CA1295753C - Printed circuit board cooling system employing bellows and layer of thermal grease and method for forming the layer - Google Patents
Printed circuit board cooling system employing bellows and layer of thermal grease and method for forming the layerInfo
- Publication number
- CA1295753C CA1295753C CA000566836A CA566836A CA1295753C CA 1295753 C CA1295753 C CA 1295753C CA 000566836 A CA000566836 A CA 000566836A CA 566836 A CA566836 A CA 566836A CA 1295753 C CA1295753 C CA 1295753C
- Authority
- CA
- Canada
- Prior art keywords
- heat transfer
- thermally conductive
- pressure
- conductive compound
- cooling
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K3/00—Apparatus or processes for manufacturing printed circuits
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L23/00—Details of semiconductor or other solid state devices
- H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
- H01L23/46—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements involving the transfer of heat by flowing fluids
- H01L23/473—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements involving the transfer of heat by flowing fluids by flowing liquids
Abstract
ABSTRACT OF THE DISCLOSURE
A cooling system used with a printed circuit board having at least a solid circuit component thereon, comprising a cooling header and cooling modules connected to the cooling head-er. Each of the cooling modules engages one of the components.
The cooling module has a heat transfer plate connected to one end of a bellows which is connected to the cooling header at the other end. A layer of thermally conductive compound such as a layer of thermal grease is interposed between the heat transfer plate and the corresponding circuit component. The thermally conductive layer is initially pressed with a pressure higher than a critical pressure, and thereafter, the pressure is reduced to working pressure exerted on the circuit component provided by the resilient force of the bellows and the hydraulic pressure of the coolant. The critical pressure is predetermined experimentally.
As a result, the thermal contact resistance between the heat tran-sfer plate and the circuit component is favorably reduced and stabilized.
A cooling system used with a printed circuit board having at least a solid circuit component thereon, comprising a cooling header and cooling modules connected to the cooling head-er. Each of the cooling modules engages one of the components.
The cooling module has a heat transfer plate connected to one end of a bellows which is connected to the cooling header at the other end. A layer of thermally conductive compound such as a layer of thermal grease is interposed between the heat transfer plate and the corresponding circuit component. The thermally conductive layer is initially pressed with a pressure higher than a critical pressure, and thereafter, the pressure is reduced to working pressure exerted on the circuit component provided by the resilient force of the bellows and the hydraulic pressure of the coolant. The critical pressure is predetermined experimentally.
As a result, the thermal contact resistance between the heat tran-sfer plate and the circuit component is favorably reduced and stabilized.
Description
TITLE OF THE INVENTIO
Cooling system used with an electronic circuit device for cooling circuit components included therein having a thermally conductive compound layer and method for forming the layer.
BACKGROUND OF EE IN~ENTION
The present invention relates to cooling system used with a printed circuit board holding a number of solid electronic circuit components, such as integrated circuit (IC) semicon-ductor devices. More particularly, it relates to a cooliny mod-ule, being included in the cooling system and contacting with each of the electronic circuit components through a thermally conduct-ive compound layer to cool these components.
There have been developed various types of cooling structures for cooling IC semiconductor devices or large scale IC (LSI) semiconductor devices mounted on a printed circuit board as disclosed, for example, in U.S. Patents Ser. Numbers 3,993,123 issued to Chue et al., 4,203,129 issued to Oktay et al., 4,254,431 issued to Babuka et al., and 4,323,914 issued to Berndmaier, and in not-examined provisionally published Japanese Patent Applica-tions, No. 61-15353 invented by K.D. Ostergrane et al., No. 60-160149 invented by Yamamoto et al. and No. 62-109347 invented by Tajima. In some of these cooling structures a heat transfer ele-ment, such as a heat transfer plate or a heat tranfer piston, is placed in direct contact with the circuit components, being urged to a surface of a circuit component by pressure pro~ided from a spring, bellows, hydraulic pressure of coolant, etc., to remove ~. , ;7753 the heat dissipa-ted Erom -the circuit components. The heat transfer elements are exposed to a coolant direc-tly or indirectly.
The hea-t is transferred to -the coolant through the corresponding heat transfer elements in contact with the circuit components.
In yeneral, however, the heat contact resistance of an interface between the heat -transfer elements and the circuit components in the above described cooling structures is rather high and unstable, because the actual contacting area therebe-tween is rather small and unstable due to the roughness of the surfaces which are thermally contacting with each other. In additlon, any change of the pressure of the spring, bellows, or coolant pressure affects the heat contact resistance delicately and seriously, resulting in a large loss of the heat transfer efficiency of the cooling modules. Particularly, the use of a spring for urging a heat transfer member to the corresponding circuit component to be cooled, tends to cause mechanical reson-ant vibration triggerd by an external mechanical shock, resulting in variation of the pressure exerted.
In order to overcome the aforesaid disadvantage caused by the prior art cooling structures, various fluid thermal con-ductive materials such as thermally conductive inert gas, or a li~uid metal or thermal silicon grease, or a compliant thermal conductive material is adhesively inserted into the interface be-tween the surfaces of a heat transfer element of a cooling module and a circuit component. For example, thermal conductive inert gas is introduced into the interface by Chue et al., and a low boiling point liquid i9 utilized to immerse a heat transfer piston and a circuit component by Oktay et al.. However, a complicated and costly sealiny structure for sealing the gas or the liquid is required for both cooling modules, which is a draw-back. In addition, the thermal conductivity of the associated inert gas and liquid set the reduction of the relevant thermal contact resistance within an upper limit.
While Berndmaier et al. and Babuka et al. employ liquid metal or alloy to fill up a contact interface. Ostergrane et al disclose the use of thermal grease in the interface of conieal surfaces of a piston and a hat, and the use of a liquid metal layer between the piston and a circuit element. In this struct-ure, a rather thick layer of the thermal grease may be required to maintain the layer on the conical surface of the piston, causing undesirable increase in thermal resistance of the layer. In add-ition, liquid metal of some kinds usually has a probability of ch mical reaction with contacting material, requiring various counter measures to prevent the reaction.
Yamamoto et al. insert a compliant sheet between a cir-cuit component and a heat transfer plate urged toward the circuit component by a bellows to reduce thermal contact resistance across the interface between the component and the heat transfer plate.
A relatively thick compliant sheet, however, is required in order to realize a desirable perfect thermal contact between the sheet surfaces and the contacting surfaces of the relevant circuit ele-ment and the heat transfer plate by expelling small air voids re-57~
Cooling system used with an electronic circuit device for cooling circuit components included therein having a thermally conductive compound layer and method for forming the layer.
BACKGROUND OF EE IN~ENTION
The present invention relates to cooling system used with a printed circuit board holding a number of solid electronic circuit components, such as integrated circuit (IC) semicon-ductor devices. More particularly, it relates to a cooliny mod-ule, being included in the cooling system and contacting with each of the electronic circuit components through a thermally conduct-ive compound layer to cool these components.
There have been developed various types of cooling structures for cooling IC semiconductor devices or large scale IC (LSI) semiconductor devices mounted on a printed circuit board as disclosed, for example, in U.S. Patents Ser. Numbers 3,993,123 issued to Chue et al., 4,203,129 issued to Oktay et al., 4,254,431 issued to Babuka et al., and 4,323,914 issued to Berndmaier, and in not-examined provisionally published Japanese Patent Applica-tions, No. 61-15353 invented by K.D. Ostergrane et al., No. 60-160149 invented by Yamamoto et al. and No. 62-109347 invented by Tajima. In some of these cooling structures a heat transfer ele-ment, such as a heat transfer plate or a heat tranfer piston, is placed in direct contact with the circuit components, being urged to a surface of a circuit component by pressure pro~ided from a spring, bellows, hydraulic pressure of coolant, etc., to remove ~. , ;7753 the heat dissipa-ted Erom -the circuit components. The heat transfer elements are exposed to a coolant direc-tly or indirectly.
