Guide · Soldering stations and irons
Why ground planes are hard to solder
A ground plane pulls heat out of the joint as fast as a small tip supplies it. The fixes in order: bigger tip, flux, a moderate rise, more power, then preheat.
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Short answer
A ground plane is a large area of copper, and copper carries heat away from your joint about as fast as the tip can supply it, so the joint struggles to reach the solder's melting point. SparkFun's fix is a larger tip, a higher setting (720 °F, about 380 °C), extra flux and a little more time on the joint.[1] If that fails, you need more power, such as a C245 handle, which JBC says suits ground-plane soldering,[2] or a board preheater.
What is going on
A ground plane is a wide area of copper tied to the circuit's ground. Copper conducts heat very well. When your tip touches a pad joined to the plane, heat flows out into the copper almost as soon as it arrives.
The joint has to reach the solder's melting point: 183 °C for 63/37, or 217–220 °C for SAC305.[3] On a plane, the pad can stay below that even with a hot tip pressed on it. The result is solder that balls up, or a dull, grainy cold joint, which Adafruit defines as one where the solder did not melt completely.[4]
Three things make it worse:
- Solid connections. Some boards join a pad to the plane through a few thin spokes, called thermal relief, which slow the heat loss. A pad joined solidly, with no spokes, is the hardest case.
- Inner layers. Multi-layer boards can have whole layers of copper inside. Hakko markets its FR-830 hot-air preheater as best suited to preheating multi-layer boards.[5]
- Lead-free solder. It melts higher, and Adafruit says it may need more heat and more flux.[6]
The setting is not the power
The temperature setting is a target. What decides whether the tip keeps up is how quickly the station can put heat back into it while the joint drains it away. That is a question of thermal mass and heater power, not of the number on the display.
Makers rate their handles very differently. JBC rates its T210 precision handle at 40 W peak[7] and its T245 general-purpose handle at 150 W peak.[2] Hakko lists 70 W power consumption for its T12/T15 iron.[8] These are each maker's own ratings, measured in different ways, so compare within a brand rather than across brands.
Where the heater sits matters too. Hakko credits its cartridge design, with the heater and sensor built into the tip, for faster thermal recovery, which it says allows lower temperature settings.[9]
USB-C irons have less in reserve. By Pine64's own arithmetic, a Pinecil with a standard 8-ohm tip draws 50 W from a 20 V USB-C supply,[10] and Pine64's official rating for the Pinecil V2 is up to 88 W at 24 V.[11]
Fixes, in order
- Use a bigger tip. A wide chisel puts more metal on the copper. It is SparkFun's first step.[1]
- Add flux. Fresh flux helps the solder wet the pad as soon as the pad is hot enough.
- Make a heat bridge. Melt a small blob of solder between the tip and the joint. Molten solder carries heat far better than a dry point of contact.
- Raise the setting moderately. SparkFun suggests 720 °F (about 380 °C) for heavy joints.[1] Kester's highest hand-soldering recommendation, for its rosin-flux wires, is about 400 °C (750 °F).[12] Beyond that, look at the tool rather than the dial.
- Hold a little longer, as SparkFun suggests,[1] but not indefinitely. If the solder does not flow, move on to the next step instead of pressing harder.
- Use a more powerful handle. JBC positions its T245 handle and C245 cartridges for high-power jobs such as ground planes, as well as SMD work.[2] See C210 vs C245.
- Preheat the board. Warming the whole board means the tip only has to supply the last part of the heat. Hakko's FR-830 is a hot-air preheater rated 150–300 °C,[5] and its FR-872 is an infrared preheater for boards up to 330 × 250 mm, which Hakko recommends for lead-free work.[13] See do you need a PCB preheater?
When to stop
If the solder still will not flow after a bigger tip, fresh flux and a moderate rise in temperature, stop and change the tool. Holding a hot tip on a pad for a long time is not a fix. Never lever a part out of a joint that has not fully melted. Step up to a higher-power handle, a preheater, or both.
Plan for it next time
If heavy joints are a regular part of your work, choose the bench for them:
- A C245-class handle as your main iron, with a wide chisel tip. The tip shape guide covers sizes.
- Leaded solder, if you can keep lead hygiene, because its lower melting point leaves more margin. See 63/37 vs 60/40 vs SAC305.
- A preheater if you regularly work on multi-layer boards.
Next
Questions
Why won't solder melt on a ground pad when it melts fine elsewhere?
The copper plane draws heat away from the pad as fast as the tip supplies it, so the joint never reaches the solder's melting point. SparkFun's fix is a larger tip, a higher setting, extra flux and a little more time on the joint.[1]
Should I just turn my iron up to the maximum?
No. SparkFun suggests 720 °F (about 380 °C) for heavy joints, and Kester's highest hand-soldering recommendation is about 400 °C. Past that, a bigger tip, more flux, a more powerful handle or a preheater will do more than extra degrees.[1][12]
Which tip system is best for ground planes?
A high-power one. JBC rates its T245 handle for C245 cartridges at 150 W peak and says it suits high-power work such as ground-plane soldering. See C210 vs C245.[2]
Is a USB-C soldering iron enough for ground planes?
It has less in reserve than a large station handle. By Pine64's arithmetic, a Pinecil with an 8-ohm tip draws 50 W at 20 V, and its official maximum is 88 W at 24 V, against 150 W peak for JBC's T245 handle.[10][11][2]
Do I need a preheater to solder ground planes?
Not for occasional joints, but it helps on multi-layer boards. Hakko markets its FR-830 hot-air preheater as best suited to preheating multi-layer boards. See do you need a PCB preheater?[5]