In PCB design, you develop a schematic diagram and layout for a PCB. This design carries information such as components’ placement and electric path routing. Simultaneously, in PCB assembly, PCB manufacturers install electronic parts following the PCB design. These components are capacitors, resistors, and ICs.

What is a PCB?

A printed circuit board is a flat board with many electric components. They have conductive copper tracks. These components are pretty common like capacitors, ICS, and resistors. Generally, you are carrying these green boards with you every time. Interesting? Check your smartphone or any gadget. You will find a small flat board that ensures seamless function of your device.

What are Circuit Boards made of?

A printed circuit board is not a single plate. It has numerous layers. Interestingly, each layer is developed to deliver a specific function. You will read the details below.

Substrate

The substrate is the basic substrate. What is its function? It makes the conductive layers stable. Subsequently, it fights against heat, strain, and electrical loads.

Common Substrate Materials:

FR4:

FR4 is a pretty popular epoxy. In contemporary gadgets, water-repellant features have become crucial. Therefore, contemporary PCB manufacturers prefer to work with FR4 materials.

Polyimide:

Polyimide material makes the PCB base flexible. So it helps the PCB to flex and be compliant with surfaces. This material offers low electronic noise and perform under high temperatures.

Ceramic:

They arrange conductive pathways in PCB surfaces. Because this material contains great electrical properties, it does not let the PCB parts like communication systems and RF hold excessive heat.

Metal-Core Substrates:

Metal core substrates are usually made with aluminum or copper. They tackle problematic heat generation. That is the must-feature for applications like power equipment and LEDs.

Copper Layers

The electric routes that connect components are made of layers of copper. These are the layers used for the transmission of signals and power on the PCB.

Properties of Copper Layers:

Conductivity: Copper, being a highly conductive metal, allows for better signal and power transmission.

Copper thickness: The copper thickness affects the amount of current that PCB will carry.

Common Copper Thicknesses:

Standard Copper (1 oz/ft²):

1 oz/ft² indicates the weight of copper spread over one square foot, corresponding to a thickness of approximately 35 microns.

Heavy Copper (2-10 oz/ft²):

It is a thicker film for the conduction of large currents. You can find this material in power supplies and motor controllers.

Dielectric Layer

Between the copper-made layers is a layer of dielectric, an insulating material. This prevents short circuits from occurring, ensuring the PCB will operate correctly.

Dielectric Materials properties list:

Dielectric Constant

The dielectric constant measures the storage capacity of material electrical energy. Higher DK sees how much material absorbs electrical charge compared to vacuum. Lower ones are suitable for parts enabling larger signal speeds. Like microwave transmission lines, RF, and digital circuits.

Loss Tangent

It indicates the propagation of signal power. That is absorbed by the material as thermal energy. Depending on its structure and glass resin induction, Df is good for high-frequency assemblies.

Material Options:

●      Epoxy Resin

●      PTFE (Polytetrafluoroethylene)

●      Dielectric Ceramic

Solder Mask

Solder masks are the thin lacquer. It is made of polymer. This layer protects the copper traces. In many cases, there always remains a chance for oxidation.

Functions of the Solder Mask:

Reduces Bridges: Stops solder from flowing in the wrong direction

Copper Protection: Prevents oxidation and corrosion.

Easier to View: Copper traces and pads are more visible.

Silkscreen

Silkscreen—the uppermost layer printed on the solder mask. It provides labels and hints to aid in assembling and organizing the problems.

Purpose of Silkscreen:

Component Labeling: Labels parts, pins and directions.

Assembly Guidance: Assists in placing components, whether manually or through automation.

Testing Aid: Marks the testing points and critical connections for testing purposes.

Examples of Advanced Manufacturing Material

A specialized use case for PCBs requires advanced PCB materials because there are additional demands to be met.

How to Design a PCB?

Where to start for making PCB assemblies? It involves the same few steps. But precision, creativity, and technical capability are paramount. That will cater to each stage, like well-working, productive, and budget.

Detailed Design Steps:

●      Identify the Design Needs

●      Routing

●      Power and Ground Planes

●      Simulation and Verification

●      Design Rule Checks

●      File Generation

Identify the Design Needs

Take the first step by making a functionality list of PCBs. That is subject to a particular product weighing environmental conditions. Mention the required size, detailed dimension, necessity of layers, and component placements.

Schematic Design:

PCB designers create the visual design of a PCB. Why do they make it? The reason is to show how components will be interconnected. Moreover, it will be easy to detect errors. Therefore, it is recommended to focus on precise documentation.

