Does screen printing affect the insulation of the PCB between pins or pads?

[Etna.]

Hi!

I am new here and hopefully you can help me out with this one. I have noticed, that a few power supplies have additional screen printing on the pcb between pins/pads that carry higher voltages. So I was wondering: How would that affect the insulation? I am asking this, because I can't think of another reason why you print additional lines betweens those pins/pads or circles around pins and let the lower voltages be.

Regards,
Etna.

[Doctorandus_P]

sometimes there are marks every 5 or 10 pads to for easier counting during testsing, sometimes higher voltage tracks are marked to indicate the high voltage and lower the chance for accidental / casual measurements.

In general silkscreen is not used for voltage isolation. It's likely to improve isolation (a bit), but it can not be guaranteed or relied upon. But there are also other options such as conformal coatings that are especially designed to improve insulation, moisture and dirt resistance, etc.

[Etna.]

Thanks for your thoughts. I think the same but still find it odd to finde additional markings.

Like here: The SO14 has dividers drawn between the pads. The cap left to it has also a big line between pins. And the MOSFET above has a circle surrounding the middle pin. All parts there see a bit of higher voltages. The rest of the board is lacking any additional screen printing.

Regards,
Etna.

[jpanhalt]

I don't do anything requiring high resistance.  However, according to Grok, TiO2 is the pigment used in white silkscreen on PCB's.  One rarely sees other colors, but Grok said carbon black is used for black pigment.  So, in something extremely sensitive, nearby white or black might have an effect.

[Kean]

There is going to be negligible insulating effect from the silkscreen, and as jpanhalt mentioned it could actually end up being the opposite.  There is typically no production guarantees of silkscreen thickness, material, line width, quality, etc.  I am sure this cannot be considered for safety approvals, and certainly the safety consultants I've dealt with would laugh at the concept.

I've seen this done on many PCBs, especially on Chinese designed products.  I think it has become popular as people often copy from other designs.  It could be considered an indication that someone was at least thinking about clearance requirements.  I generally would use silkscreen for mechanical clearance markings like around screw heads, and use my EDA tool keepout, restrict, & net class rules for critical stuff like electrical clearance and component interference (e.g where a plastic housing touches a PCB).

Use slots or conformal coating if you cannot otherwise maintain required creepage/clearances.

[Doctorandus_P]

I guess you're going in much too deep. Sure conductive inks exist, (for example thick film or "wire" bridges on single sided PCB's sometimes seen in mass produced FR2 such as remote controls, but I've never seen a PCB manufacturer using conductive ink for silkscreen.

The reason behind this can be as simple as being default footprints in some PCB program used. Another possibility is for AOI (Automatic Optical Inspection).

[HwAoRrDk]

Like here: The SO14 has dividers drawn between the pads. The cap left to it has also a big line between pins. And the MOSFET above has a circle surrounding the middle pin. All parts there see a bit of higher voltages. The rest of the board is lacking any additional screen printing.

In that example, it's not done for voltage isolation, but because the board has been wave soldered. The extra silkscreen between pads acts as a kind of "fence" or "dam" for the molten solder so it's less likely to form bridges.

[tooki]

I guess you're going in much too deep. Sure conductive inks exist, (for example thick film or "wire" bridges on single sided PCB's sometimes seen in mass produced FR2 such as remote controls, but I've never seen a PCB manufacturer using conductive ink for silkscreen.

Nobody suggested that anyone uses conductive inks for silkscreen. The issue is that everything is a little bit conductive, given enough voltage, it’s only a question of degrees.

[Doctorandus_P]

Yes, I exaggerated a bit in that part of my last post. The whole black and white ink thing is a bit of a sidetrack and not relevant, even though this is a topic about screen printing.

[BH3XON]

Silkscreen markings between pins are mainly added to make it easier for AOI or visual inspection to detect solder bridges or shorts.

[Kean]

Silkscreen markings between pins are mainly added to make it easier for AOI or visual inspection to detect solder bridges or shorts.

Yes, that clearly applies to some examples I've seen, such as a large filled rectangle of silkscreen around a multi-pin through-hole connector.
Like the attached photo I saw in a recent Reddit post found at https://www.reddit.com/r/PrintedCircuitBoard/comments/1m4gzn4/silkscreen_on_the_soldering_side_of_throughhole/

It doesn't seem to be the reason for example silkscreen usage of thick lines in the photo in reply #2.  I would expect slots or use of larger silkscreen regions - but maybe the white lines are enough to help spot an uncommon solder bridge that would be disastrous if powered...