JPH03255690A - Heat pipe buried circuit board and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve a circuit board in thermal conductivity to the heat absorbing part of a heat pipe and to make the circuit board thin by a method wherein the heat absorbing part of the heat pipe is formed flat. CONSTITUTION:A circuit board 11 is provided with circuit patterns 12 and 26 formed on both the sides of a board 18, and a heat absorbing part 17a of a heat pipe formed so flat as to be provided with a plane in parallel with the plane of the board 18 is buried inside an insulating board 16. The heat pipe 17 is formed circular in cross section before it is buried and previously annealed. The heat absorbing part 17a of the heat pipe 17 is inserted into a recess 28 provided to an insulating board 22, and a cladding piece is laminated on both the upside and the underside of the inserted heat absorbing part 17a respectively, which is thermocompressed by a hot press to make the heat absorbing part 17a of the heat pipe flat and as thick as the insulating board 22, adhesive material sheets are fused, and all are bonded into an integral structure.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat pipe embedded circuit board and a manufacturing method thereof.

[Prior art]

Conventionally, it has been used as a circuit board to mount components that generate a large amount of heat.
It is well known that a heat pipe is used to improve thermoforming properties. Its basic configuration is shown in Figures 9 and 10.

This circuit board 11 includes an insulating sheet 13 having a circuit pattern on its surface (only the heat generating component mounting part 12a is shown, the others are not shown), an adhesive layer 14, a metal plate 15 for soaking heat, and an insulating substrate. 16 are laminated and integrated, and the heat absorbing portion 17a of the heat pipe 17 is embedded within the insulating substrate 16. The heat absorption part 17a of the heat pipe 17 is buried directly under the heat generating component mounting part 12, and the heat radiation part 17b is exposed to the outside.

In this way, the heat of the heat generating component is absorbed by the heat absorption R17a of the heat pipe 17, is transported to the heat radiation part 17b with high efficiency, and is released from the heat radiation part 17b to the outside.
It is possible to suppress the temperature rise of the circuit board 11 and heat generating components.

〔assignment〕

Conventional heat pipe-embedded circuit boards use thin heat pipes with an outer diameter of about 3 mm to reduce the board thickness, and are embedded with a circular cross section, meaning that they face the heat-generating component mounting part of the heat pipe. Because the projected area of the surface is small and the surface is an arcuate surface, the thermal conductivity from the heat generating component mounting part to the heat absorbing part of the heat pipe is poor, and it is not always possible to obtain a sufficient temperature rise suppression effect. I couldn't say yes.

[Means for solving problems and their effects]

The present invention provides a heat pipe-embedded circuit board that solves the above-mentioned problems, and has a structure in which a heat-absorbing part of a heat pipe is embedded in a board having a circuit pattern on its surface. , the heat absorbing portion of the heat pipe is formed flat so that the dimension in the direction perpendicular to the thickness direction of the substrate is larger than the dimension in the thickness direction of the substrate in the cross section.

In this way, the heat-absorbing part of the heat pipe will face the heat-generating component mounting part on the board surface with a flat or nearly curved surface, and the opposing area will become large, so that the heat-absorbing part of the heat pipe will be able to pass from the heat-generating component mounting part to the heat absorbing part of the heat pipe. Improves thermal conductivity. Furthermore, if the size of the heat pipe is the same, the thickness of the board can be made thinner, and if the thickness of the board is the same, a heat pipe of a larger size (transporting a larger amount of heat) can be used.

The present invention also provides a method for easily manufacturing a heat pipe-embedded circuit board as described above, and the method includes laminating the circuit board materials with the heat absorbing part of the heat pipe sandwiched therein; A method of manufacturing a heat pipe embedded circuit board by heating and pressurizing with a hot press is characterized in that when pressurizing with the hot press, the heat absorbing portion of the heat pipe having a circular cross section is pressed flat.

According to this method, the heat pipe heat absorbing portion can be flattened at the same time as the circuit board is manufactured, and the heat pipe embedded circuit board as described above can be easily manufactured.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of a heat pipe embedded circuit board according to the present invention.

This circuit board II has circuit patterns 1 on both sides of the board I8.
2.26, an insulating sheet 13 having a circuit pattern 12 on its surface, an adhesive layer 14, a metal plate 15 for soaking heat, an adhesive layer 21, an insulating plate 22, an adhesive layer 23 , a metal plate 24 for soaking heat, an adhesive layer 25, and an insulating sheet 27 having a circuit pattern 26 on its surface (lower surface side).
The insulating plate 22 and the adhesive layers 21 and 23 are laminated and integrated.
A heat absorbing portion 17a of a heat pipe, which is formed into a flat shape so as to have a plane parallel to the surface of the substrate 18, is embedded in an insulating substrate 16 composed of the following.

