Working with copper clad and RF. - Page 1
Forum section: electronics / projects

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: December 17, 2015, 01:14:43 am
content: I buy my clad a Radio Shack usually it is double sided 4x5, it was on sale a while back to I bought maybe 8 pieces or so. Most of my projects have been point to point on RS veriboard cut to size. I have just recently started using copper clad to do Manhattan and ugly style. I also glue cheap e-bay smd breakouts to the clad for SMT chips.What I would like to know is how to get nice straight traces on to the clad, I have tried a glass cutter, a dremel with routing attachment and even a razor knife with carbide razors! The dremmel works well with diamond attachments, but wether it be routing or a cutting wheel it is very had to get nice neat lines. I have though about using some wood and drawer sliders to make a simple hand guided type of mill for straight lines. I was hoping there may be an easier way.The next thing is how do I make 50/75 ohm impeadence strip lines on these boards? Is there a way to calculate that? I ordered someAD5934chips hoping to learn to use them to make an LCR/Z meter along with the AD programmable current sources. Could these chips help me figure out the impeadence of a copper clad trace?

author: tggzzz
author_rank: Super Contributor
timestamp: December 17, 2015, 01:31:36 am
content: Quote from: rwgast_lowlevellogicdesin on December 17, 2015, 01:14:43 amSure, seehere.QuoteAt 250kSPS, only for impractically long traces.Out of curiosity, what type of callsign is KK6WKK?

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: December 17, 2015, 02:21:42 am
content: There are many tools available to help you with that, but most of them use empirical formulas, in other words, they'll only be valid for certain ranges of proportions and only be maybe within 10% of the reality. The only other way I know of to get more accurate predictions is with a field solver.Here's a free-ish field solverhttp://www.sonnetsoftware.com/products/lite/The Saturn PCB toolkithttp://www.saturnpcb.com/pcb_toolkit.htmI don't know why you tried all those ways to makes traces, what's wrong with the good old chemical etching? Even better, just outsource the work to OSH Park/whoever of the month.

author: GreyWoolfe
author_rank: Unknown
timestamp: December 17, 2015, 02:25:45 am
content: Quote from: tggzzz on December 17, 2015, 01:31:36 amTechnician class Amateur Radio OperatorTom, NW0LF, Amateur Extra class

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: December 17, 2015, 07:17:40 am
content: Yes just a technician class call sign.Thanks for the software, I guess oshpark or whatever is not very handy for experimenting im not a patient guy... and I have tried toner transfer it has never worked, maybe one day I will pick up a lamination machine. I dont mind doing Manhattan style or even veriboard I just need to figure out a quick dirty way to to do a 50/75 ohm stripline on clad for crtain components or even coaxail connections from board to board. SMA connectors etc get expensive quick and dont really help when it comes to the impeadence an LNA wants to see or something like that.Maybe I am mistaken but I thought doing transmission lines by hand was pretty common in the ugly construction RF world?

author: krivx
author_rank: Frequent Contributor
timestamp: December 17, 2015, 08:17:20 am
content: Quote from: rwgast_lowlevellogicdesin on December 17, 2015, 01:14:43 amI have had good luck with scoring with a Stanley knife and then snapping the board along the line, sometimes in a vice. W2AEW has a video on this

author: KJDS
author_rank: Super Contributor
timestamp: December 17, 2015, 09:41:29 am
content: Quote from: Alex Eisenhut on December 17, 2015, 02:21:42 amIf you're after transmission lines of sensible impedance, then Hammarstad and Jensen's equations are more accurate than Sonnet.

author: tggzzz
author_rank: Super Contributor
timestamp: December 17, 2015, 09:52:42 am
content: Quote from: Alex Eisenhut on December 17, 2015, 02:21:42 amIndeed, are there any cheap places which use anything other than FR4?

author: ZeTeX
author_rank: Frequent Contributor
timestamp: December 17, 2015, 06:44:35 pm
content: Quote from: rwgast_lowlevellogicdesin on December 17, 2015, 01:14:43 amI usually just cut the copper clad with an hacksaw, and then place it in a vise (like milling vise for example) and then file it for a minute and it gives me perfect straight edge with not burrs or sharp edges.the only only downside that it might take some time.belt sander \ bench grinder might work too.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 17, 2015, 08:30:08 pm
content: No problem:1mm pitch:Both done freehand with a utility blade. Use good quality blades, harder the better (be careful not to use them for prying: if it's good and hard, the edge breaks very easily). Sketch the layout beforehand if you're unsure, and score with the help of a metal ruler if you aren't very straight by freehand.I make cuts by first scoring straight with the blade perpendicular to the board, then making more passes, tilting the blade to either side for each cut. This slices out a vee of copper and a little core, ensuring the gap is anywhere from 5-30 mils. The cut can be steered somewhat by twisting the blade on axis; the initial cut helps track it in place but don't go too crazy or it will jump out of the groove.For wider gaps, isolation slots/bands, etc, score the perimeter of the region then try to peel it up. Get the blade under a corner and undercut it so you can begin lifting the copper; if you're lucky, it will peel off in a few tries. 2oz really pays for this: you can usually peel complicated regions in one piece. 1oz tears easily and is hard to get started; don't bother with 1/2oz.Tim

