Ceramic Carrier Research Articles

Effect of matrix on ( S)- p-chlorodiphenylmethanol production by immobilized Debaryomyces marama

The product ( S)- p-chlorodiphenylmethanol is obtained through stereoselective reduction of p-chlorobenzophenone using Debaryomyces marama cells, immobilized on Raschig rings. This process involved continuous fermentations in bioreactors for a period of 10 days. The conversion was 86% with a volumetric productivity of 0.248 litre −1 d −1. Comparative experiments with D. marama cells, incorporated in alginate, k-carrageenan or agar–agar gels were also performed. These results demonstrated superiority of the immobilization on ceramic carriers compared to other methods. Passive immobilization of D. marama cells on ceramic carriers has many advantages in comparison with gel-incorporation of the cells. For example, during a long bioreactor run, only a limited amount of cells could remain incorporated within the gel. Therefore immobilized cell preparations will be a convenient methodology in the production of optically active compounds such as pharmaceutical drugs.

Continuous production of structured lipid containing γ‐linolenic and caprylic acids by immobilized Rhizopus delemar lipase

AbstractProduction of a structured lipid containing γ‐linolenic acid (GLA) achieved by the continuous acidolysis of borage oil with caprylic acid (CA) using 1,3‐specific Rhizopus delemar lipase as a catalyst. The lipase immobilized on a ceramic carrier was activated by feeding the borage oil/CA (1:2, w/w) mixture saturated with water into a column packed with the enzyme. However, the generation of partial glycerides (20%) in the reaction mixture showed that hydrolysis occurred concomitantly with acidolysis. The concomitant hydrolysis was completely repressed by feeding the oil/CA substrate mixture without adding additional water. When the substrate mixture was fed at 30°C and a flow rate of 4.5 mL/h into a column packed with 8 g of the carrier with immobilized lipase, the content of CA incorporated in glycerides was 50 to 55 mol%. The acidolysis activity scarcely changed even though the substrate mixture was continuously fed for 60 d; then it gradually decreased. The CA content in glycerides was decreased to 73% of the initial value after 100 d, but returned to the initial level when the flow rate was reduced to 3.1 mL/h. Molecular distillation was employed to separate the transesterified oil from the reaction mixture. No glycerides were detected in the distillate, and the transesterified oil was recovered as the residue (acid value, 2.6). Regiospecific analysis of the transesterified oil showed that only fatty acids at the 1‐ and 3‐positions of borage oil were exchanged for CA. It was additionally found by high‐performance liquid chromatography analysis that all the triglycerides contained one or two CA, and that the triglyceride with two GLA and one CA was also present, because the lipase acted on GLA very weakly.

Void-effect modeling of flip-chip encapsulation on ceramic substrate

A detailed numerical and experimental study of the thermal-mechanical stress and strain in the solder bumps (C4s) of a flip-chip ceramic chip carrier has been completed. The numerical model used was based upon the finite element method. The model simulated accelerated thermal cycling (ATC) from 0/spl deg/C to 100/spl deg/C. Several parametric studies were conducted, including the effects of chip size, micro-encapsulation, and the effect of the presence of voids in the micro-encapsulant. It was notably found that the presence of voids in the encapsulant does not significantly increase the stress/strain in the C4s, with the exception of very large voids and voids at or near the edge of the chip.

Evaluation of immobilized modified lipase: Aqueous preparation and reaction studies in n‐hexane

AbstractLipase Saiken 100 (Rhizopus japonicus) and its immobilized form displayed very poor activity (hydrolysis and interesterification) in microaqueous n‐hexane solutions. Enzyme modification by the addition of stearic acid or sorbitan monostearate significantly improved activity. A ceramic carrier (SM‐10) was used to immobilize modified lipase Saiken (stearic acid, sorbitan monostearate, and lecithin) and was found to further enhance hydrolysis and interesterification rates in n‐hexane. In addition, the biocatalysts were re‐used for four consecutive batch reactions with no significant shortfall in activity. Reaction rates were also greatly affected by the total reaction water content. Careful control of the biocatalyst water content prior to use and additional reaction water were required to optimize activity and minimize hydrolytic diglyceride byproducts. Hydrolysis and interesterification reaction rates were favored with immobilized biocatalyst water contents of 6.25 and 0.43 wt% with additional reaction water contents of 600 and 20 mg/L, respectively.

Bone regeneration by implantation of purified, culture-expanded human mesenchymal stem cells.

Bone marrow contains a population of rare progenitor cells capable of differentiating into bone, cartilage, tendon, and other connective tissues. These cells, referred to as mesenchymal stem cells, can be purified and culture-expanded from animals and humans and have been shown to regenerate functional tissue when delivered to the site of musculoskeletal defects in experimental animals. To test the ability of purified human mesenchymal stem cells to heal a clinically significant bone defect, mesenchymal stem cells isolated from normal human bone marrow were culture-expanded, loaded onto a ceramic carrier, and implanted into critical-sized segmental defects in the femurs of adult athymic rats. For comparison, cell-free ceramics were implanted in the contralateral limb. The animals were euthanized at 4, 8, or 12 weeks, and healing bone defects were compared by high-resolution radiography, immunohistochemistry, quantitative histomorphometry, and biomechanical testing. In mesenchymal stem cell-loaded samples, radiographic and histologic evidence of new bone was apparent by 8 weeks and histomorphometry demonstrated increasing bone formation through 12 weeks. Biomechanical evaluation confirmed that femurs implanted with mesenchymal stem cell-loaded ceramics were significantly stronger than those that received cell-free ceramics. These studies demonstrate that human mesenchymal stem cells can regenerate bone in a clinically significant osseous defect and may therefore provide an alternative to autogenous bone grafts.

Immobilized enzymes – A simple calorimetric method for the determination of the catalytic activity

The results communicated in this paper show that rapid and reliable information about the activity of immobilized enzymes follows from calorimetric measurements. The study was done using spherical and plain carriers as well as different enzymes (urease, glucose-oxidase, invertase). The enzyme thermistor developed by Danielsson et al. was used as a measuring system. This measuring system was applied to investigate the activity of enzyme carrier complexes produced by the sol–gel technique. The influence of processing parameters could be pointed out at complexes of different forms (xerogel, gel on ceramic carrier, thin gel layers on foil, etc.). With the described calorimetric method, a fast and reliable technique for comparative determination of the activity of immobilized enzymes is available. A special advantage of this method is its variability in carriers and the generally applicable thermal measuring principle. Therefore, it seems useful for the development of new immobilization techniques.

Degradation of benzene by a Rhodococcus sp. using immobilized cell systems

The continuous degradation of benzene by a Rhodococcus sp. using free and immobilized cell systems was compared. Cell entrapment in calcium and strontium alginate beads and adhesion on support materials such as glass beads were found to be unsatisfactory. Degradation of benzene by cells immobilized in either ceramic or cellulose carriers proved to be more efficient than its non-immobilized counterpart. A retention time of 36 h was required to effect a 97% degradation of benzene using suspended free cells while cells immobilized on cellulose or ceramic carriers effected 97% degradation at 24 and 18 h, respectively. Recycling of the ceramic carriers was also possible and resulted in an even shorter retention time of 12h to effect a 97% degradation of benzene. Cell adhesion on the support materials was confirmed by scanning electron microscopy.

Wastewater Treatment in a Packed-Bed Reactor with Immobilized Cells onto a New Ceramic Carrier

A new porous ceramic carrier based on casting sand, sawdust and zeolite was used to immobilize microorganisms for continuous wastewater treatment in a packed-bed bioreactor. Scanning electron microscopy showed that the ceramic carrier has a high porosity with diameters of around 5~300µm. Immobilization capacity of the carrier was 62 mg/ g dry carrier, in terms of mixed liquor volatile suspended solids. When synthetic wastewater (chemical oxygen demand 250 mg/l) as a model feed solution and 30 mg kaolin/l as a suspended solid (SS) were used, the removal efficiency as measured by the total organic carbon and SS were 91% and 71%, respectively, at a hydraulic retention time of 3 h.

Electrical characteristics of interconnections for high-performance systems

A review is presented of the electrical characteristics of high-density, high-performance interconnections used in digital and communication applications. These interconnections behave as lossy transmission lines for the frequency range of interest. A brief theoretical explanation of the key properties of lossy, coupled transmission lines is given. A new short-pulse propagation technique used for characterizing a large category of wiring is described. A detailed description is made of each of the major interconnect types encountered namely, shielded cables, printed circuit boards, ceramic carriers, thin-film wiring, and on-chip wiring. Representative examples are given in each case to highlight the key performance-limiting parameters. The modeling and measurement techniques used are explained and examples are given. Future technological directions and their effect on performance are discussed.

Analytical and Experimental Hybrid Study on Thermal Fatigue Strength of Electronic Solder Joints. 1st Report. Rationalization of Accelerated Thermal Cyclic Test and Evaluation of Thermal Fatigue.

Stress-strain analyses for Sn-Pb cutectic solder joints in a thin single outline package (STOP), a ball grid array (BGA) assembly, and a leadless ceramic chip carrier (LCCC) were carried out for investigation of plastic-creep behavior, and of stress relaxation behavior due to accelerated thermal cycling tests or the operating conditions. the temperature dependence of plastic behavior (yield stress) and creep behavior (creep properties) were taken into account in all numerical analyses. The results of finite element analysis (FEA) show that in an accelerated terperature cycling test, long high-temperature and low-temperature dweel times do not contribute to an increase in the cyclic inelastic equivalent strain range in solder joints, although the creep behavior occurring during the dwell times under operating conditions is very important in estimation of the fatigue life of solder joints. Based upon the results of the strain analyses, an efficient temperature cycling test process for microelectronic solder joints was proposed, and cycling tests were carried out. The experimental results show that the thermal fatigue life of microelectronic Sn-Pb eutectic solder joints can be predicted by an associated fracture parameter of total equivalent inelastic strain range, and the fatigue life of solder joints follows Coffin-Manson's law.

Thermomechanical analysis in electronic packaging with unified constitutive model for materials and joints

A unified constitutive modeling approach based on the disturbed state concept (DSC) provides improved characterization of thermomechanical response of joining (solders), ceramics and printed wire board (PWB) materials in electronic packaging. Various versions in the DSC approach are calibrated and validated with respect to laboratory test data, and are implemented in a nonlinear finite element (FE) procedure. The hierarchical nature of this procedure permits the user to choose a constitutive model, simple (elastic) to sophisticated (elastovisco-plastic with disturbance), depending upon the material and need. The FE is used to analyze thermomechanical behavior of two typical problems: (1) leadless ceramic chip carrier (LCCC) package; (2) solder ball connect (SBC) package. The FE results under cyclic thermal loading are compared with experimental data for the two packages, and with a previous FE analysis for the SBC package. In conjunction with the idea of critical disturbance at which thermal fatigue failure can occur, the analyzes allow identification of cycles to failure, N/sub f/, and evaluation of reliability of the package. In the case of the SBC package, the analysis permits an evaluation of ball spacing on the thermomechanical behavior. The DSC approach can provide an integrated and improved procedure compared to available models for elastic, plastic, creep strains, and microcracking leading to degradation of strength and fatigue failure for a wide range of problems in electronic packaging under thermomechanical loading.

Characterizing the Commercial Avionics Thermal Environment for Field Reliability Assessment

Defining environmental loading is often the most uncertain part of the electronics reliability calculation. This paper demonstrates a practical methodology to measure and characterize the dynamic thermal history of the commercial airplane environment. To reduce irregular field thermal cycles, an algorithm is presented that preserves key information necessary for viscoplastic solder fatigue analysis. As an example. the IPC solder model will be used to evaluate 20 termination leadless ceramic chip carriers on nonconstrained printed wiring boards. This methodology will enable more realistic thermal fatigue reliability assessments and acceleration test specifications.

Enrichment of ethyl docosahexaenoate by selective alcoholysis with immobilized Rhizopus delemar lipase

We attempted to purify ethyl docosahexaenoate (E-DHA) by the alcoholysis of fatty acid ethyl esters with lipase. Fatty acid ethyl esters originating from tuna oil (E-DHA content, 23 mol%; E-tuna-23) were used as starting materials, and Rhizopus delemar lipase immobilized on a ceramic carrier was used as a catalyst which acted only very weakly on E-DHA. Because the immobilized lipase did not exhibit the alcoholysis activity, it was activated by shaking at 30°C for 24 h in the E-tuna-23/lauryl alcohol mixture to which water (2%) was added. The alcoholysis activity of the lipase increased markedly as a result of this pretreatment, but the hydrolysis activity also increased. The hydrolysis activity was completely repressed by repeating the reaction after transferring the immobilized enzyme into a fresh E-tuna-23/lauryl alcohol mixture without adding additional water. Several factors affecting the alcoholysis of E-tuna-23 were investigated to determine the optimum reaction conditions. When alcoholysis was conducted at 30°C with shaking in a reaction mixture containing E-tuna-23/lauryl alcohol (1 : 3, mol/mol) and the activated lipase (4% of the mixture volume), E-DHA was efficiently enriched in the ethyl ester fraction. By alcoholyzing E-tuna-23 with lauryl alcohol for 50 h under these reaction conditions, the E-DHA content was increased from 23 mol% to 52 mol% in a 90% yield. In addition, when the fatty acid ethyl esters, of which the E-DHA contents were 45 mol% and 60 mol%, were alcoholyzed for 50 h, the contents of E-DHA were increased to 72 mol% and 83 mol%, respectively. In these reactions, the recovery of E-DHA in the ethyl ester fraction was greater than 90%. We termed this new reaction system selective alcoholysis because advantage of the fatty acid specificity of the lipase was taken in this reaction system. To investigate the stability of the immobilized lipase, continual batch reactions were carried out by replacing the reaction mixture with a fresh E-tuna-23/lauryl alcohol mixture every 24 h. The decrease in the extent of alcoholysis was only 15% even after the 47th batch reaction.

Fatty acid specificity of Rhizopus delemar lipase in acidolysis

We investigated the fatty acid specificity of 1,3-positional specific Rhizopus delemar lipase in acidolysis using a randomly interesterified oil, of which the constituent fatty acid contents were approximately the same, as a substrate. Acidolysis was carried out at 30°C with shaking in a reaction mixture containing caprylic acid (CA)/the randomly interesterified oil (2 : 1, w/w) and the lipase immobilized on a ceramic carrier (4% of reaction mixture). The activity on each fatty acid was experimentally determined as the ratio of the content of the fatty acid exchanged for CA to that of the fatty acid existing at the 1(3)-position of the substrate oil, and regarded as the fatty acid specificity in acidolysis. The fatty acid specificity in hydrolysis was investigated by analysis of the composition of fatty acids liberated from the same randomly interesterified oil. The lipase acted strongly on myristic, palmitic, palmitoleic, stearic, oleic, linoleic, and α-linolenic acids, and moderately on arachidonic and eicosapentaenoic acids. The activities on these fatty acids relative to that on oleic acid were almost the same in acidolysis and hydrolysis. On the other hand, the lipase acted moderately on γ-linolenic and docosahexaenoic acids in the hydrolysis, but only very weakly on these fatty acids in the early stage of acidolysis. This shows that the fatty acid specificity in acidolysis is stricter than that in hydrolysis. Since the kinetics of acidolysis of borage oil, arachidonic acid-containing oil (TGA-25), and tuna oil could be easily predicted from the fatty acid specificity in acidolysis, it was concluded that the specificity was accurately evaluated. In addition, the fatty acids at the 1(3)-position of borage oil and TGA-25 were completely exchanged for CA in a total of three cycles of the reaction, and the contents of fatty acids other than CA in the transesterified oils agreed with that at the 2-position of the oils. Therefore, it was shown that repeated acidolysis using the immobilized 1,3-specific lipase could be applied to regiospecific analysis.

Fatigue-strength prediction of microelectronics solder joints under thermal cyclic loading

The stress-strain analyses for the solder joints in a thin single outline package (TSOP), a ball grid array (BGA) assembly, and a leadless ceramic chip carrier (LCCC) are carried out to investigate the plastic-creep behavior, and stress relaxation behavior due to the temperature cycling or isothermal cyclic loading. The temperature dependence of plastic behavior (yield stress) and creep behavior (creep properties) are taken into consideration in all numerical analyses. The results of finite element analysis (FEA) show that in an accelerated temperature cycling test, long high-temperature and low-temperature dwell times do not contribute to the increase of the cyclic inelastic equivalent strain range in solder joints (although the creep behavior occurring during the dwell times in an operating condition is important enough to be taken into consideration for estimating the fatigue life of solder joints). Based upon the results of the strain analyses, some efficient testing processes of temperature cycling and isothermal fatigue tests for the microelectronic solder joints are proposed, and the cycling tests are carried out. The experimental results show a good agreement with the analytic results.

Effect of intermetallic compounds on the thermal fatigue of surface mount solder joints

The effect of Cu-Sn intermetallic compounds (IMC) on the fatigue failure of solder joints during thermal cycling has been studied. The samples consist of components [leadless ceramic chip carrier (LCCC)] soldered onto FR-4 printed circuit board (PCB), and are prepared by conventional reflow soldering using a 63Sn-37Pb solder paste. The specimens are subjected to thermal cycling between -35/spl deg/C and 125/spl deg/C with a frequency of two cycles per hour until failure. The results indicate that the fatigue lifetime of the solder joints depends on the thickness of IMC's layer between Cu-pad and bulk solder, and the relation of the lifetime to the thickness can be described as a monotonically decreasing curve. The lifetime is very sensitive to the thickness of the IMC when the thickness is less than 1.4 /spl mu/m. During thermal cycling the thickness of the IMC layer increases and then the interface between IMC and solder becomes gradually flatter. The results of X-ray diffraction and scanning electron microscope (SEM) analysis show that cracks propagate along the interface between the IMC layer and the solder joint. The Cu/sub 3/Sn (/spl epsiv/-phase) is also found to form between the Cu-pad and /spl eta/-phase during thermal cycling. On the basis of the above results, the thick and flattened IMC layer is shown to responsible for the fatigue failure of solder joint during thermal cycling. The results of this paper can be used to optimize the reflow soldering process for the fabrication of robust solder joints.

Finite element simulation of the temperature cycling tests

Temperature cycling tests are commonly used in the semiconductor industry to determine the number of cycles to failure and to predict reliability of the solder joints in the surface mount technology packages. In this paper, the thermomechanical fatigue of Pb40/Sn60 solder joint in a leadless ceramic chip carrier package is studied and temperature cycling test is simulated by using a finite element procedure with the disturbed state concept (DSC) constitutive models. The progress of disturbance (damage) and the energy dissipated in the solder joint during thermal cycling are predicted. It is shown that the disturbance criterion used follows a similar path as the energy dissipation in the system. Moreover, the comparisons between the test data and the finite element analysis show that a finite element procedure using the DSC material models can be instrumental in reliability analysis and to predict the number of cycles to failure of a solder joint. Furthermore, the analysis gives a good picture of the progress of the failure mechanism and the disturbance in the solder joint.

