What are SMD Resistors? [caption id="attachment_944" align="alignright" width="103"] SMD resistors on a circuit board from a USB memory stick[/caption] SMD stands for Surface Mounted Device. An SMD is any electronic component that is made to use with SMT, or Surface Mount Technology. SMT was developed to meet the ongoing desire for printed circuit board manufacture to use smaller components and be faster, more efficient, and cheaper. SMDs are smaller than their traditional counterparts. They are often square, rectangular or oval in shape, with very low profiles. Instead of wire leads that go through the PCB, SMD's have small leads or pins that are soldered to pads on the surface of the board. This eliminates the need for holes in the board, and lets both sides of the board be more fully used. The manufacture of PCBs using SMT is similar to that for components with leads. Small pads of silver or gold plate or tin-lead are placed on the board for attaching the components. Solder paste, a mixture of flux and small balls of solder, is then applied to the mounting pads by a machine similar to a computer printer. Once the PCB is prepared, SMDs are placed on it using a machine called a pick-and-place machine. The components are fed to the machine in long tubes, on rolls of tape or in trays. These machines can attach thousands of components per hour; one manufacturer advertises a rate as high as 60,000cph. The board is then sent through a reflow soldering oven. In this oven, the board is slowly brought up to a temperature that will melt the solder. Once cooled, the board is cleaned to remove solder flux residue and stray solder particles. A visual inspection checks for missing or out-of-position parts and that the board is clean. SMD...
Standardization is a key element in the design of electronic components. A huge amount of effort and money is saved by having standards for resistor sizes, values, markings, symbols and measurement methods. Although international standards like the IEC (International Electrical Commission) and national standards such as ANSI (American National Standards Institute) are widely accepted, resistor manufacturers often use their own definitions. Therefore it is always important to carefully check the manufacturers’ documentation. Resistor color code Practically all leaded axial resistors up to one watt are marked with the electronic color code (international standard IEC 60062). The resistor color code is a marking system with colored bands that are painted on the resistor body. Together they indicate the resistor value and tolerance. Resistors can have 3, 4, 5 and 6 bands. The resistor color code chart is a handy table to decipher the coding system. Resistor color code calculator This interactive tool let’s you adjust a resistor within seconds and returns the resistance value, tolerance and temperature coefficient. It even indicates if the resistor belongs to an E-series (preferred values). [caption id="attachment_1600" align="alignright" width="100"] Surface mount[/caption] Resistor SMD code SMD (Surface Mount Device) resistors are marked with a (alpha)-numerical code to indicate the resistor value and tolerance. Often these resistors are too small for the resistor color code. Two popular marking systems exist: the 3 and 4 digit code and the EIA-96 code. Resistor values [caption id="attachment_2006" align="aligncenter" width="368"] The E12 series of resistor values, including their color codes.[/caption] Soon after resistors became mass produced, a system with preferred values was developed to minimize the number of different sizes that had to be produced. Now preferred values for resistors and other electronic components are defined in the international standard IEC 60063. The preferred values for electronics are defined in E-series. Resistors...