[SI-LIST] Re: Regarding etch factor calculation
- From: steve weir <weirsi@xxxxxxxxxx>
- To: sai krishnan <sai_krishnan_s@xxxxxxxxx>
- Date: Wed, 25 May 2011 05:44:31 -0700
A 10% variation in impedance takes either a 20% difference in effective
dK or around a 10% variation in effective trace width, or a
combination. First make sure that the you are getting the right
physical numbers from your fab house for the etch profile. Are you
etching very narrow traces?
Steve.
On 5/25/2011 5:36 AM, sai krishnan wrote:
> Hi Steve,
> Thanks for the reply. For microstrip, I included soldermask thickness
> as 0.6mils. I have not done any measurement. As mentioned in my
> email, my observations are based on the caculcations from the Polar
> tool. the difference is around 5ohms.
> I am seeing in my previous posting, alignment got distorted. I am
> posting my query again:
> I am trying to understand the EtchFactor value in the stackup. I am
> checking the PCB stackup received from fab house. The impedance
> value resulting from my calculation using Polar for microstrip lines,
> differs from the values provided by the fab house. For striplines,
> it comes closely to the fabhouse calculations.
> I am using the following approach:
> Etch factor = W1 (bottom side width of a trace ) â?? W ( top side width
> of a trace) = copper thickness (T)
> For microstrip traces, I included the plating thickness and copper
> thickness for the total thickness (T). For stripline traces, just
> the copper thickness of trace.
>
> Does my approach on calculating Etchfactor requires any
> modifications. Why I am getting different impedance value for
> microstrip . Any inputs will be helpful.
> Thanks & Regards,
> Sai
>
> --- On *Wed, 5/25/11, steve weir /<weirsi@xxxxxxxxxx>/* wrote:
>
>
> From: steve weir <weirsi@xxxxxxxxxx>
> Subject: [SI-LIST] Re: Regarding etch factor calculation
> To: si-list@xxxxxxxxxxxxx
> Date: Wednesday, May 25, 2011, 5:46 PM
>
> How far off are you from what your fab house says? Have you measured
> test traces?
>
> Microstrip effective dielectric constant is affected by the solder
> mask.
> If the surface treatment includes Ni, that will also have an impact.
>
> Steve
>
> On 5/25/2011 5:07 AM, sai krishnan wrote:
> > Hi All,
> > Ã?
> > I am trying to understand the EtchFactor value in the stackup. Ã? Ã?
> > Ã?
> > I am Ã? checking the PCB stackup received from fab house.Ã? Ã? Ã?
> The impedance value resulting from my calculation using Polar for
> microstrip lines, Ã? differs from the values Ã? provided by the fab
> house.Ã? For striplines, it comes closely to the fabhouse
> calculations.
> > Ã?
> > I am using the following approach:Ã? Ã?
> > Etch factor = W1 (bottom side width of a trace ) Ã? ââ?¬â?? W ( top
> side width of a trace) Ã? Ã? Ã? = copper thicknessÃ? (T) .
> > Ã?
> > For microstrip traces, I included the plating thickness and
> copper thickness for the total thickness (T). Ã? Ã? For stripline
> traces, just the copper thickness of trace.
> > Ã?
> > Does my approach on calcualating Etchfactor requires any
> modifications.Ã? Why I am getting different impedance value for
> microstrip Ã? .Ã? Any inputs will be helpful.
> > Ã?
> > Regards,
> > Sai
> > ------------------------------------------------------------------
> > To unsubscribe from si-list:
> > si-list-request@xxxxxxxxxxxxx
>
> <http://us.mc342.mail.yahoo.com/mc/compose?to=si-list-request@xxxxxxxxxxxxx>
> with 'unsubscribe' in the Subject field
> >
> > or to administer your membership from a web page, go to:
> > //www.freelists.org/webpage/si-list
> >
> > For help:
> > si-list-request@xxxxxxxxxxxxx
>
> <http://us.mc342.mail.yahoo.com/mc/compose?to=si-list-request@xxxxxxxxxxxxx>
> with 'help' in the Subject field
> >
> >
> > List technical documents are available at:
> > http://www.si-list.net <http://www.si-list.net/>
> >
> > List archives are viewable at:
> > //www.freelists.org/archives/si-list
> >
> > Old (prior to June 6, 2001) list archives are viewable at:
> > http://www.qsl.net/wb6tpu
> >
> >
> >
>
>
> --
> Steve Weir
> IPBLOX, LLC
> 150 N. Center St. #211
> Reno, NV 89501
> www.ipblox.com
>
> (775) 299-4236 Business
> (866) 675-4630 Toll-free
> (707) 780-1951 Fax
>
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx
>
> <http://us.mc342.mail.yahoo.com/mc/compose?to=si-list-request@xxxxxxxxxxxxx>
> with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx
>
> <http://us.mc342.mail.yahoo.com/mc/compose?to=si-list-request@xxxxxxxxxxxxx>
> with 'help' in the Subject field
>
>
> List technical documents are available at:
> http://www.si-list.net <http://www.si-list.net/>
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
>
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
--
Steve Weir
IPBLOX, LLC
150 N. Center St. #211
Reno, NV 89501
www.ipblox.com
(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
