PCB Board Assembly and the Differences between PCB and PCBA

PCBs are crucial parts of electronic circuits because they hold and provide all the electrical connections between different components. Although some people use PCB and PCBA interchangeably, the two do not mean the same thing.

In simple terms, a Printed Circuit Board Assembly builds on a PCB and forms a complete circuit with all the components. We will look at the PCBA in detail below, including how it differs from a PCB. Take a look!

Definition of PCB & PCBA

A PCB is a blank board consisting of conductive copper pathways sandwiched in fiberglass or epoxy laminate material (base material). It forms the mechanical foundation to mount various electrical components for your circuit.

A PCB

When you fit in the electrical components by soldering them to the contact fingers on the outer edge of a PCB, the outcome is a PCB assembly. Therefore, a PCBA is a PCB that has gone through the assembly process. In simple terms, it is a complete electronic assembly.

A PCBA with capacitors, resistors, and integrated circuits mounted on the PCB

Differences Between PCB Assemblies: THT Assembly, SMT Assembly, and Mixed Technology

Although all PCBAs are the same, there are some differences in the assembly process, and there are three ways to do it.

Thru-Hole Technology

Thru-Hole Technology is a traditional assembly process that involves manual and automatic procedures to mount the components.

The process requires drilling holes into the PCB and comes in handy when installing parts with leads that need plugging into the board. These include coils, capacitors, and the like.

Even though the process is old, it creates a stronger bond between the board and its components. THT assembly has four steps:

• Hole drilling
• Component placement
• Inspection and rectification
• Wave soldering

Surface Mount Technology

As the name suggests, Surface Mount Technology involves fixing the electronic components on the surface of the PCB. It is a fully automatic and flexible process that allows higher assembly densities because manufacturers can fit complex circuitries into small boards.

Surface-mounted components

SMT assembly has four steps:

• Solder paste printing
• Component placement
• Reflow soldering
• Inspection

Mixed Technology

With advancements in science and technology, circuits have become increasingly complex, so having only one component type is impossible.

Therefore, modern electronic products usually have PCBAs with Thru-hole components (THC) and surface mount device (SMD) components. These components include a mix of capacitors, integrated circuits, coils, resistors, etc.

Assembly Types of PCBA

Since surface mount technology is a more practical assembly technique than THT, assembly services usually implement SMD only or a mix of the two.

PCBA Manufacturing Process

Step 1: Solder Paste Stencil

This process is like screen-printing a t-shirt, and it prepares the board for soldering by applying solder paste to the exact places in the right quantities. The screen, in this case, is a thin stainless steel stencil that enables assemblers to place the paste at the right spots.

A stencil for soldering chips

The soldering paste consists of tiny grey balls of metal 96.5% tin, 3% silver, and 0.5% copper. The paste application and spreading happen in an assembly line, so everything is automated.

Step 2: Pick and Place

Traditionally, assembly experts used to pick and place SMD by hand, but robots automated the process making it faster and more accurate.

They set the electronic components over the spots with solder paste applied earlier.

With the solder paste in place, the next step is picking and placing SMD using a robotic machine.

Step 3: Reflow Soldering

Reflow soldering is a process that solidifies the solder paste to bond the SMD permanently to the board. The board goes into an oven and gets heated at about 250°C or 450°F to melt the solder paste.

Molten solder paste fuses with the SMD, then cools to form a permanent solder joint between the components and the board.

If making a two-sided PCB assembly, the process gets repeated to fit the components on the other side.

Step 4: Inspection and Quality Control

Poor connections, no connections, or short circuits might occur due to movements in the assembly line, which cause the soldering of SMD in the wrong spots. Therefore, checks and tests are necessary before the board moves to the next step.

Checks usually include manual, automatic optical (for larger batches of PCBAs), and X-ray (for complex, layered PCBAs). Malfunctioning PCB assemblies either get discarded or reworked.

Vision measuring instrument inspecting PCBA

Step 5: Through-Hole Component Insertion

If the board has a mixed assembly, the next step is to fit the plated thru-hole components (PTHC). Using soldering paste is not practical for mounting PTHC because the paste would melt right through the drilled holes.

Instead, manufacturers either use manual soldering, a lengthy process done by hand, or wave soldering. The latter is faster because it runs the boards with PTHC inserted over a molten solder wave on a conveyor belt. Liquid solder washes the underside of the PCBs, fusing the components permanently.

A wave soldering machine

Step 6: Final Inspection and Functional Test

The last step is to inspect and test the complete board by checking its electrical characteristics (current, voltage, and signal output). These factors must be within the predetermined range, or the board gets discarded or recycled.

How to Get a Custom PCBA?

These steps will guide you through the process if you want to get a custom PCBA.

Step 1: Create a Schematic

Using software like CAD (computer-aided design), Eagle, or Multisim, begin designing the PCBA by creating a schematic view. Layout all the required components on a canvas, then join their pins with lines representing the electrical connections.

Step 2: Board Layout Check

After creating the schematic, check the board layout via the electrical rule check to ensure no evident faults.

Step 3: Rearrange Components

Next, move the components to the right places that make good sense for the PCBA.

Green printed circuit board (PCB) with components. 

Step 4: Assign Signals

Assign signals to each PCB layer while ensuring varying signals on a single layer don't come into contact.

