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Damage to thick-film resistors due to surges(r_what10)

Chip Resistor Failure Modes

Damage to Thick-Film Resistors Due to Surges

Surges are large voltages or currents instantaneously applied to circuits. Well-known examples include lightning and static electricity.

Surge voltage applied to a resistor may affect the resistance characteristics due to excessive electrical stress or result in damage (worst-case scenario).

Schematic:Surge  - Resistive material is damaged by load concentration, possibly resulting in resistance change.

Increasing Surge Resistance

One method for improving surge resistance is explained below.

  • Utilize materials with strong surge resistance
  • Increase the distance between electrodes, minimizing chip damage due to a smoother potential gradient.

Increasing the chip size will lengthen the distance between electrodes and provide greater surge resistance, but requires a larger mounting area.

For Sets With Insufficient Board Space Requiring Further Miniaturization but Need to Protect Against Surges

Anti-surge chip resistors provide superior surge resistance in a compact size.

ESD Test (EIAJ Compliant) Human Body Model
TypeSizeGuaranteed Surge Resistance Value
ESR011005mm
(0402inch)
2kV
ESR031608mm
(0603inch)
3kV
ESR102012mm
(0805inch)
3kV
ESR183216mm
(1206inch)
3kV
ESR253225mm
(1210inch)
5kV
LTR102012mm
(0805inch)
3kV
LTR183216
(1206inch)
3kV
LTR505025mm
(2010inch)
3kV
LTR1006432mm
(2512inch)
3kV

ROHM Anti-Surge Chip Resistors:

  1. Utilize materials that provide superior surge resistance
  2. Adopt a proprietary resistive element design that minimizes damage to the chip by providing a smooth potential gradient
Schematic:Differences Between Conventional and Anti-Surge Resistors - ROHM's anti-surge resistors feature a longer conduction path between electrodes, minimizing chip damage by smoothing out the potential gradient.
graph - Surge Resistance Characteristics Comparison ESD Test (EIAJ Compliant) Human Body Model

ROHM's anti-surge chip resistors feature improved the power handling characteristics and a revised element shape to achieve higher rated power than conventional types.

SizeESR SeriesMCR Series
10050.2W0.063W
16080.25W0.1W
20120.4W0.125W
32160.33W0.25W
32250.5W0.25W
5025-0.5W

ROHM's ESR and LTR series provide improved surge-resistance characteristics and higher rated power while maintaining size.

Lineup

Part No.SizeRated Power
(70℃)
Maximum
Element
Voltage(V)
Resistance
Tolerance
Temperature Coefficient
of Resistance (ppm/℃)
Resistance RangeOperating Temp. Range(℃)Automotive Qualified
(AEC-Q200)
SDRSeries
NewSDR0316081/4W
(0.25W)
150J(±5%)±2001~10MΩ(E24Series)-55~
+155
Yes
F(±1%)±200
±100
1~9.76Ω(E24,96Series)
10~10MΩ(E24,96Series)
D(±0.5%)±10010~1MΩ(E24,96Series)
ESRSeries
ESR0110051/5W
(0.2W)
50J(±5%)+500/-250
±200
1Ω~9.1Ω(E24Series)
10Ω~10MΩ(E24Series)
-55~
+155
Yes
F(±1%)±10010Ω~976kΩ(E24,96Series)
1MΩ~2.2MΩ(E24Series)
ESR0316081/4W
(0.25W)
150J(±5%)±2001Ω~10MΩ(E24Series)Yes
F(±1%)±200
±100
1Ω~9.76Ω(E24,96Series)
10Ω~10MΩ(E24,96Series)
D(±0.5%)±10010Ω~1MΩ(E24,96Series)
ESR1020122/5W
(0.4W)
150J(±5%)±2001Ω~30MΩ(E24Series)Yes
F(±1%)±1001Ω~10MΩ(E24,96Series)
D(±0.5%)±10010Ω~1MΩ(E24,96Series)
ESR1832161/3W*1
(0.33W)
200J(±5%)±2001Ω~15MΩ(E24Series)Yes
F(±1%)±1001Ω~10MΩ(E24,96Series)
D(±0.5%)±10010Ω~1MΩ(E24,96Series)
ESR2532251/2W*1
(0.5W)
200J(±5%)±2001Ω~10MΩ(E24Series)Yes
F(±1%)±1001Ω~10MΩ(E24,96Series)
D(±0.5%)±10010Ω~1MΩ(E24,96Series)
LTRSeries
LTR10 20121/4W
(0.25W)
150J(±5%)±2001Ω~1MΩ (E24Series)-55~
+155
Yes
F(±1%)±1001Ω~1MΩ(E24,96Series)
D(±0.5%)±10010Ω~1MΩ(E24,96Series)
LTR1832163/4W
(0.75W)
200J(±5%)±2001Ω~1MΩ(E24Series)Yes
F(±1%)±1001Ω~1MΩ(E24,96Series)
D(±0.5%)±10010Ω~1MΩ(E24,96Series)
LTR5050251W200J(±5%)±2001Ω~1MΩ(E24Series)Yes
F(±1%)±1001Ω~1MΩ (E24,96Series)
D(±0.5%)±10010Ω~1MΩ(E24,96Series)
LTR10064322W200J(±5%)±2001Ω~1MΩ(E24Series)Yes
F(±1%)±1001Ω~1MΩ (E24,96Series)
D(±0.5%)±10010Ω~1MΩ(E24,96Series)

※E24:Standard Products/ E96:Custom Order Products

※Please contact a ROHM representative regarding commercial-grade products

Resistance Failure Due to Solder Cracks

Why Do Solder Cracks Occur?

