Eyelet Failure in Etched Wiring

This paper points out that eyelets used on etched wiring boards, to receive component-part leads and to provide wiring connections, have been a source of unreliability. A study of the eyeletfailure problem is described, based upon microscopic examination of over 15OO eyeleted connections on defective assemblies. Inspection of failed eyelet connections shows solder separations between the crimped eyelet flanges and the etched conductors of as much as four thousandths of an inch. Laminate deformation and conductor lifting at the eyelet are also observed. The large thermal expansion of the board during soldering, and eyelet relaxation appear to place large stresses on the eyelets, resulting in failures. Solder Joints made with tightly crimped eyelets are found to be mechanically weak, due to the lack of an adequate solder fillet. This study helps to explain why circuit failures occur at eyelets and shows how they may be minimized through the use of improved design. An eyelet with a tapered flange is described which provides a much stronger solder Joint, with a possible smaller diameter, and with a greater effective lead-entrance diameter.