Designing my first PCB - Page 1
Forum section: electronics / beginners

author: obiwanjacobi
author_rank: Super Contributor
timestamp: April 12, 2015, 07:47:37 am
content: I am planning on making a PCB for something I am working on. I plan to get as few boards as possible made by a cheap PCB manufacturer. I probably only gonna build one (prototype).I am looking to learn about 'best practices' and requirements for PCB layout. The circuit is a MIDI hub that has a MCU for intelligent processing. The LCD display is external/standard. 6 Din MIDI female connectors (in/thru and 4 out) and some buttons for programming it. So no RF, Audio or critical stuff. The clock/crystal for the MCU is most critical, I think.Are there any standards for drill hole sizes, pad sizes etc. (don't want to incur extra cost for stupid choices)Why is it better not to route traces in sharp angles (heard Dave say this)?Does it matter what copper layer you put your components on? Also if it's a mix between thru hole/SMD.Is a poly-fill ground plane (1- or 2-sided board) 'always' a good thing?What are typical easy fixes (low hanging fruit) for cheapest production cost / best quality of PCBWhat are the typical assets the PCB manufacturer needs for production?What choices are 'a good idea' to pick/follow? Anything that is a standard or help reduce cost/complexity.Any advice on (closed) case construction (PCB related)? I was thinking about an alu extruded standard case.I understand it's all very general, just share your ideas and experiences.I (think I) am pretty good at laying out and finding the best routes etc.

author: lutkeveld
author_rank: Regular Contributor
timestamp: April 12, 2015, 11:02:20 am
content: 1) No not really. It's good to minimize hole size variety, but don't do it at the cost of loose fitting components. Most hobby-grade board houses like Seeed and iTead don't charge you extra anyway.2) 45 degree angles result in shorter tracks (lower impedance, less board space, less inductance etc) compared to 90 degrees. 90 degree angles can also cause certain issues with very high speed signals and can cause issues when etching your board.3) No, but try to do as much stuff on one side. Makes it easier to assemble. If you switch to the other side, you can route further from your through hole components instead of using additional via's.4) GND planes are handy, but can partially block signals. So if you have BT on your board for example, make sure there is no plane in the way of the signal.5) Make sure everything fits on 50x100 or 50x50mm. This yields very low price per board with the common chinese board houses.6) Gerber and NC drill files, packaged in a ZIP7) For what?8 ) 3D printed enclosures are very cool for low volumes. Does it need to be closed?

author: obiwanjacobi
author_rank: Super Contributor
timestamp: April 12, 2015, 11:58:02 am
content: Lost of good answers and info. Thanx!4) With BT you mean BlueTooth? So don't block antenna's with your ground plane. Got it (duh!).5) I could not fit 6 din MIDI connectors on 100mm! Are there any larger dimensions that are cheap(er)?7) I am looking for best practices and standards or things that help reduce cost (complexity)..8 ) Yes a closed case is my plan. I hope to use it in my studio setup and guitar rig (that is why I thought of alu and not plastic)... I do not necessarily want to design a case around the PCB - wouldn't mind designing the PCB 'around' the case...

author: lutkeveld
author_rank: Regular Contributor
timestamp: April 12, 2015, 12:48:26 pm
content: 4) yes5) Have a look at the Seeed website to see what each option costs.If the only reason you need space is the connectors you can get away with multiple smaller boards (you get 10 anyway)6) Main thing is using SMD. While prototyping I like to use DIP with sockets though.7) A lot of cases use rails where you can slide the PCB in. Keep in mind that you don't populate the board edges if you choose such an enclosure!

author: PeterFW
author_rank: Frequent Contributor
timestamp: April 12, 2015, 02:23:10 pm
content: One important thing ist forgotten most times, when building something that has to go in a case.You have to work backwards and think about everything else all at once!Select the connectors and think about how you will mount them, directly to the PCB, screwed to the case, loose wires and so on.Search for a box wich will fit them and the electronics.Search for buttons, switches and everything else wich will fit in the box.Then decide how big the PCB has to be, this is related to part one.Then try to fit everything together and make it look good.If you are stuck with a pre-determined board size, you can go two routes.Either search a box wich fill fit everyting nicely related to the board size and then start routing and part placement, this can work very well too!Some PCB fabs will sell the "euro board" at a reduced price for example, at least that was my experience.There are many enclosures out there dedicated to this 160x100mm standard wich work very well and look decent.Or just pick the biggest, cheapest box you can find and trow everything in there and call it a day

author: PeterFW
author_rank: Frequent Contributor
timestamp: April 12, 2015, 02:29:00 pm
content: I forgot... mounting holes, do not forget about mounting holes on the board.Do not try to wegde them in somewere when you are done.Incorporate them into the design early on, think about grounding from the mount holes/studs to the enclosure.If your box has rails to but the board in, think about how to keep the board from sliding around once assembled.And one other thing... if possible avoid tight tolerances but do not leave gaping holes a gaps either.Do not loose all sense for reality, print the stuff out, make a mockup out of glue, sticky tape and paper to get real feeling for the dimensions.It happend more then once to me that i spend hours shifting parts around just to kick myself in the head later because the naked eye could not see the difference if the part was 0.5mm to the left or right.

