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How to use chip resistors smartly
- 1.Basic knowledge of resistors
- 2.Manufacturing methods and characteristics of thin film resistors
- 3.Performance characteristics of thin film resistors
- 4.High precision and high reliability
- 5.Trimmable chip resistors and altering resistive values
- 6.Application and recommended usage of thin film chip resistors
- 7.Application and recommended usage of small high power thin film ship resistors
- 8.Various methods of current sensing and advantage of current sensing resistors
- 9.Application and recommended usage of current sensing resistors
- Smart usage of High Frequency Chip Components
- Application Information
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Product Technical Report
Standard Specification for surface mount chip resistors
- Recommended land patterns
- Recommended reflow and flow soldering profile
- Dimensions of the packaging reel
- Dimensions of the packaging tape
Standard Specification for High frequency surface mount components
- Recommended reflow soldering profile
- Dimensions of the packaging tape
- Dimensions of the packaging reel
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Technical FAQ
High Precision Thin Film Chip Resistors
- ・Part numbering
- ・Performance characteristics
- ・Quality, reliability
- ・Mounting, packaging
Current sensing chip resistors
- ・Part numbering
- ・Performance characteristics
- ・Quality, reliability
- ・Mounting, packaging
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Product Introduction Videos
Current Sensing Resistors
Susumu USABrief Technical Presentation
- Top
- Introduction
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Basics of Current
Sensing - Structure
- Heat Dissipation
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Low Surface
Temperature -
Small Power
Coefficient of
Resistance - Small TCR (1)
- Small TCR
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Small Equivalent
Series Inductance - Low Noise
- Small Thermal EMF
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CTE &
Thermal Cycle -
Shear Deformation
Stress - KRL is Different
- Two Types of KRL
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Advantage of KRL:
Summary
Welcome to Susumu USA’s Product Training module on the KRL series.
This PTM will highlight some of the excellent characteristics of Susumu’s new current sensing low Ohmic
chip resistors, the KRL series. Characteristics covered include heat dissipation/power handling capability,
power coefficient of resistance, TCR, ESL, thermal cycle resistance, EMF, as well as the structure and
specifications.
Power efficiency and conservation of energy are indispensable in current electronics. The typical way to
monitor and control voltage is to use low Ohmic resistors in a current sensing circuit such as the one
shown above. An excellent current sensing resistor must offer many important characteristics such as low
Ohmic values, high power handling capabilities, small resistance tolerance, small TCR, small ESL etc.
This diagram illustrates the structure of Susumu’s latest current sensing chip resistor, the KRL series.
This “face down” structure has several advantages including excellent heat dissipation/distribution, low
terminal resistance and small TCR.
In conventional current sensing resistors, the relatively small resistive element generates a significant
amount of heat which is conducted through the alumina substrate and land pattern and reaches the PC
board. This can cause heat damage to the board. The resistive element itself may also experience
irreversible changes due to its own heat. In the KRL series, the large resistive element and the alumina
over it distribute the heat evenly without creating any hot spot, thus causing no damage to the resistive
material or to the PC board. In addition, the alumina helps the generated heat move up and radiate out
into the ambient air.
The highly heat conductive adhesive that adheres the resistive element to the alumina is the key to the
heat dissipation of the KRL series. This is shown in the heat diagram here. When a conventional current
sensor was tested under the same conditions, the peak temperature reached 165?C; termination
temperature and PCB temperature were 107?C and 75?C respectively. Thermal resistivity was 57?C/Watt,
which is significantly higher than the KRL’s 19℃/Watt.
TCR in most cases refers to ambient temperature. However, if power is applied, the resistive material itself
gets hot. This heat affects the resistive value resulting in current sensing errors. This is why the Power
Coefficient of Resistance (PCR) is important. The smaller the PCR, the fewer errors in current sensing.
A large PCR can lead to an increased number of errors in the higher power range. As this data shows, the
KRL series shows ideal linearity as the amount of current increases.
