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Printed wiring board inner layer contamination study
World Abstracts on Microeleetronics and Reliability silicon integrated circuits (ICs) (chips) encapsulated with Dow-Corning 96-084 RTV silicone rubber dispersion are described. The simulated chips were made out of glass. Three types of voids have been observed: voids originating at the center under a chip and progressively spreading outward (or the solvent vapor voids), voids formed by air entering under a chip through a tunnel in the RTV dispersion (or the tunnel voids), and voids originating at the sides under a chip and progressively spreading under it without tunnel formation (or the air diffusion voids). The process of formation of each void type has been documented with the aid of photographs. Analyses have been made of the first two types of voids. The results of the analysis of the solvent vapor voids allow determination of the highest initial encapsulant viscosity for which void-free coverage can be obtained of a chip having a given side length. The results of the analysis of the tunnel voids give the smallest encapsulant height-to-chip side length ratio needed for tunnel-free coverage of chips with and without a tilt.
Solder joint reliability of fine pitch surface mount technology assemblies. JOHN LAU, LAURAM. POWERS-MALONEY,JAMES R. BAKER,DON RICE and BOB SHAW. IEEE Trans. Compon. Hybrids mfg Technol. 13(3), 534 (1990). The reliablity of fine pitch solder joint interconnection has been studied. It consists of two different fine pitch surface mount components (SMC), namely, the Electronic Industry Associates of Japan (EIAJ) 160-Pin Quad Flat Pack (QFP) and the Joint Electronic Device Engineering Council (JEDEC) 132Pin Plastic Quad Flat Pack (PQFP). They each have a lead-spacing (from lead-center to lead-center) of approximately 0.025 in. For comparison purposes the conventional JEDEC 68-Pin Plastic Leaded Chip Carrier (PLCC) and the 84-Pin PLCC have also been used in the same manufacturing process. Solder joint reliability of these 4 SMCs has been quantified for the mechanical shock, mechanical vibration, and thermal environmental stress factors. Redundant-system demonstrated-reliability approximation using piece-part failure rates. HSmN-LU HUANG.IEEE Trans. Reliab. 40(I), 15 (1991). This paper provides a method of obtaining the reliability of a redundant system when only the part force-of-mortality estimates (hazard rates) for electronic parts are available. Part failures are reported without specifying whether the parts are configured in series or parallel. The calculations involved are: (1) Sum of all the part failure rates in the system, recorded since the turn-on date of the system up to the present time of monitoring--whether the parts are configured in series or parallel; (2) Sum of the failure rates of all the parts in the system recorded up to a certain previous time since the system turn-on date; and (3) The system reliability for a certain critical mission time, with or without redundancy, calculated at that previous time. The method is useful in field-equipment reliability monitoring because exact computation is impossible without knowing whether the failed parts are configured in series or parallel. Generally, Monte Carlo simulation should be used only to verify the results calculated through an analytic method, if such a method is available and is not time consuming nor cost prohibitive. A new, dimensionless reliability parameter is introduced. Impact of network failures on the performance degradation of a class of cluster-based multiprneessors. ANuIP KUMARet al. IEEE Trans. Reliab. 40(1), 39 (1991). Cluster-based multiprocessor systems are being widely accepted because their performance has been shown close to the crossbar-based systems. This paper investigates the impact of increased unreliability of network components on the performance of one such system. A generalized model has been developed for computing the closed-form bandwidth expressions for
285
fault-free as well as faulty systems. Performance curves illustrate the degradation when unreliability is increased in terms of number of cluster-network failures.
