Spraying photoresist - Page 2 - Electronic Circuits Projects Diagrams Free

Hero999 · 24th February 2008, 06:02 PM

A 1mm air gap is fine for 1kV

A 2mm air gap is fine for 2kV.

But neither of these measurements account for tracking which can occur at much greater distances.

Tracking occurs when water condenses on the surface of a material placed between the electrodes, forming microscopic droplets which effectively reduce the electrical distance between the two conductors.

If you don't have enough room leave a 5mm gap between the mains and DC side and don't want to bother with a conformal coating you can cut a slot in the PCB between the traces. This stops the tracking as there is no surface where condensation can build up on.

There are different classes of insulation, single insulation. and double or reinforced insulation.

On a 200VAC to 250VAC circuit:

Single insulation only needs to hold off the nominal mains voltage and must have a minimum breakdown voltage of at least 500V.

Double or reinforced insulation must not ever fail under any circumstances and must have a minimum breakdown voltage of at least 2kV.

Single insulation between an exposed metal part and the mains is fine, providing the part is earthed. If the part isn't earthed, double or reinforced insulation must be used.

An example of single insulation is a 1mm gap between PCB traces or some thinly insulated wrapping wire.

An example of double insulation is a mains appliance's cord - there are literally two layers of insulation between the user and the mains (the insulation on the cores and the outer sheath).

An example of reinforced insulation is a multimeter test lead - the insulation is very thick and won't break down at 2kV.

Another example of reinforced insulation is a 5mm gap between PCB traces because there's no chance of tracking even at 2kV.

The same rules apply to separating a SELV (Safety/Separated Extra Low Voltage) circuit (a circuit with a nominal voltage not exceeding 25VAC or 60VDC), (which is what the DC side of your circuit is) and the mains. You can earth the SELV circuit (in which case it becomes a protected ELV circuit) and use single insulation or no earth it and use double insulation.

In short electrical safety can be a nightmare which is why home building of mains powered projects is discouraged.

EDIT:
Is the copper filling between the mains connectors a ground plane?

Just earth it, it'll prevent the ELV side from floating at mains potential.

pitronix · 24th February 2008, 06:09 PM

I have been doing small quantities PCB manifacturing for some time and again I have to advice people to try using silk screening with PVC colors. It is easy enough and pays out in a long run much more then all other methods. You just print as many pices as you need and etch it with H202 and HCl solution. For using Positiv 20 and another sprays you need lot of practice but it can be done if you realy take some time to finde right way to do it :-)

HerbertMunch · 24th February 2008, 06:49 PM

Quote:

Originally Posted by pitronix

I have been doing small quantities PCB manifacturing for some time and again I have to advice people to try using silk screening with PVC colors. It is easy enough and pays out in a long run much more then all other methods. You just print as many pices as you need and etch it with H202 and HCl solution. For using Positiv 20 and another sprays you need lot of practice but it can be done if you realy take some time to finde right way to do it :-)

would you recommend silkscreening for single boards?

Hero999 · 24th February 2008, 06:56 PM

Here's a couple of links regarding clearances.
http://www.ce-mag.com/archive/01/Spring/Lamothe.html
http://www.ce-mag.com/ce-mag.com/arc...uctSafety.html

It's quite complicated, so just sticking with earthing, conformal coating or ensuring that the secondary side has more than 5mm of clearance from the primary side should keep you safe enough.

**3v0** · 24th February 2008, 07:32 PM

Quote:

Originally Posted by pitronix

I have been doing small quantities PCB manifacturing for some time and again I have to advice people to try using silk screening with PVC colors. It is easy enough and pays out in a long run much more then all other methods. You just print as many pices as you need and etch it with H202 and HCl solution. For using Positiv 20 and another sprays you need lot of practice but it can be done if you realy take some time to finde right way to do it :-)

It is my GUESS that anyone who can not manage a toner transfer will have little chance of making and using a silk screen. Could be that the process has changed since I used it.

What chemicals does it take?
How do you create the mask?

picbits · 24th February 2008, 08:42 PM

Quote:

Originally Posted by Nigel Goodwin

Your mains connections are really badly (and dangerously) designed, why on earth have you got copper filling in between the mains pins?.

