Implementation and Characterization of a Medical Ultrasound Phased Array Probe With New Pb-Free Soldering Materials

The application of the European Directive on the Restriction of Hazardous Substances, named RoHS, and correlated documents concerning the restriction of the use of hazardous substances in electrical and electronic equipment is critical and expensive, above all when the use of new substances needs to review consolidated production processes. The use of innovative materials (Sn-Ag-Cu alloys or electrically conductive adhesives (ECAs), for instance) instead of the traditional Sn-Pb solder joints and the design review of the electronic equipment when “not-RoHS-compliant” components must not on sale in the market are typical examples. In this context, this paper takes into account a new soldering production process with a conductive adhesive. In particular, we focus on the soldering phase with the adhesive for the design and implementation of ultrasound transducers for an industrial biomedical application. The use of new Pb-free soldering materials, such as a silver conductive adhesive, is considered in this paper in order to implement an ultrasound array transducer. With this component being fundamental for the functionality of the equipment (echocardiography system), a measurement system for the electroacoustic probe characterization is proposed, and some results, in terms of both joint performance and electrical properties of the new electronic device with Pb-free solder joints, are presented. This paper shows the use of conductive adhesives for the implementation of a medical phased array probe, where the soldering material is located among a platelet of the piezoelectric and fingers. A comparison between electroacoustic measures on the elements soldered with an ECA and with the traditional technology Sn-Pb will be also shown. Moreover, in the field of biomedical application, it is also fundamental to assure that the performances of the transducer are maintained in the time. To this aim, some laboratory tests for the evaluation of the reliability performances of the new Pb-free soldering material are proposed, and the preliminary results are presented in this paper.