Printed Circuit Boards
Written by a world-renowned electronics expert, this reader-friendly guide helps engineers and technicians solve issues in PCB layout, fabrication, assembly, and testing.
TABLE OF CONTENTS Printed Circuit Boards
Chapter 6: Copper Clad Laminates
6.1 Anatomy of Laminates
The basic function of the laminate is to provide mechanical support for electronic components and to interconnect them electrically. Laminates for PCBs are composite materials. They can be simply described as products obtained by pressing layers of a filler material impregnated with resin under heat and pressure. The resulting thin insulating material, which is the mixture of filler (reinforcement) and resin on which all conductors and components are mounted, is called base material. This can be either rigid or flexible material.
6.1.1 Fillers (Reinforcements)
Fillers are meant to provide mechanical strength, stability and rigidity to the laminate. The commonly used fillers are a variety of papers, cotton fabric, asbestos sheet, glass in various forms such as cloth and continuous filament mat, ceramic material, molybdenum, etc. However, the most common materials used are paper and glass fibre.
Paper has been used as reinforcement in a vast majority of printed circuit boards. They are low priced and are easily machinable. However, they have a tendency to absorb a lot of moisture.
Fibre-glass as reinforcement has gained popularity because of its high tensile strength and dimensional stability. It offers a high resistance to temperature variation and has a low moisture absorption property.
6.1.2 Resins
Resins are used to impregnate the selected fillers. The commonly used resins in the manufacture of base materials are phenol, polyester, cyanate ester, epoxy and polyimide. Of these, the epoxies and phenolics are used for about 90 per cent of all laminates. They are...
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