A Quick Guide to Resistor Sizes and Packages PDF
Resistors are available in a large number of different package styles and sizes. The most commonly used today are the rectangular surface mount (SMD) resistors, but also the good old axial resistor is still used extensively in through-hole designs. This page provides information on the dimensions of SMD, axial, and MELF packages. It also provides some recommended land patterns for SMD components for solder attach to PCBs.
A Brief Introduction to Resistors
What is a Resistor?
Resistor is electrical or electronic components which resist the flow of current across the resistor device.
The resistance to current flow results in a voltage drop across the resistor device. Resistors are used extensively throughout electrical and electronic circuits.
Resistor devices may provide a fixed, variable, or adjustable value of resistance. Adjustable resistors are refers to as rheostats, or potentiometers. Resistor values are expressed in Ohms, the electric resistance unit.
Resistors are incorporated within an electrical or electronic circuits create a known voltage drop or current to voltage relationship.
If the electrical current in a circuit is known (current is measured in amperes), then a resistor can be used to create a known potential difference (voltage difference) proportional to that current. Conversely, if the voltage drop (potential difference) across two points in a circuit is known, a resistor can be used to create a known current proportional to that difference.
An attenuator is a network of two or more resistors (a voltage divider).
A line terminator is a resistor at the end of a transmission line or daisy chain bus, designed to match impedance and minimize reflections of the electronic signal.
SMD Resistor Sizes
The shape and size of surface mount resistors are standardized, with most manufacturers using the JEDEC standards. The size of SMD resistors is indicated by a numerical code, such as 0603. This code contains the length and width of the package. So, the imperial code 0603 indicates a length of 0.060″ and a width of 0.030″.
The length and width of an SMD resistor case can be identified by the package code used. For example, an imperial 0805 resistor case will have a length of 0.08 inches and a width of 0.05 inches, while an imperial 0603 resistor package will have a length of 0.06 inches and a width of 0.03 inches. The imperial code is more commonly used in the PCBA industry.
The table below lists the different commonly used resistor packages and resistor cases in SMT assembly for PCBA:
MELF Resistor Sizes
A metal electrode leadless face (MELF) is another kind of surface mount resistor package. MELF packages have lower thermal coefficients and are more stable than standard SMD packages. Typical thin film MELF resistors have a temperature coefficient of resistance (TCR) ranging from 25 to 50 ppm/K, in contrast to standard thick film SMD resistors with TCR above 200 ppm/K. MELF resistors have a lower TCR due to their cylindrical design.
Solder Pad Land Pattern
When designing with surface mount components, the right solder pad size and land pattern should be used
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