What do you think of my PCB design? - Page 1
Forum section: electronics / projects

author: lamja
author_rank: Contributor
timestamp: July 26, 2010, 08:57:50 am
content: Hi.I'm using FreePCB to design my PCB's. I use the laser toner transfer methode for creating PCB's at home. I find it easy to have wide traces (60 mil) and not using 45 degree but only 90 degree routing. I also only have one trace for each 100 mil raster.This board is not tested yet. the finnished design will contain two of these and a AVR micro chips as well.What do you think? Is it ugly as hell?

author: Zero999
author_rank: Super Contributor
timestamp: July 26, 2010, 09:13:28 am
content: Best practise is actually avoid angles equal to or less than 90°, because it can create problems with etching but with traces as wide as that, it's a non-issue.I do agree with using thick traces because it uses less etchant, will etch better and result in lower impedance connections..

author: MTron
author_rank: Regular Contributor
timestamp: July 26, 2010, 12:21:13 pm
content: Post pics of the final product! Making my own custom PCB is something i would like to try in the near future, i would love to see how yours turns out.

author: RayJones
author_rank: Frequent Contributor
timestamp: July 26, 2010, 07:53:57 pm
content: If you are etching this board yourself you are giving yourself heaps of extra problems by failing to keep the wide tracks correctly centered on the pads.Many of the inter pad clearances are being compromised by the track intruding upon this gap.The end result is you are more likely to have etching problems where these occur.If you can use a grid to keep the tracks and pads on the same plane.Likewise if you use more conventional narrow tracks the 90deg turns can become troublesome also in the etching phase as others have stated, and are best avoided.

author: lamja
author_rank: Contributor
timestamp: July 26, 2010, 08:43:25 pm
content: Quote from: RayJones on July 26, 2010, 07:53:57 pmHi. Thanks for your reply.There is a problem with the IPAK MOSFET, the pads are slightly to close together. They are not 100 mil raster. But I think I will get the traces centered on the pads anyway. That will be better. I agree.

author: lamja
author_rank: Contributor
timestamp: July 26, 2010, 09:03:39 pm
content: A bit more centered traces on MOSFETs and connectors:

author: Zero999
author_rank: Super Contributor
timestamp: July 26, 2010, 11:39:00 pm
content: How are you going to be doing the silk screen?Do you have some special paper to make a nice white silk screen or do you do as I do: perform toner transfer as usual and cover it with a layer of conformal coating to stop it from being scratched off?

author: lamja
author_rank: Contributor
timestamp: July 27, 2010, 07:06:57 am
content: Quote from: Hero999 on July 26, 2010, 11:39:00 pmI have done the toner transfer for the silk screen as well. I did once try to cover it with a thin coat of plastic spray, byt when it dryed up, I could almost not see the text. It became too white. After that I have usually just smeard a thin layer of oil to let the toner shine trough the paper that I did not manage to remove, and it works really well.I will make this PCB in the weekend. When I get home from work abroad.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 27, 2010, 09:27:53 am
content: Quote from: pilleyuppo23 on July 26, 2010, 08:57:50 amno! its nice! just looks like the maze in Triwizard Contest in Hogwart U. everybody is suggesting to avoid 90 degrees turn, but for me, for a low speed circuit, i think your PCB is totally fine... as long as you designed it correctlybut why did u mirrored the "to be" toner transferred track?

author: Zero999
author_rank: Super Contributor
timestamp: July 27, 2010, 11:20:08 am
content: Trace width is more of a problem for <90 degree angles than speed, although at HF it can be an issue, at lower frequencies and thin traces, acid traps can cause over etching in the corners, although with the huge traces on his board, it won't be a problem.http://www.blackstick.co.uk/pcb%20tips.html

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 27, 2010, 11:37:32 am
content: @Hero999: its funny i think from the link... or is it me that misunderstood... the lettering dimension, i think it should be the other way around:Silkscreen rulesSilkscreen should be kept between 0.10 mm(4 thou) and 0.20 mm(8 thou) away from anything conductive, not covered by solder mask. The minimum line thickness should be 1mm(40 thou) and the minimum letter height should be 0.15 mm(6 thou).ps: man! i think my world is going upside down now.

author: Zero999
author_rank: Super Contributor
timestamp: July 27, 2010, 11:42:37 am
content: Yes it looks wrong to me, 1mm is quite thick for a silk screen, 0.15mm sounds more sensible and 1mm letter height is the smallest letter size readable and even then most people will need a magnifying glass.

author: lamja
author_rank: Contributor
timestamp: July 27, 2010, 01:45:51 pm
content: Quote from: shafri on July 27, 2010, 09:27:53 amOoops... I always do that miss. Thanks for reminding me(It's the silk screen that should be mirrored...)

author: lamja
author_rank: Contributor
timestamp: August 01, 2010, 07:44:18 pm
content: Some pictures of the work so far.Next will be populating the board...

author: Zero999
author_rank: Super Contributor
timestamp: August 01, 2010, 07:50:07 pm
content: Looks good to me.You can't possibly go wrong with traces like that, for example, I notice some of the holes are slightly off centre but that doesn't matter since it hasn't broken the pads and the pins will bend enough to compensate.

