surface of the counterbore 9. The counterbore 9 is filled with a transparent resin so as to cover the light emitting diode 1. In this conventional example, the heat generated from the light emitting diode 1 is transmitted to the heat sink 12 through the insulating layer 5 containing an inorganic filler. Further, the heat is transmitted from the circuit pattern 2 provided on the upper surface of the substrate to the heat dissipation plate 12 through the heat dissipation via 7 and the wiring pattern 31. Here, the heat flow is indicated by a broken line with an arrow.

  In the example shown in Patent Document 2, the heat pipe 13 is fixed to the main body of the circuit board 5 having a thickness of 100 μm with a resin 16 as shown in FIG. By providing the heat pipe 13, heat conduction is increased, and the heat generated in the circuit board 5 is released to the opposite surface. Again, the heat flow is indicated by broken lines with arrows. In the figure, 1 is a light emitting diode, and 2 is a circuit upper surface pattern layer.

Japanese Patent Laid-Open No. 2004-39691

Japanese Patent Laid-Open No. 03-242997

  In the method described in Patent Document 1, it is described that the thermal conductivity is set to 1 to 10 W / (m · K) by including an inorganic filler in the insulating layer 5. This is about 3 to 30 times that of a normal glass epoxy resin, but is only a small value of about 1/40 to 1/400 compared to a metal (for example, copper). Furthermore, since the insulating layer 5 is smaller than the thermal conductivity of the semiconductor element to be mounted, the insulating layer 5 becomes a thermal resistance and does not lead to a dramatic temperature drop of the semiconductor element. In Patent Document 1, heat is transmitted from the upper surface of the substrate to the vicinity of the heat radiating plate 12 by using the heat radiating via 7. In this method, since the metal layer that is the circuit pattern 2 is thin, it is difficult for heat generated from the semiconductor element to be transmitted to the via 7 and the cross-sectional area of the metal part on the inner surface of the via is small, so that a sufficient heat conduction path can be obtained. As a result, the temperature drop of the semiconductor element is suppressed. In addition, it is not always preferable to provide such a heat dissipation via 7 on the upper surface of the circuit because it hinders high-density mounting.

  In the example of Patent Document 2 using the heat pipe 13, although it depends on the number of the heat pipes 13, it is expected that the heat dissipation performance is considerably increased. However, there are problems such that the entire circuit board becomes as thick as about 2 mm, and it is difficult to make a multilayer circuit for high-density mounting.

  An object of the present invention is to solve the above-described problems, and is an improved print that improves heat dissipation, can be mounted at high density, and can easily make multiple circuit patterns. It is to provide a circuit board.

  Another object of the present invention is to provide a circuit module using such a printed circuit board.

  A printed circuit board according to the present invention includes a top pattern layer and an intermediate pattern layer provided with a first insulating layer interposed therebetween. A lower surface pattern layer is provided on the opposite side of the intermediate pattern layer with a second insulating layer interposed. At least one of the first insulating layer and the second insulating layer is provided with a first counterbore hole formed inward from the surface. Thermal conductivity of 50 W / (m · K) or more in which any one of the upper surface pattern layer or the lower surface pattern layer and the intermediate pattern layer are continuously formed on the inner wall surface of the first counterbore hole. Connected by body membranes. The upper surface pattern layer and the lower surface pattern layer may be formed of a circuit pattern, and the intermediate pattern layer may be formed of a metal and may be a circuit pattern.

  According to this invention, either one of the upper surface pattern layer or the lower surface pattern layer and the intermediate pattern layer are continuously formed on the inner wall surface of the first counterbore hole. K) Since the heat conductor films are connected to each other, it is possible to efficiently transfer the heat generated in the mounting component provided in the first counterbore to the intermediate pattern layer. Further, it is possible to efficiently transfer and dissipate the heat that has reached the intermediate pattern layer to the back surface.

  According to a preferred embodiment of the present invention, the connection between the one of the upper surface pattern layer or the lower surface pattern layer and the intermediate pattern layer is the thermal conductor formed on the bottom surface portion of the first counterbore hole. It is preferably carried out through a membrane. By comprising in this way, it will thermally radiate via the intermediate | middle pattern layer located directly under the exothermic component mounted in the component mounting surface, and heat dissipation improves.

