I'm thinking about using the photo method for etching PCBs so I need a developer for the positive photo resist.

There is this sodium metasilicate based universal developer that people online seem to praise (e.g. this ebay item) it sometimes goes by the name of SENO 4007, RS components has its own label on what appears to the same thing because the safety datasheets between the RS components one and the ebay one are very similar and both mention "sodium metasilicate" as the sole ingredient.

On the Mike's electric stuff blog he writes that this developer's formula is Na2SiO3*5H2O and the substance's name is sodium metasilicate pentahydrate but then he gives a recipe of mixing liquid glass with sodium hydroxide to produce this developer, I'm not strong in chemistry so I'm not sure this would produce Na2SiO3*5H2O and I don't wont to make things complicated for myself if I can get the same thing as a crystals and just dissolve it in water.

So I wounder would dissolving sodium metasilicate pentahydrate crystals (which is a more generic checmical that I can get locally and don't have to order by mail from abroad which I'm not sure my customs will allow through) in water give me the same results as this "universal developer" thing?

My crude understanding of this development process is that you need an alkaline (base) solution to wash off the exposed photoresist so things like caustic soda (NaOH) are used because of their base qualities. This sodium metasilicate pentahydate description says

Sodium Metasilicate forms highly alkaline solutions when dissolved in water.

So it looks like this will produce a base when dissolved in whater and this should make it into a positive photoresist developer.

I've searched online but it looks like most of the people there are no better chemists than me so I've not found a clear answer if this sodium metasilicate pentahydrate would work.

Edit: I can confirm that sodium metasillicate pentahydarate crystals work.

I've tried ordering universal developer crystals and sodium metasilicate pentahydrate crystals, both work for developing positive photoresist. The metasillicate pentahydrate I've used was labeled 57%. In both cases I've used a teaspoon of the powder per 200ml of warm tap water. The solution doesn't last as a developer so developing should be done right after dissolving the crystals. My exposure time was about 3.5 minutes, but this will vary depending on the exposure box.


1 Answer 1


Even simple Sodium Hydroxide will do fine, but like PerOxide etching it's taken a back seat, because it's more sensitive to correct dosing to get the right balance between effective and not too aggressive (on the product and/or your hands).

Yes you can make MetaSilicates yourself, yes you can order them. Ordering them will be much more pure.

As for the whole pentahydrate thing, as you should know if you're strong in Chemistry, is just an indication of the amount of water molecules the thing hangs off itself. If you have dry "Sodium MetaSilicate" it'll be a fine-ish powder. If you then leave it open long enough in a normal household you will eventually get clumps of PentaHydrate, because it absorbs water to go to its preferred state of with water molecules.

The only difference between them is the weight of the powder per amount of active ions, so find the right mixing guide for the stuff you order, or you'll be off by quite some. (5 water molecules are quite noticeable in weight against a simple MetaSilicate)


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