First production run - design PCB for through-hole or surface-mount?

Question

I am nearing the stage after testing everything on a breadboard where I'm ready to fire up Eagle CAD and start developing my circuit board. This will be my first ever circuit board design. My question now is: Should I design for through-hole or just go straight to surface-mount?

I have a pretty good soldering station (Weller WSM-1), so I think if I use reasonably large SMD components I should be able to hand-solder things with no problem. On the other hand, with through-hole components it would be impossible to not be able to solder them. The board is very basic, with just one ATtiny85, three resistors, a bunch of LEDs, two ceramic capacitors and a 32.768 kHz crystal. The crystal is another point I'm unsure of: Every electronic device I've opened up has these as hand-soldered through-hole, even if the rest of the board is all surface-mount. Why is that? Are 32.768 kHz crystals not available in surface-mount packages?

I would really appreciate any input on helping select the best way to go on the board design (through-hole vs surface-mount). I'm thinking that in the unlikely even that my board becomes popular, having it as an SMD board would facilitate production at a plant that can do automated assembly. On the other hand, I have no idea if through-hole manufacturing would be a cheaper option for certain quantities.

Answer 1

There's no reason to go with through hole. There, I said it.

With a decent microscope, a pair of soldering irons (to lift double sided components), hot air, solder paste and some flux you can easily solder components and modify things. I do 0201 on a daily basis with this setup. 0402, 0603 are no big deal. Also TSSOP, QFNs can be soldered (QFN with flux and hot air is pretty easy).

Through hole forces a completely different architecture for the board layout and the results of using a through hole design could differ, especially as it concerns EMI (think FCC certification). You want your board to resemble as close as possible the final product. Through hole requires space on both sides of the board for the holes and so wastes precious PCB area. Smaller PCB usually means lower emissions too (as well as lower costs etc).

BTW, this doesn't mean the whole design has to be surface mount. 32kHz crystals do come in SMD. There are plenty of them at digikey.

I realize this is an opinion but the reality is SMD isn't the terrible thing that its been made out to be, even for hobbyists.

Answer 2

If you believe you are likely to make tens rather than thousands, use whichever you are happier assembling, testing and soldering. There is no point tooling up and spending more on new equipment and taking time to perfect new soldering techniques if you could hand solder the entire production run in an hour or two.

That leaves time to spend on the actual product - or the beach, if you have better weather than we do here!

(You will notice that I haven't specified either technology : I agree that SMD is not so difficult; use it if you're already familiar and tooled for it. I just don't think that a first board and a first batch is the time to add another first)

If the market takes off, there are likely to be lessons learned and changes made before mass production, whichever technology you use for the prototypes. That is the time to decide which technology is best for building thousands.

An automated assembly process is likely to have PCB requirements (SMD land sizes for reliable soldering, component orientation for placement, ATE test point location) that aren't usually worth considering for a small batch hand assemble/test process, so you can virtually count on a new layout at that stage, whatever you do now.

Answer 3

If you've got the room (not constrained by a particular case size), I like to use through-hole components to start with, particularly for IC's in DIP packages (like the ATtiny85). This lets you use a socket, and if changes need to be made, you can often just lift the pins of the IC and solder wires to them instead of cutting traces. Same goes for passive components -- you can just lift one side of a resistor or capacitor.

And of course it's easier to hand-assemble through-hole boards than those using SMDs. Again, if you are not constrained by space requirements, you can always go into initial production with a through-hole board. SMT is really only necessary once you get into high-volume production where you want to use a contract manufacturer with automated equipment.

Answer 4

there are 32.768 kHz crystals for through hole mount and for surface mount too. But the through hole mount version might be easier to get and cheaper for small orders.