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 02, 2010, 03:39:20 am
content: nice. but if we have a way to make that silkscreen white, will be nicer. maybe i can experiment, spill it with white paint and run it below water flow. maybe the paint will stick to the toner but not the RF4 board. there should an etching technology for that as well.

author: shodan
author_rank: Contributor
timestamp: August 02, 2010, 06:41:12 am
content: lookup direct pcb printingI think this could be a way to first print etch-resistant ink for the traces(maybe to some tin plating here)then change the ink for soldermask and print it directlythen change to white ink and print silk screen

author: joelby
author_rank: Frequent Contributor
timestamp: August 02, 2010, 06:53:36 am
content: The PulsarProFX toner transfer kit comes with a white toner reactive foil that can be used as a silk screen.

author: Zero999
author_rank: Super Contributor
timestamp: August 02, 2010, 08:48:04 am
content: I think the black silk screen looks fine, it does its job, which is to make assembly and debugging easier which is the mains thing.If you're bothered about looks, use the old phenolic impregnated paper PCB which looks better with a black silk screen. I don't use fibreglass unless I really need to because it's more expensive and harder on cutting tools. I don't see why fibreglass is so popular, it may be stronger but I find it more difficult to work with; phenolic impregnated paper is fine for most applications.Here's a couple of pictures of a board I made awhile ago.

author: lamja
author_rank: Contributor
timestamp: August 08, 2010, 07:54:36 pm
content: Quote from: shodan on August 02, 2010, 06:41:12 amI have thought about it. Was thinking just go and bya a cheap 50$ incjet printer, and tear it apart, modifying it for direct printing. Have someoune actually done something like this?Anyway. The board is populated and next thing will be to test it in in an inductive load. Think I will start at 12V an slowly increase voltage. To bad I only have 12V and 56V power supplies.The heatsink is not so fancy. Home made. I might increase the size of it also.Actually I have only simulated the design in LTSpice. I hope it will work. Last design I did't use double voltage configurration on the opamps. That did NOT work ...

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 09, 2010, 02:38:40 am
content: i just noticed... is that ground loop on the periphery? i read that we should avoid ground loop, it will increase noise, just cut the track anywhere to avoid looping... i think.

author: lamja
author_rank: Contributor
timestamp: August 09, 2010, 04:21:29 am
content: Quote from: shafri on August 09, 2010, 02:38:40 amI read that somewhere also. But I think since it is ground it will work as a ground-plane. But anyway this isn't faster than 20kHz, so I dont think it will matter...

author: Zero999
author_rank: Super Contributor
timestamp: August 09, 2010, 08:36:28 am
content: I don't see how that's a bad thing, I've read about problems with ground loops but they aren't always bad.Aren't you going to remove the flux?The only trouble is you need a solvent that will not remove the silk screen, fortunately the solvent I use is comparable with the conformal coating I use on the silk screen.

author: shodan
author_rank: Contributor
timestamp: August 12, 2010, 08:04:57 am
content: about direct pcb printinghttp://www.fullspectrumengineering.com/pcbinkjet.htmlthese guys made a kit apparently to use some CD printer as a pcb printerall the messing around taken care of for 65$

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 12, 2010, 11:30:02 am
content: i've been thinking about it a time ago since my epson printer got a sibling R2800 which can print on CD and can be modded to put a smaller than CD sized PCB inside the CD compartment for printing. this R280 is cheaper... good!, but will be better if there is a "white" pigment ink, so we can print more professional look white silkscreen on green PCB

author: shodan
author_rank: Contributor
timestamp: August 13, 2010, 07:31:06 am
content: shafri, I'm not sure if this is still true but I think the printer head comes with the cartrige in epson printersif it's still true, then we could try different inks (by drilling the tank, draining it and injecting new ink in it)even better than whitesilkscreen I was thinking of applying green soldermask and conductive ink (to make conductive through-holes )also I think I will just mod a HP printer instead because I don't want to be limited to 3.5" wide pcbs

author: Mechatrommer
author_rank: Super Contributor
timestamp: August 13, 2010, 03:17:11 pm
content: Quote from: shodan on August 13, 2010, 07:31:06 amgreat idea! if this is achievable, no more messing with toner transfer and etching the copper. and no more need to send to remote pcb maker.

author: lamja
author_rank: Contributor
timestamp: August 20, 2010, 10:43:51 pm
content: A little update.- First power on with no load => no smoke...- Power on with load => shorted out power supplyI found one MOSFET burnt in the h-bridge, but changed all 4.Then I tested some more with a lot of 2.2 Ohm resistors on both load and input for the h-bridge.. with lots of smokeAfter a lots of hours testing, I found that I had mounted one diode the wrong way. Even though my silk screen was correct...But anyhow. its seems to be working good for now, but I had some problems with noise. Then I put 2 capasitors on the supply for the opamp, and the noise almost dissapeared.What is the best way using capasitors for a double rail opamp? Two from ground, or from + to -?Should these be as close to the opamp as possible?

author: allanw
author_rank: Frequent Contributor
timestamp: August 21, 2010, 01:46:59 am
content: Quote from: lamja on August 20, 2010, 10:43:51 pmOne 0.1uF cap on each rail to ground. These should be as close as possible to the op amp. You'll also want a larger capacitor near the op-amp if you need to drive a higher current. If you look up op amp layout, you'll find lots of application notes that discuss this in much detail.