Forming high temperature solder joints through liquid phase sintering of solder paste

Eutectic lead-tin has been the solder of choice throughout the history of the electronics industry. Alternatives to this material are now being considered because of environmental concerns, as well as the strength and temperature limitations of eutectic lead-tin. Identifying and using these alternative materials poses significant challenges, many of which we believe can be addressed if one forms solder joints through liquid phase enhanced sintering. First, most alternative solder materials have significantly higher melting temperatures (than eutectic lead-tin), and their use would require the replacement of much of the manufacturing infrastructure. In this work joints with shear stresses approaching that of eutectic lead-tin solder were formed by sintering a eutectic tin-sliver solder paste (T_m=221°C) doped with 3 v/o eutectic Sn-Bi powder at 210°C for 30 min. Second, to date the industry has limited its consideration to eutectic or near-eutectic alloys because of the concern of forming cold solder joints. In this work joints have been prepared by sintering solder pastes with a wide thermal range at temperatures just above the solidus, where a small amount of liquid will form and therefore enhance the rate of sintering, which have shear strengths of 6 MPa or higher. These findings indicate that it may be worthwhile to investigate developing a sinterable solder paste, which can be used to prepare surface mount assemblies.     

Regions outside of the CAAX motif influence the specificity of prenylation of G protein gamma subunits

A family of GTP-binding regulatory proteins (G proteins) transduces signals across the plasma membrane from a large number of receptors to a smaller number of effectors. Recent studies indicate that a series of post-translational modifications are required for their association with the plasma membrane and for their function. In the case of the G protein gamma subunits, the post-translational modifications include the prenylation of a cysteine residue within a carboxyl-terminal CAAX motif. Although prenylation has been shown to involve the addition of either a C15 farnesyl or a C20 geranylgeranyl group to proteins, the structural requirements and functional consequences of adding different types of prenyl groups to various members of the gamma subunit family have not been examined. In the present study, we have employed the baculovirus expression system to study the structural requirements for attaching different types of prenyl groups to various members of the gamma subunit family. We show that the gamma 2 subunit is modified by a C20 geranylgeranyl group, consistent with the presence of a geranylgeranylation target sequence in this protein. However, we found that the gamma 1 and mutant gamma 2(Ser-71) subunits are modified by both C15 farnesyl and C20 geranylgeranyl groups, despite the presence of an accepted farnesylation target sequence in both of these proteins. Using chimeras of the gamma 1 and gamma 2 subunits, we provide evidence indicating that structural elements upstream of the carboxyl-terminal CAAX motif play a role in the recognition of members of the gamma subunit family by the appropriate insect and mammalian prenyltransferases.     

Dietary fatty acids modulate hormone responses in lactating cows: mechanistic role for 5''-deiodinase activity in tissue

Eight Salmonella typhimurium (Copenhagen) and eight Salmonella dublin isolates from cattle were compared by their antibiotic resistance patterns, by their production of colicin, aerobactin, haemolysin and capsule, by their possession of transmissible R plasmids and the spvC gene, and by their ability to invade and replicate within cultured epithelial cells. The two groups differed in their antibiotic resistance profiles, with more of the host-adapted S. dublin isolates resistant to tetracycline than were the non-host-adapted S. typhimurium (Copenhagen) group, but more of the S. typhimurium (Copenhagen) isolates resistant to the other antibiotics tested. None of the isolates produced colicin, but all produced aerobactin. One isolate in each group was encapsulated. All of the S. typhimurium (Copenhagen) and S. dublin isolates contained plasmids, and all of them contained the spvC-homologous sequences. Four of the S. typhimurium (Copenhagen) isolates were able to transfer an R plasmid to a recipient organism by conjugation. One of the five S. dublin isolates, which showed resistance to some of the antibiotics tested, was able to transfer an R plasmid by conjugation. Both groups of isolates invaded cultured epithelial cells to a similar degree after 1 h, but the S. dublin isolates reached significantly higher levels within the cells than did S. typhimurium (Copenhagen) after 9 h. This ability may, in part, explain the association of S. dublin with more severe forms of salmonellosis and prolonged carrier states. Further study of the intracellular growth of these isolates seems warranted.     

