# Ground pads soldering problems

Hello to all,
I have a beginner question, probably (KICAD 6).
On my PCB, the pads connected to the ground have a thermal barrier (I don’t know the exact term in english). The pad itself has a diameter of 1.6 mm.

1. It is very difficult to solder the component, even with a very fine tip soldering iron. Is there a trick to make this type of soldering work?
2. Can increasing the diameter of the pad to 2 mm improve things?
3. Is there any disadvantage to removing this thermal brake, and how to do it?

Thanks in advance for your advice.

Pascal

They are called thermal reliefs: Thermal relief - Wikipedia

Why are these pads difficult for you? What about normal pads for you? Without thermal reliefs it’s harder for the soldering iron to raise the temperature sufficiently.

How is it difficult?

When a small irong (tip) is used, it doesn’t give much heat power to the copper/component pad. If the pad isn’t separated from the surrounding copper area somehow, soldering will be very difficult because heat is spread to the surrounding copper instead of the pad. Therefore there is space around the pad and it is connected to the rest of the copper with thermal spokes (reliefs). If the spokes are narrower, less heat goes to the surrounding copper and it’s easier to solder with a less powerful iron. You can control the thermal connection in footprint properties, pad properties and zone properties. The amount of space and width of spokes is controlled only in the zone properties.

If, on the other hand, you have difficulties in hitting the copper pad/component leg with the iron, then of course you can make the pad larger.

Hi,

And thank you for your answers.
I increased the length of the spoke in the pad properties and it works perfectly:

But the width of the spokes is 0.5 mm and I can’t reduce it, the setting value is already 0.
For my next PCBs, if I have room enough, I will set the pad diameter to 2 mm and give a value of 0.8 to the spoke length.

I use a Gordak 936 soldering iron, and the temperature can be adjusted from 200 to 480°. I usually use 350°. Is this optimal?

Regards,

Pascal

I’ve never had a problem with the standard reliefs. There are multiple dimensions in this issue, whether your iron is regulating the temperature properly, the length and size of the tip, whether the tip has oxidised, the solder wire diameter you use, and so forth. But it sounds like not enough heat rather than too much and you have to experiment a bit.

From the pictures the Gordak 936 is a knock-off of the famous Hakko 936. But it should work, like my Huako (hahaha) 936 knock-off.

Check the footprint properties, pad properties and zone properties.

But as others mentioned, there should be no problem soldering these pads. Use decent equipment and practice.

@pvrx
Don’t trust the temperature indicator to be correct. There is probably a calibration adjustment somewhere that will need adjustment.
I’d bet only genuine Hakkos are accurately calibrated.
Also, the bigger the pad, the larger the soldering iron tip needed.

Thank you !
I had not encountered any soldering issues with the “normal” 1.6 mm diameter pads.
I will redo my soldering on the ground pads by increasing the temperature…

Hello to all,
I redid my soldering after increasing the temperature of the soldering iron, I got a correct result.
As my needs are very limited, I will make do with my current soldering iron, whose only flaw seems to be the temperature calibration.
Thanks again for your contributions.

Pascal

What type of solder are you using? Most lead free has a much higher melting point.

Looking at the advertising, this appears to be much the same product as my old Wellers.

This sentence does not feel right:

Thin tips have difficulty in transferring heat from the tip to whatever you want to solder.
Both round tips and sharp points are also to be avoided.
A conical tip has a point contact with the thing you want to solder, and this complicates heat transfer.
If the sides of the tip are slightly flattened, then you have a line contact and heat transfer is much better.
For THT parts a chisel tip with a width of around 1.2mm to 1.5mm works well.

And the soldering technique itself is also an important factor.
Generally it’s best to first add a very small amount of solder between your soldering tip and what you want to solder, The goal here is only to increase the surface area between your soldering iron and what you want to solder to increase heat transfer. Then you have to wait a few seconds for the heat transfer, and in these few seconds most of the flux will evaporate, and the solder will not “wet” anymore.

In the next stage, you add more solder, and flux with it, to the solder joint, Ideally this added solder is melted by heat transfer from the thing you want to solder, and does not directly touch your iron. Your soldering iron is the hottest part, and there the flux evaporates the fastest. Adding flux to your soldering iron is also useless, you want the flux on the metal to be soldered.

Right after you’ve added the right amount of solder, wait another second or two. In these seconds you see the solder spreading over the joint and it will also get further into the hole in plated through holes. Plated through holes do not have to be completely filled with solder. If your solder gets into the hole to about half the PCB thickness then it’s already plenty. An often made mistake is to stop right after the right amount of solder is added, but the solder has not flowed around the joint to it’s full extent. The flux needs some time to do it’s job.

Soldering can also only be done as long there is still flux present. When the flux has evaporated (which takes about 10seconds) then the solder will not wet anymore. In that case you have to add more flux (or solder if that contains flux).

There are quite a lot of youtube video’s which show soldering in detail.

I generally solder with a temperature of 300 celcius. When I’m soldering with “enameled” wire I increase the temperature to 350c because else the lacquer won’t burn off. In general, you can solder quicker with a hotter iron, but you also have to solder quicker because the flux evaporates a lot faster.

If you ever mix leaded and lead-less solder, be aware that if there is a small amount of lead in the mix (somewhere between 0.5% and 3%) something very weird happens in the alloy and the solder can loose more then 80% of it’s strength.

There is a quality difference between soldering irons, but anything with an adjustable temperature will already be much better then the old PTC self regulating irons. Those get both too hot, and cool too much during soldering.

I have a weller PU81 station with a WSP-80 station and I don’t like it much. It’s ok-ish, but far to expensive for the mediocre quality you get. If I had to buy a new iron now, it would be one of the T12 clones for around EUR 40.
If you want to go cheap, you can save some money by making an extra power output on your lab power supply. If you’ve got a (fairly common 30V3A power supply, you can take the raw voltage (around 35 to 40V), put it through a small SMPS module to get 24Vdc for your iron. This also saves desk space. There is a risk of overloading the power supply if you use both it’s output and the soldering iron at the same time.

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Thank you paulvdh,

And bravo for the precision of the advice!
The recommended method is the one I use.
I have not had the slightest difficulty in soldering on the “normal” pads of 1.6 mm diameter.
The difficulties I have encountered only concern soldering on pads with thermal relief (diameter 1.6 mm, brake length 0.5 mm).
For my next projects, I will increase the diameter to 2 mm, and the brake length to 1 mm.

Pascal

Don’t be sure of it.
As you have a problems with thermally isolated pads then the pads you think you had no problems with them can only look as being well soldered but in real the diffusion process could have been not enough good and after some time the contact can be lost.

Insufficient Wetting and Cold Joints. @pvrx, it is worth a few minutes on the internet viewing photos of these problems.

Pretty much any soldering iron will do the job ( the cheaper ones just take longer to heat or reheat the tip), just turn the heat up a bit, use lots of flux, a tip as large as you can get away for the job and use a variety of different diameter solders to make the correct joints (depending on the pad sizes).

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