| Electronics > Projects, Designs, and Technical Stuff |
| SMD prototyping techniques -- looking for advice |
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| Siwastaja:
1) Bare copper clad PCB for a ground plane. 2) Deadbug ICs 3) Air wires using thin, colored leads. 4) Decoupling caps, pulldown resistors etc. directly soldered to the ground plane, like poles. 5) Series resistors etc. directly soldered to the deadbugged component legs If large non-GND planes are needed, make cuts to the ground plane copper clad using a Dremel like tool to isolate a section. Another option is to cut another piece and glue it on the top. I don't tend to use specialized SMD protoboards. |
| hagster:
--- Quote from: KE5FX on July 27, 2019, 11:32:13 am ---Meh, everybody makes this 10x more complicated than it really is. You don't need protoboards, just a bare piece of copper-clad board. Flip the chips over, glue them down if you like, and treat their pins, lands, or balls like solder terminals. You will need a good microscope and some very fine wire. It's good to have 30 AWG tinned copper and 40 AWG enameled copper handy. I like to use 0402 parts, but 0603 is OK for most purposes too. (Use the fine wire to provide some stress relief for the MLCCs, or they will break.) Some people like to use gold-plated boards and Dremel tools and multilevel copper islands and other methods to make this technique 10x as complicated as it needs to be, but the electrons don't give a hoot how it looks. --- End quote --- We call this ’Dead-bug' style. Personally, if it's anything mor than a small test for a circuit sub-system, I prefer just getting a cheap PCB designed. I have seen some amazing dead bug builds, but they generally aren't very reproducible once the first batch of changes are made. |
| Siwastaja:
< 50 total component legs: deadbug > 50 total component legs: design and order a PCB. > 50 total component legs, and you must have a proof of concept prototype finished tonight: deadbug, and good luck! Manual prototyping without a custom PCB is painfully slow, no matter what methods and tools you have. It's used when actual calendar time is more important than work hours. Otherwise, designing and ordering a PCB tends to be less painful. |
| ebastler:
Thanks all for the input so far! In summary, the recommendations seem to fall into three categories: * SMD chips on DIP adapters, everything else on 0.1" perfboard using through-hole components. Fine for non-critical (low speed) circuits. * Mount SMD ICs dead-bug style or with Kapton tape under the pins; solder wires (preferaly thin, enamelled) directly to the pins. Should allow for higher speed, due to shorter wires, SMD passives, and availability of a ground plane. * Do a proper PCB layout right away. Surprisingly, no votes for dedicated SMD protoboards, unless I overlooked something. That's great information -- exactly the kind of practical feedback I was hoping for. Approach (1) is what I have mostly used so far. Sometimes I have used (3), but only when I felt reasonably sure of my design, and was hoping to actually use it in my project. So approach (2) is what I will try! I have a preference for the "sunny side up + Kapton tape" style, I think, rather than using dead-bug mounting. And while I see the point of a ground plane, I like holes and solder pads for the occasional though-hole component and connector. Come to think of it -- I used to have some plated-through perfboards with square pads on one side, and very small pads and a ground plane on the back. Haven't seen those in a while, but they must still be available? |
| magic:
--- Quote from: ebastler on July 27, 2019, 11:42:50 am ---In the meantime, I also found a post by forum member electronic_eel from early last year. His perfboard for combined through-hole and SMD prototypes looks quite plausible to me. (Pads with holes on a 2.54mm pitch, with smaller SMD-only pads fitted inbetween.) Anybody using it? How do you like it, with a year's worth of hindsight? https://www.eevblog.com/forum/manufacture/improved-protoboardperfboard-for-direct-soic-mounting/ --- End quote --- That's neat. I sometimes mount SMD passives and SOT23 transistors on normal perfboards similar way, it makes the circuit smaller than using THT stuff. 0805 size is just right for mounting on 2.54mm pitch perfboard. 0603 works too. I prefer resistors in 0805 because markings are easily visible. I have good eyesight and can read that 0603 stuff, but 0805 really make it easier. Higher power too and less likely to get lost. OTOH, I have 100nF capacitors in every size down to 0201, for soldering directly to IC pins when power is next to ground. A quick and dirty option for simple one-off PCBs is to draw them by hand with a felt pen and etch. |
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