The design of PCB and its assembly involves different components. The smart era has resulted in a compact PCB design and the components’ polarity is hard to identify now. Here, we will see how to recognize the polarity of the SMT components to avoid its reversal during production, ensure a correct PCB, and enhance the quality of engineers’ knowledge regarding the polarized components’ direction.

Understand the Polarity of Components In PCB?

The polarity of SMT components is the position of the SMT components’ first pin or it’s the direction of the component. In other words, when you mount a component during the SMT assembly process, it should be installed in a specific direction and that is polarity.
You have to make sure that both negative and positive poles of the components are connected to the circuit board. If the components’ direction is wrong while mounting, it would result in a blocked circuit, causing a short circuit. Moreover, the body of the component gets burned and the circuit does not function correctly due to wrong placement.

Polar Components and Their Type

PCB has several SMT components having polarity, such as
• Shaped capacitors
• Transistors
• Diodes
• Field effect tube
• IC integrated circuit
• Coil
• Crystal oscillator
• Transformer
• Shielding frame
• Row socket

All these connectors have different symbols, however, there are also several other types of components.

Marking of Polar Components

Components with polarity have specific marks that show the direction of both poles or the direction of the components’ first pin. The two-pin components have mostly positive and negative marks. Whereas in the case of multi-pin components, the mark is the placement of the components’ first pin.

The poor reverse happens if the circuit board has polar components with the wrong polarity. Reverse components are not suitable in terms of Printed Circuit Board function even their mounting and soldering are fine on the board pad. This issue can also burn the PCBA while testing it, making the board less functional.

You have to identify the SMT components’ polarity considering a few things

Identifying The Body Polarity of The Component

It is the position or direction of components’ positive and negative poles. You can also say that it is the first pin of the part marked on the component body.

Identifying the Component Polarity in The Circuit

• It is the position or direction of the positive and negative poles of electronic components. It can also be the direction of the first pin in the circuit.
• Another thing to consider is the mounting of the electronic components on the PCB. Whereas the component body’s polarity corresponds to the circuit’s polarity.

PCB has electronic components mounted on it through surface mount technology. The component body’s polarity corresponds to the circuit’s required polarity.

Printed circuit boards made by SMT are getting more integrated with precise components layout. Moreover, the components are getting smaller than before due to smart PCBs.

In mobile phones’ motherboards, you won’t find any components. So, you can’t identify the components’ polarity intuitively. In such products, the components tag map is used to create a material release map to identify the polarity, and the location specification to help quality personnel ensure the first piece which also becomes a sample for testing. This test ensures a flawless identification of the component polarity.

Identifying the Capacitor Polarity

• The chip resistors have no polarity.
• The ceramic capacitor is non-polarized.
• Polarity of the tantalum capacitors is determined by positive and color band marking of the components on PCB and diagonal marking.
• The capacitance and electrolysis of aluminum come up with polarity. The color band of components shows a negative marking. Whereas the PCB mark is positive.

Identifying the Inductor Polarity

• There is no need to identify the polarity for a chip coil package and welding areas.
• There are polarity requirements for multi-pin inductors. The polarity point is indicated by dot/1. Whereas the PCB mark is indicated by dot /circle / “*” for the polarity point.

Identifying the Diode Polarity

The surface-mounted LED in PCB has polarity. The components’ negative polarity is indicated by green. Whereas PCB’s negative polarity is indicated by the vertical bar, color band, and silk screen’s sharp corner.

Identifying the IC Polarity

• You can identify the polarity of the integrated circuit through SOIC packaging. It is indicated as a color band, groove, symbol, concave point, and bevel.

• The polarity of the SOP and QFP packaging is indicated by groove, concave, and two different points.

• The polarity of the QFN packaging is indicated by a beveled edge to the marking, a symbol like a horizontal bar, and two different points in terms of size and shape.

Identifying the Polarity of Ball Grid Array, BGA

In this case, the component polarity is indicated by a dot, concave point, groove, and a circle mark. Whereas the PCB polarity is indicated by dot, circle, and diagonal to mark. Moreover, the components’ polarity point corresponds to PCB’s polarity point.

Things To Consider In PCB Manufacturing For Components Direction

PCB assembly gets wrong if the components are not compatible with their orientation. However, certain warning signs regarding the PCB design guidelines can help in this case. The manufacturer has to consider a few things while reviewing a PCB design, such as:

Quality of design: the CM can enhance PCB production by finding the defective parts during assembly and replacing them with the right material or parts.

Standard assembly: PCB design should be compatible with assembly and the CM can ensure low-cost manufacturing by reducing the time and labor.

Assembly issues: the CM can also enhance PCB production by removing the potential assembly problems. This can also reduce the overall assembly cost due to reduced time and labor.

Thermal performance: certain components have to be positioned at a certain angle to enhance the airflow around the circuit board. This step keeps the parts cool and effective.

PCB going through a solder reflow also has issues with components orientation. Sometimes, the passive parts are placed together to connect all the pins to one power bus. When the direction of such components is unable to change, the power bus connection should be through a thin trace to remove the large metal areas that flood the pin.

The passive components having irregular metal connections between two pins might be vulnerable to floating on the pad surface or can cause tombstoning in solder reflow.

The direction of the parts is also a concern if they lie on PCB edges. In the case of V-groove scoring, the direction and placement of the components should allow some space for the scoring tool to work. It helps to remove the defects in PCB and the parts also stay safe. Moreover, you should also consider the direction of the components in terms of their function.

Frequently Asked Questions

What Is SMT Component Polarity In PCB?
The polarity of SMT components is the position of the SMT components’ first pin or it’s the direction of the component. When you mount a component through SMT, it should be installed in a specific direction and that is polarity.
What is SOP in PCB?
SOP means the small outline package that is an IC package of SMT.

What is QFP in PCB?
QFP in PCB means the quad flat package and it is also an integrated package for surface mounting.
What is QFN in PCB?
QFN in PCB means the quad flat no-lead package and it is leadless, small, and provides heat dissipation in PCB.
What are some SMT components with polarity?
PCB has several SMT components having the polarity, such as shaped capacitors transistors, diodes, field-effect tube, IC integrated circuit, coil, crystal oscillator, transformer, shielding frame, and the row socket.

Final Thoughts

The polarity of SMT components is the position of the SMT components’ first pin or it’s the direction of the component. In other words, when you mount a component through SMT, it should be installed in a specific direction and that is polarity.
You have to make sure that both negative and positive poles of the components are connected to the circuit board. If the components’ direction is wrong while mounting, it would result in a blocked circuit, causing a short circuit. Moreover, the body of the component gets burned and the circuit does not function correctly due to wrong placement.
Components with polarity have specific marks that show the direction of both poles or the direction of the components’ first pin. The two-pin components have mostly positive and negative marks. Whereas in the case of multi-pin components, the mark is the placement of the components’ first pin.

The poor reverse happens if the circuit board has polar components with the wrong polarity. Reverse components are not suitable in terms of PCB function even their mounting and soldering are fine on the board pad. This issue can also burn the PCBA while testing it, making the board less functional.

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