Showing papers by "National Physical Laboratory published in 1986"

Data compilations: their use to improve measurement certainty in surface analysis by aes and xps

Abstract: Data compliations are an integral and vital part of the development of the measurement scheme for surface analysis. They have three main functions that will be considered in this survey: (i) the provision of numerical values for use in calculations of quantitative surface analysis, (ii) the provision of unbiased data for the development of theory, and (iii) the establishment of a benchmark to judge the value of current research. A brief review will be made of practical data relating to AES and XPS instruments; electron guns, x-ray sources, spectrometers and detectors. Next, data compilations of experimental measurements of relative sensitivity factors, attenuation lengths and backscattering factors will be contrasted. Finally, theoretically derived data banks of cross sections, inelastic mean free paths, asymmetry parameters, etc will be considered and conclusions drawn of the need for further work.

Correction methods for integrating‐sphere measurement of hemispherical reflectance

Abstract: Integrating-sphere reflectometers in spectrophotometers and colorimeters suffer from several types of systematic error. The properties of an ideal sphere and the main shortcomings of practical spheres are discussed. Some common errors that occur in measurements of hemispherical reflectance have been investigated using a Cary 14 spectrophotometer fitted with two different integrating spheres: a Cary type 1411 attachment and another made at NPL using a G. E.-Hardy spectrophotometer sphere. The methods described here can be applied to almost any sphere instrument, and possible solutions to problems with other sphere designs are also suggested. It is shown that significant corrections are necessary in many cases.

Measurements of the Refractive Index of Air Using Interference Refractometers

Abstract: Comparisons have been carried out between interference refractometers built in different countries. Individual measurements of the refractive index of air have been made using air from the same sample volume. Direct comparison of refractometers was realized by coupling the instruments to the same air-inlet system. In order to compare the measured results the refractive index was also calculated from accurate measured values of pressure, temperature, humidity and CO2 content, using Edlen's formula. Most of the individual measurements show an agreement within 1 part in 107 while direct comparisons show an agreement within 5 parts in 108. Over a period of five days an increase in CO2 content of 400 ppm per day was measured in a 300 m3 laboratory room. The results show the great importance of correcting calculated results for the CO2 content of the air.

Constant-geometry edge-flaking of brittle materials

Abstract: Lithic tool manufacture was the earliest technological exploitation of the brittle fracture of hard materials, and archaeologists have traced and reproduced the evolution of flake tools through various stages of development from the early simple flake knives (Fig. 1) to the sophisticated multi-faceted edges of stone axes. The technology advanced during the period of gunflint manufacture. Of special interest are the simple geometrical relationships between the dimensions of flakes formed in certain controlled conditions1,2. The phenomenon of edge-flaking is also encountered in the attrition of tool cutting edges and in the chipping of precision edges of metrological components, where it is avoided rather than understood, by empirical radiusing (rounding-off). In our effort to improve the efficiency of cutting edges, we have observed that a law of constant geometry seems to apply to the flakes formed at rectangular edges, and the effect is relatively insensitive to the test material.

Comparison of surface tension measurements using the levitated droplet method

Abstract: Measurements of the surface tension of some metals by the levitating drop technique have been carried out by two independent laboratories in order to establish the levels of agreement. Results obtained for pure iron, cobalt, and copper showed reasonable agreement, but in the case of stainless steel, significant differences were apparent, which were shown to be a consequence of the different hydrogen concentrations in the respective environmental gases. Surface tension values for pure gold obtained by this method showed good agreement with the data obtained by established methods and show that the levitating drop technique is capable of yielding reliable results.

Automatic Gauge Block Measurement Using Multiple Wavelength Interferometry

Abstract: A new multiple wavelength interferometer makes use of stabilised helium-neon and argon ion lasers to measure the length of engineer's gauge blocks. The combination of television and computing techniques to analyse the resulting interferogram makes the instrument less dependent on operator skills and is able to provide data about the gauge surface.

A new model for photodiffusion of silver in amorphous chalcogenides

Abstract: The experimental results of various investigators on photo diffusion of silver in amorphous chalcogenides are reviewed in detail. The models proposed so far are compared to these results. It is shown that these models are not in accordance with experimental facts, particularly results obtained recently. A new model based on the formation of a semiconductor heterojunction is proposed; experimental evidence is cited to justify the assumptions of the model. It is shown that the model explains qualitatively all the work reported so far in a coherent way.

High-pressure sintering of cubic boron nitride

Abstract: Cubic boron nitride (cBN) powder was compacted at high pressure and high temperature using a solid solution of titanium carbide and titanium nitride (TiC x N1−x ) as binding material in the presence of a small amount of aluminium. Different compositions of (TiC x N1−x ), 0

Intercomparison between two independent primary radiometric standards in the visible and near infrared: a cryogenic radiometer and the electron storage ring BESSY.

