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!
PCB vs. PCBA: What is the Difference
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.
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 PCBAs: 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 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.
SMT assembly has four steps:
- Solder paste printing
- Component placement
- Reflow soldering
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.
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
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.
Since the design lacks hanging wires that can easily be cut, PCBAs create a durable and more reliable electronic component setup.
Removing a damaged component and soldering a new one is relatively more manageable on a board than handling wire connections.
PCBAs are cheap to build, which translates to lower costs for your project.
Applications of PCBA
- Medical sector
- Electrical equipment
- Consumer electronics
- Safety and security equipment
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.
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.
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.
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.
What To Consider For The Best PCB for 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
- Has 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
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.