Shielded patterned ground structure filter for EMI reduction

Patent metadata

Field	Value
Publication number	US-9717140-B2
Application number	US-201514927405-A
Country	US
Kind code	B2
Filing date	Oct 29, 2015
Priority date	Oct 29, 2015
Publication date	Jul 25, 2017
Grant date	Jul 25, 2017

Abstract

The present disclosure generally relates to a shielded patterned ground structure in a PCB. The PCB may be disposed in a hard disk drive. Conductive traces in PCBs can have the problem of common mode current flowing through the traces and thus increasing the magnitude of EMI noise. By providing a shielded patterned ground structure, the common mode current is reduced as is the magnitude of EMI noise, yet there is no negative impact to the differential signal.

First claim

What is claimed is:

1. A printed circuit board, comprising:
a pair of conductive traces; and
a first patterned ground structure disposed below the pair of conductive traces, wherein the first patterned ground structure includes a first shield layer, a second shield layer, a pair of anchor vias, and a first resonator cavity disposed between the first shield layer and the second shield layer.

2. The printed circuit board of claim 1 , further comprising a third shield layer, a fourth shield layer and a second resonator cavity disposed between the first shield layer and the second shield layer, wherein the third shield layer, fourth shield layer and second resonator cavity is disposed over the pair of conductive traces.

3. The printed circuit board of claim 1 , wherein the second shield layer includes a first portion and a second portion spaced from the first portion by a gap that is filled with dielectric material, wherein the gap creates a shielding box.

4. The printed circuit board of claim 1 , further comprising a second patterned ground structure disposed in series with the first patterned ground structure.

5. The printed circuit board of claim 1 , wherein the patterned ground structure has a length that is one fourth a common-mode wavelength of the pair of conductive traces.

6. A printed circuit board, comprising:
a first shield layer comprising a first conductive material;
a second shield layer that is spaced from the first shield layer, wherein the second shield layer comprises a second conductive material, wherein the second shield layer is spaced from the first shield layer by a first dielectric material, wherein the second shield layer has a first outer portion and a first middle portion, wherein the first middle portion is spaced from the first outer portion on all sides by the first dielectric material when viewed from a top view;
at least one conductive trace spaced from the second shield layer such that the second shield layer is disposed between the first shield layer and the at least one conductive trace, wherein the second shield layer is spaced from the at least one conductive trace by a second dielectric material;
a first anchor element extending between the first shield layer and the second shield layer, wherein the first anchor element is coupled to both the first shield layer and the second shield layer, wherein the first anchor element is spaced from the at least one conductive trace when viewed in cross-section, wherein the first anchor element extends through the first middle portion of the second shield layer; and
a second anchor element extending between the first shield layer and the second shield layer, wherein the second anchor element is coupled to both the first shield layer and the second shield layer, wherein the second anchor element is spaced from the at least one conductive trace when viewed in cross-section, wherein the second anchor element extends through the first middle portion of the second shield layer, and wherein the first anchor element, second anchor element, first shield layer and first middle portion of the second shield layer collectively form a first resonator cavity.

7. The printed circuit board of claim 6 , wherein the at least one trace comprises two traces.

8. The printed circuit board of claim 6 , further comprising:
a third shield layer that is spaced from the at least one trace, wherein the third shield layer comprises a third conductive material, wherein the third shield layer is spaced from the at least one trace by a third dielectric material, wherein the third shield layer has a second outer portion and a second middle portion, wherein the second middle portion is spaced from the second outer portion on all sides by the third dielectric material when viewed from a top view; and
a fourth shield layer that is spaced from the third shield layer, wherein the fourth shield layer comprises a fourth conductive material, wherein the first anchor element extends through the second middle portion of the third shield layer, and wherein the first anchor element, second anchor element, third shield layer and fourth shield layer collectively form a second resonator cavity.

9. The printed circuit board of claim 8 , wherein the second shield layer further comprises a third middle portion that is spaced from the first outer portion on all sides by the first dielectric material, wherein the third shield layer further comprises a fourth middle portion that is spaced from the second outer portion on all sides by the third dielectric material.

10. The printed circuit board of claim 9 , further comprising a third anchor element and a fourth anchor element, wherein the third anchor element and the fourth anchor element both extend through the third middle portion and the first shield layer, wherein the third anchor element, the fourth anchor element, the third middle portion and the first shield layer collectively form a third resonator cavity, wherein the third anchor element and the fourth anchor element extend through the fourth middle portion and the fourth shield layer, and wherein the third anchor element, the fourth anchor element, the fourth middle portion and the fourth shield layer collectively form a fourth resonator cavity.

11. The printed circuit board of claim 10 , wherein the third resonator cavity has a different size compared to the first resonator cavity.

12. The printed circuit board of claim 10 , wherein the third resonator cavity has the same size as the first resonator cavity.

13. The printed circuit board of claim 10 , wherein the first anchor element is spaced a first distance from an edge of the first middle portion, wherein the third anchor element is spaced a second distance from an edge of the third middle portion, and wherein the first distance is greater than the second distance.

14. The printed circuit board of claim 10 , wherein the first anchor element is spaced a first distance from an edge of the first middle portion, wherein the third anchor element is spaced a second distance from an edge of the third middle portion, and wherein the first distance is equal to the second distance.

15. The printed circuit board of claim 6 , wherein the second shield layer further comprises a third middle portion that is spaced from the first outer portion on all sides by the first dielectric material.

16. The printed circuit board of claim 15 , further comprising a third anchor element and a fourth anchor element, wherein the third anchor element, the fourth anchor element, the third middle portion and the first shield layer collectively form a third resonator cavity wherein the third anchor element and the fourth anchor element both extend through the third middle portion and the first shield layer.

17. The printed circuit board of claim 16 , wherein the first middle portion and the third middle portion have different sizes such that the first resonator cavity and the third resonator cavity are sized different.

18. The printed circuit board of claim 17 , wherein the first anchor element is spaced a first distance from an edge of the first middle portion, wherein the third anchor element is spaced a second distance from an edge of the third middle portion, and wherein the first distance is the same as the second distance.

19. The printed circuit board of claim 17 , wherein the first anchor element is spaced a first distance from an edge of the first middle portion, wherein the third anchor element is spaced a second distance from an edge of the third middle portion, and wherein the first di

Assignees

• Western Digital Tech Inc

Inventors

• Contreras John T
• Liu Junjia
• Nakamura Satoshi
• Nguyen Jack
• Wallash Albert John

Classifications

• H05K1/0245

  Lay-out of balanced signal pairs, e.g. differential lines or twisted lines · CPC title

• G11B33/1493 Primary

  Electro-Magnetic Interference [EMI] or Radio Frequency Interference [RFI] shielding; grounding of static charges · CPC title

• H05K1/0224

  Patterned shielding planes, ground planes or power planes (H05K1/0253 takes precedence) · CPC title

• H01P7/065 Primary

  integrated in a substrate · CPC title

• G11B33/122

  Arrangements for providing electrical connections, e.g. connectors, cables, switches · CPC title