Advanced liquid cooling apparatus

Abstract: An advanced liquid cooling system with an advanced cooling characteristic and high reliability, which is small in size and light in weight, is provided. In the liquid cooling system, heating units (2), which are semiconductors, are fixed on a base (5) having high thermal conductivity. A liquid-passage hole (7) in the base (5) allows a liquid refrigerant (6) to pass through. Since the base (5) is made of material with high thermal conductivity, and the liquid-passage hole (7) extends in the vicinity of the heating unit (2) in the base, it is sufficient to transfer the heat of heating unit (2) to the liquid refrigerant (6). This enables control of the temperature rise of the heating unit to be maintained low.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an advanced liquid cooling apparatus, and more specifically to a liquid cooling apparatus which circulates a liquid refrigerant around electronic equipment such as a TV transmitter, which generates heat. Description of the Related Art In general, an electronic apparatus such as a TV transmitter comprises multiple printed circuit boards on which many semiconductor devices are provided, in its own rack. A fan or a blower attached inside or outside the rack performs forced-air cooling for the printed circuit board. In recent years, since many circuitry elements are integrated as large scale or mounted in high-density packaging, the density of the heating locations in the rack becomes increased. Such apparatus frequently makes use of a liquid cooling method which provides a high heat exchange performance. For example, to transfer heat outside, a liquid refrigerant is provided and flows on a flat board (cold plate), on which circuitry elements are contacted. As shown in FIG. 4, in a conventional cooling system, the liquid refrigerant circulates around an electronic apparatus 50, which generates heat, removing the heat from the electronic apparatus 50. In FIG. 4, reference numeral 50 denotes an electronic apparatus which generates heat; reference numeral 60 denotes a pump rack; and reference numeral 70 denotes a heat exchange unit to cool the liquid. Reference numerals 51 and 52 denote cold plates in the electronic apparatus. Reference numerals 53 and 54 denote copper pipes in the cold plates 51 and 52. Reference numeral 55 denotes a pipe arrangement which is connected to a return pipe arrangement 83. Reference numeral 61 in a pump rack 60 denotes a tank which absorbs possible volume changes caused by the temperature change of the liquid refrigerant. Reference numeral 62 denotes a pump to send the liquid refrigerant to the electronic apparatus 50. Reference numeral 63 denotes a pipe which is used to connect a transmission pipe arrangement 81 to the pump 62. The reference numeral 64 is a pipe arrangement which is used to connect the tank 61 to the pump 62. Reference numeral 65 denotes a pipe arrangement which is used to connect the tank 61 to the return pipe arrangement 82. Reference numeral 71 in the heat exchange unit 70 denotes a condenser which is used for heat exchange. Reference numeral 72 denotes a fan. Reference numeral 73 denotes a motor to rotate the fan 72. Reference numeral 74 denotes a pipe arrangement which is used to connect the return pipe arrangement 82 to the condenser 71. Reference numeral 75 denotes a pipe arrangement which is used to connect the condenser 71 to the return pipe arrangement 83. The detailed configuration of the conventional cold plate is shown in FIG. 8 of EP 942640A. Briefly, a semiconductor device 2, such as a power transistor (hereinafter a heating unit), is mounted on the cold plate, and a copper pipe runs through the cold plate. Grease is used for transmission of the heat from the cold plate to the copper pipe. German Patent Specification DE 43 22 665 A describes a cooling device for a semiconductor device stack where each thyristor in a stack is located between two cold plates. Refrigerant passes through passages in the cold plates to cool the thyristors. There is a need in liquid cooling apparatus to increase the effectiveness of the heat transfer from the heating unit to the liquid refrigerant. SUMMARY OF THE INVENTION According to the invention there is provided liquid cooling apparatus, comprising a base having front and back sides with a liquid-passage hole provided in said base to allow liquid refrigerant to pass therethrough, and heating units disposed on said base, characterized in that said heating units are disposed on said front and back sides of said base in a zigzag manner, and said liquid-passage hole follows a corresponding zigzag path in said base such that liquid refrigerant in said liquid-passage hole flows at locations in the vicinity of the heating units disposed on the front and back sides of said base. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described in more detail by way of example taken in conjunction with the accompanying drawings, wherein: FIGS 1A and 1B are a plan view and a side view showing the configuration of a first embodiment of the present invention; and FIG. 1C is a cross-section of FIG. 1A along a line AA; FIGS 2A and 2B are a plan view and a side view showing the configuration of a second embodiment of the present invention; and FIG. 2C is a cross-section of FIG. 2A along a line BB; FIG. 3 shows the relation between the rate of flow and the temperature rise explaining the operation of the present invention; and FIG. 4 shows the configuration of a conventional cooling system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be explained with reference to the drawings. With reference to FIGS. 1A, 1B and 1C showing as a plan view, a side view and a cross-section along the line AA in FIG. 1A, respectively, the configuration of the first embodiment of the present invention, a lead wire 3 of a heating unit 2, which is a semiconductor device such as a power transistor, is soft-soldered on a printed circuit board 1, which accommodates a pattern of signal wiring (not shown in the figures) and a ground pattern (not shown in the figures). The heating unit 2 is contacted on a base 31 which has a high thermal conductivity. A liquid refrigerant 6 passes through a liquid-passage hole 32 in the base 5. In this embodiment, water is used for the liquid refrigerant 6. Since the base 31 is made of copper having high thermally conductivity, and the liquid-passage hole 32 extends in the vicinity of the heating unit 2 (close right under the heating unit 2), it is effective to transfer the heat of heating unit 2 to the liquid refrigerant 6. This enables control of the temperature rise of the heating unit to be maintained under a lower level. In FIGS. 1A and 1B, the base 31 is fixed to a plate 8, and a ditch or recess is prepared on the plate 8 to receive the base 31 on which the heating unit 2 is disposed. On the other hand, the printed circuit board 1 is disposed on the plate 8 and the lead wire 3 from the heating units 2 is connected to a circuit pattern on the printed circuit board 1. Two lines of the liquid-passage holes 32 in the base 31 are connected together by a connective pipe 4, and liquid refrigerant 6 sent to one of the two water-passage holes 32, is drained out through the other of the two lines of water-passage holes 32. In the first embodiment where the copper base is used, by attaching the heating unit 2 along the water-passage hole 32 in a closed manner, it becomes possible for the base 31 to be small in size and light in weight. Moreover, since grease for the heat transfer from the heating unit is not necessary, no aged deterioration is expected and, thus, the stability and reliability is enhanced. As is seen from FIG. 1C, the heating units 2 are fixed on the front side and the back side of the base 31 in a zigzag manner so that it becomes possible to locate the adjacent heating units 2 very closely. The liquid-passage hole 32 is also prepared in the base 31 in a zigzag manner, that is, so as to follow a zigzag path. In detail, the liquid-passage hole 32 runs in the vicinity of the contact surface of the heating unit 2-1, fixed on the front side 31 a of the base 31, and, after this, runs in the vicinity of the contact surface of the heating unit 2-2, fixed on the back side 31b of the base 31, and, then, runs in the vicinity of the contact surface of the heating unit 2-3, fixed on the front side 31 a of the base 31. In addition, according to the first embodiment, in the vicinity of the contact surface of the heating units 2-1 to 2-3, the liquid-passage hole 32 runs parallel to both the front side 31a and the back side 31b of the base 31. With this configuration, the liquid refrigerant 6 flowing through the liquid-passage hole 32 collides with the inside of the base 31 in the vicinity of the contact surface of the heating units 2-1 to 2-3. This improves the thermal conductivity and makes the cooling efficiency high. FIGS. 2A, 2B and 2C show the configuration of a second embodiment of the present invention. In FIGS. 2A and 2B showing a plan view, a side view and a cross-section along a line BB of FIG. 2A, respectively, the configuration has the same configuration as the first embodiment except that reservoirs (or chambers) 42a to 42c are provided in the base 41 in the vicinity of the contact surface of the heating units 2-1 to 2-3, and the liquid-passage hole 42 is arranged so that the liquid refrigerant 6 perpendicularly collides with the inside of the base 41 at the reservoirs 42a to 42c. In the second embodiment, the liquid-passage hole 42 in the base 41 is also arranged to follow a zigzag path the same as in the first embodiment. In addition, the insides of the reservoirs 42a to 42c in the base 41 are shaped to be parallel to both the front side 41a and the back side 41b of the base 41, so that the liquid refrigerant 6 flowing through the liquid-passage hole 42 perpendicularly collides with the inside wall of the reservoirs 42a to 42c, where the heating units 2-1 to 2-2 are located. Therefore, the thermal conductivity is further enhanced more than that of the first embodiment of the present invention, and the cooling efficiency is further enhanced. In the above configuration, the size of the cross-section of the liquid-passage hole 42 connecting between the reservoirs 42a to 42c, is decreased in comparison with the size of the reservoirs 42a to 42c. Thereby, the liquid refrigerant 6 flows faster through the liquid-passage hole 42, and accordingly, the liquid refrigerant 6 collides with the inside wall of the reservoirs 42a to 42c while the speed of flow of the liquid refrigerant 6 is increased, thereby improving the thermal conductivity. FIG. 3 shows the result of the measurement of the rate of flow of the liquid refrigerant 6 versus the temperature rise in the heating unit. Curve a shows the temperature rise for a conventional cold plate type liquid cooling apparatus as shown in FIG. 8 of EP 942640 A. Curve c shows the temperature rise for the second embodiment of the present invention, utilizing