Can I get a peer review, please? - Page 1
Forum section: electronics / beginners

author: aalbri
author_rank: Contributor
timestamp: September 28, 2013, 02:05:41 am
content: I am making a PCB for my final project at university. Could someone look over my design and point out anything fundamentally stupid? This is the first PCB I've ever made, but I have been an intern at a PCB manufacturer for 2 years now, so you can go harder or get technical on me. The school has control over specifics like dielectric material, thickness, etc. They will go with whatever is cheapest lol.I want to make sure everything's good for the board house, so I can get it made once, the way I want. I included my schematic if that helps at all.FYI I did not put component values on it, but I have breadboarded and tested and it should work. I did consider a filter cap, but I don't think it's really necessary. Correct me if I'm wrong.Thanks yall!

author: kizzap
author_rank: Unknown
timestamp: September 28, 2013, 03:06:24 am
content: Had a quick look, a number of pointers.Firstly, your gerbers are a little messed up. Ensure that you are using 2:4 Leading for your gerbers, looks like you have something different there. Unfortunately I don't use any Cadence software (if cam350 picked that up correctly) so I can't help you there.Looking at the board though I can see a couple of things. Firstly you have a MASSIVE space in the middle of the board there. If there is no reason for such a large board, you should look at compressing the board down a bit. PCB can be cheap, but it is cheaper when it is smaller.Secondly, it looks like you have zero mounting holes in the board. This isn't a massive issue if you are mounting in some form of slot system, but it is generally a good idea to add some if you can.Third, while not a major issue generally, but the traces could be a little thicker. Sure they might work as intended, but if you have the space, why not go for a larger trace?Fourth, it looks like there are +V and GND connections in those interconnects, but I can't tell because no connections are labelled. If there is a ground reference, you should consider using a ground plane instead of running a trace. Makes things a little easier.You also have a trace up top left that looks like you could route it through without using a via.-kizzap

author: Rufus
author_rank: Super Contributor
timestamp: September 28, 2013, 03:08:05 am
content: Kinda all round grotty I'm afraid.Mostly empty space - perhaps there is a reason.No apparent mounting holes - perhaps there is a reason.No identification of what the board is or issue which should appear on every layer to identify the artwork if nothing else.Solder resist layers are negative - not what any board house I have used expects.The one via on the board is relatively microscopic - probably smaller than the drill but I didn't look at drill sizes.Silk sceen overlaying copper all over the place.Some resistors have no silkscreen outline.Silk screen for the J2 connector is rubbish.Text should read from the bottom or the right not left.Resistor designators will be hidden by the resistors when fitted - silly when the board is 80% empty.If Q1 really is a TIP41 the footprint is wrong.Should be enough to be going on with.

author: aalbri
author_rank: Contributor
timestamp: September 28, 2013, 03:44:52 am
content: Sorry guys, I could have told you about what this is. For reference, it should be about 5" by 4.5".The massive empty space fits a 4 line, 20 character LCD tightly, but I agree the traces could be thicker, since its no extra fee. Mounting holes are TBD and I will do them myself with a drill press.I have had problems creating the artwork. I followed several different guides online, and they all come out with weird scales that don't work with my CAD software. Will that be an issue for the boardhouse?For the little via, I didn't see a way around using that. Do you see a more sensible solution?I wasn't sure about the solder mask... so it's normal for that to be positive? And what do you mean by text reading from bottom/right?The resistors will be mounted from the back. I only put designators on top for convenience when I display it, so my audience can follow me.The transistor is not really a TIP41, just used it for convenience (its a P2N2222A).

author: aalbri
author_rank: Contributor
timestamp: September 28, 2013, 03:49:46 am
content: By the way, thank you guys for takin time to look at it.I'm not trying to make something that will be mass-produced and look nice. I just want something the PCB fab can use and not get something seriously wrong.

author: IanB
author_rank: Super Contributor
timestamp: September 28, 2013, 04:45:01 am
content: Quote from: aalbri on September 28, 2013, 03:49:46 amIf you are making something for a university design project, you should try to make it as correct as possible; treat it as if it might indeed be mass produced. In a design project you are aiming to demonstrate as much as possible of what you have learned. This is your chance to shine.Remember also that when you are looking for a job, you may find it helpful to take your design project along as something to demonstrate and talk about. If you can show that you made every attempt to do professional quality work it will speak volumes for your aptitude. (When I was interviewing for my first job I was grilled in some depth about the details of my final design project and how I approached it.)

author: aalbri
author_rank: Contributor
timestamp: September 28, 2013, 05:01:00 am
content: Quote from: IanB on September 28, 2013, 04:45:01 amI agree, but the school I go to teaches nothing about things like this. Until I got my internship, I didn't know a transistor could be used as a switch (the focus at this school is IC design and microelectronics) and I was taught a transistor is for amplifying signals. There are many other examples, where the things are focused on how they work in ICs, which is great if you want to do IC design. I have taught myself how to use Cadence Allegro PCB Editor and don't really have anyone to go to for help. This is why I posted here, where I know most of you guys do PCB design for a living.

author: IanB
author_rank: Super Contributor
timestamp: September 28, 2013, 05:23:41 am
content: Quote from: aalbri on September 28, 2013, 05:01:00 amI'm not sure what kind of school you are attending, but you used the word "university" in your opening post. Whatever the case, you are in higher or tertiary education now and not in high school anymore. In such an environment it is incumbent upon you to learn as much as you can by your own means and not simply rely on what you are taught. I look poorly on interview candidates who simply recite what they have been taught in class and cannot tell me what they have learned on their own initiative.So you did a great thing by asking here and I commend you for it. It is a chance to get input from industry experts on how things really should be done.What I am saying to you is to take advantage of that advice and use it to make your end result as good as you can. Don't simply say "it only has to work", say rather, "I want to make this thing as professional looking as possible!". Be proud of your work and make it something that tells how good you are.

author: aalbri
author_rank: Contributor
timestamp: September 28, 2013, 05:41:07 am
content: Quote from: IanB on September 28, 2013, 05:23:41 amAh I see the point you're making now. I didn't mean that I don't care about this project and how it turns out, but this PCB is only a fraction of the total design. The PCB really isn't even necessary. I wanted to do it because I want to design them someday, not ICs. If you look at my fellow student's projects, they use a breadboard and some custom ICs for their design. Which is fine, that's what they want to do.I don't mean to argue but I have poured many, many hours (plus my intern experience) into learning about PCBs and the design software from scratch. On top of that, I have several other components to worry about in my design. All of which is due, functionally working, in 2 months lol.

author: aalbri
author_rank: Contributor
timestamp: September 28, 2013, 06:18:38 am
content: And don't get me wrong... I'm taking all of the questions in my first reply into consideration. I will figure out how to at least fix those issues, which are important to get the circuit working, before I start on any aesthetics.