Manufacturing of Double-Sided and Multi-Layer Printed Circuit Boards
This is the first in a series of articles that will explain what is involved in the Printed Circuit Board (PCB) manufacturing process of a double sided PCB and a multilayer PCB. This will be very high-level overview to provide someone who is not familiar with the manufacturing process the basics of how a PCB is manufactured.
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 is the difference between a doubled sided PCB and a multilayer PCB?
Double Sided PCB
First, a double sided PCB and single sided PCB are essentially the same. The difference being is that a single sided board has copper on one side of the board. Technically speaking, a single-sided board will not have copper plated in the drilled holes either.
A multilayer PCB has more than two layers. That is, anything more than a double sided PCB.
Let’s start with the raw materials that make up PCBs. The foundation of the PCB is the rigid fiberglass laminate. When it comes to the manufacturing process, there are many types of PCB materials that may be used. 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 FR4 material is already clad with copper when purchased by the PCB Manufacturer. A standard thickness would be .059″ of material clad with 1 oz of copper (1.34 mils) thick. The amount of copper weight that covers a square foot of area is what determines the 1 oz. 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″.
Multilayer PCBs are only a little different that the Double Sided PCBs.
As you can see in the image to the right, 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.
There is the B stage PrePreg, which is fiberglass that is still soft that will need 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 the basics of the starting material for a Double Sided PCB and Multi Layer PCB. Is it what you expected or thought it would be?
Feel free to ask your questions in the comments below!