Floating captive screw

Abstract

A captive screw for securing together two panels has a screw and a spring extending between the screw head and a ferrule. A collar is formed on the screw shank under the ferrule to limit penetration of the screw threads in a bottom panel so that the upper panel floats on the spring.

What is claimed: 
     
         1 . A captive screw configured to attach a first panel to a second panel comprising:
 a ferrule having a bore;   a screw having a head, a shank extending from the head, a threaded portion at an end of the shank opposite the head, and a collar on the shank proximate the threaded portion; and   a spring,   wherein the shank extends through the bore and the spring, such that the spring is between the ferrule and the head of the screw,   wherein the bore includes at least one diameter and the collar includes a maximum diameter, the maximum diameter is greater than the at least one diameter of the bore, and the at least one diameter of the bore is located between the maximum diameter of the collar and the head of the screw, and   wherein the collar is configured to limit penetration of the threaded portion into the second panel, so that the first panel, when attached to the ferrule, floats on the spring.   
     
     
         2 . A captive screw according to  claim 1 , wherein the ferrule includes an inner annular ring extending from an internal circumferential surface of the ferrule and the inner annular ring provides the at least one diameter of the bore. 
     
     
         3 . A captive screw according to  claim 2 , wherein the ferrule has at least one collapsed groove in an external circumferential surface of the ferrule. 
     
     
         4 . A captive screw according to  claim 1 , wherein the ferrule has an end portion configured to be flared to retain the ferrule on the first panel. 
     
     
         5 . A captive screw according to  claim 1 , wherein the ferrule has an end portion configured to be bent upwardly to form an inner annular ring by plastic deformation of ferrule material, and the inner annular ring provides the at least one diameter of the bore. 
     
     
         6 . A captive screw according to  claim 1 , wherein the ferrule includes an annular lip configured to limit penetration of the ferrule into the first panel. 
     
     
         7 . A captive screw according to  claim 6 , wherein at least one circumferential groove on an external surface of the ferrule is configured to receive material of the first panel when the ferrule is pressed into the first panel. 
     
     
         8 . A captive screw according to  claim 7 , wherein the at least one circumferential groove is adjacent to the annular lip, and the annular lip is between the at least one circumferential groove and the head of the screw. 
     
     
         9 . A captive screw according to  claim 1 , wherein at least one circumferential groove on an external surface of the ferrule is configured to receive material of the first panel when the ferrule is pressed into the first panel. 
     
     
         10 . A captive screw according to  claim 1 , wherein an external circumferential surface of the ferrule includes a plurality of knurls. 
     
     
         11 . A captive screw according to  claim 1 , wherein the collar is tapered. 
     
     
         12 . A heat dissipating system comprising:
 a first panel comprising a heat sink,   a second panel comprising a PC board, and   a captive screw attached to the first panel and the second panel,   wherein the captive screw comprises
 a ferrule having a bore; 
 a screw having a head, a shank extending from the head, a threaded portion at an end of the shank opposite the head, and a collar on the shank proximate the threaded portion; and 
 a spring, 
 wherein the shank extends through the bore and the spring, such that the spring is between the ferrule and the head of the screw, and 
 wherein the bore includes at least one diameter and the collar includes a maximum diameter, the maximum diameter is greater than the at least one diameter of the bore, and the at least one diameter of the bore is located between the maximum diameter of the collar and thehead of the screw, and 
   wherein the threaded portion is inserted into the second panel, the collar contacts the second panel, the ferrule is attached to the first panel, and the first panel floats on the spring.   
     
     
         13 . A heat dissipating system according to  claim 12 , wherein the ferrule includes an inner annular ring extending from an internal circumferential surface of the ferrule, and the inner annular ring provides the at least one diameter of the bore. 
     
     
         14 . A heat dissipating system according to  claim 13 , wherein the ferrule has at least one collapsed groove in an external circumferential surface of the ferrule. 
     
     
         15 . A heat dissipating system according to  claim 12 , wherein the end portion is flared to retain the ferrule on the first panel. 
     
     
         16 . A heat dissipating system according to  claim 12 , wherein the ferrule includes an annular lip that limits penetration of the ferrule into the first panel. 
     
