Method and apparatus for grounding a heat sink in thermal contact with an electronic component using a grounding spring having multiple-jointed spring fingers

• US 7,327,577 B2
• Filed: 11/03/2005
• Issued: 02/05/2008
• Est. Priority Date: 11/03/2005
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Gilliland, Don Alan, Koschmeder, Max John Christopher
• Primary Examiner(s): Lea-Edmonds; Lisa
• Assistant Examiner(s): HAUGHTON, ANTHONY MICHAEL
• Application Number:
  US11/266,743
• Publication Number:
  US 20070097653A1
• Time in Patent Office: 824 Days
• Field of Search: 361/683, 361/686, 361/688, 361/704, 361707-710, 361/715, 361717-720, 361/748, 361/752, 361/753, 361/796, 361/799, 361/800, 361/802, 361/816, 361/818, 720648-650, 257/706, 257/707, 257/712, 257/713, 257/718, 257/719, 257/726, 257/727, 174/16.3, 174/35.R, 174/35.GC, 174/51, 438/122, 165/80.2, 165/80.3, 165/185, 439607-609, 439/939
• US Class Current: 361/719
• CPC Class Codes: H01L 23/4093 Snap-on arrangements, e.g. clips
• CPC Class Codes: H01L 23/552 Protection against radiation, e.g. light or electromagnetic waves
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 2924/15311 being a ball array, e.g. BGA
• CPC Class Codes: H01L 2924/3025 Electromagnetic shielding

Abstract

A grounding spring for electromagnetic interference (EMI) suppression is interposed between a heat sink and a printed circuit board (PCB). The grounding spring comprises a conductive material having an opening formed at its base through which the heat sink makes thermal contact with an electronic module mounted on the PCB. The base makes electrical contact with a peripheral surface of the heat sink, and multiple-jointed spring fingers extend from the base to make electrical contact with conductive pads on the PCB. During compression, the movement of each spring finger'"'"'s tip is substantially limited to the z-axis. Accordingly, the final installed location of the tip can be precisely controlled even when the grounding spring must accommodate a wide variety of installed heights of the heat sink relative to the PCB. Preferably, the spring fingers terminate with a concave tip that is less susceptible to sliding off the conductive pads.

Claims

1. A heat sink grounding spring, comprising:

a base comprising a conductive material having a generally planar portion, wherein the generally planar portion of the base is configured to contact at least a portion of a peripheral surface of a heat sink;

a multiple-jointed spring finger comprising a conductive material extending from the generally planar portion of the base, wherein the multiple-jointed spring finger is double-jointed and includes a first v-shaped joint connecting the generally planar portion of the base to a central finger portion, and a second v-shaped joint connecting the central finger portion to a distal finger portion, and wherein the generally planar portion of the base includes a cut-out from which are formed the central finger portion, and the central finger portion includes a cut-out from which is formed the distal finger portion.

2. A heat sink grounding spring, comprising:

a base comprising a conductive material having a generally planar portion, wherein the generally planar portion of the base is configured to contact at least a portion of a peripheral surface of a heat sink;

a multiple-jointed spring finger comprising a conductive material extending from the generally planar portion of the base to form a generally Z-shaped spring element, wherein the multiple-jointed spring finger is double-jointed and includes a first v-shaped joint connecting the generally planar portion of the base to a central finger portion, and a second v-shaped joint connecting the central finger portion to a distal finger portion, and wherein the distal finger portion includes a concave finger tip extending in a direction substantially parallel to the generally planar portion of the base, the concave finger tip having a concave surface configured to receive a portion of a solder ball.

3. The heat sink grounding spring as recited in claim 2, wherein the multiple-jointed spring finger is configured so that movement of the concave finger tip thereof is substantially limited to a direction perpendicular to the generally planar portion of the base as the multiple-jointed spring finger is compressed toward the generally planar portion of the base.

4. A circuit card assembly, comprising:

a printed circuit board having an electronic module mounted on a surface thereof;

a heat sink disposed over the surface of the printed circuit board and in thermal contact with the module;

a grounding spring comprising a conductive material having an opening formed in a generally planar base portion thereof through which the heat sink and the module are in thermal contact with each other, wherein the base portion makes electrical contact with at least a portion of a peripheral surface of the heat sink, wherein a plurality of multiple-jointed spring fingers extend from the base portion to make electrical contact with conductive pads on the surface of the printed circuit board, wherein each of the multiple-jointed spring fingers is double-jointed and includes a first v-shaped joint connecting the base portion of the grounding spring to a central finger portion, and a second v-shaped joint connecting the central finger portion to a distal finger portion, and wherein the base portion of the grounding spring includes a plurality of cut-outs from which are formed the central finger portions, and each central finger portion includes a cut-out from which is formed the distal finger portion.

5. A method for grounding a heat sink in thermal contact with an electronic module, comprising the steps of:

providing a printed circuit board having an electronic module mounted on a surface thereof;

disposing a heat sink over the surface of the printed circuit card and in thermal contact with the module;

interposing a grounding spring between the printed circuit board and the heat sink, wherein the grounding spring comprises a conductive material having an opening formed in a generally planar base portion thereof through which the heat sink and the module are in thermal contact with each other, wherein the base portion of the grounding spring makes electrical contact with at least a portion of a peripheral surface of the heat sink, wherein a plurality of multiple-jointed spring fingers extend from the base portion of the grounding spring to form a plurality of generally Z-shaped spring elements that make electrical contact with conductive pads on the surface of the printed circuit board, wherein each of the multiple-jointed spring fingers is double-jointed and includes a first v-shaped joint connecting the base portion of the grounding spring to a central finger portion, and a second v-shaped joint connecting the central finger portion to a distal finger portion, wherein the distal finger portion includes a concave finger tip extending in a direction substantially parallel to the base portion of the grounding spring, and wherein the interposing step includes a step of engaging each concave finger tip with one of the conductive pads on the surface of the printed circuit board.