Rigid flexible circuit board with impedance control

Abstract

A rigid-flexible circuit board includes at least one flexible circuit board and at least one rigid circuit board. The flexible circuit board includes a flexible-board substrate, a plurality of flexible circuit board differential mode signal lines, at least one flexible circuit board grounding line, a flexible circuit board insulation layer formed on the upper surface of the flexible-board substrate and covering the flexible circuit board differential mode signal lines and the flexible circuit board grounding line. The rigid circuit board is stacked on the stacking section of the flexible circuit board. A shielding layer is formed on the flexible circuit board insulation layer of the flexible circuit board and corresponds to the extension section of the flexible circuit board. The shielding layer further extends from the extension section to the stacking section. An impedance control structure is formed on the shielding layer to control the impedance of the flexible circuit board differential mode signal lines.

What is claimed is: 
     
       1. A circuit board with an impedance control structure, comprising:
 at least one flexible circuit board, which defines a stacking section and an extension section, the extension section extending from an end of the stacking section, the flexible circuit board comprising:
 a flexible-board substrate, which extends in an extension direction and comprises an upper surface and a lower surface; 
 a plurality of first flexible-board differential mode signal lines, which is formed on the upper surface of the flexible-board substrate and extends in the extension direction from the stacking section to the extension section; 
 at least one first flexible-board grounding line, which is formed on the upper surface of the flexible-board substrate and extends in the extension direction; 
 and a first flexible-board insulation layer, which is formed on the upper surface of the flexible-board substrate and covers the first flexible-board differential mode signal lines and the first flexible-board grounding line; and 
 
 at least one first rigid circuit board, comprising:
 a first rigid-board substrate, which comprises an upper surface and a lower surface, the lower surface corresponding to and stacked on the stacking section of the flexible circuit board; 
 a plurality of first rigid-board differential mode signal lines, which is formed on the upper surface of the first rigid-board substrate and extends in the extension direction; 
 a first shielding layer, which is formed on the first flexible-board insulation layer of the flexible circuit board and corresponds to the extension section of the flexible circuit board, the first shielding layer being connected through at least one first via hole to the first flexible-board grounding line; and 
 a first impedance control structure, which is formed on the first shielding layer and corresponds to the first flexible-board differential mode signal lines of the flexible circuit board, whereby the first impedance control structure controls impedance of the first flexible-board differential mode signal lines; and 
 wherein: the lower surface of the first rigid-board substrate of the first rigid circuit board comprises an extended grounding section formed thereon, the extended grounding section extending beyond an end of the first rigid-board substrate that laces the extension section to form an extended section; and the first shielding layer has at least one portion adjacent the extended section to cover and electrically connect with the extended section. 
 
 
     
     
       2. The circuit board as claimed in  claim 1 , wherein the extended section has a length extending beyond the first rigid-board substrate, which is between 1-10 mm. 
     
     
       3. The circuit board as claimed in  claim 1 , wherein the first shielding layer extends from the extension section to reach in between the first flexible-board insulation layer and the first rigid-board substrate of the first rigid circuit board to correspond to the stacking section. 
     
     
       4. The circuit board as claimed in  claim 3 , wherein the lower surface of the first rigid-board substrate comprises a rigid circuit board grounding section formed thereon, the rigid circuit board grounding section being bonded by a bonding layer to a surface of the first shielding layer that corresponds to the stacking section, the rigid circuit board grounding section and the first shielding layer being electrically connected to each other by at least one fifth via hole. 
     
     
       5. The circuit board as claimed in  claim 1 , wherein the upper surface of the first rigid-board substrate comprises at least one first rigid-board grounding line formed thereon, the first rigid-board grounding line being electrically connected by at least one second via hole to the first flexible-board grounding line. 
     
     
       6. The circuit board as claimed in  claim 1 , wherein the first shielding layer is formed by printing one of copper paste and silver paste on the first flexible-board insulation layer. 
     
     
       7. The circuit board as claimed in  claim 1 , wherein the first shielding layer comprises one of a copper foil, a sliver foil, and an aluminum foil laminated on or bonded to the first flexible-board insulation layer. 
     
     
       8. The circuit board as claimed in  claim 1 , wherein the extension section has an end opposite to the stacking section and an exposed conduction section extends from the end in such a way that the exposed conduction section is not covered by the first flexible-board insulation layer. 
     
     
       9. The circuit board as claimed in  claim 1 , wherein the flexible circuit board comprises a plurality of slit lines that is formed by slitting in the extension direction, whereby the extension section forms a plurality of cluster lines. 
     
     
       10. The circuit board as claimed in  claim 9 , wherein the cluster lines are bundled by a bundling member. 
     
     
       11. The circuit board as claimed in  claim 10 , wherein the bundling member is made of an insulating material. 
     
     
       12. The circuit board as claimed in  claim 10 , wherein the bundling member comprises a wrapping layer that is made of a non-shielding material and a shielding layer formed on an outer circumferential surface of the wrapping layer. 
     
     
       13. The circuit board as claimed in  claim 1 , wherein the first impedance control structure comprises a plurality of openings formed in the first shielding layer of the flexible circuit board. 
     
     
       14. The circuit board as claimed in  claim 1 , wherein the first rigid-board substrate is made of a material of one of glass fiber substrate, polyimide, ceramics, and aluminum board. 
     
     
       15. The circuit board as claimed in  claim 1 , wherein the lower surface of the flexible-board substrate is further provided with:
 a plurality of second flexible-board differential mode signal lines, which is formed on the lower surface of the flexible-board substrate to extend in the extension direction from the stacking section to the extension section; 
 at least one second flexible-board grounding line, which is formed on the lower surface of the flexible-board substrate to extend in the extension direction; 
 a second flexible-board insulation layer, which is formed on the lower surface of the flexible-board substrate and covers the second flexible-board differential mode signal lines and the second flexible-board grounding line; 
 a second shielding layer, which is formed below the second flexible-board insulation layer and corresponds to the extension section of the flexible circuit board, the second shielding layer being electrically connected by at least one third via hole to the second flexible-board grounding line, the first flexible-board grounding line, and the first shielding layer; and 
 a second impedance control structure, which is formed on the second shielding layer and corresponds to the second flexible-board differential mode signal lines, whereby the second impedance control structure controls impedance of the second flexible-board differential mode signal lines. 
 
     
     
       16. The circuit board as claimed in  claim 15 , wherein the lower surface of the second flexible-board insulation layer is further provided with at least one second rigid circuit board, the second rigid circuit board comprising:
 a second rigid-board substrate, which comprises an upper surface and a lower surface, the upper surface being stacked on the lower surface of the second flexible-board insulation layer and corresponding to the stacking section; 
 a plurality of second rigid-board differential mode signal lines, which is formed on the lower surface of the second rigid-board substrate to extend in the extension direction; and 
 at least one second rigid-board grounding line, which is formed on the lower surface of the second rigid-board substrate to extend in the extension direction, the second rigid-board grounding line being electrically connected by at least one fourth via hole to a first rigid-board grounding line formed on the upper surface of the first rigid-board substrate.