kicad-lib-committers team mailing list archive

[Jean-Paul Louis <louijp@xxxxxxxxx>]

Let’s get back to the basics.

WHY A SILKSCREEN?

Originally, PCB were assembled by hand, and the markings were dual purpose, Assembly and Inspection.
They were printed on the PCB using colored paint and silk (plastic) or metal screens, So the outline of the component was helping the operators to stuff the board, and the RefDes was to make sure you were using the right part, and also for trouble-shooting a failed test.
When the board is fully assembled, the outline is meaningless, only the RefDes keep its value.

And there is no difference in purpose between Through Hole and Surface Mounted parts.
For polarized capacitors, I have seen a lot of different options, the most efficient one being a circle or a square with a “+” sign to show the polarity, The “+” sign or sometimes a dot being outside the shape.
What is important is that the marking eliminate ambiguity, but does not jeopardize reliability. So it is VERY important that it does not touch or cover a solder area.

my $0.02,

Jean-Paul
AC9GH


On Jun 8, 2014, at 11:14 AM, Carl Poirier <carl.poirier.2@xxxxxxxxx> wrote:

> About these rules for the silkscreen, are they only for SMD? I am under the impression it does not apply well to THT components, for example an electrolytic capacitor where we often see a circle with one half full to indicate polarity. This would be partly hidden once the board is assembled.
> 
> 
> On Thu, Jun 5, 2014 at 5:24 PM, Bernd Wiebus <bernd.wiebus@xxxxxx> wrote:
> Hello Pawel.
> 
> Am Montag, den 02.06.2014, 09:57 +0200 schrieb Paweł Dras:
> 
> > With pads over the silk is the same situation, in many cases after
> > silk erasure by solder mask it don't looks good on final product.
> 
> It is not only about "looking good". Silkscreen print over Pads is
> nasty, if someone forgets to distract the pads from the silkscreen.
> It may be expensiv, but shure will cost time at last.....
> 
> If you place your silksceen across pads, and erase it over the pads,
> your silkscreen will be chopped. so better you chopp it by yourself and
> make it looking good.
> 
> 
> > Another problem is to wide placed silk.
> 
> Think about, that you perhaps need place for rework tools.
> And wave soldering needs more space around the devices than reflow.
> 
> Some years ago, KiCad insisted in thik lines, because you could not
> change the wide of silk screen lines. Of course, it was possible by
> editing the library file by hand.
> 
> But this thick lines are sometimes needed, because a manufacturer who
> use a real silk-screen printing process and not a optical process, meeds
> the wide lines.
> 
> So bee careful, if you use thin lines. Think about the spacing.
> 
> > I have a question, can be ref and value placed as in my attachment or
> > should  be above and below resistor?
> 
> It is a bad idea, to place text under devices, because it cannot be read
> anymore, if the device is once mounted......so i put text to this
> positions, only if there is nowhere a better place for the text.
> 
> Personally, i switch the value at layouts and silkscreens to invisible,
> and keep only reference as a designator.
> 
> Having reference AND value at the layout costs place and is terrible to
> read. So better i use only the reference, and the BOM of course. ;O)
> 
> For big boards with few devices, it migt be ok to have both, but for
> growing sisze, it will get diffcult to read.
> 
> the exeption is, if you use the silk-screen not as an silk-screen at the
> board, but as an assembly layer. So you are not stuck to board
> dimensions, but can make DIN A2 prints for boards the size of a small
> stamp. ;O)
> 
> With best regards: Bernd Wiebus alias dl1eic
> 
> 
> 
> 
> 
> --
> Mailing list: https://launchpad.net/~kicad-lib-committers
> Post to     : kicad-lib-committers@xxxxxxxxxxxxxxxxxxx
> Unsubscribe : https://launchpad.net/~kicad-lib-committers
> More help   : https://help.launchpad.net/ListHelp
> 
> -- 
> Mailing list: https://launchpad.net/~kicad-lib-committers
> Post to     : kicad-lib-committers@xxxxxxxxxxxxxxxxxxx
> Unsubscribe : https://launchpad.net/~kicad-lib-committers
> More help   : https://help.launchpad.net/ListHelp