[sdiy] SMD part availability, manufacture

John Luciani jluciani at gmail.com
Wed Nov 12 16:57:48 CET 2008

On Wed, Nov 12, 2008 at 10:12 AM, Seb Francis <seb at burnit.co.uk> wrote:
> So, continuing with my thoughts for a generic digital module PCB, I'm
> wondering now about availability of parts in SMD, specifically:
> Odd resistor values - the balanced analog I/O of the CODEC IC I'm planning
> to use calls for some quite obscure resistor values such as:  634R, 715R,
> 1K33, 2K32, 4K42.  Or am I simply reading the datasheet too literally and
> when using 1% resistors the nearest standard E24 values will be close
> enough? - in some cases maybe.

I would be surprised if standard 1% resistors could not be used in most
audio applications. If you really do need a few odd values you could parallel
two resistors.

> And what about power supply components like regulators and large
> electrolytics?  I've seen SMD regulators but I'm not sure how easy it would
> be to heatsink these.  And large electrolytics are surely all through-hole?

How large is large? You can get some large caps in SMD. Try a quick
Digikey search.

The typical way to heatsink an SMD regulator is with a large copper area
on the PCB. In the regulator datasheet there should be thermal resistance
graphs for different size copper pads.

> I'm assuming PCB headers will have to be thru-hole.

SMD headers are widely available (I use the Molex 68301 single row headers
on one of my boards).

> If at some point I go the route of selling pre-populated PCBs, I'm wondering
> what are the implications of using some thru-hole components for automatic
> manufacture?  Do these then have to be soldering by hand?

If you are selling boards to DIY types you could let the customer solder the TH
parts. The downside is that you won't be able to a final test on the completed

(* jcl *)


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