frgmnt org

26 April 2022

NaPS Etchant Chemistry

What is happening in my Etchant? ..and what should

My etchant of choice for PCB production is sodium persulfate (Na2S2O8). Chemists call it sodium peroxosulphate, short form NaPS, sodium persulfate is its trade name, the salt of peroxodisulphuric acid. It is a strong oxidizer. It is a severe irritant of the skin, eyes, and respiratory system. It is almost non-hygroscopic and has particularly good ability to be stored for long time. It is easy and safe to handle. It is not combustible, but releases oxygen easily and assists combustion of other materials. (Wikipedia)

Since copper is quite a noble metal it is not easy to etch with just an acid, it needs an oxidizer like NaPS.

A typical PCB etching solution contains:
• 1000 ml water
• about 250 g sodium peroxodisulfate
optionally you can boost the etching rate by adding a catalyst:
• 1 ml HgCl2 solution (about. 5 mg Hg) Degussa company recipe, but we don´t want mercury
• use silver ions (Ag+) instead as silver flakes or some drops of silver nitrate solution (AgNO3).

Etching process should be carried out in the temperature range of ca. 40 to 45 °C – higher temperatures lead to higher decomposition with the release of oxygen gas.  About 40g/l of copper can be dissolved in the etching solution, that is all the copper on 10cm * 127cm of 35µ PCB and approx. 6 kg of sodium peroxodisulfate are needed to dissolve 1 kg of copper. The copper and sodium peroxodisulfate content in the etching solution can be determined by the usual analytical methods i.e. colourimetry.

In sum the etching reaction mechanism is: Cu + Na2S2O8 ->  CuSO4 + Na2SO4

The ionic equation for this redox reaction is: Cu0 +  [S2O8]2- -> Cu2+ + 2[SO4]2-+ energy

We can write this overall reaction as two half-reactions:

the copper oxidation reaction: Cu0 -> Cu2+ + 2e   with E0 = +0.340V

and the reduction reaction of  peroxosulphate to sulphate: [S2O8]2- + 2e -> 2[SO4]2-   with E0 = +2.010V

From the solubility curves of the components we can guess that the clear crystals are, which sometimes precipitate in older solutions – sodium sulfate:
Sulphate Solubility Graph


Waste water treatment & Disposal of etching baths

For waste water treatment the spent etching solution should be diluted in a big container & steel-wool added.

Etching solutions containing Cu ions, which are highly toxic to fish & bacteria in the biological stages of your city´s wastewater treatment plant and must not enter drains. The copper content of the discharged wastewater must not exceed a value of 2 mg per litre. Etching baths must therefore either be disposed of as hazardous waste or be prepared so that this limit is met. Since etching baths are treated as inorganic laboratory waste, the special disposal is very expensive.

It is therefore worthwhile to reduce these costs significantly by processing the solution yourself.

Processing: Etching baths are diluted to double the volume. Fill a maximum of three quarters of a 2l bottle & add steel wool (size 00, available at hardware stores) – this reduction will happen:  Cu2+ +  Fe -> Cu + Fe2+ , what means we get metallic copper & iron sulfate in this reaction: Fe + Na2S2O8 ->  FeSO4 + Na2SO4.

Steel Wool

It is exothermic – so be careful not to add steel wool too fast. The solution is allowed to stand for 3 hours, adding bits of steel wool, until they no longer dissolve & the reaction is complete. During this time the colour changes from blue to the pale green of Fe(II) ions.  Take some ml of the liquid & mix it with 1 ml of concentrated ammonium hydroxide (NH4OH): If no blue colour appears the copper concentration is below the permissible level for waste water discharges. If a blue color occurs, the process must be continued with more steel wool.


Before & after this Process

If you have time allow the yellowish-green solution to stand 1-2 days in an open container or by passing air to oxidize the Fe(II) ions to Fe(III) ions. This step is not really necessary. The solution can then be added to the waste water. It only contains non-toxic iron-, sodium- & sulfate ions.

Decant the solution or filter out deposited copper (eventually together with sodium sulfate crystals) then let dry and place in a sealed polyethylene bag as household waste, metallic copper is no more toxic….

Copper residue, Sodium sulfate crystals above

30 September 2018

Fu:bar Expo 2018

Filed under: specific — Tags: , , , , , — .. @ 17:27

PCB production for my Fu:bar Expo 2018 workshop in Zagreb, Croatia

3 April 2018

zoom test GIGA

Filed under: specific — .. @ 09:06
HaHa_8 (ONE Gigapixel), Jo frgmnt Grys, 2017

zoom test

Filed under: specific — .. @ 08:53
haha_8 CUT (4000x4000), Jo frgmnt Grys, 2017

22 April 2015

PCB of a Lenovo T61p

The backlight of my notebook was no longer working, finally I took it apart and checked the fuses on the motherboard (FRU: 44C3928):
F7 was blown, I will put in a new 3A type. Littlefuse´s  433003 is now obsolete, but there are replacements.