The hea-t is transferred to -the coolant through the corresponding heat transfer elements in contact with the circuit components.
In yeneral, however, the heat contact resistance of an interface between the heat -transfer elements and the circuit components in the above described cooling structures is rather high and unstable, because the actual contacting area therebe-tween is rather small and unstable due to the roughness of the surfaces which are thermally contacting with each other. In additlon, any change of the pressure of the spring, bellows, or coolant pressure affects the heat contact resistance delicately and seriously, resulting in a large loss of the heat transfer efficiency of the cooling modules. Particularly, the use of a spring for urging a heat transfer member to the corresponding circuit component to be cooled, tends to cause mechanical reson-ant vibration triggerd by an external mechanical shock, resulting in variation of the pressure exerted.
In order to overcome the aforesaid disadvantage caused by the prior art cooling structures, various fluid thermal con-ductive materials such as thermally conductive inert gas, or a li~uid metal or thermal silicon grease, or a compliant thermal conductive material is adhesively inserted into the interface be-tween the surfaces of a heat transfer element of a cooling module and a circuit component. For example, thermal conductive inert gas is introduced into the interface by Chue et al., and a low boiling point liquid i9 utilized to immerse a heat transfer piston and a circuit component by Oktay et al.. However, a complicated and costly sealiny structure for sealing the gas or the liquid is required for both cooling modules, which is a draw-back. In addition, the thermal conductivity of the associated inert gas and liquid set the reduction of the relevant thermal contact resistance within an upper limit.
While Berndmaier et al. and Babuka et al. employ liquid metal or alloy to fill up a contact interface. Ostergrane et al disclose the use of thermal grease in the interface of conieal surfaces of a piston and a hat, and the use of a liquid metal layer between the piston and a circuit element. In this struct-ure, a rather thick layer of the thermal grease may be required to maintain the layer on the conical surface of the piston, causing undesirable increase in thermal resistance of the layer. In add-ition, liquid metal of some kinds usually has a probability of ch mical reaction with contacting material, requiring various counter measures to prevent the reaction.
Yamamoto et al. insert a compliant sheet between a cir-cuit component and a heat transfer plate urged toward the circuit component by a bellows to reduce thermal contact resistance across the interface between the component and the heat transfer plate.
A relatively thick compliant sheet, however, is required in order to realize a desirable perfect thermal contact between the sheet surfaces and the contacting surfaces of the relevant circuit ele-ment and the heat transfer plate by expelling small air voids re-57~
maining on the contactiny surfaces. As the result, the reduction of the whole thermal contact resistance across the interface is adversely afEected. Tajima provides a cooling structure compris-ing a cap having a spherical top surface, a stud haviny a concave spherical bottom surface engageable with the spherical surface of the cap, and a cooling hat. The cap contacts with a circuit ele-ment with a small gap therebetween which is filled with thermal grease, while the stud is secured to a cooling header. The cap and the hat are in contact with each other through a layer of thermal grease which has a considerable thickness sufficient to protect the circuit element from being subject to a pressure.
Tajima discloses nothing about pressure to be exerted to the thermal grease layer.
In these prior art cooling modules, much effort has been made to reduce the heat transfer resistance across a thermal contact interface utilizing various thermally conductive compound material, however, the results are not suEficient to maintain a desirably low, stable and reproducible thermal contact resistance.
SUMMARY OF THE INVENTION
The primary object of the present invention is to eli-minate the aforementioned drawbacks of the prior art cooling structures, and to provide a cooling system of an electronic cir-cuit with a high performance cooling structure which can effect-ively, steadily, and uniformly cool circuit components contained in the circuit. The next object is to provide a stable and a re-liable cooling structure having a stabilized and a thermally well-;7~3 - 5 - 25307~192 conductive layer of a liquid ma-terial in a thermal contact in-terface between a heat transfer plate and a circuit component.
To achieve the aforesai.d objects, according to the present invention, at first, the:re is previously conducted an experiment to define a critical pressure Pc, namely the minimum value of a pressure which is to be initially exerted to a layer of thermally conductive compound located in a thermal contact interface between a heat transfe:r plate and a circuit component.
The relationship between the heat contact resistance across the interface and the pressure exerted thereon, represents a hyster-esis characteristic. The heat contact resistance decreases as the initially exerted pressure Pi increases before exceeding a pressure, defined as a critical pressure Pc. Thereafter, the heat transfer resistance remains unchanged as the pressure is further increased till a maximum pressure Pm. Then the pressure Pi is gradually decreased. Then, the heat contact resistance of the thermal contact interface remains at the same value until the initial pressure Pi is reduced to a small value Pa approximately equal to zero pressure. The utilization of the above described hysteresis characteristics between the pressure exerted on a thermally conductive compound layer and thermal contact resist-ance is the focus point of the present inven-tion.
In practice, an initial pressure higher than an ex-perimentally defined critical pressure Pc, is exerted to a therm-ally conducti~e compound layer which is already disposed in a thermal contact interface by using a jig or a hydraulic pressure ~57~3 of the associated coolan-t. Thus previously pressed thermally conductive compound has a favorably low heat contact resis-tance and is capable of maintaining the value in a stable manner under a low pressure~ This phenomenon was found by the inventors by conducting and repeating a number of experiments and practices.
As the result, during the operation of the relevant electronic circuit, a pressure Pa lower than the initially exerted pressure Pm but higher than zero, is exerted to -the thermal in-terface sufficiently to maintain a small heat contact resis-tance across the interface, enabling a stable and effective heat re-moval from the relevant components. Of course, during a period where the electronic circuit is out of operation~ the pressure Pa is exerted to the circuit element. Hereinaf-ter, therefore, the pressure Pa is referred to as a working pressure. With respect to a multi-chip printed circuit board mounting a number of components theron, pressurizing jigs of two types for exerting the initial pressure Pi to the thermally conductive compound layers are dis-closed in first and second embodiments. ~The use of hydraulic pressure of the associated coolant for processing the thermally conductive compound layer is disclosed in a third embodimen-t.
; Means for preven-ting the thermally conductive compound from flowing off the located interface is disclosed in a fourth em-bodiment. In all the embodiments, bellows are used as a resilient member for elastically pressing the heat transfer plate toward the corresponding circuit component in combination with a hydraulic pressure of fluid coolant.
Tajima discloses nothing about pressure to be exerted to the thermal grease layer.
In these prior art cooling modules, much effort has been made to reduce the heat transfer resistance across a thermal contact interface utilizing various thermally conductive compound material, however, the results are not suEficient to maintain a desirably low, stable and reproducible thermal contact resistance.
SUMMARY OF THE INVENTION
The primary object of the present invention is to eli-minate the aforementioned drawbacks of the prior art cooling structures, and to provide a cooling system of an electronic cir-cuit with a high performance cooling structure which can effect-ively, steadily, and uniformly cool circuit components contained in the circuit. The next object is to provide a stable and a re-liable cooling structure having a stabilized and a thermally well-;7~3 - 5 - 25307~192 conductive layer of a liquid ma-terial in a thermal contact in-terface between a heat transfer plate and a circuit component.
To achieve the aforesai.d objects, according to the present invention, at first, the:re is previously conducted an experiment to define a critical pressure Pc, namely the minimum value of a pressure which is to be initially exerted to a layer of thermally conductive compound located in a thermal contact interface between a heat transfe:r plate and a circuit component.
