[SI-LIST] Re: Dielectric constant of silk screen ink

  • From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
  • To: "MSeverini@xxxxxxxxxxxx" <MSeverini@xxxxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
  • Date: Tue, 4 Jun 2013 19:26:11 +0000

I'm sure someday we'll reach the point where we have to worry about this, but I 
don't think we're near there yet.  My bet is that, if you TDR'ed traces running 
under the screen printing, you couldn't discern the irregularities induced by 
the printing from the myriad of other irregularities of microstrip due to 
variations in plating, dielectric thicknesses, soldermask, routing near voids 
in pin fields, etc.

What I would be very careful of is inducing a disparity between two halves of a 
differential pair - running the edge of the ink or a label right between them 
for significant distances.

Sorry, but I don't have any well documented data, just lots of experience 
TDR'ing microstrip, which usually looks very irregular, regardless of printing.

Jeff Loyer


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On 
Behalf Of Matthew Severini
Sent: Tuesday, June 04, 2013 11:24 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Dielectric constant of silk screen ink

Hello Experts,
I am working on a design that sends relatively high speed signals (10gbps) over 
microstrip (I know not the best choice, but it is a short run, and would 
require several design tradeoffs to run on an internal layer). It has been 
brought to my attention that we need to put some labeling on the board, and the 
only open area is right on top of these traces. I nixed the Idea of using a 
paper label there, but then they asked what if we screened the label on the 
board. I am not terribly excited about the idea, but as Eric loves to say you 
have to put in the numbers before you can get an answer. So the question is, 
does anyone know what the dielectric constant is of the ink that is used in 
screen printing? Is there some other reason why this is a terrible idea?

Thanks for the help,

Matt Severini





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