For reference and because I could not find a good photo of this specific model, here is in 3002 x 2432 (3,5MB JPEG)


1 November 2013

A Soldermask for free

Filed under: specific — Tags: , , , , , — .. @ 03:08

Here I show your how to integrate some new steps in your photographic PCB-production process.

After the usual step of exposure with a positive of your track patterns & development & etching you just add another exposure with a negative of your solder mask pattern. As a result you get the rest of the etch resist as solder mask to stay on your PCB as protection & solder repellent. The idea comes from a Bungard datasheet.


28 April 2013

Advanced SMD Soldering

Since I wrote “Secrets of SMD” it is now more an a year. At that time a soldering iron was my favourite soldering tool. In between I tried table grill ovens and a pizza skillet (=electric pizza pan) as reflow device. Success rate varied a lot with molten dark parts (=high absorption) & unsoldered silver ones (=low absorption), no possibility to interfere in the running process & generally quite dark PCBs (overheated boards).
Today I mainly use SMD soldered on a clothing iron, use a hot air gun for the back of double sided or very simple single sided PCBs & the soldering iron mainly for small corrections or soldering connectors.

This is an overview  of my recent process of DIY production of PCBs. I hope it is not too sketchy, cause I do this write-up in the pauses of board making with exactly this process – I am quite new to it – it´s fresh!

See it is a starting point for your own fast prototype-production or just a way to share some ideas.

Toolz of our Business

First we have the hot air gun, a gas burner with catalyst, you can get it for about 20 EUR. Its useful for any re-work (de-soldering & repair) of multi-pin devices. Be careful not to overheat parts.

The hot air gun

The Hot Air Gun

Hot air gun, catalyst glowing

Hot Air Gun, Catalyst glowing

Next comes a hot plate, which can also be an electric pizza pan I used before. A clothing iron has the advantage that you can also use it for the toner PCB method or heating etching solution, it´s flat & heats up very fast. Fix it to a table with a clamp in a horizontal position:

Clothing iron fixed to table

Clothing Iron fixed to Table

Next we need hypodermic needles for the application of solder paste. I prefer the black 22G size, sometimes 20G. (Updated with this nice table)

Table with Needle Colour Codes

Table with Needle Colour Codes

Hypodermic needles

Hypodermic Needles / CC 3.0 Attribution: Zephyris

For breaking the needle I scratch the surface with an electronic cutter, rotating the needle several times:

Needles cutting

Scratching the Needle Surface

Then it is like breaking glass tubes, pull & bend at the same time:

Breaking a Needle

Breaking a Needle

After deburring on sandpaper or a sharpening stone we get a nice blunt shortened needle – as syringe I use a 1ml size with a silicone stopper, types with plastic stopper do not have a smooth action (the needed ones are sold as “latex-free” insulin syringes):

Cut needles

Cut & deburred

Against drying out of the solder paste I store the filled syringes in an old marmalade container with a tight lid, some drops of IPA (Iso Propyl Alcohol) or pure ethyl alcohol are added, the cap I shortened by melting with hot air:

Syringe Container with Alcohol Vapor against drying out

Syringe Container with Alcohol Vapor against drying out


Flux is used to cover the PCB before soldering. I produce it in two forms, as a liquid and with a honey like consistency by dissolving violin rosin in IPA. 1:10 volume ratio for the liquid, about 2:1 for the paste, which means dissolving as much as possible in warm IPA. Crystallisation forming the paste occurs on cooling. It´s more like making jam.

DIY Fluxes from Violin Rosin

DIY Fluxes from Violin Rosin

Here is the cheap Chinese solder paste I use. I guess it is meant for silk-screening. Adding IPA drop-wise may be necessary to get the heavy sticky liquid state we need for our purposes.
If you know some really good lead-free solder paste I may switch in the future. But most probably the 20..30°C higher process temperature needed will force us to use some different techniques.

Solder Paste

Solder Paste


I almost forgot the most important point: Try out things to get a feeling for the process & check your materials.
In this example you can see how I marked two cleaned areas, one with the excellent “Mechanic” solder paste to the far left, the other area with a more “professional” paste which needs a totally different process & does not work here.
In the right area I tried my first needle looking for dot sizes & how the paste performs on  a oxidized/uncleaned copper surface:

Experiments with Solder & Fluxes

Experiments with Solder & Fluxes

Solder Paste Application

A little drop of solder paste is squeezed from the blunt needle and applied as a small dot on the PCB. Pointed tweezers are helpful in placing SMD parts.
(BTW: I don´t  like comments like “your fingernails need cutting” – no, they are useful for work!):

SMD Placement

SMD Placement

On complex boards, think strategically. Try to put fine-pitched parts (small distance between neighbouring legs) first, you may have to correct their placement a lot or even to wipe off all their paste. This is hard to do in a stuffed corner.

All two-terminal parts are easy – I just apply paste for the next two to five parts & drop them in position. I don’t know if that is necessary or even harmful, but I press them down a bit – I don’t want to loose parts when handling the board later.

Bulky parts come last. They are always in the way & it needs more concentration to not touch them erroneously.

