width of the components in tenths of millimeters or hundredths of inches. For example, a metric 2520 component is 2.5 mm by 2.0 mm which corresponds roughly to 0.10 inches by 0.08 inches (hence, imperial size is 1008). Exceptions occur for imperial in the two smallest rectangular passive sizes. The metric codes still represent the dimensions in mm, even though the imperial size codes are no longer aligned. Problematically, some manufacturers are developing metric 0201 components with dimensions of , but the imperial 01005 name is already being used for the package. These increasingly small sizes, especially 0201 and 01005, can sometimes be a challenge from a manufacturability or reliability perspective. Two-terminal packages Rectangular passive components Mostly resistors and capacitors. Tantalum capacitors Aluminum capacitors Small-outline diode (SOD) Metal electrode leadless face (MELF) Mostly resistors and diodes; barrel shaped components, dimensions do not match those of rectangular references for identical codes. DO-214 Commonly used for rectifier, Schottky, and other diodes. Three- and four-terminal packages Small-outline transistor (SOT) Other DPAK (TO-252, SOT-428): Discrete Packaging. Developed by Motorola to house higher powered devices. Comes in three or five-terminal versions. D2PAK (TO-263, SOT-404): Bigger than the DPAK; basically a surface mount equivalent of the TO220 through-hole package. Comes in 3, 5, 6, 7, 8 or 9-terminal versions. D3PAK (TO-268): Even larger than D2PAK. Five- and six-terminal packages Small-outline transistor (SOT) Packages with more than six terminals Dual-in-line Flatpack was one of the earliest surface-mounted packages. Small-outline integrated circuit (SOIC): dual-in-line, 8 or more pins, gull-wing lead form, pin spacing 1.27 mm. Small-outline package, J-leaded (SOJ): The same as SOIC except J-leaded. Thin small-outline package (TSOP): thinner than SOIC with smaller pin spacing of 0.5 mm. Shrink small-outline package (SSOP): pin spacing of 0.65 mm, sometimes 0.635 mm or in some cases 0.8 mm. Thin shrink small-outline package (TSSOP). Quarter-size small-outline package (QSOP): with pin spacing of 0.635 mm. Very small outline package (VSOP): even smaller than QSOP; 0.4-, 0.5-, or 0.65-mm pin spacing. Dual flat no-lead (DFN): smaller footprint than leaded equivalent. Quad-in-line Quad-in-line: Plastic leaded chip carrier (PLCC): square, J-lead, pin spacing 1.27 mm Quad flat package (QFP): various sizes, with pins on all four sides Low-profile quad flat-package (LQFP): 1.4 mm high, varying sized and pins on all four sides Plastic quad flat-pack (PQFP), a square with pins on all four sides, 44 or more pins Ceramic quad flat-pack (CQFP): similar to