The EPAR program addresses the issues critical for the design, manufacture, and qualification of more cost-effective and reliable electronic products. An active research program and a wide range of dedicated and cross-disciplinary courses are complemented by extensive computer systems and laboratory facilities. Current areas of interest include the development of reliability assessment methodology for electronic products, accelerated testing, failure analysis, materials characterization, connectors and contacts, thermal management, high-temperature electronics, optoelectronics, advanced electronic products manufacturing, micro-electromechanical systems, and sensors.
Instruction is achieved through a "just-in-time" teaching approach, whereby the latest research results and topics of significant industry interest are directly incorporated into the curriculum, educating tomorrow's engineers, researchers, and leaders. The EPAR instruction is carried out by a combination of industry lecturers, researchers, and university faculty who are well known nationally and internationally. Full utilization is made of the rapid growth of information services, including multi-media techniques and the Internet, for the dissemination of educational materials. All courses in the EPAR program involve group projects on topics of industry interest. For example, in a recent offering of the course on surface mount manufacturing, a mechanistic models-based virtual factory approach to surface mount assembly was demonstrated.
Offered through the Mechanical Engineering Department, the EPAR program includes a sequence of senior undergraduate and graduate courses. Students from all engineering disciplines, including Electrical Engineering, Materials Science, and Reliability Engineering, enroll in the program. All graduates of this program have enjoyed excellent job opportunities. Contact CALCE EPSC.
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Past research has suggested a relationship between a reduction in cracking in PEMs and to a lower elastic modulus of the encapsulant material. Unfortunately, a lower elastic modulus in encapsulant material is also related to a reduction in long-term reliability, making the material characterization important. Research has also shown that as the moisture content of the encapsulant increases, its elastic modulus decreases. Opposingly, as the moisture content increases, the probability that the package will damage during reflow rises.
We have sectioned several PEMs to examine the die pad and the encapsulant interface to determine a relationship between surface roughness of the die pad and adhesion of the encapsulant material. Preliminary results suggest micro-structural defects between the die pad and the encapsulant may be areas for water to collect and increase the likelihood of delamination.
Previous experimental work conducted at CALCE has shown that it is possible to control the amount of delamination by altering the reflow ramp rate. Armed with this knowledge, researchers at CALCE have developed a virtual reflow laboratory for mounting PEMs on printed wireboards (using the material parameters found from our experimental testing, combined with our extensive materials parameters database). Within this virtual laboratory design, engineers will be able to optimize a solder reflow ramp for most PEM's commonly used in industry and for future PEM designs. We have chosen a fine-pitch quad-flat pack (FPQFP) as our initial test package.
To calibrate our virtual reflow laboratory, researchers at CALCE have embedded thermal-couples in FPQFP to generate reflow profiles of moisture-saturated and dry packages as they pass through the reflow oven in our micro-factory. Thermal-couples have also been attached to the lead-frame, under the FPQFP, and on the PWB to determine temperatures at those locations. Research shows that the temperature profiles vary as much as 10% through the various thermal-couple locations as the assemble goes through reflow. Data collected from this part of the study, as well as previous research conducted at CALCE, will validate our virtual reflow laboratory. Contact CALCE EPSC.
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A preliminary study of the solder reflow process has been initiated for a near-eutectic Sn63/Pb37, no-clean flux, solder paste applied to a microelectronic assembly using the hot-stage within the ESEM chamber. The stage and assembly were heated until the solder melted and then cooled to allow resolidification of the solder around the lead. The ESEM allowed continuous observation of the flux activation and cleaning, melting of the solder and wetting of the leads followed by subsequent solidification and microstructure formation. The sequence of events was captured on video with time and temperature recorded per frame to allow easy reference for subsequent analysis. Using this technique it was observed that organics remaining after flux activation do not all burn off prior to melting of the solder. Further studies of the effects of residual organics on joint integrity are being pursued. This powerful technique is being optimized to allow the detailed study of process variable effects (such as temperature and cycle time) on microstructure formation and degradation, joint integrity and defect formation. This technique will lead to a reduced- time-to-optimization of these variables for improved reliability of solder attachments. Contact CALCE EPSC.
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