Brochure

MELF Resistors - The World’s Most Reliable and
Predictable, High-Performing Film Resistors
www.vishay.com For technical questions, contact: [e-mail]
Document Number: 28802
2 Revision: 18-Jun-10
Application Note
Vishay Intertechnology, Inc.
APPLICATION NOTE
The ability to withstand these operating conditions is
ensured by the devices’ cylindrical construction. Compared
to chip resistors of the same mounting space, the area of the
effective resistive film is about three times greater, and the
larger volume of the ceramic body ensures sufficient heat
dissipation.
TEMPERATURE COEFFICIENT, TOLERANCE,
AND STABILITY
The resistors’ dedicated metal alloy material, applied by a
sputtering process followed by thermal treatment, offers
excellent properties with respect to temperature coefficient
and load-life stability. The smooth helical laser, cutting
without damaging the ceramic body, enables very narrow
tolerances and creates a current path of constant width for
a uniform heat distribution. Consequently, resistor
temperature coefficients down to ± 5 ppm/K are available,
as well as tolerances down ± 0.02 %. Long-term stability
results in a superior maximum resistance change (ΔR/R) of
0.05 % after 8000 h operation for high precision MELF
resistors.
PULSE LOAD CAPABILITY
Another aspect of the resistors is their reliability when
exposed to various overload conditions. The metal film
technology, together with the cylindrical construction of the
MELF devices, provides an advantage compared to
standard thick and thin film chip resistors in regard to pulse
load capability. As shown in the diagram below, thick film
flat chip resistors fail at much lower pulse loads than thin film
flat chips, and both types are outperformed by thin film
MELF resistors.
Fig. 1 - Pulse load test - resistance change for different
1 kΩ resistors of comparable body size
RELIABILITY
Tens of billions of MELF resistors have been delivered
to customers in the automotive, general industrial industries
and telecommunication infrastructure. The devices’
approved manufacturing process and certified quality
management system are the base for the resistors’ excellent
observed failure rate of FIT
OBSERVED
≤ 0.1 x 10
-9
/h.
APPROVALS
Vishay’s MELF resistors are tested in accordance with
several international standards, such as EN140401-803
(superseding CECC40401-803). Approval of conformity is
indicated by the CECC logo on the package label.
Furthermore, the components meet the requirements of
AEC-Q200, which is the most important standard requested
by the automotive industry. Environmental aspects are also
respected. All products are completely lead (Pb)-free and
comply with the Global Automotive Declarable Substances
List (GADSL), which includes full compliance with the RoHS
directive.
HIGH-TEMPERATURE APPLICATIONS
Further development of the existing MELF series has
enabled operation at ambient temperatures to + 175 °C
(MELF HT series). This improvement comes along with a
higher power rating capability (e.g. from 0.4 W to 0.5 W for
the MMA 0204 HT).
For the MELF HT series, three operation modes are
specified (e.g. data for size 0204):
• Standard: 0.25 W (derating from + 70 °C)
• Power: 0.40 W (derating from + 70 °C)
• Advanced temperature: 0.50 W (derating from + 70 °C)
Fig. 2 - Derating diagram for MMA 0204 HT
The maximum resistance change (ΔR/R) after 1000 h of
operation is specified for the operation modes:
• Standard: 0.10 %
• Power: 0.15 %
• Advanced temperature: 0.25 %
This performance is unrivalled by thick film or even by most
thin film flat chips available on the market. With their
improvements in stability and moisture resistance, and by
achieving a higher operating temperature, MELF resistors
continue to be the first choice for high-reliability professional
electronics.
20
- 20
10
0
- 10
1 100010010
Resistance Change (%)
Pulse Load (W)
Thick Film Chip
Thin Film Chip
Thin Film MELF
0.6
0
0.5
0.4
0.3
0.2
0.1
0200175150125100
70
5025
Power (W)
T
amb
(°C)
High Temperature
Power
Standard