developer

Discussion in 'General Electronics Chat' started by mik3ca, May 21, 2008.

  1. mik3ca

    Thread Starter Active Member

    Feb 11, 2007
    189
    0
    First the transparencies, now the developer???

    obviously I wasted $20 trying to get a good board going.

    so I changed it up a bit this time. I printed TWO copies of my artwork on TWO separate sheets of transparencies from the same box and stapled them together so that I can get darker tracks.

    so I go through the exposure for over 1 hour, and place it in strong developer. turns out that 95% of the tracks disappeared.

    now I need an honest answer from everyone here. How many parts of water do I mix with one part of MGchemicals developer solution? I don't want to wait 30 minutes for the developer to work, and I don't want to find out after 2 seconds that my tracks are disappearing.

    thanks
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,699
    907
    Can you get sodium or potassium hydroxide where you are? How about sodium or potassium carbonate (Na2CO3)?

    I have used simple potassium hydroxide (sodium hydroxide, lye, will also work) and have never had a problem for over 10 years. I use 9 g of KOH per 300 mL of water (about 0.54 molar). A solution of 8.4 g/300mL (0.5 M) will also work, but I get a little better removal with the more concentrated solution. If you have NaOH, an equivalent amount would be about 6.4 g/300mL. In the US, it has become hard to buy lye at regular hardware stores, but it and KOH is readily available from suppliers for making biodiesel.

    I use sensitized boards from Injectorall. I believe, but am not certain, the chemistry of the MG Chemicals boards is the same.

    The carbonates are weaker bases than the hydroxides. They are supposed to work too, but you will have to experiment with the concentrations. I would start with 0.5 molar (about 15.9 g Na2CO3 per 300 mL) and work up.

    The real problem may be overexposure. I use a single 15W lamp for only about 15 minutes. My transparency film is relatively thick. A thinner, more UV transparent material would require a shorter exposure.

    John
     
    Last edited: May 21, 2008
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    I tried the photographic method, way back when, with bad results throughout. It was with a friend and I, and he was into photography.

    The toner transfer technique was a major relief when we discovered it. You have everything you need to use this method, is there a reason you don't want to use it?
     
  4. mik3ca

    Thread Starter Active Member

    Feb 11, 2007
    189
    0
    I have presensitized boards.

    wouldn't toner transfer make a mess on the circuit board?
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Well, sounds like the board you just tried to develop doesn't have any of the photosensitive film left on it anyway.

    Why not try Tom Goot's recipie for dry transfer on it? At this point, seems like it's either Tom Goot's method, try to manually draw your artwork on it with a Sharpie, or throw the board away.
     
  6. mik3ca

    Thread Starter Active Member

    Feb 11, 2007
    189
    0
    tom goot?

    I can't find his method on google, unless you misspelled his name.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    http://www.fullnet.com/~tomg/gooteepc.htm

    Sorry, I thought you had the link already.

    It's a lot of reading. But read it through a few times, and follow the steps. Don't try shortcuts, unless you enjoy disasters.
     
  8. Pich

    Active Member

    Mar 11, 2008
    119
    4
    What kind of light are you using? Sounds like you are overexposing the board. My best rusullts are with a utraviolet flurescent light ( the safe type). Exporesure of 7 to 10 minutes at 4 inch distance seems to work good. The developer is mixed 4 parts water to 1 part developer. The developing process is much quicker if you mix with warm water. takes less that a minute. the board needs to be pulled out of the developer and rinced with water as soon as the shiny copper can be seen.
     
  9. mik3ca

    Thread Starter Active Member

    Feb 11, 2007
    189
    0
    I'm using a "blacklight" that you can find from specialty shops. Its the same kind of light that is used in nightclubs, but you see it as purple.

    I think I'll increase the water in the mix.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I've never used the photograpic method for boards, but I did a fair bit of black & white photography many years ago. I've forgotten much of it, however...

    The strength of the light you're using vs the duration of the exposure need to be pretty carefully controlled. For a given exposure recipie with a given light source, if you double the distance of the light source to the object being exposed, you must quadruple the exposure time to make up for it.

    The ratio of developer to water is critical, as is the temperature of the solution when in use. Cold developer takes much longer to do it's work than warm developer. You can compensate for that by the time the board is in the developer solution.

    There are techniques to increase or reduce contrast, but I don't remember what they are. You basically want the highest contrast you can get.

    You might want to have a look at this black & white photography site:
    http://www3.telus.net/drkrm/
    While it isn't completely applicable to photo-resist PCB production, it has quite a few parallels.

    Here's a link to a photoresist PCB technique from the University of Arkansas EE department:
    http://www.coe.uncc.edu/~jmconrad/hsed/eleg_4tm.pdf

    They're showing 10 minutes exposure to a UV source, but there is no mention as to what the strength of their UV source is!

    However, since your traces were practically non-existant, over-exposure and over-development are pretty good bets as to what happened in your case.
     
    Last edited: May 22, 2008
  11. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,699
    907
    mik3ca,

    When your black light is not turned on, is the bulb clear or is it coated with a white phosphor? Most of the set-ups I have seen use a phosphor-coated tube. John
     
  12. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    I use a Kepro exposure frame with uncoated UV lamps. My exposure times for good results are about 90 seconds and all 5 lamps. I use plastic (3M) transparencies made on a HP Laserjet 4 at 300 dpi. the boards are positive resist by Ever-Muse, from Circuit Specialists. I get consistently good results on line widths down to 8 mills.

    It is better to mix the developer with too much water than too little. The foil should be printed so the toner side of the transparency is in contact with the resist to avoid light scattering under the plastic.

    If your resist shows a color change on exposure - mine does - then you could experiment with a window in some opaque material over a line on a transparency. You can expose limited areas at a time for various durations, and check the color change in the resist and the result in the developer to see what the best exposure time is for your setup. just make sure none of the exposed areas overlap.
     
  13. mik3ca

    Thread Starter Active Member

    Feb 11, 2007
    189
    0
    the bulb is not clear. I dont see the filament inside. the colour of it is purple.

    I think I got lucky this time because I only had the circuit in the developer for 4 seconds.
     
  14. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    You must have the concentration too strong. I mix one packet of developer (50 g) into 1 litre of water. The label simply says it's alkaline in nature. Developing time is 30 sec - 2 min. My results agree with that. A greater amount of water is not particularly problematic.

    If the concentration is too strong, that developer will go through unexposed resist about as fast as exposed. That may be your problem.
     
  15. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,699
    907
    There must be something very different in the chemistry. An unexposed board in my system (Injectorall/KOH) can sit in the developer for a long time without visible change. In fact, my greatest problem is under-removal of resist, which I why I increased the concentration of the KOH.

    I generally make a line of "zero" width in Eagle around the perimeter of my boards as a sand-to dimension. I have no problem with the developer removing it, and after etching, the width measures approximately 6 to 8 mils.

    The time in developer is not at all critical. Mine usually sit for a minute or so, then I scrub with a sponge, and if the copper doesn't look bright, I put it back in for another minute or two. (My resist is slightly more orange than the bare copper.) I watch the thin line and also dip an edge in ferric chloride to be sure all of the exposed resist is off.

    Based on these clear differences in behavior, the recipes I gave for developer may not work with your boards.

    John
     
  16. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Ever-Muse photoresist is green. Injectorall seems to be orange (I can get those boards from Digi, but they are pricier than E-M).

    mik3ca, does your developer state time and concentration, and what color is the photoresist? And are you using purple incandescents rather than fluorescents?
     
  17. mik3ca

    Thread Starter Active Member

    Feb 11, 2007
    189
    0
    my purple lights have to be flourescents. they are about 12 inches long. the bulb model is CH lighting model #F8T5/BLB

    my developer bottle is made by MG chemicals and it suggests 1 part developer to 5 parts of water. My photoresist color is green. Most of my circuit board equiptment comes from MG chemicals.

    I think it is my developer as well.
     
  18. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    That 4 seconds on the developer still suggests that there is a problem. Even an overexposed board shouldn't have the photoresist come off that fast. On the other hand, MG should know the proper developer dilution and so on.

    I see from their site that they seem to have both positive and negative resist. Which is yours? Have you watched their presentation on how to do PCB's?
     
  19. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,699
    907
    The following may not help mik3ca directly, but others may gain from it.

    As for the exposure lamps, the series of FxTx/BLB and FxTx/BL are slightly different, aside from the differences in wattage and physical size indicated by the two X's. The BLB appears dark blue, because the glass used in the bulb is different. It is a bit more difficult to pin down the differences in the phosphor, but there must be differences as the glass is just a passive filter (See: http://en.wikipedia.org/wiki/Black_light ) .

    F8T5/BLB is 8W total, maximum emission @368nm, UV power 1.2W
    F15T8/BL is 15W total, maximum emission @352nm, UV power 2.6W (This is the lamp I use.)

    The data above are from http://www.topbulb.com/find/Product_Description.asp_Q_intProductID_E_44433

    As for the resist, I could not find much on brand-specific chemistry. Here is a general article that is not too long. Scan down it to the section about Novolaks. Apparently, many if not all of the positive resists include photosensitizers in the formulation. That could explain some of the differences in color and exposure times observed. There are also differences in the resin chemistry that could contribute as well. Exposed areas on Injectorall boards turn a deep purple when exposed to caustic (presumably from formation of an azo dye). What color does the exposed resist on MG boards turn in the developer?

    One added hint I picked up was that some of the developers contain accelerants, such a choline or other organic amines. That makes sense, as the Novolaks are pretty hydrophobic, and the presence of an organic amine would help penetrate that surface. See: http://www.pcbfab.com/strppng.html

    Thus, the short story is to follow the manufacturer's directions. It appears there are few generic answers. I am sorry if my earlier comments added confusion. I was under the mis-impression that positive resists were all pretty similar. John
     
  20. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Always a surprise to find out how many different approaches there are. I went straight from Kepro boards - negative resist and solvent chemistry developer - to Ever-Muse. The price is good, as are results, so I have never experimented with Injectorall or MG boards. Or the toner transfer stuff, for that matter.

    Just for the record, the E-M green resist turns blue in the developer.
     
Loading...