author: Pjotr
author_rank: Frequent Contributor
timestamp: December 17, 2015, 10:08:50 pm
content: Quote from: T3sl4co1l on December 17, 2015, 08:30:08 pmIt helps a lot when you heat the copper to be removed with a soldering iron. Put a solder blob on a corner, keep it heated and you easily can peel it off by prying a scalpel underneath the heated copper and without tearing. It works best by first lifting a small heated corner and peel off the rest with tweezers and keeping the already removed copper heated with the iron. With some practice and you do it fast, this goes without damaging the epoxy.

author: tggzzz
author_rank: Super Contributor
timestamp: December 17, 2015, 11:43:21 pm
content: Don't etch, simply use a guillotine...An old product, no longer sold AFAIK, was pre-fabricated stick-on controlled impedance lines.Picture a piece of FR4 1.5mm thick, copper on one side and adhesive on the other. Shape is 3mm wide, and you simply cut it to whatever length you need. Then position it on another piece of unetched PCB acting as a ground plane, and you have a 50ohm transmission line.

author: hendorog
author_rank: Super Contributor
timestamp: December 17, 2015, 11:55:00 pm
content: Quote from: tggzzz on December 17, 2015, 11:43:21 pmSelf adhesive copper tape could be used for that, and is easy to work with.

author: tggzzz
author_rank: Super Contributor
timestamp: December 18, 2015, 12:24:41 am
content: Quote from: hendorog on December 17, 2015, 11:55:00 pmI've thought of that, but not tried it.Possible problems are that some types have conductive adhesive (for sealing gaps against EMI ), and the separation from the groundplane would be poorly controlled.You can also get very thin Duroid PCB material, which might be advantageous at microwave frequencies.

author: hendorog
author_rank: Super Contributor
timestamp: December 18, 2015, 12:59:45 am
content: Quote from: tggzzz on December 18, 2015, 12:24:41 amI was meaning to just use single sided copper clad. I remember reading that it was used in a uni class in one of the microwave books.Something else which might be of interest - solder panel tabbing ribbon (2mm), copper tape groundplane and 3d printed PLA substrate. Hard to solder due to the low melting point of the PLA but it works OK at microwave frequencies.

author: KE5FX
author_rank: Super Contributor
timestamp: December 18, 2015, 01:41:41 am
content: Never understood the motivation behind slicing and dicing a perfectly good ground plane.

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: December 18, 2015, 12:42:27 pm
content: I agree there is no reason to slice for the mostt part i use a small diamond hole saw to make round pads. The rs board is also dbl sided so i drill hole and jumper vias to the bottom. What im after is just 50/75 ohm slices of even cut out of another piece of clad to to glue on to the existing one. Like i said i would rather solder coax between boards/at antennas/and lnas when i need proper terrmination than use a bunch of exspensive connectors.... just make more sense finacially. I thought it would be easy to make a stripline. The old stickers metioned seemed lime a good non fuss way to bad they dont exist :/.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: December 18, 2015, 01:59:16 pm
content: While this will not directly solve your question, and I haven't the experience with this myself, a few RF-oriented professors tend to say that you only need impeadance matching for anything longer than 1/10th of the wavelenght, which is often the case in home brew HAM pcb's.

author: tggzzz
author_rank: Super Contributor
timestamp: December 18, 2015, 04:41:51 pm
content: Quote from: hendorog on December 18, 2015, 12:59:45 amDoh! Silly of me not to think of that!Quote

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 19, 2015, 12:54:54 am
content: Of course, for < 1/10 wavelength, you still have the equivalent inductance and capacitance of the trace. Which are more pronounced for circuit impedances far from Zo (which is typically the case for switching supplies, with circuit impedances of ~ohms, and this is why "stray inductance" is so important).And wavelength is not at your discretion: high fT transistors are more than happy to oscillate at frequencies you might've neglected.Tim

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: December 19, 2015, 08:16:03 am
content: Quote from: T3sl4co1l on December 19, 2015, 12:54:54 amDidn't think of that. Makes a lot of sense tho.

author: G0HZU
author_rank: Super Contributor
timestamp: December 19, 2015, 05:57:25 pm
content: If you can find a used one at a cheap price then the other option is a T-Tech or LPKF PCB milling machine for RF prototyping. I went down this route about 12 years or so ago and it does offer a useful alternative to other PCB prototyping methods.It doesn't replace dead bug style etc but it does mean you can mill accurate traces and shapes for RF work. I paid just £800 for mine.However, if you read this thread here the experts seem to think that PCB milling machines don't work...https://www.eevblog.com/forum/eda/help-buying-a-good-pcb-mill/Here's an image of my main PCB milling bench. This is an old T-Tech 7000S model. When you consider that newbies on here are quite happy to cough up $1000 for a bench DMM then this isn't a luxury item by any means