Thermal conductive substrate and the method for manufacturing the same

Abstract

A thermal conductive substrate includes a first electrical insulator layer, a second electrical insulator layer and a lead frame serving as a circuit pattern. The first electrical insulator layer is formed of a thermal conductive resin composition containing a thermosetting resin and an inorganic filler, and is joined to the lead frame. The second electrical insulator layer is provided on the side of the first electrical insulator layer not in contact with the lead frame, and is formed of a thermal conductive resin composition containing the inorganic filler and a resin composition containing the thermosetting resin. The second electrical insulator layer has a higher thermal conductivity than the first electrical insulator layer. Thus, it is possible to achieve higher heat-radiating characteristics and component packaging reliability without deteriorating formability and adhesive characteristics of the electrical insulator layers.

What is claimed is:  
     
         1 . A thermal conductive substrate comprising: 
 a first electrical insulator layer;    a second electrical insulator layer; and    a lead frame serving as a circuit pattern;    wherein the first electrical insulator layer is formed of a thermal conductive resin composition comprising a thermosetting resin and an inorganic filler, and is joined to the lead frame,    the second electrical insulator layer is provided on a side of the first electrical insulator layer not in contact with the lead frame, and is formed of a thermal conductive resin composition comprising the inorganic filler and a resin composition comprising the thermosetting resin, and    the second electrical insulator layer has a higher thermal conductivity than the first electrical insulator layer.    
     
     
         2 . The thermal conductive substrate according to  claim 1 , wherein the second electrical insulator layer has a higher blend ratio of the inorganic filler than the first electrical insulator layer.  
     
     
         3 . The thermal conductive substrate according to  claim 1 , wherein the first electrical insulator layer has a ratio of the inorganic filler of 70 to 95 wt %.  
     
     
         4 . The thermal conductive substrate according to  claim 1 , wherein the inorganic filler is at least one powder selected from the group consisting of Al 2 O 3 , MgO, BN, Si 3 N 4 , AlN, SiO 2  and SiC.  
     
     
         5 . The thermal conductive substrate according to  claim 1 , wherein the inorganic filler has a mean particle size ranging from 0.1 to 100 μm.  
     
     
         6 . The thermal conductive substrate according to  claim 1 , wherein the second electrical insulator layer is thicker than the first electrical insulator layer.  
     
     
         7 . The thermal conductive substrate according to  claim 1 , wherein a total thickness of the first and second electrical insulator layers is at least 0.4 mm, and the first electrical insulator layer has a thickness of not larger than 0.1 mm.  
     
     
         8 . The thermal conductive substrate according to  claim 1 , wherein the second electrical insulator layer further comprises a reinforcing material.  
     
     
         9 . The thermal conductive substrate according to  claim 8 , wherein the reinforcing material is a non-woven fabric or a woven fabric of a ceramic fiber or a glass fiber.  
     
     
         10 . The thermal conductive substrate according to  claim 9 , wherein the fiber diameter is not larger than 20 μm.  
     
     
         11 . The thermal conductive substrate according to  claim 1 , wherein the first electrical insulator layer has a thermal conductivity of at least 1 W/m·K (Watt/Meter·Kelvin) and not higher than 5 W/m·K, and the second electrical insulator layer has a thermal conductivity of higher than 5 W/m·K and not higher than 15 W/m·K.  
     
     
         12 . The thermal conductive substrate according to  claim 1 , wherein an end face of the circuit pattern of the lead frame is covered with the first electrical insulator layer in a portion where the circuit pattern is in contact with the first electrical insulator layer.  
     
     
         13 . The thermal conductive substrate according to  claim 1 , wherein the lead frame is embedded in the first electrical insulator layer so as to be flush with a surface of the first electrical insulator layer.  
     
     
         14 . The thermal conductive substrate according to  claim 1 , wherein a heat-radiating board is further joined on an outer side of the second electrical insulator layer.  
     
     
         15 . A method for manufacturing a thermal conductive substrate comprising: 
 producing a first thermal conductive resin composition by mixing an inorganic filler and a resin composition comprising a thermosetting resin that is not cured;    producing a second thermal conductive resin composition having a higher thermal conductivity than the first thermal conductive resin composition by mixing the inorganic filler and the resin composition comprising the thermosetting resin that is not cured; and    stacking a lead frame, the first thermal conductive resin composition and the second thermal conductive resin composition in this order and integrating them by heating and pressing, as well as curing the thermosetting resin.    
     
     
         16 . The method for manufacturing the thermal conductive substrate according to  claim 15 , wherein the second thermal conductive resin composition that has a higher thermal conductivity and a higher content ratio of the inorganic filler than the first thermal conductive resin composition is produced when producing a second thermal conductive resin composition.  
     
     
         17 . The method for manufacturing the thermal conductive substrate according to  claim 15 , wherein the first and second thermal conductive resin compositions further are processed into sheets respectively after producing a first thermal conductive resin composition and a second thermal conductive resin composition.  
     
     
         18 . The method for manufacturing the thermal conductive substrate according to  claim 15 , wherein a reinforcing material is impregnated with a mixture of the inorganic filler and the resin composition comprising the thermosetting resin that is not cured so as to produce the second thermal conductive resin composition when producing a second thermal conductive resin composition sheet.  
     
     
         19 . The method for manufacturing the thermal conductive substrate according to  claim 15 , wherein a heat-radiating board further is stacked on a side of the second thermal conductive resin composition when integrating by heating and pressing.  
     