  According to another embodiment of the present invention, the other first insulating layer or the second insulating layer not provided with the first counterbore hole is formed inward from the surface, and A second counterbore hole having a distance of 100 μm or less between the bottom surface and the intermediate pattern layer is provided.

  The thermal conductor film having a thermal conductivity of 50 W / (m · K) or more is preferably formed of a material containing any one of nickel, copper, gold, and silver.

  A circuit module according to another aspect of the present invention is formed by mounting circuit components inside the first or second counterbore hole. The circuit component is preferably a semiconductor laser element.

  According to the present invention, it is possible to efficiently transfer the heat generated in the mounted component to the intermediate pattern layer. Further, it is possible to efficiently transfer and dissipate the heat that has reached the intermediate pattern layer to the back surface. The intermediate pattern layer can be set larger than the component mounting area, and the heat radiation surface can be made larger than before. For this reason, the diffusion effect is increased, and there is an effect of suppressing the temperature rise of the mounted component and consequently the substrate.

  In particular, when heat is radiated from the intermediate pattern layer directly under the mounted component, the heat transfer path is minimized, and the effects of reducing the thermal resistance and suppressing the temperature rise of the component are further improved.

  When the thermal conductivity of the thermal conductor film is 50 W / (m · K) or more, the heat conductivity of the semiconductor material itself is about 50 W / (m · K) at the maximum, so the heat generated in the semiconductor is mounted on the mounting surface. There is an effect that does not become a bottleneck that accumulates in the circuit pattern provided in the circuit.

  For the purpose of providing a printed circuit board that has improved heat dissipation, can be mounted at high density, and can be easily multi-layered with a circuit pattern, one of an upper surface pattern layer and a lower surface pattern layer is used. The intermediate pattern layer is connected by a thermal conductor film having a thermal conductivity of 50 W / (m · K) or more continuously formed on the inner wall surface of the first counterbore hole. Examples of the present invention will be described below. In the following drawings, the same or corresponding parts are denoted by the same reference numerals.

  FIG. 1 is a cross-sectional view of a circuit module using a printed circuit board according to the first embodiment. First, after describing a manufacturing method, its function will be described.

  A glass epoxy substrate 5 having a thickness of 0.4 mm with copper foil formed on both sides is prepared, and circuit upper surface pattern layer 2a and intermediate pattern layer 3 are formed on the upper surface and lower surface of the copper foil from the copper foil using a normal photolithography technique. Form. At this time, the thickness of the copper foil forming the intermediate pattern layer 3 can be set to a thickness of 0.1 mm or more, for example, when this layer is not used as a high-frequency line. Next, a 0.4 mm thick glass epoxy substrate 6 having a circuit lower surface pattern layer 4 formed on one surface thereof is prepared, and these substrates 5 and 6 are bonded using an adhesive, as shown in the figure. A circuit board composed of three layers (circuit upper surface pattern layer 2a, intermediate pattern layer 3, and circuit lower surface pattern layer 4) is formed. Through holes 7 and 17 extending from the upper surface (the surface of the circuit upper surface pattern layer 2a) to the lower surface (the surface of the circuit lower surface pattern layer 4) are formed in the circuit board after bonding. And the counterbore hole 9 for mounting the components 1 with large calorific value and high heat dissipation required is formed from the upper surface side. At this time, the depth of the counterbore 9 is set so as to extend beyond the intermediate pattern layer 3 and into the glass epoxy substrate 6. After the through holes 7 and 17 and the counterbore 9 are formed, the inside of the through holes 7 and 17 is plated in the order of copper, nickel and gold, and the inner wall surface of the counterbore 9 is simultaneously plated in the order of copper, nickel and gold. Processing is performed to form a continuous heat conductor film 2b to be a circuit pattern. These metals have high adhesion to the glass epoxy substrates 5 and 6, and a stable circuit pattern can be obtained.

