Hardest PCB layout  - Page 1
Forum section: electronics / projects

author: filssavi
author_rank: Frequent Contributor
timestamp: August 19, 2015, 04:58:58 pm
content: HiI'm a MS student in EE and I quite like doing PCB Layout, and I've designed few Control Unit Board (High-endish MCU I/O protection and power supply section)and i properly enjoyed it...Out of shear curiosity I wanted to ask to all the people on the forum what they think is the most complex (and by that i don't mean time consuming) type of board to design-High end digital (think DDR3/4, PCIe, big FPGA's kind of thing)-Power electronics (High power SMPS stuff)-high precision analog circuits (picoammeter, very high/very low resistance meters spring to mind)-whatever other kind of category you think is fitEDIT: apart from microwave/RFPlease, this is genuine curiosity not an attempt to start a flame war, so i beg you not to engage in d**k stroking contests about who designs the most complexest things out thereP.S. In my opinion digital works like PC motherboards or other stuff, even if they have a lot of high speed signals, are just time consuming to design, in the sense that if the impedances are matched and the lengths sufficiently mathched the thing will work, so in a sense it's very repetitive stuff, power or analog on the other end is much more circuit dependent, and require more "thinking" since following rules set in stone can't work and so more "difficult", Am I right? there is something I'm missing?

author: mikerj
author_rank: Super Contributor
timestamp: August 19, 2015, 05:14:08 pm
content: Microwave frequency systems (either analog of digital) have to be one of the most difficult from the design perspective.

author: filssavi
author_rank: Frequent Contributor
timestamp: August 19, 2015, 05:19:55 pm
content: Ok aI think that microwave/RF vodoo black magic is the clear winner in term of difficulty so i havent even listed it

author: coppice
author_rank: Super Contributor
timestamp: August 19, 2015, 05:52:21 pm
content: As a practical point, RF layout is often the easiest of all. Its so tough for most people that devices often come with an exact layouts you just copy, and use with the correct board material.

author: free_electron
author_rank: Super Contributor
timestamp: August 19, 2015, 06:19:32 pm
content: high power electronics.due to all the creepage , clearance rules and the high currents.try ramming 120 ampere through a 6 layer board... then try ramming 2000 ampere through a 6 layer board ... ( using 16 mils thick copper .. ) while it needs to hold 800 volts...high speed digital is relatively easy. set up the design rules and send it through the router.HDI and rigid/flex boards are difficult too due to manufacturing limitations. that is difficult to cast into rules for the software.

author: tomlut
author_rank: Regular Contributor
timestamp: August 20, 2015, 07:11:26 am
content: I wouldn't have found power layouts requiring 40kA (20usec pulses) too taxing except for the constant requirement to "make it smaller".8 layer digital PCBs with fine pitch BGAs drove me loopy though.

author: KJDS
author_rank: Super Contributor
timestamp: August 20, 2015, 07:38:10 am
content: I worked on an early 3g mobile phone, before most of the functionality was integrated into a couple of chips. Technically it was fairly straightforwards, except that there was so little room for so many components.

author: lgbeno
author_rank: Frequent Contributor
timestamp: August 20, 2015, 08:09:05 am
content: I think each type of layout has its own unique challenges that make it difficult, there is no one answer. But that high power stuff sounds pretty tough.Honestly for RF layouts, its easy, keep the path as straight as possible, use controlled impedance, add gnd vias everywhere. RF circuits always flow nicely. Any complex fans or other things are usually auto generated by a tool like ADS.Digital routing on few layers can be a real puzzle to solve, especially when considering all of the length matching of wide busses.Sent from my iPhone using Tapatalk

author: MyElectronsFellOut
author_rank: Regular Contributor
timestamp: August 20, 2015, 08:40:15 am
content: Only designed a few boards, mostly digital stuff so nothing overly complex. The only challenging aspect on one was the size of the pcb being wuite small and trying to squeeze traces through bottlenecks.

author: mikerj
author_rank: Super Contributor
timestamp: August 20, 2015, 09:57:54 am
content: Quote from: lgbeno on August 20, 2015, 08:09:05 amYeah, piece of cake. No more difficult than DC right?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 20, 2015, 10:50:37 am
content: Quote from: mikerj on August 20, 2015, 09:57:54 amNot much more, considering the dimensions of the transmission lines, wedges and such will be coming from an EM simulator -- you don't have much freedom on placement, just some gradual bends, or which side the structures get placed alongside. You can only do actual routing on the low level parts (baseband or at least downconverted, and system-impedance transmission lines of uncontrolled length).Driving the EM simulator, and going back and forth between PCB edit and simulation results, might be quite a challenge. Expensive software generally doesn't scale well with user experience...Tim

author: lgbeno
author_rank: Frequent Contributor
timestamp: August 20, 2015, 11:53:43 am
content: Quote from: mikerj on August 20, 2015, 09:57:54 amWell I didn't say that RF layout was a walk in the park, as mentioned its is a lot of back and forth between the EM tool and the physical design BUT you can certainly trace the signal part and see it flow from one part to the next.Not sure what to say, its difficult but so is what Free Electron is talking about. There is no one answer.Sent from my iPhone using Tapatalk

author: lgbeno
author_rank: Frequent Contributor
timestamp: August 20, 2015, 12:21:40 pm
content: So reading my first post, I go as far as using the word "easy". I'll take that back, it is difficult.Not any more or less difficult than the other stuff though.Sent from my iPhone using Tapatalk

author: ajb
author_rank: Super Contributor
timestamp: August 20, 2015, 03:39:35 pm
content: Sometimes the difficulty is externally enforced. A device that would be a piece of cake to put in a 19" rack could become a nightmare when you need to build into a portable instrument. Or maybe the connectors need to be in places that make the layout a PITA.

author: tree
author_rank: Regular Contributor
timestamp: August 20, 2015, 08:11:12 pm
content: I think all of those are equally 'difficult'. Commercial RF boards such as those in a spectrum analyzers don't have size and weight constraints, unless they're portable. Try designing any one of those type of boards where every mm has to be used, then it becomes difficult, especially at high voltages. Cramming stuff into a small area while working with kV can definitely be tricky. free_electron probably knows the difficulty here considering he has to lay out boards which are sensitive to size and weight and have to support high power.

author: MagicSmoker
author_rank: Super Contributor
timestamp: August 20, 2015, 10:50:07 pm
content: I agree with tree *and* free_electron - any circuit that has to be crammed into the tiniest possible space (and, as is typically the case, cost the least amount of money to manufacture) is often the most difficult to design, but laying out high power switchmode converters (which a 3ph inverter for an EV can be classified as) requires a lot of black magic and other dark arts.That said, I would fail miserably if asked to lay out, say, a modern PC graphics card. Well, I might get it right by the 5th or 6th iteration. Assuming I wasn't standing in line for unemployment benefits before then.