JPS60249351A - Boil-cooled type circuit board - Google Patents

Abstract

PURPOSE:To improve the cooling efficiency by a method wherein a gap is provided between a circuit element and a circuit board by recessing the circuit board surface opposed to the circuit element surface, and the recess is provided with through-holes. CONSTITUTION:Electrode pads 6p to which the semiconductor element 6 has been connected was excluded. The surface of the circuit board 10 opposed to the element 6 is recessed 11: e.g. the gap between the element and the board is made about 3mm. or so, and the recess 11 provided in the board is provided with e.g. many through-holes 12 of approx. 2mm.phi. Such a formation of the board 10 allows rising air-bubbles to be separated off from the surface of the element 6 opposed to the board 10, to come up from the recess 11 through the through- holes 12, and to cool the elements by stirring and circulating the coolant. Therefore, the element 6 comes to be cooled by boil-stirring from both of the back and opposed surfaces, and the cooling efficiency becomes about double.

Description

DETAILED DESCRIPTION OF THE INVENTION +al Technical Field of the Invention The present invention relates to an evaporative cooling type circuit board on which circuit elements such as semiconductor elements and other heat generating elements are mounted.

(bl Background of Technology As is well known, semiconductor devices have become extremely dense and highly integrated in the form of ICs and LSIs, and for this reason, the amount of heat generated per unit area of semiconductor devices is proportional to the degree of integration. In addition, even if semiconductor devices have the same degree of integration, semiconductor devices that operate at high speed tend to consume more current and generate a larger amount of heat.For example, bipolar devices tend to be more expensive than MOS devices. The amount of heat generated is greater than that of
Resistance elements and the like are also becoming smaller, and the amount of heat generated per unit area is increasing.

In such electronic circuits, methods have been devised to dissipate and cool the heat generated by semiconductor elements, other circuit elements, and the circuit boards on which they are mounted. be. The reason why this cooling is necessary is that, for example, in the case of a silicon device, if it is heated above 85 degrees Celsius, the characteristics of the device become unstable, and even thermal runaway occurs, destroying the device and rendering it inoperable. It is from.

However, there are limits to air cooling, and as semiconductor devices become more highly integrated, it is difficult to apply it to semiconductor devices that generate heat of f/wand or more.

On the other hand, liquid cooling has long been known as an efficient cooling method, but liquid cooling of semiconductor devices has not been used much in the past because it requires a complicated structure. However, as mentioned above, the liquid cooling method has begun to attract attention due to the limitations of the air cooling method, and semiconductor devices have also become highly integrated to the extent that they cannot be cooled by anything other than liquid cooling.

In addition, liquid cooling methods include an indirect cooling method in which heat is conducted from a semiconductor element to a thermal conductor to cool it, and a direct water cooling method in which water is passed through a semiconductor element, but these methods are not related to the present invention. The liquid cooling method is a so-called boiling cooling method in which a circuit board on which semiconductor elements are mounted is immersed in a low boiling point refrigerant such as Freon and cooled by boiling circulation. There is.

This kind of boiling cooling type uses the latent heat of evaporation of the liquid, so it has the highest cooling efficiency and has a cooling efficiency of 15 to 20 watts/cI.
This method can also be applied to semiconductor elements that generate a heat amount of approximately . Moreover, the recently developed HEMT uses liquid nitrogen (-196℃)
Among these, it is a transistor that promises high-speed operation, and the boiling cooling type is also applied to this HEMT.

(C1 Prior Art and Problems Figure 1 illustrates a schematic cross-sectional view of a boiling-cooled electronic circuit device in which a semiconductor element is mounted. 1 is a circuit board storage container;
2 is the refrigerant liquid, and 3 is the space in the same container.

4 is a cooler, 5 is a circuit board, and 6 is a semiconductor element (or other circuit element). The principle of cooling such a circuit board is that when the circuit is switched on, the semiconductor element generates heat, which causes the temperature of the liquid to rise, and a refrigerant with a low boiling point (
For example, Freon (which has a boiling point of 47.6°C) boils and foams.

This causes a stirring action of the refrigerant, and the refrigerant evaporated in the space 3 is cooled by the cooler 4 and returned to liquid, and is returned to the liquid. In this way, the temperature of the semiconductor element is prevented from rising above the boiling point temperature of the refrigerant.

2nd FXJ shows a perspective view of one circuit board, and the circuit board 5 is often made of ceramic T7 resin, and most of the many circuit elements mounted at high density are semiconductor elements 6. FIG. 3 shows a partial cross-sectional view of the circuit board on which the semiconductor element 6 is mounted, and since the semiconductor element 6 is normally connected to the circuit board 5 by an electrode pad 6p, the relationship between the semiconductor element 6 and the circuit board 5 is The spacing is extremely narrow, with only a gap of about 0.1 to 0.3 mm.

