Join our Ask Me Anything about controlled impedance where you can ask us questions on:
• Component placement
• Through-hole vs SMT assembly
• Assembly cost
• And much more!
Question submission window: Through November 6th
How can I place components on double-sided boards to avoid warping or alignment issues during reflow?
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How do you recommend customers place fiducials and tooling holes for alignment and handling?
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What are the ideal clearances to maintain around diff types of components to ensure compatibility with your automated assembly equipment? Specifically, are there minimum spacing requirements around connectors, large components, or delicate parts that could impact placement accuracy or reflow quality?
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And what sort of fiducials do you recommend?
I’ve seen recommendations of “always use a precise 1mm diameter circle of copper, and pull the surrounding solder mask back enough for a 2mm diameter”, but I’ve also seen suggestions for copper of “at least 1.5mm, preferably 2.0”, solder void of 3 times the copper area, and shapes other than circles.
Do different tools have different preferences? Would it ever make sense to include multiple sets of fiducials? Is there a size/shape that works best for your tools in particular?
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- Heavy Components on the Bottom Side First
- Optimize Reflow Profiles
- Use Pallet Fixtures
- Balanced Layer Stack-up/proper copper balancing.
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- Global Fiducials: Place at least three global fiducials in a triangular arrangement on the board, ideally at opposite corners and one near the center or at the remaining corner. This helps establish board orientation and ensures accurate alignment across the entire PCB.
- Avoid placing fiducials too close to the edge of the PCB to reduce potential misalignment due to handling or warping.
- A fiducial should typically be a solid, round copper pad with a diameter of 1–2 mm, with a 2–4 mm solder mask clearance around it. This provides clear visibility and contrast for the vision system.
- Place at least two tooling holes on opposite sides of the PCB to provide stable handling and prevent rotation during assembly processes.
Fiducials are mainly used for equipment to recognize and position the board to achieve a precise component placement and inspection result.
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If surface mount devices are required to populate on the board, fiducials (minimum 2) are required for that side of the board. Fiducials are located diagonally apart, the further the better. Fiducial edges should have a minimum 5mm space away from the PCB edge.
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If boards are panelized, the panel shall have minimum two (maximum four) global fiducials at opposite corners of the break-away coupon.
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Fiducial comes in various shapes and dimensions, but circular or rounded shapes are commonly used.
Are fiducials something where we should avoid minimums or something where the goal is to be as typical as possible?
In other words, if there is room, would it better to have a 2mm diameter copper fill, or is that just “we can do it, but 1mm is preferred”? Is pulling it a full centimeter from the edge better, or is that just another chance for miscommunication?
Is a solder mask pullback of 2mm (for 5mm diameter) better or worse?
Or are these details all at the “it won’t really matter” level?
For the PCB design, if there is sufficient space, a fiducial diameter of 1-2 mm is acceptable. Additionally, a solder mask pullback of 2-5 mm is suitable for processing.
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