What are the advantages of thick film resistors vs thin film resistor technology? In this post, we define the ideal resistor and discuss how thick film and thin film resistors compare with that ideal.
The Ideal Resistor
The perfect resistor has zero capacitance and inductance. It has a fixed resistance value that does not vary over its entire in-service life.
External harsh environmental factors and electrical and mechanical stresses have no impact on resistance value. The ideal resistor has a high resistance per unit area.
Thick Film Resistor Construction
A paste, composed of metal oxides in a coarse film form, is blended with an organic solvent-based carrier and a binder. This mixture is then applied to a flat substrate (usually Alumina).Sequential layers of the resistance material are added to deliver the required resistance value.
The carrier stabilises the resistor pattern. During the firing process the glassy frit acts to securely bond the resistor material to the substrate.
In some cases, the resistance pattern may undergo a final abrasion process. This final step fine-tunes the resistance value to meet exact specifications.
Thin Film Resistor Construction
Thin film resistor technology uses a deposition rather than a printing process. The resistor layer is typically 1000x thinner than used in thick film.
Substrate materials include Alumina, Silicon and GaAs substrate. The thin film consists of a layer of resistive material (typically 50 to 250 Angstroms) thick.
A multi-step sputtering process adds mechanical and electrical foundation layers. This is followed by a bulk conductor layer of copper. A photo-lithographic process forms both a conductor and resistor pattern.
Comparing Thick Film & Thin Film Preformance
The main differences in performance between thick film and thin film resistors are discussed, below:
Capacitance and inductance. Thin film resistors feature lower parasitic inductance and capacitance. They are, therefore, generally more suited to very high frequency applications than thick film resistors.
Thick film resistors are adequate for most applications and given their cost advantage, tend to be the first choice up to the RF frequency range.
Resistor value: Thin film resistors tend to be available with lower resistor values than thick film.
Resistor tolerance: Thick film resistor tolerances tend to be 10x higher than Thin Film.
Stability: Thin film resistors have higher long-term resistance stability than thick film.
Environmental factors: Thin film technology is vulnerable to environmental factors and mishandling damage. Thick film resistor technology is more robust than thin film.
TCR: Thin film resistors have lower TCR values than thick film. This means they are more suited to applications that require high precision over a wide temperature range.
Specialist thick film resistor manufacturers can improve TCR performance, but, in general, thin film is superior.
Noise: The structure of thin film resistors generally makes them the first choice in low-noise applications. Specialist thick film resistors are found in low-noise applications, including audio.
External stresses: Thick film resistors are more robust than thin film. Surge and ESD event survivability of Thin film technology is poor.
Power handling: Due to their construction, Thin film resistors are not used in power applications.
Size: for a given resistance value, thin film resistors are (in general) smaller than thick film resistors
Cost Comparison
Cost depends on the cost of materials, manufacturing tools and processes and the scale of production. Thick film resistor materials are cheaper and more readily available than those used to produce thin film.
Thin film resistor manufacture requires sophisticated, precision equipment and a strictly controlled environment. In contrast, thick film utilises the long-established screen printing process. Thick film resistor manufacturing is simpler than thin film and requires less sophisticated equipment.
The cost of material tends to reduce with volume. Higher volumes means equipment costs can be amortised over more pieces. This means that the cost of thin film can approach that of thick film at very high volumes, but at lower volumes thick film has a clear cost advantage.
Resistor Application Considerations
Any thick film vs thin film resistor comparison reveals distinct advantages and applications for each type
As Thick film resistors are relatively low-cost and resistant to external stresses, they are widely used, across many applications. They offer robustness, cost-effectiveness, and suitability for power applications.
Thick film resistors exhibit higher tolerance to external stresses such as overvoltage, surge events, and ESD. This makes them the preferred choice for diverse applications where durability is paramount.
Thin film resistors excel in precision, stability, and performance at high frequencies. Thin film resistors are found in high precision, RF, microwave, and low-noise applications.
However, higher manufacturing costs and their vulnerability to moisture and mishandling restricts their use to specialised applications and high-volume production scenarios.
Ultimately, deciding on thick film vs thin film resistors hinges on specific application requirements. It is important to balance cost versus precision, stability, and environmental resilience. An Understanding of the distinct advantages of each resistor type allows for informed decision-making.