  In actual component mounting, the heat generating component 1, the other components 8a and 8b, and the like are mounted at a desired position on the pattern by a die bond / wire bond process to form a desired circuit. In some cases, the surface of the circuit upper surface pattern layers 2a and 2b may be molded with resin for the purpose of protecting the semiconductor circuit element. In this case, the counterbore 9 is preferably filled with a material such as gel or rubber having low hardness for the purpose of relieving stress on the heat generating component 1.

  Next, the flow of heat generated from the heat generating component 1 will be described. The heat generated in the heat generating component 1 reaches the heat conductive film 2b at the bottom surface portion of the counterbore 9 as shown by the dotted arrow, and immediately reaches the intermediate pattern layer 3 from the heat conductive film 2b. The intermediate pattern layer 3 is transmitted to the circuit lower surface pattern layer 4 through the glass epoxy substrate 6 and is dissipated in the air or to the casing of the connected device and the mother substrate. The intermediate pattern layer 3 has a larger area than the pattern of the heat conductive film 2b on the mounting surface, and the distance from the intermediate pattern layer 3 to the lower surface is about 1/2 of the entire thickness. The effect of reducing thermal resistance due to the presence of 3 is remarkable. Thereby, the thermal resistance which was 300 K / W was reduced to about 150 K / W. The thermal resistance indicates the degree of temperature rise with respect to the amount of heat generated. If the thermal resistance is large, the temperature of the mounted component in use is greatly increased.

  On the other hand, as a comparative example, as shown in FIG. 2, the heat generating component 1 of this time is replaced with a normal component 8b and mounted, and heat is radiated by a heat radiating via (also referred to as a thermal via) 7 leading up and down. Note that the heat dissipation mechanism itself by the heat dissipation vias 7 leading up and down is a conventional technique. In this case, the heat generated in the heat generating component 1 is dissipated through the heat dissipating vias 7 as indicated by dotted arrows. FIG. 3 shows the result of examining the thermal resistance with the structure shown in FIG. In FIG. 3, the thermal resistance in the case of Example 1 and Example 2-4 described later is also shown together.

  In the case of the comparative example, the thermal resistance of 150 K / W was finally obtained by reducing the number of thermal vias to about 10. On the other hand, when the intermediate pattern layer 3 is provided and the heat conductive film 2b formed of the high heat conductive material provided on the inner wall surface of the counterbore hole 9 is joined thereto as in the present embodiment. The thermal resistance can be greatly reduced. Here, copper, nickel, gold, etc. used for the heat conductor film 2b (formed by plating) all have a thermal conductivity of 90 W / (m · K) or more, and a normal heat conductive paste, etc. The value is 100 times or more. In general, effective heat dissipation is possible by using a material whose value does not fall below the thermal conductivity of the semiconductor material itself, and the thermal conductivity of the thermal conductor film 2b should be about 50 W / (m · K). .

  The heat dissipation via 7 as shown in FIG. 9 becomes difficult to form as the integration level of the component mounting surface increases. Therefore, it is often impossible to provide a sufficient number of heat dissipation vias on the component mounting surface, and it can be confirmed that the improvement of heat dissipation by this embodiment is effective for realizing a small circuit component. . In addition, since the heat radiating vias 7 are processed one by one with a drill, the number of steps in manufacturing the substrate is large, and it is difficult to cope with a low price. On the other hand, the counterbore 9 can be manufactured in a single process, so that the price can be reduced.

  FIG. 4 is a cross-sectional view of a circuit module using a printed circuit board according to a modification of the first embodiment. Parts that are the same as or equivalent to those in the embodiment shown in FIG. 1 are given the same reference numerals, and the description thereof will not be repeated. Here, instead of providing a countersunk hole on the upper surface, a countersunk hole 9 reaching the intermediate pattern layer 3 is provided on the back surface of the part located immediately below the heat generating component 1 as shown in the figure. In this case, even if transfer molding is performed, no stress is generated in the heat generating circuit component 1, and it is not necessary to fill the counterbore hole 9. The heat generated in the heat generating component 1 flows as shown by the dotted line in the figure and is transmitted to the circuit lower surface pattern layer 4. The subsequent heat radiation is the same as in the first embodiment.

