Chip Resistor Failure Modes

Key Takeaways

• Chip resistors are part of the surface-mount resistor family and are principal components in printed circuit boards.

• The three types of chip resistors are thin film resistors, thick film resistors, and foil resistors.

• Chip resistor failure modes usually result in either electrical open circuit conditions or large resistance variations.

Resistors are the passive elements most frequently used in electronic circuits. They are available as either fixed or variable resistance elements. Resistors are used in various circuits to deliver functions such as impedance matching, loading, current limiting, current detection, voltage division, and biasing. With each application, the resistor type changes, and with the changes in environmental and circuit conditions, various chip resistor failure modes exist. In this article, we will take a look at these chip resistors and their failure modes.

Chip Resistors 

By incorporating integrated circuit technology, chip resistors are manufactured as chip packages. They are not suitable for through-hole-type circuit boards and are surface-mount resistors without any leads. The power rating of a chip resistor is dependent on the length and width of the chip resistor, which is generally either in a square or rectangle shape. Chip resistors are most suitable for applications in small footprint circuit boards or miniaturized electronic devices. 

Structure 

The internal structure of a chip resistor consists of conductors in the top, bottom, and back of the resistor as well as substrate, glass, notch, end caps, and the resistor element. The thickness of the resistor element is constant and usually present in a square geometry. The nominal resistance of a chip resistor is established by the resistor element.

The resistor element is placed over the substrate, which is usually made of alumina-based ceramic. The resistor material is connected to the ends of the chip resistor to make circuit connection possible. The resistor material is cut to match the nominal resistance value, and the entire arrangement is overcoated with a glass-like material to form the finished product. Using surface mount technology, the chip resistor is connected to the circuits. 

Chip Resistor Types

There are three main types of chip resistors:

1. Thin film chip resistors - Thin film chip resistors use a thin metallic coating on the substrate. Their advantages are that they have a high resistance value over a small footprint and they are cheap and space-saving. 
2. Thick film chip resistors - Thick film chip resistors use a resistive metallic paste on the base. Their advantages are similar to thin film chip resistors but they lack precision and durability. 
3. Foil chip resistors - Foil resistors use metal foil on the substrate to photo-etch resistive patterns onto it. The advantages of foil resistors are low noise, high accuracy, high speed, low capacitance, low inductance, and high stability. 

Chip Resistor Failure Modes

Chip resistor failure modes are influenced by internal and/or external factors. The severity of the chip resistor failure due to internal or external factors varies with the type of construction. Chip resistor failure modes can result in two conditions:

• Electrical open circuit conditions
• Large resistance variations

Usually, environmental conditions, electrical, or mechanical stresses on chip resistors are responsible for chip resistor failure modes. Some common causes of failure modes in chip resistors are given in the table below.

Chip resistor failure modes

Elevated temperature is the main reason for most chip resistor failure modes in electronic circuits, which is why thermal management is critical. Cadence software offers tools that help designers with failure analysis efforts and the improvement of circuit reliability.  

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