Originally developed by Valor, ODB++ is an electronic database for printed circuit board manufacturing. Created in 1995, it was... READ MORE
How to Read a PCB Fabrication Drawing
A fabrication drawing specifies how the PCB is to be manufactured. There are four major sections to a fabrication drawing—Board Illustration, Drill Chart, Section A-A, Notes, and Title Block.
The board illustration shows the actual board outline with all cutouts, corners and radii. Usually only the top side of the board is shown. Board dimensions are referenced from the 0-0 point [See Figure 1 (a)]. The 0-0 point on the fabrication drawing must match the 0-0 point on the NC Drill data, which were generated earlier in the Final Extract process. All drilled holes are indicated with symbols linking them to the drill chart.
Under a column labeled, “Symbol,” the drill chart lists each drill symbol used in the board illustration [See Figure 1 (b)]. Other columns give further information regarding each hole type. The additional information is listed under columns labeled, “Diameter (in),” “Tolerance (in),” “Plated,” and “Quantity.” The hole size is the actual finished hole size after plating. The description of the hole plating is either “Yes” or “No.” The quantity is the actual number of holes drilled to this specification.
The third section of the fabrication drawing is a view of the cross-section of the board, commonly referred to as a ‘sandwich.’ Items identified in this view are the overall board thickness, the layer numbers of the board, description of the layer (e.g., component side, VCC plane, etc.), dielectric thicknesses, and impedance information [See Figure 1 (c)]. If a Section A-A diagram is shown, as is usually the case, the board illustration must contain an indication of the point from where this view is seen.
The last typical section on the fabrication drawing is the section containing fab. notes [See figure 1 (d)]. While highly standardized, there is always some item to modify for the particular board on which you are working (e.g., finish type, gold fingers, or miscellaneous silkscreen aspects).
The fabrication drawing title block should also be filled out with the name of the customer, the name of the board, any drawing or fabrication numbers specified by the customer, and the ODA job number [See Figure 1 (e)].