The relationship between the heat contact resistance across the interface and the pressure exerted thereon, represents a hyster-esis characteristic. The heat contact resistance decreases as the initially exerted pressure Pi increases before exceeding a pressure, defined as a critical pressure Pc. Thereafter, the heat transfer resistance remains unchanged as the pressure is further increased till a maximum pressure Pm. Then the pressure Pi is gradually decreased. Then, the heat contact resistance of the thermal contact interface remains at the same value until the initial pressure Pi is reduced to a small value Pa approximately equal to zero pressure. The utilization of the above described hysteresis characteristics between the pressure exerted on a thermally conductive compound layer and thermal contact resist-ance is the focus point of the present inven-tion.
In practice, an initial pressure higher than an ex-perimentally defined critical pressure Pc, is exerted to a therm-ally conducti~e compound layer which is already disposed in a thermal contact interface by using a jig or a hydraulic pressure ~57~3 of the associated coolan-t. Thus previously pressed thermally conductive compound has a favorably low heat contact resis-tance and is capable of maintaining the value in a stable manner under a low pressure~ This phenomenon was found by the inventors by conducting and repeating a number of experiments and practices.
As the result, during the operation of the relevant electronic circuit, a pressure Pa lower than the initially exerted pressure Pm but higher than zero, is exerted to -the thermal in-terface sufficiently to maintain a small heat contact resis-tance across the interface, enabling a stable and effective heat re-moval from the relevant components. Of course, during a period where the electronic circuit is out of operation~ the pressure Pa is exerted to the circuit element. Hereinaf-ter, therefore, the pressure Pa is referred to as a working pressure. With respect to a multi-chip printed circuit board mounting a number of components theron, pressurizing jigs of two types for exerting the initial pressure Pi to the thermally conductive compound layers are dis-closed in first and second embodiments. ~The use of hydraulic pressure of the associated coolant for processing the thermally conductive compound layer is disclosed in a third embodimen-t.
; Means for preven-ting the thermally conductive compound from flowing off the located interface is disclosed in a fourth em-bodiment. In all the embodiments, bellows are used as a resilient member for elastically pressing the heat transfer plate toward the corresponding circuit component in combination with a hydraulic pressure of fluid coolant.
The thermally conductive compound is selected from a thermal grease, favourably a thermal silicone grea~e.
According to a broad aspect of the invention there is provided a cooling system used with a printed circuit board having at least one solid circuit component, sald cooling system comprising: a cooling header having a coolant passage disposed therein, a heat transfer means operatively connected to said cooling header such that at least a part of sa.id heat tran.sfer means is exposed to a liquid coolant flowing through said coolant passage and such that heat may be transferred from said heat transfer means to said liquid coolant; an elastic ~eans, connected to said heat transfer means and said coolant header, for biasing said heat transfer means against said solid circuit component with a working pressure higher than zero pressure, and a thermally conductive compound means, disposed between said heat transfer means and said solid circuit component, establishing a thermal contact between said heat transfer means and said solid circuit component, wherein said thermally conductive compound means is initially pressed with an initial pressure higher than a critical pressure which is experimentally determined to reduce and stabilize the thermal contact resistance between said heat `~ transfer means and said solid circuit component under said working pressure.
According to another broad aspect of the invention there is provided, in a thermally heat conducting means comprising a first member having a first surface, a second member having a second surface, and a thermally conductive compound material i7~3 - 7a - 25307-192 interposed between said first surface and said second surface, said second surface facing said first surface, said surfaces being rough for a thermal contact, and a pressure being exerted such that said first member and said second member are pressed to each other, a method for processing said thermally conductive compound means to reduce and stabilize thermal contact resistance between said first member and said second member comprising the step~ o~:
interposing said thermally conductive compound means hetween said heat transfer means and said solid circuit component, providing said thermally conductive compound means with an initial pressure higher than a critical pressure which is experimentally determined; and reducing said initial pressure to said working pressure higher than zero pressure.
According to another broad aspect of the inventlon there is provided, in a cooling system used with a printed circuit board having at least one solid circuit component, said cooling system including a cooling header having a coolant passage disposed therein, a hydraulic pump operatively connected to said coolant passage for pressurizing a liquid coolant to flow through said coolant passage, and a cooling module disposed corresponding to said solid circuit component, said cooling module comprising a heat transfer means operatively connected to said cooling header such that at least a part of said heat transfer means is exposed to the flow of said liquid coolant and such that heat may be transferred from said heat transfer means to said liquid coolant and an elastic means connected to said heat transfer means and said coolant header, for biasing said heat transfer means against ~LZ~3~i;753 - 7b - 25307-192 said solid circuit component with a working pressure higher than zero pressure, and a thermally conductive compound means, disposed between said heat transfer means and said solid cir~uit component, establishing a thermal contact between said heat trans~er means and said solid circuit component, a method for forminy said thermally conductive compound means to reduce and stabilize thermal contact reslstance between said heat transfer means and said solid circuit component under said working pressure comprising the steps of: interposing said thermally conductive compound means between said heat transfer means and said solid circuit component; providing said thermally conductive compound means with an initial pressure higher than a critical pressure which is experimentally determined; and reducing said initial pressure to said working pressure which is lower than said initial pressure.
The features and the advantages of the present invention will be apparent upon reading the following descriptions and claims with reference to the drawings where like reference numerals denote like parts.
BRIEF D~SCRIPTION OF TH~ DRAWINGS
Fig. 1 is a schematic magnified cross-sectional view of a thermal contact interface between the members containing a thermally condu~tive compound layer therein, for explaining heat transfer thereacross;
Fig. 2 is a schematic cross-sectional view of an experi-mental apparatus for studying the relationship between the heat contact resistance across the thermal contact interface of Fig. 1 ~2~53 - 7c - 25307-192 and a pressure exerted thereon, Fiq. 3 is a diagram representing result~ of an experi-ment conducted by using the apparatus of Fig. 2, Fig. 4 is a schematic cross-sectional view of a coolin~
module according to the present invention, illustrating a typical structural configuration thereof, Figs. 5(a) and 5(b) are schematic cross-sectional views of a part of a cooling system according to the present invention, illustrating the structural configuration and a method for press-ing the thermally conductive compound layer of a first embodiment, Figs. 6(a) and 6(b) are schematlc cross-sectional views of a part of a cooling system according to the present invention, illustrating the structural configuration and a method for press-ing the thermally conduc-tive compound layer of second embodiment, Fig. 7 is a schematic cross-sectional view of a part of cooling system according to the present invention, illustrating its structural configuration and a method for pressing the therm-ally conductive compound layer of a third embodiment, and Fig. 8 is a perspective view of circuit component mounted on a printed circuit board, illustrating the structural configuration of a barrier means of a fifth embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
.
Generally, thermal contact resistance across any inter-face between two surfaces of bodies is a function of contact area, surface finishing and flatness, and applied load between the surfaces. Actually, contact area varies dependiny on the above-described factors e~cept the filling material. In most appli-cations, improvement in the surface finish and the flatness is expensive in this field and is not economical. Therefore, a thermally conductive layer is interposed between the two surfaces, filling small gaps in the interface area and expelling air micro-2Q voids remaining on the surfaces, to reduce the -thermal contact resistance thereacross.
