Photoresist etching

FWIW, any photoresist I've used takes a lot to fully expose it, and it takes UV. Commercially they use things like mercury arc lamps. What's great for exposing the stuff is really bad for your skin and eyes. Maybe the lamps from an EPROM eraser would work, or some quartz halogens with no protective cover- blocks the UV. Bright sun perhaps?
 

EssB

Member
2009-01-02 1:49 pm
Hang on, if all your resist dissolves away in the developer then you've over exposed it. At least that's the way the stuff I use works - exposed parts dissolve away and then get etched away, non exposed parts ... leave copper.
Have you tried doing a test strip ?
FWIW I use 2 mins UV exposure in a fairly 'bright' UV box.
 
If you are using MG Chemicals presensitized boards (from Fry's) about 30 seconds under bright midday sun with a piece of glass usually works. The image on the transparency film needs to be dark. I take my artwork to the local reprographics shop and print black only on a Canon color laser copier ($2-3 for an 8.5x11) and spot with a black Sharpie to cover any pinholes. Keep trying!
 
Another vote for doing a test strip. It's the only way to be sure.

With inkjet or laser-printed artwork, I use two layers so it's completely opaque.

I've never used sunlight to expose boards; I started with a photoflood intended for home movies, then used incandescent tanning bulbs, and finally got a pair of fluorescent tubes, probably F15T8/BL.
 
Hang on, if all your resist dissolves away in the developer then you've over exposed it. At least that's the way the stuff I use works - exposed parts dissolve away and then get etched away, non exposed parts ... leave copper.
Have you tried doing a test strip ?

Chimed in to say the same: in **positive** boards light *destroys* emulsio, so you are overexposing.
Much worse, you already expose them too much *before* even exposing :eek:
Peel them only inside a room, use only a 25W yellow lamp; incandescent!! , not CFL nor Fuorescent tubes.
Tape your transparency over the PCB or the glass so you don't move it and get a piece of cardboard.
expose 1 minute, cover 1/4 of the image, then complete 3 minutes, cover an extra 1/4; then 9 minutes and finally 27 minutes, so you have 4 widely different exposed areas.
Develop.
Then repeat, splitting time between the best 2.
In a couple tests you'll have the proper time.
 
I go to a local print shop that has an image setter and get a film made, trying to get a truly opaque layout at home is near futile. I use an unfiltered blacklight fluorescent and an 8 minute exposure through a pane of glass with the MG positive boards. Also ensue the developer isn't too strong. I get my best results at home with the photo method but the big key is absolutely opaque artwork.
 

gentlevoice

Member
Paid Member
2007-10-20 7:46 pm
Denmark
@buzzforb:

Hi,

I've actually had a similar "challenge" - the photoresist just disappeared when I tried to develop the board no matter how long/short I made the exposure time. Took me days to figure it out :-(

Eventually I ended up getting a different developer from the vendor and now everything works fine. FYI I was using Seno develop 110 (which for some reason didn't work) and now I use Seno 4006 (a concentrate) together with Seno positiv 100 (the photoresist lacquer). Also, I use a pre-made photoresist PCB and that works as well. According to the vendor the Seno products are also very environmentally friendly.

To expose the PCBs with UV light (needs to be UVA range) I use a Babyliss Hawaii UVA "face browner" (like this - in Danish:

http://www.dba.dk/ansigtssol-babyliss-uva/id-89392883/

which I found second-hand for about 14 Euros. Works excellently with exposure times of 35 seconds for my self-applied photoresist lacquer and about 2 minutes for the pre-made photoresist PCB.

I print out the PCB tracks on overheads with a laser printer setting it to maximum blackness (as it's done on this printer). With this setup I can easily make sharply defined TSSOP28 package tracks etc.

Hope this may help.

Best regards,

Jesper
 
RTFM. Avery clever acronym. Simple, solution. 10 parts water to 1 part developer:headbash: I have been using straight developer.

I was about to post just that when I noticed you had already found the answer. MG developer needs 10:1 (water to developer), The average board needs very little to do the job. I use the cap from a can of board protector.

A few years ago I was able to obtain a Kinsten UV light box on Craigs List. It's a fantastic bit of kit. It has a vacuum system to suck the film tight on the board and a timer circuit to control top and bottom exposures. I've never needed more than 75 seconds exposure.

I do all my film on a laser printer set to 1200 dpi. It doesn't seem dark enough when you look at it and I used to double up the transparencies. This gets very difficult on double sided SMD boards and it isn't necessary. If the exposure time isn't to high then single films at 1200 dpi are fine. The photos show what you can get with a single film pre and post etch. You can easily get 5 mil traces. Notice the writing on the board.
 

Attachments

  • DTI 3.3 Pre Etch.jpg
    DTI 3.3 Pre Etch.jpg
    789.8 KB · Views: 92
  • After etching.jpg
    After etching.jpg
    660.4 KB · Views: 90