In the conventional type, the electricity must go through the narrow wrap-around area of the terminals
before reaching the land patterns. This can be considered to be a series of 3 resistors. However in the
KRL series, the terminal is formed directly beneath the resistor which is soldered directly to the land
pattern. Because of this, terminal resistance can be ignored. This makes the KRL’s TCR much smaller
than the conventional type. This is very important because current sensors’ resistive values are very low
and any terminal resistance or large TCR will affect the accuracy of the current measurement.
Our own TCR comparison reveals that the KRL’s TCR is almost 1/50 of our competitor’s current sensor.
In high speed applications, the equivalent series inductance (ESL) can be extremely important for
maintaining signal integrity. The higher the ESL, the more noise is added to the signal. As shown here, the
KRL’s ESL does not change well into GHz range and remains less than 2nH.
Actual pulse shape was compared with and without KRL. Using SMA connectors, a control microstrip line
or KRL mounted test substrate was inserted between the oscilloscope and the pulse generator. The pulse
shape between the control and KRL was compared on the oscilloscope. Almost no difference in pulse
shape was observed between the control (without KRL) and KRL because KRL has very low ESL.
KRL9045 was used for this test.
Thermal EMF (electro motive force) is the small voltage generated within the component mainly by the
non-symmetrical structure of the component and it affects both TCR and polarity of the component. KRL
has very low thermal EMF. The M series is made specifically for addressing this problem.
CTE (coefficient of thermal expansion) mismatch between neighboring materials can cause serious
problems. For example, alumina substrate and the FR-4 PC board have a CTE difference of 13ppm/℃.
If the size of the mismatched component is larger, the effect is more severe. For example, a 10mm long
alumina component can be 20μm longer if the temperature rises by 100℃.
Because of the difference in TCR between FR4 and alumina substrate, temperature change causes shear
deformation within the lead free solder. The larger the temperature difference or the larger the component
size, the stronger the sear deformation stress. The shear deformation under the temperature cycles
causes fatigue to the solder filet resulting in cracks in the solder joint eventually.
Susumu’s KRL series exhibits strong resistance to temperature cycles. Just as in other products, shear
stress occurs between the glass epoxy (FR4) and the alumina substrate. However, the elasticity of the
buffer material (adhesive resin) absorbs most of the shear deformation and minimizes stress to the solder
joints. KRL withstands 3000 temperature cycles without problems. Test conditions consisted of repeated
cycles of 30 minntes at negative 45℃, 3 minutes at room temperature, 30 minutes at 125℃, and 3 minutes
at room temperature.
We offer two types of KRL -the conventional short side terminal type and the innovative long side terminal
type. Depending on the customers’ needs, either type can be chosen. Although they are not listed here,
1005 and 0816 sizes for the short side terminal type are also available.
The new innovative structure allows Susumu’s KRL series to be one of the best low resistance current
sensing chip resistors. It provides the industry’s best power handling capability, low resistance value, small
TCR, small PCR, small thermal EMF and robustness to temperature cycling. Susumu offers a variety of
solutions for your current sensing needs in addition to the KRL series. Please contact us with your current
sensing requirements.
Activity Contents
Technical Information
How to use chip resistors smartly
- 1.Basic knowledge of resistors
- 2.Manufacturing methods and characteristics of thin film resistors
- 3.Performance characteristics of thin film resistors
- 4.High precision and high reliability
- 5.Trimmable chip resistors and altering resistive values
- 6.Application and recommended usage of thin film chip resistors
- 7.Application and recommended usage of small high power thin film ship resistors
Standard Specification for surface mount chip resistors
- Recommended land patterns
- Recommended reflow and flow soldering profile
- Dimensions of the packaging reel
- Dimensions of the packaging tape
Standard Specification for High frequency surface mount components
Smart usage of High Frequency Chip Components
Susumu International U.S.A. -Specialist in Thin Film Technology-