[SI-LIST] Re: Right Angle Bends
- From: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>
- To: "Scott McMorrow" <scott@xxxxxxxxxxxxx>, "Julian Ferry" <julian.ferry@xxxxxxxxxx>
- Date: Fri, 15 Jul 2011 15:47:08 -0700
It is odd that those who fret over right angle bends seem to ignore the fact
that there is at least on at every via where a trace connects. My old
friend, Dan Murphy, called this "looking where the light is good."
The same engineers used dual in line IC packages by the millions with as
many as three right angle bends in each lead. They weren't visible, so they
didn't count!
--------------------------------------------------
From: "Scott McMorrow" <scott@xxxxxxxxxxxxx>
Sent: Friday, July 15, 2011 2:02 PM
To: "Julian Ferry" <julian.ferry@xxxxxxxxxx>
Cc: <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Re: Right Angle Bends
> It depends on who you ask.
>
>
> Scott McMorrow
> Teraspeed Consulting Group LLC
> 121 North River Drive
> Narragansett, RI 02882
> (401) 284-1827 Business
> (401) 284-1840 Fax
>
> http://www.teraspeed.com
>
> Teraspeed® is the registered service mark of
> Teraspeed Consulting Group LLC
>
>
> On 7/15/2011 4:53 PM, Julian Ferry wrote:
>> That's a good point.
>>
>> Who's that guy who always says "It depends?".....
>>
>>
>>
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>> On Behalf Of Scott McMorrow
>> Sent: Friday, July 15, 2011 4:39 PM
>> To: si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] Re: Right Angle Bends
>>
>> Julian
>>
>> Actually, it depends on the frequency and the trace thickness, since
>> capacitive coupling on the sidewall of the trace at the corner can cause
>> a net decrease in capacitance at some frequencies.
>>
>>
>> Scott McMorrow
>> Teraspeed Consulting Group LLC
>> 121 North River Drive
>> Narragansett, RI 02882
>> (401) 284-1827 Business
>> (401) 284-1840 Fax
>>
>> http://www.teraspeed.com
>>
>> Teraspeed(r) is the registered service mark of
>> Teraspeed Consulting Group LLC
>>
>>
>> On 7/15/2011 4:05 PM, Julian Ferry wrote:
>>> OK, looks like I made one little not-so minor mistake in my previous
>>> email:
>>>
>>> The capacitance goes UP, the inductance goes DOWN.
>>>
>>> Sorry for any confusion I might have caused!
>>>
>>> Julian Ferry
>>> High Speed Engineering Manager
>>> Samtec, Inc
>>>
>>> -----Original Message-----
>>> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>>> On Behalf Of Julian Ferry
>>> Sent: Friday, July 15, 2011 3:48 PM
>>> To: Brad Brim; 'Jeff Walden'; si-list@xxxxxxxxxxxxx
>>> Subject: [SI-LIST] Re: Right Angle Bends
>>>
>>>
>>> I think one of the problems here is that like with most myths or urban
>>> legends, there is a kernel of truth to it.
>>>
>>> It is pure, unarguable physics that the capacitance will go down and the
>>> inductance will go up in a right angle bend. The question is whether
>>> that change matters in a particular application.
>>>
>>> For some applications, like in high power microwave or RF applications,
>>> this effect can be significant enough relative to other factors that it
>>> is definitely worth worrying about.
>>>
>>> But in the grand scheme of things in the current SI world, this change
>>> is way down on the list of potential problems. It is effectively swamped
>>> out by many other effects (like our relatively crappy connectors, for
>>> one example...)
>>>
>>> I think these guys wrote a pretty decent little paper with some math
>>> that can help determine whether you might need to worry about bends.
>>>
>>> http://www.millertechinc.com/pdf_files/mti_tn063_microstrip_right_angle_bends.pdf
>>>
>>>
>>> Also keep in mind that we in the SI world are mostly dealing with pulsed
>>> signals, where a large portion of the energy is contained in the lower
>>> frequency components. The excess capacitance will only affect the very
>>> high frequency components. But in the microwave environment, it's all
>>> about the high frequency signal, so a bend can be a much greater
>>> concern.
>>>
>>>
>>>
>>> Julian Ferry
>>> High Speed Engineering Manager
>>> Samtec, Inc
>>>
>>> -----Original Message-----
>>> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>>> On Behalf Of Brad Brim
>>> Sent: Friday, July 15, 2011 2:57 PM
>>> To: 'Jeff Walden'; si-list@xxxxxxxxxxxxx
>>> Subject: [SI-LIST] Re: Right Angle Bends
>>>
>>> exactly, Jeff ... and the traces that connect to the bends are also MUCH
>>> longer than typical for the RF/microwave case.
>>>
>>> In RF/mw ckt sim libraries/layouts a bend is a separate "component". The
>>> reference planes (i.e. where the traces connect to the bend) are at the
>>> edge
>>> of this component. For example, the 90-degree bend reference planes are
>>> at
>>> the edge of the square representing the area of the bend. For most SI
>>> applications the bend is NOT a separate component and the two traces
>>> simply
>>> meet at a single node. Having worked way too many hours to implement and
>>> test RF/mw ckt sim bend models over a dozen years ago I observed the
>>> parasitics are a delay of length on the order of the node-to-node
>>> distance
>>> with additional capacitive parasitics for sharp bends and inductive
>>> parasitics for aggressively chamfered bends. For a 90 degree bend the
>>> different definitions of reference plane imply 2*(W/2) additional length
>>> trace for the SI case. Given approximate parasitic delay of sqrt(2)*W/2,
>>> all
>>> implies doing nothing for SI applications is still on the order of only
>>> 30%
>>> phase delay error versus a much more precise parasitic model (for an
>>> already
>>> small parasitic). The phase delay dominates because bend capacitive
>>> parasitics are small for SI apps relative to other capacitive parasitics
>>> not
>>> modeled throughout the system.
>>>
>>> Therefore, if the trace are not wide (low impedance) and their lengths
>>> coming in/out of the bend are long relative to the linewidth, then
>>> ignoring
>>> the bend is obviously the correct choice.
>>>
>>> Where SI apps might not always want to ignore bends is for tight meander
>>> structures used to accumulate phase delay and balance skew. These
>>> geometries
>>> sometimes have short distance between bends and could therefore lose
>>> some
>>> accuracy from ignoring bend parasitics. In these cases it is probably
>>> more
>>> important to include coupling amongst the parallel traces. As we all
>>> might
>>> guess, if you need to know a meander behavior accurately you may wish to
>>> model it as a single component with more detailed simulation rather than
>>> treat it as a collection of traces (with or without bend parasitics).
>>>
>>> cheers,
>>> -Brad
>>>
>>>> -----Original Message-----
>>>> From: si-list-bounce@xxxxxxxxxxxxx
>>>> [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Jeff Walden
>>>> Sent: Friday, July 15, 2011 10:55 AM
>>>> To: si-list@xxxxxxxxxxxxx
>>>> Subject: [SI-LIST] Re: Right Angle Bends
>>>>
>>>> The difference is that today's SI traces are significantly
>>>> narrower than the typical "RF" microstrip of 30 years ago.
>>>> -Jeff
>>>>
>>>>
>>> ------------------------------------------------------------------
>>> 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
>>>
>>>
>>> ------------------------------------------------------------------
>>> 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
>>>
>>>
>>> ------------------------------------------------------------------
>>> 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
>>>
>>>
>> ------------------------------------------------------------------
>> 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
>>
>>
> ------------------------------------------------------------------
> 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
>
>
------------------------------------------------------------------
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:
