Resistors come in various packaging styles and sizes. Currently, rectangular surface mount (SMD) resistors are commonly used, but old-fashioned axial resistors are still widely used in through hole designs.

SMD resistor size

The shape and size of surface mount resistors have been standardized, and most manufacturers use the JEDEC standard. The size of the SMT resistor is represented by a numerical code, such as 0603. This code contains the length and width of the encapsulation. Therefore, the English code 0603 represents a length of 0.060 "and a width of 0.030".

The SMD encapsulation code can be provided in English or metric units. Generally speaking, English codes are more commonly used to represent packaging dimensions. It is puzzling that even with the use of imperial naming conventions, metric dimensions are often used in the design process of printed circuit boards (PCBs). Generally speaking, you can assume that the code is in imperial units, but the dimensions used are in millimeters. The size of the SMD resistor used mainly depends on the required rated power, the feature size of PCB manufacturing, and the limitations of the pickup and release equipment. The following table lists the commonly used surface mount sizes and specifications.

Resistor size

When designing surface mount components, the correct pad size and pattern should be used. The following table shows the recommended sizes for common surface mount packaging pad patterns. The following table lists the dimensions of reflow soldering. For wave soldering, use smaller pads.

Axial resistor size

The size of axial resistors is not standardized like SMD resistors, and the sizes used by different manufacturers are usually slightly different. In addition, the size of the axial resistor depends on the rated power and the type of resistor, such as carbon composition, wire winding, carbon film or metal film. The following table provides the dimensions of common carbon film and metal film axial resistors. Whenever you need to know the exact size, be sure to check the manufacturer's data sheet of the component.

Axial resistance size

MELF resistor packaging dimensions

Metal electrode lead-free surface (MELF) is another type of surface mount resistor packaging. The main advantages of using MELF instead of standard SMD packaging are lower thermal coefficient and better stability. The resistance temperature coefficient (TCR) of thin film MELF resistors is usually between 25-50 ppm/K, while the TCR of standard thick film SMD resistors is usually>200 ppm/K. The lower TCR of MELF resistors is due to their cylindrical structure. This cylindrical structure also brings obvious drawbacks to packaging, mainly when it is necessary to use a pickup and play machine to place components. Due to its circular shape, special suction cups and more vacuum are required.

There are three common MELF packaging sizes: MicroMELF, MiniMELF, and MELF. The following table lists the characteristics of these types.

MELF resistor