Abstract: An intercomparison has been performed in the visible and near infrared between two radiometric standards: the electron storage ring BESSY and a cryogenic absolute radiometer. The spectral irradiance of the continuum source BESSY can currently be predicted with a relative systematic uncertainty of 3 × 10−3, whereas the radiant power of monochromatic laser radiation can be measured by the cryogenic radiometer with a relative systematic uncertainty of 10−4. In this intercomparison the responsivity S of a specially designed transfer radiometer was measured using synchrotron radiation (SSR) and the cryogenic radiometer (SRAD). The mean of the ratios SRAD/SSR for different measurement conditions was 1.0013 with a standard error of the mean of 0.0006 for a wavelength of 676 nm and 0.9990 with a standard error of 0.0007 for a wavelength of 799 nm. The systematic uncertainty of the ratio is 3.8 × 10−3 caused by the uncertainty of SRAD of 1.5 × 10−3 and by the uncertainty of SSR of 3.5 × 10−3. Both radiometric standards agree well within the combined systematic uncertainties of the two methods. The result confirms the 3 × 10−3 uncertainty of BESSY. This source standard has therefore a smaller uncertainty than present source standards based on high temperature blackbody radiators. The work also demonstrates how detector- and source-based radiometric standards can be intercompared or transferred between laboratories with a relative uncertainty of <3 × 10−3.

Blowholing in PTH Solder Fillets: Part 3 Moisture and the PCB

Abstract: This is the third paper in the series of eight, studying voids and blowholes in PTH printed circuit boards. In the previous papers the industrial significance of this problem has been established and moisture identified as the primary cause of the gassing. Now, particular attention is focused on the understanding of the mechanisms and kinetics of moisture uptake in the FR‐4 laminate. From the authors' data the rate of moisture uptake and the rate of drying of laminate can be predicted as a function of temperature and relative humidity.

Measurement and characterisation of the acoustic output of medical ultrasonic equipment Part 2

Abstract: A review of measurement techniques for the determination of the acoustic output of medical ultrasonic diagnostic, Doppler and therapeutic equipment is presented. In Part 1 a brief survey of a wide range of techniques was given followed by a discussion of acoustic output specification methods. In this second part of the review two techniques widely used for measurements, the radiation pressure balance and the hydrophone, are considered in detail together with guidelines for good measurement practice. The review concludes with a discussion of a rapid assessment system, BECA2, which has been developed for the characterisation of ultrasonic transducers. Much of the emphasis is on techniques developed at the UK National Physical Laboratory.

Blowholing in PTH Solder Fillets: Part 1 Assessment of the Problem

Abstract: This paper introduces a series of eight describing the research work undertaken into the most pervasive of quality assurance problems in the mass soldering of plated‐through‐hole (PTH) printed circuit boards, namely the occurrence of voids and blowholes in the solder fillets. The research programme has been carried out at NPL with advice and practical involvement of members of the Soldering Science and Technology Club whose contributions have played a large part in its successful outcome. The work has led to an understanding of the mechanisms giving rise to this problem and recommendations for production procedures to fully control it. In this first paper, results are presented of a UK‐wide survey of the electronics assembly industry and of the assessment made regarding the extent, the harmfulness and the cost of the problem of voids and blowholes.

Blowholing in PTH Solder Fillets: Part 2 The Nature, Origin and Evolution of the Gas

Abstract: This paper is the second of a series dealing with the blowholing problem on through‐hole plated printed circuit boards. In the previous paper the authors have considered the impact of the problem on the UK electronics assembly industry. Here they consider the nature of the gas causing blowholes and voids, its origin and the kinetics of its generation and evolution. When a printed circuit board with plated‐through‐holes is wave soldered, the thermal spike of the molten solder activates the evolution of gas, sometimes in relatively enormous quantities. The gas is seen bubbling from the surface of the molten solder in the joint. Upon freezing, the solder either traps the gas in a void enclosed within the fillet or, if the gas is escaping from the surface as freezing occurs, forms a blowhole.

Surface chemical analysis—report on the vamas project

Abstract: The VAMAS project on surface chemical analysis is a multi-national cooperation for the provision of standards data and materials for surface chemical analysis measurement and for the provision of the basic understanding necessary for these activities. This project is one of a rapidly growing suite of projects initiated as a result of decisions following the 1982 Versailles Summit Meeting of the Heads of State or Government of Canada, France, Germany, Italy, Japan, UK, USA and the representatives of the Commission of the European Communities. During the past year national representatives to this VAMAS project have been appointed and national committees established. This article summarizes the philosophy, scope, and organization of the project and describes specific activities that have been initiated. Information is given on how individuals, both within and outside the group of member states, may participate.

Wetting and spreading of liquid metals: the rôle of surface composition

Abstract: Quantitative measurements of the surface compositional changes which occur during the wetting of copper substrates in vacuum by liquid SnPb solder alloys have been made in situ, by Auger electron spectroscopy. Five different spatial regions associated with the wetting front have been identified. Away from the spreading front, the liquid solder shows a surface enhancement of lead. Approaching the front, adjacent bands of Cu3Sn intermetallic compound, and tin-depleted liquid occur, both of width ∼ 20 μm. The lead-enriched surface of the solder extends over these two regions, and out over the copper to form approximately 50% monolayer ‘halo’ of ∼ 80 μm width. Beyond the halo, in the fifth region, very small amounts of tin and lead were detected. The lead halo forms rapidly by surface diffusion, and precedes wetting. In the absence of other limitations, it is the reduction of the copper substrate surface energy by the lead halo that restricts the spread of the molten alloy. Intermetallic compound formation is relatively slow and only takes place once spreading has ceased and a quasiequilibrium reached.