     
         20 . The method for manufacturing the thermal conductive substrate according to  claim 15 , wherein the second thermal conductive resin composition is made thicker than the first thermal conductive resin composition.  
     
     
         21 . The method for manufacturing the thermal conductive substrate according to  claim 15 , wherein insulator layers formed of the first and second thermal conductive resin compositions are processed to be at least 0.4 mm thick in total, and the insulator layer formed of the second thermal conductive resin composition is processed to have a thickness smaller than the total thickness of the insulator layers and not smaller than a thickness 0.1 mm smaller than the total thickness of the insulator layers.  
     
     
         22 . The method for manufacturing the thermal conductive substrate according to  claim 15 , wherein the first thermal conductive resin composition has a ratio of the inorganic filler of 70 to 95 wt %.  
     
     
         23 . A method for manufacturing a thermal conductive substrate comprising: 
 processing a first thermal conductive resin composition that has been produced by mixing an inorganic filler and a resin composition comprising a thermosetting resin that is not cured into a sheet;    producing a second thermal conductive resin composition having a higher thermal conductivity than the first thermal conductive resin composition by mixing the inorganic filler and the resin composition comprising the thermosetting resin that is not cured;    processing the second thermal conductive resin composition into a layer having a substantially constant thickness and adhering the layer onto a heat-radiating board; and    stacking a lead frame, the first thermal conductive resin composition and the heat-radiating board provided with the second thermal conductive resin composition in this order so that the first and second thermal conductive resin compositions contact each other and integrating them by heating and pressing, as well as curing the thermosetting resin.    
     
     
         24 . The method for manufacturing the thermal conductive substrate according to  claim 23 , wherein the second thermal conductive resin composition is made thicker than the first thermal conductive resin composition.  
     
     
         25 . The method for manufacturing the thermal conductive substrate according to  claim 23 , wherein insulator layers formed of the first and second thermal conductive resin compositions are processed to be at least 0.4 mm thick in total, and the insulator layer formed of the second thermal conductive resin composition is processed to have a thickness smaller than the total thickness of the insulator layers and not smaller than a thickness 0.1 mm smaller than the total thickness of the insulator layers.  
     
     
         26 . The method for manufacturing the thermal conductive substrate according to  claim 23 , wherein the first thermal conductive resin composition has a ratio of the inorganic filler of 70 to 95 wt %.  
     
     
         27 . The method for manufacturing the thermal conductive substrate according to  claim 23 , wherein the second thermal conductive resin composition is in powder or paste-like form and is heated and pressed so as to be adhered to the heat-radiating board, when processing the second thermal conductive resin composition into the layer having the substantially constant thickness and adhering the layer onto the heat-radiating board.  
     
     
         28 . The method for manufacturing the thermal conductive substrate according to  claim 27 , wherein the second thermal conductive resin composition is heated and pressed so as to be adhered to the heat-radiating board, and at the same time, the thermosetting resin in the second thermal conductive resin composition is cured, thus producing a heat-radiating board provided with a second insulator layer.  
     
     
         29 . A method for manufacturing a thermal conductive substrate comprising: 
 processing a second thermal conductive resin composition produced by mixing an inorganic filler and a resin composition comprising a thermosetting resin that is not cured into a layer having a substantially constant thickness and adhering the layer onto a heat-radiating board;    processing a first thermal conductive resin composition produced by mixing the inorganic filler and the resin composition comprising the thermosetting resin that is not cured and having a lower thermal conductivity than the second thermal conductive resin composition into a layer having a substantially constant thickness, and adhering the layer onto the second thermal conductive resin composition that has been adhered onto the heat-radiating board in the first process; and    stacking a lead frame and the heat-radiating board provided with the first and second thermal conductive resin compositions so that the lead frame and the first thermal conductive resin composition contact each other and integrating them by heating and pressing, as well as curing the thermosetting resin.    
     
     
         30 . The method for manufacturing the thermal conductive substrate according to  claim 29 , wherein the second thermal conductive resin composition is made thicker than the first thermal conductive resin composition.  
     
     
         31 . The method for manufacturing the thermal conductive substrate according to  claim 29 , wherein insulator layers formed of the first and second thermal conductive resin compositions are processed to be at least 0.4 mm thick in total, and the insulator layer formed of the second thermal conductive resin composition is processed to have a thickness smaller than the total thickness of the insulator layers and not smaller than a thickness 0.1 mm smaller than the total thickness of the insulator layers.  
     
     
         31 . The method for manufacturing the thermal conductive substrate according to  claim 29 , wherein the first thermal conductive resin composition has a ratio of the inorganic filler of 70 to 95 wt %.  
     
     
         32 . The method for manufacturing the thermal conductive substrate according to  claim 29 , wherein the second thermal conductive resin composition is powder or paste-like form and is heated and pressed so as to be adhered to the heat-radiating board when processing the second thermal conductive resin composition into the layer having the substantially constant thickness and adhering the layer onto the heat-radiating board.  
     
     
         33 . The method for manufacturing the thermal conductive substrate according to  claim 32 , wherein the second thermal conductive resin composition is heated and pressed so as to be adhered to the heat-radiating board, and at the same time, the thermosetting resin in the second thermal conductive resin composition is cured, thus producing a heat-radiating board provided with a second insulator layer.