Your wisdom about prototypes - Page 1
Forum section: electronics / general

author: king.oslo
author_rank: Frequent Contributor
timestamp: June 04, 2012, 08:11:03 pm
content: Hello everyone,I order prototypes of my circuitboards from iTead. Often, it is a month before they arrive in Oslo, where I live. I hate myself when they arrive, having made a dumb mistake before submission, or spotting that I could have done something clever.I thought it was a good idea to make a thread with collected wisdom about what to check/how to utilize the potential of making a prototype circuit board.I've designed a circuit. I think I am ready to submit to board house. But what do you recommend carrying out before submission?Wisdom I have gathered:- Check footprints and pinouts 3 times.- Consider using the backside of the prototype as front panel for the finished project- Prototype two projects on one board. One on each side of the pcb.Dave, good or poor idea for a video? You can let your creativity flourish.Thank you for your time.Kind regards,MariusPS: I attached one of my boards to stimulate to fault finding and creative suggestions

author: Twistx77
author_rank: Regular Contributor
timestamp: June 04, 2012, 08:31:27 pm
content: Great idea!I would add:- Getting a good look to your gerber files (Most people do I think)- If it's a prototype, add components that you might need but you are sure and in case of not needing it just short circuit the pads.- Try to add testpoints to the critical parts of the circuits.- Try no to put vias under IC's because if one isn't well made, its a pita to check it if you find there is something wrong.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: June 05, 2012, 10:31:36 am
content: I would suggest making proto-pcb at home with laser printer transfer technique. I use the pulsar-pro dextrin paper and an hp laserjet p2055dn with real hp toner. You can use ferric chloride or other etchant and fully test and revise your boards at home before sending gerbers out.

author: AntiProtonBoy
author_rank: Frequent Contributor
timestamp: June 05, 2012, 12:57:44 pm
content: If you are going to house the PCB in a chassis, print it out to scale on paper, glue it on a cardboard and cut it out. Check whether the mechanical specs fit the chassis, particularly mounting screws and the component clearance with respects to other stuff inside the case. This is particularly if you use big/tall components, or heat sinks. Also check for connector footprint alignment with respect to their chassis cut-outs, etc. I had several "FFFFFUUU" moments where things like heat sink needed that extra 1mm space to fit properly. With that said, also allow plenty of slack in your mechanical design to accommodate a comfy clearance for big components.

author: metalphreak
author_rank: Frequent Contributor
timestamp: June 05, 2012, 02:27:13 pm
content: Whatever side is going to be your "front" or visible side, make sure its the bottom layer in the gerbers you submit. Itead and Seeed Studio's board houses always put their marking codes on the top side silkscreen.

author: free_electron
author_rank: Super Contributor
timestamp: June 05, 2012, 02:43:18 pm
content: Quote from: chickenHeadKnob on June 05, 2012, 10:31:36 amFor single side this works great. I've done a few using the pulsarpro stuff.Etching is quick if you use the spunge technique.Cut a 2 *2 inch piece of and soak it in fecl.Put pcb and spunge in a ziplock bag and close it.Grab spunge and dab it on the board repeatedly. Make sure to make bubbles.What you are doing is a double action. Every time you dab , there is just enough friction to clear off the thin layer of spent fecl-copper ions.And you are aerating the material as well..Plus you make no mess or spillAs for the checks, i do not use different rules for proto or release builds.That said.. @king.oslo :The layout of the switcher is very bad ... The recirculation diode should be tacked directly to ground and not with a long trace To the output connector.You are not following 'logical current flow'. You need to go coil - capacitor - out.Now you go coil -out-capacitor.The pulse currents in the caps are large and rise fast... They will follow top trace..Time for a ' how to layout switchin regulator video '...

author: siliconmix
author_rank: Frequent Contributor
timestamp: June 09, 2012, 04:55:24 am
content: yeah good idea to get your prototypes proof read.but be careful who you show them to.we are all ok an here.

author: Short Circuit
author_rank: Frequent Contributor
timestamp: June 09, 2012, 05:56:44 am
content: Advice #1: Just Do It.Often there will be some mistakes which could have been avoided by double checking everything (the kind of errors you find out between ordering and receiving the actual prototypes;)Almost equially as often there will be issues which will not be found by double checking, mostly on a subtle schematic level, such as pullups, different I/O pins preferred on a uC, wrong footprint, pins that need to be gorunded or vcc'ed (Analog Devices likes to do that). Even with the most extensive reviews, you'll catch only a few of such problemsThen, 9 out of 10 will have some issues which are no deal breaker, but which could be done nicier, things like layout, component placement, pcb outline, texts & logos on the pcb, etc. By having to do a respin anyway, those issues can be done along.When you're doing electronics commercially, yust do it and respin is a no-brainer; a typical small to average PCB cost less than 2 hours of your time. And 2 hours ain't much if you're looking for unknown problems.And yes, a few of the obvious problems can be avoided with a checklist, things like via soldermask, texts, fiducials. I used to have such checklist too. Guess what I usually remembered to have forgotten after ordering a new PCB... But I never forget to create an issues.txt in the design folder when the first problem is found. This files contains a plain list of problems and the state of solving (todo/schematic/pcb/misc).I do electronics comemrcially, and in my quotations I simply assume 1 or 2 respins before the design will be ready. Customer knows this and pays for it, but also gets the opportunity on each spin to incorporate (small) changes to the design. Only one-off projects are supposed to go in one shot, things like test fixure PCBs. These still have some issues usually, but those are fixed by botch wires or parts.