In this post we are going to learn about SMD resistors, what are they, how to read SMD resistor values and also how to read network resistor values.
What is a SMD resistor?
SMD stands for Surface Mound Devices, meaning the terminal of the component are soldered directly on the board unlike THT or “through hole technology” where the leads of the components are inserted and soldered at back of the circuit board.
SMD Resistors are also known as “Chip resistors”.
The SMD resistors are the resistors which utilizes this SMD technology. The SMD resistor soldered on a circuit board is highlighted on the below picture.
Here is the image of soldered SMD resistor on a PCB:
How to Identify SMD resistor?
There could be tons and tons of surface mound components on a circuit board and debugging the circuit can be a head ache if any issues arise. If you have a blown resistor, how you will say that the blown component is SMD resistor or SMD capacitor?
Here is how you will identify the SMD resistor:
Every SMD resistor can be identified by visually inspecting the component; it will always have a black body and silver line at both ends, which are the terminals.
Now you know how to identify a SMD resistor.
Construction of SMD resistor:
The SMD resistors consist of mostly filled with ceramic material which is substrate onto which the metal oxide layer film is deposited, which is the resistive layer.
The thickness and length of the metal oxide layer determines the resistance of the SMD resistor.
The ceramic substrate contains high concentration of “aluminium oxide” which is good insulator onto which the metal oxide layer is deposited.
The SMD resistor terminals should able to make good contact with resistive material internally and able to provide good soldering capability externally. The high temperature should not affect the internal contact with the terminal.
To make good soldering capability with least damage as possible is achieved by applying nickel based layer internally and tin based layer externally.
Why we use SMD instead of normal sized resistor?
SMD resistors are used where the space is limited, if your product or your project consists of higher number of components where you need to pack the components into a tight space.
They are generally cost effective than THT based resistors. They can be used in automated circuit assembly process.
They have least parasitic effects than THT resistors; this is most important point on the list. The resistors don’t just have resistance, but it also have some amount of inductance and capacitance.
The inductance is the culprit who mess our circuit’s proper operation. If your circuit is operating at or above 1 MHz, you must choose SMD components. At higher frequency the inductance will resist the flow of power.
Due to the construction of THT components the ESR (Equivalent Series Resistance), ESL (Equivalent series Inductance) and parasitic capacitance at higher frequency the power to the microcontroller or to the microprocessor or to the ICs is going to hinder a lot.
At higher clock cycles microprocessor or microcontroller needs a big pulse of energy during each clock cycle to keep the system at operating voltage level.
But due the parasitic affects especially the inductance, which will make the high frequency circuits go below operating voltage and shutdown the circuit.
That’s why our computers, laptop and smartphones are constructed from SMD components and they don’t behave crazy at GHz frequency range.
How to read SMD resistor values:
The SMD resistors are easiest to calculate than THT resistors which require to memorize colour code, don’t believe me? Let us see…..
SMD resistor can be 3 digits or 4 digit numbering.
Let’s see the following examples (For Three digit):
Take first two digits “22” as it is and the last digit is the multiplier 100
So, 22 x 1 = 22 ohms.
Take first two digits “68” as it is and the last digit is the multiplier 100
So, 68 x 1 = 68 ohms.
Take first two digits “33” as it is and the last digit is the multiplier 104
So, 33 x 10000 = 330000 ohm or 330 Kilo ohm.
Take the first two digits “10” as it is and the last digit is the multiplier 103
So, 10 x 1000 = 10000 ohm or 10 Kilo ohm.
Where ever “R” comes this is decimal point so R42 is 0.42 Ohm
1R5 becomes 1.5 ohm.
1K5 becomes 1.5 Kilo ohm.
K24 becomes 0.24 kilo ohm.
M24 becomes 0.24 mega ohm.
Now let’s see for 4 digit resistor code:
Take first 3 digits “160” as it is and the last digit is multiplier 102
So, 160 x 100 = 16000 ohm or 16 Kilo ohm.
Take first 3 digit “470” as it is and the last digit is multiplier 100
So, 470 x 1 = 470 ohm
If the SMD resistor is written as “0” or “000” it means zero ohm, yes you read it correct, zero ohm. They are used as jumper on SMD circuits.
If you never heard of network resistor, well you are not alone but, you might have seen this component this is called network resistor.
The above image is “through hole technology” or “THT” network resistor. SMD network resistors are also available.
It is a pack of resistors. The dot you see on the resistor is the common terminal the other 9 terminal are resistors. If you measure resistance between the common terminal and to any one of the terminal you will read the 100K (which is the resistance of this pack) which means it has 9 individual 100 K ohm resistors.
How to read the value? Well it is exactly same as SMD calculation
- 104 is written on the body
Which means 10 x 104 = 100000 ohm or 100 Kilo ohm.
Network resistors are used for:
- Analog to digital converters
- Digital to analog converters
- Voltage dividers
We hope you able grasp something useful from us, If you have any further question, please ask us in the comment, you may anticipate a guaranteed reply from us.