The IPC-7351A only recommends local fiducials for QFP parts with a pitch of less than 0.625mm and BGA parts with a pitch less than 1mm.
The local fiducial size is 1mm diameter with a 2mm solder mask clearance to prevent shiny reflection when optically bombsiting. Because of the 2mm solder mask removal, a trace, via and copper keepout area of 2mm diameter is used to prevent those elements from entering into the exposed solder mask area.
Here is a picture that illustrates the proper location of local fiducials. Pin 1 is in the upper left corner.

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Fiducial Mark Design Guidelines


Scope: To provide a generic guideline for the design and placement of Fiducial marks. The guidelines adhere to design rules standardized by the Surface Mount Equipment Manufacturers Association and are supported by IPC.




            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 two types:


                        Global Fiducials – 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.

                        Local Fiducials- Used to locate the position of an individual component that

                                    may require more precise location, such as a .020” pitch QFP.


            Global and/or panel fiducials should ideally be located on a three point grid based

            system, with the lower left fiducial located at the 0,0 datum point and the other two

            fiducials located in the positive X and Y directions.


            Global fiducials should be located on all PCB layers that contain components to be

            mounted with automated equipment. While other circuit objects (via-holes, etc.) can be    used, this can compromise accurate component placement regardless of the component      type.

                        A minimum of two global fiducial marks is needed for correction of translational

                        offsets (x and y position) and rotational offsets (theta position). These should be

                        located diagonally opposed and as far apart as possible on the circuit or panel.


                        A minimum of three fiducial marks is required for correction of non-linear                                                distortions (scaling, stretch and twist). These should be located in a triangular                             position as far apart as possible on the circuit or panel.


            All Fine Pitch components should have two local fiducials designed into the land

            pattern of the component. This will allow for correction of translational offsets (x and y    position) and rotational offsets (theta position). This can be two marks located diagonally           opposed within the perimeter of the land pattern.

            If space is limited, a minimum of one local fiducial mark may be used to correct

            translational offsets (x and y position). The single fiducial should be located in the

            center of the land pattern.





            Shape- The optimal fiducial mark is a solid filled circle. Fiducials should have a

                        soldermask opening large enough to provide good contrast and be free of                                 soldermask to enable accurate identification by all vision alignment systems.


            Size-     The minimum diameter of the fiducial mark should be 1mm (0.040 in) and the

                        maximum at 3mm (0.120 in).

                        Fiducial marks located on the same PCB should not vary in size by more than                             25 microns (0.001 in). Some assembly equipment is less flexible in its ability to                                recognize different size marks on the same printed circuit board.


            Clearance- A clear area devoid of any other circuit features or markings should be                                   maintained around the fiducial mark. The size of the clear area should be equal                                 to the radius of the fiducial mark. A preferred clearance around the mark is equal                              to the mark diameter.


            Material- The fiducial may be bare copper; protected by a clear anti-oxidation coating,                             nickel or tin plated, or solder coated (HASL).

                        The preferred thickness of the plating or solder coating is 5 to 10 microns                                   (0.0002 to 0.0004 in). Solder coating should not exceed 25 microns (0.001 in).                                 If solder mask is used, it should not cover the fiducial or the clearance area.


            Flatness- The flatness of the surface of the fiducial mark should be within 15 microns                              (0.0006 in).


            Edge Clearance- The fiducial marks should be located no closer to the PCB edge than                            7.62mm (0.300 in) (SMEMA Standard Transport Clearance) and the minimum                                fiducial clearance required.


            Contrast- Most machine vision recognition systems perform best when a consistent high

                        contrast is present between the fiducial mark and the PCB base material.