Network Resistor Design Considerations
To achieve maximum system performance, in a range of applications, resistor networks or arrays with low TCR, close ratio tolerances and long term in circuit stability are required. In this post, we consider the key network resistor design and manufacturing issues the system designer should consider.
Network resistors are used in a wide range of precision amplifier applications as difference amplifiers, voltage reference divider circuits and precision sum/subtraction circuits. A network resistor design may deliver system board space savings and reduced overall component and logistics costs but their key advantages include increased reliability, improved temperature performance, improved stability and precision resistor matching.
Network Resistor Reliability
At the system level a network resistor can improve reliability as the on-board interconnect and circuit board connections may be reduced. Instead, interconnect between resistors may be routed on the network resistor substrate.
At the resistor component level an experienced thick film network resistor designer will recognise failures are generally due to external environmental factors such as mechanical and electrical stresses and will design the network resistor component accordingly. It is essential therefore that all relevant information on the application is shared to ensure this is fed into the design process and an appropriate selection of resistor material, substrate material and process technology may be made.
The choice of substrate material is directly linked to thermal performance and operation under pulse or surge conditions. The design parameters of the substrate impact on its mechanical performance, particularly when vibration or other mechanical stresses are present in the application.
The granular composition of the resistor material can make it susceptible to thermal and electrical stresses. Transient stress conditions can often lead to a long-term change in performance rather than a complete failure. Correct selection of materials, resistor component design and appropriate manufacturing processes can minimise the impact of mechanical and thermal stress.
Stability And Drift
One of the key advantages of a network resistor is the long-term stability of resistor values (in relation to each other). By manufacturing multiple resistors at the same time, on the same substrate, using the same materials and process long term stability is maximised while the impact of external factors is minimised.
One of the major disadvantages of using discrete resistors is variations in Temperature Coefficient of Resistance. With different TCR’s the same change in temperature can result in a different change in resistance over two discrete devices. The situation is made worse if two discrete resistors are not in close physical contact as the proximity of external heat sources may impact on the resistance of one resistor more than the other.
With resistors manufactured at the same time, through the same process, using the same materials the potential of temperature effects is reduced. With resistor devices in close proximity differential temperature effects are reduced. If the network resistor designer is provided with details of the required thermal performance a network resistor may be manufactured specifically to meet the demands of the application.
With common resistor element, substrate materials, design rules and manufacturing processes a network resistor component is an ideal choice for matched resistor applications. The resistors may be also trimmed if necessary for optimal resistance matching.
By working with an application specific resistor design and manufacturing partner the system designer can be confident they will achieve a network resistor design that is fine tuned to the demands of their application. Contact TSEC for advice on your next network resistor requirement.