On a single-layer board with no through-hole and no machine placed components, is there any need for fiducials (for example to route the board outline)? Board house has asked for permission to add fiducials to gerbers. Of course I will say yes, but I am surprised. I definitely don't need the fiducials for assembly. But the vendor seems to be saying that the fiducials will assist in cutting the board outline.
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3\$\begingroup\$ I'd believe them. They are probably using a fiducial camera rather than set pins. \$\endgroup\$– jonkCommented Aug 31, 2018 at 5:37
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3\$\begingroup\$ Wouldn't they be required for solder mask and silk-screen alignment? \$\endgroup\$– TransistorCommented Aug 31, 2018 at 6:23
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\$\begingroup\$ No silkscreen on this board. Soldermask, yes. That is a good point. \$\endgroup\$– user57037Commented Aug 31, 2018 at 6:28
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1\$\begingroup\$ Is your design panelized? Are they asking for fiducials on the panel or on the boards? \$\endgroup\$– ArsenalCommented Aug 31, 2018 at 6:55
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2\$\begingroup\$ I would think that if they needed them to cut panels, they would just add fiducials to the runners, and you would never know about them. \$\endgroup\$– Scott SeidmanCommented Aug 31, 2018 at 14:19
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4 Answers
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According to this application note from norcott, three global fiducials are used to determine the correct orientation of the board (or panel).
Relevant quote:
It is important that only three fiducials are used. This ensures that if a panel is accidently inserted into the placement equipment rotated through 180°, the equipment can detect it and halt assembly.
And for a single board without a panel, those fiducials are placed on the board, and will show up in the end:
(images taken from the application note)
There is no specific mention of routing the board outline in that document, but I can imagine that they use this also in the routing machine to make sure that the board has the right orientation.
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\$\begingroup\$ Those fiducials would never show up on the end-product, so the maker wouldn't need to add them to the customer gerbers. \$\endgroup\$ Commented Aug 31, 2018 at 14:20
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1\$\begingroup\$ @ScottSeidman if the board is produced without a panel, the fiducials are placed on the board and then show up on the end product. \$\endgroup\$– ArsenalCommented Aug 31, 2018 at 14:27
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Fiducials are required when you use any kind of computer vision. The fiducials are the calibration point for the vision system and the board coordinates.
You need them for vision assisted drilling, pick and place, but also Automated Optical Inspection (AOI).
Basically any machine that automatically recognizes the board position and angle.
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\$\begingroup\$ Thanks. Do you think they use computer vision during fab to cut the outline on a single layer board (with no holes of any kind?) \$\endgroup\$ Commented Aug 31, 2018 at 5:43
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\$\begingroup\$ @mkeith why should the amount of layers matter for the way they align the board in their cutting process? \$\endgroup\$– PlasmaHHCommented Aug 31, 2018 at 5:58
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\$\begingroup\$ @PlasmaHH I don't think layer count has anything to do with cutting. I just wanted to re-emphasize that it is one layer, so inter-layer registration is not needed. And there are no vias or through hole components. \$\endgroup\$ Commented Aug 31, 2018 at 6:00
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1\$\begingroup\$ @mkeith but why are you doing that? You seem to imply that this is somewhat important. You say they say they need them for cutting the board outline. Sounds reasonable \$\endgroup\$– PlasmaHHCommented Aug 31, 2018 at 6:03
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\$\begingroup\$ Yes. I am familiar with fiducials and their importance in pick-and-place. But this board has no machine-placed components. \$\endgroup\$ Commented Aug 31, 2018 at 6:03
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You don't know their process, and just how many things they have automated, requiring machine vision, for processing and maintaining the quality of their boards.
Perhaps the most important thing is that they want to process your boards through their standard flow. If your board is a 'special', so it doesn't need this station, and it can't be put through that station, then it has to be handled differently, and it will cost them 10x more.
If their outline router uses fiducials, they will want to add them.
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\$\begingroup\$ I guess I was hoping to have a definitive answer about whether outline routing sometimes uses machine vision. I guess the answer is probably yes. \$\endgroup\$ Commented Aug 31, 2018 at 6:23
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Fiducials are also used to line up stencils for applying solder paste.
answered Aug 31, 2018 at 18:56