The heat absorbing part 17a of the heat pipe is buried directly under the heat generating component mounting part 12H, as in the conventional case, and the heat dissipating part (not shown) is exposed to the outside. Further, a heat generating component mounting portion may also be provided on the circuit pattern 26 on the lower surface side.

Next, a method for manufacturing the heat pipe-embedded circuit board as described above will be explained with reference to FIGS. 2 and 3.

The heat pipe 17 has a circular cross section before being embedded, and is previously annealed to facilitate pressure immersion.

The insulating plate 22 is made of a glass epoxy substrate, a paper phenol substrate, etc., and has a thickness equivalent to the thickness when the heat absorbing portion 17a of the heat pipe 17 is pressed flat, and has a recess into which the heat absorbing portion 17a of the heat pipe is inserted. 28 is formed. If such an insulating plate 22 is used, the heat pipe 17 can be positioned in a fixed position during hot pressing, and the heat absorbing part 17a will not be compressed below the thickness of the insulating plate 22, so that it can be flattened after being formed. It has the advantage that the thickness can be kept constant.

The heat absorbing part 17 of the heat pipe 17 is placed in the recess 28 of the insulating plate 22.
a, as shown in Figure 2, the adhesive sheet 21', the metal plate 15, and the adhesive sheet 1
At 4°, the laminate of the insulation seam 3 and the copper foil 12' is laminated, and the adhesive sheet 23° and the metal plate 24 are similarly placed on the lower side.
, adhesive sheet 25', insulating sheet 27 and copper foil 26'
Laminate the laminates. A prepreg sheet or the like is used as each adhesive sheet.

The laminate as described above is heated and pressed by a hot press 31. Then, the heat absorbing part 17a of the beat vibrator is connected to the insulating plate 22.
The adhesive sheet is pressed to a thickness of 100 mL to make it flat, and each adhesive sheet is melted to bond and integrate the entire adhesive sheet. This hot pressing operation is preferably performed in a vacuum to prevent voids from forming within the substrate. The gap between the heat absorbing portion 17a of the heat pipe and the insulating plate 22 is filled with resin flowing out from the adhesive sheets 21° and 23°.

After hot pressing, pattern etching is performed on the copper foils 12° and 26' on both sides to form a circuit pattern, as shown in Figure 1.
A circuit board with embedded heat pipes as shown in the figure is obtained.

Note that when a heat pipe embedded circuit board is manufactured using the method described above, the heat absorbing portion 17a of the heat pipe becomes flat, but its upper and lower surfaces are not flat, as shown in Figure 4. The center part is slightly concave (almost eyebrow-shaped)
Sometimes it becomes. The heat absorbing portion 17a of the heat pipe may have such a flat shape. In addition, figure-
4, the other configurations are the same as those in FIG.

Next, a prototype example will be explained.

A glass epoxy substrate with a thickness of 2 mm is used as the insulating plate 22, and a recess 28 with a width of 3.6 mm is formed at the heat pipe installation position.
was formed.

Heat pipe 17 is 3■φ×110I11111
A copper micro heat pipe was used. Each heat pipe is 100% isothermal and can transport 20W of heat. This heat pipe is heated to 200℃ x 1 hour → room temperature → 200℃
It was annealed and softened in a cycle of 1 hour at ℃.

As the metal plate 15, a copper plate with a thickness of 0.3 mm was used.

As the insulating sheet 13 and the copper foil laminate at 12° and the insulating sheet 27 and the copper foil 26', a glass epoxy sheet having a thickness of 0.1 mm and a copper foil laminated were used.

As adhesive sheets 14°, 21°, 23°, and 25°, one prepreg sheet with a thickness of 0.1 mm was used, respectively.

The above circuit board materials were laminated as shown in Figure 2 and hot pressed in a vacuum. The degree of vacuum is 10 to 15 Torr.

Press pressure is 4 kg/Cr1x 5 minutes → 40 kg/
CIl! x 135 minutes, press temperature 140℃ x 20
minutes → 175°C x 120 minutes. After hot pressing, the copper foils on both sides were pattern etched to form a predetermined circuit pattern.

As a result, as shown in FIG. 5, a heat pipe-embedded circuit board having a square shape with each side of 150 mm and two heat pipes 17 embedded at intervals of 75 mm was manufactured. For comparison, a conventional heat pipe-embedded circuit board with the same size and a heat absorption part of the heat pipe 17 having a circular cross section was manufactured as shown in FIG. 6.

