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From: "Evan Foss (evanfoss AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
Date: Thu, 1 Sep 2016 09:16:18 -0400
Message-ID: <CAM2RGhSUSwjhF0B50LxKLNrAdgDZ=KyQQEmevNAC64EytJqx9w@mail.gmail.com>
Subject: Re: [geda-user] Microwave PCB layout simulation or How to eat all
 your processing power in 3 easy steps
To: gEDA users mailing list <geda-user AT delorie DOT com>
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On Thu, Sep 1, 2016 at 4:25 AM, Larry Doolittle
<ldoolitt AT recycle DOT lbl DOT gov> wrote:
> Evan -
>
> On Thu, Sep 01, 2016 at 12:07:28AM +0000, Evan Foss (evanfoss AT gmail DOT com) [via geda-user AT delorie DOT com] wrote:
>> On Wed, Aug 31, 2016 at 9:39 PM, Larry Doolittle <ldoolitt AT recycle DOT lbl DOT gov> wrote:
>> > On Wed, Aug 31, 2016 at 03:53:25PM -0400, Evan Foss (evanfoss AT gmail DOT com) [via geda-user AT delorie DOT com] wrote:
>> >> I thought soldermask issues were why most of the microwave and other
>> >> RF hardware I have seen has no soldermask.
>> > For the long lines, yes, depending on the designer, but eventually
>> > those lines usually touch chips.  And high-speed serial lanes (with
>> > the interesting frequency range now going up to 40 GHz) usually don't
>> > have soldermask stripped off.
>> At those frequencies I would actually think the chip would be supplied
>> as bare die and wire bonded.
>
> These days Xilinx BGAs have I/O rated for 25 Gb/s, with pretty broad spectral
> content up to 40 GHz.  I'm used to microwave circuits mostly ranging from
> 1 - 3 GHz, and all the Mini-Circuits and Hittite chips that cover that range
> (and higher) are in relatively conventional packages.

Ok. I have no experience with anything digital at that scale. I do
know that BGA soldering at that scale is impossible with out solder
mask because of capillary action.

I was wrong to dismiss that limitation so out of hand. That said it is
still on the user to model both corners (high and low) for board and
solder mask impedance.

> All this rambling is getting a bit off topic for the gEDA list.  Sorry.

No, I really appreciate it. Better I should be wrong and corrected
quickly than have my bad notions propagate farther and worse in code.

>     - Larry

PS: I really liked the days when the list was more active and people
asked about more off topic stuff. Like DJ's clock that had the piezo
electric ceramic cap problem.

Evan

-- 
Home
http://evanfoss.googlepages.com/
Work
http://forge.abcd.harvard.edu/gf/project/epl_engineering/wiki/

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