Evaluation of the flexibility of silver circuits screen-printed on polyimide with an environmental reliability test

The flexibility of screen-printed silver (Ag) circuits on a polyimide (PI) substrate was investigated under a high temperature and relative humidity (RH). The conductive circuits were constructed on a PI film with a commercial Ag nanopaste via screen printing. The printed patterns were sintered at 200 degrees C for 30 min in a box-type furnace, after which they were placed in a chamber at 85 degrees C/85% RH for various durations: 100, 300, 500, and 1000 h. The Institute for Interconnecting and Packaging Electronic Circuits (IPC) flexural resistance endurance test was conducted to measure the flexibility of the conductive circuits, and the flexibility of the printed patterns was evaluated by detecting the variation of the electrical resistance. The flexibility of the screen-printed conductive circuits decreased as the duration of the 85 degrees C/85% RH test increased. After the 1000 h run of the 85 degrees C/85% RH test, the flexibility of the printed circuits was almost halved compared to that after the 100 h test. To demonstrate the decreased flexibility, the microstructural evolution and partial volume were investigated with a field emission scanning electron microscope (FE-SEM) and a 3D surface profiler, respectively.     

Flexibility of silver conductive circuits screen-printed on a polyimide substrate

The microstructural evolution and mechanical characteristics, especially folding endurance, of screen-printed Ag circuits under various sintering conditions were investigated. The circuits were constructed on a polyimide (PI) film by a screen printing technique using a commercial Ag nanopaste. The sintering temperature and time were raised from 150 to 300 degrees C and from 15 min to 1 hour while the sintering time and temperature were fixed at 30 min and 200 degrees C, respectively. The Massachusetts Institute of Technology (MIT)-type folding endurance tester was used to measure the flexibility of the screen-printed Ag circuits. We observed the change of electrical resistance while the printed Ag patterns were being folded. The folding endurance was better at lower sintering temperature and time, which was explained by the microstructural evolution and macrostructural change of the screen-printed Ag circuits; however, the electrical characteristics were generally poor. Further research is therefore required to improve the electrical and mechanical properties of patterns using direct printing technologies simultaneously.     

Electrical reliability of different alloying content on copper alloy fillers in electrically conductive adhesives

The thermal stability and electrical reliability of electrically conductive adhesives (ECAs) filled with Cu fillers alloying with different amount of Ag and Mg (0.2–1.5 at.%), respectively, were studied by comparing their electrical resistivity under high temperature exposure at 125 and 85 °C/85% RH for 1,000 h. Results showed that the Cu-Ag filled ECAs were superior to Cu-Mg filled ECAs in terms of thermal stability during aging under high temperature exposure and high humidity condition. A final resistivity on the order of 10⁻⁴ Ω.cm could be maintained for Cu-Ag filled ECAs after aging at 125 °C for 1,000 h. Cu-Mg filled ECAs showed relatively high electrical resistivity compared to Cu-Ag filled ECAs. Resistivity of Cu-Mg filled ECAs increased rapidly over time during high temperature exposure at 125 °C except for Cu-0.5 at.% Mg filled ECA which was thermally stable after 400 h of aging. The ECAs in this study could withstand high temperature exposure at 125 °C better than aging under a combination of elevated temperature and high humidity at 85 °C/85% RH.     

Electrochemical migration characteristics of screen-printed silver patterns on FR-4 substrate

We evaluated the electrical reliability of screen-printed silver (Ag) patterns sintered at various temperatures under variable bias voltages. Comb-type patterns were screen-printed onto a flame resistance-4 substrate using a commercial Ag nanopaste (24 nm in diameter, 73 wt% of Ag nanoparticles). The printed patterns were then sintered for 30 min in air at various temperatures ranging from 100 degrees C to 200 degrees C. The microstructures and thickness profiles of the sintered conductive patterns were identified with a field emission scanning electron microscope and a 3-D surface profiler, respectively. In this study, the phenomenon of electrochemical migration was investigated with a water drop test with deionized water. These results showed that the time required by dendrites to bridge from a cathode to an anode was affected by the sintering temperature and applied voltage; when the sintering temperature was 200 degrees C, the time to achieve a short circuit was nearly four times that of the sample sintered at 100 degrees C, and while the applied voltage increased from 3 V to 9 V, the time to reach a short circuit decreased, on average, by 11%.     

