Is there any conductive putty for temporary circuits?

Thread Starter

Enrique Zamora

Joined Jul 19, 2022
1
I am beginning with RF circuits, and had some problems when passing from breadboard to the final device. As I was browsing, found that the reason is the parasitic capacitance that the breadborad generates between connections. So, in order to make temporary circuits for RF devices it came to me the idea of some kind of conductive putty in which you could insert the component pins, and found some conductive paste online, but it's quite expensive, and I don't even know if it hardens like epoxy or if it stays soft. Do someone know an alternative for this or how to make a similar material?
 

Ya’akov

Joined Jan 27, 2019
6,260
Welcome to AAC.

RF circuits are very sensitive to layout in addition to parasitics. They are not as sensitive to DC resistances which would probably be high for such a putty but the putty itself would almost certainly be a source of parasitic capacitance.

The effects of the different issues that pertain when laying out RF circuits multiply proportional to the frequency. It is not only capacitance but even the inductance of a PCB trace or wire that can prevent a circuit from operating.

To layout a test RF circuit really requires doing the things you would need to do if it was a final product. Breadboarding logic and simple audio circuits works because those don’t have the same sensitivity to physical layout and parasitIcs.

One method that works quite well is the “dead bug” style. It got its name because the components are often oriented with their legs up, like a dead bug. For RF circuits it is usually done using a copper clad board as the base for a ground plane.

1658274283928.jpeg
[source] Dead bug style RF layout
It‘s worth looking into, it’s simple and works well. I don‘t think you will be very successful with temporary connection methods, they will always cause unexpected results.
 

DickCappels

Joined Aug 21, 2008
9,062
Just hanging the components in the air, supported over the ground plane with their grounded pins seems it would be ideal. Not only is Manhattan style beautiful, but it is time consuming and the pads add a few pf per pad depending upon the dielectric. In any case, plug-in breadboards are not your friend when it comes to RF.

1658336513262.png
SOLDER GOOD! NYLON BAD!
 

atferrari

Joined Jan 6, 2004
4,647
Just hanging the components in the air, supported over the ground plane with their grounded pins seems it would be ideal. Not only is Manhattan style beautiful, but it is time consuming and the pads add a few pf per pad depending upon the dielectric. In any case, plug-in breadboards are not your friend when it comes to RF.

View attachment 271880
SOLDER GOOD! NYLON BAD!
Air hanging technique was formally recommended in several National's app notes (op amps) appearing in what was the last printed version I was lucky to get from them.
 

atferrari

Joined Jan 6, 2004
4,647
To implement a 1,2 MHz Clapp oscillator I built this

Oscilador Clapp 1,2 MHz.jpg

In my very first attempts using this technique (for a different circuit designed by member Dick Cappels) I made the boards extremely small, making changes very hard, risking to easily damage parts when desoldering or adding components.

In spite of some videos where they seem to "create" the distribution as it goes, found quite convenient to me, planing the distribution in graph paper, somewhat to scale. I enjoyed the experience.
 

Ya’akov

Joined Jan 27, 2019
6,260
To implement a 1,2 MHz Clapp oscillator I built this

View attachment 271897

In my very first attempts using this technique (for a different circuit designed by member Dick Cappels) I made the boards extremely small, making changes very hard, risking to easily damage parts when desoldering or adding components.

In spite of some videos where they seem to "create" the distribution as it goes, found quite convenient to me, planing the distribution in graph paper, somewhat to scale. I enjoyed the experience.
Nice work, AT. A very neat layout and result.
 
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