What’s a Printed Circuit Board? 8 Key Points to Be an Expert
Jan 17, 2022
A PCB or Printed Circuit Board is a bare board that serves 2 purposes
- Mechanically support components
- Electrically connect electronic components using
- Using conductive pathways
- Signal traces made from copper sheets laminated onto a non-conductive substrate.
Just so you know, some people use the term PWC ( printed wiring boards) or etched wiring board to refer to a PCB; if the board has no components mounted on it and only has copper tracks and features, then both terms are acceptable.
Here’s a photo of what a printed circuit board looks like
Every electronic device on earth has a PCB; it simply wouldn’t be able to exist without one.
And like everything else in the technology world, things change fast.
Here are 10 things you need to know to sound like an expert when talking about a PCB
- 1.What are printed circuit boards made of?
- 2.Printed Circuit Boards – The Layers
- 3. Printed Circuit Boards – Rigid or Flex PCBs
- 4. Printed Circuit Boards – The Finish
- 5.Printed Circuit Boards – Electronic Components
- 6. Printed Circuit Boards – How to Design It?
- 7. Printed Circuit Boards – The Cost
- 8. Printed Circuit Board Assembly Process
1.What are printed circuit boards made of?
This is so basic that many forget to research it, but here’s what a printed circuit board’s materials usually consist of.
- The core consists of a fiberglass epoxy resin; totally non-conductive.
- On both sides (next to the core) comes a layer of copper foil; you may apply a layer of gold or silver for a final finish. This is a conductive layer.
- The conductive layers are covered with a thin solder mask that protects the conductive layer; it’s made of polymer ink.
- On top of the solder mask comes the silk print overlay; this comes with the components’ references or markings for assembly guidance.
Now you know what a printed circuit is made of
2.Printed Circuit Boards – The Layers
This section will talk about how printed circuit boards are classified. So when someone talks about rigid PCBs, rigid-flex PCBs, flexible PCBs, multi-layer PCBs, or any other kind of printed circuit board, you know what they’re talking about.
Quick printed circuit board categorization
- Single-Sided PCBs
- Double-Sided PCBs
- Multilayer PCBs
- Rigid PCBs
- Flex PCBs
- Rigid-Flex PCBs
Let’s talk a bit about each one.
Single-Sided Printed Circuit Board
This is the most common type of printed circuit board; its name already explains much of this PCB.
Only one of its sides has a conductive copper layer, which means that electronic components, whether through-hole components or surface mount components ( more on this later), can only be assembled on one side of the PCB.
Here’s an illustration of what a single-sided printed circuit board is composed of
Single-sided PCBs are the go-to choice for low-cost and low complexity electronics; think of radios and basic calculators.
They’re very basic, and people still use them because they’re
Advantages of single-sided PCBs
- Easy to manufacture
- Great for low-density designs
- Easy to repair and design
Double-Sided Printed Circuit Board
You guessed it right, both sides of this type of PCB have a conductive layer; they’re also known as two-layer PCB.
Circuits on one side of the board can be connected on the other side of the board with the help of holes drilled on the board; this makes it extremely useful for those electronics that require many components packed in a reduced space.
Cellphones and other complex electronics use double-sided PCBs; this puts them in the middle / high complexity electronics applications.
Advantages of Double-sided PCBs
- It allows for more components in small spaces
- Relative low cost
- It allows for more design flexibility
- Higher circuit density
Multi-Layer Printed Circuit Board
If it has more than two conductive inner layers of copper, then it is a multi-layer printed circuit board.
Here’s something I want to explain because it’s a question many beginners ask; it goes something like this.
A printed circuit board only has two sides; there can be more than 2 copper layers?
If you think that is most likely because you believe that a double-sided PCB means that you can mount components on both sides of the printed circuit board.
That’s not the case.
The following illustration will clear things up
It’s like a sandwich
- Solder mask
- Non-conductive substrate – fiberglass epoxy resin
- Non-conductive substrate – fiberglass epoxy resin
- Non-conductive substrate – fiberglass epoxy resin
- Solder mask
No matter the type of PCB, all of the components will be mounted on one side of the PCB; the one with the silk print overlay.