     
         17 . A heat dissipating system according to  claim 12 , wherein the ferrule includes at least one circumferential groove and material of the first panel is located within the at least one circumferential groove. 
     
     
         18 . A heat dissipating system according to  claim 12 , wherein an external circumferential surface of the ferrule includes a plurality of knurls. 
     
     
         19 . A heat dissipating system according to  claim 12 , wherein the collar is tapered. 
     
     
         20 . A heat dissipating system according to  claim 12  further comprising a sheet of flexible material between the first and second panels. 
     
     
         21 . A floating captive screw capable of being mounted in a preformed first aperture of a first panel, being a microcircuit heat sink flange, for attachment to a second aperture in a second panel, being a PC board, said captive screw comprising:
 a ferrule having a generally cylindrical portion having an inner bore, said ferrule being adapted to be received into said first aperture of said first panel;   a screw having a head, a shank and a threaded portion at the end of the shank opposite the head, said shank and said threaded portion being adapted to pass through said ferrule bore;   a collar being fixed on said shank at a position between said ferrule and the screw threaded portion after said screw shank and said threaded portion have passed through the ferrule bore, wherein said collar limits penetration of the screw when engaging said second panel and wherein said collar captivates said screw to said ferrule;   a spring positioned over said screw shank between said head and said ferrule;   wherein said collar is formed by being rolled onto said screw shank under the ferrule to limit penetration of the screw threads in the second panel so that the first panel floats on the spring;   wherein the ferrule has an annular lip formed on an exterior cylindrical surface proximate the top of the ferrule for limiting the penetration of the ferrule in the preformed aperture in the first structure, and the ferrule has an annular circumferential groove formed in the exterior cylindrical surface adjacent to and below the annular lip for receiving a plastic flow of material when the ferrule is pressed into a preformed aperture.   
     
     
         22 . A captive screw comprising:
 a ferrule having a first and a second opposed ends, the ferrule having:   a first annular lip at one of the first and second opposed ends;   an annular circumferential exterior groove adjacent the first annular lip; and   a second annular lip adjacent to the annular circumferential exterior groove and located across the annular circumferential exterior groove with respect to the first annular lip;   a screw having a head, a shank adapted to pass through the ferrule, a threaded portion at one end of the shank opposite the head, the shank having a collar, the collar being fixed on the shank between the ferrule and the threaded portion of the shank; and   a spring extending on the shank of the screw between the head and the ferrule;   wherein the screw is captivated on the ferrule between the head and the collar, and the ferrule is dimensioned such that the ferrule does not permit movement of the collar past the ferrule.   
     
     
         23 . The captive screw according to  claim 22  wherein the ferrule has a generally cylindrical interior surface. 
     
     
         24 . A floating captive screw capable of being mounted in a preformed first aperture of a first panel, being a microcircuit heat sink flange, for attachment to a second aperture in a second panel, being a PC board, said captive screw comprising:
 a ferrule having a generally cylindrical portion having an inner bore with an inner annular ring on an interior surface of said bore, said ferrule being adapted to be received into said first aperture of said first panel;   a screw having a head, a shank and a threaded portion at the end of the shank opposite the head, said shank and said threaded portion being adapted to pass through said ferrule bore;   wherein said inner annular ring is formed by plastic deformation of material during assembly wherein pressure is applied uniformly on the exterior of the generally cylindrical portion of the ferrule to form said inner annular ring, wherein said ferrule has a first annular circumferential groove which allows the formation of the ring;   a collar being fixed on said shank at a position between said inner annular ring of said ferrule bore and the screw threaded portion after said screw shank and said threaded portion have passed through the ferrule bore, wherein said collar limits penetration of the screw when engaging said second panel and wherein said collar captivates said screw to said ferrule;   a spring positioned over said screw shank between said head and said inner annular ring;   wherein said collar is formed by being rolled onto said screw shank under the ferrule to limit penetration of the screw threads in the second panel so that the first panel floats on the spring;   wherein the ferrule has an annular lip formed on an exterior cylindrical surface proximate the top of the ferrule for limiting the penetration of the ferrule in the preformed aperture in the first structure, and the ferrule has a second annular circumferential groove formed in the exterior cylindrical surface adjacent to and below the annular lip for receiving a plastic flow of material when the ferrule is pressed into a preformed aperture.