0805 or 1206?

[Andrew Cowan]

Hi all.

I'm working my way into the world of SMD, and I'm going to buy 5000 resistors to play with. Just wondering - should I get 0805 or 1206? I don't know which is more widely used - what do you lot use on your PCBs? And what about capacitors - what sizes should I go for there?

Thanks,

Andrew

 

[ylp88]

I usually use 0805 - I've only ever purchased 1206 once before and that was because the 0805 version was out of stock. Of course, you should consider that the 1206 versions may have a higher rated power dissipation (due to its larger size), but I've not yet hit that need (and you can always substitute for a TH part if you get stuck!). 0805 is also still quite easy to handle with tweezers, however I find that 0603s are considerably more difficult as their the distance between their "pads" are much thinner (duh!) thus requiring more precise locating on the PCB and they have a tendancy to still slip under the self-closing tweezers I use to clamp the part to the PCB before soldering.

As for capacitors, my range isn't usually that large and my choice is usually dictated by availability, design requirement and price, although I try and avoid 0603 for the reasons mentioned above.

ylp88

 

[stocky]

0805 for me
Still big enough to run tracks between the pads on single sided boards

 

[womai]

0805 is fairly easy to use (and I'm not an expert in soldering!). 1208 is quite large and thus negates one of the advantages of SMT - smaller footprint compared to through-hole components. 0603 is doable, 0402 is my personal limit (my 0402 solder joints look horrible under a microscope, soldering them is more a game of "heat it up and hope I got the right spot so it makes contact" ).

Some general hints: get yourself a second soldering iron - it's difficult to remove/rework SMT components with just one iron (you need 2 to heat both sides simultaneously to remove the component).

To solder, put a bit of solder on one pad, then heat it up again and place the component. Let it solidify and then do the other side. After that, heat up the first side again to reflow the solder to reduce permanent stress on the component.

There are also special SMT tweezer irons available, haven't worked with them yet.

Also, get some copper solder wick to remove solder from the landing pads during rework. Also handy to remove solder bridges when soldering multi-pin SMT components (e.g. SOIC or QFP packaged chips).

Wolfgang

 

[ylp88]

There are also special SMT tweezer irons available, haven't worked with them yet.

I think I've seen these around but I always felt that I don't deal with enough SMD stuff to justify the price of getting one (plus I'm not sure how they help when soldering things like QFN, and finer pitch, packages...). Has anyone used these before and found any significant ease or advantage in using them over a decent solering iron?

ylp88

 

[Dippy]

No, never used those special tips. I just use a 0.5mm tip iron. I usually use solder paste and then stick the component and then apply the heat to the pad/blob. Conduction and capillary action will do the rest.
And life is so much easier with a solder resist layer, especially if you have little inter-pad tracks.

I've used both sizes mentioned, ultimately down to board size requirements, power requirements and if my glasses are working.

If board size is not a major issue I'd suggest the larger 1206 just from the handling point of view. Going smaller won't impress the neighbours.