Rf prototyping techniques .....

[ashwanthh]

Hi all,

I am doing an RF project, I want to know how to prototype rf circuits, as Bread board cannot be used. I am using components which works upto 2ghz.

Anyone Help..

 

[jayce3390]

what is the difference between prototype and bread board?
Rf prototype = RF bread board

A lot of companies provide printed circuit production, multilayer, flexible or double-sided technologies...Just send them you DXF or GDSII files.

 

[210MeV]

If i understgand corectly. Talk about how to prototype rf circuits without manufacturing printed circuit board.
I also wonder how this can be done

 

[keith1200rs]

I would guess the best you could do is use something like this

I tend to prefer a PCB, but it takes time and speeding things up gets expensive.

Keith.

 

[G0HZU]

I invested in one of these T-Tech milling machines for prototyping about 8 years ago (secondhand)

**broken link removed**

Mine is the older version of the one above. I actually have two of them as I was able to buy a second one cheaply (faulty) for spares.

They are pretty much essential if you want to do lots of rapid prototyping on various PCB dielectrics etc.

eg accurate milling of microwave filters, antennas or PCBs with fine pitch SMD devices.
Also, it can be used to make front panels for boxes with accurately drilled holes. Also it can make templates for various non RF applications.

Best bit of dev kit I've ever bought plus it paid for itself within a year as I also made numerous one off PCBs for a local company for the first year I had it.
It takes about 1 hour to mill and drill and cut a small dev PCB (eg an LNA or a BPF)

A more complex PCB, eg a double sided 180x180mm digital board with LOTS of tracks can take several hours. You can do accurate double sided boards and also fit decent through hole rivets to make a really good quality dev PCB.

Plus you can use the same CAD data to make the real version from a PCB manufacturer.

 

[123jack]

Interesting but I'm always less than enthusiastic when a company
hides the price of the product they are trying to sell.

It doesn't encourage me to ask for more info - it encourages me to just go elsewhere. Very bad marketing trick IMO.

jack

 

[G0HZU]

The alternative is to look at LPKF. They make similar machines.
Rapid PCB Prototyping - LPKF Laser & Electronics AG

We have an LPKF machine where I work. These generally cost more and are more versatile.
However, if you buy a new one you need deep pockets. I think our company paid over £10k for our LPKF machine and that was about 6 years ago.

The T-Tech machines probably cost a similar amount today although you can pick up secondhand ones on ebay for much less.

I paid a fraction of the new cost for my T-Tech machine from a dealer (my machine was prev owned by Hewlett Packard!)

I bought the second one for a few hundred pounds although it has a faulty drill motor. I didn't bother to fix it as I keep it for spares for the main machine.

 

[biff44]

T-tech and lpkf do what they say they will, they route pcbs. As long as the lines are not too narrow, and as long as you do not need ground vias. If you do need ground vias, then you have to do some of the processing that you would have to do with a normal pcb, ie the plated thru holes. Also, they are not the easiest machines to run...need some adjustments for depth, etc, and the dust is toxic so you need a hepa vaccum to clean it up.

With the low cost and fast turn around of pcbs, if you are below 3 ghz, getting a fast turn fr4 pcb board is a lot easier and cheaper.

 

[G0HZU]

You can do ground vias with a special rivet gun and the vias come in various sizes. They end up looking flush with the PCB. But it does take time to fit them.
You can also do very fine tracks. I made a flexi cable once from wafer thin double sided flexi material. Now that's 'fine'

The reset accuracy of the machine is less than 0.001" (typ 0.00025") so fine work is possible with a skilled operator.

Also I can mill pretty much any material and have a PCB within an hour (or a few hours if it is large)
This can be really useful if you are in a hurry and need to make rapid changes to a design. eg a drop in hairpin BPF. I milled several iterations of a 9GHz hairpin filter (on Rogers PCB material) for a client within one day. eg I milled it, they tested it, then tweaked it and remilled again etc

---------- Post added at 17:24 ---------- Previous post was at 17:19 ----------

T-tech and lpkf do what they say they will, they route pcbs. With the low cost and fast turn around of pcbs, if you are below 3 ghz, getting a fast turn fr4 pcb board is a lot easier and cheaper.

My first machine cost me £900. Also FR4 is no good for RF narrowband filter design (eg hairpin, interdigital or combline etc etc) as the results are not predictable or repeatable on FR4.

 

[biff44]

Where can you get the rivet gun and rivets? Sounds like a useful thing to have lying around!

I haven't used one in a long while, and back then we had to drill the holes, take it to a plating house, and then bring it back and finish it on the T Tech. We had a guy dedicated to programming/running it. Seemed a little complicated.

 

[G0HZU]

We get the rivets at work via LPKF. Basically, you have to drill the correct hole size and have sufficient pad size for a given rivet size.
eg 0.9mm hole and 1.5mm pad size. Then you poke the rivet through the hole (best to do half a dozen at a time) and then you use an impact tool (provided by LPKF) to 'click' the rivet into shape.
The impact tool looks like a metal screwdriver but it has an internally loaded spring so when you press down on it, it gives out a large click and forces the rivet into place. It's a noisy and slow process but the results are good. Also, the holes are hollow just like a plated hole so you can fit leaded parts if you wish. (can be useful for connectors)

I'd hate to do a board with lots of ground holes LOL.

This looks like it below although I think the one I use is an older model.

**broken link removed**

Boards milled and riveted and then tin plated can look pretty good

I use this stuff for tin plating. It doesn't need a hot tank and it doesn't smell etc.

When mixed up it looks like cloudy white water and it can tin a PCB in a few minutes.
MEGA|600-020|TIN PLATING POWDER 90G FOR 1 LITRE | Farnell United Kingdom

---------- Post added at 20:44 ---------- Previous post was at 20:34 ----------

There are other techniques, eg using ferric chloride to etch PCBs and this can work well. Especially if you are doing RF designs with basic signal paths.

Otherwise, at 2GHz the PCB construction could be done by scalpelling out very basic signal paths on a bare board, but this is hard work...