Choosing fiducial lineup reference points on the PCB (Mark Reference 1, 2, etc.)

In printed circuit board manufacturing fiducial marks "fiducial points" allow SMT placement equipment "pick & place" to accurately locate and place parts on the PCB. Most "pick & place" machines are fed boards for assembly by a conveyor. During the clamped down of the PCB on the conveyor small variances introduced of maybe tenths of a millimeter are enough to ruin the placement of precision components without further calibration and these "fiducial points" add this further calibration. In addition to conveyors other factors can create variances on pick & place machines.

In addition to pick-and-place assembly, fiducial points are sometimes needed for other operations in printed circuit board manufacturing such as AOI optical inspection, PCB Test, selective soldering programming, etc. There are a number of options available with the Unisoft software for choosing and making these fiducial points. These points in the Unisoft software are referred to as Mark Reference 1, 2, etc.

Companies and Engineers have different preferences for the fiducial points they like to use. Also it depends on the type of data that they may receive for the project which may have limited or no fiducial point data readily available to run the job, this can be especially true for Electronic contract manufacturers who experience a large variance in the type of data they get from their customers. Some examples of these lineup points are the actual fiducial marks placed on the pcb or a pin on a component or the edge corners of the pcb or a point off the pcb or plated mounting screw holes, etc.

The Unisoft software is quite flexible in choosing and creating these lineup points. In some cases it's as simple as just choosing the fiducials that are readily available from the data files that are displayed in the Unisoft software and in other cases a bit of creativity is sometimes needed.

Below are a few options for lineup points and we have assumed you are an experience Unisoft software user. Obviously use the easiest and most sensible method listed below as your first choice as your Mark Reference 1, 2, etc. Please contact Unisoft for help.

Note: When using the Unisoft software for creating the assembly programming file it is recommended that the   MARK REFERENCE 1   point for the top side of the PCB be located on the bottom left corner of the board when viewed in the Unisoft software. Also it is recommended that the point that is chosen for   MARK REFERENCE 1   on the top side is also set to the XY 0,0 origin of the PCB using the SET ORIGIN feature.

By doing this the coordinates displayed for the components in the Unisoft software will typically be the same as the coordinates exported to the file to program the assembly machine making verification, if needed, easier. Also the PC board will then usually be located in the first quadrant where the component coordinates (x;y) will both be positive.

reference-1-quadrant-1


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