Pyrolysis conditions and ozone oxidation effects on ammonia adsorption in biomass generated chars

Ammonia adsorbents were generated via pyrolysis of biomass (peanut hulls and palm oil shells) over a range of temperatures and compared to a commercially available activated carbon (AC) and solid biomass residuals (wood and poultry litter fly ash). Dynamic ammonia adsorption studies (i.e., breakthrough curves) were performed using these adsorbents at 23 degrees C from 6 to 17 ppmv NH(3). Of the biomass chars, palm oil char generated at 500 degrees C had the highest NH(3) adsorption capacity (0.70 mg/g, 6 ppmv, 10% relative humidity (RH)), was similar to the AC, and contrasted to the other adsorbents (including the AC), the NH(3) adsorption capacity significantly increased if the relative humidity was increased (4 mg/g, 7 ppmv, 73% RH). Room temperature ozone treatment of the chars and activated carbon significantly increased the NH(3) adsorption capacity (10% RH); resultant adsorption capacity, q (mg/g) increased by approximately 2, 6, and 10 times for palm oil char, peanut hull char (pyrolysis only), and activated carbon, respectively. However, water vapor (73% RH at 23 degrees C) significantly reduced NH(3) adsorption capacity in the steam and ozone treated biomass, yet had no effect on the palm shell char generated at 500 degrees C. These results indicate the feasibility of using a low temperature (and thus low energy input) pyrolysis and activation process for the generation of NH(3) adsorbents from biomass residuals.     

Reaction characteristics of Ca(OH)2, HCl and SO2 at low temperature in a spray dryer integrated with a fabric filter

The objective of this research was to evaluate the reaction characteristics of CaOH2, HCl and SO2 in the flue gas emitted by a laboratory incinerator. The amount of sulfur retained in the residues (including the spray dryer ash and baghouse ash) was also evaluated in this study. The experimental parameters included HCl concentration (500-2000 ppm), SO2 concentration (500-2000 ppm), relative humidity (40-80% RH), and the addition of CaCl2 (30 wt.%).The results indicated that an HCl concentration of 500-2000 ppm did not affect HCl removal efficiency in the spray dryer at 150 degrees C and 45+/-5% RH. On the other hand, increase in SO2 concentration from 500 to 2000 ppm enhanced SO2 removal at 150 degrees C and 75+/-5% RH. Moreover, increase in removal efficiency of SO2 was more obvious when the relative humidity was greater than 80%. When the flue gas contained both HCl and SO2 simultaneously, the removal efficiency of SO2 could increase from 56.7 to 90.33% at HCl concentration of 236 ppm. However, when the concentration of HCl exceeded 535 ppm, the removal efficiency of SO2 decreased with increasing concentration of HCl. The removal efficiency of SO2 could be increase to 97.7% with the addition of CaCl2.     

Effects of temperature/humidity treatments on the peel strength of CuCr alloy films on polyimide

A single layer of CuCr alloy was sputter deposited on polyimide films instead of Cu/Cr double layers. The adhesion strengths of the metal/polyimide thin films were measured by the peel test. In order to study the effects of temperature and humidity on the adhesion strength, 85 C/85% R.H. (T/H) treatments were applied to the specimens. Results showed that the peel strength without T/H treatments increased proportionally with the Cr content in the CuCr alloy layer(x) up to 17 at%, and then saturated. Among the samples studied, the peel strength decreased with hold time under T/H conditions for all the cases, but most drastically for the sample with x=8.5. The very poor peel strength of that sample (x=8.5) was attributed to the occurrence of interfacial failures, which were thought to take place along CuCr oxide/polyimide interfaces.     

