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Alberto Caravantes , 04-21-2024, 04:44 PM

I am creating the footprint for a Gigabit Ethernet QFN IC. However, as the pads are really close to each other, the top solder that Altium generates around each pad almost overlaps between each.
Will this cause any problem? How can I reduce this? The pad top solder layer shape is set to rule expansion (sets automatically to 0.102mm).

Please let me know about this, as I am realatively new to PCB design and Im trying to learn in this process.

Thanks! 🙂

QDrives , 04-21-2024, 10:12 PM

This in in you PCB library. Unfortunately, Altium does not have the ability to set rules for PCB libraries, nor check it to those rules.

With the pad being 0.2mm wide and almost overlapping soldermask of 0.102mm, tells me 0.4mm pitch. And therefore also 0.2mm between the pads.
If your fabricator uses LDI (Laser Direct Imaging) for the solder resist, then 0.03mm soldermask expansion is not a problem. That would leave 0.14mm solder dam which is more than the 0.075 needed for LDI.
However, if they use LPI (Liquid Photo Image), then the tolerances are much bigger.
The technique may depend on the color of the solder resist.
For the PCB I have always set the solder mask expansion to 0.05mm. That would leave a dam of 0.1mm.

All in all, I am yet to find a fabricator that does not alter the solder mask regardless of the settings you use.
https://www.eurocircuits.com/pcb-design-guidelines/soldermask/

BTW in case you did not know: solder MASK is the design you make, solder RESIST is the material itself.

Robert Feranec , 04-23-2024, 01:34 PM

in the library you can set the mask expansion to manual (select all the pins in the footprint and set them manually). In this cases I use 1mil (0.025mm) as minimum expansion (but 0.065mm can be better value if that works ok). Not every PCB manufacturer will be able to manufacture 1mil - if not, they will probably just draw a big rectangle around all the pins and in the final PCB and there will be no mask bridges between the pins.

QDrives , 04-23-2024, 04:19 PM

I do not prefer to set the expansion to manual in the library with the possibility to forget 'resetting' it.
However, it does make checking things very difficult.