The Printed Circuit Board (PCB) is the heart of every electronic gadget, directing the functionality of the device. Creating this central &#;command centre&#; happens at a PCB manufacturing plant. It is a highly-sophisticated, multi-step process from concept to prototype to assembly to testing. Some manufacturers only offer PCB fabrication, just one part of the process required to turn an idea into a completed PCB product. Other manufacturers offer turnkey PCBA (Printed Circuit Board Assembly) which covers both board fabrication and the assembly of all components on the fabricated chip. This important distinction between the two processes is sometimes unclear, resulting in disappointment.

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Let&#;s look at the difference between PCB assembly and PCB fabrication in more detail:

PCB Fabrication

PCB fabrication starts with the design of the circuit board followed by prototype production, followed by testing. When you&#;re shopping around for a manufacturer, take heed that this testing is for the board only&#;not for a completed, function circuit board.

At the fabrication stage, the PCB consists of a flat sheet of insulating material and a layer of copper foil laminated to the substrate that supports electric components that are connected to it later. The flat sheet consists of 4, 6, or 8 layers depending upon the number of signal layers.

Chemical etching creates pads for connections. Vias connect different layers of copper by dividing the copper into separate lines called circular traces or tracks. The tracks act as fixed wires and are kept apart from each other via insulation of air and board substrate material. Further, the surface of the PCB often also has a coating to protect the copper from corrosion and reduce the chances of solder shorts between tracks or any other electrical contact with stray bare wires. This coating is known as the solder resist.

Thus, the PCB, in its most basic form, consists of four layers that are heat-laminated together to create a single board. These four layers are:

1. Substrate

The substrate is the layer that provides structure and shape to the PCB. It is what holds the components of the circuit board together. The substrate can be made of different kinds of materials such as fibreglass (which is the most commonly used) or more flexible materials like polymers. 

2. Copper

The copper layer is the most important&#;it is the conductor layer that performs the function of wires. The copper traces form pathways to carry electric charges from one component to another on the circuit board. The high conductivity of copper ensures that these traces transfer signals without losing electricity. The thickness of this layer is generally around 35 microns, but it varies depending upon the power requirements.

3. Solder Mask

This layer insulates the copper tracks from the solder, metallic part, and other conductive items. It&#;s a protective layer that ensures only those specific areas of the board are exposed to the solder. The solder mask (solder resist) is usually green in colour, but any colour can be used for the solder mask. The material used is a liquid photopolymer and the technology used is called epoxy or epoxy-acrylate resin technology.

4. Silkscreen

The silkscreen identifies components on a PCB for engineers and manufacturing teams. A non-conductive epoxy ink is used for the silkscreen in colours that vary from yellow to white to black. While the silkscreen does not contribute to board functionality, it flags components quickly and is, therefore, an important part of the PCB fabrication process.

Once these steps are complete, engineers make necessary modifications to the design or materials of the prototype. A green light here means the board read for assembly&#;it is a bare circuit board that is essentially a blank canvas! There are no electronic components&#;capacitors, inductors, transistors, and resistors&#;yet that make the gadget work. These components are soldered to the fabricated PCB at the PCBA or Printed Circuit Board Assembly stage. 

That comes next.

PCB Assembly

Printed circuit board assembly (PCBA) is the complete process of transforming a bare printed circuit board into a functional unit by soldering components onto the board. Without components, the electronic device can&#;t accomplish pre-decided electronic functions. The assembly process starts after bare-board fabrication. First, a DFM (Design For Manufacturing) review ascertains that the PCB design fits manufacturing capability. This review cuts manufacturing costs and eliminates unforeseen delays due to design issues that would require re-engineering.

Next, a process called surface encapsulation assembles all the electronic components on the circuit board. Manufacturers use technologies like Through-hole, Ball-Grid Array, or Surface Mount Technology (SMT) to place and solder all the electronic components onto a PCB. With Through-hole technology, electronic components are attached to the PCB by threading them through pre-drilled holes that are surrounded by conductive pads. Using Surface Mount Technology (SMT), components are placed onto the PCB with automated pick-and-place machines, ensuring perfect alignment of the pins with the conducting pads. Glue or solder paste fastens the components onto the board.

