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Questions relating to designing PCBs
By UberGoober
#156520
I'm a software guy, but have tinkered with electronics since I was a kid. Haven't done it in years though, until a couple months ago I came up with an idea for a little project. Its amazing what a small-time tinkerer can do now compared with just a few years ago. Anyway, I'm so tickled with how this is turning out I thought I'd share it. No reason really haha, but its: my first PCB ever, my first SMT, my first reflow soldering. So I wasn't sure if I could pull it off. I've also never used Eagle, so I had lots of learning to do. But I've used PIC microcontrollers in the past and I had my breadboard prototype up and running surprisingly quick considering I haven't touched a PIC in about 15 years. So I decided to get half serious and make a small batch of prototypes. I used BatchPCB - AMAZING! Well- after submitting my files 5 times until I finally passed the DRC it was amazing. The quality to cost ratio is ridiculously awesome, what a great service. They even threw in a bunch of extra boards - I guess just in case some were bad or something. This was helpful because i used some of them to put together a frame for the solder paste template. I got the templates made at pololu, but when I go for a larger batch I think I'll use a metal template. For the enclosure, I'm using laser-cut acrylic. Its amazing what you can do now. I could have invested a bunch of money into tools and could never come close to the precision or flexibility that I get from the laser cut acrylic. I was going to use pololu for the laser cutting as well but found a local shop that would do it for about the same price.

Well, I ordered parts for 6 units and waited for the boards to come. Everything was all ready to go. I wasn't sure if I could pull it off. Well I did- all 6 boards came out perfect. Not a single short, missing connection or any other significant production issue. I attached a photo of my boards and also the little jig I made for a stencil frame.

I made some silly noob mistakes, but nothing fatal:
- The worst was that I wired the 12v barrel connector backwards. Not a big deal these are prototypes so I'll just cut the wires on the wall warts and switch the polarity. But I double checked that a bunch of times. Doh.
- Maybe worse than that is that I didn't leave room for the screw heads around my screw holes. Well I thought I left room but when a 1"x1.75" board is blown up onto your computer screen, everything looks nice and big. Only 2 of my holes will be able to hold screws. 2 is enough for the prototype haha.
- When I started I had never heard of 0603 or 0805 or anything like that. I didn't know what they meant and what the decision criteria was. I guess I could have googled that. But to keep things easy I went with things that I could find in the Eagle library (and some useful libraries from sparkfun). So when the default package for capacitors was 0402, I figured that must be the one everyone uses. At least I was sure to order the parts that matched the footprint I selected in Eagle. You can imagine my surprise when I opened the box from DigiKey and discovered how tiny 0402 capacitors are haha. Actually it wasn't that hard to place them anyway. But just to avoid problems I'll probably stick to slightly larger parts in the future.
-I ordered a tub of solder paste well before the boards arrived. I also had a small syringe of solder paste I experimented with. Well when I got things ready I realized my solder paste was actually "solder paste flux". Doh. So all I had was this small syringe that had been sitting un-refrigerated for over a month. I wasn't sure if there was enough to spread on 6 boards but I was bound and determined to get this done before the weekend was over. I got the idea to mix some of the flux into the solder paste- increasing the volume about 20%. I don't know if this is advisable, but it didn't seem to hurt anything on this project.
-I explored lots of options for reflowing the boards at home. Based on the recommendations here on sparkfun I went with a skillet- well actually a $15 hot plate from amazon with a 6x6 aluminum plate on top of the burner. I went a little crazy here- I wanted to have a super awesome precision temp control that could match the reflow curves exactly. I invested a huge amount of effort into researching and acquiring a PID ramp/soak controller, software to program it, and thermocouples to use with my hot plate. Well this was a waste. The hot plate couldn't heat fast enough to match the profile - so I quickly plugged the hot plate directly into the wall and tried timing with a stopwatch like everyone else does. Even that turned out unnecessary- again it just wasn't heating fast enough for that to matter. I ended up just turning on the hot plate and watching for the solder pads to reflow, let it stay on the burner a few extra seconds, then removed it. It worked perfect every time. Actually this PID controller is very cool and it very well could be a part of a precise closed loop setup in the future. But not with a $15 hot plate.

Well these certainly aren't the most complex boards you'll see anywhere. But I'm pretty stoked that I was able to pull this off. Now that I know what capabilities are at my fingertips, I will definitely have to build out some other ideas. The sky is the limit. Well, that and 0402 capacitors.
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By macegr
#156654
Looks really good, for a first or even fifth try.

I think it's pretty hilarious that you labeled the LED as "LED" instead of what it means. :D
By mattylad
#156872
What on earth are those pics meant to be?

I see some superglue and what looks like a jigsaw?
Above that is just plain brown.
By UberGoober
#156912
mattylad wrote:What on earth are those pics meant to be?

I see some superglue and what looks like a jigsaw?
Above that is just plain brown.
It seems that the forum didn't scale the pictures I uploaded, so what you are seeing is only a small piece of the pic. If you right click and "view image" you'll see. I just have pics of the finished boards and a jig I made for applying solder paste.
By UberGoober
#156913
Oops! I actually did find a problem on one board. So much for my 100% success rate. One of the 0402 capacitors is missing from one of the boards. Looks like it never got placed. Lord knows what happened to it I probably inhaled it. If it was just a decoupling capacitor I wouldn't worry about it but in the case of that cap its suppressing noise on a signal amplifier- it will really be too unstable without the cap. So looks like I had a 1/6 failure rate. I had all the parts meticulously laid out for pick/place so something happened to the cap after placement I"m sure.
By mattylad
#157087
That will be George the purple octopus that lives under the desk.

He pinches your teaspoons too :)

Pics look a lot better.

RE the DC jack - does it have alignment pins underneath? (one of them looks skewed.)

I take it the mounting holes are for use with plastic snap in standoffs (otherwise there is no room for a screw head)
By Joe5
#160611
I've been making my own proto boards for decades. I tell ya, I think I've lost more SM components then I've used esp. the little two terminal type. Ideally a vacuum pump and sucker probe would work. Don't bother with those little hand jobs. Solder wick will only get u so far so you could use the vacuum also for sucking solder off. Aside from that I love using SM components.