This article is for DSPCB users.
DesignSpark Pro has additional features which provide greater control and simplify the process to allow a fiducial library component to be produced.
DesignSpark Pro - creating a fiducial component
DesignSpark Pro-fiducials and pad style exceptions
For DSPCB users, before discussing the fiducial, the following article is a technique to allow DSPCB users to create a fiducial. The process described is performed in the PCB editor, not the Component editor.
What is a fiducial mark?
Fiducial marks are used for position referencing by imaging systems when components are being placed.
They consist of a small filled circle of copper and a clear area from the solder resist layer and usually a minimum of two are placed in diagonally opposite corners of the board. In some situations with high density areas of small surface mount components additional fiducial marks are required local to that area.
There is not an official recommendation on the size, number or positioning of fiducial marks so it is recommended that you discuss with your manufacturer for their recommendations.
Various suggestions are made on the internet that the solid copper area should be 1 to 2mm diameter and the clearance in the solder mask twice this, e.g. 1.5mm diameter copper and a 3mm diameter clearance in the resist.
Pads cannot be used as they do not have the required control over solder mask and paste mask, however it is quite simple to create the fiducial on your PCB layout as follows.
Creating a fiducial.
The use of the "Add Shape Circle" provides the required flexibility for this.
However before adding the shape, assuming you wish to add a 1mm diameter copper area and a 3mm aperture in the solder mask it is easier if you set the grid to 1mm and snap to grid to half or quarter grid. This allows the easy location of the shape and snapping to a 1mm diameter.
Select the "Add Shape Circle" and right click before placing and ensure "Filled Shape" is set, you may also select the Layer or change layers after placing as shown.
Place the circle shape and expand to the next half grid line. Note grid setting in this example are 0.5mm.
If required then change the layer using the "L" key shortcut or select the object, right click and select "Layers". Change the layer to Top Copper.
Repeat for solder mask exclusion area by adding another closed circle shape over the copper shape and change the layer to Top Solder Mask. The solder mask is a negative image, the shape will correspond to the excluded area of solder resist.
The fiducial is now created, use F5 to redraw the view.
At this point it is good practice to select the fiducial, right click and select 'Group', this will prevent the copper circle and solder mask becoming misaligned.
Further fiducials can be simply placed by selecting the fiducial and copying by CTRL+C and pasting by CTRL+V.
Although the fiducial cannot be saved as a library component a quick and easy solution for future use is to save the fiducial as a PCB design with the fiducial. When working on a new design also open this PCB design and you can copy and paste the fiducial to your current design as shown below.
The fiducials.pcb file contains various fiducials for you to examine and use as required and is attached.
NOTE. When you produce your plot files please ensure that "Pads-Only" is not selected or your "shapes" will not be included in the plots!
Comments
5 comments
Thanks very much for an excellent explanation!
I used pads from the BGA Package instead of a circle, so that the magnetization was to the center of the pad. But I do not have solder paste on the board.
I used this successfully for one pcb but the next board I made the gerber files generated did not have the mask for the fiducial. The difference was that the check box for adjusting the pad sizes [Pads-Only (Resist/Mask) Plot] was selected. Apparently if you want fiducials then you can't adjust the size for the mask for the pads.
I just tried doing this, but I suppose in V10.0 things changed and you cannot add a filled circle and change the layer to Top Copper or any other electrical layer. Only non-electrical layers can be selected. So, you can't create a copper filled circle and no fiducial. The other problem with this approach is that fiducials need to be in the Pick and Place file but not the BOM. The BOM is easy enough to edit, but the Pick and Place requires specific coordinates.
EDIT: I can do this from the PCB Editor, but then I can't classify this as a component, therefore it doesn't get placed in the PNP file. Also, maybe I'm missing something here, but a fiducial mark shouldn't have anything in the area surrounding the copper, just bare FR4.
Roger Keay, I have requested the article be updated to clarify the process.
DSPCB does not support copper shapes in the Component Editor, hence fiducials cannot be saved as a library component. The procedure is a workaround to allow you to create them in the PCB Editor. The second from the last images shows that if you create a PCB design just with various fiducials this can be opened alongside your current design and the selected fiducial copied and pasted into your current design.
There isn't anything surrounding the copper circle, the green area around the copper circle is the opening in the Solder Mask layer as these are negative image layers.
Please sign in to leave a comment.