There are several thick film resistor types, each designed for specific applications. In this post, we discuss each of the main resistor types, their construction, key parameters and applications.
The Thick Film Resistor Marketplace
The global thick film resistor market was valued at just over $100m in 2020. It is supported by over ten major manufacturers based in Europe, the USA and the Far East. They produce a vast range of devices to support automotive, industrial, telecommunication commercial and medical markets.
Although the major manufacturers tend to only support volume markets, some do deliver devices for military and space markets in lower volumes. Specialist resistor manufacturers also cover these markets and satisfy the demand for custom thick film resistor devices in low to medium volume.
Chip (Surface Mount) Resistors
Chip resistors are by far the most common type of thick film resistor. As they tend to be
small and well suited to surface mount pick and place, they are often used in high-volume applications.
The construction of chip resistors is relatively simple. A resistive pattern is formed on a ceramic (often Alumina) substrate using the standard thick film manufacturing process. Metal end caps connect to the resistor pattern and complete the assembly. A surface mount
connection is made directly to the end caps.
Chip resistors are available with resistances between 0.1 and 100MOhm. Due to their size (and, therefore, their power handling capability), max power ratings are usually up to one Watt.
Thick Film Power Resistors
Power resistors are often used as protection devices. They protect against surge and electrical pulse events and ESD. They are also found in load bank and heat dissipation applications.
When selecting a thick film power resistor, the prime concern is the dissipation of energy (heat). The thermal performance and mass of substrate materials are, therefore, a key concern. Heat sinks can help and the ease of substrate to heat sink interface is a major advantage of thick film technology.
A wide range of power resistor packages is available. The TO style package is the most
common type, but there are also axial, MELF and surface mount options. Thick film power resistor power ratings generally vary between 5W and 2KW for general purpose devices.
Higher power ratings are available for specialist applications, but these are often immersed in oil or deionised water for cooling. Resistance values vary between 0.01Ohm and 500KOhm.
High Voltage Resistors
Thick film high voltage resistors are found in voltage regulation, balancing and voltage
conversion applications. They are also used as protection and safety devices.
In applications where stability and precision are critical, voltage coefficient of resistance
(VCR) is an important consideration. This impacts the choice of materials and the resistor construction.
High voltage resistor values are typically between 0.1Ohm and 50GOhm. Maximum working voltages can be up to 100KV.
Most heater resistors are relatively simple devices used in automotive and other high-volume applications. Lower volume, more specialised applications include medical applications and food processing industries.
While in many resistor applications removing excess heat is a concern with heater resistors, the reverse is true. Specialised substrate materials are often used to maximise heat transfer.
Thick film resistor networks are space-saving devices. They can also improve system reliability and reduce manufacturing costs.
High volume resistor network applications include pull-up/pull-down resistors and termination resistors. More complex devices are used in lower volumes in a wide range of applications. These include devices with several different resistor values in a single network.
Other Types Of Resistor – Overview
Thick film is one of many resistor technologies. It is widely used due to its relatively low cost, small size and low inductance.
Other resistor technologies such as thin film and metal foil can have superior performance in some precision applications. Ceramic resistors can have better pulse withstand capability and wirewound high power handling capability, but thick film resistors are suitable for most applications.
A vast range of thick film resistor types is available. The challenge is to choose the correct resistor for the application. The perfect resistor does not exist, and all resistor types have advantages and disadvantages. Should a standard device fail to match your requirements TSEC engineering team is always available to help.