Fig. 1 is a magnified cross-sectional view of an inter-face between surfaces of a heat transfer plate 103 and a circuit component 133 thermally contacting with each other through a layer of thermally conductive compound, typically thermal grease 131. The roughness and irreguralities ranging below 1 um of the 57~3 two surEaces are inevitable, causing a number of air ~icro--voids 100 thereon where air tends ~o be trappcd. Therma] contact re-sistance across the in-terface can be reduced by eliminating -the trapped air and replacing it with thermal ~rease 131, since silicone oil has a -thermal conductivity several times higher than that of air. Usually, the viscosit~ of a thermal grease is ad-justed so that -the thermal grease is semi-flowable, for maintain-ing a paste-like consistency. The thermal grease 131 con-tains fillers consistin~ of fine particles of metal oxides or ceramics, suspended in a carrier fluid such as silicone oil. Increase in the mutual contact between the fine particles, or between the fine particles and the surfaces of the interface, is considered to reduce the thermal contact resistance of the interface filled with the thermally conductive compound layer. ~ccording to accumulated experience of an inventor, the heat contact resistance across a thermal contact interface containing a thermally conduct-ive compound therein has a hysteresis relationship with a pressure exerted thereon as described before. The reason why this phen-omenon occurs is not sure bu-t may be caused according to the above-described consideration.
Fig. 2 is a schematic cross-sectional view of an ex-perimental apparatus for studying the relationship. In the appa-ratus, a first copper disk plate 214, a layer of thermal grease 215, a second copper disk plate 211, a heater disk 223, and a load sensor 224 are stacked in the recited order coaxially forming a cylinder block which is surrounded by a thick thermal insulator ~2 ~ J~
According to a broad aspect of the invention there is provided a cooling system used with a printed circuit board having at least one solid circuit component, sald cooling system comprising: a cooling header having a coolant passage disposed therein, a heat transfer means operatively connected to said cooling header such that at least a part of sa.id heat tran.sfer means is exposed to a liquid coolant flowing through said coolant passage and such that heat may be transferred from said heat transfer means to said liquid coolant; an elastic ~eans, connected to said heat transfer means and said coolant header, for biasing said heat transfer means against said solid circuit component with a working pressure higher than zero pressure, and a thermally conductive compound means, disposed between said heat transfer means and said solid circuit component, establishing a thermal contact between said heat transfer means and said solid circuit component, wherein said thermally conductive compound means is initially pressed with an initial pressure higher than a critical pressure which is experimentally determined to reduce and stabilize the thermal contact resistance between said heat `~ transfer means and said solid circuit component under said working pressure.
According to another broad aspect of the invention there is provided, in a thermally heat conducting means comprising a first member having a first surface, a second member having a second surface, and a thermally conductive compound material i7~3 - 7a - 25307-192 interposed between said first surface and said second surface, said second surface facing said first surface, said surfaces being rough for a thermal contact, and a pressure being exerted such that said first member and said second member are pressed to each other, a method for processing said thermally conductive compound means to reduce and stabilize thermal contact resistance between said first member and said second member comprising the step~ o~:
interposing said thermally conductive compound means hetween said heat transfer means and said solid circuit component, providing said thermally conductive compound means with an initial pressure higher than a critical pressure which is experimentally determined; and reducing said initial pressure to said working pressure higher than zero pressure.
According to another broad aspect of the inventlon there is provided, in a cooling system used with a printed circuit board having at least one solid circuit component, said cooling system including a cooling header having a coolant passage disposed therein, a hydraulic pump operatively connected to said coolant passage for pressurizing a liquid coolant to flow through said coolant passage, and a cooling module disposed corresponding to said solid circuit component, said cooling module comprising a heat transfer means operatively connected to said cooling header such that at least a part of said heat transfer means is exposed to the flow of said liquid coolant and such that heat may be transferred from said heat transfer means to said liquid coolant and an elastic means connected to said heat transfer means and said coolant header, for biasing said heat transfer means against ~LZ~3~i;753 - 7b - 25307-192 said solid circuit component with a working pressure higher than zero pressure, and a thermally conductive compound means, disposed between said heat transfer means and said solid cir~uit component, establishing a thermal contact between said heat trans~er means and said solid circuit component, a method for forminy said thermally conductive compound means to reduce and stabilize thermal contact reslstance between said heat transfer means and said solid circuit component under said working pressure comprising the steps of: interposing said thermally conductive compound means between said heat transfer means and said solid circuit component; providing said thermally conductive compound means with an initial pressure higher than a critical pressure which is experimentally determined; and reducing said initial pressure to said working pressure which is lower than said initial pressure.
The features and the advantages of the present invention will be apparent upon reading the following descriptions and claims with reference to the drawings where like reference numerals denote like parts.
BRIEF D~SCRIPTION OF TH~ DRAWINGS
Fig. 1 is a schematic magnified cross-sectional view of a thermal contact interface between the members containing a thermally condu~tive compound layer therein, for explaining heat transfer thereacross;
Fig. 2 is a schematic cross-sectional view of an experi-mental apparatus for studying the relationship between the heat contact resistance across the thermal contact interface of Fig. 1 ~2~53 - 7c - 25307-192 and a pressure exerted thereon, Fiq. 3 is a diagram representing result~ of an experi-ment conducted by using the apparatus of Fig. 2, Fig. 4 is a schematic cross-sectional view of a coolin~
module according to the present invention, illustrating a typical structural configuration thereof, Figs. 5(a) and 5(b) are schematic cross-sectional views of a part of a cooling system according to the present invention, illustrating the structural configuration and a method for press-ing the thermally conductive compound layer of a first embodiment, Figs. 6(a) and 6(b) are schematlc cross-sectional views of a part of a cooling system according to the present invention, illustrating the structural configuration and a method for press-ing the thermally conduc-tive compound layer of second embodiment, Fig. 7 is a schematic cross-sectional view of a part of cooling system according to the present invention, illustrating its structural configuration and a method for pressing the therm-ally conductive compound layer of a third embodiment, and Fig. 8 is a perspective view of circuit component mounted on a printed circuit board, illustrating the structural configuration of a barrier means of a fifth embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
.
Generally, thermal contact resistance across any inter-face between two surfaces of bodies is a function of contact area, surface finishing and flatness, and applied load between the surfaces. Actually, contact area varies dependiny on the above-described factors e~cept the filling material. In most appli-cations, improvement in the surface finish and the flatness is expensive in this field and is not economical. Therefore, a thermally conductive layer is interposed between the two surfaces, filling small gaps in the interface area and expelling air micro-2Q voids remaining on the surfaces, to reduce the -thermal contact resistance thereacross.
Fig. 1 is a magnified cross-sectional view of an inter-face between surfaces of a heat transfer plate 103 and a circuit component 133 thermally contacting with each other through a layer of thermally conductive compound, typically thermal grease 131. The roughness and irreguralities ranging below 1 um of the 57~3 two surEaces are inevitable, causing a number of air ~icro--voids 100 thereon where air tends ~o be trappcd. Therma] contact re-sistance across the in-terface can be reduced by eliminating -the trapped air and replacing it with thermal ~rease 131, since silicone oil has a -thermal conductivity several times higher than that of air. Usually, the viscosit~ of a thermal grease is ad-justed so that -the thermal grease is semi-flowable, for maintain-ing a paste-like consistency. The thermal grease 131 con-tains fillers consistin~ of fine particles of metal oxides or ceramics, suspended in a carrier fluid such as silicone oil. Increase in the mutual contact between the fine particles, or between the fine particles and the surfaces of the interface, is considered to reduce the thermal contact resistance of the interface filled with the thermally conductive compound layer. ~ccording to accumulated experience of an inventor, the heat contact resistance across a thermal contact interface containing a thermally conduct-ive compound therein has a hysteresis relationship with a pressure exerted thereon as described before. The reason why this phen-omenon occurs is not sure bu-t may be caused according to the above-described consideration.
Fig. 2 is a schematic cross-sectional view of an ex-perimental apparatus for studying the relationship. In the appa-ratus, a first copper disk plate 214, a layer of thermal grease 215, a second copper disk plate 211, a heater disk 223, and a load sensor 224 are stacked in the recited order coaxially forming a cylinder block which is surrounded by a thick thermal insulator ~2 ~ J~
layer 225 for thermally insulating the bottom side and the cylind-rical side of the block. A coolan-t passage 212, namely a water-passage is disposed in a cooliny header 220. The first copper disk plate 214 is connected to the one end of a bellows 213 which is water tightly secured to the cooling header 220 at the other end, being operatively connected Io the coolant passage 212. 'rhe coolant, water, flows through the coolant passage 212 as indicated by an arrow 217, and then the flow direction is -turned toward the first copper disk 214 by means of a deflector 216 disposed inside of the water passage 212, as indicated by an arrow 218, removing heat generated in the heater disk 223. Hereby, the cooling head-er 220 is fixed and the cylindrical block is vertically movable by the vertical movement o~ a table 210 on which the thermal in-sulator 225 and the cylinder block is placed.
By the structure of the above-described configuration, the whole heat generated in the heater disk 223 can be considered to flow in an upward direction as indicated by an arrow 219 in good approximation. The temperature tl of the first copper disk plate 214 and the temperature t2 of the second copper disk plate 211 are measured by thermo-couples 221 and 222 attached to the disk plates 214 and 211 respectively. Thus the heat contact resistance Rcont of the thermal interface of the thermal grease layer 215 can be easily figured out by measuring the temperatures tl and t2, and the heating power Q inputted to the heater disk 223, following a formula:
Rcont = (t2 - tl)/Q
i7~3 - 11 - 25307-~92 The load pressure P loaded to the thermal grease layer 215 is detected by the load sensor 224, a piezoresistive device such as a silicon pressure transducer available in the market.
Hereby, the pressure exerted to the thermal grease 215 is the sum oE the hydraulic pressure of the coolant and the resilient press-ure of the bellows 213. The hydraulic pressure is changeable using a hydraulic pump and a piping line (both not shown), and the resilient pressure of the bel:Lows 213 can be changed in some range by adjusting the vertical position of the base table 210 upwardly or downwardly as indicated by a twin heads arrow 221.
E'ig. 3 is a diagram representing an experimental result.
The heat contact resistance Rcont is taken on the ordinate and the load pressure P on the abscissa. At the beginning of this experiment, the load pressure P is gradually increased from zero to a maximum pressure Pm and kept for 3 minutes~ Thereafter, the load pressure P is gradually reduced toward zero value. Each experimental datum is plotted as indicated by a small circle, initially in the leftward direction indicated by an arro~ R/ and after reaching a point M, toward the le~tward direction indicated by an arrow L. Apparently, the curve of Fig. 3 represents a hysteresis character. The curve has a turning point C at a load pressure which is referred to as a critical pressure Pc. At a pressure higher than Pc, the heat contact resistance remains unchanged, being maintained until the load pressure P is in-creased to Pm, and then decreased from Pm to Pa near the zero value. It is confirmed that the heat contact resistance at a ~5~'i3 load pressure of 10 grams, as indicated b~ a point A, is still almost the same value as that at a higher load pressure. This hysteresis character is fully utilized in the present invention.
Basically, the present invention relates to a printed circuit board mounting a number of circuit components such as IC
chips thereon, namely a multi-chip printed circuit board. At first, however, a single cooling module applied to a single chip and an associated thermally conductive compound layer, are de-scribed to explain the principle of the present invention. Fig.
4 is a schematic cross-sectional view of a cooling module, illu-strating its structural configuration. Corresponding to the cooling module, a circuit component 11, such as a semiconductor IC device, is mounted on a printed circuit board 10. A thermally conductive compound layer 15, such as a layer of thermal grease, is interposed between the top surface of the circuit component 11 and a heat transfer plate 14 made of metal having high thermal conductivity, such as copper. The heat transfer plate 14 is connected to a bellows 13 in liquid tight fashion at its one end.
At the other end thereof, the bellows 13 is tightly secured to a cooling header 20, being operatively connected to a coolant passage 12 disposed in the cooling header 20. The coolant which may be liquid coolant or gaseous coolant, flows through the cool-ant passage 12, contacting the exposed surface of the heat trans-fer plate 14. The flow of the coolant is directed toward the heat transfer plate 14 guided by the coolant passage 12 as represented by an arrow X such that the heat generatèd in the circuit ! I
By the structure of the above-described configuration, the whole heat generated in the heater disk 223 can be considered to flow in an upward direction as indicated by an arrow 219 in good approximation. The temperature tl of the first copper disk plate 214 and the temperature t2 of the second copper disk plate 211 are measured by thermo-couples 221 and 222 attached to the disk plates 214 and 211 respectively. Thus the heat contact resistance Rcont of the thermal interface of the thermal grease layer 215 can be easily figured out by measuring the temperatures tl and t2, and the heating power Q inputted to the heater disk 223, following a formula:
Rcont = (t2 - tl)/Q
i7~3 - 11 - 25307-~92 The load pressure P loaded to the thermal grease layer 215 is detected by the load sensor 224, a piezoresistive device such as a silicon pressure transducer available in the market.
Hereby, the pressure exerted to the thermal grease 215 is the sum oE the hydraulic pressure of the coolant and the resilient press-ure of the bellows 213. The hydraulic pressure is changeable using a hydraulic pump and a piping line (both not shown), and the resilient pressure of the bel:Lows 213 can be changed in some range by adjusting the vertical position of the base table 210 upwardly or downwardly as indicated by a twin heads arrow 221.
E'ig. 3 is a diagram representing an experimental result.
The heat contact resistance Rcont is taken on the ordinate and the load pressure P on the abscissa. At the beginning of this experiment, the load pressure P is gradually increased from zero to a maximum pressure Pm and kept for 3 minutes~ Thereafter, the load pressure P is gradually reduced toward zero value. Each experimental datum is plotted as indicated by a small circle, initially in the leftward direction indicated by an arro~ R/ and after reaching a point M, toward the le~tward direction indicated by an arrow L. Apparently, the curve of Fig. 3 represents a hysteresis character. The curve has a turning point C at a load pressure which is referred to as a critical pressure Pc. At a pressure higher than Pc, the heat contact resistance remains unchanged, being maintained until the load pressure P is in-creased to Pm, and then decreased from Pm to Pa near the zero value. It is confirmed that the heat contact resistance at a ~5~'i3 load pressure of 10 grams, as indicated b~ a point A, is still almost the same value as that at a higher load pressure. This hysteresis character is fully utilized in the present invention.
Basically, the present invention relates to a printed circuit board mounting a number of circuit components such as IC
chips thereon, namely a multi-chip printed circuit board. At first, however, a single cooling module applied to a single chip and an associated thermally conductive compound layer, are de-scribed to explain the principle of the present invention. Fig.
4 is a schematic cross-sectional view of a cooling module, illu-strating its structural configuration. Corresponding to the cooling module, a circuit component 11, such as a semiconductor IC device, is mounted on a printed circuit board 10. A thermally conductive compound layer 15, such as a layer of thermal grease, is interposed between the top surface of the circuit component 11 and a heat transfer plate 14 made of metal having high thermal conductivity, such as copper. The heat transfer plate 14 is connected to a bellows 13 in liquid tight fashion at its one end.
