Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

YAET (Yet Another Etching Thread)

Status
Not open for further replies.

arhi

Member
Hi guy's

Quick question. Can someone give me a good argument why not to use H2O2 + HCl for etching my PCB's??? I see that everyone is talking about ferichloride and few other solutions, but not many ppl are mentioning this solution that is purchasable on every corner (you can get HCl in better grocery store as it is used for cleaning, and you can get hydrogen peroxide in any farmacy).... I'm using this solution for years without a problem but after reading that much about ferichloride ... I decided to ask if there's a reason?

thanks
 
Last edited:
Hi guy's

Quick question. Can someone give me a good argument why not to use H2O2 + HCl for etching my PCB's??? I see that everyone is talking about ferichloride and few other solutions, but not many ppl are mentioning this solution that is purchasable on every corner (you can get HCl in better grocery store as it is used for cleaning, and you can get hydrogen peroxide in any farmacy).... I'm using this solution for years without a problem but after reading that much about ferichloride ... I decided to ask if there's a reason?

thanks
what time it takes to etch a board with artwork covering 50% of area for say 3*2 inches board, with your etchant?

I feel , though I was not a chemistry student in graduation, that HCl is likely to retain its acidity effect in the phenolic or epoxy substrate and thus lower the insulation property, and this aspect is not desirable, to what ever extant you try to neutralize the effect.
 
Last edited:
the board I etched few days ago ... (my camera is with my wife out of town so cannot take a pic now) is 10x10cm covered maybe 20% (so 80% of the surface needed to be removed).... the etching took 10minutes with 60% HCl (10%) and 40% H2O2 (8%). If you increase the amount of H2O2 (the original recipe is 40% HCL and 60% H2O2 but that etch too fast and can "pull up the copper") you can go much faster.

What I often do is make a (double the acid) solution and then add drops of H2O2 with syringe on top of "large areas" that need to be removed... that way I get 10x10cm board etched in 3-5min and with "nice edges"... I'm waiting for a new toner (this one is dead) to make few new boards so I will post a pictures (press n peel + laminator -> etched with HCL+H2O2)... no warming needed - outside temperature (was around 3-5 degrees when I did this one)

I used to use this etching solution some 15-20 years ago (made boards with letraset then, with lines and circles and ...) ... ferichloride show up later and it was "non transparent", you had to "warm it up", it was "eating trough anything", leaving marks on the kitchen sink ... so I skipped it...
 
H2O2 + HCl works. I tried it a few times, but didn't like it as well as ferric chloride or cupric chloride. I have now changed to the latter, which can be regenerated easily.

Why didn't I like the peroxide method?
1) It is quite aggressive and tended to eat my photoresist too. That may vary with different photoresists. I suspect tonor is quite resistant, so the TT people may not have that problem. Edit: This is the main reason.
2) I live in a cold climate and do not have a heated "outside" place. I do my etching in the kitchen. I didn't like the fumes and splatter from the HCl.
3) Perhaps surprisingly, I find it easier to get reagents for the other methods than to get anything more than 3% hydrogen peroxide in my community. 3% was just too slow.

John
 
Last edited:
jpanhalt, thanks for sharing the exp.... as I do use TT and 30% H2O2 can be purchased in pharmacy some 10m from my house (I purchase 8 or 12%, but tried once with 30% was funny) ... I do not have a problem :)

did not know that ferric chloride / cupric chloride are "less aggressive" .. that's interesting, so you might get "better edges" with ferric chloride??
 
I suspect most of the information on under cutting is purely empirical. Chemcut, a maker of commercial PCB etching equipment, has a very good technical note. See:
https://www.electro-tech-online.com/custompdfs/2009/02/cupric-chloride.pdf

Here is one chart from that note:
etch-rate-gif.26124


Since the HCl concentration in the peroxide method may be quite high, or perhaps harder to control, I would expect variation in the extent of undercutting as your initial solution is used multiple times. That is not to say HCl concentration cannot be controlled, but I suspect few hobbyists do that. Of course, using fresh solutions each time also controls the acidity, once you get your formula right. Ferric chloride and cupric chloride may simply allow higher chloride concentrations without corresponding increases in the H+ concentrations.

Also, you may find this interesting about cupric chloride:

**broken link removed**

John
 

Attachments

  • etch rate.gif
    etch rate.gif
    8.8 KB · Views: 572
Just to let ppl know, hydroponics stores carry 35-50% H2O2 for not much money at all really.. The stronger the peroxide, the better its shelf life, but be careful, this stuff ain't usable as mouthwash..:)
They also typically sell 10% and 85% phosphoric acid for pretty cheap if you need that for anything..
Anybody know the common molarity of HCl (muriatic acid) commonly sold for cleaning?
 
20°Baume is about 10M or 32%. See: Wikipedia for a complete table.

John
 
Thats some strong HCl.. When I was in grade 11 chemistry we had a general procedure lab in September to refresh our wafting protocol etc.. Anyways, we were to compare the physical properties of 1.2M and 12M HCl..
I had quite a bit of labs that used 1.2M HCl before and had no fear of it.. I grabbed the flask, and shoved my nose in it instead of wafting for an odour description..
Oops!!!! Somebody thought it was funny to draw in a decimal with black pen..:(
I momentarily lost consciousness, fell backwards into the bench behind me, spilled the flask all over myself ruining my clothes and causing serious irritation, and I had nose bleeds for about 6 months..
Somehow though I got lucky and it missed my eyes..
 
