PCBA or PCB assembly is the manufacturing process of an assembled PCB where the required electronic components are mounted on the PCB.

The PCBA process consists of several automated and manual steps. There are three basic PCB assembly technologies which include some fast PCB assembly processes. They are:

• Through-Hole Technology (THT) Assembly Process
• Surface Mount Technology (SMT) Assembly Process
• Mixed technology Assembly Process

Through-Hole Technology (THT) Assembly Process

Through-Hole Technology (THT) is a process in which component leads are placed into the drilled holes of the bare PCB and the ends are soldered to the pads on the opposite side. This process is called through-hole assembly.

Through-Hole Technology (THT) Assembly Process involves three major steps.

Step 1: Component placement

• The components are placed in the corresponding holes according to the required design.
• Components must be placed according to the regulation and operation standards of THT assembly process to ensure quality.

Step 2: Inspection and Rectification

• The board with the inserted components is automatically inspected by placing in a matching transport frame to check the accuracy of positions of the components.

STEP 3:  Wave Soldering

• The board is moved slowly over a wave of liquid solder at high temperature.

Surface Mount Technology (SMT) Assembly Process

In this method, the components are directly placed on the surface of the PCBs with solder paste. Surface-mount devices (SMDs) are made this way.

This involves three steps.

Step 1: Solder Paste Printing

• Solder paste printed is used to apply solder paste where a template is used to ensure that the paste is placed at the right places.

Step 2: Components Mounting

• After step 1, the pick-and-place machine places the components on the respective pads due to solder tension.

Step 3: Reflow Soldering

• The board is passed through the reflow oven which heats the solder to the proper temperature and then cools it down to solid again so that the components attach to the surface of the board.

Mixed Technology

Electronic products need more complicated, integrated and smaller size PCB boards with recent developments. So these boards need both SMD and through-hole components to perform complex tasks.

PCBA with the application of mixed technologies should be carried out in the following situations:

Single Side Mixed Assembly:

It involves the following processes in the given order:

1. Solder Paste Printing
2. SMD Parts Placement
3. Reflow Soldering
4. THT Component Placement
5. Wave soldering

One Side SMT and One Side THT:

It involves the following processes in the given order:

1. Surface Mount Adhesive
2. SMD Parts Placement
3. Solidification
4. Flipping
5. THT Component Placement
6. Wave Soldering

Double Side Mixed Assembly:

In this case, there are two alternatives:

1. PCBA with application of adhesives which involves the following processes in the given order:
   • Solder Paste Printing
   • SMD Parts Placement
   • Reflow Soldering
   • Flipping
   • SMT Adhesive
   • THT Component Placement
   • Wave Soldering

2. PCBA without the application of adhesives involves the following steps in the given order:
   • Solder Paste Printing
   • SMD Parts Placement
   • Reflow Soldering
   • Flipping
   • Solder Paste Printing
   • SMD Parts Placement
   • Reflow Soldering
   • THT Component Placement
   • Wave Soldering or Hand Soldering

Conclusion:

PCBs are an integral part of the electronics we use in our daily lives. Today the use of PCB is widespread. They can be single-sided, double-sided or multilayered. It’s used in medical devices, automotive components, aerospace components and so on.