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Document Number: 28802 For technical questions, contact: [e-mail]
www.vishay.com
Revision: 18-Jun-10 1
VISHAY INTERTECHNOLOGY, INC.
Resistive Products
Application Note
MELF Resistors - The World’s Most Reliable and
Predictable, High-Performing Film Resistors
APPLICATION NOTE
By Udo Tribess, Vishay Draloric/Beyschlag Resistors
ABSTRACT
For more than 25 years, Vishay’s MELF resistors have
successfully met the demanding requirements of the
automotive industry. They offer superior SMD resistor
performance in terms of accuracy, stability, reliability, and
pulse load capability. The cylindrical construction of MELF
devices provides an optimal power rating and pulse load
capability related to the mounting space. Continuous
development has led to improved long-term stability and
moisture resistance, and allows high-temperature operation
to + 175 °C.
This paper explores why this resistor series has become so
successful, and why there is often no alternative to it today
in professional applications.
APPLICATION REQUIREMENTS
The continuously increasing requirements in professional
applications call for electronic components that provide
superior properties regarding:
• High-reliability electronics
• Predictable behavior of components
• Zero-defect philosophy
• Harsh operating environments
• Environmental awareness
The application areas with the most severe requirements
are:
• Automotive industry
• General industrial electronics
• Telecommunication infrastructure
For these applications, MELF resistors have been the
customers’ first choice for more than 25 years, meeting the
requirements for:
• Long-term stability
• Moisture resistance
• Reliability
• Temperature cycling in lead (Pb)-free assembly processes
MELF CONSTRUCTION
MELF resistors consist of a homogeneous film of metal
alloy deposited on a high-grade ceramic body. Nickel-
plated steel termination caps are pressed on the metalized
rods, before a special laser cuts a helical grove in the
resistive layer to achieve the target resistance value. The
resistor elements are covered by a protective coating,
designed for electrical, mechanical, and climatic protection.
The terminations receive a pure tin plating for best
solderability, either in lead (Pb)-free or lead-containing
soldering processes.
ELECTRICAL PERFORMANCE AND THERMAL
MANAGEMENT
The resistors’ cylindrical 0102, 0204, and 0207 case sizes -
equivalent to flat chip sizes 0805, 1206, and 2512 - are
suitable for various application requirements. Operating
voltages can be applied from 150 V (0102) up to 300 V
(0207); rated power dissipation at + 70 °C ambient
temperature ranges from 0.3 W (0102) up to 1 W (0207). The
maximum film temperature at the specified maximum power
rating is + 155 °C.
85 % Alumina Ceramic Rod
(96 % for MMU)
Metal Film Resistive Layer
Color Code Rings
Protective Lacquer
Steel Temination Cap
Plated Pure Tin on Nickel