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Electronics Buyers' Guide

Electronics Manufacturing & Production Handbook 2019


 

Thermistors designed for durability
10 September 2002, Passive Components

PTC thermistors used as heating elements are self-adjusting and have no glowing parts. They are mainly used in automotive electronics (diesel preheating, auxiliary heating of passenger compartment, and protection of valves against condensation and icing, etc) and in domestic appliances (washing machine door locks, radiator thermostats). Further applications are found in evaporators for vapour dispensers and insect sprays as well as small household appliances. Passives maker Epcos offers rectangular and disk PTC heating elements for various temperature and voltage ranges in standard and customer-specific geometries.

Component service life is particularly important in automotive electronics and domestic appliances. This is influenced mostly by the type of contact electrodes used. The electrical contacts of PTC thermistors must be built-up in two layers. The outer layer of a PTC heating element is a thick-film silver electrode (about 10 µm thick), which makes possible the clamp contact common in heating applications. The inner metallisation layer serves to overcome the barrier layer between the high-resistance ceramic material and conductive contact surface. Until recently, this was done by silk-screen printing with silver containing a small quantity of zinc. Epcos has now switched to sputter technology to produce the inner metallisation layer. Here the barrier layer is broken down by a thin layer of chrome (less than 1 µm), which is protected by an equally thin layer of nickel.

Sputter films feature outstanding uniformity, density, purity and adhesion (used to make semiconductors, CDs and optical devices). In a plasma discharge in a vacuum chamber, metal atoms are dislodged from a pure metal target. These particles cross a vacuum and are precipitated on the surface to be metallised. This process permits metallisation without the use of contaminating binding agents. Long-term tests have shown that under conditions of continuous load, elevated temperature and humidity, the mean variation in resistance is more than halved thanks to the improved electrode. This is an overriding advantage in critical safety applications in automotive electronics or white goods. The new metallisation also makes it possible to attach a migration-free silver electrode, which improves long-term performance further, especially in ambient humidity.


Credit(s)
Supplied By: Electrocomp
Tel: +27 11 458 9000
Fax: +27 11 458 9034/5
Email: andrew@electrocomp.co.za
www: www.electrocomp.co.za
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Further reading:

  • Big is beautiful: The benefits of large capacitors
    28 August 2019, Passive Components
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  • N-channel enhancement mode FET
    26 June 2019, Electrocomp, Power Electronics / Power Management
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  • Shielded power inductors
    31 July 2019, RF Design, Passive Components
    High-temperature power inductors from Coilcraft are available with inductance values from 22 to 47 µH, current ratings up to 5,5 A, and low direct current resistance (DCR). The inductors in the XAL7050 ...
  • Sealed enclosures for industrial electronics
    26 June 2019, Electrocomp, Enclosures, Racks, Cabinets & Panel Products
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  • Consumer grade power inductors
    26 June 2019, Electrocomp, Passive Components
    Bourns is introducing the Model SRP7028C, SRP1038C and SRP1770C high-current shielded power inductor series, designed to meet today’s high current density requirements in various types of consumer electronics ...
  • High-current shielded power inductors
    26 June 2019, Electrocomp, Passive Components
    The inductive components product line at Bourns has created the Model SRP5050FA and Model SRP7030CA high-current shielded power inductor series, designed to meet today’s high current density requirements ...

 
 
         
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