An electrical connector having a fusible element for mounting on a substrate includes an insulative housing and a contact terminal retained in the insulative housing. The contact terminal includes a resilient contacting arm extending beyond a mating face of the insulative housing and a soldering portion for mating with the fusible element. A gelatinous flux is deployed on the fusible element, and/or on the soldering portion, and/or between the fusible element and the soldering portion, and then flux is dried to immovably fix the fusible element with respect to the soldering portion. The dried flux will be re-juvenile to clean and remove an oxidized layer originally existed on the soldering portion so as to achieve robust welding quality. Besides, a method for trimming an electrical connector to have robust welding properties is also disclosed.