[PCB_FORUM] Re: Is silkcreen affects the traces with impedance

Hello to all

Thanks for the explanation.

I have a  RF design, most of the traces need to match the impedance, My EE
ask me to remove the silkscreen on top of those traces that need to match
the impedance, basically the silkscreen is only those component notations,
text , lines . which my EE wants me to remove as he said it  affects the
impedance of that traces. I was just confused as this particular silkscreen
is white color paint and dont have any electrical propertirs, or might not
affects even the thickness of the materials. Yap Richard soldermask
sometimes might affects the impedance but the silkscreen (text, lines,
component notataion) the white color paint , I am a little bit confused if
this one affects impedance.

On Mon, Sep 29, 2008 at 9:22 AM, richard moffat <
richard.moffat@xxxxxxxxxxxxxxxxxxx> wrote:

> Hello Marie
>
> I just ran a model on our software.  The impedance may drop a bit more, say
> 2-3 ohms, but it really, really depends how thick the soldermask is.
>
> It would pay to have a word to your friendly fabricator.  They will easily
> help you and they will have better software than I've currently got.
>
> Hope this helps.
>
> Cheers,
> Richard
>
> >>> "richard moffat" <richard.moffat@xxxxxxxxxxxxxxxxxxx> 29/09/2008 2:02
> p.m. >>>
>  Hi Jerry
>
> That's true - but I was speaking in terms of impedance, not loss.  I think
> that was what Marie was asking.
>
> I do not believe the impedance will not change much, at least not because
> of a coating such as soldermask or silkscreen.  In real terms the impedance
> sometimes goes all over the show but for different reasons, usually the
> material.  Correct me if I'm wrong.
>
> The loss from covering the strips with soldermask or silkscreen certainly
> will be greater to sensitive RF designs or digital multi-multi-GHz.
>
> Cheers,
> Richard
>
> >>> "Schwartz, Jerome" <jschwa01@xxxxxxxxxx> 29/09/2008 1:35 p.m. >>>
> Richard,
>
> Solder mask and silkscreen, even in close proximity at high frequencies can
> have an effect.
> Lot's of  my designs are in the 6-80 GHz range. We will use solder dams for
> assembly instead of blanket solder mask. Silkscreen on active components
> only and
> far, far away from RF traces and elements. These are PCB's not PWB's.
>
> General statements do not apply. The frequency's must be supplied for a
> proper answer.
>
> Jerry
>
> ________________________________
>
> From: icu-pcb-forum-bounce@xxxxxxxxxxxxx on behalf of richard moffat
> Sent: Sun 9/28/2008 5:43 PM
> To: icu-pcb-forum@xxxxxxxxxxxxx
> Subject: [PCB_FORUM] Re: Is silkcreen affects the traces with impedance
>
>
>
>
> Hi
>
> The silkscreen will have little effect unless you have the silkscreen
> absolutely plastered over everything.  Even then it will not lower it very
> much at all.  Bits of text or lines will have no measurable effect.
>  Soldermask will most likely lower it more, by 1-2 ohms say (depending on
> the type of mask.)
>
> Cheers,
> Richard
>
> __________________________
> Richard Moffat
> PCB Specialist Engineer
> Allied Telesis Labs
> ph. +64 (3) 3393000
> richard.moffat@xxxxxxxxxxxxxxxxxxx
>
>
> >>> "malou teoxon" <malou.teoxon@xxxxxxxxx> 26/09/2008 8:27 p.m. >>>
> Hi friends
>
> I have a question here. Do you have any idea if the silkscreen on  top of
> traces with impedance affects the impedance matching of that traces.
>
> Regards
> Marie.
>
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