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I can't stand seeing or using non-SMD parts. Am I sick?
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T3sl4co1l:
Another important difference: SMDs perform better.

There is unfortunately a dearth of heatsinkable parts in SMT, making it difficult to do anything that handles much power.

This alone does prioritize switching supplies quite a bit: if you can't afford to dissipate even a whole watt in say a SOT-89 linear regulator, you're forced to use a switching converter, and you'll just have to suffer the improved efficiency... ;D

When you do need to handle power, you don't have much choice but to stick with THT parts, TO-220s and such (and power resistors in various packages).  These all have long, spindly legs: in a high efficiency switching converter, or a wideband amplifier, the lead inductances of ~10nH are very significant.  This puts an upper limit on switching speed and losses.

Whereas D2PAKs have maybe 3-5nH inductance, and DFNs can have almost nothing.

There are somewhat more options these days, from DirectFETs, to exposed-die or thermal-plate DFNs, to CSPs and bare dies; and with device performance continuing to improve, achievable efficiency continues to rise.

Tim
exe:
yeah, heat dissipation is an issue, and I wonder why smd components are so unfriendly to heatsinks. I've seen parts with, say, a thermal pad on top, but that's an exception, most datasheets just say "have enough board area and solid planes to soak the heat". There are a few heatsinks that can be soldered to the board, but they are only good for a watt or two. So, for my power supply I'm going to use to-264, even though it's going to be laying on the board (just like to-252, but thermal pad upwards so I can screw to a heatsink).

BTW, how do you prototype smd parts? For prototyping I still use breadboards. I use smd-to-th adapters quite frequently. I don't have any hate for TH, and I use quite a lot in prototypes. Making PCBs is fun, but I put my order (actually my first pcbs ever) on jlcpcb three weeks ago and it's still not delivered yet. May be if wasn't so greedy and order a DHL delivery it would be faster, but I'm worried they'd charge me with VAT and paperwork taxes.
tszaboo:

--- Quote from: T3sl4co1l on February 24, 2020, 10:51:39 am ---Another important difference: SMDs perform better.

There is unfortunately a dearth of heatsinkable parts in SMT, making it difficult to do anything that handles much power.

This alone does prioritize switching supplies quite a bit: if you can't afford to dissipate even a whole watt in say a SOT-89 linear regulator, you're forced to use a switching converter, and you'll just have to suffer the improved efficiency... ;D

When you do need to handle power, you don't have much choice but to stick with THT parts, TO-220s and such (and power resistors in various packages).  These all have long, spindly legs: in a high efficiency switching converter, or a wideband amplifier, the lead inductances of ~10nH are very significant.  This puts an upper limit on switching speed and losses.

Whereas D2PAKs have maybe 3-5nH inductance, and DFNs can have almost nothing.

There are somewhat more options these days, from DirectFETs, to exposed-die or thermal-plate DFNs, to CSPs and bare dies; and with device performance continuing to improve, achievable efficiency continues to rise.

Tim

--- End quote ---
Oh, yeah, dont even get me started on power dissipation. I have a constant need for high power Zeners. It is for fault conditons, that is supposed to protect other electronics components. So I have a need of 3-4W rated zener diodes, and there just isnt any. TVS would do, but they dont have DC specifications.


--- Quote from: exe on February 24, 2020, 11:38:40 am ---BTW, how do you prototype smd parts?

--- End quote ---
You design a board quickly and order it on 2 days service.
T3sl4co1l:
Yeah, that's a good way to mount things, against the board. Can even use the board as a clamp, for more even pressure than the normal screw hole provides (just don't place SMT chips too close to the screws, because strained PCB).

I do SMTs this way,



Use a utility blade (to cut V-grooves) or rotary tool to slice up islands and traces on blank copper clad.  Hit it with some sandpaper to remove burrs and clean the surface, then tin it, then place and solder components.

SOIC is easy to do this way, but TSSOP and such are not so easy.  Ordering pre-baked or custom breakout boards is probably the better way.  PCBs are easy to make and very cheap to order (if you don't mind a longer lead time due to current events).

And you can surface-mount THT components too.  Those are easier done between Manhattan style pads, just cut off chunks of copper clad then solder them to the base.

Tim
tom66:
I'm pretty much the same. 

The exceptions are for large capacitors (I hate SMD electrolytics with a passion and avoid them where possible because they are a right pain to hand solder) and for power electronic parts where it isn't possible to fit an SMD part for one reason or another (power dissipation, voltage standoff, etc.)

I quite like mixed SMD and through hole boards - e.g. plasma TV sustain boards. 
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