Single and double sided circuit boards
A single sided board is made from rigid laminate consisting of a woven glass epoxy base material clad with copper on one side of varying thickness. Double sided boards are made from the same type of base material clad with copper on two sides of varying thickness
Multi-layer boards are made from the same base material with copper foil on the top & bottom and one or more
“inner layer” cores. The number of “layers” corresponds to the number of copper foil layers.
multi-layer board fabrication
Multi-layer fabrication begins with the selection of an inner layer core –or thin laminate material of the proper thickness. Cores can vary from 0.038”to 0.005”
thick and the number of cores used will depend upon the board’s design.
Dry-film Resist Coating Inner Layer Core Material
A light sensitive film or photo image-able “resist”is then applied by heat and pressure to the metal surfaces of the core.
The film is sensitive to ultraviolet light. You will find “yellow light”used in most Image processing areas to prevent inadvertent exposure of the resist. The filters remove the wave length of light that would affect the resist coating.
Photo Tools or Artwork
The gerber data or electronic data for the part is used to plot film that depicts the traces and pads of the board’s design. The photo tools or artwork include solder mask and legend or nomenclature as well as the copper features. This film is used to place an image on the resist
Each of the circuit and land patterns are unique to that part number and each layer has its own artwork pattern or piece of film. Inner layer film is negative and outer layer film is positive
Inner layer film is “negative”. That means that the copper patterns left behind after processing the core are the “clear”areas on the film.
Outer layer film is “positive”. The traces and pads that are “opaque”on the film are copper on the outside of the board and the clear areas will be clear of copper.
Panels are then exposed to a high intensity ultraviolet light source coming through the film. Clear areas allow light to pass through and polymerize (harden) the film resist thus creating an image of the circuit pattern –similar to a negative and a photograph