A process known as reflow soldering melts the solder paste in a reflow oven to create solder joints. It then passes the board through coolers to solidify the paste once more and thereby hold all the components firmly in place.

A thorough quality check identifies and corrects any misalignments of components or errors in the layout.

The final process is box assembly, where the PCB&#;with its components soldered on&#;is finally encased with the outer covering to form the final product.

PCB Testing

The finished PCB goes through multiple tests:

• Power-off testing: an analog signature performed with the circuit board in switched-off mode. 

• In switched-off condition, the finished board is inspected visually by design engineers or expert inspectors.

• In a switched-on condition, in-circuit testing checks working functionality of the PCB functionality.

• Automatic optical inspection (AOI) uses high-speed camera scans to inspect assembled PCBs.

• X-ray inspection uses high-resolution scans to detect flaws like opens, shorts,, or voids on large boards, BGAs, and micro-BGAs.
• Functional testing establishes if the PCB performs as per the original design.

Fabricating a PCB and assembling a PCB are two separate processes. Any faults or errors in these processes can cause the device to fail or malfunction. Error-proof fabrication and flawless assembly together is the key to a successful electronic device.

Both PCB fabrication and PCB assembly must be undertaken by reputed, experienced PCB manufacturers to ensure quality and reliability. 

MIS electronics is a turnkey, one-stop PCB manufacturer. We provide PCB design, fabrication, and assembly (PCBA) services. One-stop PCB manufacturing is cost-effective as end-to-end fabrication and assembly facilities are available under one roof. It reduces the cost of transportation and labour; it reduces the chances of friction between different teams, leaves less room for errors, and aligns responsibility (and recourse) in one spot. Our experienced designers and engineers ensure that you get your electronics to the market fast and at an optimal cost. Get a no-obligation quote from us today.

I wrote a letter to a former teacher the other day, and given his impact on my career, I wanted to ensure I presented myself well. I used online tools to smooth over spelling and grammatical errors, but upon a reread, I realized I had used some imprecise (yet roughly synonymous) language. Most wouldn&#;t notice or care. But as a stickler for details, I couldn&#;t let it slide.

Language is tricky, especially wrapped within an industry&#;s nomenclature (or perhaps jargon)&#;for example, PCB vs. PCBA. A few people may be knowledgeable of the latter and certainly fewer than that of the former. As one may surmise from two acronyms separated by a single letter, their definitions are incredibly close and can be somewhat chaotic. Let&#;s take a closer look below.

Link to Shenzhen Thriver Digital Tech Co., Ltd.

PCB vs. PCBA: What&#;s the Difference?

Fabrication produces a

&#;a bare board or a printed wiring board (PWB).

Assembly creates a

, a printed circuit assembly (PCA), or a circuit card assembly (CCA). In some contexts, a fully assembled board is also a PCB.

PCB vs. PCBA: An Origin Story

The origins of the &#;printed&#; date back to the early days of PCB manufacturing, where mylar was the medium to recreate a photomask image of the circuit before photolithographically transferring it onto a copper-clad laminate. While the spirit remains the same with modern PCB computer-aided design (CAD) and computer-aided manufacturing (CAM), significant improvements must support manufacturing ease and performance. 

After placement and routing are complete, the layout designer will output all relevant manufacturing files. These files then transfer to CAM, where necessary adaptations are made, such as scaling the artwork and performing panelization (arranging PCBs on the same production panel to increase efficiency). At this point, pre-production processes have concluded, and the intricate, technical machining begins.

Fabrication Starts the PCB Manufacturing Process

As the foundation of the printed circuit board, fabrication acts as the first of the two major stages of manufacturing. Below is a list of the processes that comprise a standard fabrication job, but steps may be omitted or substituted depending on the exact requirements of the board:

1. Patterning: As described, the artwork output as design files must be transferred to a laminate with an etch-resistant ink before an acid etch application. Direct subtractive methods like milling and laser etching are also an option, but these methods scale poorly and generally only see use in prototyping.