On the other hand, since the bubbles that bubble up have a size of 0.5fl to 1111φ, they cannot bubble (bubble treatment) from the gap between the opposing surfaces of the semiconductor element and the circuit board, and cooling is not performed from this opposing surface. Not yet. Therefore, the semiconductor element 6 is cooled by boiling and bubbling only from the back side, and the cooling efficiency of the semiconductor element 6 is insufficient, and the cooling efficiency is only about 50% of that when both sides of the semiconductor element are cooled.

Currently, the amount of heat generated by cooling only one side is 15 watts.
/ell! The design is such that no more heat is generated. That is, it is the circuit board 5
Semiconductor elements 6 are arranged roughly on top, and 1
The design limits high integration so as not to generate more than 5 watts/aI+.

Object of the Invention The present invention proposes a boiling-cooled circuit board that corrects such cooling efficiency.

tel Structure of the Invention The purpose of the invention is to form a recess in the circuit board surface facing the circuit element surface, excluding the electrode pad portion where the circuit element and the circuit board are connected, and to create a gap between the circuit element and the circuit board. This can be achieved by using an evaporative cooling type circuit board in which a gap of 0.5 mm or more is provided and a through hole is provided in the recessed portion of the circuit board.

(f) Examples of the invention Examples will be described in detail below with reference to nine drawings.

FIG. 4 shows a partial cross-sectional view of a mounted circuit board according to the present invention, and shows electrode pads 6p to which semiconductor elements 6 are connected.
A recess 11 is formed on the surface of the circuit board 10 facing the semiconductor element 6, excluding the part, so that the gap between the semiconductor element and the circuit board is approximately 311 m, and the recess provided in the circuit board 10 11 is provided with a large number of through holes 12 having a diameter of approximately 2 mm.

In this example, the circuit board 10 has a thickness of 10 fl, and the semiconductor element has a thickness of 0.5 inches and a size of about 10 m square.
Also from the surface of the semiconductor element 6 facing the surface of the semiconductor element 6, bubbling air bubbles (diameter 0.5 to 1 fiφ) are separated from the element and formed in the recess 11.
The refrigerant floats up through the through hole 12, stirs and circulates the refrigerant, and cools the element. In this way, the semiconductor element 6 will be boiled and stirred and cooled from both the back surface and the opposing surface, and the cooling efficiency will be approximately doubled.

The gap between the recesses 11 should have a width that allows bubbles to move, that is, Q, 5 m+m or more, and the diameter of the through hole 12 should be about the same or larger so that bubbles can be released. FIG. 5 fa) is a plan view of the recess 11,
Five through-holes have been created, but the through-holes are not only circular holes, but also rectangular through-holes 12' with an allowable width that allows air bubbles to pass through, as shown in the other example shown in the same figure (bl), or other holes. It may be formed in the shape of

The circuit board 10 having such a shape is obtained by shaping the green sheet (raw sheet) in advance and firing it. FIG. 6 shows a perspective view of the mounting structure of the circuit board 10 according to the present invention.

(Along with the effects of the invention) As is clear from the above embodiments, according to the present invention, cooling by boiling and stirring of the refrigerant liquid occurs on both sides of the semiconductor element.
Cooling efficiency is doubled. According to the results, while the conventional structure had a limit of 15 watts/d on the amount of heat generated, the structure of the present invention was able to reduce the limit to 35 watts/d.

Therefore, by applying the present invention, semiconductor elements can be mounted on circuit boards with higher density, and the semiconductor elements themselves can also be more highly integrated, doubling the density of electronic circuits and significantly improving their performance. It is effective.

[Brief explanation of drawings]

Figure 1 is a schematic cross-sectional view of a boiling-cooled electronic circuit device;
The figure is a perspective view of a conventional circuit board, FIG. 3 is a partial sectional view thereof, FIG. 4 is a partial sectional view of a circuit board according to the present invention, and FIG.
Figures FAN and TBL are a plan view of the recessed portion, and FIG. 6 is a perspective view of the circuit board according to the present invention. In the figure, 1 is a circuit board storage container, 2 is a refrigerant liquid, 3 is a space in the container, 4 is a cooler, 5 is a conventional path board, and 6 is a semiconductor element (or other circuit element). 6p is a connection pad, and 10 is a circuit board according to the present invention. 11 indicates a recess, and 12.12' indicates a through hole. 1st city, 2nd decoy, Figure 3

Claims (1)

[Claims] ill The surface of the circuit board opposite to the surface of the circuit element, excluding the electrode pad portion where the circuit element and the circuit board are connected, is formed into a concave shape to create a gap between the circuit element and the circuit board. What is claimed is: 1. A boiling-cooled circuit board, characterized in that a through hole is provided in a recessed portion of the circuit board. (2) The evaporative cooling type circuit board according to claim 1, characterized in that the gap provided between the circuit element and the circuit board is 0.5f1 or more.