Apparatus and method for controlling common mode impedance in disk drive head suspensions

• US 6,714,385 B1
• Filed: 04/16/2001
• Issued: 03/30/2004
• Est. Priority Date: 04/16/2001
• Status: Expired due to Term

• Current Assignee: Hutchinson Technology Incorporated (TDK Corporation)
• Original Assignee: Hutchinson Technology Incorporated (TDK Corporation)
• Inventors: Webb, Larry C. Jr., Even, Marc A.
• Primary Examiner(s): KLIMOWICZ, WILLIAM JOSEPH
• Application Number:
  US09/835,891
• Time in Patent Office: 1,079 Days
• Field of Search: 360/244.2, 360/244.3, 360/244.9, 360/245.8, 360/245.9, 360/246
• US Class Current: 360/246
• CPC Class Codes: G11B 5/484 Integrated arm assemblies, e.g. formed by material deposition or by etching from single piece of metal or by lamination of materials forming a single arm/suspension/head unit
• CPC Class Codes: G11B 5/486 with provision for mounting or arranging electrical conducting means or circuits on or along the arm assembly
• CPC Class Codes: H05K 1/0224 Patterned shielding planes, ground planes or power planes H05K1/0253 takes precedence
• CPC Class Codes: H05K 1/0253 Impedance adaptations of transmission lines by special lay-out of power planes, e.g. providing openings H05K1/0251 takes precedence
• CPC Class Codes: H05K 1/056 the metal substrate being covered by an organic insulating layer
• CPC Class Codes: H05K 2201/09681 Mesh conductors, e.g. as a ground plane
• CPC Class Codes: H05K 2201/0969 Apertured conductors
• CPC Class Codes: H05K 2201/09781 Dummy conductors, i.e. not used for normal transport of current; Dummy electrodes of components

Abstract

Apparatus and method of adjusting the common mode impedance while enabling maintenance of the differential mode impedance of a pair of traces located with respect to a ground plane formed by a load beam or trace assembly of a disk drive head suspension. The ground plane has apertures with isolated conductive islands in the apertures for setting a desired common mode impedance. The method includes a cut and try approach using sample coupons to adjust the ratio of backed area to island area to adjust the common mode impedance while maintaining the differential mode impedance by maintaining the ratio of unbacked area to the sum of the backed and island areas.

Claims

1. A trace and load beam assembly for controlling the common mode impedance of printed circuit electrical traces on a head suspension assembly of the type having a load beam formed of a conductive layer and at least one aperture in the conductive layer of the load beam, the improvement comprising a conductive island in the at least one aperture wherein the island is electrically isolated from the conductive layer of the load beam.

2. The assembly of claim 1 wherein the conductive layer includes a plurality of apertures and the improvement comprises a plurality of islands in at least some of the apertures.

3. A trace assembly for controlling the common mode impedance of printed circuit electrical traces on a head suspension assembly of the type having the trace assembly formed of a layer made up of a plurality of conductive traces, an insulator layer, and a conductive layer making up a around plane layer and at least one aperture in the conductive layer of the trace assembly, the improvement comprising a conductive island in the at least one aperture wherein the island is electrically isolated from the conductive layer of the trace assembly.

4. The apparatus of claim 3 wherein the conductive layer includes a plurality of apertures and the improvement comprises a plurality of islands in at least some of the apertures.

5. A load beam assembly having a load beam forming a conductive layer in a first plane spaced from and generally parallel to a second plane containing a plurality of printed circuit electrical traces, the load beam conductive layer including a backed area with respect to the traces and having at least one aperture therein, the aperture forming an unbacked area for the traces, wherein a ratio of the percentage area of unbacked area to backed area is controlled to control the differential mode impedance for the traces and wherein the conductive layer further includes at least one conductive island in the at least one aperture and in the first plane, and with the island electrically isolated from the conductive layer of the load beam, wherein a ratio of the backed area formed by the conductive layer of the load beam and the backed area formed by the at least one conductive island is controlled to control the common mode impedance for the traces.

6. The assembly of claim 5 wherein the conductive layer of the load beam includes a plurality of apertures making up the unbacked area and wherein a plurality of islands in at least some of the apertures reduces the unbacked area, with at least some of the islands electrically isolated from a surrounding portion of the unbacked area.

7. An assembly controlling the differential and common mode impedances of a pair of traces forming a transmission line separated by an insulating layer from a ground plane layer, with the ground plane layer including an electrically connected conductive region and at least one electrically isolated conductive island surrounded by the electrically connected conductive region, the assembly comprising:

i) a predetermined percentage of unbacked area in the ground plane layer in combination with the total backed area in the ground plane layer resulting in a desired differential mode impedance for the traces, and

ii) a predetermined percentage of the electrically connected conductive area to the electrically isolated island area in combination with a relatively constant total backed area formed by the sum of the electrically connected conductive area and electrically isolated island area resulting in a desired common mode impedance.

8. An assembly controlling the common mode impedance of printed circuit electrical traces on a head suspension assembly of the type having a trace assembly with a conductive layer forming a backed area for the traces and having at least one aperture in the conductive layer of the trace assembly, the aperture forming an unbacked area for the traces, the assembly comprising:

a) a predetermined ratio of a percentage area of unbacked to backed area for the traces resulting in a desired differential mode impedance for the traces; and

a) a conductive island in the at least one aperture with the island located in the same plane as, but electrically isolated from the conductive layer of the trace assembly resulting in a desired ratio of the backed area formed by the conductive layer of the trace assembly and the backed area formed by the island.

9. The assembly of claim 8 wherein the conductive layer of the trace assembly includes a plurality of apertures making up the unbacked area and a plurality of islands in at least some of the apertures, with at least some of the islands electrically isolated from a surrounding portion of the unbacked area.