Need some kind of substance...

[throbscottle]

Well, I thought I'd had a genius moment when my wife threw a Baby Bel at me and after eating it I realised the wax casing is about the right consistency for pushing into holes and staying there.
So I tried it today, and can wholeheartedly say it's a really bad idea. The wax goes into the holes reasonably well, you can force it in with your fingers. Seems to clean off the board surface well enough too.
I've now wasted the 2nd lot of photo-resist applied to this board as it won't stay stuck, even with extra soapy board cleaning. The wax gets drawn out of the holes during cleaning and makes an invisible film that just keeps hanging around, even if the water sheets over the board, normally indicating it's clean enough.

As an aside, I tried a hydrochloric acid "pickle" for the board before plating it this time. Quite scary but very effective!

 

[Nigel Goodwin]

Hmmmm - love Baby Bels

 

[throbscottle]

New information!
(I'm calling this the "long series of c*ck ups" board)
I've attached some photos to illustrate what I'm talking about.
I have discovered there is quite a difference in how dry film photoresist behaves, depending on how old it is!
It wasn't the wax causing the problem, well it was a little bit. What I've discovered is the old photoresist I was using which is quite old and has gone a pale violet colour, works really well if it's wet. It loves water and a good hot laminator.
The new photoresist I've got is much fresher, and it's blue, much bluer than the old stuff ever was. It likes slight dampness, and a lower temperature laminator. With a completely dry board, I was able to re-position the film, but on the other side I tried breathing on the board before applying the film, and it stuck down quite well before even putting it in the laminator. So now I'm having to wind the clock back in my dry film process.
All this took 5 attempts to find out. Wasted quite a lot of photoresist, with two sides, glad it's a small board.
So the next thing, etching, again didn't go right. Thin copper left between the tracks in some places which I couldn't see until way too late. I've had it before with this copperclad so it may be a problem with the cheap crappy stock I'm using. Of course I only found this after I'd stripped the resist off and done my short/open tests. Colouring in the tracks with a Sharpie and sticking the board back in the ferric chloride cured that. Harder to clean though.
Something that went really well and I'm really pleased with, all the signal vias are conducting, all the pads with connections on both sides connect through the board. Can't individually test the ground vias but I put lots in to make up for any duff ones. So the wax has done a good job there. Last board I did wasn't tented properly on some pads so the plating got etched out.
The solder resist (the main point of the whole business with the wax, in case you forgot) went on really well, no problem with it going through the holes, except the corner ones which I took the wax out of. No more air bubbles than for a single sided (therefore, not pre-drilled) board.
However, more trouble with that, over-exposed the component side so some pads have resist on them, and the board mustn't have been clean enough with all the messing about as some cured resist peeled off with the cover sheet.
So I just need a better hole filling material and some better methods...

 

[rjenkinsgb]

How about a paste or putty made from white PVA glue and a filler powder such as cornflour to minimise shrinkage?

Once it's dried hard,it should be stable enough to last while the photoresist dries, but once you are done with it a few hours soak in soap and water should allow it to wash away cleanly?

 

[throbscottle]

I had been thinking exactly the same thing, having just learned of "oogoo" made of silicone and cornflour, however silicone isn't practical to keep around for occasional slight use. PVA (or at least, the PVA I've got) is fairly waterproof so it shouldn't wash away easily, but should push out easily enough.
The photo-resist doen't require any drying time. The "substance" just needs to survive accidental exposure to etchant, though the holes are supposed to be protected by the resist "tenting" anyway.
Slight concern, I suspect PVA reacts with copper in some way. Guess I'll just have to experiment.
I pushed some components into the board , came out with little blobs of wax on the end, so it came out cleanly enough.

 

[throbscottle]

Ah ha!
I think this is what I need: https://www.ebay.co.uk/itm/50ml-5-l...hash=item41b835d84c:m:mEijl6eTRxPOjY_401Pq-Tg
possibly with a thickener - cornflour is cheap but known to work (well enough for me, anyway).
I can make my halloween costume whilst I'm about it, then....