A heat generating component with a heat generation amount of 2 W was mounted on each heat generating component mounting portion 12a of both circuit boards, and the temperature distribution was measured after 20 minutes had elapsed. The results are shown in Figures 5 and 6 by isothermal lines (-dotted and dashed lines). From this, it is clear that the circuit board according to the present invention has a lower temperature overall, a gentler temperature gradient, and a smaller temperature rise in heat-generating components.

Next, another embodiment of the method for manufacturing a heat pipe embedded circuit board according to the present invention will be described with reference to FIG.

This method does not use the insulating plate used in the previous example,
A large number of prepreg sheets 29 are laminated to form an insulating substrate. The prepreg sheet 29 of the intermediate layer has a recess 28 similar to that formed in the insulating plate in the previous embodiment, and the heat absorbing part 17a of the heat pipe is installed in the recess 28. On top of the prepreg sheet 29, a metal plate 15, an adhesive sheet 14°, an insulating sheet 13, and a laminate of copper foil 12° are laminated and heated and pressed with a hot press 31. At this time, the prepreg sheet 29
In order to prevent the heat-absorbing portion 17a of the heat pipe from moving or bending due to the resin flowing laterally, weirs 32 are provided on both sides to prevent the resin from flowing laterally. It applies pressure.

In this way, the heat pipe can be embedded in a fixed position without using an insulating plate as in the previous embodiment.

An example of a heat pipe embedded circuit board according to the present invention manufactured by this method is shown in FIG.

16 is an insulating substrate with integrated prepreg sheet, 17
15 is a metal plate bonded to an insulating substrate 16;
14 is an adhesive layer that adheres the metal plate 15 and the insulating sheet 13; 12 is a circuit pattern formed by pattern etching the copper foil on the insulating sheet 13; 12a is the heat-generating component mounting portion thereof; 18 is the board. .

〔Effect of the invention〕

As explained above, in the heat pipe-embedded circuit board according to the present invention, the heat-absorbing portion of the heat pipe is embedded in a flat shape, so that the thermal conductivity from the heat-generating component mounting portion to the heat-absorbing portion of the heat pipe is improved. It has the advantage of being able to efficiently suppress temperature increases in circuit boards and heat-generating components. Another advantage is that if you use a heat pipe of the same size as before, you can make the circuit board thinner, and if you keep the thickness of the circuit board the same as before, you can use a larger heat pipe that can transport a large amount of heat. .

Further, according to the manufacturing method of the present invention, it is possible to easily manufacture a heat pipe-embedded circuit board in which the heat-absorbing portion of the heat pipe is embedded in a flat shape.

[Brief explanation of drawings]

Figure 1 is a sectional view showing an embodiment of the heat pipe embedded circuit board according to the present invention, Figure 2 is a sectional view showing an embodiment of the method for manufacturing the heat pipe embedded circuit board according to the present invention, and Figure 3 is a plan view showing the positional relationship between the insulating plate and the heat pipe in the same manufacturing method, FIG. 4 is a sectional view showing another embodiment of the heat pipe embedded circuit board according to the present invention, and FIGS. An explanatory diagram showing the temperature distribution of the circuit board of the invention and a conventional circuit board, FIG. 7 is a cross-sectional view showing another embodiment of the manufacturing method according to the invention, and FIG. 8 is another example of the circuit board according to the invention. 9 is a plan view showing an example of a conventional heat pipe embedded circuit board,
FIG. 10 is a sectional view taken along line AA in FIG. 9. 11: Heat pipe embedded circuit board 12.26-circuit pattern 12a: Heat generating component mounting part 1
3.27: Insulating sheet 14.21.23.25: Adhesive layer 15.24: Metal plate 16: Insulating substrate 17: Heat pipe 17a: Heat absorption part 17b: Heat radiation part 18: Substrate 28: Concave part 29 Niblip preg sheet 31: Hot breath 32: Weir diagram - Figure - 2 Figure - 3 Figure - Figure - 8 Figure -

Claims (2)

[Claims] 1. In a heat pipe embedded circuit board in which a heat absorbing portion of a heat pipe is embedded in a substrate having a circuit pattern on the surface, the heat absorbing portion of the heat pipe has a dimension in a direction perpendicular to the thickness direction of the substrate in a cross section. A heat pipe embedded circuit board characterized by being shaped flat to increase its size. 2. In a method of manufacturing a heat pipe-embedded circuit board by laminating circuit board materials with the heat absorbing part of the heat pipe sandwiched inside and heating and pressurizing them with a hot press, the cross section becomes circular when pressurized with the hot press. A method of manufacturing a circuit board with a heat pipe embedded therein, comprising compressing the heat absorption part of the heat pipe into a flat shape.