HOW-TO GUIDE
How to Solder Surface Mount Resistors Without Hot Air
By the OhmSavvy Research Team ·
Safety: hot tip, flux fumes and flying parts
- The tip commonly runs at 300–350°C. Keep the iron in its stand whenever it is not in your hand, and never reach across it for tweezers.
- Flux fumes rise straight into your face when you work close under magnification. Use a fan or fume extractor that draws them away, and wear eye protection: flux can spit.
- Tiny chips can flick out of tweezers. Wear glasses, and wash your hands after handling leaded solder.
Chip resistor sizes: 1206, 0805, 0603 and 0402
Chip resistors are named by a four-digit size code. The common imperial code gives the length and width in hundredths of an inch, so 0805 is about 0.08 × 0.05 inch. There is also a metric code, and the two overlap confusingly: imperial 0603 is metric 1608, while metric 0603 is the much smaller imperial 0201. Always check which system a parts list uses. Power ratings below are typical for standard thick-film parts; the datasheet gives the real figure.
| Imperial code | Metric code | Size (L × W) | Typical power rating | Hand soldering |
|---|---|---|---|---|
| 1206 | 3216 | 3.2 × 1.6 mm | 1/4 W | Easy, good for learning |
| 0805 | 2012 | 2.0 × 1.25 mm | 1/8 W | Easy with tweezers |
| 0603 | 1608 | 1.6 × 0.8 mm | 1/10 W | Needs magnification |
| 0402 | 1005 | 1.0 × 0.5 mm | 1/16 W | Fine tip, steady hands, magnification |
Larger parts are marked with a value code: three digits such as 103 mean 10 followed by three zeros, so 10 kΩ; four digits such as 1002 add one more significant figure, also 10 kΩ. Many precision parts use the EIA-96 code (for example 01C = 10 kΩ), and 0402 parts are usually unmarked, so keep them in labeled packaging until they are on the board.
1Gather the tools
Temperature-controlled iron
Stable, adjustable tip temperature so a tiny part heats quickly without overheating.
Fine tweezers
Pointed, non-magnetic tweezers; steel ones that are magnetised make chips jump.
Flux
Gel or liquid flux. It does most of the work of making solder flow onto small pads.
Thin solder
Around 0.3–0.5 mm diameter makes it easy to add only a little.
Solder wick
For removing excess solder and flattening pads.
Magnification
A loupe or head magnifier for 0603, a microscope helps with 0402.
For help choosing wire size, see the solder wire diameter guide.
2Choose the tip and temperature
A small chisel or bevel tip, roughly the width of the part's end, transfers heat well and suits 1206 to 0603. A fine conical tip helps on 0402, where a wider tip touches both pads at once. With leaded solder, a setpoint around 300–330°C is a common starting point, and lead-free alloys typically need higher; these are typical values, so check your solder manufacturer's recommendations and the part's datasheet. Our tip types guide and temperature guide go further. Whatever the tip, keep it clean and tinned; an oxidised tip is the most common reason small joints won't flow.
3Flux the pads and tin one pad
Clean the pads first. If an old part has just come off, run wick over both pads so they are flat; a leftover lump on one pad tilts the new part. Apply a thin layer of flux, then touch a small amount of solder to one pad only. Right-handed people usually tin the right-hand pad so the tweezers come in from the left. You want a low dome of solder, not a ball.
01
Flux + tin
Small dome of solder on one pad
02
Place
Tweezers hold the part centred
03
Reflow
Melt the tinned pad, part drops flat
04
Second end
Iron + solder on the bare pad
4Place with tweezers and reflow the tinned pad
Pick the resistor up with tweezers and lay it across the two pads, centred, with the value marking face up. Hold it lightly against the board. Touch the iron to the tinned pad where it meets the end of the resistor. The solder melts, flows onto the resistor's end cap, and the part settles flat. Remove the iron, then keep the tweezers still for a second or two until the joint freezes. If the part is crooked or raised, reheat that one joint and nudge it with the tweezers.
5Solder the other end
With the part held by the first joint, the tweezers are free. Place the tip so it touches both the bare pad and the resistor's end cap, then feed a small amount of solder into the point where they meet. It should wick up the end cap and form a small concave fillet. Remove the solder, then the iron.
Go back to the first end and touch it again with a little fresh flux. That first joint was made with solder that had already lost some of its flux core, so a quick reflow gives it the same clean fillet as the second.
Working a row of resistors? Batch the steps: tin one pad on every footprint first, then place and reflow each part, then go back along the row soldering all the second ends. You change tools less often, and each part gets a moment to cool before you return to it. Keep the reels or labeled strips in the order you will use them, because loose chips of different values look identical once they are out of their tape. Hot air is still the better tool for parts with hidden pads, such as QFN chips, but for two-terminal resistors and capacitors an iron does the job well.
