[time-nuts] GPS down converter question

Herbert Poetzl herbert at 13thfloor.at
Thu Dec 3 19:30:56 UTC 2015


On Thu, Dec 03, 2015 at 01:53:25PM +0100, Attila Kinali wrote:
> On Wed, 2 Dec 2015 21:12:42 -0500
> Ian Stirling <is at opus131.com> wrote:

>>   Here's a video of Dave Jones soldering a QFN chip.
>> http://www.eevblog.com/2013/01/08/eevblog-408-schmart-board-0-4mm-qfn-smd-soldering/

> Unfortunately, this technique only works if you don't have
> a ground pad to solder, which most of the RF chips have.

If you plan for hand soldering, this is one of the easier
problems to solve: just make a somewhat larger via where
the ground pad is so that you can easily solder and fill
it from the other side.

> Actually, a lot of them have no other ground pins than the
> ground pad. 

> Also, the long traces for the breakout are prohibitive 
> for RF stuff. 

No need for long traces, about 1mm (0.04") should be more
than enough to solder the traces to the QFN chip.

Been there, did that, worked just fine :)

> Even if you just run it at 70MHz, the chip is designed for 
> GHz operation, which means you have to treat all signals 
> as if they were operating there. 

> Otherwise you will have some funny effects.

> 			Attila Kinali

> PS: Please be aware that Dave Jones is often borderline wrong
> with what he presents in his videos. So take them with a grain
> of salt and check any "facts" independently before relying on
> them.

I totally agree here.

Best,
Herbert

> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
>                  -- Miss Matheson, The Diamond Age, Neil Stephenson
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