Reliability Study of Holographic Optical Elements Made with DuPont Photopolymer

We report reliability-test results of transmission-type holographic optical elements (HOE's) made with the DuPont photopolymer HRF-600. The reliability tests performed include 6000 cycles of liquid-to-liquid thermal-shock cycling (-55 degrees C-125 degrees C), 2200 cycles of air-to-air thermal cycling (-55 degrees C-125 degrees C), 1500 h of humidity testing (85 degrees C and a relative humidity of 85%), and 675 h of burn-in testing at 125 degrees C. A total of 210 holograms was tested, with 532 data points collected for diffraction-efficiency measurements. The results show that the average efficiency change after these tests is in the range of -4% to 0% and the standard deviation is only ~10%.     

Oxidative desulfurization: kinetic modelling

Toxicity of hexavalent chromium (Cr(6+)) was focused on with a publication of EU RoHS directive, a novel method to determine hexavalent chromium is developed. It is a combination of energy dispersion X-ray fluorescence spectrometry (EDXRF), spot test, alkali digestion and UV-vis spectrophotometric analysis. First, by EDXRF screening, the presence or absence of element Cr was established. Spot test was followed to identify the valent state of chromium because Cr(6+) and Cr(3+) normally coexist. After alkali digestion, Cr(VI) was separated without an undersired Cr(VI)-Cr(III) interconversions. With a color reagent (DPC) to chelated with Cr(VI), the solution was finally detected by a UV-vis spectrophotometer at a wavelength of 540 nm which is the basis of analyzing Cr(VI) quantitatively. Some parameters affecting analyses were studied. It was found that when pH in the final solution was 2.0, the extraction time was 60 min, the extraction temperature was 90 degrees C, pH during the extraction process was 7.5-8.5, and a mixed buffer solution (0.5M K(2)HPO(4)/0.5M KH(2)PO(4)) was added up to 1 ml, colorimetric reagent was added to 2 ml, it is optimal for extraction. Under this condition, interferences from Fe(3+), Pb(2+), Ag(+), etc., were overcome. It was also found that the curves are rectilinear in the range of 0-500 microg l(-1), the correlation coefficient is up to 0.999924, and the recovery rates are more than 85%, the Cr(III)-DPCO complex can be kept stable for 24h with a relative humidity (RH) range of 60-90%, and a temperature range of 5-40 degrees C. So it can be concluded that the proposed method has a good sensitivity and high precision. It is a more convincing and reliable method due to its relative standard deviation (R.S.D.) <1% after six replicate determinations of Cr(VI) in an Fe-Ni alloy sample.     

Effect of different copper fillers on the electrical resistivity of conductive adhesives

The effects of different copper fillers with different morphology and particle size have been studied in terms of electrical resistivity and thermal stability on the electrically conductive adhesives. The copper fillers used in this study were prepared by wet chemical reduction, electrolytic and gas atomization method, respectively. The as cured ECAs filled with different type of Cu fillers showed significant difference in electrical resistivity. Cu filler with smaller particle size showed higher packing density and larger surface area, which would enhance formation of conductive channels and increased conductive network in the ECAs, leading to a lower electrical resistivity. In addition, thermal stability of the ECAs were investigated under high temperature exposure at 125 °C and high humidity aging at 85 °C/85% RH for 1,000 h. Results showed that ECAs with Cu fillers of relatively small particle size and rough particle surface have excellent thermal stability due to enhanced adhesion and contact area between Cu fillers and the polymer matrix. A very low resistivity at an order of magnitude of 10^?4 ?? cm could be maintained for these ECAs after 1,000 h at 125 and 85 °C/85% RH.     

Electrical characteristics of printed Ag nanopaste on polyimide substrate

We investigated the effects of sintering temperature on the microstructural evolution and electrical characteristics of screen-printed Ag patterns. A conducting paste containing 20 nm Ag nanoparticles (73 wt%) was screen printed onto a polyimide (PI) substrate and sintered at a temperature of 150, 200, 250 and 300 degrees C for 30 min. The microstructures of the sintered patterns were examined using field emission scanning electron microscopy (FESEM). The resistivity under the application of a DC signal decreased with increasing temperature. In the frequency range from 10 MHz to 20 GHz, the S-parameters of the sintered Ag conducting patterns were measured. The S-parameters indicated that the insertion losses at high frequency decreased with increasing sintering temperature due to the formation of interparticle necking after sintering.     