Power and Ground Plans:

It represents the wider continuous areas. That is focused on distributing the power supply voltage and electric signals. The noise in the signals can often be minimized by separation.

Simulation and Verification:

Use specialized software to build a virtual model. In this way, you can analyze the signal reflections, electronic behavior, thermal hotspots, or crosstalk issues.

Design Rule Checks:

Automated checks ensure your layout is compliant with the manufacturable tolerances such as minimum trace width, distance between traces (spacing), and via size.

File Generation:

Exporting files such as Gerber and drill files and other manufacturing documents. You should check these diligently to ensure they match what you are designing.

What is a PCB Assembly?

PCB assembly (PCBA) converts an ordinary PCB to a complete electronic circuit by mounting and soldering components. This means that there is technology and concrete measures that allow every part to do its own job efficiently.

Common Assembly Techniques:

Surface-Mount Technology

Components are attached to the PCB surface. Surface Mount Technology (SMT) aids in more components per unit area and is thus well suited for modern miniaturized devices.

THT

To solder components with leads, you should insert them in pre-drilled holes. For the mechanical strength, connector components are removed from THT.

Mixed Technology:

Integrates SMT and THT to benefit from the best of both worlds.

How to Assemble a PCB?

You have made a PCB design and manufactured it so what is next? The next step is assembly. PCB manufacturers install small parts all over the board. Let’s read the different steps involved in PCBA.

Solder Paste Application

PCB manufacturers can apply solder paste on the board, which provides temporary adhesion for parts.

Process:

A stainless-steel stencil with holes is placed over the PCB. Solder paste—a mix of flux and solder powder—is applied over the stencil with a squeegee. That paste only sticks where pads are exposed. Components to be will be laid on top of it.

Component Placement

Components are placed on the PCB in areas where voids of solder paste were already applied. This step can be done machine or handwork based on design.

Machines that get products from one point in a factory to another automatically are called automated pick-and-place machines. Components are placed with pinpoint accuracy by miniaturized high-speed machines.

These machines read the design file to know where each component goes. Parts are taken from reels or trays and placed directly onto the solder paste.

Manual Placement:

Suitable for one-off, bigger, and lower volume designs. Operators manually place large components, for example, connectors or transformers.

Reflow Soldering

Reflow soldering, used for surface mount technology (SMT) components This allows solder paste to liquefy and later harden. It creates electrical connections that are not only very long-lasting but also possess mechanical strength.

Process:

The solder paste PCB was placed on-belt running into a reflow oven. The board goes through the following stepwise heating in an oven:

Preheating: Start with slow heating to ensure thermal shock is avoided.

Soak: Holds the temperature steady to obtain flux activation from the solder paste.

Reflow: Rises to a temperature that liquidates the solder (~250°C for lead-free solder).

Cooling: Slowly reduce the temperature to freeze the solder.

Wave Soldering

For through-hole (THT) components, we use wave soldering. This is most effective when you have leads of parts that go into holes in the PCB.

Process:

Held at an angle, the PCB is tracked across a stream of molten solder. Solder applies to the exposed leads, and it fills the holes so there are strong connections.

Cleaning

PCB assembly companies incorporate IPA into clean-soldered components. It helps significantly to clear flux residue and dust from the board.

AOI

Cameras scan the board for wrongly installed components. AOI also identifies poor solder joints, such as insufficient solder, bridging, etc.

X-ray Inspection:

Apply to invisible solder joints like in Ball Grid Array (BGA) parts. In-situ detection of voids, cracks, or insufficient solder below the component.

Functional Testing

Functional testing is important to check the entire assembly instead of the components. At this step, the power sources are applied to run the device.

It is the final stage to examine. That, whether the parts are working properly or not under simulated real-time practice.

Tips from PCB Design to Assembly

You would be an expert in PCB design basics and assembly. However, here, you will read some very useful tips to improve your design and assembly.

The first stage is Design:

    1. Precise schematic is something you must be very careful about. It is recommended to incorporate visible symbols and labels.
 
    2. The second tip is to double check your layout. Why this is important because it will reduce your crosstalk and signal length.

    3. The best tip is to incorporate DRC so you can identify the issues on time.

2nd Stage is Assembly:

    

    1. Always go to a reliable supplier because he can supply you with top-rated parts.

    2. Simultaneously, choose reflow or wave soldering to make very powerful joints.

    

    3. Never forget to run an inspection test. It will help you to identify any missing components.

Conclusion:

Before coming to a conclusion, you must have understood the fundamentals of PCB design and assembly. You have read the steps above for designing a PCB and core substrate materials. Moreover, how can you make PCB assembly successful?

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