Bearing currents and their relationship to PWM drives

This paper examines AC motor shaft voltages and the resulting bearing currents when operated under pulse width modulation (PWM) voltage source inverters. The paper reviews the mechanical and electrical characteristics of the bearings and motor in relation to shaft voltages and bearing currents. A brief review of previous work is addressed, including the system model and experimental results. The theory of electric discharge machining (EDM) is presented, including component calculations of the system elements. The effect of system elements on shaft voltages and bearing currents are evaluated experimentally and the results compared to theory. A design calculation is proposed that provides the relative potential for EDM. Finally, the paper presents quantitative results on one solution to the shaft voltage and bearing current problem     

Chemiluminescent microwell hybridization assay for direct detection of human parvovirus B19 DNA

A method for the direct detection of human parvovirus DNA in serum samples that uses a digoxigenin-labeled RNA probe to hybridize with target B19 DNA, followed by capture of the hybrid onto a microtiter plate wells previously coated with a second oligonucleotide probe was developed. The captured hybrid is then detected with anti-digoxigenin-alkaline phosphatase conjugate and chemiluminescent substrate and the reaction read on a scintillation counter. The relative sensitivities of the microwell and standard dot blot hybridization assays were compared. The chemiluminescent microwell hybridization assay was more sensitive than dot-blot hybridization and could be performed in a few hours. This format, therefore, permits rapid and sensitive detection of parvovirus DNA suitable for the clinical setting.     

Dose response to recombinant bovine somatotropin from weeks 15 to 44 postpartum in lactating dairy cows

Forty Holstein cows were used in an experiment to determine the response of cows to daily subcutaneous injections of 0, 10.3, 20.6, and 30.9 mg of recombinant bST. Injections began between 98 and 104 d postpartum and continued for 29 wk, up to 70 d prepartum, or a maximum of 400 d postpartum. Increasing recombinant bST increased milk yield and 3.5% FCM yield in a linear fashion and by 5.2 and 5.7 kg/d, respectively. Milk composition was not changed, and DM intake as a percentage of BW increased from 3.39 to 3.80% with increasing (30.9 mg/d) bST. Feed efficiency (3.5% FCM/DM intake) was increased from 1.35 to 1.64 with increasing dose, suggesting improved efficiency of use of DM intake, primarily by dilution of maintenance. Increasing bST reduced BW gain linearly from .46 kg/d for the control to .22 kg/d for the 30.9 mg/d bST. Calf birth weight, weight of cows at calving, and incidence of metabolic diseases during subsequent calving were not affected by bST. Somatotropin treatment resulted in somewhat smaller increased in milk yield than that reported in previous studies. Long-term health effects and effects on reproduction could not be determined from the relatively few cows used in this study.     

Effect of rumen ammonia concentration on in situ rate and extent of digestion of feedstuffs

Three dry Holstein cows fitted with rumen fistula were fed a 7.4% crude protein diet consisting of 47.4% corn, 50% cottonseed hulls, and 2.6% minerals and vitamins during a 44-d experiment. Treatments consisted of rumen infusion, 0, 33, 67, and 100 g/d of urea nitrogen applied in a four period Youden Square design. Increasing urea infusion increased rumen fluid ammonia nitrogen from 4.3 to 25.0 mg/dl. Estimated effective dry matter degradation based on in situ rates of digestion were increased from 67.9 to 74.4% for corn and 77.5 to 80.3% for soybean meal with maximums at 100 g/d infused urea nitrogen. Up to 67 g/d infused nitrogen increased dry matter degradation of corn gluten feed from 67.0 to 71.4% and cottonseed meal dry matter degradation from 56.7 to 60.1%. Alfalfa hay dry matter and neutral detergent fiber degradation were not increased by urea infusion. Minimum rumen ammonia required in feeds in this trial were pooled with literature data and suggest that lowest ammonia concentrations required for maximal digestion was a function of the rumen fermentability of the diet or feed. The equation: minimum ammonia concentration (mg/dl) = .452 fermentability % - 15.71, accounted for 50% of the variation in minimum ammonia requirements. We conclude that rumen ammonia concentrations required for maximum digestion are not constant but rather are a function of fermentability of the diet.     

Dietary sodium bicarbonate and magnesium oxide for early postpartum lactating dairy cows: effects on production, acid-base metabolism, and digestion

In two experiments with cows in early lactation fed 40% corn silage and 60% concentrate diets (dry basis), we examined effects of 1.0% dietary sodium bicarbonate and .8% magnesium oxide in a 2 x 2 factorial arrangement on performance, acid-base metabolism, and digestion. In Experiment 1 with 20 Holstein and 4 Jersey cows, intake and milk production were not affected by treatment through 12 wk postpartum. In digestion trials at 3, 6, 9, and 12 wk postpartum, addition of magnesium oxide increased digestibility of dry matter 1.8% units by sodium bicarbonate whereas acid detergent fiber digestion increased 9 to 12% units with addition of either buffer. In Experiment 2, with four fistulated Holstein cows in a Latin square design, intake per unit body weight was increased .18% units by dietary sodium bicarbonate while milk production was unaffected. Dry matter and acid detergent fiber digestion were increased slightly by sodium bicarbonate plus magnesium oxide addition whereas nitrogen balance increased 23 g/day in cows fed magnesium oxide alone. Because of the low fiber content of the ration, milk fat percent increased .5 to .9% by addition of either buffer in both experiments and resulted in corresponding increased in fat-corrected milk. Sodium bicarbonate and magnesium oxide prevented rapid declines in rumen pH associated with feeding in Experiment 2, which related to changes in acid detergent fiber digestion. Blood acid-base metabolites were relatively unchanged by treatment in either experiment. Urinary bicarbonate and net acid excretion rates were changed on the average by +41 and +43 meq/h by sodium bicarbonate or magnesium oxide but could not be related to changes in intake and production.     

