Fiducials

[JMFernandez]

Hi.

I want to ask a question about FIDUCIALS. Is there a specific way to create them in Altium? Any recommendation about how to create them and the best way to position them in the board?

Thank you in advance!!

[robertferanec]

In our designs, fiducials are simple components. In SCH Library, there is no PIN and Type is set to "Standard (No BOM)". Footprint is a simple PAD. We normally use three kind of fiducials:

- board fiducials, standard: 40mil pad / 120mil mask opening
- board fiducials, small: 30mil pad / 52mil mask opening
- panel fiducials: 40-60mil + mask opening at least 40mil greater than fiducials

We place them into board corners and we also include following note on Manufacturing notes layer:
PANELIZE THE BOARD (2PCS PER PANEL). PLACE FIDUCIALS ON THE PANEL STRIPS AS FOLLOWS:
- FIDUCIAL DIAMTER 1-1.5MM, SOLDER MASK OPENING AT LEAST 1MM GREATER THAN FIDUCIAL
- MINIMUM 4MM DISTANCE FROM THE PANEL EDGE
- 3 FIDUCIALS SHOULD LIE ON TWO LINES THAT INTERSECT AT A RIGHT ANGLE
- PLACE ONE FIDUCIAL INTO EACH PANEL CORNER (FOUR ON THE TOP AND FOUR ON THE BOTTOM LAYER)

I hope this helps.

[JMFernandez]

So, I should include fiducials in the board itself. One on each corner. I should also include fiducials on the panel. Again, one on each panel corner. I do not understand "3 fiducials should lie on two lines that intersect at a right angle". Don´t you say they has to go on each panel corner? Thank you!!

[mairomaster]

What this statement means is that if you connect the 3 fiducials with imaginary lines (yes the fiducials might be in the corners as they often are), you will get a right angle between two of the lines.



And just for the topic - I normally use 1mm fiducials with 3mm solder mask opening placed in the corners of the board. I could have fiducials either on the board, on the panel, or on both depending on if I have space or not.

You also need fiducials on the bottom side of the board if you have components on that side.

[JMFernandez]

Ok, thank you. I have one more question. How do you do to left an opening region around the fiducial (the mask opening)? I have been looking for the best way to do it and I have found one way, but I do not know if it is the best one. I have defined a CLEARANCE RULE for the fiducial I am using. I have set the clearance to 1mm (this is what I need) so, when I put a fiducial with a 2mm diameter, I have 1mm around the pad free of copper or anything else. Is this a good way to do it?

Thank you in advance.

[mairomaster]

You can do it in different ways.
I have my fiducials as components in my libraries. The fiducial itself is a top layer only pad, with diameter of 1mm and specified solder mask expansion value of 1mm (so that we have 3mm mask opening). For the clearance, I have a copper circle (made by 360 degrees thick arc) with external diameter of 3mm, which in the properties is marked as keep-out.

[JMFernandez]

Thank you, but I do not understand what do you mean with 360 degrees arc. Could you post an image of it. Thank you in advance.

[mairomaster]

For the keepout region you need it to be a filled circle which covers the fiducials and solder mask expansion. However, in Altium you can't draw a filled circle so you have to cheat it. You can draw an arc, which is a part of a circle with parameters angle, radius and width of the line. To make a full filled circle, you need to make the arc 360 degrees, give it a radius of D/4 (D is the diameter of the filled circle you need) and give it a line width of D/2. Arc is one of the standard drawing elements available from the Place menu. Here is an example of a keep-out region used for the fiducial (the diameter in the example is 10mm because it is just an example, with the actual fiducial I am using 3mm):



Play around with drawing arcs and you will get what I mean.

[robertferanec]

This is how we create fidutials - a pad with Solder Mask Expansion -> Specify Expansion Values = 40mil (see the picture below)

[JMFernandez]

Yes, I do it the same way, but you need to specify a clearance, for example when you draw a polygon or a plane. How do you do it? Clearance rule? Keepout?
Thanks!!

[mairomaster]

You can practically achieve it either way, but I think using keep-out region in the footprint is better. That way you always have the required clearance automatically, when you place a fiducial in the board. Otherwise you have to set up a rule for each board you work on and sometimes you might forget.

[robertferanec]

Ah, you mean keep-out. We do not specify any special keep out areas for fiducials, but mairomaster's solution looks really good.

[k.ifantidis]

Also a good solution is found here in this link: https://www.eevblog.com/forum/altium/fiducials/
I've just read your post and I wanted to add this solution