SMD may have some advantages for non-critical applications but it has some severe disadvantages in high power circuitry:
- The power handling capability for pulse loads for most types of SMD resistors is abysmal
- The ability of SMD resistors to withstand high peak voltages is poor
- The ability to withstand thermal cycling stress with pulsed loads is poor, especially when using lead-free solder
- If the application requires power dissipations more than several watts the heating of the PCB material and surrounding components becomes excessive with SMD parts
If any of the above situations applies the best option is often to stick with leaded parts.
Limiting factor is PCB heat handling properties, not SMT resisors as such. 35W SMT resistor for example: RHFH4Q050R0FE. If you need smaller heater on your PCB, then consider Vishay RCP series or similar.
Of course the limiting factor is the ability for the PCB to handle the heat but by just blindly insisting on using SMT resistors isn't going to suddenly make the PCB perform better; it will just make the problem worse. Just because the letters SMT appear on the datasheet it it doesn't mean you can magically bypass the laws of physics.
If you actually read the datasheet for the suggested RHFH4Q050R0FE resistor you will see that it needs a heatsink to dissipate its rated power. In fact it needs a massive heatsink of 0.4degC/W to achieve its rated power even if you limit the maximum ambient temperature to a paltry 25C. Without the heatsink, and mounted on the recommended PCB footprint, this resistor is only good for 2W dissipation and should have been advertised as such rather than the practically unobtainable figure of 35W.
Similar comments apply to the suggested Vishay RCP parts. These are also heavily reliant on the heatsinking effect of the PCB to achieve their apparent high power ratings. Just sticking the part down on a bit of FR4 is not going to led to success. Unfortunately the datasheet offers no guidance on how to heatsink these resistors and it is left to the circuit designer to sort out the thermal engineering issues
The advantage of using leaded components in these situations is that the component manufacturer has already done most of the thermal engineering work for you. If you mount the leaded component in accordance with the manufacturer's recommendations and not restrict the air flow around it you can pretty much expect it to perform as advertised without having to put in a lot of effort into thermal engineering issues. With leaded components quite a bit of the heat is taken away by convection before it reaches the PCB so the PCB material and surrounding components run cooler.
Thermal engineering can be one of the most difficult aspects of product design and unfortunately most circuit engineers neither have the knowledge or experience to be proficient in thermal engineering issues. If this thermal engineering it not done properly the product can fail on the market due to unreliability, short lifetime or product warranty costs. Even with an experienced designer thermal engineering can be very expensive in terms of the engineering time and product development timetable.
Low voltage rating of small SMT resistors is due to their (surprise surprise!) size. Simple solution - put multiple resistors in series or use higher voltage rating SMT resistors, usually both. Open parametric search of your parts distributor and see for yourself - plenty of choices.
It's not that simple.
If your circuitry using using fast pulse waveforms then you have to be very concerned about unequal voltage sharing across a string of resistors due to circuit parasitic capacitances and inductances. In some cases you even have to put balancing capacitors across each resistor to force equal sharing of pulse voltages. This requires extra engineering time not to mention the extra cost of additional BOM items, assembly and test time and additional PCB area.
Again, using a single leaded part is often a much better solution. The component manufacturer has done all the hard work of characterising the component under the pulse operating conditions and all the circuit designer has to do is follow the manufacturer's mounting recommendations to successfully use the product.