Milk composition and apparent digestibilities of dietary fatty acids in lactating dairy cows abomasally infused with Cis or Trans fatty acids

Fat supplementation of diets for dairy cows produces changes in nutrient supply and milk composition. The effect of abomasal infusion of either cis-C18:1 or trans-C18:1 fatty acid isomers on the digestibility of fatty acids and milk composition was determined in lactating dairy cows. Six multiparous midlactation Holstein cows were used and fed a control diet containing 50% forage and 50% concentrate. Treatments were (per day): no infusion, infusion of a 630-g fat mixture high in cis-C18:1 isomers, and infusion of a 623-g fat mixture high in trans-C18:1 isomers using two 3 x 3 Latin squares with 4-wk experimental periods. Fat infusion did not affect total dry matter intake and increased apparent digestibilities of total fatty acids. Apparent digestibilities of C18 fatty acids were directly related to the number of double bonds within isomers, and cis-C18:1 isomers were slightly more digestible than trans-C18:1 isomers. The lower yield of C12:0, C14:0, and C16:0 fatty acids in milk fat and higher milk citrate observed when cows were infused with trans-C18:1 suggests a depressed de novo milk fatty acid synthesis. Effects of trans infusion on milk fat were independent of ruminal fermentation, fatty acid apparent absorption, and fatty acid plasma concentrations. Lower milk protein yield in cows infused with fat may have been caused by a decrease in milk protein synthesis.     

Principal component and multivariate analysis of milk long-chain fatty acid composition during diet-induced milk fat depression

The objective of this study was to assess the relationship between individual milk fatty acids (FA) and diet-induced milk fat depression (MFD) using principal component analysis (PCA) and multivariate analysis (MA). Cow treatment observations (n = 63) from 3 published feeding experiments with lactating dairy cows were used in the analyses. In the PCA, principal component loading plots 1 (PC1) and 2 (PC2) described 55.9% of the total variation in milk FA and fat concentrations. Saturated FA (14:0, 16:0, and 17:0) and milk fat percentage showed negative loading for PC1. Trans-18:1 isomers (trans-6+7+8 to trans-15), trans-7, cis-9 conjugated linoleic acid (CLA), and trans-10, cis-12 CLA showed positive (opposite) loading, suggesting a negative relationship between these isomers and milk fat percentage. Cis-11, trans-13 CLA and cis-9, trans-11 CLA were associated with the PC2 axes (neutral), indicating that they were not associated with MFD. Multivariate analysis with milk fat percentage as the dependent variable and individual PC1 positive loading variables showed a breakpoint relationship for trans-6+7+8-, trans-9-, trans-10-, and trans-13+14-18:1 and a linear relationship for trans-11-, trans-12-, trans-15-18:1, trans-10, cis-12 CLA, and trans-7, cis-9 CLA. Subsequent MA was conducted on 41 treatment means from 12 independent experiments from the literature, in which concentrations of trans-6+7+8-, trans-9-, trans-10-, and trans-11-18:1, and cis-9 trans;-11, and trans-10, cis-12 CLA were reported. Significant negative effects of trans-9-18:1, trans-10-18:1, and trans-10, cis-12 CLA on milk fat percentage were observed. In this study, the PCA and MA showed that among trans-18:1 isomers, trans-10-18:1 was the most negatively correlated to milk fat percentage. However, the threshold concentration related to maximum MFD indicated that the relative potency was greatest for trans-6+7+8- and lowest for trans-10-18:1. These results suggested that trans-6+7+8-18:1 might be more important than trans-10-18:1 in MFD. Principal component analysis also showed that trans-10, cis-12 and trans-7, cis-9 CLA were the isomers most negatively correlated to milk fat percentage, implying a possible role of trans-7, cis-9 CLA in MFD. Additional experiments are needed to establish whether trans-7-18:1 is involved in MFD or that its effects are mediated via the endogenously synthesized trans-7, cis-9 CLA.