FIG. 1 shows a conventional captive screw 5 for using with a printed circuit board (PCB). The captive screw 5 includes a screw head 51, a threaded shank 52, and a sleeve 53 having a free end with an axially extended toothed flange 531. The sleeve 53 normally encloses the threaded shank 52 and is retractable into the screw head 51 under pressure to expose the threaded shank 52, as shown in FIG. 2. To assemble the captive screw 5 to a PCB 7, first align the sleeve 53 with a through hole 71 provided on the PCB 7, as shown in FIG. 3. Then, apply a downward force on the screw head 51, so that the toothed flange 531 of the sleeve 53 is pressed into the through hole 71, as shown in FIG. 4. And, keep applying the downward force until the toothed flange 531 is completely fitted in the through hole 71 to connect the captive screw 5 to the PCB 7.
The above conventional manner of assembling the captive screw 5 to the PCB 7 has some disadvantages: (a) The sleeve 53 is directly aligned with the through hole 71. However, since the screw head 51 and the sleeve 53 could not be held together through compression, the captive screw 5 must be manually positioned above and aligned with the through hole 71. (b) Since the captive screw 5 is very small in volume and the through hole 71 has a relatively small diameter, the manual position of the captive screw 5 above the through hole 71 is subject to error, preventing the flange 531 of the sleeve 53 from being easily and accurately aligned with the through hole 71 and resulting in a poorly assembled or even a damaged PCB 7. (c) In the event the flange 531 of the sleeve 53 is not pressed into the through hole 71 in one single operation, the flange 531 tends to be incompletely fitted in the through holes 71 and becomes deviated or skewed due to inaccurate planeness of the PCB 7. (d) To assemble the captive screw 5 to the PCB 7 by pressing the toothed flanges 531 of the sleeves 53 into the through holes 71, the captive screw 5 is individually picked up and moved to the PCB 7. Therefore, the assembly of a large amount of captive screws 5 to the PCB 7 could not be efficiently carried out using the surface mount technology (SMT) that has been widely employed in the electronic industrial field.
USPTO Backgrounds
USPTO Backgrounds