Thursday, September 12 , 2019 1
Fundamentals 09/12/19 2 A printed circuit board (PCB) consists of an insulating base material that supports the copper traces
Base Material of PCB Phenolic base material was used in the past for applications in which performance was not critical because it was inexpensive Most of the PCB have an insulating base material is typically epoxy fiberglass, but ceramic and Teflon are also used as base material in special cases A majority of printed circuit boards made in the United States start with a solid copper foil that is bonded to the insulating base material, which is typically epoxy fiberglass. The standard base thickness was typically 1/16″ or 0.062″ • . 09/12/19 3
Example of Epoxy Fibreless PCB 09/12/19 4
Ounce • The copper in a PCB is rated in ounces , and represents the thickness of 1 ounce of copper rolled out to an area of 1 square foot • One ounce refers to the weight of copper spread over one square foot • One ounce copper plating is approximately 0.003″ thick. Two-ounce copper is 0.006″ thick and so on. 09/12/19 5
Etched Printed Circuit Board 09/12/19 6 The desired traces are printed onto the copper with a material called resist . The board is then placed in a chemical tray with a chemical for etching, referred to as an etchant, to remove the copper not covered by the resist. The etchants often used for etching small quantities of printed circuit boards are either ferric chloride or ammonium persulphate Commercial printed circuit board fabricators generally use different chemicals that are less expensive, such as ammonium chloride
Etched Printed Circuit Board 09/12/19 7 After washing and cleaning the etched board, the result is a copper circuit pattern on an insulating base—a Printed Circuit Board
Layers of PCB after Etching There are also two additional layers of a printed circuit board after it is etched. These additional layers are nonconductive. These layers are as: Component layout layer The Solder mask layers. 09/12/19 8
Layers of PCB after Etching The component layout layer acts as a map when assembling and troubleshooting the printed circuit board. This layout layer consists of text and graphic symbols that identify each component with its proper orientation. A good component layout layer can save a tremendous amount of time The solder mask controls or indicates where the solder will be placed on the printed circuit board pads during a process called wave soldering . This solder will only connect the components to the solder pads. When making only one or two boards with a simple design a solder mask may not be needed. Additionally, the solder mask adds corrosion protection to the printed circuit board traces Wave soldering is a large-scale soldering process by which electronic components are soldered to a printed circuit board (PCB) to form an electronic assembly.
You've reached the end of your free preview.
Want to read all 31 pages?
- Fall '19
- Printed circuit board