SMD board layout - tips wanted

[ElectricDruid]

Hi all,

I'd like some tips for laying out surface mount PCBs.

I've been looking at it and my usual tricks aren't going to work. For example, on a through-hole device, you can connect a track on either side of the board, so I often run horizontal tracks on one side and vertical tracks on the other. But I can't easily do that on a surface mount chip.

Also ground plane - how do I do that without making it impossible to route anything at all?

Do people just finish up using tons of vias to get to the other side of the board? In general, on a through-hole PCB, I regard needing to use a via as an admission of failure, although sometimes it makes sense to have one or two rather than do something torturous to some poor track. However, it seems like SMD is going to need loads of them. Is that right?

Any pointers you can give would be much appreciated!

Thanks,
Tom

[vigilante397]

I feel like everyone kind of has their own "style" of layout, none of which are inherently right or wrong, just a preference. Personally I put all my components on the top layer for ease of soldering (I use stencils and an oven). I route as much as I can on the top layer first, ignoring the bottom, starting with whatever is easiest to route. Naturally this is just like through-hole layouts in that smart placement makes for easy routing, so be thinking about routing as you're placing components.

I usually route everything besides the ground first, then I fill leftover space on top and bottom with ground pour and let it connect however it will, be it direct connecting or using a via to drop to the bottom layer.

Tons of vias. TONS of vias. My last board was fairly conservative and only had 36 vias, but I've done more complicated boards with as many as 100 or so vias. It's not as pretty, and maybe vias add negative mojo, but there's nothing wrong with it and it is not considered bad practice. As long as you're getting professionally fabbed boards may as well throw the vias on there, they don't charge per hole.

Also one trick I've started doing the past couple years is putting vias on top of pads. It saves a little bit of space, and since it makes the via less conspicuous I like to think it saves a little mojo as well

[ElectricDruid]

Thanks Nathan. I like the trick with the via-on-a-pad. That's handy.

Also very useful to hear what order you approach things on one of these layouts. Some stuff is the same as TH, but some isn't.

Totally agree about everyone having their own style. But my current style is very much a through-hole thing, and I need to learn some practical techniques to actually get an SMD laid out properly.

[alanp]

Vias not being preferred dates back to when PCB fabrication was not quite there, and vias were not always plated reliably, IIRC.

I'm finding that SMD layout is much more reliant on dead cunning component placement than thru-hole is.

[jubal81]

If you're not using solder paste and an oven, I recommend aligning all the parts you possibly can either north-south or east-west. It's a huge pain to have to keep turning the PCB to different angles for hand soldering.

I also made a 'beak' to hold down the parts. It's a dental pick, a shaft from a pen and those screw-tight metal collars I can't remember the name of. Works really well and saves a lot of time spent tack soldering parts to hold them in place.



Also agree with Vigilante. Don't fear the via. They're free. And you can stick them right in the SMD pads.