Mechanical Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/2263
Browse
5 results
Search Results
Item HARMONIC VIBRATION TESTING OF ELECTRONIC COMPONENTS ATTACHED TO PRINTED WIRING BOARDS WITH SAC305 AND EUTECTIC SnPb SOLDER(2010) Paquette, Beth Miller; Barker, Donald B; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ball grid arrays attached to printed wiring boards with conventional tin-lead solder (63/37) and one of the leading lead-free tin-silver-copper solders (SAC305) were tested at high and low load levels of harmonic vibration. Leadless chip resistors attached to printed wiring boards with conventional tin-lead solder and lead-free solders (SAC105 and SAC305, and tin-nickel-copper, SN100C) were tested at low levels of harmonic vibration. The tests were conducted near the natural frequency of the assemblies to accelerate testing and to generate high cycle fatigue failures in a reasonable amount of time. The results showed that there are nearly negligible differences in the high cycle fatigue life between the SnPb and SAC305 solders. SN100C and SAC105 were less durable. A master durability plot was generated for SAC305 and SnPb to confirm the negligible-difference between the solders. A safe area was defined be used as a design goal for survivablity for circuit board design.Item LEAD-FREE ELECTRONICS USE AND REPAIR DYNAMIC SIMULATION(2009) Chaloupka, Andrew Charles; Sandborn, Peter A; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The conversion from tin-lead to lead-free electronics has increased concern amongst engineers about the reliability of electronic assemblies. In order to communicate the impact of the conversion in terms of cost and availability, a simulation of electronic systems at the LRU level to and through a repair facility was created. The model includes the effects of repair prioritization, multiple possible failure mechanisms, no-fault-founds, and un-repairable units. Example analyses were performed on electronic assemblies that use SAC and SnPb solder using a repair process modeled after a NSWC Crane Aviation Repair Process. The case studies revealed that LRUs exposed to usage profiles characteristic of aerospace and high performance applications, high thermal cycling temperatures with short dwell times, SAC exhibited significantly increased repair costs when compared to tin-lead. Prioritizing LRUs and increasing the rate of deployment had no significant impact on the cost or availability metrics for the cases considered.Item Characterization of FR-4 Printed Circuit Board Laminates Before and After Exposure to Lead-free Soldering Conditions(2008-08-04) Sanapala, Ravikumar; Pecht, Michael; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The transition to lead-free soldering of printed circuit boards (PCBs) using solder alloys such as Sn/Ag/Cu has resulted in higher temperature exposures during assembly compared with traditional eutectic Sn/Pb solders. The knowledge of possible variations in the PCB laminate material properties due to the soldering conditions is an essential input in the selection of appropriate laminates. An experimental study was conducted to investigate the effects of lead-free processing on key thermomechanical, physical, and chemical properties of a range of FR-4 PCB laminate materials. The laminate material properties were measured as per the IPC/UL test methods before and after subjecting to multiple lead-free soldering cycles. The effect of lead-free soldering conditions was observed in some of the material types and the variations in properties were related to the material constituents. Fourier transform infrared (FTIR) spectroscopy and combinatorial property analysis were performed to investigate the material-level transformations due to soldering exposures.Item A Cost Model for Assessing the Transition to Lead-Free Electronics(2008-05-01) Jafreen, Rifat; Sandborn, Peter; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Actions such as the WEEE Directive and RoHS Directive are forcing electronics suppliers to transition their products from tin-lead to lead-free solder in order to support consumer goods. The defense and avionics industries obtain their parts from the same suppliers and must adapt to these new lead-free products. In this thesis, a cost model was created to evaluate the transition from lead-free to tin-lead electronics. The model provides the industry with multiple transition options and determines the costs associated with each of these options. The options modeled are an all tin-lead assembly, a lead-free assembly and a mixed assembly. The cost model assimilates all the costs involved in the transition to lead-free and includes changes in reliability, and plan development and maintenance costs. The model requires users to input information specific to their organization. The model also predicts costs incurred when more than one plan, i.e., a specific set of materials and qualifications, must be