Investigation of Capacitive-Based Relative Humidity Sensors and Their Stability at High Temperature

The performance of high-temperature, polymer-based RH sensors was investigated in order to evaluate their long-term stability. The work is aimed at understanding how severe temperature cycles may alter the characteristics of relative humidity (RH) sensors, how they impact the measurements, and how they contribute to the measurement uncertainty. The tests involved 10 high-temperature RH sensor probes available from five European manufacturers. They were initially calibrated against suitable humidity standards in the range from 10%rh to 85%rh with air temperatures from 20 °C to 80°C, and subsequently, they were exposed to air temperature at about 145 °C for several cycles, each cycle lasting (50–100) h. After each high-temperature exposure, a calibration check at 80 °C was carried out. The test lasted until the sensor exposure time exceeded 300 h. The paper presents the characteristics of such probes, the investigation results, and the comparison of the specified versus the experimental performances.     

Fire-through Ag contact formation for crystalline Si solar cells using single-step inkjet printing

Inkjet-printed Ag metallization is a promising method of forming front-side contacts on Si solar cells due to its non-contact printing nature and fine grid resolution. However, conventional Ag inks are unable to punch through the SiN(x) anti-reflection coating (ARC) layer on emitter Si surfaces. In this study, a novel formulation of Ag ink is examined for the formation of fire-through contacts on a SiN(x)-coated Si substrate using the single-step printing of Ag ink, followed by rapid thermal annealing at 800 degrees C. In order to formulate Ag inks with fire-through contact formation capabilities, a liquid etching agent was first formulated by dissolving metal nitrates in an organic solvent and then mixing the resulting solution with a commercial Ag nanoparticle ink at various volume ratios. During the firing process, the dissolved metal nitrates decomposed into metal oxides and acted in a similar manner to the glass frit contained in Ag pastes for screen-printed Ag metallization. The newly formulated ink with a 1 wt% loading ratio of metal oxides to Ag formed finely distributed Ag crystallites on the Si substrate after firing at 800 degrees C for 1 min.     

Fabrication and application of polyimide plastic molds for nanoimprint lithography

In this work, we have developed low-cost, high modulus, flexible, and UV transparent polyimide plastic molds for nanoimprint lithography (NIL). Different structures of poly(amic acids) (PAA) and polyimides (PI) have been synthesized. By casting the PAA or PI solutions on a silicon master, flexible but still rigid plastic molds can be produced. The advantages of the PI molds are: (1) high glass-transition temperatures (Tg) up to 310 degrees C, (2) high thermal stability over 500 degrees C, (3) high tensile modulus, and (4) UV transparency for use in UV-NIL. Various micrometer and nanometer scale patterns could be obtained from the PI molds on a large area (4 inch wafer). The imprinting results showed that the PI molds could be faithfully used for both hot embossing NIL and UV-NIL.     

Durable metal-enhanced fluorescence flexible platform by in-situ growth of micropatterned Ag nanospheres

Here, we demonstrate an in-situ growth of micropatterned silver nanospheres(Ag NS) array on transparent polyimide(PI), namely PI-Ag substrate, applied as a flexible platform for metal-enhanced fluorescence(MEF). The scheme proposed here can easily control the grid formation of Ag NSs and the particle size inside, thus achieving patterned fluorescence imaging and MEF efficiency optimization. Meanwhile, the magnitude of enhanced intensity, relying on the distance between Ag NSs and emissive molecules, was systematically investigated by exploring diverse polyethyleneimine(PEI) spacer thickness. Consequently,an optimal enhancement factor of 7.9 and a pattern of grid fluorescence imaging was obtained with an insertion of 10 nm PEI on the PI-Ag(25 nm) platform. Moreover, owing to robust adhesion between Ag NSs and PI film by in-situ growth, this flexible PI-Ag MEF platform maintained a stable MEF efficiency even after taking mechanical bending for 1000 cycles. This new surface-confined micropatterned Ag NSs PI film provides a promising candidate in design flexible MEF platforms for future analytical and clinical sensing applications.     

