This is the first in a series of articles that will explain what is involved in the Printed Circuit Board (PCB) manufacturing process. Most of what we will cover will be very high-level to provide someone who is not familiar with the manufacturing process the basics of how a PCB is actually made.
Those who will find this series most useful will be hobbyists, students, and those who are new to the industry. Of course if you are in the PCB industry, I would invite you to comment and share your thoughts as well.
What I want to start with is an explanation of the difference between Double-Sided and Multi-Layer PCBs. I will share some images with you as well to help explain these differences.
First, a double-sided board and single sided board are basically the same, apart from a single sided board having, of course, copper on one side of the board. Technically speaking, a single-sided board will not have copper plated holes either.
A multi-layer board is a PCB that has more than two layers. It is basically anything more than a double-sided board.
Let’s start with the raw materials that make up PCBs. The foundation of the PCB is the rigid fiberglass laminate. There are many types of PCB materials that may be used in the manufacturing process. Which material gets used is determined by the PCB designer in order to meet electrical, temperature, and other related properties. For this discussion we will just talk about the standard material that is used, which is fiberglass and often referred to as FR4.
The PCB manufacturer will buy the FR4 material already clad with copper. A standard thickness would be .059″ of material clad with 1 oz of copper (1.34 mils) thick. The 1 oz is based on how much copper weight covers a square foot of area. The total then, would be close to .062″ in final thickness. Solder Mask and Legend, which we will discuss later, can be added as well and adds a tiny bit to the overall thickness.
There are many different thicknesses available for double-sided boards. Some examples are .020″, .031″, .047″, .059″, .093″, .125″.
Multi-Layer PCBs are only a little different that the Double-Sided Boards.
As you can see in the image below, a four-layer board starts with a rigid core of FR4 and copper. The internal core is processed for traces on those prior to the other fiberglass and copper being added, and the entire board is laminated together.
You have the B stage PrePreg, which is basically fiberglass that is still soft needing to be heated in order to become rigid. It acts like a glue to keep the inner core adhered to the outer copper foil.The copper foil added consists of very thin and loose sheets of copper. They are sandwiched together with the Prepreg and inner core, and placed in a PCB Lamination Press. Pressure and heat are applied to the material,which causes the Prepreg to “flow” and bind the layers together. Once it cools, the fiberglass is then hard and the entire board is very rigid.
After lamination of the board, the outer layers are processed for traces and drilling. We will discuss those steps in greater detail in later articles.
That gives you the basics of the starting material for a Double-Sided
and Multi-Layer Printed Circuit Board. Is it what you expected or
thought it would be?
Feel free to ask your questions in the comments below.
Much more coming on the many steps and processes involved in manufacturing a Printed Circuit Board.