Effect of intermetallic compounds on the shear fatigue of Cu/63Sn-37Pb solder joints

The effect of Cu-Sn intermetallic compounds (IMC) on the fatigue failure of solder joints has been studied by means of shear cycling. The samples consist of leadless ceramic chip carriers (LCCC) soldered onto FR-4 printed circuit boards (PCB), and are prepared by conventional reflow soldering using a 63Sn-37Pb solder paste and then aged at 150/spl deg/C for 1, 4, 9, 16, 25, 36, and 49 days. The specimens are subjected to low cycle fatigue shear tests controlled by the displacement. The results indicate that the fatigue lifetime of the solder joints depends on the thickness of the LMC layer between the Cu-pad and bulk solder, and the quantitative relationship between the lifetime and thickness can be described as a monotonically decreasing curve. The greatest decrease is over the thickness range up to 2.8 /spl mu/m, when the IMC/bulk solder interface becomes flat, corresponding to a lifetime decrease to 62% of the as assembled value. For further increase in IMC thickness the lifetime decreases more slowly. Evidently, the effect of the Cu-Sn intermetallic compounds on the joint fatigue lifetime is not only concerned with the IMC thickness hut also the interface morphology. A thick and flat LMC layer has a deleterious effect. The results of X-ray diffraction and metallographic analysis show that cracks initiate underneath the component metallization, and propagate along the IMC/solder interface, then toward the fillet. The Cu/sub 3/Sn (/spl epsiv/-phase) is formed between the Cu-pad and p-phase, and grows more quickly than the /spl eta/-phase during storage and long term operation or aging tests. However, the Cu/sub 3/Sn makes only a small direct contribution toward fatigue failure.

Conversion of corticosteroid hormones by immobilized cells of Flavobacterium dehydrogenans , Curvularia lunata and Arthrobacter simplex on ceramic carriers

Different possibilities for converting pregnenolone triacetate to prednisolone using immobilized preparations of Flavobacterium dehydrogenans, Curvularia lunata and Arthrobacter simpelex in a fixed-bed loop reactor were investigated. The effects of the carrier, substrate concentration, pH and temperature on the rate of the substrate conversion were studied also. The biotransformations were performed with a continuous or semicontinuous substrate supply. A convenient pathway for the formation of prednisolone is proposed on the basis of the results obtained.

Production of structured lipids containing essential fatty acids by immobilizedRhizopus delemar lipase

AbstractAn attempt was made to produce structured lipids containing essential fatty acid by acidolysis with 1,3‐positional specificRhizopus delemar lipase. The lipase was immobilized on a ceramic carrier by coprecipitation with acetone and then was activated by shaking for 2 d at 30°C in a mixture of 5 g safflower or linseed oil, 10 g caprylic acid, 0.3 g water and 0.6 g of the immobilized enzyme. The activated enzyme was transferred into the same amount of oil/caprylic acid mixture without water, and the mixture was shaken under the same conditions as for the activation. By this reaction, 45–50 mol% of the fatty acids in oils were exchanged for caprylic acid, and the immobilized enzyme could be reused 45 and 55 times for safflower and linseed oils, respectively, without any significant loss of activity. The triglycerides were extracted withn‐hexane after the acidolysis and then were allowed to react again with caprylic acid under the same conditions as mentioned above. When acidolysis was repeated three times with safflower oil as a starting material, the only products obtained were 1,3‐capryloyl‐2‐linoleoylglycerol and 1,3‐capryloyl‐2‐oleoyl‐glycerol, with a ratio of 86∶14 (w/w). Equally, the products from linseed oil were 1,3‐capryloyl‐2‐α‐linolenoyl‐glycerol, 1,3‐caprylol‐2‐linoleoyl‐glycerol, and 1,3‐capryloyl‐2‐oleoly‐glycerol (60∶22∶18, w/w/w). All fatty acids at the 1,3‐positions in the original oils were exchanged for caprylic acid by the repeated acidolyses, and the positional specificity ofRhizopus lipase was also confirmed to be strict.