But the actual PCB looks really great!.

My exact thoughts.

If I dont leave at least a couple of miles between any high and low voltage stuff on the PCBs I design (even 12v and 5v) then I don't feel comfortable with them.

Having traces that close for 220v is asking for trouble though.

picbits · 24th February 2008, 08:46 PM

I've got a complete silk screening setup here in the workshop (with 50kgs of fabric ink rather than the solvent based stuff unfortunately).

I'll probably try using it for screening PCBs when I go into quantity production of some stuff I'm working on to see how it goes.

I'll be looking at making up around 50-100 double sided boards a week so the silkscreen and etch method could be quite handy.

The only problem I can see is removing the ink from the solder pads but with a small cnc machine this could be achievable.

jpanhalt · 24th February 2008, 10:15 PM

Quote:

Originally Posted by picbits

The only problem I can see is removing the ink from the solder pads but with a small cnc machine this could be achievable.

Here are two other options:
1) Use something like conformal coating (acrylic lacquer) as your "ink" and solder though it. Of course, you need the right lacquer/coating for that.

2) Remove all of the ink/paint, then re-silkscreen the areas that won't be soldered.
John

kchriste · 24th February 2008, 11:06 PM

Sexy PCB!

As mentioned by Hero999, adding an AC ground termination to the fill pad around the 220V input would be prudent. It appears that the fill area is already connected to the DC negative supply so this should not be too much of a problem to retrofit. You could almost bodge a 3 pin screw terminal block in place of the 2 terminal one, though it would hang off the edge of the board a bit and would detract from the sexiness a bit.

pitronix · 25th February 2008, 11:16 AM

Quote:

Originally Posted by HerbertMunch

would you recommend silkscreening for single boards?

No I would not

**3v0** · 25th February 2008, 11:59 AM

Quote:

Originally Posted by pitronix

I have been doing small quantities PCB manifacturing for some time and again I have to advice people to try using silk screening with PVC colors. It is easy enough and pays out in a long run much more then all other methods...

If you are going to suggest people try a process you need to specify what you are talking about.

HerbertMunch · 25th February 2008, 12:36 PM

Quote:

Originally Posted by pitronix

No I would not

ok thanks.

AtomSoft · 25th February 2008, 01:41 PM

Would it be safe to say i can follow this tutorial:
http://www.ele.tut.fi/~telok/MakePCBs/

From Step 9 and up using
http://www.rapidonline.com/productin...catref=34-0150

?

mvs sarma · 25th February 2008, 02:29 PM

while the positve20 is also costly process, for those who prefer to use, I suggest that they try spin the copper clad immediately after spay. This would make uniform distribution and even drying of the material sprayed. This was what a friend was doing when he made few PCBs way back in 1985.

on1aag · 25th February 2008, 02:48 PM

Hi Chris,

Quote:

Originally Posted by HerbertMunch

Does anyone have any experience with spraying + photo resist on to pcbs?

When i use commercially coated boards, i get really good results, however when i spray my own, the caustic soda just rips off all the coating during developing.

Also I cant seem to achieve a consistent coating. speckles appear all over the surface, like if you were spraying water onto a water proof surface.

Id really like to use the spray, as its much cheaper than buying the ready sprayed ones.

Many thanks,
chris.

If you (or your board) have speckles when spraying that's because there
is a residual layer of dirt and/or grease on you(r board). It is absolutely
necessary to degrease the surface of the board before spraying.
About the spraying itself, you have to start spraying beside the board
and then gradually and evenly move the can over the board from left to
right and back. So start and stop spraying when you are beside the board.

on1aag.

