Difference between smd and through hole passive elements

[at89atbits]

Hi,
Is there any elemental difference between smd and through hole passive elements other than the mounting technology,
I opened the casing other day for a consumer appliance product and i noticed some of the capacitors were smd while some were through hole. However there was no particular logic to the ratings of the capacitors taken smd or through hole.
Nor was there any correlation of it to the area of the board used.

So does it depend on the circuit requirement which mounting technology to be used in any way?
Or what are the things to consider?

 

[zsolt1]

hi,
smd is a general trend now days because of many advantages , one of them is that production costs can be reduced since there is no need to drill holes trough pcb (1 operation in minus in technological flux), and of course devices get smaller . The circuit requirement is also important, in radio frequency ranges smaller devices, shorter connections/tracks are preferred. Still, trough hole devices can't disappear because they offer also qualities that smd don't have. They usually offer better thermal dissipation of the heat generated by the device and a better mechanical integration in the circuit (in the case of larger components)

 

[shaiko]

Generally speaking - there should be no electrical difference in the component and if there're then they're listed in the datasheets.

Some components simply don't make sence using in through hole packages - for example: very small capacitors are useless - because with the through hole leads they become inductors.

Also, SMD packages often conduct heat better to the PCB (because of more contact area with the board)

 

[zsolt1]

regarding the dissipated heat, it's a thing of the point of view. From the point of view of the smd component shaiko has right, it's like the smd component has a radiator (to conduct away the heat). From the point of wiew of the pcb, the pcb is burned by the component. So it depends on which do you prefer. For example, i hate to see pcb's burned by LM7805 smd type stabilizers.

 

[shaiko]

Another important (and almost obvious) aspect is mechanical strength.
When not dealing with high speed signals or VERY dense boards, I prefer through hole connectors they tend to be very hard to solder out for replacement - but for the same reason they offer a very secure mechanical link to the PCB.