Reliability testing of polyimides for GaAs MMIC applications

Submission of test components and representative MMICs to an extensive range of environmental and endurance tests has confirmed the suitability of polyimide as a dielectric layer for a high performance, reliable GaAs foundry process. In particular, the ability to withstand 1000 hours of 85 per cent RH, 85°C humidity testing has been demonstrated.     

Effect of high temperature conditioning,fungicide treatment and film wrapping on the keeping quality of 'Nova' tangelo during cold storage

'Nova' tangelo fruits harvested at the end of January 1996 were stored at 6°C and 90–95% relative humidity (RH) for 4 or 8 weeks; each storage period was followed by an additional week of simulated marketing conditions at 20°C and 70% RH. Before storage the fruits were dipped in a solution of chlorine or imazalil at 500 p.p.m., packaged in polystyrene trays with a 15 μm thick heat shrinkable film and conditioned at 38°C and 85–90% RH for 48 h. High temperature conditioning was not effective in reducing ageing and decay incidence, moreover, film wrapping resulted in poor fruits, which turned brown on the skin and were unsaleable when unwrapped. The incidence of decay at the end of the trial was about 30% for fruit treated with chlorine, 40% for fruit treated with no fungicide and only 3.5% for those treated with imazalil. Wrapped fruit which received no fungicide treatment had 47% rotten fruit, but losses were only 3.5% in the wrapped ones treated with imazalil. The combination of film wrapping with imazalil gave the best results in reducing ageing, weight losses and had a beneficial effect in reducing the severity of chilling injury. Treatments had no influence on chemical parameters, with the exception of vitamin C, which was lower in fruit conditions at 38°C. © 1997 John Wiley & Sons, Ltd.     

Single-mode optical waveguides fabricated from fluorinated polyimides

Buried channel optical waveguides were fabricated from fluorinated polyimides. They operated in single mode and showed an optical loss of less than 0.3 and 0.7 dB/cm for TE and TM polarizations, respectively, at a wavelength of 1.3 mum. Moreover, these waveguides had high heat and moisture resistance; the optical loss did not significantly change after heating at 380 degrees C for 1 h or after exposure to 85% relative humidity at 85 degrees C for over 200 h.     

Adhesion characteristics of Cu/Ni–Cr/polyimide flexible copper clad laminates according to Ni:Cr ratio and Cu electroplating layer thickness

The adhesion strength of Cu/Ni–Cr/polyimide flexible copper clad laminate (FCCL) was evaluated according to the composition ratio of the Ni–Cr layer and the thickness of the Cu electroplating layer, by using a 90° peel test. The changes in the morphology, chemical bond and adhesion property were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The peel strength of the FCCL increased with increasing Cr content and increasing Cu electroplating layer thickness. This increasing FCCL peel strength was attributed to a lower C–N bond and higher C–O and carbonyl (C=O) bonds in the polyimide surface compared to the FCCL with a lower adhesion strength. The adhesion property of the FCCLs was significantly affected by the Ni:Cr ratio.     

Adhesion force approximation at varying consolidation stresses for fine powder under humid conditions

Interparticle adhesion forces in fine powders are greatly influenced by varying relative humidity (RH) conditions. The present study estimated the interparticle adhesion forces developed in corn starch powder under humid conditions at varying applied consolidation stresses using tensile strength determination approach. Shear test was used to determine tensile strength of powder at 1–9 kPa consolidation pressures and extrapolated values of tensile strength at zero stress were used for force estimation in non-consolidated powders. A strong dependence of interparticle adhesion force on consolidation and RH conditions was observed, mainly due to alteration in the number of adhesive contacts and contact area. The results indicated that, at low consolidation and high RH, capillary force is the prevailing force contributing to the total interparticle adhesion in contrast to higher consolidation conditions where load induced contact force plays a dominant role. Furthermore, for nonconsolidated samples, the adhesion forces registered a steep jump above 60% RH which was primarily attributed to dominance of the liquid bridge forces. Also, forces determined from tensile strength approach and those predicted theoretically, as a summation of individual forces, yielded a similar trend. Overall, a simple and effective approach for interparticle force estimation of consolidated as well as loosely packed powders under varying humidity conditions is presented here.