1. >
  2. >

What are resistors?

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 filet at the junction between the materials.

Material Thermal Expansion Coefficient
(10-6/℃)
Alumina 7.1
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.

Solder cracks can be prevented by shortening the distance between electrodes or reducing chip size.
However,

However, there is often a tradeoff relationship between electrical characteristics such as chip size, rated power, and maximum element voltage.
Typically, chacteristics values tend to decrease as products become smaller.

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.
Size LTR series MCR series
2012mm
[0805inch]
0.25W 0.125W
3216mm
[1206inch]
0.75W 0.25W
5025mm
[2010inch]
1W 0.5W
6432mm
[2512inch]
2W 1W

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. Size Rated Power
(70℃)
Maximum
Element
Voltage(V)
Resistance
Tolerance
Temperature Coefficient
of Resistance (ppm/℃)
Resistance Range Operating Temp. Range(℃) Automotive Qualified
(AEC-Q200)
LTR10 2012 1/4W
(0.25W)
150 J(±5%) ±200 1Ω~1MΩ (E24 Series) -55~
+155
Yes
F(±1%) ±100 1Ω~1MΩ(E24,96 Series)
D(±0.5%) ±100 10Ω~1MΩ(E24,96 Series)
LTR18 3216 3/4W
(0.75W)
200 J(±5%) ±200 1Ω~1MΩ(E24 Series) Yes
F(±1%) ±100 1Ω~1MΩ(E24,96 Series)
D(±0.5%) ±100 10Ω~1MΩ(E24,96 Series)
LTR50 5025 1W 200 J(±5%) ±200 1Ω~1MΩ(E24 Series) Yes
F(±1%) ±100 1Ω~1MΩ (E24,96 Series)
D(±0.5%) ±100 10Ω~1MΩ(E24,96 Series)
LTR100 6432 2W 200 J(±5%) ±200 1Ω~1MΩ(E24 Series) Yes
F(±1%) ±100 1Ω~1MΩ (E24,96 Series)
D(±0.5%) ±100 10Ω~1MΩ(E24,96 Series)

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

Electronics
Fundamentals