supported.Item MICROSTRUCTURAL CHANGES UNDER ISOTHERMAL AGING AND THEIR INFLUENCE ON THERMAL FATIGUE RELIABILITY FOR TIN-LEAD AND LEAD-FREE SOLDER JOINTS, INCLUDING MICROSTRUCTURAL CHANGES UNDER ISOTHERMAL AGING IN MIXED SOLDER JOINTS(2007-11-26) choubey, anupam; Pecht, Michael; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Most electronics companies have transitioned to lead-free processes, both to comply with government legislation and to avoid issues related to mixing of tin-lead and lead-free metallurgies. However, exemptions from lead-free legislation have been granted for certain products, especially those intended for high-reliability applications. One major concern with these exempt products is that, during assembly or rework, lead-free components will have to be used due to the unavailability of tin-lead components. This will result in the mixing of tin-lead and lead-free metallurgies. The mixing of metallurgies can induce new reliability concerns. This study is focused on mixed solder joints formed by attaching lead-free components with tin-lead paste. Solder interconnect reliability is influenced by the environmental imposed load, solder material properties and the microstructure formed between the solder and the metal surfaces to which the solder is bonded. Several lead-free metallurgies are being used for component terminals, board pad plating and solder materials. These metallurgies react to form the microstructure of a solder joint. Microstructure of a solder joint continuously evolves and affects solder joint properties. A fundamental understanding on the microstructure is required to analyze the changes occurring in a solder joint with time and temperature and make predictions on solder joint reliability under thermal loading conditions. This dissertation determines key microstructural features present in SnPb, lead-free and mixed solder joints. Changes in the microstructural features were determined for SnPb, lead-free and mixed solder joints exposed to isothermal aging conditions. The effect of microstructural changes on reliability was determined by conducting thermal fatigue reliability tests for SnPb and lead-free solder joints. Whereas, for mixed solder joints, hypotheses has been determined based on microstructural analysis on their thermal fatigue performance compared to SnPb joints. This dissertation doesn't include the effect of microstructural changes on the reliability of mixed solder joints. This dissertation doesn't include the reliability tests for mixed solder joints. Two microstructural features namely, intermetallic compounds (IMC) and Pb phase were characterized for SnPb, lead-free and mixed solder joints. IMCs are formed at the solder to pad metallization interface and in the bulk solder. It was determined that reaction between Sn3.0Ag0.5Cu solder and Ni/Au component side metallization result in interfacial IMCs consisting of Ni3Sn4 IMC in the as-reflowed stage and IMCs such as (NiCu)3Sn4, (Cu,Ni)6Sn5 and (Au,Ni)Sn4 after thermal aging of 350 hours at 125ºC. With pad metallization of ImAg, ImSn and OSP, IMCs such as Cu6Sn5 are formed after reflow followed by formation of a new Cu3Sn IMC phase after thermal aging of 350 hours at 125ºC. Cu6Sn5 and Ag3Sn IMC were found distributed in bulk solder joints in the as-reflowed and aged (125ºC for 100, 350 and 1000 hrs) solder joint. This dissertation demonstrated that under thermal cycling, intergranular crack propagates between Sn grains in the bulk solder and Cu6Sn5 IMCs present at Sn grain boundaries in the bulk solder influence crack propagation. It was demonstrated that isothermal aging for 350 hrs at 125ºC causes coarsening of Cu6Sn5 IMC particles in the bulk solder which results in a 50% reduction in number of Cu6Sn5 IMC particles in the bulk solder, thus promoting the crack to propagate faster along the grain boundary. This dissertation determined that isothermal aging for 350 hrs at 125ºC would cause a 25% reduction in characteristic life for lead-free solder joints due to the changes associated with Cu6Sn5 IMC particles. In conventional SnPb solder joints Pb phase present in the bulk solder coarsens as a function of time and temperature and influences thermal fatigue reliability. Due to the presence of Pb in mixed solder joint, this dissertation determined the extent of coarsening in mixed solder joints compared with SnPb joints. It was determined that mixed solder joints are not prone to Pb phase coarsening under aging for 350 hrs at 125ºC as opposed to SnPb solder joints and therefore would have better thermal fatigue performance compared to SnPb joint under these conditions. This dissertation demonstrated that the presence of Pb in mixed solder results in a 30 to 40% lower IMC thickness compared to Pb-free and SnPb solder joints by being present at the interface as a diffusion barrier between Ni and Sn for IMC formation. Presence of Pb has been known to act as diffusion barrier for SnPb solder joints.