  As shown in FIG. 5, the heat resistance from the heating element to the external environment surrounding the entire circuit is the first thermal resistance R1 from the heating element to the intermediate pattern layer and the second thermal resistance from the intermediate pattern layer to the external environment. It consists of thermal resistance R2 and these act as series resistance. Therefore, when the power consumption W and the external environment temperature Ta, the temperature reached by the heat generating circuit element 1 is Ta + (R1 + R2) * W, and the effect of the second embodiment in which these thermal resistances R1 and R2 are switched is as follows. Same as Example 1. Thus, the counterbore 9 connected to the intermediate pattern layer 3 may be provided on the component mounting surface side or on the back surface thereof. However, in consideration of the temperature gradient inside the circuit lower surface pattern layer 4, it is expected that Example 1 has a slightly lower overall thermal resistance.

  FIG. 6 shows an embodiment in which the present invention is applied to an optical communication module. Parts that are the same as or equivalent to those in the embodiment shown in FIG. 1 are given the same reference numerals, and the description thereof will not be repeated. Specifically, the heat generating component 1 is a semiconductor laser element, and the circuit components 8a and 8b are light receiving elements. A structure shown in FIG. 6 was fabricated through substantially the same steps as in Example 1. However, in this example, the layer thickness of the intermediate pattern layer 3 was set to 0.1 mm. Moreover, the epoxy resin 10 with a lens was formed in the component mounting surface by the transfer mold process after circuit formation. This optical communication module is mounted on, for example, a motherboard of a mobile phone or a notebook personal computer, and heat is radiated through the mother board and the casing.

  However, as in this example, when the epoxy resin 10 covers the surface of the heat generating component 1 thickly (the lens is necessary to be thicker than a resin mold for protection purposes only), the component mounting surface is used. The amount of heat released by convection is reduced. Therefore, in the case of this example, it is necessary to further reduce the module thermal resistance. In this example, a copper foil having a thickness of 0.1 mm is used as the intermediate pattern layer 3. When there is such a thickness, the counterbore hole 9 can be set to have a bottom surface directly above or inside the intermediate pattern layer 3. In this example, the intermediate pattern layer 3 is in direct contact with the bottom surface portion of the heat conductive film 2b formed of a high heat conductive material plated in the counterbore 9. In this case, the heat generated in the heat generating component 1 does not flow from the side surface of the counterbore hole 9 to the intermediate pattern layer 3 as in the first embodiment, but instead of the heat conductor film 2b as shown by the dotted arrow in the figure. The intermediate pattern layer 3 is reached from a portion located immediately below the heat generating component 1. The state of the subsequent heat dissipation is the same as in the first embodiment.

  In this way, when the intermediate pattern layer 3 and the portion of the heat conductor film 2b located on the bottom surface of the counterbore 9 are bonded and the bonding area is large, the thermal resistance can be greatly reduced, and this embodiment is performed. In the example, a thermal resistance of 135 K / W was obtained (see FIG. 3). In particular, the output of analog parts such as semiconductor lasers is directly affected by temperature, resulting in a reduction in the distance for optical communication. Therefore, circuit boards and modules with improved heat dissipation are indispensable.

  FIG. 7 shows an example of an optical communication module using a substrate with further improved heat dissipation. The counterbore hole 11 is also formed in the structure of the third embodiment from the back side of the counterbore hole 9. The diameter of the counterbore 11 is formed to be equal to or larger than the diameter of the bottom surface of the counterbore 9. Of course, the effect of heat dissipation is reduced, but it may be smaller than the counterbore 9 depending on the layout. The inside of the counterbore 11 is plated in the order of copper, nickel, and gold, and the heat generated in the heat generating component 1 is, as shown by the dotted arrows in the figure, the heat conductor film 2b, the intermediate pattern layer 3 is transmitted to the circuit lower surface pattern layer 4 through the glass epoxy substrate 6 and is diffused in the air, or to the casing of the connected device and the mother substrate.

