[SI-LIST] Re: PCB Insertion loss prediction
- From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
- To: "pcb_layup@xxxxxxx" <pcb_layup@xxxxxxx>, "si-list (si-list@xxxxxxxxxxxxx)" <si-list@xxxxxxxxxxxxx>
- Date: Wed, 31 Oct 2012 21:33:48 +0000
I'm surprised at the tone of the responses to this posting (but perhaps I
shouldn't be, unfortunately); I don't see anything untoward in it. I would
like to provide some context (with some assumptions on my part) for the message
lest other innocent postings meet with similar fates. I'll also (eventually)
provide my answer to the question, as I understand it.
There is a significant portion (majority?) of the industry which is extremely
cost constrained. For instance, to them rotating a design 10 degrees is
impractical, much less 22 or 45 degrees. Thus, they find other cost-effective
yet effective means of solving problems (such as zig-zag routing), even though
those don't appear efficient to others to whom cost is not an issue.
There are new pressures being applied to this segment - designers are now not
only requiring impedance control, but are also insisting on insertion loss
control. This is a HUGE paradigm shift, very similar to what we encountered
when traceable impedance control was first introduced. That was a very
challenging evolution, and this will be also.
As an example, PCB vendors are now being advised to smooth their copper, after
years of purposely roughening it for best mechanical integrity. It should come
as no surprise that this is not a trivial change, considering the effort that
has gone into ensuring mechanically robust designs.
Likewise, many other basic assumptions that we've been able to apply for years
are now being drawn into question, and PCB vendors are looking for help to
intelligently and cost-effectively explore options - "How much effect does
rougher copper have on insertion loss?". I believe Terry is highlighting the
fact that, while there are many tools available for impedance prediction,
insertion loss modeling is much less accessible. I don't think it is
inappropriate to ask if there are cost-effective, reliable tools available to
predict insertion loss based on a proposed stackup.
Unfortunately, I believe the answer to the question is that there are no
reliable, cheap (~free) modelers available to predict insertion loss. And, the
ones that are available require a great deal more knowledge about the stackup
than impedance modeling does, and that information is not easily obtained.
There are some of us working with a vendor to test their modeler against a
variety of stackups and we'll present results at DesignCon. My personal goal
is not so much to test a specific modeler but to judge how effective a modeler
can be given information that can reasonably be gleaned prior to building with
various materials, copper types, etc.
In the absence of a modeling tool, or in addition to one, I believe empirical
data is the best predictor of insertion loss. To do this, however, you have to
build a stackup representing the final design, and it's not clear at this point
how broadly you can extrapolate those results to other stackups. But, I know
many material vendors and PCB shops are engaged in similar efforts.
I think this is very similar to what we went through with impedance control -
the shops which most quickly were able to predict and control that
characteristic had an advantage. I think successful PCB vendors will need
reliable modeling software and empirical data on insertion loss for their
particular choices of materials, etc. - they will be able to find the most cost
effective solution.
Bottom line: I doubt a reliable modeling tool is going to be cheap, but is
going to be necessary, and you'll want to compare any tool you do purchase
against empirical data before you trust it.
I hope this helps,
Jeff Loyer
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx<mailto:si-list-bounce@xxxxxxxxxxxxx>
[mailto:si-list-bounce@xxxxxxxxxxxxx]<mailto:[mailto:si-list-bounce@xxxxxxxxxxxxx]>
On Behalf Of Terry Ho
Sent: Monday, October 29, 2012 5:52 PM
To: si-list@xxxxxxxxxxxxx<mailto:si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] PCB Insertion loss prediction
Hello experts,
I'm from PCB house. Recently we have producted some insertion loss test
boards(16L, SET2DIL coupon, IS415/IT150DA/I-Speed Mid/low loss material with
RTF copper foil). We found that the multiply core and high resin PP will result
a lower loss result. It's a trouble to MI engineer. I would like to know how
to predict the loss base on stackup. Please help to suggest (papers, script,
free software etc ). Thanks a lot!
Best regards,
Terry Ho
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