SMD resistor packages SMD resistors come in a variety of packages. As the technology has moved forward so the size of the resistor packages has fallen. The main packages with their sizes are summarised below: y y y y y y 1812 - 4.6 mm x 3.0 mm (0.18 1206 - 3.0 mm x 1.5 mm (0.12 0805 - 2.0 mm x 1.3 mm (0.08 0603 - 1.5 mm x 0.8 mm (0.06 0402 - 1.0 mm x 0.5 mm (0.04 0201 - 0.6 mm x 0.3 mm (0.02 0.12 ) 0.06 ) 0.05 ) 0.03 ) 0.02 ) 0.01 ) It can be seen from the dimensions in Imperial measure
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  SMD resistor packages SMD resistors come in a variety of packages. As the technology has moved forward so the sizeof the resistor packages has fallen. The main packages with their sizes are summarised below: y   1812 - 4.6 mm x 3.0 mm (0. 18  0. 12 )   y   12 06 - 3.0 mm x 1 .5 mm (0. 12  0.06 )   y   0 8 05 - 2 .0 mm x 1 .3 mm (0.0 8  0.05 )   y   0603 - 1 .5 mm x 0. 8 mm (0.06  0.03 )   y   040 2 - 1 .0 mm x 0.5 mm (0.04  0.0 2 )   y   0 2 0 1 - 0.6 mm x 0.3 mm (0.0 2  0.0 1 )  It can be seen from the dimensions in Imperial measurements, that the package namescorrespond to the dimensions in hundredths of an inch. This an SMD resistor with an 0 8 05 package measures 0.0 8 by 0.05 inches.Other sizes including 121 0, 2 0 1 0, 2 5 12 , 36 1 6, and 40 22 are available for some high power or specialist SMD resistor applications. Specifications SMD resistors are manufactured by a number of different companies. Accordingly thespecifications vary from one manufacturer to the next. It is therefore necessary to look at themanufacturers rating for a specific SMD resistor before deciding upon exactly what is required.However it is possible to make some generalisations about the ratings that might be anticipated.  Power rating: The power rating needs careful consideration in any design. For designs usingSMDs the levels of power that can be dissipated are smaller than those for circuits using wireended components. As a guide typical power ratings for some of the more popular SMD resistor sizes are given below. These can only be taken as a guide because they may vary. y   12 06: 1/8 watt y   0 8 05: 1/1 0 watt y   0603: 1/1 6 wattSome manufacturers will quote higher power levels than these. The figures given areconservative. T  olerance: In view of the fact that SMD resistors are manufactured using metal oxide filmthey available in relative close tolerance values. Normally 5%, 2 %, and 1 % are widely available.For specialist applications 0.5% and 0. 1 % values may be obtained. T  emperature coefficient: Again the use of metal oxide film enables these SMD resistors to provide a good temperature coefficient. Values of  2 5, 50 and 1 00 ppm / C are available.  C eramic SMD capacitors The ceramic SMD capacitors form the majority of SMD capacitors that are used andmanufactured. They are normally contained in the same type of packages used for resistors. y   1812 - 4.6 mm  3.0 mm (0. 18  0. 12 )   y   1206 - 3.0 mm  1 .5 mm (0. 12  0.06 )   y   0805 - 2 .0 mm  1 .3 mm (0.0 8  0.05 )   y   0603 - 1 .5 mm  0. 8 mm (0.06  0.03 )   y   0402 - 1 .0 mm  0.5 mm (0.04  0.0 2 )   y   0201 - 0.6 mm  0.3 mm (0.0 2  0.0 1 )   Construction: The SMD capacitor consists of a rectangular block of ceramic dielectric in whicha number of interleaved precious metal electrodes are contained. This structure gives rise to ahigh capacitance per unit volume. The inner electrodes are connected to the two terminations,either by silver palladium (AgPd ) alloy in the ratio 65 : 35, or silver dipped with a barrier layer of plated nickel and finally covered with a layer of plated tin (NiSn ) . Ceramic capacitor manufacture: The raw materials for the dielectric are finely milled andcarefully mixed. Then they are heated to temperatures between 11 00 and 1 300C to achieve therequired chemical composition. The resultant mass is reground and additional materials added to provide the required electric properties.The next stage in the process is to mix the finely ground material with a solvent and bindingadditive. This enables thin sheets to be made by casting or rolling.For multilayer capacitors electrode material is printed on the sheets and after stacking and pressing of the sheets co-fired with the ceramic compact at temperatures between 1 000 and 1 400C. The totally enclosed electrodes of a multilayer capacitor guarantee good life test behaviour as well. T antalum SMD capacitors Tantalum SMD capacitors are widely used to provide levels of capacitance that are higher thanthose that can be achieved when using ceramic capacitors. As a result of the differentconstruction and requirements for tantalum SMT capacitors, there are some different packagesthat are used for them. These conform to EIA specifications. y   Size A 3. 