Summary of Make a proper PCB exposure unit out of a cheap UV nail curing lamp
This article explains how to repurpose inexpensive UV nail curing lamps as low-cost, high-intensity UV exposure units for PCB production (dry film photoresist and UV-curable soldermask). It covers improving collimation, achieving uniform illumination across the exposure plane with reflector design, and fast exposure times, enabling fine feature exposure comparable to pricier commercial units for about $20 in materials.
Parts used in the Make a proper PCB exposure unit out of a cheap UV nail curing lamp:
- UV nail curing lamp (high-intensity UV light source)
- Reflector material or custom reflector design
- Support structure or enclosure to hold lamp and reflector
- Spacer or mount to set distance to exposure plane
- PCB exposure plane or flat board support
- Power supply for the UV lamp
- Optional collimation accessories (lenses or tubes)
What do PCB production and fake fingernails have in common? They both use UV light sources of high intensity and, as luck would have it, those light sources have exactly the same wavelength. Only the ones for PCB production are usually quite costly and the ones for fake fingernails are a bit more competitively priced.
This instructable is about how to use such a device to build a low cost light source, suitable for exposing the various UV sensitive materials encountered in printed circuit board production, like dry film photoresist and UV curable soldermask.
As well as being very low cost (around $20 for all required materials), this build addresses a few issues I’ve seen on other devices on the intertubes:
- Collimation: To simply expose a board with fairly coarse features, you wouldn’t need to do any of this. You could just use the nail dryer as is and call it a day. But to be able to expose small features (down to 5mil, according to this site), you have to make sure all your UV rays come from the same direction, which is exactly perpendicular to the board you are exposing.
- Uniformity of illumination across the whole exposure plane. Imagine you want to expose a really big board, e.g. A4 or letter sized. You’d want the same amount of energy over the whole board, without hot or dark spots. For this, the energy source has to have a certain distance from the exposure plane and you need either a very tightly packed array of UV sources (like UV-LEDs, which can be rather pricey), or an effective reflector design for the UV sources you have at hand, which is what I came up with.
- Exposure time: I have no idea how fast this source is with pre-sensitized positive copper clad material, as I’ve never used that stuff, but with dry film photoresist it feels really fast. Like under two minutes fast. The thing is, I’m not really qualified to properly interpret the results, so I have to gather a few more opinions on this one.
So, while being very low cost, this build will enable you to achieve results that match, or (in some cases) even surpass those of devices that are up to 10 times more expensive.
For more detail: Make a proper PCB exposure unit out of a cheap UV nail curing lamp
- Can a UV nail curing lamp be used for PCB exposure?
Yes, because the lamp uses the same high-intensity UV wavelength suitable for PCB photoresist and soldermask exposure. - What advantages does this build offer over using the lamp as-is?
It improves collimation, uniformity of illumination, and can achieve fast exposure times for fine PCB features. - How does the build ensure uniform illumination across large boards?
By positioning the energy source at a certain distance from the exposure plane and using an effective reflector design to avoid hot or dark spots. - Is expensive equipment required to expose fine PCB features?
No, with proper collimation and reflector design a cheap nail lamp can expose small features down to around 5 mil according to cited information. - How long are exposure times with this device for dry film photoresist?
Exposure with dry film photoresist feels very fast, under two minutes according to the author. - Does this build work for pre-sensitized positive copper clad material?
The author has not tested pre-sensitized positive copper clad material and does not know the exposure speed for it. - How much does the build cost?
About $20 for all required materials according to the article. - What is the main goal of adding collimation?
To make sure UV rays come from the same perpendicular direction to achieve fine feature resolution on the PCB.
