Building a PiDP-10 - what is the liquid being used here?

[Francis King]

Hello.

My PiDP-10 kit arrives tomorrow!

Here is an interesting YouTube video: https://www.youtube.com/watch?v=ybO6bPcRmlY

There is a soldering montage from 8:30 onwards. The presenter is washing the circuit board with a liquid from time to time. Is this Isopropyl Alcohol?

Also, why does it say which side of the circuit board should the Raspberry Pi connector be soldered??

Francis.

[Charley Jones]

It’s a really great build.  And yes, to revoked the acid flux, use a toothbrush with isopropyl alcohol.  The build instructions are great, and the pi is mounted on the opposite side.  This is well presented in the build instructions.  I have built 3 of these now and love each one, 

Sent from my iPhone 15pm!

Charley Jones, PMP

On Aug 19, 2025, at 10:15 AM, Francis King <francis...@gmail.com> wrote:

Hello.

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[Michael J. Kupec]

Beat me to the PI response!

Hope you don’t really mean acid flux! Leave that for sweating copper pipe together!

Electronic soldering flux is a neutral balanced flux that cleans the contacts and surfaces to be soldered. 

A good high % isopropyl alcohol is best to clean board after soldering is done. 

Best stuff to use is Chemtronics Flux Off, but pricey at $18 for 6 oz can! 

https://www.digikey.com/en/products/detail/chemtronics/ES896B/10244092?gclsrc=aw.ds&gad_source=1&gad_campaignid=20232005509&gbraid=0AAAAADrbLljjj7IlsPQ9EMrgoHo0j2y3k

Have a great Day!

Michael J Kupec 

Sent from my iPhone

On Aug 19, 2025, at 1:21 PM, Charley Jones <data...@gmail.com> wrote:

It’s a really great build.  And yes, to revoked the acid flux, use a toothbrush with isopropyl alcohol.  The build instructions are great, and the pi is mounted on the opposite side.  This is well presented in the build instructions.  I have built 3 of these now and love each one, 

To view this discussion visit https://groups.google.com/d/msgid/pidp-10/84DF269F-8282-4C06-8CE2-F17F86906380%40gmail.com.

[John Blackburn]

Yes, over a long time, acid in the flux can damage the board:

Here is more information:  https://www.conro.com/Blog/How-do-I-remove-flux-after-soldering-the-PCB-board/#:~:text=Isopropyl%20alcohol%20is%20a%20good,also%20cheap%2C%20and%20evaporates%20quickly.

[Tim Radde]

Sorry, but acid flux is used in plumbing.  Not with circuit boards.

[terry-...@glaver.org]

On Friday, August 29, 2025 at 3:48:23 PM UTC-4 timr...@gmail.com wrote:

Sorry, but acid flux is used in plumbing.  Not with circuit boards.

It's still a good idea to remove any flux residue. I have enough rolls of

leaded solder to last several lifetimes, so I know what's in my flux.

The flux in the newer RoHS solders may be more aggressive due to

 the decreased 'wetting' ability of the new formulations.

I also use a flux pen on some particularly difficult-to-solder areas.

It is prone to dumping excessive flux on occasion, so I also remove

the flux for aesthetic reasons.

I use MG Chemical's lower-strength flux remover and a boar bristle

brush for cleaning. Alcohol and a (new) toothbrush should work

just as well. Be sure to get 90+% alcohol - the typical 70% stuff is

diluted with water, and you don't want to sit around waiting for the

water to evaporate.

[Tim Radde]

Myabe it is a good idea.  I have never done so and never had an issue. I won't use anything but leaded solder and have plenty also.

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[Chris Jordan]

As an alternative, they do make lead free solders that include a "No-clean" flux.  I used Kester K100LD when I assembled my PiDP-11, seemed to work fine.  Fingers crossed that it stays that way.

Chris Jordan