Circuit board

Abstract

This invention relates to circuit boards and methods of fabricating circuit boards. A circuit board includes a core layer and a surface layer. The core layer includes a number of fibers and the surface layer has a thickness that is between about 10% and about 30% of the circuit board thickness. Including fibers in the core layer increases the strength of the circuit board. The surface layer is essentially free of fibers and relatively thick. The thickness of the surface layer inhibits the formation of cracks in the circuit board, which improves the reliability of circuits and systems coupled to the circuit board.

1 . A method of fabricating a circuit board having a circuit board thickness, the method comprising: 
 forming a core layer including a number of fibers; and    forming a surface layer on the core layer, the surface layer having a surface layer thickness that is between about 10% and about 30% of the circuit board thickness, the surface layer being free of fibers.    
   
   
       2 . The method of  claim 1 , wherein forming a core layer including a number of fibers comprises embedding the number of fibers in a resin.  
   
   
       3 . The method of  claim 1 , wherein forming a core layer including a number of fibers comprises embedding the number of fibers in a polymeric composite material.  
   
   
       4 . The method of  claim 1 , forming a core layer including a number of fibers comprises embedding the number of fibers in phenolic.  
   
   
       5 . A method of fabricating a circuit board having a circuit board thickness, the method comprising: 
 forming a core layer including a number of fibers; and    forming a surface resin layer on the core layer, the surface layer having a surface layer thickness that is between about 10% to 30% of the circuit board thickness.    
   
   
       6 . The method of  claim 5 , further comprising forming a number of slots in the circuit board.  
   
   
       7 . The method of  claim 5 , further comprising mounting a die using an adhesive over each of the number of slots.  
   
   
       8 . A method of fabricating a circuit board having a circuit board thickness comprising: 
 forming a core layer including a number of fibers;    forming a first layer on the core layer, the first layer having a thickness between about 10% and about 15% of the circuit board thickness and the first layer being free of fibers; and    forming a second layer on the core layer, the second having a thickness that is between about 10% and about 15% of the circuit board thickness.    
   
   
       9 . The method of  claim 8 , wherein forming a core layer including a number of fibers comprises embedding the number of fibers in a resin.  
   
   
       10 . The method of  claim 8 , wherein forming a core layer including a number of fibers comprises embedding the number of fibers in a polymeric composite material.  
   
   
       11 . The method of  claim 8 , forming a core layer including a number of fibers comprises embedding the number of fibers in phenolic.  
   
   
       12 . A method of fabricating a circuit board having a circuit board thickness comprising: 
 forming a core layer including a number of fibers;    forming a first layer on a first side of the core layer, the first layer having a thickness between about 10% and about 15% of the circuit board thickness and the first layer being free of fibers; and    forming a second layer on a second side of the core layer, the second having a thickness that is between about 10% and about 15% of the circuit board thickness.    
   
   
       13 . The method of  claim 1 , wherein forming a core layer including a number of fibers comprises embedding the number of fibers in one of a group consisting of a resin, a polymeric composite material, and phenolic.  
   
   
       14 . A method of fabricating a circuit board having a circuit board thickness comprising: 
 forming a core layer including a number of fibers;    forming a first resin layer on the core layer, the first resin layer having a thickness between about 10% and about 15% of the circuit board thickness; and    forming a second resin layer on the core layer, the second resin layer having a thickness that is between about 10% and about 15% of the circuit board thickness.    
   
   
       15 . The method of  claim 14 , wherein forming the core layer includes embedding the fibers in a resin layer.  
   
   
       16 . The method of  claim 14 , wherein forming a core layer including a number of fibers comprises embedding the number of fibers in one of a group consisting of a polymeric composite material and phenolic material.  
   
   
       17 . A method of fabricating a circuit board having a circuit board thickness, the method comprising: 
 forming a core layer including a number of fibers; and    forming a surface layer on the core layer, the surface layer having a surface layer thickness that is about 20% of the circuit board thickness, the surface layer being free of fibers.    
   
   
       18 . The method of  claim 16 , wherein forming a core layer including a number of fibers comprises embedding the number of fibers in one of a group consisting of a resin, a polymeric composite material, and phenolic material.  
   
   
       19 . A method of fabricating a circuit board having a circuit board thickness, the method comprising: 
 forming a core layer including a number of fibers having a diameter of between about 0.0005 inch and about 0.001 inch and a second dimension; and    forming a surface layer on the core layer, the surface layer having a surface layer thickness that is between about 10% and about 30% of the circuit board thickness, the surface layer being free of fibers.    
   
   
       20 . The method of  claim 19 , wherein the core layer has a thickness of between about 0.006 inch and about 0.012 inch.  
   
   
       21 . The method of  claim 20 , wherein the surface layer is about 20% of the circuit board thickness.  
   
   
       22 . The method of  claim 21 , wherein the surface layer includes a first resin layer on the core layer and a second resin layer.  
   
   
       23 . A method of fabricating a circuit board having a circuit board thickness, the method comprising: 
 forming a core layer including a number of fibers;    forming a surface resin layer on the core layer, the surface layer having a surface layer thickness that is between about 10% and 30% of the circuit board thickness;    forming a number of slots in the circuit board; and    mounting a die using an adhesive over each of the number of slots.    
   
   
       24 . The method of  claim 23 , wherein mounting the die includes mounting a memory over the slots.  
   
   
       25 . The method of  claim 24 , wherein the memory includes a dynamic random access memory.