Expanding surface mount compatible retainer post

Abstract

A retainer post for tightly engaging a printed circuit board employing surface mounted technology. The retainer post has a hollow neck portion for insertion in a hole in a printed circuit board, an adjoining shoulder section for engaging the surface of the printed circuit board and, preferably, a retaining means for retaining said post in the printed circuit board. The retaining means preferably is formed of a circumferential, radially projecting barb containing longitudinal notches so that it may be inwardly compressed as the retaining post is inserted in a hole in a printed circuit board. The neck section contains a plurality of longitudinal spaced (i) grooves on its outer surface forming opposing frangible webs or (ii) cuts through said neck section. The neck section contains a cavity in which is disposed a material that expands upon heating. Expanding materials include shape memory effect alloys, such as nitinol, and a structure in which a material having a relatively high thermal coefficient of expansion is coated with a material having a lower thermal coefficient of expansion. Upon heating a retainer post in a vapor phase soldering step, the expanding material creates an internal bursting pressure that expands portions of the neck section. The portions are defined by the longitudinal cuts or by the webs that are fractured by the bursting pressure. The expanded neck portions tightly engage the printed circuit board through which the retainer post is inserted. A stable mechanical contact between the post and circuit board is achieved so that the retainer post may be used to attach electrical connectors and other components to the printed circuit board without threatening the integrity of electrical connections.