DIY PCB manufacture - etching problems.

Other Hardware General Electronics
1

I'm new to the business of making PCB's and am having mixed results from my efforts. I'll describe what I'm doing before getting into the problems. I use the free version of eagle CAD (conveniently its size limits just allow a mega shaped board). I design my boards with 0.254 inch track and 0.254 spacing. I print the designs on a Samsung ML-2525W printer onto LaserStar translucent film (http://www.megauk.com/artwork_films.php), then I expose to UV using a commercial light box (http://www.megauk.com/uv_exposure_units.php) before developing for about 30 seconds and then etching in ferric chloride.

When I first started doing this my printer was new and everything seemed to be working fine, after dozens of successful boards , something started to go wrong, after examining the boards under a 20x microscope I noticed that many of my tracks were 'over etched' and in some cases etched right through. I tried reducing the etch time, but this just left a lot of the board incomplete. After a lot of head scratching I compared some of my early artwork (from successful boards) to my latest artwork (from unsuccessful boards) and discovered that the printer had started laying down quite thin layers of toner, which was probably leading to poor development of the board, and hence to poor etching.

I bought a new cartridge for the printer, but the error remained. I then tried a genuine Samsung toner cartridge (thinking the 1st might have been a cheap Chinese knock-off) but still no improvement.

Any suggestions? Is my guess that the thinness of the toner layer is the root of the problem likely to be correct? Or could there be another problem ? The chemicals and acetates haven't changed, the only difference I'm aware of is the toner cartridge, I've tried running the acetate through the printer multiple times to build up a thicker layer of toner, but it's impossible to get the two layers to align, I've tried using two copies of the same artwork (on two sheets), but again its almost impossible to get them to match up.

The only other solution I can think of is to start using much thicker tracks with greater clearance but this would force me to use larger designs and larger boards.

2

You have said toner and ink.

Which is it.

Edit

You do not mention the boards.

Are they old ?

The latest boards from cie require 1/2 the exposure of megas own, have you done an exposure test.

3

You have said toner and ink.

Which is it.

Is it significant? aren't the two the same? It's the black stuff that comes out of a laserjet cartridge

4

You have said toner and ink.

Which is it.

Having re-read my own post, where did you spot the work 'ink' - I can't see any use of the word!

5

I was sure i saw it, sorry.

I dislike mega laserstar specificaly because its opacity makes it difficult to double up.

Need a lightbox for a proper result, for small boards i photograph a plain surface with ipad.

I have a samsung laser which i have never had a satisfactory result from and use inkjet.

However clearly something has changed , if its not due to the boards as mentioned above i can only think its the printer.

One problem i encounter sometimes with my inkjet is that some of the advanced printing options get fiddled with by other programme use.

Being acetate a much heavier print is required, just selecting acetate in the print dialogue does not work , i have to fiddle in the advanced settings.

6

Hi,
In the printer window that comes up when you want to print, you need to explore preferences, the tabs/buttons to find a parameter that sets the contrast/darkness and even quality of your print.
You may have toner save on.
I use a brother printer and it has a density control.
Sorry I have not used it for PCB prints.

Tom.... :slight_smile:

7

I find that laser prints are not sufficiently opaque especially on large areas, well not from my HP Laserjet. My inkjet printer is much better if used in Photo mode. Exposure time is also critical. Before use do a test strip with various exposure times.

My UV source is sunshine. Coming from a source 93 million miles away it is as even as you can get. Three seconds is about right for the dry film resist I'm using.

Are you really using ¼ in tracks and spacing!

Russell.

8

Sorry to hijack , dry film resist , is that posotive working please ?

9

Boardburner2:
Sorry to hijack , dry film resist , is that posotive working please ?

Negative.

This is the one I'm using.

Russell.

10

Thanks for the input guys.

Are you really using ¼ in tracks and spacing!

No! The width is shown on eagle as 0.254, but doesn't mention units, I guess it must be millimeters. Basically very fine tracks very closely spaced. (must get into the habit of re-reading my own posts!)

The boards and chemicals have always been from the same supplier, and are rarely more than a few months old. Since I first encountered problems I have been scrupulous in ensuring I've always used fresh chemicals (particularly developer)

Before use do a test strip with various exposure times.

Yes, I did this when I first started with making my own boards, I have tried tweaking the times but with no significant improvement.

i can only think its the printer.

my conclusion to!

In the printer window that comes up when you want to print, you need to explore preferences, the tabs/buttons to find a parameter that sets the contrast/darkness and even quality of your print.

I have searched all the options I can find. I have selected "darken text" and "best quality" there is no "black as hell" option that I can find!

clearly something has changed

Yes, the only noticeable change is that the tracks on my old artwork were very, very black, but the tracks on my new artwork are just dark grey. The printer itself is the same as I have always used, my understanding is that all the clever stuff in the printer is actually in the printer cartridge, so when this gets replaced you're effectively getting a new printer. I think the issue is that the new cartridges I can currently buy just aren't as good as the one that came with it when it was new. The cynic inside me makes me think that the manufactures supply printers with very good toner cartridges to make them appear to be top quality, and then supply low grade replacement cartridges to force you to buy a new printer!