author: zapta
author_rank: Super Contributor
timestamp: April 12, 2015, 02:30:41 pm
content: Dave has a very good manual about designing PCBs, available on the internet as a free PDF.For PCB vendors, check pcbshopper.com.Once you design the PCB, you can pay it here and people will give you feedback.Edit: here it ishttp://www.alternatezone.com/electronics/files/PCBDesignTutorialRevA.pdf

author: rdl
author_rank: Super Contributor
timestamp: April 12, 2015, 02:45:18 pm
content: Quote from: obiwanjacobi on April 12, 2015, 07:47:37 amYes, absolutely design the PCB to fit the case.Knowing what switches, controls, and other connections to the outside world your board will need, plan a general layout and then go looking for a case that will work. Once you choose a case, then you can start on the PCB.It is thousands of times cheaper to make a PCB fit a case than it is to make a case fit a PCB.Clam shell type cases, where the front and rear panels are separate,flat pieces, are by far the easiest to work with. Those that are made from two pieces of bent, interlocking metal are a real pain to work with.

author: Wilksey
author_rank: Super Contributor
timestamp: April 12, 2015, 11:01:06 pm
content: Sharp angles can cause acid traps and you should pick a case before designing the PCB, take note of the selected board houses minimum tolerances on drill sizes and trace widths etc, drill sizes are best kept to the same size if possible, so through hole components for example, if possible make sure that all of the drill holes use the same size drill bit, and vias, i.e. don't have several different size vias unnecessarily scattered across the board.Read Dave's PCB tutorial also.I realise I have just pretty much echoed what has already been said, but they are important points.One thing I find people overlook is current carrying capability of copper traces, if you have high current, if you are driving motors for example, take note of the current!

author: cellularmitosis
author_rank: Unknown
timestamp: April 13, 2015, 05:17:45 am
content: Here is the "standard" I follow for pad sizes.Note: I mostly do through-hole stuff.

author: obiwanjacobi
author_rank: Super Contributor
timestamp: April 13, 2015, 05:37:09 am
content: Great, thanx guys.Also thanx for posting the link to that PCB doc Dave wrote, I was looking on the EEVBlog site...Some very good pointers, some stuff I already knew, but good info.

author: skyjumper
author_rank: Regular Contributor
timestamp: April 13, 2015, 06:43:19 am
content: You didn't mention what software you're using. Most people use Eagle although there are others. The PCB pooling service may have libraries and standards you can download and use when you lay out your board. If they do you'll want to use them to make sure your board meets their standards.

author: obiwanjacobi
author_rank: Super Contributor
timestamp: April 13, 2015, 07:40:39 am
content: I have KiCad, DipTrace and Eagle installed O0I am not very experienced with any of them - can get the basics done in all of them, though - so I can switch to whatever is best suited or easiest.With "The PCB pooling service" you mean the PCB manufacturer that have open source designs available??I have not researched what specific PCB-house is best/cheapest for my needs. I have looked around a bit to get a ballpark figure, but not delved into the details yet.

author: void_error
author_rank: Frequent Contributor
timestamp: April 13, 2015, 08:00:36 am
content: Quote from: cellularmitosis on April 13, 2015, 05:17:45 amFor through-hole stuff I stick with 1.8mm pads which can easily fit 0.4mm traces between them for the standard dip package spacing for home-made boards. Sorry, I can't imperial.

author: obiwanjacobi
author_rank: Super Contributor
timestamp: April 13, 2015, 09:08:30 am
content: Me neither

author: Wilksey
author_rank: Super Contributor
timestamp: April 13, 2015, 10:07:24 am
content: PCB Pooling is a cheaper way to get your PCB's produced by the manufacturer taking a standard panel size and putting other peoples designs on as well as yours, so for example, if you wanted 10 board of a particular size, the panel might be able to produce 50 or 60 boards of such size, but they will charge you for the panel as the rest will be thrown away, by pooling you can get 4 or 5 people's designs on one panel, so the manufacturer will make use of an entire panel, splitting the costs between you and 4 or 5 other people.The above is just an example of the principal behind pooling.I have found that Chinese and Indian manufacturers are the cheapest at the moment, I use smart prototyping mainly, they seem to produce good stuff and are helpful / friendly and their prices are very good for what I want.

author: obiwanjacobi
author_rank: Super Contributor
timestamp: April 13, 2015, 11:12:05 am
content: So I have to calculate if the added cost of adding inter-board connectors outweighs the savings for cheaper board - in a multi board solution... Stacking boards will probably be cheaper than multiple boards in one plane...I wish there was more support for these experimentation scenarios in the CAD programs...

author: Wilksey
author_rank: Super Contributor
timestamp: April 13, 2015, 03:25:53 pm
content: There is a fella on here that owns a website that will help you to determine price and variation of boards, the website is pcbshopper.comI am in no way affiliated with this website, but it's a bloody handy site to keep bookmarked!!