In case you missed it.Materials "Low Outgassing Outgassing (sometimes called "Offgassing," particularly when in reference to indoor air quality) is the slow release of a gas that was trapped, frozen, absorbed or adsorbed in some material. Materials for Electro-Optic and Electronic Systems" Authors: Bill Riegler, Steve Bruner, Rob Thomaier, Katie Young; billr@nusil.com. Abstract: This paper explores the need for low outgassing, thermally stable, high-performance materials for electro-optic and electronic systems, citing various applications of low outgassing materials in such applications. Also described: the chemistry of silicone polymerization polymerization Any process in which monomers combine chemically to produce a polymer. The monomer molecules—which in the polymer usually number from at least 100 to many thousands—may or may not all be the same. , how to identify the source of outgassing components in silicones and the procedures for eliminating these volatile materials--solvent washing or wipe film evaporating. A comparison of low outgassing versus non-outgassing materials verifies the performance quality of low outgassing materials, even after additional processing. Reliability "Measurement of Creep Rates and Stress Relaxation for Micro-Sized Pb-Free Solder Joints" Authors: Milos Miloš, prince of Serbia Miloš or Milosh (Miloš Obrenović) (both: mĭ`lôsh ōbrĕ`nəvĭch) Dusek and Dr. Christopher Hunt; npl.co.uk/ei/publications/ Abstract: Stress relaxation is an alternative approach in generating relevant and credible material properties for low cycle fatigue Low-Cycle Fatigue is cycle conditions that result in 1.) fatigue (material) in less than 105 cycles (some sources say 103cycles). 2.) macroplastic deformation in every cycle. , in which it is possible to estimate the actual stress in solder joints as a function of time. The method offers advantages for obtaining data from micro-sized joints; e.g., it takes account of primary creep, is relatively quick and can estimate stress in solder joints during thermal cycling temperature dwells. Using the method, SnAg3.5, SnAg3.8Cu0.7 and SnPb37 solders were evaluated during creep and stress relaxation, as the basis for an efficient fatigue test and a source of data for FEA (Finite Element Analysis) A mathematical technique for analyzing stress, which breaks down a physical structure into substructures called "finite elements." The finite elements and their interrelationships are converted into equation form and solved mathematically. modeling purposes. Although the differences between the secondary creep rates of SnAg and SnAgCu alloys are marginal, when tested under constant stress and temperature the secondary creep rate of SnAgCu or SnAg can exceed that of SnPb at stresses above a shear stress of 20 MPa. Below this level the SnPb solder creeps faster than Pb-free solders. This implies that the calculations of acceleration factors, as well as the temperature test profiles, have to be modified to match service conditions. (NPL Report DEPC-MPR 021) "Shear Strength of Pb-Free Solder Joints" Authors: Milos Dusek, Martin Wick-ham, Dr. Christopher Hunt; npl.co.uk/ei/publications/ Abstract: This note describes the assessment of the reliability of solder joints using accelerated thermal cycling followed by shear strength measurements. It is particularly relevant to the assessment of solder joints assembled using Pb-free solders. Test procedures and requirements are detailed, and factors influencing the choice of thermal cycling regime are discussed. Work previously reported was used as the basis for comments and discussion, especially regarding understanding of the effects of thermal excursions, ramp rates and temperature dwells on the accumulation of damage in the joints. (NPL Measurement Note MN57) "Effect of PCB PCB: see polychlorinated biphenyl. PCB in full polychlorinated biphenyl Any of a class of highly stable organic compounds prepared by the reaction of chlorine with biphenyl, a two-ring compound. Finish, Processing and Microstructure mi·cro·struc·ture n. The structure of an organism or object as revealed through microscopic examination. microstructure Noun a structure on a microscopic scale, such as that of a metal or a cell on Pb-Free Solder Joint Reliability" Authors: Milos Dusek, Martin Wick-ham, Dr. Chris Hunt; npl.co.uk/ei/publications/ Abstract: This work compares effects of thermally induced microstructural changes on the performance of Pb-free and SnPbAg solder joints formed on PCBs after accelerated thermal cycling. Test vehicles were assembled with combinations of three alloys (SnAgCu, SnAg and SnPbAg), two board finishes (ENIG ENIG Electroless Nickel Immersion Gold (printed circuit board manufacturing process) and immersion silver), various component sizes and two substrate materials (FR-4 and CTE (Coefficient of Thermal Expansion) The difference between the way two materials expand when heat is applied. This is very critical when chips are mounted to printed circuit boards, because the silicon chip expands at a different rate than the plastic board. matched). Thermal history effects were established using multiple reflow passes, wave soldering or isothermal i·so·ther·mal adj. Of, relating to, or indicating equal or constant temperatures. isothermal, isothermic having the same temperature. aging for 1000 hrs. at 125[degrees]C. The manufactured assemblies were then subjected to thermal cycling between -55[degrees]C and 125[degrees]C with 5 min. dwells and 10[degrees]C/min ramp rate. The study found a measurable difference between the reliability of joints soldered with SnAgCu and SnPbAg alloys. Evidence did not suggest that thermal pretreatment pretreatment, n the protocols required before beginning therapy, usually of a diagnostic nature; before treatment. pretreatment estimate, n See predetermination. was detrimental to the joint's long-term reliability. (NPL Report DEPC-MPR 028) |
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