Patent Publication Number: US-2002003693-A1

Title: Heat sink

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to a heat sink for radiating the heat from devices, such as electronic parts and elements.  
       [0002] Semiconductor devices used in domestic electric products, automobiles and computers hate heat and it is strongly required to prevent their inner temperature from exceeding an allowable maximum temperature.  
       [0003] Power transistors and semiconductor rectifiers consume a great deal of power and it is impossible to discharge generated heat by way of their cases of the semiconductor elements and leads and therefore, the devices are destroyed by increasing of the inner temperature. To avoid the thermal destruction, a heat sink with large radiation area is attached to the cases of the semiconductors. The effect of the heat radiation is getting bigger in proportion to the increase of the radiating area and the thickness of the heat sink. As a result, the devices is able to control higher power.  
       [0004] In the ordinary devices, it is well-known to prepare a circular hole or long hole for radiation to the radiating palate, or to attach radiating fins to the surface of the radiating plate.  
       SUMMARY OF THE INVENTION  
       [0005] An object of the present invention is to provide a heat sink with high radiation effect and capable of decreasing the inner temperature of the devices.  
       [0006] One feature of the present invention is to provide a heat sink comprising a heat radiating plate having a plurality of radiating through holes and a plurality of radiating fins formed on the heat radiating plate, and the radiating fins being extended from the surface of the heat radiating plate. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0007]FIG. 1 is a diagrammatical view showing an experimental facility for confirming the radiation effect of the heat sink according to the present invention;  
     [0008]FIG. 2 is a model view showing a heat sink according to an embodiment of the present invention;  
     [0009]FIG. 3 is a view showing measuring result of the heat sink according to the present invention;  
     [0010]FIG. 4 is a view showing a temperature measuring result of the heat sink of the comparison example;  
     [0011]FIG. 5 is a view showing temperature measuring result of a heat sink according to the second embodiment of the present invention; and  
     [0012]FIG. 6 is a view showing measuring result of the sink according to third embodiment of the present invention.  
     [0013]FIG. 7 is a plane view showing a heat sink according to fourth embodiment of the present invention.  
     [0014]FIG. 8 is a sectional partial view along the line IIX-IIX in FIG. 7. 
    
    
     DETAILED EXPALANATION OF THE PREFERRED EMBODIMENTS  
     [0015]FIG. 1 is a diagramatical view showing an experimental facility for confirming the heat radiation effect of the heat sink according to the present invention.  
     [0016] The confirmation on radiation effect by heat sink is carried out by the following steps:  
     [0017] (1) As shown in FIG. 1, an iron cover  1  with fins (heat sink), a heating unit  2  (heater) a heat insulating material  3  a thermometers  4  (thermocouple) are prepared.  
     [0018] (2) The heating unit  2  is covered with the cover  1  and the room temperature is maintained at a predetermined value.  
     [0019] (3) When the measured temperature become stable, the temperature is measured at the steady-state.  
     [0020] Above temperature measurement steps are repeated on every cover  1  as shown in FIGS.  2  to  6 . If the temperature of the heating unit  2  becomes law, it shows that radiation characteristic of the cover  1  is well.  
     [0021]FIG. 2 is a model view of a heat sink showing an embodiment of the present invention.  
     [0022] The surface of a heat radiation plate  1  has a plurality of radiating holes  1   a  and fins  1   b  as shown in FIG. 2.  
