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Glossary of Terms



Flex Circuit - A printed circuit designed with flexible materials to allow it to comply with a non-linear surface or in some applications to move with a mechanical mount that is not stationary.


Fingers - i.e. a sometimes used term for edge connector features etched into the edge of the board to interconnect with a standard edge type receptacle.

Fiducials - The SMEMA 3.1 standards define the parameters that governs the size and shape of standard Fiducial Marks.



 Fiducial Marks provide common measurable points for all steps in the assembly process.

 This allows all automated assembly equipment to accurately locate the circuit pattern. Fiducial Marks are generally categorized in the following types:



Global Fiducials:
Fiducial marks used to locate the position of all features on an individual printed circuit board. When multiple boards are processed as a panel, the global fiducials may also be referred to as panel fiducials if used to locate the circuits from the panel datum.

Local Fiducials:
A fiducial mark (or marks) used to locate the position of an individual land pattern or component that may require more precise location, such as a .020 pitch QFP.


Image Fiducials:
Global fiducial marks on a multiple printed circuit board fabrication panel that are located within the perimeter of an end-product printed circuit board.

Panel Fiducials:
Global fiducial marks on a multiple printed circuit board fabrication panel that are located outside the perimeters of the end-product printed circuit boards.


Board flatness is described in terms of a deviation from a theoretical perfectly flatness in inches square... with the effective deviation from that datum being .0075 in per in for surface mount technology boards. (Through hole technology allows .0150 in. per in. deviation). What that means is that any given square inch of board surface will not exceed a difference of .0075 inches in it's flatness with respect to any adjacent square inch of board surface around it. An example of this would be like the figure shown below, where we have a board that is 10 inches wide and is illustrated in a typical arc at the extreme bow or warp that still would pass under the .0075 in. per in. rule. The total deviation for the board at it's center is only .0375 inches from edge to center assuming the maximum allowable deviation inch per inch across it's surface from end to end.


For the specification regarding testing for surface flatness see IPC-TM-650 Method 2.4.22. http://www.ipc.org/4.0_Knowledge/4.1_Standards/test/2.4.22c.pdf








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