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

• US 7,564,690 B2
• Filed: 09/11/2007
• Issued: 07/21/2009
• Est. Priority Date: 11/03/2005
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Koschmeder, Max John Christopher, Gilliland, Don Alan
• Primary Examiner(s): Gandhi; Jayprakash N
• Assistant Examiner(s): HAUGHTON, ANTHONY MICHAEL
• Application Number:
  US11/853,418
• Publication Number:
  US 20080002367A1
• Time in Patent Office: 679 Days
• Field of Search: 361/720, 361/704, 361/709, 361/719, 257/706, 257/707
• 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 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, and 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 configured so that movement of a concave tip thereof is substantially limited to a z-axis as the multiple-jointed spring finger is compressed toward the base portion of the grounding spring, and wherein the concave tip makes electrical contact with one of the conductive pads by receiving in ball-in-socket fashion at least a portion of a conductive pad on the surface of the printed circuit board.

2. The method as recited in claim 1, wherein the interposing step includes a step of attaching the grounding spring to the peripheral surface of the heat sink using a plurality of screws.

3. The method as recited in claim 2, wherein the step of attaching the grounding spring to the peripheral surface of the heat sink using a plurality of screws is performed before the heat sink is brought into thermal contact with the module and before the generally Z-shaped spring elements are brought into electrical contact with the conductive pads on the surface of the printed circuit board.

4. The method as recited in claim 3, wherein the step of attaching the grounding spring to the peripheral surface of the heat sink using a plurality of screws is performed by passing the screws through a plurality of through-holes in the generally planar base portion of the grounding spring and threading the screws into a plurality of threaded-holes in the peripheral surface of the heat sink.