Selection and Testing of Electronic Components for LM

More documents

Recommendations

Info

Fig. 2 Curve tracer The special type of oscilloscope, which is called a curve tracer, Is a universal Instrument tor testing semiconductor components. A family of curves are displayed on the screen. These give an overall picture of the electrical characteristics of the component. The curves can provide Important data, such as amplification factor, breakdown voltage and reverse current Fig. 3 Light microscope Microscopes are valuable aids in construction and fault analyses of electric components. By means of direct observation or photography using light or electronic microscopes It Is possible to study and assess the design of component details or determine the causes of faults. Mlcroscoplng is indispensable when studying intricate conductive patterns or wire bondings on semiconductor crystals Coordination between different divisions and companies in the Ericsson Group in questions relating to choice of electronic components takes place, for example, through a special component and circuit committee, within specialist groups and through centrally distributed component information. Rules for use. The conditions that are to apply for the use of the new component in circuit designs are considered in connection with the component selection. In order to attain the desired reliability and life it is often necessary to reduce, to a greater or lesser extent, the values given in the manufacturer's component data for permissible electrical loads and operating temperatures. Permissible design data are given in special documents which also contain additional information for the designers. Production engineering aspects. When manufacturing equipments it must be possible to check, assemble and connect the components using rational methods and production aids. This means, for example, that questions concerning automatic assembly, soldering and cleaning of components must be considered. Current component range Equipments belonging to different exchange systems, which have been designed at different times, are manufactured continuously and often in parallel. The components have been selected during different development epochs. In order to prevent this from having any negative effects the component range is continously standardized and modernized. The most important types of passive components, discrete semiconductor components and micro circuits used in the LM Ericsson exchange equipments are described below. PASSIVE COMPONENTS Passive components comprise various types of resistors, capacitors and transformers. Resistors Carbon film resistors constitute the most common type. The resistive element consists of a carbon film on a ceramic rod. Operational experience has shown that the carbon film resistor is the most reliable type of component in telecommunication equipment. In addition to carbon film resistors, metal film resistors are used where low temperature dependence is required. This type of resistor is being used to an increasing extent in electronic equipment. A third type of film resistor that has recently been introduced is the metallic oxide resistor, where the resistive element consists of tin oxide with antimony oxide added. Thick-film resistors, manufactured by means of screen printing and firing a resistive paste on to a ceramic substrate, are used as attenuators and fuse resistors. Capacitors This category of component includes many different types, whose characteristics and thus fields of use are mainly determined by their dielectric. Aluminium electrolytic capacitors of the long-life type are used for regulating the operating times of relays. In this case a large capacitance per unit of volume is an essential characteristic. Tantalum electrolytic capacitors are usually chosen for electronic circuits when the requirements are small size and moderate capacitance values at low voltages. Polyester film capacitors are being used to a great extent nowadays in transmission, time and contact protection circuits instead of the traditional paper capacitors Polystyrene capacitors are used when close tolerances and good stability are required, for example in tuned circuits. Both polystyrene and polyester film capacitors are manufactured with a moulded epoxy cover and are constructed for mounting on printed hoarriffc nnfi lion irt ralnw QjatQ
Fig. 4 X-ray camera The Inner construction and manufacture of components can be of great importance to function characteristics and life. One way of Investigating the Inside of the component Is to open the case and cut through the component. However, this method Is usually destructive, so that the component properties are changed entirely. It Is often possible to obtain valuable Information regarding the structure of the component by means of an X-ray photograph. Inner mechanical faults can also be detected on such pictures. In addition the possibility remains of carrying out supplementary electrical measurements on the unaffected component after the X-ray Investigation Fig. 5 Desk calculator Agreatnumber of measurements.provldlng large amounts of measured values, are often carried out In connection with component Investigations. These values must be processed In order to obtain essential data in a clear form. A desk calculator is used for this purpose which can be programmed to process the test material In a suitable way and give the result as a printout or on a diagram. The desk calculator Is also used for certain component data calculations, for example when dimensioning transformer wind- Transformers and inductors Transformers with a core of plate frames or tape are used in transmission circuits that transmit alternating current superposed on a direct current. Ferrite transformers with different types of cores, in certain cases adjustable, are used as current transformers and for filtering in power equipment, in tuned circuits and oscillators, for impedance matching and pulse transmission. DISCRETE SEMICONDUCTOR COMPONENTS These components contain individual semiconductor components, each of which performs just one single function. They are still used in modern exchange systems along with micro circuits, and consist mainly of transistors and diodes, but thyristors and optical semiconductor components are also included in this category. Transistors All modern transistors are made of silicon and usually manufactured by means of so-called planar technology. For quality reasons a metal can with glass lead-throughs for the conductors is used. Diodes The diodes used in exchange systems 97 can be divided into three main categories: rectifier diodes, switch diodes and voltage regulation diodes. The switch diodes are used in logic circuits and must therefore have a short recovery time in the reverse direction. The voltage regulation diodes give a defined voltage level in circuits where a stable reference voltage is required. Special semiconductor components Among semiconductor components that are used to a limited extent for special functions may be mentioned the thyristor, which closes a circuit when a pulse is applied to its gate electrode, and the unijunction transistor, which is used for starting time circuits and thyristors. Opto-electronic components have recently been introduced that use visible or infra-red light for their operation. Among them are light-emitting diodes, displays and opfo couplers. Red, yellow and green light-emitting diodes are used for indicating different states in equipments, and displays show a figure or a letter depending on the applied electrical signals. The opto coupler, on the other hand,
Page 1: ERICSSON REVIEW 3 1977 SELECTION AN
Page 4 and 5: Selection and Testing of Electronic
Page 8 and 9: Fig. 6 Humidity test High air humid
Page 10 and 11: 100 Type of check Type of component
Page 12 and 13: Fig. 12 Computer-controlled test sy
Page 14 and 15: 104 Fig. 16 Comparison of fault tra
Page 16 and 17: Fig. 2 Cable groups with the conven
Page 18 and 19: 108 Fig. 9 Take-up stand lor connec
Page 20 and 21: Insulation: Solid polyethylene Cond
Page 22 and 23: New Telephone Set Arne Boeryd and G
Page 24 and 25: Digital Line Equipments for 8 Mbit/
Page 26 and 27: Fig. 5 ALBO network for automatic e
Page 28 and 29: Fig. 8 Block diagram of the line te
Page 30 and 31: Fig. 13 Small repeater housing of t
Page 32 and 33: 122 Fig. 16 Fault detector shelf an
Page 34 and 35: 124 References 1. Lindquist, S. and
Page 36 and 37: LARS G ERICSSON AKE PERSSON Telepho
Page 38 and 39: 128 Fig. 3 Standardization of progr
Page 40 and 41: 130 Fig. 6 The control room in an A
Page 42 and 43: Table 3 Number of component faults
Page 44 and 45: 134 ence this as congestion or a "s
Page 46 and 47: ABJ 101-the Modern Public Magneto S
Page 48 and 49: Fig. 3 Line unit for 10 magneto lin
Page 50 and 51: " The maximum number of lines that
Page 52: TELEFONAKTIEBOLAGET LM ERICSSON ISS

Selection and Testing of Electronic Components for LM

Create successful ePaper yourself

Delete template?

Save as template?