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  1. #1
    nuskulu
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    UV Photo PCB development problem

    Hey guys,

    I've been reading some posts on this forum so I figured out I'd ask you guys, since you tend to give good info here.

    I'm trying to build the UV lamp method to be able to use the UV method of PCB manufacturing.

    So far I've had to bother my neighbor to land me his UV lamp and the process has never failed me.

    So I know it's a simple circuit, and I don't need a schematic for it, however I do have a question:

    I own a bug zapper that kinda has 2 UV fluorescent lamps in it (that's used to attract the bugs to it). I was thinking of dissembling that device and use the UV lamps from there.

    Only problem is: I also own a pair of glasses that react to the Sun and they shade automatically with sunlight. However, when exposed to this UV lamp, the one from the bug catcher, they don't shade at all, even after long exposure.

    So my question is: is the UV lamp from the bug zapper any good to be used for the PCB manufacturing, and if so, what would be a good distance from the PCB to use the lamp on, and for how long. I can give you the dimensions and power of the lamp if needed.

    Thanks in advance,
    Nusku

  2. #2
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    Re: UV Photo PCB development problem

    It really depends on the brand and the intensity of the UV light



    •   Alt18th December 2010, 15:29

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  3. #3
    nuskulu
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    Re: UV Photo PCB development problem

    They are 2 x 6W and the markings on the tube are: YF6T5BL

    I don't know if that helps at all, they are about 23 cm long, 15 mm in diameter and they are white on the inside, like a normal fluorescent light,

    also on their choke they have the following info:
    A = 0' 16 and the Lambda = 0,53

    Does this help tell if they are good?



    •   Alt18th December 2010, 15:47

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  4. #4
    FvM
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    Re: UV Photo PCB development problem

    they are white on the inside, like a normal fluorescent light
    The UV lamps I know from EPROM erasers and PCB exposure machines have a clear glass tube. They are regular low pressure mercury vapour lamps, but without a fluorescent (white) layer inside the tube. Insect lamps have a special fluorescent material to achieve maximum UVA (350 nm) intensity. They may be suited for PCB exposure as well, even standard CFL or halogen quarz incandescent lamps can be used with sufficient exposure time. The latter have the advantage of giving sharper reproduction compared to using mutiple CFL. I would do a test before diassembling the bug catcher.


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    •   Alt18th December 2010, 16:59

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  5. #5
    nuskulu
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    Re: UV Photo PCB development problem

    I've already dissembled the bug catcher, i took out the UV lamps and the choke, as well as the starter.

    any idea on the minimal exposure from these types of lamps to achieve the necessary effect? also could you recommend a good distance from the pcb in order to achieve the optimal result?



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    Re: UV Photo PCB development problem

    for UV about 10 sec should be enough. I use CFL, took me about 10 to 15 mins :)

    ---------- Post added at 17:49 ---------- Previous post was at 17:49 ----------

    You will be able to see the light sensitive layer changes colour from light green to dark blueish green :)



  7. #7
    nuskulu
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    Re: UV Photo PCB development problem

    i'm using the store-bought photoresist pcb's so i can't see the color difference. any suggestion how far from the PCB shoulf i place the UV light for optimal performance?



  8. #8
    FvM
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    Re: UV Photo PCB development problem

    Distance, as near as acceptable for uniform exposure, e.g. 10 - 20 cm. I would start with a test exposure over a wider range (by stepwise moving an opaque cover), may be 10 sec to a few minutes.


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  9. #9
    nuskulu
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    Re: UV Photo PCB development problem

    thanks for the advice, I'm working on the project now, however for some reason I can't get the damn lamp to turn on, i think it's because of the choke, it has 4 poles and I can't seam to figure which 2 are the right ones... -.- annoying.



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    Re: UV Photo PCB development problem

    To identify the correct photoresist exposure I suggest you to use a "21 step Stouffer transmission wedge" like 1, 2, ...
    I bought mine from Cape Fear Press*

    To my knowledge, the most used photoresists (like ORDYL Alpha 930 I'm using) require an exposure between 6 and 9 of the Stouffer scale.
    Some Soldermasks (like Dynamask 5000) require a value from 12 to 15; Dynamask KM instead require a value from 8 to 10.
    If you get a wrong exposure value, it is enough to modify your exposure accordingly to the instructions on the first 2 links.
    Using the Stouffer scale will help you to get the best results for the material you are using: you have only to ask to the photoresist producer what are the suggested exposure values.

    Please remember that the efficency of your lamps will be different if they were heated before the use or not. Because of this, I suggest you to keep the distance from the lamps and your PCB more than 15-20cm: your exposure will be longer but you will get a more uniform light distribution and (due to longer exposure) a more repeatable total light output.
    I NEVER suggest to use an exposure less than 60 seconds: if your lamps are more powerful, put them at a greater distance.

    - - - - - -

    Regarding the wavelength required by typical photoresists, in general it is accepted from 350 to 450 nm, so your "insect killer" lamps are more than good enough.
    Please DO NOT use UV lamps with a shorter wavelenght than 350nm (like UVB lamps or EPROM erase lamps): they can be really dangerous to your eyes.

    - - - - - - -

    When you work with photoresists, I suggest you to use as an inactinic lightning device like those (first link I got using google). The CFL ones like this one are very good because they permits you to work with a very good illumination.


    *) Just an happy customer: even if living in a different continent, I got it in a very few days (12USD).


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