Printed circuit boards are found in just about anything electronic, from industrial manufacturing equipment to vehicles, to children’s toys. Made from fiberglass, metal components, epoxy, and a green solder mask, PCBs are essential to a plethora of applications.

And while many people know a PCB when they see one, not many understand how they are made. We have taken the time to remove the mystery and show you how it’s done. Our guide to the different types of PCB assembly processes explains the intricacies of each.

Different Types of PCBs

Before we dive into the different production processes for PCBs, it is important to note the different types. There are three main types of printed circuit boards, including:

• Rigid PCBs – these are the most popular type of printed circuit board. They feature a solid core and are typically made from fiberglass, epoxies, and phenolics.
• Flexible PCBs – these boards are often made from pliable, high-temperature plastic.
• Metal Core PCBs – fabricated with a sturdier solid core than rigid PCBs, metal core PCBs are excellent at distributing heat. Consequently, they are often used in heat-sensitive applications.

The Base of the Printed Circuit Board

All assembly processes begin with the base of the printed circuit board. This base is made from multiple alternating layers, all of which are critical to the PCB. These layers are made from substrate and copper. Depending on the PCB type, the substrate could be made from fiberglass, plastic, or metal. The thin layer of copper foil is added to the PCB on one or both sides, depending on the PCB’s functionality. If the PCB is single-sided, the copper foil will be added to the single functional side. If the PCB is double-sided, the copper foil will be added to both sides.

Layered on top of the copper foil is a green solder mask. This mask prevents the copper from interacting with other conductive materials and holds everything beneath it in place. The solder mask features holes, which is where solder paste is applied.

Finally, there is the silkscreen layer. Ink (usually white, but ink can also be yellow, black, or another custom color) is placed on the final outer layer of the PCB. The silkscreen ink portrays important labels, characters, and symbols to spell out critical information and highlight warnings for the engineer or technician to see.

Printed Circuit Board Assembly (PCBA)

PCBA is the most straightforward of the PCB fabrication processes. This method calls for the following steps:

Step 1: Apply Solder Paste

The first step in the PCBA process is applying solder paste. The printed circuit board’s intricacies, small size, and need for paste to be applied only in certain areas makes it difficult to apply the paste all at once. Therefore, different stencils are used to ensure paste is applied only where it needs to be.

Step 2: Place the Components

Once the solder paste is applied, the board’s electronic components are placed. Depending on the board, these components can be placed by hand or via robotic mechanism.

Step 3: Reflow

This process requires the PCB to go through a 500-degree reflow oven. During its voyage, the solder paste is melted. The PCB with melted paste is then solidified by exposure to a cooler.

Step 4: Inspection

Next, the PCB is closely inspected to ensure that all components function properly. Often, any ill-fitting components, electrical shorts, or poor connections are discovered through the inspection phase. Manual, X-ray, and automated inspections are utilized.

Step 5: Insertion of Through-hole Parts

When applicable, through-hole and surface mount components are inserted at this stage.

Step 6: Final Inspection

The printed circuit board is inspected one last time and is tested using varying currents and voltages.

Step 7: Cleaning

The completed PCB is washed carefully with deionized water and dried under compressed air.

Step 8: Packaging

The clean, finalized PCB is packaged.

Through-Hole Technology Assembly (THT)

The THT assembly process follows the same stages as PCBA, with a few exceptions. The exceptions are discussed below.

Place the Components

Components are placed on the board by hand. Only the most experienced engineers complete this step due to the need for speedy and highly accurate results.

Inspection

The board is compared to a design transport frame to ensure that all components are placed properly. Any changes to component placement must be made at this stage.

Wave Soldering

During this stage, the board is moved over 500-plus-degree liquid solder in a slow, wavelike motion. Connections are then solidified via exposure to coolers.

Surface Mount Technology Assembly (SMT)

Surface mount technology assembly is ideal for complex applications. Because automated features are utilized in this process, manufacturers can guarantee precision and a faster turnaround time.

Step 1: Apply Solder Paste

During the SMT process, a special solder paste printer applies the solder paste.

Step 2: Place the Components

Once the solder paste is applied, components are placed via robotic pick and place mechanisms.

Step 3: Reflow

After the components are placed, the board is placed in a furnace to melt the solder paste. Then, the board is exposed to coolers to solidify the components.

Mixed Technology Assembly

This assembly process allows for greater customization capabilities for small and complex printed circuit boards. These processes include:

Fabricating Single-Side PCBs

When printed circuit boards only feature one functioning side, mixed technology assemblies prove useful. A variety of techniques are made available for this process. For example, hand soldering can be used in place of wave soldering.

Fabricating Double-Side PCBs

During this production process, PCBs often follow the PCBA process with or without the application of adhesives. When adhesives are used during this process, the overall cost is increased. Efficiency is also lowered since the heating stage must be carried out a total of three times.

Entrepreneurs, established manufacturers, or customers in need of quality PCB manufacturing in the USA will find excellent solutions with the experts at Advanced Assembly. From turnkey PCBs to prototype assembly, companies find working with Advanced Assembly a pleasant, speedy, and positive experience.