Laptop PCs propel progress in haft-pitch connectors. HmOFUMI OHNO. JEE (Japan), 40 (September 1990). The growing use of half-pitch connectors has paralleled the development of high density electronic equipment. The solid establishment of half-pitch connectors today owes much to the emergence of laptop computers; the rapid popularization of laptop computers resulted in the rapid growth of the half-pitch connector market and the evolution of today's new connector trends. Analyzing the mechanical strength of SMT attached solder joints. WAYNE CHEN. IEEE Trans. Compon. Hybrids mfg TechnoL 13(3), 553 (1990). Analytic approaches to the pull strength and the shear strength of SMT attached solder joints have been studied by mathematical models. The predicted pull/shear strength of leaded ceramic quad packages was correlated with the experimentally measured data, The predictive models have been used for defining the design guidelines for selecting the optimum lead/pad configurations, the minimum solder volume, as well as the maximum component misalignment for fine pitch SMT assemblies. Printed wiring board inner layer contamination study. A. S. L. CHAN,T. A. SHANKOFFand D. CULVER. Circuit WId 17(1), 10 (1990). Electrical leakage beyond control levels did not occur in high temperature and humidity stressing of surface insulation resistance patterns when the relatively high contamination levels of 5 and 10/zg LiBr/cm 2 were laminated into a simple test multilayer board structure. When sputtered layers of LiF, LiBr and NaCI were covered by a thin 0.002 in. lamination layer, generally similar results were obtained at 35°C/90% relative humidity and even at 85°C/85% relative humidity. Biasing of some samples at 85°C/85% relative humidity out to 400 hr did cause leakages which vary from one to three decades above the controls, but drifting with time beyond 96 hr towards a shorting condition, or to the level of unlaminated samples, on a leakage per square basis was not observed. Because the surface insulation resistance per square concept did not hold in these experiments, the surface leakage mechanism is apparently overridden by bulk leakages which occur in parallel in the laminations. Thermal fatigue life of Pb-Sn alloy interconnections. RYon~I SATOH, KIYOSHI ARAKAWA, MASAHIDE HARADA, and KATSUI-IIRO MATUI. 1EEE Trans. Compon. Hybrids mfg TechnoL 14(1), 224 (1991). A highly accurate estimation of Pb-Sn alloy solder thermal fatigue life is made for surface mount solder joints. Experiments are carried out on Pb-5Sn and Pb-63Sn alloy solders under thermal cycle conditions of - 5 5 to 150°C/cycle/hr. The thermal fatigue fracture of Pb-Sn solder joints develops when cracks, initially generated from large scale plastic deformation of the solder, propagate gradually through the joint. On the fracture surface, striations of 500 A to l # m in size are observed and crack propagation rates (da/dN) are obtained for these solders. Additionally, thermal stess and strain in solder joints is studied by the finite element method (FEM) using three-dimensional and thermoelastoplastic models. The equivalent strain range based on Mises criterion, obtained by FEM, relates strongly to thermal fatigue life. A thermal fatigue life equation considering crack propagation related to bonding size and thermal strain range, is developed. Automated apparatus for long-term testing of electrical brushes. DANIEL M. ALLEY et al. IEEE Trans. Compon. Hybrids mfg Technol. 14(1), 31 (1991). The meaningful evaluation of electrical brushes, and even more so the development of novel electrical sliding contacts, can require
Solder joint reliability of fine pitch surface mount technology assemblies. JOHN LAU, LAURAM. POWERS-MALONEY,JAMES R. BAKER,DON RICE and BOB SHAW. IEEE Trans. Compon. Hybrids mfg Technol. 13(3), 534 (1990). The reliablity of fine pitch solder joint interconnection has been studied. It consists of two different fine pitch surface mount components (SMC), namely, the Electronic Industry Associates of Japan (EIAJ) 160-Pin Quad Flat Pack (QFP) and the Joint Electronic Device Engineering Council (JEDEC) 132Pin Plastic Quad Flat Pack (PQFP). They each have a lead-spacing (from lead-center to lead-center) of approximately 0.025 in. For comparison purposes the conventional JEDEC 68-Pin Plastic Leaded Chip Carrier (PLCC) and the 84-Pin PLCC have also been used in the same manufacturing process. Solder joint reliability of these 4 SMCs has been quantified for the mechanical shock, mechanical vibration, and thermal environmental stress factors. Redundant-system demonstrated-reliability approximation using piece-part failure rates. HSmN-LU HUANG.IEEE Trans. Reliab. 40(I), 15 (1991). This paper provides a method of obtaining the reliability of a redundant system when only the part force-of-mortality estimates (hazard rates) for electronic parts are available. Part failures are reported without specifying whether the parts are configured in series or parallel. The calculations involved are: (1) Sum of all the part failure rates in the system, recorded since the turn-on date of the system up to the present time of monitoring--whether the parts are configured in series or parallel; (2) Sum of the failure rates of all the parts in the system recorded up to a certain previous time since the system turn-on date; and (3) The system reliability for a certain critical mission time, with or without redundancy, calculated at that previous time. The method is useful in field-equipment reliability monitoring because exact computation is impossible without knowing whether the failed parts are configured in series or parallel. Generally, Monte Carlo simulation should be used only to verify the results calculated through an analytic method, if such a method is available and is not time consuming nor cost prohibitive. A new, dimensionless reliability parameter is introduced. Impact of network failures on the performance degradation of a class of cluster-based multiprneessors. ANuIP KUMARet al. IEEE Trans. Reliab. 40(1), 39 (1991). Cluster-based multiprocessor systems are being widely accepted because their performance has been shown close to the crossbar-based systems. This paper investigates the impact of increased unreliability of network components on the performance of one such system. A generalized model has been developed for computing the closed-form bandwidth expressions for
285
fault-free as well as faulty systems. Performance curves illustrate the degradation when unreliability is increased in terms of number of cluster-network failures.
