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With printed circuit board fabrication there are two basic types of technology you will need to understand. These are design and manufacturing. Design focuses on the processes needed to make the actual printed circuit board once the masks have been produced from the design database. Printed circuit boards used to be built on ceramic or FR4 substrates coated in photosensitive resin. This exposes the board to UV light with a mask or stencil between the light source and the board. The purpose is to set the features included in the mask into the resin. The materials was made using a chemical that attacks the non-reacted resin. Then copper or aluminum plating was done to create the circuitry on the channels created. To help protect the metal traces and only leave the areas for component attachment exposed, cover the board with second coat of photosensitive resin. While this second layer of resin only allows one layer of circuitry on the printed circuit board, it should be still be sufficient if the application is not too demanding. In other words, your board should have a low number of components with relatively moderate requirements of power and heat dissipation. To create a multi-layered printed circuit board with a more complex design, the above process will need to be repeated several times. Alternate with coatings of resin, exposure, development, etching, plating and recoating to grow metal and isolator layers. This recoating is required to enable sufficient escape lines for all signals and enough input lines for power and groud The core of a printed circuit board is normally made of FR4 or a similar epoxylated material reinforced with fiber glass. An alternate build up comes after that between the Cu planes and the isolating layers. These are normally constructed using a glass fiber or epoxy laminate called prepreg or ABF. To connect all the different metal layers there are holes drilled through the core called vias, or blind buried vias that connect from one plane to the next. Areas that are no blocked on your printed circuit board allow light to pass through and set the resin. After some time has passed and the material has had a chance to develop, the lighted areas will remain while all the non-exposed areas get etched away. Copper plating ensues on the open areas; the hardened resin is stripped away and more prepreg material is laminated to create another layer. It is essential that you give yourself plenty of time for careful preparation and quality control during all of these individual steps. The more care you give to each step, the higher quality printed circuit board you will end up with. Many control steps are implemented to make sure the right processing paramenters are used. Underexposure in UV will usually result in shorts, while overexposure in UV could ensure the sharp features of your board. It can all be a costly and time consuming process.
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