Thermal Stress on Silver Conductive Adhesive Solder Joints: Performance Evaluation of Medical Ultrasound Array Transducer

RoHS European Directive, recently introduced [1], makes a restriction of hazardous substances, e.g. Lead (Pb) and so on, traditionally used in soldering process of electric components and equipments. The paper presents preliminary results concerning new electronic Pb-free solder joints, in terms of both joint performances and electronic properties. A particular application of silver conductive adhesive solder joints between a plate of piezoelectric material and fingers, brass micro-connections between the substrate of piezoelectric material and the printed circuit, is considered. Factors that influence the soldering process like "thickness of the conductive glue" and "temperature of polymerization" are analysed by means of the Design of Experiments technique [2]. The aim is to realise samples for the experimental tests. Measurements of electrical resistance, parameter chosen like failure pointer, and morphologic and micro-chemical analyses were carried out in order to verify the samples behaviour to the thermal stresses.