Solder paste applied with 0603 SMD parts

Solder Paste applied with 0603 SMD parts


First we need to bake the paste for some minutes. I use 10mins on “Silk” then heat up 20secs to “Cotton” – here the solder paste smokes a bit, the flux does its cleaning & flowing. Finally boost up to “Linen”.

Then reflow (= melting) occurs, stay there 15secs, eventually pressing down the PCB with some pointed instrument like a small screwdriver for to reach peak temperature. Then slide off to an unheated non-metallic surface to cool down slowly. Listen to the clicks of the iron´s temperature regulator, they give acoustic feedback of the temperature you reached. Use no steam 🙂

At the reflow point you may notice several wonderful things: surface tension of the molten solder pulls together smeared solder paste & parts start sliding a bit to “click” in position if unprecisely placed. This sliding effect depends on the board design – datasheets provide you with optimized PCB patterns for this to happen if you run into problems with your design program´s generic patterns. Don’t expect everything to work the very first time.

Some caveats: An over-rapid heat transfer can cause solder splattering and the production of solder balls, bridging and other defects. If the heat transfer is too slow, the flux concentration may remain high and result in cold solder joints, voids and incomplete reflow.
When I have to deal with through hole connections I put aluminium foil under the PCB.

Reflow on the hot iron

Reflow on the Hot Iron


Finally check for shorts between adjacent IC legs. SMD-probes are useful. In any case do a visual inspection with a magnifying glass, I use a 6x & have the feeling 10x is best for our work.
Because our flux is pure rosin, it is “no clean” and can stay on the the final PCB. Cleaning with IPA and a toothbrush is also possible.

Finished soldering

Finished soldering

7 July 2012

SMD Probes DIY

Filed under: specific — Tags: , , — .. @ 21:21

More on the  little “secrets” of SMD – some measurement probes for debugging in awkward places:


As you can see in the first picture these probes are made from thick 1mm hypodermic needles – i got them in the pharmacy around the corner. They were cheap, 10 for a Euro (much less on Bay) – dont hesitate, it´s just a normal product to buy.
In the beginning I used them un-isolated but then found some tubing I removed from PC power supplies. Heating the needle a little bit & some oil as lubricant helped a lot.

But the easiest way to isolate the needles is to use heat shrink tube, that also gives the thinnest probes..

Close-up of a tip:

SMD Probe Tip

A DIY oscilloscope probe & another earlier mini probe isolated with an AWG  18 cable tube:


23 February 2012

Secrets of SMD

Filed under: specific — Tags: , , , , , — .. @ 19:19

Here is a little “secret” how I hold SMD parts in place for soldering:

SMD secrets

My version of this tool is made from a “third hand“. The lense-holder part (green) is attached to the vertical rod´s end instead of the crocodile clamp, now holding a M4-sized screw which was screwed into a piece of spring of a ball pen. This contraption can hold in place even the tiny 0603 parts.

Helping hand (tool)

From Wikipedia, the free encyclopedia

A typical helping hand

A helping hand, also known as a third hand or X-tra Hands, is a type of jig used in soldering and craftwork. A commonly produced version consists of a weighted base, arms ending in alligator clips, and optionally a magnifying glass, held together by flexible joints. The clips are used to hold a light workpiece in place while the joints allow the user to change the position or angle. ..

Helping Hand Tool

Addendum 2013:

When using solder wire nowadays it is 0,3mm Sn60Pb40 flux type F-SW 32 (Non-corrosive rosin without halides)

26 August 2011

Electrochemical Etching

Filed under: specific — Tags: , , , — .. @ 08:39


PCB etched with plain salt! Electrochemical (anodic) etching.

First test setup:

– 5% Sodium Chloride NaCl (as table salt) solution
– Warm water ca. 60°C starting temperature
– Stirring (magnetic stir bar)
– 17V DC, 1 .. 5A
– Copper clad PCB as anode with Toner Pattern (HowTo)
– Copper clad PCB also as cathode.
– measured pH 6,8 about neutral.

Here it´s only done on a scrap sample, but hey – better than expected!
The reddish slur on the bottom of the jar seems to be Cu2O, maybe with CuOH and not metallic Cu (what I wrote first)..
No toxic blue waste water! (Blue is the colour of copper in solution.). We want the copper in the residue and not in solution.
.. I will find out it turns blueish after a while. Must be some interaction with the chloride ions. Must investigate further. But in the end, I dont care  because all dissolved copper will end up on the cathode in the next electrolysis.  Btw.  the white fog is caused by the table salt, it contains a small amount of insoluble anticaking agents.

Reaction Scheme

Reaction Scheme – First Preview

Etching Setup 0

Etching Setup 0

Etching Jar CloseUp

Etching Jar CloseUp

CloseUp of the PCB

CloseUp of the PCB

The red slurry Residue

The red slurry Residue

Resulting PCB_0

Resulting PCB

Unetched PCB

Unetched PCB




Still foggy Copper everywhere..

The Etching Solution some hours later

Some hours later there is BLUE 🙁

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