Chip resistors are integrated circuit (IC) devices manufactured in square or rectangular chip packages. Resistors are components that oppose the flow of electrical current. They can be used to protect, operate, or control circuits. Resistors can have a fixed value of resistance, or they may be variable or adjustable within a certain range. As passive components, resistors can only reduce voltage or current signals and cannot increase them. Resistors — particularly chip resistors — make up the building blocks of many modern electronic devices.

Resistance

The resistance of an element measures its opposition to electric flow, expressed in ohms (Ω). Every material has a specific resistivity, which measures the strength of this opposition. For an even cross section of an element, the resistance ® is proportional to the material's resistivity (ρ) and length (L), and inversely proportional to area (A).

This principle is analogous to a roadway or pipe, where congestion (larger ρ) and longer paths (larger L) make flow more difficult (increasing R), while wider or large diameter sections (larger A) improve flow (decreasing R). Consequently, the construction (size, shape, and material type) of a resistor determines its resistance value, as described in the table below.

Specifications

Packaging

Chip resistors are typically surface mount devices (SMD) in that they do not have leads like through hole technology (THT) devices. Instead, they are mounted directly onto a printed circuit board (PCB). Chip resistors are almost always square or rectangular, with the length and width of the device determining their power ratings.

 A cross-section of a thick film chip resistor. Image credit: Mini-Systems Inc.

The table below illustrates the most common chip resistor sizes and designations. A chip's nominal dimensions can easily be determined by dividing its metric designation in two and placing a decimal point between the numerals of each pair. For example, a 0402 chip measures 0.4 mm x 0.2 mm, while an 1812 package measures 1.8 mm x 1.2 mm; the latter package also features a higher power rating due to its larger size.

Resistor Technology

Chip resistors may use a variety of technology or construction types, each with significant advantages and disadvantages. Some common types are listed below.

Thin film technology relies on the deposition on a thin metallic coating onto a ceramic substrate. Thin film resistors feature very high resistance per given area, making them economical and space-efficient. Disadvantages include the film's susceptibility to failure due to elevated temperatures, water vapor, and chemical contamination.

A thin film resistor. Image credit: EEWeb

Thick film resistors are produced by stenciling a resistive metallic paste onto a base. They provide high resistance per area and cost much less than comparable technologies such as wirewound resistors. While their frequency response is comparable to foil and thin film devices, thick film resistors are much noisier. Despite their drawbacks, they are widely used in circuit sections requiring less precision and durability.

Foil resistors feature a metal foil applied to a ceramic substrate which has been photo-etched with a resistive pattern. This process creates a resistor with the favorable characteristics of high stability, non-inductance, low capacitance, and low noise without sacrificing accuracy and speed.

Metal Foil Resistor. Image credit: EETimes 

Standards

Chip resistors may be designed, manufactured, and tested according to various standards. Common chip resistor standards include:

• BS EN 140401-801 Specification for rectangular low power SMD resistors
• Fixed film chip resistors
• Film chip resistors

References

EETimes - Strengths and weakness of common resistor types

Image credits:

Anaren | Mini-Systems Inc. | EEWeb | EETimes