● Board material
● Core material
● The pre-preg material
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There are many steps in the PCB design process and set-up comes first, from which we might know the importance of step of set-up. Generally speaking, set-up is the initial choices and determinations of materials, processes and requirements. Now let’s take a view about the material set-up in PCB design.
Nowadays, the types of board materials are decreasing, and higher quality materials are being used more commonly. Class and reliability are more related with the design than the board manufacturing. In fact, coupons and cross sections of the hole are required to be specified for the hole wall evaluation, along with board numbering. All these requirements contribute to the PCB quality tracking and responsibility determination.
Core material is another material set-up. Most materials provided by manufacturers are up to IPC standards. As a fiberglass dielectric with copper clad, the material set-up should not only include the thickness of copper, but also specify the dielectric thickness.
The pre-preg material
The Pre-preg is a fiberglass-type material and should be included in material set-up of PCB design. In order to serve as an insulator between the copper layers, it is pre-impregnated with an adhesive used to the core material. The tolerance for this material should be less than +/-.001’’[.0254], while the pre-preg comes in sheets with the thickness of .002’’[.0508]each. Besides, the material tolerance will be additive when the pre-preg is stacked to create the desired thickness. Considering this point, you’d better not expect the manufacturers for the minimum pre-preg thickness tolerance, unless the thickness is vital in cases such as controlled impedance boards.