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Soldering Pi0W headers

Sat Feb 03, 2018 7:50 am

Now, I consider myself a fairly reasonable solderer.
I have a fine point tip, nice hot iron and some old 40/60 solder.
I have successfully soldered 4 lots of headers to different Pi0/W. (And many Arduino projects on veroboard over the years).
But, I recently purchased a couple of PHATS from Pirmoroni that needed their headers soldering on too.
The PHATS were MUCH, MUCH easier to solder to. The solder flowed very easily and in a very short time.
All the Pi's on the other hand take much longer for the solder to flow. And I'm always fearful of holding the iron on for too long or ending up with dry joints.
I did notice that the PHAT holes were more silvered whereas the Pi's are gold. But I don't think the PHAT's were pre-tinned.
Is it that I need to use a more modern solder mix with the Pi's?

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Re: Soldering Pi0W headers

Sat Feb 03, 2018 11:53 am

60/40 tin/lead solder is good, as is the flux in it, so you don't need anything different.

As I understand it, gold is used as a coating to prevent the underlying copper from oxidising.
Probably the PHAT holes are pre-tinned - there's a layer of tin protecting the copper.

Many years ago, on a course at Cranfield, the lecturer told us that gold is not the best metal for soldering - it desolves in the tin (or is it the lead?) and forms an alloy which is reluctant to wet copper!
His advice was to wash the gold off with solder, then apply fresh solder to complete the joint.

I'm not sure what modern flux is - rosin (from pine trees) used to be used, and I once had some based on a relative of terylene that had a higher operating temperature. They all do a similar job, and you're unlikely to find anything better than what's used in common multicore solder.

Lead-free solder is more difficult to use but better for the environment, but the amount of solder used by amateurs is miniscule compared to industry, so we don't need to worry.
(The lead spread into the environment by the car industry in the '60s and '70s is still leaching into the water supply and sea water, and will continue to do so for centuries. And light aircraft continue to use leaded petrol, so spreading the pollution today)

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Re: Soldering Pi0W headers

Sat Feb 03, 2018 11:54 am

The pi zero PCB is certainly not pre tinned as you can clearly see the copper track around the GPIO holes and the various test points, so the solder will take longer to flow across the copper, if the Pirmoroni PHATS have a more silvery finish and the solder flows more easily then the PCB probably does have pre tinned holes were the header fits, solder will always flow easier on a pre tinned surface.


looking at various Pirmoroni PHATS pictures on their web site they look to have un tinned cooper holes for the headers but may be that's changed form when the pictures were taken.
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