     [0023] (1) In FIG. 2, the meaning of the reference signs areas follows:  
     [0024] A:area  
     [0025] C:specific heat  
     [0026] Gr:Grashof number  
     [0027] h:heat conductivity  
     [0028] l:length, n:number of fins  
     [0029] Pr:Prandtl number  
     [0030] q:heat flux  
     [0031] r:radius  
     [0032] t:thickness of wall  
     [0033] T:temperature  
     [0034] Ub:non-dimension number  
     [0035] v:exchange flow speed of radiating hole  
     [0036] Ö:efficency of fin  
     [0037] ó:density  
     [0038] sufix 0,1,s,f:position  
     [0039] sufix g:air of vessel  
     [0040] sufix h:heat radiating hole  
     [0041] (2-1) Heat balance formulas of FIG. 2 are expressed as follows:  
     [0042] q   0   =h   0   A   0 ( T   0   −T   g )  
     [0043] q   1   =h   1   A   1 ( T   g   −T   1 )  
     [0044] q   s   =(K   s   A   1   /t )( T   g   −T   s )1  
     [0045] q   h   =V   h   A   h   ó   g   C   g ( T   g   −T   i )  
     [0046] q   f   =h   s   A   s ( T   s   −T   i )+ Önh   f   A   f ( T   s   −T   i )  
     [0047] q   0   =q   1   +q   h   =q   s   +q   h   =q   f   +q   h    
     [0048] (2-2) heat transfer coefficient is expressed by the following formula:  
     [0049] (2-3) brief formula to heat transfer of natural convection of laminar flow(10 4 &lt;GrPr&lt;10 9 ) at atmospheric pressure are expressed as follows:  
     [0050] (2-4) vertical plane palate  
     [0051] h   0 =1.42{( T   0   −T   g )/ l   s}   ¼   
     [0052] h   1 =1.42{( T   g   −T   1 )/ l   s}   ¼   
     [0053] h   s =1.42{( T   s   −T   i )/ l   s}   ¼   
     [0054] (2-5) horizontal column  
     [0055] h f =1.32{(T s −T i )/(2r f )} ¼   
     [0056] (2-6) efficiency of the fin  
     [0057] Ö=tanh U p /U b    
     [0058] U b =2 ½ l f {h f /K s r f )} ½   
     [0059] (2-7) setting of parameters  
     [0060] q=2W, T i =15degC, K=204W/mK(at20degC), C g =1000J/KgK(at 300K)  
     [0061] ó g =1.18 kg/m 3  (at 300K)  
     [0062] l 0 =l 1 =l s =0.1 m,  
     [0063] A 0 =0.014 m 2 ,r f   =0.001 m,l   f   =0.005 m,t   =0.001 m,n =160  
     [0064] v h =0.002 m/s  
     [0065] A   h =(0.01×0.003×80)/(0.14×0.1) ×A   0 =0.171 A   0 =0.0024  m   2    
     [0066] A   1   =A   s   =A   0   −A   h =0.0116 m 2    
     [0067] A   f   =πr   f   2 +2π rl   f =3.46×10 −5   m   2    
     [0068] (2-8) basic calculation  
     [0069] (calculation of heat transfer coefficient)  
     [0070] Assuming ( T   s   −T   i )=14 degC, h   s =1.42{( T   s   −T   1 )/ l   1 )} ¼ =4.88 W/m   2   K h   s =1.32{( T   s   −T   1 )/2 r   f )} ¼ =12.1 W/m   2   K.    
     [0071] Assuming ( T   g   −T   1 )=27 degC, h   1 =1.42{( T   g   −T   1 )/ l   s } ¼ =5.76 W/m   2   K.    
     [0072] Assuming ( T   0   −T   g )=25 degC, h   0 =1.42{( T   0   −T   g )/ l   s } ¼ =5.65 W/m   2   K.    
     [0073] (2-9) calculation of efficiency of the fins  
     [0074] U b =2 ½ l f {h f /K s r f )} ½ =0.0545  
     [0075] ö=tanh U p /U b =0.999  
     [0076] (2-10) Calculation of Heat flux and temperature  
     [0077] q   1   =h   s   A   s ( T   s   −T   1 ) +{fraction (O)}nh   f   A   t ( T   s   −T   1   =a ( T   s   −T   1 )  
     [0078] q   h =( V   h   A   h   óC   g ( T   g   −T   1 )=b( T   g   −T   1 )  
     [0079] q   s   =K   s   A   1   /t )( T   1   −T   s ) =c ( T   1   −T   s )  
     [0080] q   1   =h   1   A   1   /t )( T   g   −T   1 ) =d ( T   g   −T   1 )  
     [0081] q   0   =h   0   A   0   /t )( T   0   −T   g ) =e ( T   0   −T   g )  
     [0082] a=0.124,b=0.00566,c=2370,d=0.0668,e=0.0791  
     [0083] From  q   s   =q   1 , ( a+c ) T   s   −cT   1   =T   1    
     [0084] From  q   1   =q   f   , aT   s   −dT   g   +dT   1   =aT   1    
     [0085] ( ac+ad+cd ) T   1   −d ( a+c ) T   g   =acT   1 - - - (1)  
     [0086] From  q   0   =q   1   +q   h , ( b+d ) T   g   −öT   1   =q   0   +bT   1 - - - (2)  
     [0087] By inserting values into formulas (1) and (2),  
     [0088] 452.2 T   1 −158.3 T   g =4408  
     [0089] 0.07246 T   g −0.0668 T   1 =2.085  
     [0090] T 1 29.27degC  
     [0091] T g =55.76degC  
     [0092] T s ={c/(a/(a+c)}T 1 +{a/(a+c)}T 1 =29.27degC  
     [0093] T   0 =2 /e+T   g =81.04 degC    
     [0094]FIG. 3 shows the above result.  