11

The cynic inside me makes me think that the manufactures supply printers with very good toner cartridges to make them appear to be top quality, and then supply low grade replacement cartridges to force you to buy a new printer!

That would be a valid conclusion.

Maybe it is time to start using the photo resist method.
I have never had a problem with it and can easily do 5 thou traces reliably.

.

12

@russellz

How do you laminate the sheet to the PCB copper?

13

Im not russel but what i do is float the resist on water and lift laminate up under then squeegee and hot roller laminate.

Thats for negative working solder resist.

I do not use negative working etch resist though.

The same method works for lamination of photoresist but i have never had much luck due to the large areas of black required from the printer.

With a proper photo black master however i find this method to be fine.

Using inkjet and positive resist i can also do 5 thou tracks but i have to double up for reliability.
Contrast of the photomaster seems to be the key.

OP
i do not understand whats happening. I have never had any joy with using laser toner as a photomaster and thats having tried many different lasers.
The fact you had sucess with your first attempts which failed later surprises me.

Can i suggest you try with thinner tracks.
Toner deposition depends upon electrostatic charge, i noticed that large areas were always much less dense than small ones, largely noticed whe trying to use negative resist.

14

Fulliautomatix:
I have searched all the options I can find. I have selected "darken text" and "best quality" there is no "black as hell" option that I can find!

I do not have pc acess at the moment but from memory the options i was referring to were not available from the print dialog.

They were acessed via the file (save as ?) menu.
I will try to chack tomorrow where i found them.

15

Can i suggest you try with thinner tracks.

Please see my subsequent correction, I'm actually using very thin tracks quite closely spaced.

i noticed that large areas were always much less dense than small ones

Very true, it's noticeable that large areas of black (i.e. the ground-plane on the circuit) come out particularly thin. I often have to go over some areas of the artwork with a pen to make some areas more opaque. But this is very difficult to do with the more complex and fiddly areas.

I have never had any joy with using laser toner as a photomaster and thats having tried many different lasers.

I first started making PCB prototypes about 25 years ago (as part of my job), like you I found laserjet printers produced poor artwork. When I came back to making PCBs about two years ago (just as a hobby) I was pleasantly surprised to find laser-jet technology seemed to have moved on and better quality PCB artwork could be produced. It's a shame the improvement didn't last!

16

Fulliautomatix:
Please see my subsequent correction, I'm actually using very thin tracks quite closely spaced.
Very true, it's noticeable that large areas of black (i.e. the ground-plane on the circuit) come out particularly thin. I often have to go over some areas of the artwork with a pen to make some areas more opaque. But this is very difficult to do with the more complex and fiddly areas.
I first started making PCB prototypes about 25 years ago (as part of my job), like you I found laserjet printers produced poor artwork. When I came back to making PCBs about two years ago (just as a hobby) I was pleasantly surprised to find laser-jet technology seemed to have moved on and better quality PCB artwork could be produced. It's a shame the improvement didn't last!

Blue and red tape ?

I had a laserjet II.

When i replaced it i removed the scan head to try making a photoplotter.
Costly mistake, did not realise how sensitive the film is (its sensitive to safelights) has to be totally dark.
At 300 per roll i only had one go.

17

OK I found the settings I was looking for.

Unfortunatley they are specific to the driver of the rather old inkjet that I use.

I assume you have tried reinstalling the original driver.

If your printer has had a lot of use it may require cleaning, I recall on one printer the corona wire caused problems and needed regular cleaning.

Its possible that the transfer roller has become tired though if its had a lot of use.

18

LarryD:
@russellz

How do you laminate the sheet to the PCB copper?

  1. Clean the board. I use Micro-mesh abrasive sheet, expensive but lasts indefinitely, and water.

  2. Remove protective film from resist.

  3. Mist the board with water and lay the resist film on. Rub with soft cloth to remove any air.

  4. Lay paper over the top and iron on with a hot domestic iron. (I don't have a laminator.)

  5. You're ready to expose and go.

Russell.

19

Its possible that the transfer roller has become tired though if its had a lot of use.

Isn't the transfer roller part of the toner cartridge? (there's definitely a roller of some sort on the cartridge). I thought that 99% of the clever bits of the printer are actually in the cartridge, not the printer, so when I replace the cartridge, I'm almost getting a new printer?????

I have replaced the cartridge recently, with what is claimed to be a proper samsung spare.

20

Hi,
If I were you, I'd buy another printer, then when the toner runs out, either buy a refill kit on ebay, or buy a new printer.
Here the printers are just about given away, cheaper than the replacement cartridges.

Seriously when you change the cartridge do you change the drum and do you clean the charge on and charge off wires.
Might be worth googling the problem, or how to service your laser printer.

Tom..... :slight_smile: