Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Alternative design for spring-loaded heatsink attach fastener

IP.com Disclosure Number: IPCOM000004810D
Publication Date: 2001-Jun-11
Document File: 4 page(s) / 344K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a design alternative for the spring﷓loaded fork﷓lock and rivet-type fasteners that are used to attach heatsinks to motherboards. Benefits include low insertion force, high retention, improved trace compatibility, and improved rework capacity.

This text was extracted from a WORD97 document.
This is the abbreviated version, containing approximately 47% of the total text.

Alternative design for spring-loaded heatsink attach fastener

Disclosed is a design alternative for the spring-loaded fork-lock and rivet-type fasteners that are used to attach heatsinks to motherboards. Benefits include low insertion force, high retention, improved trace compatibility, and improved rework capacity.

The key elements in the proposed design are:

Design uses slots that are smaller than holes used in the other designs

Fastener is rotated between the locked and unlocked positions instead of forcibly inserted into holes in the PCB

Anti-rotate feature is designed into the spring-loaded fastener to prevent accidentally disengaging the system

Fastener requires zero or very low insertion force during actual board assembly because the spring can be pre-loaded

Fastener can be repeatedly reworked with little wear or damage

The disclosed design addresses the lack of low-insertion force, high retention force fasteners for attaching passive heatsinks to motherboard devices. Conventional fasteners in the marketplace pose several major problems for use on-board designs. Supply is constrained and cost is increased due to proprietary designs. Holes break up the motherboard design because of size in the dense core routing area. High insertion force of conventional fasteners does not allow for hand-assembly without assistance from semi-automated tools. Insertion and retention force wear the fastener and may cause it to be discarded.

Conventional spring-loaded fasteners are either the fork-lock type (see Figure 1) or the rivet type (see Figure 2). The fork-lock type employs barbs and a plastic split pin. The pin is forcibly inserted into a PCB hole where the split pin deflects and then snaps back open when through the board. The barbs prevent the pin from retracting. The rivet type is similar in that a slotted pin allows the bulge on the ends of the pin to be pushed through a PCB hole smaller than the diameter of the bulge. A second pin is inserted into the barrel of the rivet when the bulge is through the PCB hole. The center pin prevents the bulge from collapsing and backing out of the board.

With both types of conventional fasteners, a ~0.125-inch diameter round hole is required. Insertion and retention forces make the fasteners very sensitive to hole size. With the fork-lock fastener, for example, a 0.003-inch diameter variation can cause insertion force to vary between 5 to 20 lb. Retention force also varies accordingly. Wear on the barb of the fastener adversely affects retention capability. Reworked sink assemblies are typically discarded.

The technical advantages of the disclosed design are numerous. Narrower slots (0.060-inch width x 0.120-inch length) are used on the PCB. The slots can be oriented such that the narrow cross section is presented to routing breakout. Routing is constricted by 0.060 inch instead of 0.125 inch. The insertion ...