Francesco Bertocci

Optimization of the Soldering Process With ECAs in Electronic Equipment: Characterization Measurement and Experimental Design

With the introduction of the European Directives restrictions of hazardous substances, electrically conductive adhesives (ECAs) have received great attention in the field of electronics as a possible replacement of the traditional tin-lead soldering technology. So, in this new context, the analysis and the characterization of these alternative materials represent a fundamental topic, above all, from the industrial point of view. Nevertheless, studies on ECAs have rarely been reported in the literature, but more recently research has started to focus on this specific topic. After a comparative assessment concerning soldering materials, this paper focuses attention on their characterization through measurement in order to verify the electrical behavior of the isotropic silver conductive adhesive. In addition, since the soldering process is affected by a large number of variables such as the thickness of the conductive adhesive film, radial velocity, and curing temperature, the optimal selection of the factors is carried out through experimental design theory and the dual-response approach by means of generalized linear models. In this paper, the experimental and comparative studies on soldering made up of epoxy adhesives are carried out, in particular, the adhesives constituted by metallic particles (silver), normally in the form of flakes, in a polymer matrix are considered. The novelty of the kind of adhesive considered is the Ag filler loadings of 50-65% by volume. At these loadings, the materials achieve the percolation threshold and are electrically conductive in all directions after the materials are cured. Two different types of conductive adhesives, characterized by different chemical structures and compositions, are experimented and tested. Then, since the lead-free soldering process is characterized by several critical factors, a statistical approach is used to optimize this process. Experimental results obtained by testing samples with ECA materials prove the validity of this paper. The value of this paper is in the application of a statistical approach to these adhesive materials in order to achieve the optimization of the soldering process with a small number of treatment combinations, satisfying at the same time the stringent requirements and achieving robust electrical interconnections.

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.

Thermal stress on silver conductive adhesive solder joints: Performance evaluation of medical ultrasound array transducer

RoHS European Directive, recently introduced, 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. 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.

Experimental Stress Characterization of a Biomedical Ultrasound Probe Soldered With Innovative Silver Isotropically Conductive Adhesive

In the coming years, biomedical instrument manufacturers will have to inform the Notified Body of RoHS conformity assessment of the new medical instruments. In particular, in the case of lead-free solders, the Notified Body will require evidence that such solders are equally reliable as tin-lead, for the proposed use and lifetime of the product. So, biomedical instrument manufacturers are strongly interested in evaluating the performance of new soldering lead-free material used for the implementation of electronic parts. In order to support them and fill the technology knowledge gap, this paper presents a novel 128-channel phased-array probe for echocardiograph applications realized by new soldering technique where isotropic silver electrically conductive adhesive is used. In particular, the new soldering material is taken into consideration in the design phase of ultrasound array transducer, which is the core of a linear phased-array probe that is able to monitor the cardiac muscle. Being such material innovative in the application, a detailed study of the failure condition regarding the phased-array probe by means of accelerated qualification testing is proposed in order to assure its performances under stress and over time. A comparison of the electroacoustic measurement results with respect to the conventional probe, soldered with Sn-Pb, is also presented in this paper.

A Biochemical Approach to Detect Oxidative Stress in Infertile Women Undergoing Assisted Reproductive Technology Procedures

Oxidative stress plays a major role in critical biological processes in human reproduction. However, a reliable and biologically accurate indicator of this condition does not yet exist. On these bases, the aim of this study was to assess and compare the blood and follicular fluid (FF) redox status of 45 infertile subjects (and 45 age-matched controls) undergoing in vitro fertilization (IVF), and explore possible relationships between the assessed redox parameters and IVF outcomes. Reactive Oxygen Species (ROS) production, assessed by flow cytometry analysis in blood leukocytes and granulosa cells, significantly increased (p < 0.05) in infertile patients. Also, oxidative stress markers—ThioBarbituric Acid-Reactive Substances (TBARS) as an index of lipid peroxidation, and Oxygen Radical Absorbance Capacity (ORAC) to account for total antioxidant capacity, both assayed by fluorometric procedures—in blood and FF were significantly (p < 0.001) modified in infertile patients compared to the control group. Moreover, a significant correlation between blood redox markers and FF redox markers was evident. An ORAC/TBARS ratio, defined as the redox index (RI), was obtained in the plasma and FF of the patients and controls. In the patients, the plasma RI was about 3.4-fold (p < 0.0001) lower than the control, and the FF RI was about six-fold (p < 0.0001) lower than the control. Interestingly, both the plasma RI and FF RI results were significantly correlated (p < 0.05) to the considered outcome parameters (metaphase II, fertilization rate, and ongoing pregnancies). Given the reported findings, a strict monitoring of redox parameters in assisted reproductive techniques and infertility management is recommended.

Optimization of Perovskite Gas Sensor Performance: Characterization, Measurement and Experimental Design

Eight different types of nanostructured perovskites based on YCoO3 with different chemical compositions are prepared as gas sensor materials, and they are studied with two target gases NO2 and CO. Moreover, a statistical approach is adopted to optimize their performance. The innovative contribution is carried out through a split-plot design planning and modeling, also involving random effects, for studying Metal Oxide Semiconductors (MOX) sensors in a robust design context. The statistical results prove the validity of the proposed approach; in fact, for each material type, the variation of the electrical resistance achieves a satisfactory optimized value conditional to the working temperature and by controlling for the gas concentration variability. Just to mention some results, the sensing material YCo0.9Pd0.1O3 (Mt1) achieved excellent solutions during the optimization procedure. In particular, Mt1 resulted in being useful and feasible for the detection of both gases, with optimal response equal to +10.23% and working temperature at 312∘C for CO (284 ppm, from design) and response equal to −14.17% at 185∘C for NO2 (16 ppm, from design). Analogously, for NO2 (16 ppm, from design), the material type YCo0.9O2.85+1%Pd (Mt8) allows for optimizing the response value at −15.39% with a working temperature at 181.0∘C, whereas for YCo0.95Pd0.05O3 (Mt3), the best response value is achieved at −15.40% with the temperature equal to 204∘C.

High-voltage pulse stress on biomedical ultrasound probe soldered with Ag-ECA

In this paper the results from a study of high-voltage pulse stressing effects on ultrasound array transducers are presented. The ultrasound transducers have been implemented with a new Pb-free soldering technology, using Silver Electrically Conductive Adhesive. The conductive adhesive have been used among the platelet of piezoelectric and fingers of connection for the implementation of phased array transducer. In order to evaluate the reliability of the biomedical instrument electrical tests are proposed. Some experimental results through a measurement system for the electro-acoustic characterization of the medical probe before and after stress test are obtained and analyzed.

Vibration tests on prototypes of ultrasound array transducer: Evaluation of soldering electrical performances

Mechanical stresses, as vibrations, are the main common types of solicitation to which electronic equipment can be subjected during its useful life. For this reason drop or shock tests become important for such device; the use of a shaker system, able to produce sinusoidal and random vibrations, can simulate the operating conditions in a less expensive and faster way. In this paper the planning and implementation of vibration tests on prototypes of piezoelectric transducers is proposed. In fact the devices taken into consideration are subjected to an innovative soldering process in compliance to RoHS directive. In particular, silver conductive adhesive as soldering material is used and measurements of the electrical resistance are carried out in order to evaluate the resistance degree of the samples to mechanical stresses.