How will the electronic components reach the second or third layer of copper?
One must drill holes on the printed circuit board so the components can reach those copper layers.
Advantages of Multi-Layer PCBs
- Super compact size
- High level of design flexibility
- Great for high-speed circuits
Great, now you know what a printed circuit board is made of and that it can be a one-sided, double-sided, or multi-layer.
3. Printed Circuit Boards – Rigid or Flex PCBs
Another essential thing to understand about a printed circuit board; does your PCB design require a rigid or flexible printed circuit board?
Their names are pretty self-explanatory; one you can bend, and the other one, well, is rigid.
Here’s a photo of what a flexible printed circuit board looks like
Here’s what the typical rigid printed circuit board looks like
Reasons to use a flexible printed circuit board.
- This PCB design allows for excellent product design flexibility as you can bend, fold and even crease the circuit board.
- The circuit design adapts to the product shape, not the other way around.
- They provide reliable connectivity for electronics that will bend constantly.
- A flex PCB can connect 2 or more rigid PCBs
- Flexible circuits are ideal for laptops, foldable and wearable electronics.
- This type of printed circuit board PCB is exceptionally lightweight.
- You might think that rigid PCBs last longer, but not necessarily; a flexible printed circuit board is better at absorbing shock and vibrations.
- Flex PCBs are better at resisting heat, chemicals, or radiation damage.
Reasons to use a rigid printed circuit board.
- Rigid printed circuit boards remain popular thanks to their low cost
- If space is not a concern, then rigid PCBs are usually the best choice
- For large electronics of low complexity
I mentioned that flexible printed circuit boards are great for connecting components and other PCBs, too; well, that’s what’s referred to as a rigid-flex printed circuit board.
Here’s a photo
When to go for a rigid-flex circuit card assembly?
- You need high reliability. Your device will be exposed to repeated shock and high vibration
- High-density application. Your device is too small to accommodate a lot of wiring and connectors. A rigid-flex PCB is easier to fit in small spaces and removes the need for wires.
- Many rigid boards. If your device contains many rigid boards, connecting them with a flexible PCB is more cost-effective than flex cables.
4. Printed Circuit Boards – The Finish
What is this exactly? Well, we need to protect the copper traces from any external environment threat; they need to make it to the printed circuit board assembly process intact.
This is exactly what the finish does.
The most common types of printed circuit board finish are
- ENIG – Electroless Nickel Immersion Gold
- HASL – Hot Air Solder Leveling
- OSP – Organic Solderability
- ISN – Immersion Tin
- IAG – Immersion Silver Plating
I wrote another article going into the details of each of these finish types; to find out which is the right one for your printed circuit board PCB, please click the following link.
ENIG RoHs vs. OSP vs HASL vs. ISN vs IAG Comparison Table
Go there, and you’ll find all the details on this topic, but I’ll leave here the most important questions you have to ask yourself to decide which type of finish you need for your printed circuit board
How to decide which PCB finish I need?
- Will my circuit board be exposed to many solder cycles?
- Is flatness critical?
- What’s the minimum shelf life required?
- Is budget a constraint?
- How wettable/solderable do I need the PCB to be?
- Does my PCB need to be RoHS compliant?
- What kind of storage conditions will I have to keep the PCBs?
- Does the PCB need gold or aluminum wire bonding?
Perfect, now you know what a PCB is made of, the types of PCB there are, and the types of finish you can apply on them.
Now we’re going to talk about the most exciting part, at least for me.
- Mounting components
- Component placement
- Through-hole components
- surface mount components
What’s all this? Let’s find out
5.Printed Circuit Boards – Electronic Components
When it comes to electronic components for printed circuit board assembly; you have two big categories to choose from.
Please note that the components you’ll use for your PCB design will depend on what your product needs to do; it’s not about what the cheapest components are; that’s not how you approach PCB design.
