| Electronics > Projects, Designs, and Technical Stuff |
| SMD prototyping techniques -- looking for advice |
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| ebastler:
So far, I have still been building my prototypes mainly with through-hole components. (Mostly digital/µC, some audio-range analog, some analog up to a few MHz). I mainly use 2.54mm pitch protoboard with square pads, and solder on Kynar-wire connections. Where SMD ICs were required, I have either used little adapters to DIP footprint, or soldered SOICs directly onto the protoboard with every other pin bent up and wired free-floating. That kind of works, but with more and more ICs becoming avaiable in SMD-only style, it has become more and more awkward. It feels like it's time to move to SMD as the "default" prototyping technique. I could use some advice here: (a) What protoboards do people use? Is there an equivalent of the generic 2.54mm square grid -- something like pads without holes but in 1.27mm pitch? Does that even make sense, assuming I can largely stick with SOICs? What do you do if you need higher-density packages? I am aware of the various SMD protoboards which carry an assortment of specific TSSOP etc. footprints. But these seem rather limiting, almost to the point where you need to know your designs's chip complement before you order the protoboard. If these are the way to go, how do you work with them? Or is it back to individual DIP adapters? if you need to mix and match various SMD packages in a circuit? (b) What is your personal "sweet spot" size for passive? 0603, 0805? I would want to order E12 or E24 sets of resistors and capacitors, but only in a single mechanical size. (c) I think I have the soldering under control, either pad by pad or using extra flux and dragging the tip. Haven't experimented with solder paste and oven/pan soldering yet, but that would be used for small series rather than early prototyping, right? (d) Any other advice for SMD prototyping? Many thanks in advance for your help! |
| tautech:
Watch Dave’s last mailbag for SMD proto boards. I started with 0805 but proved concept on a breadboard therefore needing to use IC’s that are available in DIP and SMD. Once you dive properly into SMD you’ll love it. Oh, and get some SMD smart tweezers before too long. Oh and something else, get some K style Hakko tips or similar, they're great for rework in that they reach both ends of passives so you can grab them with tweezers or sweep them off the pads. |
| NivagSwerdna:
I have experimented with SMD breakouts etc but it quickly becomes a major PIA so now I just go straight to PCB... sometimes creating a generic layout that can be part populated and also accept that v1.00 will be unlikely to be the final revision. With DipTrace (or equivalent) and a super cheap 5 or 10-off PCB prototyping service Elecrow (or equivalent) (and a microscrope) it's a joy. Have fun! |
| KE5FX:
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. |
| ebastler:
Thank you all for the resonses so far! Thanks for the mailbag hint, I had missed that one. 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/ --- 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. --- End quote --- Hmm, I have used that approach for single SMD chips on 2.54mm perfboard, but had not considered it as a general solution for SMD prototyping. How do you mount the passives? Always solder one end directly to a chip pin, have the other end floating? |
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