The HCL sold in local stores as cleaning agent is 10% (donno about molarity). You can much higher concentration in specialised stores but I never needed it... The whole point of this is - it is cheep as hell (~1$ for 1L of HCL, ~1$ for 300mL of H2O2 12%), I always use a new solution, just do not want to think about "storage tank" etc, I do not make PCB's every day (on contrary), I dilute it, add bicarbonate soda and flush down the toilet.

jpanhalt, I'm not sure I understand the graph 1/1 ... It shows that increasing the HCL concentration in the solution will increase the speed of etching, but from what I can tell from first hand experience, more H2O2, more etching speed ?!?!?!

Anyhow, from what I can tell, there is no real reason for moving to another etching solution.

Thanks
 
The text for the graph explains a bit more what it is supposed to show.

As for your comment on costs, etc., I couldn't agree more. Use whatever works with what you can find easily. Once your PCB is in a box or in flames, who will know or care what you used to etch it.

John
 
Last edited:
Question for the ones using the photo method...

BlackLight tube (for e.g. the small ones used to check euro bills), how good they are for exposing the UV sensitive emulsion? I'd like to hear from someone who actually tried as I found bunch of different opinions on the google.
 
I am not familiar with the light used to test Euro bills. I suspect it is UVA (400 to 320 nm). In discussing UV, I prefer to refer to the wavelength, as that is not ambiguous. The manufacturer of your photoresist will tell you what wavelength is needed. It will probably be something around 366 nm +/-10 nm. However, some emulsions react to visible light.

Wikipedia gives the definitions of UVA, UVB, and UVC. Since you will be using regular glass, not quartz to press the positive image and sensitized plate together, you can be vitually certain your plates need UVA for exposure.

As for which bulb is best, check the label on the bulb. One clue is the appearance of the "glass." If it is perfectly clear, it may very well be a germicidal lamp with a quartz or quartz-like (Vicor) envelope. They emit mostly at 254 nm and are no good for making PCB exposures. For one thing, none of that wavelength light will get through the plate glass pressure plates.

If the tube looks white when it is off, if is probably a UVA bulb with a white phosphor. In the USA, it is type BL.

Different emulsions seem to be more or less sensitive to the light. MG's plates seem quite sensitive, based on reports I have read. I use Injectorall, and 3X15W new UVA bulbs at <6 inches take about 10 minutes. You can roughly judge your exposure time by the wattage, but it is not a precise calculation, and distance from the plates makes a difference too.

Good luck.

John
 
Thanks John ... the tubes I have are "purple/black" when off and "dark purple" when on. They are like ones used in this new age clubs so your teeth light up and your eyes glow .. I have no idea what is the wavelength it emits, just that fluo stuff glow in presence :)

Not too important, when I get chance I'll try it out, looks like that's the only sure way
 
The purple /black bulbs are almost certainly type BLB and are often called black lights. Wikipedia is quite confusing on the difference between BLB and BL. In one place, it shows BLB as having a max emission at 350 nm and BL at 370 nm, then in another place, it reverses the wavelength assignments. I believe the BLB's phosphor is designed not to emit as much visible light as the BL. BL bulbs are used in tanning booths and bug lamps. BLB are used in aquariums and for reptile tanks. I have never used the BLB bulb, as Injectorall recommends the BL bulb.

John
 
yes, I also found that tubes used in tanning salons are "the way to go" ... thing is I do not have those ones :(, I have few BLB ones and was wondering if I can use them ... but seams to me - I cannot ... I'm currently using the "street light bulb" from wich I removed the "outter white glass" .. but problem is that it emits UVA and UVB, and UVB is not nice, not nice at all.
 
Actually, I would give the BLB bulb a go at it. The plate glass is a good filter for UVC and a large part of UVB. At least the BLB is defined, whereas the street lamp is not.

When I made my new exposure unit, I took a single piece of PCB and calibrated it at 5 exposure times using a piece of black plastic to cover the glass. The first section exposed was the longest exposure at the end of the run. You could do something similar with your BLB bulb. So as not to waste the PCB completely, I used a small circuit I had been planning to make and just made 5 copies, two of which turned out good.

John
 
good idea ... I was planning to make a "light box" with these tubes (3 of them) .. I also have a "normal white" neon tubes of same size so I will make a light box (wooden box, 3mm glass on top) and give it a go .. if I get some results cool, if not, I will replace the blacklight tubes with normal ones and give the box to my wife to copy stencils :) (she mentioned it few times last year) so no waste of time :)

I do not have much experience with photo process, I'm using the current UVA (from the street light) to harden some epoxy resins... for PCB I'm used to TT but fancy to try photo process.
 
Here is one old PCB etched with HCl + H2O2 (this is actually the first ever board I did using blue press 'n' peal foil.. The board was not clean enough so I had to retush the board with a marker ... I used CD marker and the results were awful :( (as you can see) ... but, you can see how the etching solution did the job ... (pic is 2M 300dpi png)
 

Attachments

  • pcb2.png
    pcb2.png
    2 MB · Views: 211
Here is one old PCB etched with HCl + H2O2 (this is actually the first ever board I did using blue press 'n' peal foil.. The board was not clean enough so I had to retush the board with a marker ... I used CD marker and the results were awful :( (as you can see) ... but, you can see how the etching solution did the job ... (pic is 2M 300dpi png)

Wah! Very Nice Arhi. Good job. I really want to follow it up.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top