At the other end thereof, the bellows 13 is tightly secured to a cooling header 20, being operatively connected to a coolant passage 12 disposed in the cooling header 20. The coolant which may be liquid coolant or gaseous coolant, flows through the cool-ant passage 12, contacting the exposed surface of the heat trans-fer plate 14. The flow of the coolant is directed toward the heat transfer plate 14 guided by the coolant passage 12 as represented by an arrow X such that the heat generatèd in the circuit ! I
component ll and transferred to the heat transfer plate 14 across the thermally conductive compound layer 15, is effectively re-moved by the coolant. The thermally conductive compound layer 15 may be coated on the top surface of the circuit component ll or the bottom surface, facing the circuit component 11, of the heat transfer plate 14. As a result, both surfaces come in full con-tact with each other even when the surfaces are uneven and rouyh.
Hereby, the cooling header 20 is fixed, and a stacked block comprising the heat transfer plate 14, thermally conductive compound layer 15 and the circuit component ll is vertically moved to exert a pressure on the thermally conductive compound layer 15 by vertically moving the printed circuit board 10. With the above-described structure of the cooling module, the thermally conductive compound layer 15 can be pressed before operation in order to enhance and stabilize the thermal conductivity of the layer 15 in the manner as described before with respect to the experiment the results of which are represented in ~ig. 3. That is, the layer 15 is pressed by elevating the printed circuit board 10 or by increasing the hydraulic pressure of the coolant, or by combining both operations, to a pressure Pm higher than the critical pressure Pc which is determined by an experiment con-ducted beforehand. The pressure Pm is maintained for a prede-termined time, usually for three minutes. Thereafter, the press-ure is decreased from the pressure Pm to a working pressure Pa which may be slightly higher than zero. However, in practice, the working pressure Pa is selected to a higher value sufficient ~ 25307-192 to ahsorb an inevitable fluctuation of the relevant hydraulic pressure of the coolant or the elastic pressure of -the bellows.
Thus the thermally conductive compound layer 15 establishes a compound contact or grease contact between the heat -transfer plate 14 and the circui-t component 11.
Figs. 5(a) and 5(b) are substantially schematic, part-ial cross-sectional views of a cooling system of a first embodi-ment of the present invention, illustrating a series of cooliny modules Eor the corresponding circuit components 11 mounted on a mul-ti-chip printed circuit board 10. The cooling modules are connected to a fixed cooling header 20 through which a coolant passage 12 is disposed. The coolant is pressurized by a hydraulic pump 19 of the relevant cooling system (not wholly shown) of the electronic circuit apparatus, running through the coolant passage 12, and removing heat generated in each circuit component 11 through the corresponding cooling module. Each cooling module comprises a bellows 13 fixed to the cooling header 20 at one end, being operatively connected to the coolant passage 12, and to a hea-t transfer plate 14 at the other end. The pxinted circuit board 10 is supported a-t its peripheral edge by a flange 22 which is secured to the lower portion of the cooling header 20. The axes of the cooling modules are arranged vertically to the corre-sponding circuit components 11. Thermally conductive compound, such as silicone thermal grease available in the market, is coated to form a layer 15 on the top surface of the circuit component 11 or on the bottom surface of the heat transfer plate 14. Then, the printed circuit board 10 is vertically elevated usiny a movable base plate jig 16, namely a table elevator, and is pressed against the cooling modules. Thus, each circuit component 11 is pressed against the corresponding heat transfer plates 14, exer-ting a pressure P to each thermally conductive compound layer 15, as shown in Fig. 5(a). The pressure P is increased up to Pm higher than the critical pressure Pc which is defined by an experiment conducted beforehand. The pressure Pm is maintained for a time, for instance three minutes, and thereafter, the base table 16 is lowered decreasing the pressure P until the printed circuit board 16 is held again by the flange 22 as shown in Fig. 5(b). The printed circuit board 10 is fixed to the flange 22, In this sit-uation, a working pressure Pa higher than zero is provided to the thermally conductive compound layer 15. As the result, a stable and high heat transfer from the circuit component 11 to the cool-ant is established, providing the relevant electronic circuit apparatus with high reliability.
Figs. 6(a) and 6(b) are substantially schematic cross-sectional views of a cooling system of a second embodiment accord-ing to the present invention, illustrating a series of cooling modules engaging with the corresponding circuit components 11 mounted on a multi-chip printed circuit board 10. In the second embodiment, the cooling header 20 is separatable into a lower cooling header 20a and an upper cooling header 20b. The lower cooling header 20a has an opening 20c i~ the upper portion thereof.
The relevant heat transfer plates 14 are pushed downwardly as in-~57~;~
dicated by an arrow Y with a pushing jig 17, pressing the therm-ally conductive compound layers 15 interposed between the top surface of the circuit components 11 and the heat transfer plates 14, against the corresponding circuit components 11. The pushing jig 17 has a plural number of rods 21 having a ball shaped tip at each end, and each rod 21 is insexted into each bellows 13 through the opening 20c of the lower cooling header 20b, pressing each heat transfer plate 14 connected to the bellows 13 against - the circuit components 11. The pushing jig 21 is driven by a mechanical power source (not shown) such that the thermally con-ductive compound layers 15 are subject to a pressure changing according to the same time schedule as that of the preceding em-bodiment. Then, the opening 20c of the lower cooling header 20a is closed in a water-tight manner by the upper cooling header 20b, namely a header cover, utilizing an "Q" ring 23 and screws 24 in a conventional manner. The effect of the thus treated thermally conductive compound layer 15 is the same as that of the first em-bodiment.
Fig. 7 is a substantially schematic cross-sectional view of a cooling system of a thi~d embodiment of the present invent-ion, illustrating a series of cooling modules for the correspond-ing circuit components 11 mounted on a multi-chip printed circuit board 10. In the third embodiment, the structural configuration of the cooling system is the same as that of the first embodiment, however, instead of pressing jigs used in the preceding embodi-ments, hydraulic pressure of coolant is used by controlling the ;753 relevant hydraulic pump 19 connected to an opening of a cooling head such that the thermally conductive compound layer 15 can be subject to a pressure varying according to a similar time schedule as employed in the Eirst and the second embodiments. ~ereby, the other opening of the cooling header 20 is closed by a stopping cover 26 as shown in the ~igure, or by using a stop valve (not shown). The output pressure of the pump 19 is controlled by con-trolling a driving motor (not shown) such that the above-described pressurizing pattern is achieved. The effect of the cooling mod-ules is the same as those of the preceding embodiments. Although, the adjustment of the hydraulic pressure by controlling the re-levant hydraulic pump is necessary, the initial pressing o~ the thermally conductive compound layer is easily performed by the method of the third embodiment.
Fig. 8 is a perspective view of circuit components 11 mounted on a printed circuit board 10 having square ring-shaped barrier means 25 disposed on the top surface of the circuit com-ponents 11, for preventing thermally conductive compound layers 15 from flowing away from the area initially disposed. The bar-rier means 25 is formed to surround the area, and may be formed in a single piece body with the circuit component 11 on the top surface thereof, or may be formed separately using a material such as ceramic, silicone rubber, etc. and adhesively dispoed on the top surface of the circuit component 11. The height of the barrier 25 is selected to be slightly smaller than the thickness of the thermally conductive layer 15 in order to enable the com-~.2~53 pound layer to be pressed afterwards. The barrier means 25 may be formed on the bottom surface of the associated heat transfer plate 1~ (see Figs. 5, 6, and 7).
The many features and advantages of the present invent-ion are apparent from the detailed specification and appended claims, to cover all such features and advantages of the appara-tus which fall in the true spirit and scope of the invention.
Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction illustrated and described.
Accordingly, all suitable modifications and equivalents may be re-stored to falling within the scope and spirit of the invention.
Hereby, the cooling header 20 is fixed, and a stacked block comprising the heat transfer plate 14, thermally conductive compound layer 15 and the circuit component ll is vertically moved to exert a pressure on the thermally conductive compound layer 15 by vertically moving the printed circuit board 10. With the above-described structure of the cooling module, the thermally conductive compound layer 15 can be pressed before operation in order to enhance and stabilize the thermal conductivity of the layer 15 in the manner as described before with respect to the experiment the results of which are represented in ~ig. 3. That is, the layer 15 is pressed by elevating the printed circuit board 10 or by increasing the hydraulic pressure of the coolant, or by combining both operations, to a pressure Pm higher than the critical pressure Pc which is determined by an experiment con-ducted beforehand. The pressure Pm is maintained for a prede-termined time, usually for three minutes. Thereafter, the press-ure is decreased from the pressure Pm to a working pressure Pa which may be slightly higher than zero. However, in practice, the working pressure Pa is selected to a higher value sufficient ~ 25307-192 to ahsorb an inevitable fluctuation of the relevant hydraulic pressure of the coolant or the elastic pressure of -the bellows.
Thus the thermally conductive compound layer 15 establishes a compound contact or grease contact between the heat -transfer plate 14 and the circui-t component 11.
Figs. 5(a) and 5(b) are substantially schematic, part-ial cross-sectional views of a cooling system of a first embodi-ment of the present invention, illustrating a series of cooliny modules Eor the corresponding circuit components 11 mounted on a mul-ti-chip printed circuit board 10. The cooling modules are connected to a fixed cooling header 20 through which a coolant passage 12 is disposed. The coolant is pressurized by a hydraulic pump 19 of the relevant cooling system (not wholly shown) of the electronic circuit apparatus, running through the coolant passage 12, and removing heat generated in each circuit component 11 through the corresponding cooling module. Each cooling module comprises a bellows 13 fixed to the cooling header 20 at one end, being operatively connected to the coolant passage 12, and to a hea-t transfer plate 14 at the other end. The pxinted circuit board 10 is supported a-t its peripheral edge by a flange 22 which is secured to the lower portion of the cooling header 20. The axes of the cooling modules are arranged vertically to the corre-sponding circuit components 11. Thermally conductive compound, such as silicone thermal grease available in the market, is coated to form a layer 15 on the top surface of the circuit component 11 or on the bottom surface of the heat transfer plate 14. Then, the printed circuit board 10 is vertically elevated usiny a movable base plate jig 16, namely a table elevator, and is pressed against the cooling modules. Thus, each circuit component 11 is pressed against the corresponding heat transfer plates 14, exer-ting a pressure P to each thermally conductive compound layer 15, as shown in Fig. 5(a). The pressure P is increased up to Pm higher than the critical pressure Pc which is defined by an experiment conducted beforehand. The pressure Pm is maintained for a time, for instance three minutes, and thereafter, the base table 16 is lowered decreasing the pressure P until the printed circuit board 16 is held again by the flange 22 as shown in Fig. 5(b). The printed circuit board 10 is fixed to the flange 22, In this sit-uation, a working pressure Pa higher than zero is provided to the thermally conductive compound layer 15. As the result, a stable and high heat transfer from the circuit component 11 to the cool-ant is established, providing the relevant electronic circuit apparatus with high reliability.
Figs. 6(a) and 6(b) are substantially schematic cross-sectional views of a cooling system of a second embodiment accord-ing to the present invention, illustrating a series of cooling modules engaging with the corresponding circuit components 11 mounted on a multi-chip printed circuit board 10. In the second embodiment, the cooling header 20 is separatable into a lower cooling header 20a and an upper cooling header 20b. The lower cooling header 20a has an opening 20c i~ the upper portion thereof.
The relevant heat transfer plates 14 are pushed downwardly as in-~57~;~
dicated by an arrow Y with a pushing jig 17, pressing the therm-ally conductive compound layers 15 interposed between the top surface of the circuit components 11 and the heat transfer plates 14, against the corresponding circuit components 11. The pushing jig 17 has a plural number of rods 21 having a ball shaped tip at each end, and each rod 21 is insexted into each bellows 13 through the opening 20c of the lower cooling header 20b, pressing each heat transfer plate 14 connected to the bellows 13 against - the circuit components 11. The pushing jig 21 is driven by a mechanical power source (not shown) such that the thermally con-ductive compound layers 15 are subject to a pressure changing according to the same time schedule as that of the preceding em-bodiment. Then, the opening 20c of the lower cooling header 20a is closed in a water-tight manner by the upper cooling header 20b, namely a header cover, utilizing an "Q" ring 23 and screws 24 in a conventional manner. The effect of the thus treated thermally conductive compound layer 15 is the same as that of the first em-bodiment.
Fig. 7 is a substantially schematic cross-sectional view of a cooling system of a thi~d embodiment of the present invent-ion, illustrating a series of cooling modules for the correspond-ing circuit components 11 mounted on a multi-chip printed circuit board 10. In the third embodiment, the structural configuration of the cooling system is the same as that of the first embodiment, however, instead of pressing jigs used in the preceding embodi-ments, hydraulic pressure of coolant is used by controlling the ;753 relevant hydraulic pump 19 connected to an opening of a cooling head such that the thermally conductive compound layer 15 can be subject to a pressure varying according to a similar time schedule as employed in the Eirst and the second embodiments. ~ereby, the other opening of the cooling header 20 is closed by a stopping cover 26 as shown in the ~igure, or by using a stop valve (not shown). The output pressure of the pump 19 is controlled by con-trolling a driving motor (not shown) such that the above-described pressurizing pattern is achieved. The effect of the cooling mod-ules is the same as those of the preceding embodiments. Although, the adjustment of the hydraulic pressure by controlling the re-levant hydraulic pump is necessary, the initial pressing o~ the thermally conductive compound layer is easily performed by the method of the third embodiment.
Fig. 8 is a perspective view of circuit components 11 mounted on a printed circuit board 10 having square ring-shaped barrier means 25 disposed on the top surface of the circuit com-ponents 11, for preventing thermally conductive compound layers 15 from flowing away from the area initially disposed. The bar-rier means 25 is formed to surround the area, and may be formed in a single piece body with the circuit component 11 on the top surface thereof, or may be formed separately using a material such as ceramic, silicone rubber, etc. and adhesively dispoed on the top surface of the circuit component 11. The height of the barrier 25 is selected to be slightly smaller than the thickness of the thermally conductive layer 15 in order to enable the com-~.2~53 pound layer to be pressed afterwards. The barrier means 25 may be formed on the bottom surface of the associated heat transfer plate 1~ (see Figs. 5, 6, and 7).
The many features and advantages of the present invent-ion are apparent from the detailed specification and appended claims, to cover all such features and advantages of the appara-tus which fall in the true spirit and scope of the invention.
Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction illustrated and described.
Accordingly, all suitable modifications and equivalents may be re-stored to falling within the scope and spirit of the invention.
