Effective thermal relief settings for hand soldering

I’m looking for some advice on thermal relief settings for ground plane connections. ie, spoke width and gap. The last board I had manufactured had 0.508 for both spoke and gap but I found that I needed to ramp my iron up to 440+ and use the largest tip I had (even with extra flux) in order to get a nice joint.

The board I’m about to order has a lot of similar ground connections and I’d like to tune these parameters a little in order to save my iron from an early grave. I was thinking of reducing spoke width to 0.254 but then leaving gap at 0.508.

The device will only draw approximately 370mA max when in operation.

Will this spoke width provide sufficiently low resistance and will it make much of a difference to hand-solderability.

Thanks in advance

It depends also on other factors than just the thermal connection. How large copper areas you have, how thick copper, how much metal parts of components you have connected nearby, what kind of component you are soldering, how much current will go through that individual connection etc.

As an anecdote, I had a SMD pad which didn’t have thermal connections, and it was difficult. I scraped off some copper nearby with a scalpel, just one narrow gap, and it made easy soldering possible. There are no easy simplistic answers but 370mA for the whole device doesn’t sound much and narrow spokes may well be enough.

I had the same problem, i changed it to a 600µm gap and a 400µm width and it worked better. If 600µm is to large, 400µm gap and 200µm width should probably also work. I had a 400µm gap and 400µm width where it caused problems (was still able to solder with a 370°C soldering iron, but it took a long time) and i used 2 layer boards, with a GND plane on both layers, with 35µm Cu height for all mentioned boards.

I recommend to use a gap of 200µm*n (200µm, 400µm, 600µm, …) and not such odd numbers like 254µm, same for tracks and clearance. This way, you can place all tracks in a 200µm grid and it is immediately clear how many tracks fit between 2 components/pads/component and border/… It is just easier and faster to route. Only change it when you have to lower it in order to make the PCB small enough.

If you have to crank up soldering iron to 440 it means you have a crappy iron. Ground plane with any thermal relief spokes < 1mm should not have much issues with a decent 60+ watt iron.

Do yourself a favor and get a pinecil or ts100 or t12 tips based iron. They cost anywhere between 30 and 80 usd and will make your soldering a breeze.



My trusty old Weller PT series, quietly clicking away in its stand on the bench, has no trouble with anything on a PCB ( with or without thermal relief ), even with the 600°F (315°C) range tips. I think it is 50W.

Absolutely ! I have been using a TS100 for a couple of years now and never had any soldering problems at all. The TS does have a nice touch which allows you to ‘boost’ the power output for a short time so that if you have a couple of sturdy GND’s to solder you don’t have to mess up your normal settings.

I am not familiar with these TS designations, but

  1. I never have used thermal reliefs on my own designs. Doing power, I am usually interested in spreading heat and thermal relief is bad for that. For example soldering the tab of a Dpak transistor, I do not want to have thermal reliefs around the pad.
  2. I apply activated rosin flux (such as Kester 44) on at least one of the surfaces to be soldered. I also use a wide soldering tip; I think it is about 3 mm wide.
  3. It may be best to pre-tin the pad with a thin layer of solder before soldering the transistor.
  4. I turn up the temperature to maybe 400 degree C for the task, and then reduce it to 300 degree C as an idling condition.
  5. Not sure what type of solder you use. In the USA I can use 63/37 tin/lead. The solder alloy will make a BIG DIFFERENCE. I do not want to argue against ROHS solder but I sort of remember when regulations began pushing for it. It very much seemed like a case of environmental concerns arguing for the change and engineers pushing back; saying “cannot”. I think there were about 3 cycles of this before engineers gave in and said “OK”. The takeaway here is that the ROHS solder is more difficult to work with and requires more careful/precise control.
  6. I have been using tin/lead solder since about 1965. If others on this forum think my jokes are bad…maybe that is why? :frowning:
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If you have to crank up to 400 for leaded solder you also have a crappy iron. Soldering iron tiers used to be:

  1. Unregulated cheap crap
  2. Regulated standard heater + swappable tips
  3. Expensive Pro stations with curie point tips

Nowadays categories 1 and 3 are still there but category 2 is pretty much obsolete and is replaced with “cartridge” type tips that have integrated the heater and thermocouple into one solid package. This immensely improves heat transfer and regulation accuracy at barely any additional cost.

These tips were popularized by hakko and then an open source station for it based on stm32 got quickly mass replicated by Chinese manufacturers and made it really affordable. I got mine for $40 for a full kit.
Nowadays even genuine hakko tip (rebranded from original t12 to t15) is cheap https://hakkousa.com/products/soldering/soldering-tips.html?product_list_limit=25&product_list_mode=list&product_list_order=price&series=67

TS100 was first popular soldering station with similar style tip but it’s brains were built into the handle with a small screen and control buttons so you don’t have an external brick, only a power supply. I personally never saw the appeal because of custom shaped tips that were much pricier than t12 variants.

Pinecil is similar solution with usb-C power delivery, perfect for portability, just $25 + shipping if you already have a power supply from a laptop or something.

I have never been that much into soldering iron perfection. I have gotten along with a cheap iron from MPJA.com and I also have a Weller. I keep a wide tip on one and a fine tip on the other. Both are adjustable. I also have a Weller desolder tweezer, but its base unit is a $300 answer to a $50 problem. I also have a $100 hot air unit but I think the thermostat contacts are finnicky.

If I were going to be doing a lot of production soldering I might want to invest in some nice tools for that but what I have serves me well enough. My immediate problem is my old Tektronix TDS3034B oscilloscope which has effectively been “bricked” by the combination of front panel control issues and (I think) updates in Microsoft Windows and the loss of Internet Explorer. That is too complicated a story to present here…

400°C is too hot, you have a higher risk to damage parts with that temperature. You should be able to solder with 360°C-370°C without any Pb. And since you use a Sn/Pb mixture, you should get away with even lower temperature. Maybe you need more patience?

Don’t advice others to use Pb, for most categories it is illegal to sell new products that use Pb containing tin in large parts of the world. Maybe it is legal in the USA, but at least not in an EU country nor many countries surrounding/in the EU. There maybe exceptions for some products.

We use a plumbers iron with an 8mm copper tip for this kind of problem. Quicker & cleaner than a small tip at high temperature.
Or use low temperature solder. e.g. 185 degree.

I don’t see advice (except in the quality of jokes), but I do see quite accurate comparisons that, together with comments on irons, may help the OPs understanding of their problem.

Yes it’s good to have all the facts and I personally prefer to use and get better results from Sn/Pb so I use it.
Here in the UK you can’t manufacture with it but the rest of us are ok and as I said I don’t like unleaded.

Well I am not doing that…at least not really.

I use tin lead solder in my own lab, and I THINK that even where industrial production is not intended for export, it can use tin/lead.

And my impression is that for breadboards and prototypes even in EU that tin/lead may frequently be used. I only have second hand information from about 10 years ago. Lab boards are only a tiny percentage of what goes into the environment. If I had to use ROHS solder from the beginning I might have been frustrated to the point of not becoming an EE. Or maybe the base price of a 1965 soldering iron would have been much higher.

With respect to 400 degrees C, I think that @qu1ck was indirectly referring to the fact that the relationship between the iron set temp and the actual solder temp is not perfect. It depends upon the thermal resistance between the temp measurement point in the iron and the tip of the iron. If the solder does not melt then the solder is not hot enough…

A lot depends on the thermal mass of the soldering iron bit. A small diameter bit may struggle to transfer heat fast enough, even with the iron at a relatively high temperature, whereas a larger diameter bit holds more thermal energy and should let it transfer more quickly, even at a lower temperature.

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