Step 5: Design Check

Use the design rule check to check and approve the layout, and if you have a flawless assembly, upload the design files. These are usually multiple Gerber files, one for each layer. Also, generate the drill file, which shows where to drill the holes.

Step 6: Go to OurPCB and Upload Design Files

Compress the files, upload them to OurPCB, fill in your details, specify your needs in the message section, then submit the form.

Benefits of PCBA

Saves Time

Building PCBAs takes significantly less time compared to connecting components using wires.

Gives a Compact Design

PCBAs pack multiple components in a compact space, resulting in smaller electronic devices.

Maximizes Durability

Since the design lacks hanging wires that can easily be cut, PCBAs create a durable and more reliable electronic component setup.

Simplifies Repairs

Removing a damaged component and soldering a new one is relatively more manageable on a board than handling wire connections.

Affordable

PCBAs are cheap to build, which translates to lower costs for your project.

Applications of PCBA

• Medical sector
• Vehicles
• Electrical equipment
• Military
• Aerospace
• Consumer electronics
• Safety and security equipment
• Maritime

PCBA Manufacturing Defects and Solutions

It is almost impossible not to have manufacturing defects when building PCBAs. These are the most common issues and how to deal with them.

Wire Breaks Issue

Wire breaks are common in PCB fabrication & assembly, and the only way to deal with them is by doing a thorough inspection.

Poor Pin and Connector Placement

Pin misplacement can damage the connectors, but you can avoid this by using a pattern-matching tool. It helps to locate and accurately group the patterns for correct pin alignment.

Open Solder Joints

The separation between the component leads and the PCB, poor soldering, insufficient solder paste, or inconsistent paste can lead to open joints. To avoid this, use the right PCB design, prevent solder paste contamination, and use the right manufacturing equipment.

Solder joints of the modern circuit board

Component Shift

Components usually move when soldering due to several reasons. However, maintaining the correct humidity, melting the paste at the proper temperature range, and minimizing movement can eliminate this problem.

Overheating

PCB components can get extremely hot when in use. An SMD heat sink can keep the temperature under control, so the board should have one that has undergone a heat dissipation analysis.

A computer motherboard heat sink

Chemical Fluid Leakage

Traces of chemical fluids on the PCBA can significantly corrode the metal parts, so as a manufacturer, you should clean the board thoroughly to ensure no damage.

Shorting

The only way to eliminate shorting on circuit boards is by separating leads and solders before solidification. Use the required design rules and modify stencils to prevent solder bridging.

Key Differences Between PCB vs. PCBA

We will look at these differences in areas like functionality, manufacturing, complexity, cost, and time. But let’s begin with the definition.

PCB vs. PCBA Cost

Manufacturing PCBAs is costlier because they have to undergo the additional steps of component placement, soldering, and testing before reaching the customer. Additionally, the components are not free; their cost is included in the price of the final product.

A soldering iron tip on automated manufacturing and assembly line

But you still have to assemble the board if you order it as a PCB, which means you have to order the electronic components, buy solder paste/wire and take time to assemble the board.

Considering time is money, these extra activities can end up making the PCB cost more to get to market than PCBAs. So do your math well to determine which option gives you more value for money.

Choosing Between PCB & PCBA

You have to consider these factors to determine the board variety is most suitable for your project.

Design Complexity

You can order a PCB from your fab house, but if it has a complex design, assembling it manually will be a daunting task.

Therefore, if the circuit has a complex, high-density design, it is easier to get it as a PCBA directly from the manufacturer. Otherwise, you can order a PCB.

Manual component insertion on PCBs before wave soldering to form a PCBA

Component Availability

Some components are difficult to source or might require complex assembly techniques, especially if they are chips. If this is the case, we recommend getting a complete device.

You should also buy a PCBA if you don’t have advanced soldering skills to handle these complex component assembly processes.

Space Constraints

The professional assembly process that forms PCBAs makes the final product more compact, which means you can use these complete devices in compact devices.

But you can get a larger PCB that has more working space on the surface if you are building a larger device.

Performance Requirements

High-performance applications like RF signal transmission in satellite and military devices require PCBAs because the professional assembly creates advanced PCBAs using shielding techniques and specialized materials.

It can be challenging to attain such capabilities from a PCB with manual assembly.

Lead Time vs. Cost

PCBs are less costly because they go through fewer production processes than PCBAs. This also means they have a shorter lead time so you’ll get them delivered faster.

But they come as bare boards so you must assemble the board to make it functional. This can take some time, especially if you have a batch.

On the other hand, PCBAs take more time to produce and cost more, but once you get them, they are ready to use.

What To Consider to Choose the Best PCB & PCBA Manufacturer

If you find it cheaper and more convenient to outsource PCBA manufacturing, you need to ensure the company:

• Is the actual PCB manufacturer and assembler, not a broker
• Knows different PCB assembly techniques
• There are no limits on the minimum/maximum number of orders you can make
• Offers reasonable and competitive pricing, sometimes negotiable
• Delivers the PCBA on time and with the DFM (Design for Manufacturability) details

Summary

Overall, PCBAs are the basic building blocks of most modern electronic circuits because they hold components in a compact, durable structure.

If you need one of these built for your project, contact us to get authentic PCB assemblies at unbeatable and affordable prices.