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SMD Polarity Identification of LED, Capacitor, Diode, Inductor, IC

PCBONLINE Team

Wed, Dec 22, 2021

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Many surface-mounted devices (SMDs) are polarized components, such as light-emitting diodes (LEDs), diodes, tantalum capacitors, ICs, etc. Polarity identification of these electrolytic SMD components can avoid SMD polarity reversal during PCB assembly. This article will guide you to identify the polarity of SMD LEDs, capacitors, diodes, inductors, ICs (including BGAs) fast and easily.

Part 1. What is SMD Polarity?

Polarity means the direction of SMD components when soldering on printed circuit boards. SMD polarity has two meanings as below:

1. For LEDs, diodes, tantalum capacitors, and so on, polarity means the active/negative electrode of the component is in the same direction as the PCB's active/negative electrode mark.

2. For ICs (including BGAs), and multi-pin inductors, polarity means the component's first pin/ball is in the same direction as the PCB's first-pin mark.

If the SMD polarity is reversed on the circuit board, the whole PCBA will fail. That's why both engineers and PCBA manufacturers should be aware of the SMD polarity identification.

Part 2. What SMDs Components are Polarized?

Only polarized SMDs require polarity identification. Below are the polarized and non-polarized SMD components.

SMD components
Non-polarized
Polarized
Resistors
/
All resistors
Capacitors
Ceramic capacitors
Electrolytic capacitors, tantalum capacitors
Inductors
Chip inductors
Multi-pin inductors
Diodes
/
All diodes including LEDs
ICs
/
All ICs including BGAs

SMD resistors are non-polarized

As you can see, all resistors are non-polarized components, and all diodes, LEDs, ICs are polarized.

Part 3. SMD Capacitor Polarity Identification

There are 3 types of SMD capacitors.

non-polarized ceramic capacitor

Ceramic capacitors are non-polarized components.

Tantalum capacitors and aluminum electrolytic capacitors have polarity. Their positive electrode should be placed in the same direction as the PCB pad's positive electrode.

SMD tantalum capacitor polarity identification

SMD tantalum capacitors are polarized components. For tantalum capacitors, the polarity is marked by:

SMD tantalum capacitor polarity

  • 1. The positive electrodes of the PCB and tantalum capacitor are both marked by a color strip.
  • 2. The positive electrodes of the PCB and tantalum capacitor are both marked by a "+" symbol.
  • 3. The positive electrode of the PCB pad is marked by a bevel.

Aluminum electrolytic capacitor polarity identification

For aluminum electrolytic capacitors, the polarity is marked by:

aluminum electrolytic capacitor polarity

  • 1. The negative electrode of the aluminum electrolytic capacitor is marked by a color strip or block. Therefore, the opposite side is the positive electrode.
  • 2. The positive electrode of the PCB pad is marked by a color strip.
  • 3. The positive electrode of the PCB pad is marked by a "+" symbol.

Part 4. SMD LED Polarity Identification

The positive/negative electrode of LEDs must be in the same direction as the positive/negative electrode of the PCB. SMD LED polarity is marked by:

SMD LED polarity

  • 1. The negative electrode of the LED is marked by the green color blocks.
  • 2. The negative electrode of the PCB pad is marked by a color strip.
  • 3. The negative electrode of the PCB pad is marked by a silk screen sharp corner.
  • 4. The negative electrode of the PCB pad is marked by a silk screen 匚 frame.

Part 5. SMD Diode Polarity Identification

SMD diode polarity is marked by:

SMD diode polarity

  • 1. The negative electrode of the diode is marked by a color strip.
  • 2. The negative electrode of the diode is marked by a groove.
  • 3. The negative electrode of the diode is marked by a color strip on the glass.
  • 4. The negative electrode of the PCB pad is marked by a vertical bar.
  • 5. The negative electrode of the PCB pad is marked by a silk screen sharp corner.
  • 6. The negative electrode of the PCB pad is marked by a silk screen 匚 frame.

Part 6. SMD Inductor Polarity Identification

There are 2 types of SMD inductors.

chip inductors are non-polarized

Chip inductors are non-polarized components.

Multi-pin inductors are polarized components. The first pin of the multi-pin inductor should be in the same direction as the first pin of the PCB pad. Multi-pin inductor polarity is marked by:

polarized inductor polarity

  • 1. The first pin of the multi-pin inductor is marked by a round point.
  • 2. The first pin of the multi-pin inductor is marked by the number 1.
  • 3. The first pin of the PCB pad is marked by a round point.
  • 4. The first pin of the PCB pad is marked by a round circuit.
  • 5. The first pin of the PCB pad is marked by a * symbol.

Part 7. SMD IC Polarity Identification

All ICs (including BGAs) are polarized. Below we list the polarity identification methods for IC packages BGA, SOIC, SOP/QFP, QFN.

BGA polarity identification

BGA is an IC packaging that uses solder balls to replace the pins. The polarity of BGA means that the first ball of the BGA is in the same direction as the PCB pad of the first ball. The BGA polarity is marked by:

BGA polarity

  • 1. The first ball of the BGA is marked by a round point.
  • 2. The first ball of the BGA is marked by a round circle.
  • 3. The first ball of the BGA is marked by the number 1.
  • 4. The first ball of the PCB is marked by a round point.
  • 5. The first ball of the PCB is marked by a round circle.
  • 6. The first ball of the PCB is marked by the letter A.
  • 7. The first ball of the PCB is marked by the number 1.
  • 8. The first ball of the PCB is marked by a bevel.

SOIC polarity identification

The polarity of SOIC is marked by:

  • 1. The first pin of the SOIC is marked by a color strip/round point/round/circle/groove/bevel/slope.
  • 2. The first pin of the PCB is marked by a "*" symbol/round circle.

SOP/QFP polarity identification

The polarity of SOP/QFP is marked by:

  • 1. The first pin of the SOP/QFP is marked by a pit.
  • 2. The first pin of the SOP/QFP is marked by a point that is different from other points in size/shape.
  • 3. The first pin of the PCB is marked by a round point/round circle/color strip.

QFN polarity identification

The polarity of QFN is marked by:

  • 1. The first pin of the QFN is marked by a round point/"+" symbol/< symbol/bevel/point that is different from other points.
  • 2. The first pin of the PCB is marked by a "*" symbol/round circle.

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Conclusion

This article gives a detailed illustration of SMD polarity and identification methods to the polarity of capacitors, inductors, LEDs, diodes, and ICs. If you still have problems with SMD polarity, welcome to leave your question via our online chatting window on the right of the PCBONLINE webpage. If you need SMD components or PCB assembly, do not miss PCBONLINE, the 22-year-old source factory.


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