Let’s begin with surface mount components or surface mount device.
These components are tiny, so small that picking them up with your hands and applying solder paste it’s either difficult or impossible, so how do you mount them on your PCBs?
There’s an automated process called the SMT assembly process; this is a service all PCB manufacturers offer.
Here’s a video of this PCBA manufacturing process.
The other big category of electronic components is through-hole components.
These are bigger than SMD components; you can choose to do it by hand or using an automated process for the PCB assembly.
SMT or THT Components for your PCB Design?
Nowadays, people go for SMD components because they’re smaller, and as electronic devices continue to shrink, they become the perfect option.
Having components mounted on a PCB is also faster this way.
If you used THT components, you’ll have to drill holes on the circuit board for the component leads to go through.
This is an additional cost, and keep in mind that THT components are bigger.
Flexible PCBs can only handle SMD components.
As with many other things in the electronics industry, there’s a comparison table here.
SMD vs. SMT vs. THT Technology – What works best for the mass manufacturing process?
Your PCB design will include both types of components because there’s one thing THT components provide that SMD components don’t; thanks to the component leads, they provide stronger bonds to the printed circuit board.
6. Printed Circuit Boards – How to Design It?
If you’ve made it this far now, you know a lot about a printed circuit board.
The materials, the layers, the type, the components, and the finish; that’s a lot; you’re ready to have a basic conversation about PCBs.
However, how do you actually design one? This is a bit technical.
- Electronic systems
- PCB capabilities
- Electrical signals
- PCB traces
- Internal layers
- Insulating layers
- Alternating layers
- Plane layers
You have to understand all of that and more, way more.
I won’t go into the details of designing a PCB, as that’s not the purpose of this article; I will give you the basic steps and leave you with some resources to learn more about how to design a PCB.
10 Steps for PCB Design
- Have a great understanding of electrical connections and parameters
- Develop a schematic of the printed circuit board
- Use a tool such as Altium to create the PCB layout
- Design the PCB stack up
- Make sure the design follows the acceptability criteria from the IPC
- Move on to component placement; you must indicate where each component will go
- Indicate where the drill holes will go
- Route the traces
- Add labels, so PCB manufacturers know where specific components will go
- Generate the PCB layout design files; these are the files you’ll send to the PCB manufacturers.
Designing your Printed circuit board PCB right is extremely important; without a proper design, no device in the entirety of the electronics industry could exist.
If you’re working on a big project, make sure you hire a professional.
Design for Manufacturing Rules for PCB Layout.
7. Printed Circuit Boards – The Cost
If you want to sound like an expert when discussing printed circuit board assembly, you have to know the costs.
Here’s where many ask, is it cheaper in China?
The short answer is, yes, the manufacturing process is cheaper in China.
Allow me to give you some numbers for more clarity.
30 two-layer boards, 80x90mm in size, will cost you US$ 339 from a PCBA manufacturer in Germany.
The same units with the exact specifications will cost you US$20 in China.
Also, PCBA manufacturers in China have one week or less turnaround times.
PCB assembly in the USA will have a turnaround time of a month and a unit price of US$3.48/unit for a 1k units’ order.
The exact order made to a Chinese PCBA manufacturer would cost you US$0.37/unit and have a turnaround time of 5 days.
Even after import tariffs are calculated, PCB assembly in China is cheaper and faster.
8. Printed Circuit Board Assembly Process
Perfect; now onto the last thing you should know about to be an expert on Printed circuit board PCB.
The assembly process goes like this
- PCB Board and Laser Marking
- Applying Solder Paste
- Solder Paste Inspection (SPI)
- Pick and Place Machine
- Reflow Soldering
- Visual inspection
- Manual Inspection
- Automated Optical Inspection
- Through Hole and Manual Assembly
- Electrical Testing
- X-Ray inspection
- Functional Test
That’s the process right there; please click on the following link if you want to dig deeper into this.
PCB Assembly Process in 14 Photos
Well, that’s it for this article. If you’re looking for someone to help you with an electronics development project, please get in touch with us.
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