Breadboarding rf circuits - single or double sided pcb? - Page 1
Forum section: electronics / rf-microwave

author: medical-nerd
author_rank: Regular Contributor
timestamp: July 07, 2017, 08:55:02 am
content: HiyaWhen prototyping rf circuits using the manhattan method I know that the copper layer on the pcb is used as the ground plane.My question is does it matter if a single or double sided pcb is used, does the lower side have to be connected to the upper or is it of absolutely no consequence? If it is frequency dependent - when should I be worried?(I'm aware of transmission lines being made on double sided pcbs - but this is manhattan prototyping).Cheers

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: July 07, 2017, 09:08:51 am
content: Should be no consequence.But be aware that with Manhattan construction the pads glued to the main board act as tiny capacitors which could be an issue for high impedance parts of VHF circuits. You can minimise this risk by using small pads (eg 3x3mm instead of 6x6mm) and using no pads at all on certain parts of the circuit where they are not required for physical support.

author: CopperCone
author_rank: Super Contributor
timestamp: July 09, 2017, 06:50:24 pm
content: Quote from: vk3yedotcom on July 07, 2017, 09:08:51 amWould it be best to figure out a layout, then remove the copper from the areas under components and the signal path using exacto blade, dremel, etc? Not too much work. Like do a mockup using playdoe / thumb tack as an adhesive, then mark the copper for removal? A dremel sand wheel should make quick work of thin copper, and if you cut out the layout using a sharp tough blade, it will be very precise. Not as good as etching but still.

author: cdev
author_rank: Super Contributor
timestamp: July 11, 2017, 02:34:16 am
content: Medical nerd.. What frequency are we talking about here?For lower frequencies, just do whatever works for you. The higher you go the more the issues you brought up matter.for RF related stuff over 30 MHz, yes it does matter a lot, and thats a very good question.. If you make your own boards and dont have access to automatically generated vias the way it matters is driven by that difference.So your home made boards where vias area PITA to make will be very different than sent out boards where vias are easy.For RF - either way, always use double sided boards but the difference between a sent out board and a home made board is going to be manifested in what is done with the copper on the top thats not part of the signal path. this is something nobody it seems will teach you because they all assume you will be sending your boards out to have them made professionally.If you are making your own boards, resist the temptation to use ground planes on top OR put anything other than ground plane on the bottom.Your layout is going to be hugely different based on whether you have access to a PCB house versus home made PCBs. Home made board is best if its kept much simpler and smaller. Dont put ground plane around the edges, only put grounds to anchor your things that need grounds. Minimize stray capacitance. keep everything as short as possible.

author: medical-nerd
author_rank: Regular Contributor
timestamp: July 11, 2017, 04:04:50 pm
content: I will be homebrewing prototypes using manhattan/paddyboard/ugly construction for frequencies from 1 to 70Mhz.If I need a dedicated pcb then I will be etching it myself. 'Gasp - using stencils and hand drawn traces'.I will make many errors in this, but sorting them out will be half the fun.For higher frequencies extending to 2Ghz I have salvaged modules - oscillators/amplifiers/filters etc from surplus equipment but I don't want it all to be just plug and play.Many thanks for your replies.Cheers

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 11, 2017, 08:31:02 pm
content: If there are no holes in the top copper, then there's no difference.Well, maybe not at the lowest frequencies (has to do with skin depth of the copper layer), but that shouldn't be a big deal.You may find it's useful to carve traces out of the top layer, though. It's pretty easy with a utility knife, and it makes SMTs so much easier to use. Then you'll have to worry about how good your top-side ground is, and you may need to add vias to the bottom side (drill a hole, shove a tight fitting wire into the hole, solder it both sides) around important traces and ground paths.It takes about as long as laying out and drawing and etching and drilling a proper PCB, but it takes shape while you're building the circuit.Tim

author: medical-nerd
author_rank: Regular Contributor
timestamp: July 11, 2017, 08:47:50 pm
content: Thats's a great suggestion Tim - I'll try that method over the weekend, If I can last that long. The soldering iron is looking at me......I'm going to try it out now.CheersSteve

author: AF6WL
author_rank: Newbie
timestamp: July 12, 2017, 05:13:10 am
content: BPS make double side prototyping board with 50thou x 50thou pads on one side and solid ground on the other - it's ideal for SMTThere are regular un-plated through holes which are useful from bringing ground up to the top.http://www.mouser.com/ProductDetail/BusBoard-Prototype-Systems/SP1-50x50-GI regularly use this for quick circuits up to 1GHzJust lay wire and solder to make traces.The unwanted pads lift off easily with a longer application of the soldering iron e.g. on either side of a 50R micro-strip trace

author: CJay
author_rank: Super Contributor
timestamp: July 12, 2017, 06:58:15 am
content: I've got a few sheets of this stuff kicking about:http://www.ebay.co.uk/itm/2x-RF-Matrix-PadBoard-149x114x1-6-Prototype-Circuit-Board-/172485401698?hash=item2828ee5c62It's a double sided matrix board where one side is unetched.Handy stuff but not as cheap as plain old copperclad which is ideal for carving circuits into (if it's double sided) or you can make solder islands if you superglue down squares of copperclad onto the surface.

author: medical-nerd
author_rank: Regular Contributor
timestamp: July 13, 2017, 10:59:49 am
content: Thanks CJay - I've purchased a few of these now - they look very sturdy. I had to wait until evening as ebay is blocked at my workplace.The BPS board looks interesting but I can't justify Mouser's postage charge at the moment. I'll get a couple when I have to do a major restock of components.I've also stocked up on MeSquares and MePads for the larger components on plain copperclad.Many thanksSteve