Going off the SMDeep End

[uranium_jones]

Guys, I was converting a schematic to a pcb layout yesterday, and I was thinking about how neat/easy it would be to just have everything be SMD. I did have to solder up some mic signal conditioning boards for my grad school research, and while it was tricky at first, I do remember eventually getting the hang of it.

Any tips for doing SMD-based design? I guess the questions on my mind include:
-What size components are a good choice? I'm guessing 0805. I should be able to find a decent amount of Rs and Cs in that size, I would think.
- Where is the best place to get components? Tayda seems to be the go-to for through-hole, but their SMD selection seems to be lacking. Would prefer someplace with good shipping prices, especially.
- I'm going to see if I can find a smaller chisel tip for my soldering iron, but anything else I absolutely have to have? I've got powerful magnifiers but no microscope or anything. I've got both a flux pen and a tub of flux goop. Tweezers too. My solder is currently 0.8mm/0.031" 60/40.

Any other general advice would be good. I'm not planning on going the paste route, because there are enough videos out there showing that you can use a good old fashioned iron. It's not like I'm going to be making boards with a thousand components.

 

[Bricksnbeatles]

This is the advice I got from Jon Cusack when I asked about this a few years ago:

0603 for resistors, and 0805 for most caps. 0603 for 0.1 and 1uF caps. I try to use .012” traces on a .025” grid when possible. Shrink to .0125” grid as needed.
I do not recommend routing traces under 0805, 1206, or ANY SMT parts really, or between legs of ICs. I know it can be done, and it works, but in over 20 years of PCB layout, I’ve always found a better path. You are asking for trouble routing traces under parts that aren’t connected to them. Not only from a assembly perspective, but also from a noise/crosstalk perspective. Again just my opinion.

 

[uranium_jones]

This is the advice I got from Jon Cusack when I asked about this a few years ago:

That's interesting. Why go with different sizes of resistors and caps, I wonder?

 

[Feral Feline]

I know very little about SMD, but ...
maybe going for different sizes of resistors to caps either
A) helps differentiate them making them both easier to work with, or
B) makes them more homologous in size, making working with them more consistent.

 

[Bricksnbeatles]

I know very little about SMD, but ...
maybe going for different sizes of resistors to caps either
A) helps differentiate them making them both easier to work with, or
B) makes them more homologous in size, making working with them more consistent.

Yeah, looking back at this, I’m actually a bit confused. 1μF is much larger than the pF-nF range that a rough majority of the caps in a pedal would fall under, so you would assume they’d have a larger footprint, rather than a smaller footprint compared to the smaller cap values. Perhaps he meant 1206 for the 0.1-1μF caps, rather than 0603?

I guess this could be answered by taking a look at a Cusack or Mojo Hand pedal that uses SMD components, but I unfortunately don’t have any to confirm or deny this.

 

[vigilante398]

I use 0805 for EVERYTHING when I do designs. Partially because it looks nice to have all the passives uniform, but also because 0805 can get you just about anything you need for pedals up to about 10uF in a usable voltage. If you veer into tube territory (which I often do) you can also get 22nF, 47nF, and 100nF 250V capacitors in 0805. It's the perfect size, and basically the smallest thing I'll solder by hand, everything else I'll either use a reflow oven or get pick-and-placed at the factory.

Tayda is a great place to get passives (they have just about every 0805 part you'll need) and basic op-amps, they tend to be useless for most other stuff (though they sometimes have PT2399 I think). I alternate Mouser and Digikey, I usually keep both open and see who gets me the best price for what I need.

DON'T GET A SMALL IRON TIP. It's counter-intuitive, I know, but you want a medium chisel tip. You need to be able to heat up the joint FAST to flow the solder so you don't have to park your iron there for a long time. Heat doesn't fry components, prolonged heat fries components. Unless you're soldering teeny tiny components there's no reason to get a teeny tiny iron tip.

Magnification helps, I spoiled myself with a soldering microscope for about $150, makes the job way easier and is also really handy for inspection/debugging. If you're getting flux you will also want some form of flux remover, what you get will depend on what kind of flux you have (no clean, water soluble, alcohol soluble, or plain sticky mess).

