Surface Mount Resistors or SMD Resistors are very small rectangular shaped metal oxide film resistor. They have a ceramic substrate body onto which is deposited a thick layer of metal oxide resistance. The resistive value of the resistor is controlled by increasing the desired thickness, length or type of deposited film being used and highly accurate low tolerance resistors, down to 0.1% can be produced. They also have metal terminals or caps at either end of the body which allows them to be soldered directly onto printed circuit boards.

smd-resistorSurface Mount Resistors are printed with either a 3 or 4-digit numerical code which is similar to that used on the more common axial type resistors to denote their resistive value. Standard SMD resistors are marked with a three-digit code, in which the first two digits represent the first two numbers of the resistance value with the third digit being the multiplier, either x1, x10, x100 etc. For example:

This image shows four surface-mount resistors (the component at the upper left is a capacitor) including two zero-ohm resistors. Zero-ohm links are often used instead of wire links, so that they can be inserted by a resistor-inserting machine.

smd-resistor-102Surface mounted resistors are printed with numerical values in a code related to that used on axial resistors. Standard-tolerance Surface Mount Technology (SMT) resistors are marked with a three-digit code, in which the first two digits are the first two significant digits of the value and the third digit is the power of ten (the number of zeroes). For example:

“334”= 33 × 10,000 ohms = 330 kilohms
“222”= 22 × 100 ohms = 2.2 kilohms
“473”= 47 × 1,000 ohms = 47 kilohms
“105”= 10 × 100,000 ohms = 1 megohm

Resistances less than 100 ohms are written: 100, 220, 470. The final zero represents ten to the power zero, which is 1. For example:

“100”= 10 × 1 ohm = 10 ohms
“220”= 22 × 1 ohm = 22 ohms

Sometimes these values are marked as “10” or “22” to prevent a mistake.

Resistances less than 10 ohms have ‘R’ to indicate the position of the decimal point (radix point). For example:

“4R7″= 4.7 ohms
“0R22″= 0.22 ohms
“0R01” = 0.01 ohms

smd-resistor-1502Precision resistors are marked with a four-digit code, in which the first three digits are the significant figures and the fourth is the power of ten. For example:

“1001”= 100 × 10 ohms = 1 kilohm
“4992”= 499 × 100 ohms = 49.9 kilohm
“1000”= 100 × 1 ohm = 100 ohms

“000” and “0000” sometimes appear as values on surface-mount zero-ohm links, since these have (approximately) zero resistance.