Via structure for improving signal integrity

Abstract

The embodiment of the invention is about a novel via structure which can be incorporated into printed circuit boards, integrated circuit packages, and integrated circuits in order to reduce crosstalk, to improve signal integrity and to achieve EM emission compliance. A 4-layer (2 signal layers and 2 power layers or 2 signal layers and 2 ground layers) circuit board assembly was used for demonstrating the effect of the novel via structure. The same concept can be applied to any multi-layer circuit board. Layers that have an electrical property can be added above, under, or within the basic 4-layer circuit board to achieve a multi-layer circuit board. For 2-layer and 3-layer circuit boards, a deformed version of the proposed via structure based upon the same concept will be needed for a coplanar waveguide configuration.

What is claimed is: 
     
       1. A via structure in a circuit board or substrate having multiple layers, from top to bottom comprising:
 a first power plane or a first ground plane in the first layer; 
 a first medium in a second layer; 
 a first signal trace in a third layer; 
 a second medium in a fourth layer; 
 a second signal trace in a fifth layer; 
 a third medium in a sixth layer; 
 a second power plane or a second ground plane in a seventh layer; 
 a power via or a ground via passing through the first medium, the first signal trace, the second medium, the second signal trace, and the third medium, wherein the first power plane or the first ground plane is connected with the second power plane or the second ground plane through the power via or the ground via; 
 a signal via passing through the second medium around the power via or the ground via, and the first signal trace is connected with the second signal trace through the signal via; and 
 an anti-pad is located between the signal via and the power via or a ground via, 
 wherein the power via or the ground via is cylindrical and the thickness of the power via or the ground via is larger than the skin depth at the frequency of the signal; and 
 when a signal going through a path from the first signal trace through the signal via to the second signal trace, the signal goes through the path with complete impedance continuity. 
 
     
     
       2. The via structure of  claim 1 , wherein the first power plane or the first ground plane in the first layer and the second power plane or the second ground plane in the seventh layer have to have the same potential. 
     
     
       3. The via structure of  claim 1 , wherein the power via or the ground via is either a solid cylindrical or a cylindrical ring. 
     
     
       4. The via structure of  claim 1 , wherein the signal via are concentric to the power via or the ground via. 
     
     
       5. The via structure of  claim 1 , wherein the circuit structure comprises a printed circuit board and integrated circuit packaging. 
     
     
       6. The via structure of  claim 1 , wherein the power plane or the ground plane is deformed to a power grid or a ground grid on die. 
     
     
       7. A via structure, comprising:
 a circuit board having multiple power planes, ground planes and medium layers, wherein a power via or a ground via passes through the power planes, ground planes and medium layers along a same axis, and wherein a signal via passes through the medium layers around a power or the ground via; 
 one of the multiple power planes or the ground planes connects with a different power plane or the ground via plane through the power via or the ground via; 
 the power via or the ground via may connect all of the multiple power planes or the ground planes with same potential; 
 the power via or the ground via is cylindrical and the thickness of the power via or the ground via is larger than the skin depth at the frequency of the signal; and 
 when a signal going through the signal via, the signal goes through the signal via with complete impedance continuity. 
 
     
     
       8. The via structure of  claim 7 , wherein the signal via is concentric with the power via or the ground via. 
     
     
       9. The via structure of  claim 7 , wherein the signal via and power via or the ground via can be not only circular but also square, rectangular, or any shape. 
     
     
       10. The via structure of  claim 7 , wherein the distance between the signal via and the power via or the ground via is properly designed for impedance control of the signal via. 
     
     
       11. The via structure of  claim 7 , the dielectric material between signal via and the power via or the ground via is properly selected for impedance control of the signal via. 
     
     
       12. The via structure of  claim 7 , wherein the signal via and the power via or the ground via are perpendicular to the power planes or the ground planes of the circuit board. 
     
     
       13. The via structure of  claim 7 , wherein the signal via and power via or the ground via are located in the dielectric.