     [0095] (3-1) heat balance of the heat sink without fins of FIG. 4 is expressed as follows)  
     [0096] q   t   =h   s   A   s ( T   s   −T   1 ) +Önh   f   A   t ( T   s   −T   1 )  
     [0097] (3-2) calculation of heat transfer  
     [0098] ( T   s   −T )= 26   degC    
     [0099] h   s =1.42{( T   s   −T   1 ) /l   s )} ¼ =5.70 W/m   2   K    
     [0100] ( T   g   −T   1 )=26 degC    
     [0101] h   1 =1.42 {( T   g   −T   1 )/ I s } ¼ =5.70 W/m   2   K    
     [0102] ( T   0   −T   g )=25 degC    
     [0103] h   0 =1.42{( T   0   −T   g )/l s } ¼ =5.65 W/m   2   K    
     [0104] (3-3) calculation of heat flux and temperature  
     [0105] q f   =h   s   A   s ( T   s   −T   1 ) =a ( T   s   −T   1 )  
     [0106] a=0.0.0661,b=0.00566,c=2370,d=0.0661,e=0.0791  
     [0107] By inserting values into the formulas (1) and (2),  
     [0108] 313.3 T   1 −156.7 T   g =2350  
     [0109] 0.07176 T   g −0.0661 T   1 =2.085  
     [0110] T 1 =40.86degC  
     [0111] T g =66.69degC  
     [0112] T   s   ={c/ ( a+c ) }T   1   +{a/ ( a+c ) }T   1 =40.86 degC    
     [0113] T   0 =2/ e+T   g =91.97 degC    
     [0114]FIG. 4 shows the above result.  
     [0115] In case of the heat sink without fins, the temperature of the wall increases and it shows a great deal of effect of the fins.  
     [0116] ( 4 ) Doubling height of fins, reducing the number of fins to half: doubling length of radiating hole and reducing the number of fins  
     [0117] (4-1) Setting of parameters  
     [0118] l f =0.01m, n=80, A f =πr f   2 +2πr f l f =6.60×10 −5 m 2    
     [0119] (4-2) calculation of heat transfer)  
     [0120] Assuming (T s −T 1 )=14degC,  
     [0121] h s =1.42{(T s −T 1 )/l s } ¼ =4.88W/m 2 K  
     [0122] h f =1.32{(T s −T 1 )/2r t )} ¼ =12.1W/m 2 K  
     [0123] Assuming (T g−T   1 )=27degC,  
     [0124] h 1 =1.42{(T g −T 1 )/l s } ¼ =5.76W/m 2 K  
     [0125] Assuming (T 0 −T g )=25degC,  
     [0126] h 0 =1.42{(T 0 −T g )/l s } ¼ =5.65W/m 2 K  
     [0127] (4-3) calculation of the effect of fins  
     [0128] U b =2 ½  l f {h f /K s r f )} ½ =0.109  
     [0129] Ö=tanh U p /U b =0.996  
     [0130] (4-4) calculation of heat flux and temperature  
     [0131] a=0.120, b=0.00566, c=2370, d=0.0668, e=0.0791  
     [0132] By inserting values,  
     [0133] 442.7T 1 −178.2T g =4266  
     [0134] 0.07246T g −0.0668T g =2.085  
     [0135] T 1 =29.73degC  
     [0136] T g =56.21degC  
     [0137] T s ={c/(a+c)}T 1 +{a/(a+c)}T 1 =29.73degC  
     [0138] T 0 =2/e+T g =81.47degC  
     [0139] Fi. 5  shows the above result. Even if the height of fins become twice, the radiation effect is almost not changed.  