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24th February 2008, 06:02 PM	(permalink)
Hero999	A 1mm air gap is fine for 1kV A 2mm air gap is fine for 2kV. But neither of these measurements account for tracking which can occur at much greater distances. Tracking occurs when water condenses on the surface of a material placed between the electrodes, forming microscopic droplets which effectively reduce the electrical distance between the two conductors. If you don't have enough room leave a 5mm gap between the mains and DC side and don't want to bother with a conformal coating you can cut a slot in the PCB between the traces. This stops the tracking as there is no surface where condensation can build up on. There are different classes of insulation, single insulation. and double or reinforced insulation. On a 200VAC to 250VAC circuit: Single insulation only needs to hold off the nominal mains voltage and must have a minimum breakdown voltage of at least 500V. Double or reinforced insulation must not ever fail under any circumstances and must have a minimum breakdown voltage of at least 2kV. Single insulation between an exposed metal part and the mains is fine, providing the part is earthed. If the part isn't earthed, double or reinforced insulation must be used. An example of single insulation is a 1mm gap between PCB traces or some thinly insulated wrapping wire. An example of double insulation is a mains appliance's cord - there are literally two layers of insulation between the user and the mains (the insulation on the cores and the outer sheath). An example of reinforced insulation is a multimeter test lead - the insulation is very thick and won't break down at 2kV. Another example of reinforced insulation is a 5mm gap between PCB traces because there's no chance of tracking even at 2kV. The same rules apply to separating a SELV (Safety/Separated Extra Low Voltage) circuit (a circuit with a nominal voltage not exceeding 25VAC or 60VDC), (which is what the DC side of your circuit is) and the mains. You can earth the SELV circuit (in which case it becomes a protected ELV circuit) and use single insulation or no earth it and use double insulation. In short electrical safety can be a nightmare which is why home building of mains powered projects is discouraged. EDIT: Is the copper filling between the mains connectors a ground plane? Just earth it, it'll prevent the ELV side from floating at mains potential. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez Last edited by Hero999; 24th February 2008 at 06:09 PM.

24th February 2008, 06:09 PM	(permalink)
pitronix	I have been doing small quantities PCB manifacturing for some time and again I have to advice people to try using silk screening with PVC colors. It is easy enough and pays out in a long run much more then all other methods. You just print as many pices as you need and etch it with H202 and HCl solution. For using Positiv 20 and another sprays you need lot of practice but it can be done if you realy take some time to finde right way to do it :-) __________________ Aude, Vide, Tace

24th February 2008, 06:56 PM	(permalink)
Hero999	Here's a couple of links regarding clearances. http://www.ce-mag.com/archive/01/Spring/Lamothe.html http://www.ce-mag.com/ce-mag.com/arc...uctSafety.html It's quite complicated, so just sticking with earthing, conformal coating or ensuring that the secondary side has more than 5mm of clearance from the primary side should keep you safe enough. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez

24th February 2008, 08:46 PM	(permalink)
picbits	I've got a complete silk screening setup here in the workshop (with 50kgs of fabric ink rather than the solvent based stuff unfortunately). I'll probably try using it for screening PCBs when I go into quantity production of some stuff I'm working on to see how it goes. I'll be looking at making up around 50-100 double sided boards a week so the silkscreen and etch method could be quite handy. The only problem I can see is removing the ink from the solder pads but with a small cnc machine this could be achievable.

24th February 2008, 11:06 PM	(permalink)
kchriste	Sexy PCB! As mentioned by Hero999, adding an AC ground termination to the fill pad around the 220V input would be prudent. It appears that the fill area is already connected to the DC negative supply so this should not be too much of a problem to retrofit. You could almost bodge a 3 pin screw terminal block in place of the 2 terminal one, though it would hang off the edge of the board a bit and would detract from the sexiness a bit. __________________ --- The days of the digital watch are numbered. ---

25th February 2008, 01:41 PM	(permalink)
AtomSoft	Would it be safe to say i can follow this tutorial: http://www.ele.tut.fi/~telok/MakePCBs/ From Step 9 and up using http://www.rapidonline.com/productin...catref=34-0150 ?

25th February 2008, 02:29 PM	(permalink)
mvs sarma	while the positve20 is also costly process, for those who prefer to use, I suggest that they try spin the copper clad immediately after spay. This would make uniform distribution and even drying of the material sprayed. This was what a friend was doing when he made few PCBs way back in 1985. __________________ Regards, Sarma.