Chip resistors are mounted on boards using solder, enabling use under a variety of environments. Operation at both high temperatures (>100°C) and low temperatures (<-40°C) are also possible.

A difference in the degree of contraction (thermal expansion coefficient) due to temperature between the alumina substrate (used as a base in thick-film resistors) and FR-4 glass epoxy resin (typically adopted in mounting boards).This difference can result in excessive stress during repeated temperature cycling, leading to cracking at the solder fillet at the junction between the materials.

MaterialThermal Expansion Coefficient
(10-6/℃)
Alumina7.1
FR-4
(Glass Epoxy Resin)
14

※Highlighted for the image

※Photo of thick-film resistor

Because of stress generated due to chip contraction, a longer distance between electrodes or larger chip size is considered disadvantageous.

Preventing Solder Cracks

Solder Cracks can be Prevented by Shortening The Distance Between Electrodes or Reducing Chip Size. However, there is often a tradeoff relationship between electrical characteristics such as chip size, rated power, and maximum element voltage.

Typically, characteristic values tend to decrease as products become smaller.

Improve Junction Reliability

Some Users Seek to improve junction reliability in order to prevent solder cracks without compromising specifications such as rated power, or would like to increase rated power by increasing chip size without reducing junction reliability.

In contrast, wide-terminal types reduce the distance between electrodes while maintaining size.

Illustration: Wide Terminal Products

Solder cracks did not occur during actual temperature cycling tests.

Graph photo: Temperature Cycling Test - Clears over 3,000 cycles during temperature cycling tests

Test Conditions:
JIS C 5201-1 sec4.9 compliance

Condition: -40℃:
30min / +125℃: 30min
Air Layer 3000 cyc

Test Board:
FR-4

Solder:
Sn/3.0Ag/0.5Cu ( t = 0.100mm)

Adopting a wide terminal structure lengthens the heat dissipation pathway, improving rated power.

Schematic - Adopting a wide terminal structure lengthens the heat dissipation pathway, improving rated power.

SizeLTR seriesMCR series
2012mm
[0805inch]
0.25W0.125W
3216mm
[1206inch]
0.75W0.25W
5025mm
[2010inch]
1W0.5W
6432mm
[2512inch]
2W1W

Utilizing the wide-terminal LTR series will make it possible to prevent solder cracks and increase the rated power. In addition, high surge resistance is achieved, providing improved reliability.

Lineup

Part No.SizeRated Power
(70℃)
Maximum
Element
Voltage(V)
Resistance
Tolerance
Temperature Coefficient
of Resistance (ppm/℃)
Resistance RangeOperating Temp. Range(℃)Automotive Qualified
(AEC-Q200)
LTR10 20121/4W
(0.25W)
150J(±5%)±2001Ω~1MΩ (E24 Series)-55~
+155
Yes
F(±1%)±1001Ω~1MΩ(E24,96 Series)
D(±0.5%)±10010Ω~1MΩ(E24,96 Series)
LTR1832163/4W
(0.75W)
200J(±5%)±2001Ω~1MΩ(E24 Series)Yes
F(±1%)±1001Ω~1MΩ(E24,96 Series)
D(±0.5%)±10010Ω~1MΩ(E24,96 Series)
LTR5050251W200J(±5%)±2001Ω~1MΩ(E24 Series)Yes
F(±1%)±1001Ω~1MΩ (E24,96 Series)
D(±0.5%)±10010Ω~1MΩ(E24,96 Series)
LTR10064322W200J(±5%)±2001Ω~1MΩ(E24 Series)Yes
F(±1%)±1001Ω~1MΩ (E24,96 Series)
D(±0.5%)±10010Ω~1MΩ(E24,96 Series)

*1 Please contact a ROHM representative regarding high power products.
※E24:Standard product/ E96:Custom order product

Resistor Sulfuration

Sulfur components exist in a variety of forms in the atmosphere, such as in vehicle exhaust gases and gases emitted from hot springs. These components are adsorbed by metal surfaces, where they will gradually react.

In thick-film chip resistors, sulfur gas in the air can be introduced in the gap between the protective layer and plating, gradually reacting with the internal silver (Ag) electrode to form silver sulfide (Ag2S). (See figure below.) This will cause the internal electrodes to become disconnected, resulting in failure. This failure mode is referred to as disconnection due to sulfide.

Sulfuration Mechanism Sulfurated Chip

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