Everyone starts by saying they won't go the paste route, but I got a $200 reflow oven for my birthday a few years ago and started ordering paste stencils, and I can do boards SOOOOOO much faster. So if you're only doing one at a time and only a couple dozen components it doesn't matter, but if you're doing larger builds and/or building a bunch for customers I would absolutely recommend ordering stencils with your PCBs (only an extra $10-20) and getting a cheap reflow oven.

I think that's about it for now, if I think of any more advice I'll come back

 

[Bricksnbeatles]

My early SMD work I did 1206 for everything because I was just starting out, but I’ve done a good amount of smaller sized SMD boards from Oshpark etc. and at times where doing it by hand was too time consuming, I used solder paste and did reflow work in a toaster over that I just use for curing paint and stabilizing resin in my garage. A true reflow oven is probably ideal, but you can just as easily do SMD in a cheap $30 toaster oven— just don’t use it for food after

 

[uranium_jones]

My early SMD work I did 1206 for everything because I was just starting out, but I’ve done a good amount of smaller sized SMD boards from Oshpark etc. and at times where doing it by hand was too time consuming, I used solder paste and did reflow work in a toaster over that I just use for curing paint and stabilizing resin in my garage. A true reflow oven is probably ideal, but you can just as easily do SMD in a cheap $30 toaster oven— just don’t use it for food after

I saw a bunch of videos online where people are making fancy temperature controllers to follow a reflow profile. Are you saying that's BS and I just need to time or watch it?

 

[Bricksnbeatles]

I saw a bunch of videos online where people are making fancy temperature controllers to follow a reflow profile. Are you saying that's BS and I just need to time or watch it?

Just gotta know the right target temperature (get some cheap practice smd boards to experiment on if you’d like) and keep an eye on it while it’s in.

You probably need more precision when you’re dealing with the sophisticated chipsets and processors in complex computer stuff, where the things like trace lengths and all that stuff are calibrated for performance etc.
This is super basic stuff compared to that. Most pedals will still function fine with pretty massive tolerances for most parts, and a good majority of effects never had very much consideration put into optimizing their layouts— most of these things could be built with 20% tolerance parts in a dead bug style or on perfboard, and you’d still wind up with a working pedal.
Having a well laid out PCB and tight-spec components already puts you ahead of the curve, and the effects of using a toaster vs a reflow over will be negligible if measurable at all.

 

[vigilante398]

I saw a bunch of videos online where people are making fancy temperature controllers to follow a reflow profile. Are you saying that's BS and I just need to time or watch it?

Yeah more or less. Depending on what kind of solder you're using, what kind of components (pretty much nothing in pedals is sensitive to care), etc it doesn't really matter. Reflow profiles are designed to heat the solder enough to flow without overly stressing the components themselves, which is why they have a long ramp up, a long soak at medium hot, then a quick spike to hot before dropping back down to cool it down.

One thing I have heard from people using unmodified toaster ovens is that if you're not careful you're more likely to burn a board, but if you're watching the temperature you should be fine. Toaster ovens use a resistive heating element so the entire chamber heats up (ideal for cooking, obviously) whereas a reflow oven typically uses infrared, so it will heat differently.

 

[uranium_jones]

Having a well laid out PCB and tight-spec components already puts you ahead of the curve

Hold on there, Babalooey, who said anything about well-laid-out? I get things in a pretty grid and hit "auto route."

Also, what's "dead bug style?"

 

[Bricksnbeatles]

Hold on there, Babalooey, who said anything about well-laid-out? I get things in a pretty grid and hit "auto route."

Also, what's "dead bug style?"

Dead bug style is when components are just soldered directly to each other freestanding, with no board or terminal connections of any sort

 

[Feral Feline]

Easy to see how it got its name.


Adding a bit to "Dead Bug Style"...



If you throw down some epoxy and stick the components' bodies to the epoxy, it keeps them in place while soldering.

Upside: it's an easy-peasy way to quickly test a simple circuit.

Downside: if a component goes bad/fries/whatever, you can't easily replace it (short of gluing its replacement next to the dead one, if there's room).

Double-sided sticky tape would be better than epoxy, but when I first heard of dead bugging the guy was using epoxy...




Quick & fugly ...

Less ugly...

Dead bug executed as art form...

Is the last one really "Dead Bug" though? To me it's more fancy P2P.

I've also seen Manhattan style mixed with Dead Bug...