  In this embodiment, counterbore holes 11 are formed from the bottom surface of the substrate, and the thermal resistance can be controlled by changing the distance d between the bottom surface of the counterbore holes 11 and the intermediate pattern layer 3. In this embodiment, this distance is set to 50 μm. FIG. 8 shows the state of thermal resistance when the distance d is changed. It can be seen that the thermal resistance is reduced as the distance d is shortened, but it is confirmed that the distance d decreases rapidly particularly in the region of 100 μm or less. The maximum depth tolerance in the counterbored hole forming process is ± 50 μm. By setting the above distance to 50 μm, the actual d becomes 0 μm <d <100 μm, and the thermal resistance is 115 (K / W) or less. It became possible to reduce. As is apparent from FIG. 3, this value is a value of thermal resistance that is difficult to achieve only by increasing the number of heat-dissipating vias.

  In this example, the component mounting pattern (2a) and the intermediate pattern layer 3 are not electrically connected directly to the pattern 4 formed on the inner wall surface of the counterbore hole 11 on the lower surface side, and the degree of freedom in circuit design. It is assumed that However, it goes without saying that the patterns 2a, 3 and 4 may be connected to each other through heat dissipation vias.

  By making the entire glass epoxy layer 6 thin, the same effect as in the present embodiment can be obtained. However, in such a structure, the entire substrate becomes thin, and the warping of the substrate due to stress after transfer molding, wire breakage, etc. Problems are likely to occur.

  It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. For example, the glass epoxy layer 6 may be another insulating material. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention relates to a printed circuit board on which circuit components that generate a large amount of heat are mounted. In particular, it can be used as a circuit board that requires less resin heat radiation from the component mounting surface. In addition, when the mold resin has a function other than circuit protection and the thickness cannot be reduced (for example, an optical module component typified by IrDA), it has a significant heat dissipation effect.

It is sectional drawing of the circuit module using the printed circuit board concerning Example 1. FIG. It is sectional drawing of the circuit module using the printed circuit board concerning a comparative example. It is a figure which shows the relationship between the number of thermal via holes, and thermal resistance. It is sectional drawing of the circuit module using the printed circuit board concerning Example 2. FIG. It is the figure which showed the flow of the heat | fever from the heat generating element to the external environment surrounding the whole circuit using thermal resistance. FIG. 6 is a cross-sectional view of an optical communication module using a printed circuit board according to Example 3; FIG. 6 is a cross-sectional view of an optical communication module using a printed circuit board according to Example 4; It is a figure which shows the relationship between the distance d of the bottom face of a counterbore hole, and an intermediate | middle pattern layer, and thermal resistance. It is sectional drawing of the circuit module using the conventional printed circuit board. It is sectional drawing of the circuit module using another conventional printed circuit board.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heat-generating component 2a Circuit upper surface pattern layer 2b Thermal conductor film 3 Intermediate pattern layer 4 Circuit lower surface pattern layer 5, 6 Glass epoxy board 7 Heat radiation via 8a. 8b Circuit parts 9, 11 Counterbored holes 10 Epoxy resin (transfer mold resin)
12 radiator 13 heat pipe

Claims (6)

An upper surface pattern layer and an intermediate pattern layer provided with a first insulating layer interposed therebetween;
A lower surface pattern layer provided on the opposite side of the intermediate pattern layer with a second insulating layer interposed therebetween,
At least one of the first insulating layer or the second insulating layer is provided with a first counterbore hole formed inward from the surface,
Thermal conductivity of 50 W / (m · K) or more in which either one of the upper surface pattern layer or the lower surface pattern layer and the intermediate pattern layer are continuously formed on the inner wall surface of the first counterbore hole A printed circuit board characterized by being connected by a body membrane.   The connection between any one of the upper surface pattern layer or the lower surface pattern layer and the intermediate pattern layer is performed through the thermal conductor film formed on the bottom surface portion of the first counterbore hole. The printed circuit board according to claim 1.   The other first insulating layer or the second insulating layer not provided with the first counterbore hole is formed inward from the surface, and the distance between the bottom surface and the intermediate pattern layer is The printed circuit board according to claim 1, wherein a second counterbore hole having a size of 100 μm or less is provided.   The printed circuit board according to claim 1, wherein the thermal conductor film is made of a material containing any one of nickel, copper, gold, and silver.   A circuit module in which a circuit component is mounted in the first or second counterbore using the printed circuit board according to claim 1.   6. The circuit module according to claim 5, wherein the circuit component is a semiconductor laser element.

Images