     [0140] (5) Doubling the radiating hole area and the number of fins: same size of radiating hole and twice number of fin  
     [0141] (5-1) setting of parameter  
     [0142] n=320  
     [0143] A h =(0.01×0.003×160)/(0.14×0.1)×A 0 =0.17180A 0 =0.0048m  
     [0144] A 1 =A s =A 0 −A h =0.0092m 2    
     [0145] (5-2) calculation of heat transfer  
     [0146] Assuming (T s −T 1 )=9degC,  
     [0147] h s =1.42{(T s −T 1 )/l s } ¼ =4.37W/m 2 K  
     [0148] h f =1.32{(T s −T 1 )/2r f )} ¼ =10.8W/m 2 K  
     [0149] Assuming (T g −T 1 )=27degC,  
     [0150] h 1 =1.42{(T g −T 1 )/l s } ¼ =5.86W/m 2 K  
     [0151] Assuming (T 0 −T g )=25degC,  
     [0152] h 0 =1.42{(T 0 −T g )/l s } ¼ =5.65W/m 2 K  
     [0153] (5-3) efficiency of fins  
     [0154] U b =2 ½ l   f  {h f /K s r f )} ½ =0.0514  
     [0155] Ö=tanh U b /U b =0.999  
     [0156] (5-4) calculation of heat flux and temperature  
     [0157] a=0.160, b=0.0113, c=1880, d= 0 . 0539 , e=0.0791  
     [0158] By inserting formulas (1) and (2),  
     [0159] 402.1T 1 −101.3T g =4512  
     [0160] 0.0652T g −0.0539T 1 =2.170  
     [0161] T 1 =24.76degC  
     [0162] T g =53.76degC  
     [0163] T s ={c/(a+c)}T 1 +{a/(a+c)}T 1 =24.76degC  
     [0164] T 0 =2/e+T g =79.04degC  
     [0165]FIG. 6 show the above result.  
     [0166] When doubling the area of the heating through hole and the number of radiating fins, the radiating effect is a little improved as shown in FIG. 6.  
     [0167] According to the embodiment of the invention, the radiation effect of the present invention is improved and it is possible to reduce the inner temperature in comparison with traditional heat sink  
     [0168] The above explanation shows that iron is used as the cover  1  with fins. However, the radiation effect is improved in comparison with the traditional heat sink when using aluminum and copper, and the inner temperature of the element may be reduced.  
     [0169] The shape of the heat sink  1  may be box type and the radiating element is inserted into the box shown in FIG. 1 or to attach radiating element to the surface of the radiating surface as shown in FIGS.  2  to  3  and  5  to  6 . It is selectable to attach the element in according to the environment of use.  
     [0170] In manufacturing the heat sink according to the present invention, surface of the heat radiating plate  1  is cut and a plurality of claws are raised up as shown in FIGS. 7 and 8. The raised-up claws are used as radiating fins  1   b  and through holes  1   a  made by cutting radiating plate and raising up claws are used as heat radiating through hole  1   a.    
     [0171] The radiating through holes  1   a  may be shape of rectangular and the radiating fins  1   b  are positioned in opposition to each other at each side of the radiating through holes  1   a  as shown in FIG. 8, the sum  2 Ta of heights of the fins  1   b  positioned both sides of the radiating through holes  1   a  is larger than the distance Tb between the both radiating fins  1   b . The thickness Tr of the radiating fins  1   b  is thinner than that of the radiating plate  1  as shown in Fig.8.  
     [0172] The heat radiating fins  1   b  are arranged along horizontal lines Lh, vertical lines Lv and inclined lines Li inclined at a predetermined degree, for example, 45 degree to the horizontal and vertical lines so as to allow cooling air to flow along the aligned radiating fins as shown in FIG. 7.  
     [0173] According to the above manufacturing process , both the radiating fins and through holes are formed simultaneously only by cutting and raising up the claws on the radiating plate. Therefore, it is possible to shorten manufacturing process in comparison with the ordinary process wherein the radiating fins are attached by welding or other way to the surface of heat radiating plate after drilling the holes on the radiating plate.  
     [0174] The heat sink according to the present invention has high radiation effect in comparison with the ordinary sink, and therefore, it is possible to reduce the inner temperature of the element.