How important is solder mask in between pads?

[Blitzschnitzel]

So, I’ve asked JLCPCB what their minimum solder mask width is and the answer was 0.254 mm. When I make some pads smaller I can make that but there is one component where there is no way that I can get solder mask in between the pads.
How important is solder mask in between pads? And how much does solder paste stick to bare FR4?

[ejeffrey]

It is a tradeoff, but we pretty regularly omit solder mask between pads on fine pitch devices.  With the right solder stencil and reflow profile it isn't too bad for reflow assembly, it can be more problematic for hand soldering or rework.

[thinkfat]

Solder doesn't really stick that much to FR4, the main aspect solder mask helps with is keeping the pad area fenced against the connecting trace. Otherwise, the copper trace would wick the solder alloy away from the pad and you'll likely not get a sufficient fillet. With that in mind, solder mask between pads is not all that important. On the contrary, it's better to have no solder mask at all instead of small slivers of it flaking off because they don't stick to the FR4 during reflow.

[T3sl4co1l]

It's not much thickness but it definitely helps the solder roll around between pads, whether it's paste coalescing onto the pads, or errant balls or bridges floating around.

10 mil min web is embarrassingly wide, which I guess tells you just how bargain-barrel they've optimized their process.  Don't get your hopes up, and all that.

It's a few bucks more from a fab with better rules.  Well worth the ease of assembly.

Tim

[thinkfat]

It is a tradeoff, but we pretty regularly omit solder mask between pads on fine pitch devices.  With the right solder stencil and reflow profile it isn't too bad for reflow assembly, it can be more problematic for hand soldering or rework.

Using ample flux helps with that rework and hand assembly business.

[Blitzschnitzel]

Ok I don't need to worry then. Thank you guys!

[TheHolyHorse]

I've ordered boards from JLC with 0.2mm soldermask width between some pads with no issues at all.