[sdiy] SMT diodes: MELF vs. SOT-23 chip?

[Mattias Rickardsson]

> I hadn't realised there were 4148s in 1206, 0805, 0603 sizes - good to know.

Strangely their price are about double the price of singles in SOT-23
or mini-MELF. Would seem like the preferrable choice otherwise. But
the clean design / space-saving aspect is good.

The costs are not huge, but the diode choice could add up to some
dollar's difference in end price... and everything counts in large
amounts, so cost still makes it a relevant design parameter. That's
why it would be nice to know if there are performance aspects that
could be far more important. Sometimes the physical shapes or
production methods mean more than we might think. For instance,
reading what Douglas Self writes on the difference between thick film
and thin film SMT resistors doesn't make me calmer knowing that I've
used several millions of the thick-film variety. :-) Both noise,
linearity, temperature dependence and longevity depend heavily on the
production method and the physical shape and size of the resistor, and
some of the parameters vary in conflicting directions to each other.
I'd expect two very different-looking diodes to have some notable
performance differences too.

/mr



On 24 September 2015 at 12:46, Tom Bugs <admin at bugbrand.co.uk> wrote:
> Many interesting points coming up!
>
> Cost - personally I don't really consider these fractions, but I know why
> Mattias would (given who he is working for).
> I personally like to have 'standard' parts that I don't really have to think
> about - but this SOT23 discussion does make me wonder if replacing MELF
> silicon diodes with SOT23 duals may be useful -> you can always just ignore
> one of them and you're still getting maybe a small space saving.
> (still, not going to relay all my designs at this stage..)
>
> I hadn't realised there were 4148s in 1206, 0805, 0603 sizes - good to know.
> Nor had micro-melf really registered on my radar.
>
> Regarding shape - I actually find SOT23s somewhat annoying for hand
> soldering as they invariably seem to sit upside down and can be resistive to
> being flipped the right way up with tweezers!
>
> Tom
>
>
> On 24/09/2015 11:05, Roman Sowa wrote:
>>
>> Yes, visually, or rather in how clean the PCB design can be in terms of
>> density and ease of routing the traces.
>>
>> Roman
>>
>> W dniu 2015-09-24 o 11:34, Mattias Rickardsson pisze:
>>>
>>> On 24 September 2015 at 08:38, Roman <modular at go2.pl> wrote:
>>>>
>>>> micro-melf is much smaller than SOT23 and signal path is so much cleaner
>>>
>>>
>>> You mean visually? Not in signal quality? :-)
>>>
>>> /mr
>>>
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