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Design Engineers! Why Use Current Sensing & Shunt Resistors?Posted on March 13, 2015 | By Rick Grigalunas | Leave a response 
Design Engineers!  Why Use Current Sensing
& Shunt Resistors?

One Reason. 
To Know the amount of current being delivered to a load

“Through Thick and Thin1…Film Resistors of Course”

I was recently asked a few questions on SMT chip resistors.


What is the difference between thick and thin film resistors?  

How thick is a thick film resistor?

Let’s first discuss what is the thickness of a “thick film” versus a “thin film”.              A traditional dimensional2 dividing line has been ~5μm (~0.2 mils or ~50,000Å Angstrom3). Thick films are typically 10-50 μm thick and thin films are from 10 nm-2 μm in thickness. However, a more functional definition, based on the resistor fabrication technique, is described below.

 
Thick film resistors (Figure 1) are fabricated with an additive process where conductive; dielectrics, and resistive materials are “silk screened” with a pattern onto an alumina ceramic substrate. Electrodes are deposited with a conductive material and fired into the ceramic at about 850°C. Next the resistive film is deposited and fired. The resistor is designed on the low side (~ -20%) so that laser cuts during trimming will increase the resistance and bring it into value. The resistor is then coated, and metalized on its edges and plated.

Thin film (or metal film) (Figure 2) resistors are fabricated with a subtractive process where conductive, insulative, and resistive materials are vacuum deposited and selectively etched with a photographic pattern onto an alumina ceramic substrate. The resistor is then laser trimmed (Figure 3), coated, and metalized on its edges and plated.
             

 
The electrical attributes of some of the common resistor fabrication technologies are shown in Table I below.

Table I Resistor Fabrication Technology versus Electrical Characteristics5

“As a result, thick film resistors are generally cheaper than their thin film counterparts, but the tolerance and temperature coefficients one can get out of thin film resistors are generally better. Depending on the materials used, there is plenty of overlap between the two, but all things equal, thin film offer better performance for a cost premium.”6

References

1 Wise Geek, What are the Origins of the Phrase "Through Thick and Thin"?

2 Mil-Std-883 TM 2010 paragraph 3f 38 & 39

3 Wikipedia Angstrom

4 Questech AN009-Thick and thin film Resistor trimming Application note 

5 “Strengths and weaknesses of common resistor types” Yuval Hernik, Vishay                                         Intertechnology 5/31/2010

6 “Difference between thin film and thick-film precision surface mount resistors” 

      electronics.stackexchange

For Further Reading

PANASONIC SURFACE MOUNT RESISTORS TECHNICAL GUIDE

Selecting the best resistor technology for the application  Yuval Hernik, Director Application Engineering, Vishay Precision Group (VPG) - December 17, 2012 EDN Blog

The Electronics Handbook, Second Edition section 2.1 Resistive elements

 Edited by Jerry C. Whitaker  ‪CRC Press, ‪Apr 27, 2005 

Resistor Links on my web site

See EDN BLOG