Laptop PCs propel progress in haft-pitch connectors. HmOFUMI OHNO. JEE (Japan), 40 (September 1990). The growing use of half-pitch connectors has paralleled the development of high density electronic equipment. The solid establishment of half-pitch connectors today owes much to the emergence of laptop computers; the rapid popularization of laptop computers resulted in the rapid growth of the half-pitch connector market and the evolution of today's new connector trends. Analyzing the mechanical strength of SMT attached solder joints. WAYNE CHEN. IEEE Trans. Compon. Hybrids mfg TechnoL 13(3), 553 (1990). Analytic approaches to the pull strength and the shear strength of SMT attached solder joints have been studied by mathematical models. The predicted pull/shear strength of leaded ceramic quad packages was correlated with the experimentally measured data, The predictive models have been used for defining the design guidelines for selecting the optimum lead/pad configurations, the minimum solder volume, as well as the maximum component misalignment for fine pitch SMT assemblies. Printed wiring board inner layer contamination study. A. S. L. CHAN,T. A. SHANKOFFand D. CULVER. Circuit WId 17(1), 10 (1990). Electrical leakage beyond control levels did not occur in high temperature and humidity stressing of surface insulation resistance patterns when the relatively high contamination levels of 5 and 10/zg LiBr/cm 2 were laminated into a simple test multilayer board structure. When sputtered layers of LiF, LiBr and NaCI were covered by a thin 0.002 in. lamination layer, generally similar results were obtained at 35°C/90% relative humidity and even at 85°C/85% relative humidity. Biasing of some samples at 85°C/85% relative humidity out to 400 hr did cause leakages which vary from one to three decades above the controls, but drifting with time beyond 96 hr towards a shorting condition, or to the level of unlaminated samples, on a leakage per square basis was not observed. Because the surface insulation resistance per square concept did not hold in these experiments, the surface leakage mechanism is apparently overridden by bulk leakages which occur in parallel in the laminations. Thermal fatigue life of Pb-Sn alloy interconnections. RYon~I SATOH, KIYOSHI ARAKAWA, MASAHIDE HARADA, and KATSUI-IIRO MATUI. 1EEE Trans. Compon. Hybrids mfg TechnoL 14(1), 224 (1991). A highly accurate estimation of Pb-Sn alloy solder thermal fatigue life is made for surface mount solder joints. Experiments are carried out on Pb-5Sn and Pb-63Sn alloy solders under thermal cycle conditions of - 5 5 to 150°C/cycle/hr. The thermal fatigue fracture of Pb-Sn solder joints develops when cracks, initially generated from large scale plastic deformation of the solder, propagate gradually through the joint. On the fracture surface, striations of 500 A to l # m in size are observed and crack propagation rates (da/dN) are obtained for these solders. Additionally, thermal stess and strain in solder joints is studied by the finite element method (FEM) using three-dimensional and thermoelastoplastic models. The equivalent strain range based on Mises criterion, obtained by FEM, relates strongly to thermal fatigue life. A thermal fatigue life equation considering crack propagation related to bonding size and thermal strain range, is developed. Automated apparatus for long-term testing of electrical brushes. DANIEL M. ALLEY et al. IEEE Trans. Compon. Hybrids mfg Technol. 14(1), 31 (1991). The meaningful evaluation of electrical brushes, and even more so the development of novel electrical sliding contacts, can require