2 mm  1 .6 mm  1 .6 mm (EIA 3 21 6- 18)   y   Size B 3.5 mm  2 . 8 mm  1 .9 mm (EIA 35 28 - 21)   y   Size C 6.0 mm  3. 2 mm  2 . 2 mm (EIA 603 2 - 28)   y   Size D 7.3 mm  4.3 mm  2 .4 mm (EIA 7343-3 1)   y   Size E 7.3 mm  4.3 mm  4. 1 mm (EIA 7343-43 )      Electrolytic SMD capacitors Electrolytic capacitors are now being used increasingly in SMD designs. Their very high levelsof capacitance combined with their low cost make them particularly useful in many areas.Often SMD electrolytic capacitors are marked with the value and working voltage. There are two basic methods used. One is to include their value in microfarads (m F ) , and another is to use acode. Using the first method a marking of 33 6V would indicate a 33 Q F capacitor with aworking voltage of 6 volts. An alternative code system employs a letter followed by threefigures. The letter indicates the working voltage as defined in the table below and the threefigures indicate the capacitance on picofarads. As with many other marking systems the first twofigures give the significant figures and the third, the multiplier. In this case a marking of G 1 06would indicate a working voltage of 4 volts and a capacitance 0f  1 0 times 1 0^6 picofarads. Thisworks out to be 1 0 Q F L etter Voltage e 2 .5G 4J 6.3A 1 0C 1 6D 2 0E 2 5V 35H 50    above-board profile The height that a component such as a connector stands above thetop surface of the PCB acceptance tests A set of tests performed to determine the acceptability of a PCB. active component An electronic component whose parametric characteristics change whileoperating on an applied signal. adhesive dam A method of controlling the flow of adhesive material on inner layers of amulti layer board during lamination by providing an etched border of copper around theouter edges of the conductor layers. analogue ( circuit) (USA µanalog¶) A type of circuit that deals with continuously varyingvoltage or current values that represent physical quantities, and where the output varies asa continuous function of the input, as contrasted with a digital circuit. angle of attack The angle between the squeegee face and the stencil plane. anti-wicking contacts Contacts on components such as connectors or switches thatprevent entry of either flux or solder up into the contacts during the process that solders thecontacts to the PCB. aperture A predetermined shape (round, square, oblong, etc.), size (width, diameter), andtype (draw or flash) that is exposed on artwork film by aphotoplotter. aperture library A collection of standard aperture descriptions. aperture wheel Contains a set of individual physical apertures (or software definitions of apertures) that are specific for plotting a type or family of circuit board artworks. aqueous cleaning A generic cleaning approach that uses water in combination withneutralizers, saponifiers and surfactants. archiving data The process of relocating all the design and data files required to producean end product into a retrievable storage area. array A group of components arranged in rows and columns. artwork (master) A photoprocessing tool used to fabricate a printed circuit board thatconsists of an accurately scaled image of the required pattern on the surface of a stabletransparent film base.Confusingly, as well as describing the photoplotted film, the term µartwork¶ may refer just tothe Gerber files used to drive the photoplotter, but is also often used to include otherdocumentation used by a board house to manufacture a bare printed circuit board such asthe NC drill file. Seemaster artwork set.
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