Claims (17)
1. A cooling system used with a printed circuit board having at least one solid circuit component, said cooling system comprising:
a cooling header having a coolant passage disposed therein.
a heat transfer means operatively connected to said cooling header such that at least a part of said heat transfer means is exposed to a liquid coolant flowing through said coolant passage and such that heat may be transferred from said heat transfer means to said liquid coolant;
an elastic means, connected to said heat transfer means and said coolant header, for biasing said heat transfer means against said solid circuit component with a working pressure high-er than zero pressure, and a thermally conductive compound means, disposed between said heat transfer means and said solid circuit component, est-ablishing a thermal contact between said heat transfer means and said solid circuit component, wherein said thermally conductive compound means is in-itially pressed with an initial pressure higher than a critical pressure which is experimentally determined to reduce and stabi-lize the thermal contact resistance between said heat transfer means and said solid circuit component under said working press-ure.
a cooling header having a coolant passage disposed therein.
a heat transfer means operatively connected to said cooling header such that at least a part of said heat transfer means is exposed to a liquid coolant flowing through said coolant passage and such that heat may be transferred from said heat transfer means to said liquid coolant;
an elastic means, connected to said heat transfer means and said coolant header, for biasing said heat transfer means against said solid circuit component with a working pressure high-er than zero pressure, and a thermally conductive compound means, disposed between said heat transfer means and said solid circuit component, est-ablishing a thermal contact between said heat transfer means and said solid circuit component, wherein said thermally conductive compound means is in-itially pressed with an initial pressure higher than a critical pressure which is experimentally determined to reduce and stabi-lize the thermal contact resistance between said heat transfer means and said solid circuit component under said working press-ure.
2. A cooling system according to claim 1, wherein said thermally conductive compound means is a thermal silicone grease.
3. A cooling system according to claim 1, wherein said thermally conductive compound means is initially pressed with said initial pressure higher than said critical pressure and there-after, said thermally conductive compound means is subjected to said working pressure lower than said initial pressure.
4. A cooling system according to claim 3, wherein said working pressure is lower than said critical pressure.
5. A cooling system according to claim 1, wherein said heat transfer means and said elastic means comprise a cooling module.
6. A cooling system according to claim 1, wherein said elastic means is a bellows.
7. A cooling system according to claim 1, wherein said heat transfer means is a metal plate having a high thermal con-ductivity.
8. A cooling system according to claim 1, further compris-ing:
a hydraulic pump operatively connected to said cooling header, pressurizing said liquid coolant and enabling said liquid coolant to flow through said coolant passage.
a hydraulic pump operatively connected to said cooling header, pressurizing said liquid coolant and enabling said liquid coolant to flow through said coolant passage.
9. A cooling system according to claim 8, wherein said working pressure is provided by said elastic means and said hy-draulic pressure of said liquid coolant is provided by said hy-draulic pump.
10. A cooling system according to claim 1, further compris-ing a barrier means disposed on a surface of said solid circuit component, surrounding the area where said thermally conductive compound layer is provided.
11. A cooling system according to claim 1, wherein said cooling header is removably secured to a lower member having an opening and an upper member capable of closing said opening of said lower member in a liquid tight manner.
12. In a thermally heat conducting means comprising a first member having a first surface, a second member having a second surface, and a thermally conductive compound material interposed between said first surface and said second surface, said second surface facing said first surface, said surfaces being rough for a thermal contact, and a pressure being exerted such that said first member and said second member are pressed to each other, a method for processing said thermally conductive com-pound means to reduce and stabilize thermal contact resistance between said first member and said second member comprising the steps of:
interposing said thermally conductive compound means between said heat transfer means and said solid circuit component;
providing said thermally conductive compound means with an initial pressure higher than a critical pressure which is ex-perimentally determined; and reducing said initial pressure to said working pressure higher than zero pressure.
interposing said thermally conductive compound means between said heat transfer means and said solid circuit component;
providing said thermally conductive compound means with an initial pressure higher than a critical pressure which is ex-perimentally determined; and reducing said initial pressure to said working pressure higher than zero pressure.
13. In a cooling system used with a printed circuit board having at least one solid circuit component, said cooling system including a cooling header having a coolant passage disposed there-in, a hydraulic pump operatively connected to said coolant passage for pressurizing a liquid coolant to flow through said coolant passage, and a cooling module disposed corresponding to said solid circuit component, said cooling module comprising a heat transfer means operatively connected to said cooling header such that at least a part of said heat transfer means is exposed to the flow of said liquid coolant and such that heat may be transferred from said heat transfer means to said liquid coolant and an elastic means connected to said heat transfer means and said coolant head-er, for biasing said heat transfer means against said solid cir-cuit component with a working pressure higher than zero pressure, and a thermally conductive compound means, disposed between said heat transfer means and said solid circuit component, establishing a thermal contact between said heat transfer means and said solid circuit component, a method for forming said thermally conductive compound means to reduce and stabilize thermal contact resistance between said heat transfer means and said solid circuit component under said working pressure comprising the steps of:
interposing said thermally conductive compound means between said heat transfer means and said solid circuit component;
providing said thermally conductive compound means with an initial pressure higher than a critical pressure which is ex-perimentally determined; and reducing said initial pressure to said working pressure which is lower than said initial pressure.
interposing said thermally conductive compound means between said heat transfer means and said solid circuit component;
providing said thermally conductive compound means with an initial pressure higher than a critical pressure which is ex-perimentally determined; and reducing said initial pressure to said working pressure which is lower than said initial pressure.
14. A method for forming the thermally conductive compound layer according to claim 13, wherein said initial pressure is provided to said thermally conductive compound means by pressing said printed circuit board against said cooling module.
15. A method for forming the thermally conductive compound layer according to claim 14, wherein said printed circuit board is moved toward said cooling module using a table elevator.
16. A method for forming said thermally conductive compound layer according to claim 13, wherein said cooling header is removably secured to a lower member having an opening and an upper member capable of closing said opening of said lower member in a liquid tight manner, and said initial pressure is provided to said thermally conductive compound means by mechanically pushing said heat transfer means against said circuit component using a push-ing jig which is inserted inside said lower cooling header by re-moving said upper cooling header.
17. A method for forming the thermally conductive compound layer according to claim 13, wherein said initial pressure ex-erted on said thermally conductive compound means is varied by controlling said hydraulic pressure of said coolant using said hydraulic pump and means for stopping the flow of said coolant.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP62125732A JP2578429B2 (en) | 1987-05-25 | 1987-05-25 | Cooling body manufacturing method |
| JP62-125732 | 1987-05-25 | ||
| JP9628887 | 1987-06-23 | ||
| JP62-096288 | 1987-06-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1295753C true CA1295753C (en) | 1992-02-11 |
Family
ID=26437513
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000566836A Expired - Fee Related CA1295753C (en) | 1987-05-25 | 1988-05-16 | Printed circuit board cooling system employing bellows and layer of thermal grease and method for forming the layer |
Country Status (3)
| Country | Link |
|---|---|
| KR (1) | KR910008985B1 (en) |
| AU (1) | AU587937B2 (en) |
| CA (1) | CA1295753C (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH02231218A (en) * | 1989-03-03 | 1990-09-13 | Sanden Corp | Cooling device for controller |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1227886A (en) * | 1984-01-26 | 1987-10-06 | Haruhiko Yamamoto | Liquid-cooling module system for electronic circuit components |
| JPS60160149A (en) * | 1984-01-26 | 1985-08-21 | Fujitsu Ltd | Cooling system for integrated circuit device |
| JPS61222242A (en) * | 1985-03-28 | 1986-10-02 | Fujitsu Ltd | Cooling device |
-
1988
- 1988-05-06 KR KR1019880005235A patent/KR910008985B1/en not_active IP Right Cessation
- 1988-05-16 CA CA000566836A patent/CA1295753C/en not_active Expired - Fee Related
- 1988-05-24 AU AU16557/88A patent/AU587937B2/en not_active Ceased
Also Published As
| Publication number | Publication date |
|---|---|
| KR910008985B1 (en) | 1991-10-26 |
| KR880014847A (en) | 1988-12-24 |
| AU587937B2 (en) | 1989-08-31 |
| AU1655788A (en) | 1988-12-01 |
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| Date | Code | Title | Description |
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| MKLA | Lapsed |