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cheap soldering iron for 0402 resistors

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treez

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Please , do you know of one?
I suspect it wont need to be temperature regulated.?

For example, the following Tenma iron….(Part number 9SS-900N-SI)
https://uk.farnell.com/tenma/9ss-900n-si/soldering-iron-of-ss-207b-no-logo/dp/2565327

....has a smallest tip which is part number 5SI-216N-B
https://uk.farnell.com/tenma/5si-216n-b/soldering-tips/dp/2565329?st=5si-216nb

Will this be ok for soldering 0402 resistors? (0402's are on minimal pads on 4 layer FR4 PCB)
The tip radius is 0.5mm, and I believe that will be too thick for 0402’s?
 
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To solder tiny pieces I sometimes wind a short loop of wire around the tip of my 100W soldering gun. It quickly delivers heat to the work. I can join parts quickly. The solder cools quickly because contact time was brief.

Whereas, I've seen my little soldering iron fail to melt solder when doing a few joints. I can't be sure if it's cooled down, or whether a layer of char has developed, inhibiting heat transfer. While I wait for solder to melt, the workpiece carries heat away from the join area.
 
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A tiny-nozzle heat gun and solder paste (in syringe)
could be closer to what normal surface-mount assembly
is like. The resistors probably don't care about their
body being heated to solder liquidus temp, unlike ICs
which often spec 10 sec @ 300C max.

A fat flat tip could heat both endcaps at once and let
you "iron, dot, dot" solder the components. You might
even "sacrifice" such a tip (or few) and file out a notch
in the tip such that the "fork" now hits only the endcaps.

Cheap irons often offer only lousy tip geometries. But
back when I was a broke-a$$ student I would pick up
brass bolts at the hardware store (or steal from work)
and grind them to suit - cheapo irons use standard
threads for the tips which are nickel plated copper.
Of course a pack of cheapo replacement tips ought
to be pretty inexpensive too, if you wanted to play
with geometries (less length will let more heat flow
to the tip, you might like a short shaft and a needle
point, or pound one flat and make the "fork" like I
mention, etc.).

But a cheapo iron is also likely not temperature
controlled, only power limited, and will be inferior
for any large thermal mass (including boards with
a heavy ground plane if the solder lands are well
connected to it, thermally).
 

I use two soldering irons for all my two port surface mount devices. For 0402, I use fairly narrow tips. Both irons are temp controlled (Hakko 926). Avoid hot air - you would be surprised at how easy 0402s are blown away. And with them being unmarked, plus the size of grains of sand, once they are gone, you will have to re-place a new part.
 

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Even the cheapest soldering irons would work with its standart tip actually. I am not saying they are the perfect fit for the job, but if you just want to solder 0402 passives to your PCB you can pretty much any soldering iron.
 
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Also think about what else you might want to do with the soldering iron. By all means get a soldering iron that handles small SMT devices but (In my opinion) it would be a waste to only think of soldering 0402 resistors (or just 0402 sized devices).
To me, the key thing is the size of the tip - it has to be small enough to heat the pad and the side of the component or IC pin. The next thing is ensuring that the tip is supplied with enough heat that it will not cool down too much when it does get applied to the pad/component which generally means a more powerful element (perhaps even temperature controlled) to maintain the tip temperature.
Susan
 
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