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Thin Film SMD Precision Resistors

What are Precision Resistors?

A good starting point is an attempt to define what constitutes a precision resistor.  Back in the 1960’s a resistor with a tolerance of 1% could have been classified as a precision resistor.  Fast forward 50 years and many manufacturers have discontinued any tolerance more relaxed than 1% from certain ranges.

With modern advances in materials, production processes and quality controls, it would be sensible to classify 0.5% or tighter, a precision resistor. 

Another important consideration when specifying precision resistors is the TCR (Temperature Coefficient of Resistance).  It’s safe to say a precision resistor will have a TCR of 25ppm/DegC or less.

We now have the foundations of how we are going to define our precision resistor: Tolerance is 0.5% (or tighter) & TCR is 25ppm/DegC (or less). 

Several other factors need to be considered when specifying a precision resistor, obviously, outside the fundamental ohmic value!  These include; package type, voltage, power rating, noise, stability, inductance and VCR (Voltage Coefficient of Resistance).

For the purpose of this article, tolerance and TCR are going to be the main fundamentals we will concentrate on.

The Perception of a Precision Resistor

Myth Buster – Most precision resistors are expensive and difficult to obtain!

Maybe a more accurate statement could be “many SMD precision resistors are overpriced”.

If we probe into the past, the reasons for this become clear.  Back in the 1980’s, when SMT was just starting to become the norm, manufacturers of thru-hole precision resistors were unwilling to sacrifice their existing and well established thru-hole precision business.  When you add the necessary capital investment and associated R&D costs required to develop a new product for mass production, the result was, that in many instances, the SMD precision resistor counterpart had a higher cost per unit. 

As time has passed, technical developments have been released and now it’s possible to have a standard, off-the-shelf specification of 0.01% and 1ppm/DegC. What is unusual, in comparison to other passive technologies, is that SMD precision resistors have remained at a premium to users.

The difference – DMTL!

DMTL have always been at the forefront of SMD technology – we have a passion to work with world leading manufacturers to offer the best price, support and quality to our customers and SMD thin film precision resistors are no different.  DMTL are fully franchised for Taiwanese manufacturer Viking Tech

Viking Tech is a well-established manufacturer of resistors, including thin film SMD precision resistors and with factory approvals comprising of ISO9001/14001/TS16949, quality is a certainty.

Typical specifications include:

0402 / 0603/ 0805 / 1206 – 0.05% / 0.1% / 0.25% - 25ppm / 10ppm / 5ppm

A Little About DMTL & Viking Tech

DMTL have many OEM / CEM customers who rely on Viking Tech for SMD thin film precision resistors, offering price competitiveness, quality product, industry beating leadtimes (currently 5 weeks) and, with the combination of support from DMTL, offer consistency of supply with a proactive approach to holding buffer-stock, working to schedule orders, call-off orders etc..

Maybe we can change the perception “most precision resistors are expensive and difficult to obtain” once and for all…

The most common thin film SMD precision resistor DMTL supply is the AR Series from Viking Tech:

Viking AR Series Datasheet

This is a fit, form and function alternative to many other manufacturer’s parts including:

  • Cyntec - RR Series
  • KOA - RN73 Series
  • Panasonic - ERA Series
  • Susumu - RR Series
  • Vishay - TNPW e3 Series
  • Walsin - WF Series
  • Yageo - RT Series

These series types, along with many other passive components, are listed on the handy DMTL Cross-Reference Tool