the collision base, and the temperature rise goes down to less than half while the rate of flow is reduced by half in comparison with the conventional cold plate type. It is noted that, in the above embodiments, the bases 31,41 are made of copper, having high thermal conductivity. However, the material of the base is not limited to copper, and any material having high thermal conductivity, such as aluminium can be used alternatively. Furthermore, by processing the insides of the liquid-passage holes 32 and 42 with a knurling tool, notches (bumps) are made in the water-passage hole 32 and 42 so that the surface area is increased. Thereby, the cooling efficiency is further enhanced. As described above, by providing the liquid-passage holes 32 and 42 in the base 31 and 41, on which the heating units 2 are placed, and by allowing the liquid refrigerant 6 to flow through the liquid-passage holes, the cooling efficiency is enhanced. Further, it is better to optimise the configuration so that the thermal conductivity is more improved. To this end, it is preferable to use a base made of material having high thermal conductivity such as aluminum and copper, to enlarge an area of contacting surfaces where the liquid refrigerant contacts the bases, and to increase the flow speed of the liquid refrigerant in the liquid-passage holes. In addition, the liquid-passage holes are so arranged to run in the base in a zigzag manner that the liquid refrigerant 6 collides with the inside of the base at locations in the vicinity of the contact surfaces of the heating units 2, thereby locally providing a high thermal conductivity at the locations where the heating units are disposed. To optimize the size and shape of the cross-section of the liquid-passage holes, there is a constraint that follows among the temperature rise Δ T in the bases, the calorific value Q, the thermal conductivity hc, and the contracting surface area A where the liquid refrigerant contacts the base: ΔT = Q/(hc × A) To lower the temperature rise, the thermal conductivity needs to be improved by enlarging the surface area or increasing the flow speed of the liquid refrigerant. To attain this, it is desirable to increase the number of the liquid-passage holes and/or to form notches or knurls in the liquid-passage holes. Allowing the liquid refrigerant to collide with the base in the vicinity of the contact surface of the heating units, in other words, utilizing the thermal transfer by using jet collision, provides a high thermal conductivity at pinpoint on a base. About the jet collision using the liquid refrigerant, it is experimentally known that the temperature rise becomes less than half even when the flow speed of the liquid refrigerant is set half. Namely, in other words, four-times cooling efficiency is obtained, as compared to the conventional cold plate type cooling system. Accordingly, a comparatively small capacity power source is required. Moreover, there is a benefit that the thermal conductivity can be easily adjusted or regulated by controlling the flow speed of the liquid refrigerant . According to the present system as explained above, the advanced liquid cooling apparatus comprising the base on which heating units are fixed and a liquid-passage hole arranged in the base, is provided. With this configuration, there is a benefit that the cooling characteristics and stability/reliability are enhanced and thus the cooling apparatus can be made small in size and light in weight. The advanced liquid cooling apparatus according to the present proposal can be applied to a liquid cooling system as shown in FIG. 4, instead of the conventional cold plate 51 and 52. While the present invention has been described in connection with certain preferred embodiments, it is understood that the subject matter encompassed by the present invention is not limited to those specific embodiments. On the contrary, it is intended to include all alternatives, modifications, and equivalents as can be included within the scope of the following claims.

Claims: Liquid cooling apparatus, comprising: a base (31;41) having front and back sides with a liquid-passage hole (32;42) provided in said base to allow liquid refrigerant to pass therethrough; and heating units (2) disposed on said base; characterized in that said heating units (2) are disposed on said front and back sides (31a,31b; 41a,41b) of said base in a zigzag manner; and said liquid-passage hole (32;42) follows a corresponding zigzag path in said base such that liquid refrigerant in said liquid-passage hole flows at locations in the vicinity of the heating units (2) disposed on the front and back sides (31a,31b; 41a,41b) of said base (31;32). Liquid cooling apparatus according to claim 1, wherein liquid refrigerant in said liquid-passage hole (32) collides with an inside wall of said base (31) at turning points of said liquid-passage hole (32). Liquid cooling apparatus according to claim 1, further comprising reservoirs (42a-c) at turning points of said liquid-passage hole (42), said reservoirs being positioned closed to said heating units (2). Liquid cooling apparatus according to claim 3, wherein liquid refrigerant in said liquid-passage hole (42) is jetted toward said heating unit (2) in said reservoir (42a-c).

Inventors: KIKUCHI YOSHIHITO, MIZUGUCHI NAOTO, TSUJI KENICHI, KIKUCHI, YOSHIHITO, MIZUGUCHI, NAOTO, TSUJI, KENICHI
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1999
Main classification: H05K7
IPC codes: H05K7, H01L23