Millions of SMD resistors are used for production of the electronic equipment from cell phones to TVs and MP3 players. The small sizes allow to place them in rather small internal space. However they possess also a number of shortcomings. One of the most significant is the big level of dispersion of power.
Design of SMD resistors
SMD resistors have a rectangular shape. From two parties the rectangle has metallized sites. It gives them the chance to contact to the printed circuit board after soldering.
The resistor consists of a ceramic substrate on which the metal oxide film is besieged. The actual thickness and length of a film determines resistance of any given element. That SMD resistors are manufactured with metal oxide use they are rather reliable and, as a rule, have resistance small internally.
The substrate consists of a ceramic element with the high content of alumina. It gives very good isolation on which the resistive element is established. Connections also play an important role. They have to create reliable contact of a resistive element and the chip of the resistor and also to provide the high level of conductivity. It is reached by use of an intermediate layer on the basis of nickel and an outer layer from tin, for ensuring good soldering. Resistors for superficial installation have various standard sizes. Technologies do not stand still and therefore the sizes of radio components constantly decrease. In 2014 0.05 millimeters were the usual size for the SMD resistor.
Characteristics of the SMD resistor
SMD resistors make various companies. Therefore characteristics of elements with identical face value can differ strongly from each other. There are several key parameters to which it is necessary to pay attention. Rated power requires special attention. For designs of resistors with use of superficial installation the level of power which can be disseminated, less, than for wire components. Because SMD resistors are manufactured with use of a film of metal oxide, they have rather close values of tolerances. At the same time deviations within 5, 2 and 1 percent are the most widespread. For special details of value there can be 0.5 and 0.1 percent. SMD resistors usually have good temperature coefficient. Values 25, 50 and 100 of units of pulse modulation on 1 wasps meet most often.
Application
SMD resistors are used in many designs. The size allows to use them not only for compact payments, but also for automatic methods of assembly. Other their advantage is that they well work in radio sets. Thanks to the small size at such resistors very small false inductance and capacity. Nevertheless high levels of dispersion of power have to be taken into account when calculating an electromagnetic contour.