 

[unclejed613]

Thin copper left between the tracks in some places which I couldn't see until way too late. I've had it before with this copperclad so it may be a problem with the cheap crappy stock I'm using. Of course I only found this after I'd stripped the resist off and done my short/open tests. Colouring in the tracks with a Sharpie and sticking the board back in the ferric chloride cured that. Harder to clean though.

it's possible there's some kind of oxide or something on top of the copper causing bridges. try cleaning the copper with steel wool before applying the etch resist

 

[throbscottle]

it's possible there's some kind of oxide or something on top of the copper causing bridges. try cleaning the copper with steel wool before applying the etch resist

Hi Unclejed
It would be good advice (I believe steel wool is especially good for removing oxide) but, the original copper laminate has already been cleaned extremely thoroughly, then soaked in caustic soda (Lye), then pickled in hydrochloric acid, before being plated with a layer of fresh copper, so the original laminate doesn't have a cleaning problem. On this board I then plugged the plated holes with wax before applying resist, which worked though it made a horrible mess, so got a very very thorough cleaning. The un-exposed resist is then removed with a strong solution of washing soda and gentle brushing, which would also tend to remove any last trace of wax.

The copper which is left, giving me a problem, is like a thin film of copper, almost invisible until after you've seen it. I've only ever had it with this particular board stock (the previous time was before I could do any TPH) which is why I think the composition of the copper may be uneven since it occurs in narrow spaces as well as large areas. It seems ulikely that it's due to any residual resist because the copper goes pink as soon as it's in the ferric chloride. I do agitate the boards as much as is possible in a takeaway food container.

An interesting effect I have noticed is that in places the traces have a sort of "double edge" where the copper I've plated on doesn't etch at the same rate as the original copper.

I think I just need to etch them a bit longer.

 

[throbscottle]

Unfortunately with the wax, now I've soldered everything on, the solder wouldn't track through the holes when soldering components, even with plenty of extra flux, which I was really looking forward to seeing happen.

So now I need to design some other boards to make so I can try with this latex (arrived a few days ago, very stinky sfuff!)

Ah well, have to see how it goes with the next one...

Thanks for all the suggestions everybody!

 

[unclejed613]

An interesting effect I have noticed is that in places the traces have a sort of "double edge" where the copper I've plated on doesn't etch at the same rate as the original copper.

I think I just need to etch them a bit longer.

it's possible that the copper you are plating onto the board is a)unevenly deposited on top of the original laminate, so that there are areas where the copper is thick in some areas, and thin in other areas (which can be caused by hydrogen bubbles on the cathode surface, or uneven current flow between the cathode and anode) or b) may contain impurities from the plating process, such as traces of iron or nickel, or traces of the "carrier" salt that was mixed with the water. the surface of plated copper is also very rough compared to the original laminate, and may etch unevenly due to to variations in the surface roughness. is there any particular reason you are trying to add more copper? also, if you are going to continue trying to plate the laminate, make sure you clean the laminate with alcohol to remove traces of oil...
EDIT: is the plating step intended to plate through the holes? if so, you shouldn't be filling the holes with wax or latex during the plating process, but only during the etching process. during the plating process all of the board, except the holes should be masked so that the plating only happens inside the holes. one other thing to think about, is using the board to be etched as an anode. put the etch resist on the board and use it as an anode. this will etch the board, and allow you to recover the copper that was etched away.

 

[throbscottle]

Hi Unclejed
Yes, I am making plated through holes at home (see post #1). I've based what I do on well established commercial processes, as I understand it, it is normal to either plate the whole board (panel plating) or mask off parts to be etched away and plate only the tracks (pattern plating). I'm doing panel plating because it's simpler and always leave large ground areas so there's not much being etched away. Nobody (as far as I have read) plates only the holes.

I'm not filling holes prior to plating! Don't know how you've got that idea, though this thread has been quite meandering and I've had to explain a few times.

Filling the holes has 2 purposes.
Primarily, it's to prevent liquid epoxy solder resist going in the holes when I apply it. (see post #1)
Secondarily it's a backup means of preventing holes being accidentally etched if the resist doesn't cover them properly.

The plated copper is actually very bright and shiny, though I wonder if there is something in your uneven-ness theory. What I've noticed is there's a vertical groove above or below (not sure which) each hole. I could definitely do with a better quality anode, it's just made of very thick wire so the phosphor content will doubtless be all wrong. Can't say I've noticed any bubbles, but perhaps I should set up some sort of agitation.

 

[throbscottle]

Well, in case anybody is interested, I tried the liquid latex today. A bit too runny to fully plug the larger holes, but it filled the small ones ok. The little plugs popped out very nicely in the end although the result wasn't actually useful (though still better than nothing)
Some problems I encountered:

• When removing surplus latex from the surface of the board, it tends to pull it out of the holes as well because it sets very quickly.
• Whatever solvent is in the latex reacts with copper and oxidises it, I think it dissolves it a bit too. Not good, took the shine right out of the holes and off the board surface.
• When I pushed the rubber plugs out of the holes, there was still some resist hanging around which got dragged into the holes, completely defeating the object of plugging them!