2. Etching: Copper features are expressed by removing excess copper or electroplating treated laminate.

a. Subtractive etching uses acid to eat away at the areas of the copper uncovered by the etch resist, but careful process control is necessary. As the acid eats away at the surface copper, it exposes copper beneath the etch resist. This acid removes the copper by attacking the newly-formed sides underneath the etch resist, typically forming the trapezoidal trace shape. However, an extended time in contact with the acid can undercut the traces, lead to impedances above calculated values, and open in more extreme cases.

b. Additive etching is a complex and expensive process, although 3D printing may eventually yield a viable path forward with this methodology. 

c. Semi-additive is a hybrid of the additive and subtractive etch where a reverse image applies to a thin laminate. Copper plates to the board before image removal and the etching process begins. This sequence can improve copper features&#; fine control while reducing the undercut.

3. Lamination: The alternating layers of copper and prepreg are placed in a high-temperature press to fuse the materials and form the rough shape of the board.

4. Drilling: Connections spanning the board&#;s partial or full width require drilling. This process could be for through-hole packages or smaller layer-layer connections. Dense layouts may require laminating and then drilling between a certain number of layers before a final lamination; this increases space for layout by shrinking the size of the drilled hole at an additional cost.

5. Plating: To form the interconnectivity between layers in the drilled holes, boards undergo a plating process. Following this, a final plating prevents corrosion on exposed copper features.

6. Solder mask and silk: A solder mask is applied and developed to the surface areas of the board that require solder. Finally, a silkscreen layer provides reference designators, pin-one indicators, polarity markers, part numbers, and other essential information that needs to be available at a glance.

Tests will then verify that the board has passed through fabrication successfully, and then it&#;s on to assembly.

Assembly: The Dividing Line Between PCB vs. PCBA

Assembly is a less involved process than fabrication. However, the logistics of correctly placing thousands of components in the correct position and orientation at an acceptable production speed is nothing to sneeze at. 

There are two divergent paths that the assembly should consider:

• Through-hole packaging

  : Surface mount technology (SMT) is usually smaller, endearing it toward densely populated boards. A board with only SMT components can utilize a reflow oven to handle all its soldering applications, whereas through-hole devices require a pass through a wave solder machine. One advantage of through-hole components is the increased mechanical stability due to the greater bonding area &#; connectors that undergo constant mating cycles are prime candidates.

• Single- or double-sided assembly

  : Assemblies are simpler when mounting components on only one board side. However, double-sided assemblies are extremely common, especially with layouts that require routing on a component-side layer or when the total number and area of the parts are extensive.

Before soldering, however, the components must be placed; for mass-volume PCB lots, this requires a pick-and-place machine. Auto-feeder reels of SMT components and high-speed heads accurately place the components for dense assemblies. Like soldering, certain components may require hand placement due to their size or incompatibility with the equipment. With assembly complete, the board undergoes final testing, confirming the assembly process and the combined fabrication-assembly of PCB products. 

Some of these tests include:

• Optical inspection

  and

  power-off testing

  evaluate the board&#;s passive features, like the quality of the solder bond or impedance values measured by a meter.

• In-circuit

  and

  functional testing

  check the board&#;s performance when powered and ensure the board operates as intended.

Your Contract Manufacturer Can Clarify PCB Production

PCB vs. PCBA can be a confusing distinction, but proper context can reveal what stage of production is under consideration or even if a difference needs to be made in that case at all. Here at VSE, we&#;re a team of engineers committed to building electronics for our customers. That motivation extends to educating our customers about the assembly process and assuaging any concerns about translating their design into a fully realized board. Paired with our professional manufacturing partners, we strive to deliver the best PCBAs in production quantities from NPIs up to mass production.

For more information, please visit PCB Electronic Board Assembly.