Leveling up my circuit/PCB design skills - Page 1
Forum section: electronics / beginners

author: mjt
author_rank: Unknown
timestamp: July 04, 2013, 12:39:34 am
content: I've done some PCB design but I've hit a bit of a plateau - I've only ever done hand-assembled boards, nothing more intricate than a 0.5mm pin pitch QFP, and nothing higher performance than a 20MHz atmel or pic microcontroller.I'd like to take my skills to the next level. I figure that means an application processor with external ram and flash, which probably means BGAs and reflow assembly, which sounds expensive. Too expensive for me to do more than one or two rounds of trial and error!My question for those of you who have successfully made more advanced boards is: How should I learn to do the same?

author: marshallh
author_rank: Unknown
timestamp: July 04, 2013, 12:43:11 am
content: 1. Research2. Do it3. Address failures and iterate

author: mjt
author_rank: Unknown
timestamp: July 04, 2013, 01:12:39 am
content: Thanks for your reply. Research is what I'm doing right now by talking to youAs far as I can tell each iteration is going to require assembly with a pick-and-place machine, and the quotes I've got (from suppliers in my country) put the cost at around US$ 2000 for tooling+pcb+assembly, so addressing failures and iterating could rapidly become expensive. So if there are books or courses that would save me an iteration, I'd like to hear about them!If my cost estimate is way off, or if you have suggestions for cheap surface mount assembly companies, those would be welcome too

author: marshallh
author_rank: Unknown
timestamp: July 04, 2013, 01:27:31 am
content: 1. 4layer pcb from oshpark.com, get three for $10/sqin2. Paste stencil from ohararp.com3. Buy Chipquik (actually amtech) leadfree solder paste4. Build reflow oven (you do need temp monitoring and control, not just any toaster oven)5. Apply paste with vanilla straight razor6. Place parts with a steady hand and curved SMD tweezers or ebay pick/place vacuum pen7. ReflowFor protos placing the parts by hand is fine. For production $2k is reasonable for setup costs. You will need to buy hundred+ at a time to make that approach worth it.I suppose you could mess about with the various pick and place tables out there, but I wouldn't bother. You will need to build protos anyway.There is not really anything you couldn't do with hand placement and reflow. I hand assembled the board below. Process was just what I wrote up above.For 0402s and the bgas even though I could place them with just curved tweezers it would've been super nice to use a vacuum pen. You only get 1 shot to do it right or you have to clean off the paste and redo everything again.However you can get great results. Read up on BGA process appnotes and the like. There is so much info out there, you just have to spend 5mins looking. If you want a rigid step by step checklist you may be better off with a book approach.

author: AlfBaz
author_rank: Super Contributor
timestamp: July 04, 2013, 02:06:01 am
content: Here's a couple of little useless tipsThe importance of Design For Manufacturability (DFM) can never be overstated. I'm sure there are plenty articles on it out there.Print 1:1 scale images of the board often. When working on the PC it's easy to forget the actual scale you are working on. What may look like a huge slab of solder mask on the screen may be tiny and easily bridgeable during reflow.Try and minimise the number of components as much as possible. I recently built a prototype for a multi-rail power supply where nearly every resistor and cap was different. Nothing worse than having to spend all of your time looking for, opening packaging and placing just one tiny componentIf it's a complex design with multiple sections, and you are doubtful about certain aspects, it can be cheaper in the long run to prototype sub-sections. This way you may spend $50 on components and small pcb to find a design flaw that can't be fixed without a re-spin. It may be far more expensive if you find such a glitch on the full prototype

author: AlfBaz
author_rank: Super Contributor
timestamp: July 04, 2013, 02:09:53 am
content: P.S.Nice board marshall

author: cthree
author_rank: Frequent Contributor
timestamp: July 04, 2013, 02:21:54 am
content: Quote from: marshallh on July 04, 2013, 12:43:11 amI have to agree 100% with this advice. If it's not hard, you aren't learning anything new.Have you done anything with low power RF like WIFI, Bluetooth or ZigBee? Why not pick up an eval kit for a mesh network SoC like Atmel's ATMega128RFA1. The software stack is free and you could have a blast laying out a PCB antenna (check out Ti's app notes on trace antenna layouts), doing controlled impedance and learn a super useful skill. The app notes are excellent and the parts fairly affordable (<$10). You can use GCC to build the mesh network stack so no IAR or anything. The chip you already know so you aren't going to bite off anything crazy hard. There is so many examples you can just copy a reference design if you get stuck.Im sure you could think of some fun projects such as building battery powered, wirelessly networked cockroaches working together to take over the world, assuming commanding a robot army is your thing that is.

author: cthree
author_rank: Frequent Contributor
timestamp: July 04, 2013, 02:29:16 am
content: Try bittele.com for pick and place assembly. I got my first order SMT part assembly for free (3 prototype boards) and after that they wanted something like $20-$30 each PCB, no setup. For 5 boards they wanted $19.36 each for SMT component assembly of a dozen or so BOM lines. The will also source the parts and just the number you need, no buying a whole reel.Try them out.

author: AlfBaz
author_rank: Super Contributor
timestamp: July 04, 2013, 02:52:24 am
content: Quote from: cthree on July 04, 2013, 02:29:16 amWow! Very impressive, thanks