Influence of PCBs coatings wettability on lead-free SMT solder joints reliability
The paper presents results of wettability study of PCBs with immersion Sn, Ni/Au and SnCu coatings before reflow soldering process. Furthermore the solder joints were made in the optimal lead-free reflow soldering conditions using chosen materials with different wettability value of PCBs coatings and their reliability assessment was executed. The results of investigations have shown that exist direct influence PCBs coatings wettability on reliability of solder joints. It was find also that by using special procedure of PCBs coatings wettability assessment it is possible to predict future solder joints reliability.
Failure Modes and Fatigue Testing Characteristics of SMT Solder Joints
The work is connected with implementation of lead-free technology by small producers of electronic equipment, according to RONS Directive of European Community. Results of accelerated mechanical and thermal cycling fatigue tests of PbSn and lead-free solder joints, realized in GreenRoSE EC Project, for accelerated reliability assessment, are described. The aim of the work is development of cheap test methods, applicable by small producers of electronic equipment. Thermal shock cycling method and mechanical method of cycling bending of PCB samples with soldered SMT components are discussed. Charge factors applied by mechanical and thermal tests are compared. FEM models are applied. Thermal shock cycling is realized in two-zone climatic chamber. Developed in TU Warsaw PC controlled mechanical test stand is presented. For obtaining of relative deformation between soldered component and PCB, was applied the bending system exerting moment, flexion radius and other charge conditions, uniform for all components soldered on whole surface of the PCB sample. The failures are detected by measuring the joints resistance. Design and data of special test samples for simple resistance measurements and failures detection are shown. Relation between bending curvature of PCB sample and joint resistance, before and after the test, is shown. The failure modes are classified. Influence of test parameters on failure distribution data and characteristic of joint parameters are discussed. The failure distribution on Weibull plots for mechanical and thermal cycling are compared. The investigations showed the possibility of simplified reliability assessment of lead-free electronic products by mechanical fatigue testing. Advantage of this method is lower cost and shorter test time in comparing with thermal cycling
Mechanical behaviour and durability of high volume fly ash cementitious composites
The purpose of this research is to separate different morphological particles of ASTM class F fly ash, and study their effect on mechanical behaviour and durability of high volume cementitious mixtures. In this research wet separation of raw fly ash is carried out, which resulted in three layers of different morphological particles. The first layer of particles float, comprise of about 1-5% of fly ash, is identified as cenospheres or hollow spheres. The second layer of particles is measured to be 55-60% of raw fly ash and consisting of porous spherical and rounded particles rich in Si and Al. The third layer particles is measured to be about 35-40% of raw fly ash. High volume fly ash cementitious composites containing second or third layer particles are tested under compression and bending, highlighting a higher strength and ductility in comparison to cementitious ones containing raw fly ash particles. KEYWORDS. Cementitious matrix; Raw fly ash; Second layer particles; Third layer particles.