Reasons to use surface mount components

Hey guys,
I just found this little article and thought I'd post it for discussion:

http://www.dact.com/html/leaded_resistors.html

Just to be clear, we are NOT talking about "leaded resistors" as in the Pb content of resistors or other RoHS nonsense.

I declare the hunting season open!
(Have fun and try not to hurt anyone :grin: )

things like that are so small it's of no real concern. There is another thread on resistor noise that highlights some of the more important aspects of leaded vs. SMT resistors.

In a world with the layouts being equivalent, the "bad" leads are still there. They are the extra lengths of copper trace needed to reach the smaller SM components. In the real world, capacitive issues become even greater with SMT due to the finer line spacings associtaed with jamming all the smaller passives right on top of each other.

Bad article.

Wouldn't the leads be shorter in an SMT layout because the whole thing can be much, much smaller overall? And can't you balance the line spacing with capacitive effect to minimize capacitance...still smaller than leaded-component layouts but not so small and dense to impact performance?

I think the high speeds of PC's and such pose a bigger risk of showing ill effects from lead capacitance and noise, and they obviously use SMT with great success.

I don't know much about the article's validity, and I'm not claiming to prove or disprove anything, but I'm pretty sure one can make a circuit with shorter leads using SMT for a stepped attenuator, anyways.

Chris

I think the high speeds of PC's

Click to expand...

two completely different things.

one is designed to move logic on/off the other a myriad of signal changes. Easy to condition a logic signal for long runs, a bit harder for the analog signal.