So I think I'm going to experiment a bit and thicken it as much as it will stand, which might be enough to make the problems go away.

Apart from that, I'm starting to think of switching to transfer film resist instead of all this buggering about with the liquid.

Apart from all that, it was one of the worst f***k up boards I've made. Maybe because I was tired, grumpy, over-confident and trying to rush. Not a good day...

 

[gophert]

Well, in case anybody is interested, I tried the liquid latex today. A bit too runny to fully plug the larger holes, but it filled the small ones ok. The little plugs popped out very nicely in the end although the result wasn't actually useful (though still better than nothing)
Some problems I encountered:

• When removing surplus latex from the surface of the board, it tends to pull it out of the holes as well because it sets very quickly.
• Whatever solvent is in the latex reacts with copper and oxidises it, I think it dissolves it a bit too. Not good, took the shine right out of the holes and off the board surface.
• When I pushed the rubber plugs out of the holes, there was still some resist hanging around which got dragged into the holes, completely defeating the object of plugging them!

So I think I'm going to experiment a bit and thicken it as much as it will stand, which might be enough to make the problems go away.

Apart from that, I'm starting to think of switching to transfer film resist instead of all this buggering about with the liquid.

Apart from all that, it was one of the worst f***k up boards I've made. Maybe because I was tired, grumpy, over-confident and trying to rush. Not a good day...

Latex (a polymer that is typically not soluble in water) is stabilized with ammonia (like the household cleaner). The insoluble latex polymer chains are held into little micelles and can be compared to fat globules in milk. In other words, they are not dissolved, just dispersed but in well-defined structures (micelles). As the ammonia and water evaporates, the little micelles of latex start to lose their micelle-like structures and the acrylic polymers in each dispersion micelle spill into the water and become entangled with each other. Eventually enough micelles lose their structure to solidify the mass. The mass gets stronger/more rigid over time as more water and ammonia get out - but evaporation is slower and slower as the mass gets more and more viscous.

A new Lesson of the Week will be available next Sunday.

 

[throbscottle]

Why thank you! I thought it smelt like ammonia but I wasn't sure what ammonia smells like. So now I know it's smells like liquid latex!
So does ammonia react with copper? Or could the (apparent) oxidation be more to do with the acrylic polymers doing their stuff?
I look forward to next Sunday!

 

[gophert]

Why thank you! I thought it smelt like ammonia but I wasn't sure what ammonia smells like. So now I know it's smells like liquid latex!
So does ammonia react with copper? Or could the (apparent) oxidation be more to do with the acrylic polymers doing their stuff?
I look forward to next Sunday!

I was having so much fun explaining how latex solidifies that I forgot to tie the story back to your situation. Yes, Ammonia promotes the oxidation of copper on water - especially when the water is open to air as in your case. The copper will turn bluish to greenish as it corrodes - color depends on a lot of things.

Typically, Ammonia is a gas at room temperature but is highly soluble in water. It partially ionizes when in water and the solution is typically called ammonium hydroxide.

 

[ClydeCrashKop]

The PVA that I am familiar with is Polyvinyl Alcohol mold release agent for fiberglass.

https://fiberglasshawaii.com/How To_DIY/PVA how to.pdf

I have no idea if it would serve your purpose but it would fill the holes and it is water and alcohol soluble. It does stick to a surface when sprayed or brushed on but not very well. You can peel it off.

It might be worth looking into.

 

[throbscottle]

Looks like it would do the job nicely but I'm still dubious about traces of resist getting dragged into the holes when popping the plugs out. Any that gets in should get carried away when the PVA is cleaned off but that might not happen. It could be an expensive experiment.
The only other idea I have now is to use silicone instead of latex. I didn't try it first because it contains acetic acid. Also may be too sticky.

 

[throbscottle]

Oh hang on, you mean to use the PVA instead of latex? Interesting.

 

[gophert]

Oh hang on, you mean to use the PVA instead of latex? Interesting.

See post #13 of this thread. Someone you know well suggested that long ago.

 

[throbscottle]

Different sort of PVA but yes, I'd forgotten about that. I'll give it a go. Thanks for the reminder!