6Inspect the joints and check the value
Under magnification, both ends should show a smooth fillet climbing the end cap, the part should sit flat, and there should be no solder balls nearby. Clean flux residue with isopropyl alcohol if your flux needs it. Then measure across the resistor with a multimeter on resistance.
A reading far below the marked value usually means something else on the board is in parallel with it; see measuring resistance in a parallel circuit. An open reading points to an unsoldered end.
Removing a chip resistor with just an iron
The trick is to melt both ends at the same time, so the part lifts off without being dragged. Three iron-only methods work:
- Wide tip with a solder bridge. Add flux and a generous blob of solder across the whole part, then lay a wide chisel or blade tip across it. Both ends melt together and the part slides off on the tip or lifts with tweezers.
- Two irons. One iron on each end, used like tweezers. Dedicated soldering tweezers do the same job.
- Alternate quickly. On 0603 and smaller, adding solder to both ends and switching between them fast can keep both molten, but it is the least reliable of the three.
Never pry a part while one end is still solid; that is how pads tear. Afterwards, clean the pads with wick as described in how to remove solder from a circuit board. If a pad has already lifted, see how to repair lifted PCB pads.
Tombstoning: why a resistor stands on end
Tombstoning is when one end of a chip lifts off its pad and the part stands up like a gravestone. Molten solder pulls on whatever it wets; when one end wets while the other is still solid or dry, that pull is unbalanced and tips the part up. It is mostly discussed in reflow assembly, but hand soldering causes it too.
| Problem | Likely cause | Fix |
|---|---|---|
| Part stands on one end | Too much solder on the first pad, or the part not held down while it froze | Reheat the raised end while pressing the part flat with tweezers, then solder the free end |
| One end sits high | Leftover solder lump under the part | Remove the part, wick both pads flat, start again |
| Dull, grainy joint | Too little heat or flux, or the part moved as it cooled | Add flux and reflow briefly |
| Solder ball beside the part | Too much solder on the tip | Pick it off with a clean tip or wick |
| Open end, no fillet | Solder never wetted the end cap | Add flux, put the tip on pad and cap together, add a little solder |
Less solder on the first pad prevents most tombstones
Which iron suits SMD resistor work?
Chip resistors need very little power. What helps is a stable, adjustable temperature and the availability of small tips. Any of the temperature-controlled irons below is suitable; the choice comes down to bench versus portable. Compare them in our best soldering iron for circuit board repair guide or the full best soldering irons roundup. When you move on to ICs, our fine-pitch SMD guide builds on the same tack-and-solder technique.
Temperature-controlled irons in our reviews
100W with digital closed-loop control and five presets; ESD safe for board work.
70W with digital, ESD-safe temperature control, for dedicated workbenches and professional use.
About 60W from 20V USB-C PD (up to 88W at 24V) with an OLED display and a heat-up time of about 12 seconds; built for portability and field repairs.
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Frequently asked questions
What is the smallest SMD resistor you can solder by hand?
0603 is comfortable for most people with magnification and fine tweezers, and 0402 is manageable with practice, a fine tip and good light. 0201 and smaller are possible but difficult, because the part is barely bigger than a grain of sand and easily lost. For a first board, 0805 or 1206 parts are much more forgiving.
Can I use solder paste with a soldering iron?
You can, but it is fiddly. Paste is designed to be melted all at once by hot air or an oven, and an iron tends to scatter the solder balls before the flux has done its job. For iron work, wire solder plus a little extra flux gives more control. If you already have paste, a tiny dab on each pad melted with the iron does work.
Do SMD resistors have a polarity or orientation?
No. A chip resistor works either way round, so you only need to center it on its pads. Printing the value face up makes it easier to check later, but it does not affect the circuit. Polarity matters for parts such as diodes, LEDs, tantalum capacitors and ICs, which carry a marking for pin 1 or the cathode.
How long can I hold the iron on an SMD resistor?
Aim for a few seconds per end. Chip resistors are small and heat almost instantly, so if solder has not flowed within about three seconds the problem is usually an oxidised tip, too little flux or a temperature that is too low, not a lack of time. The component datasheet gives the soldering heat limits for that part.
Should I use leaded or lead-free solder for SMD resistors?
Leaded solder such as 63/37 is easier to learn on: it melts at a lower temperature, flows readily and freezes at a single point, so small joints form quickly and look shiny when good. Lead-free alloys need a hotter tip and more flux, and a good joint looks duller. Use lead-free when the product must meet RoHS rules, and ventilate the bench either way.
