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Old 29th September 2013, 01:18 PM   #11
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Quote:
Originally Posted by akis View Post
Many thanks! The UV light box is coming over from China or from Hong Kong. I have not tried using my laser printer yet on the special transparencies I have bought - I presume one printing pass will be enough?

I use two UV tubes on a wooden boad, two tins of beans and a sheet of glass !!
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Old 29th September 2013, 01:21 PM   #12
akis is offline akis  United Kingdom
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How about pre-drilling the 4 mounting holes on the 4 corners first and use these holes to align the transparencies?
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Old 29th September 2013, 01:56 PM   #13
marce is offline marce  United Kingdom
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If you are printing from a laser or inkjet, use the heaviest weight transparency sheets you can, they are more stable and always print the image so the print side will be against the PCB to be exposed (emulsion side down), this will give the best image on your PCB. If you do a few PCBs of a regular size make yourself a jig. professional PCB fabricators work by having standard panel sizes (12" x 18" is common) and have tooling holes and alignment marks around the outside of their working panel, these correspond to jigs and carriers that hold the blank PCB and artworks.
For smaller boards use your mounting holes, for registration always use a minimum of 3 holes.
One printing pass is best, up the contrast and darkness to get the darkest image, then inspect your artworks on a light box using some paint to cover any pin holes or defects and a blade or eraser to clear any unintentional blobs. Printing twice never lands in the same place exactly leading to ghosting on the edges, you want a clear defined edge.
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Old 29th September 2013, 03:23 PM   #14
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I'm assuming that you haven't made DIY boards using this process:-

DO, DO, DO a test piece. Using a small piece of board, test your exposure, every UV tube and board will be slightly different.

Once exposed you can't go back, the aerosol cans of photo resist are a poor substitute for pre-treated boards.
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Old 30th September 2013, 07:18 PM   #15
2wice is offline 2wice  South Africa
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When you get your light box make a dummy run with pretreated boards. Take a 10cm long piece and expose at one minute each cm by sliding an opaque material out every minute. After developing and etching you will then have your exposure time for that box and brand of board.

For double sided you can make a very easy jig out of another piece of scrap board of the same thickness in the shape of a woodworking square, 90 L shape. Tape your two transparencies together at one corner only i.e. top/right, cutting one transparency slightly smaller than the other well help. Slide your jig under the bottom/left corner and tape down, tape at the other corner will keep it perfectly aligned. You can then remove the top/right tape. When you slide your board into the 90 angle, tape it down tightly onto onto the jig so you can handle it safely. You can now tape down your duplicate prints if you need it. If your prints are not so good, a once over with a white board marker will help. It adheres to the printed areas but wipes off the other. When you expose both sides one after the other, put a brick on top for a nice flat exposure. It will also help if you have a nice easy off tape. I use "invisible tape". Flux your board if not being use immediately. I have an awesome cheap homemade flux that works great. Shout if you want the recipe.
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Old 30th September 2013, 07:25 PM   #16
2wice is offline 2wice  South Africa
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When you get your light box make a dummy run with pretreated boards. Take a 10cm long piece and expose at one minute each cm by sliding an opaque material out every minute. After developing and etching you will then have your exposure time for that box and brand of board.

For double sided you can make a very easy jig out of another piece of scrap board of the same thickness in the shape of a woodworking square, 90 L shape. Tape your two transparencies together at one corner only i.e. top/right, cutting one transparency slightly smaller than the other well help. Slide your jig under the bottom/left corner and tape down, tape at the other corner will keep it perfectly aligned. You can then remove the top/right tape. When you slide your board into the 90 angle, tape it down tightly onto onto the jig so you can handle it safely. You can now tape down your duplicate prints if you need it. If your prints are not so good, a once over with a white board marker will help. It adheres to the printed areas but wipes off the other. When you expose both sides one after the other, put a brick on top for a nice flat exposure. It will also help if you have a nice easy off tape. I use "invisible tape". Flux your board if not being use immediately. I have an awesome cheap homemade flux that works great. Shout if you want the recipe.
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Old 30th September 2013, 07:38 PM   #17
AuroraB is offline AuroraB  Norway
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Developing and etching each side separately may or may not work - depending on how accurately you manage to seal the side not in the process.

I've been making prototype and smll series PCBs for almost 40 years with slightly different processes. If you want to process both sides simultaneously, you need to fix both sides of the artwork to the raw PCB, so that it doesn't move in the process. I usually make an envelope of the films, and tape the envelope to a slightly oversized raw PCB. If your new light box is single sided, you need to make sure that stray light does not fing the other side. Also - if you etch one side at the time, make sure to properly seal the side not in process.

Do make a test strip at appx 30 sec intervals, to get a feel for the intensity of the light source. BTW - which light source do you have? The rather common version with 8 15W tubes for each side usually gives appx 2m30sec per side....

You mention special foils for laser printer - If these are LaserStar foils, they are good - I've used them for 20years+++
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Old 4th October 2013, 06:41 PM   #18
MADS is offline MADS  United States
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I've made hundreds of boards as you describe. For alignment I make my overall layout 1" larger on all sides and put a target or moire on all four corners. this looks like a gun sight scope's cross hairs or a ringed target. Align both transparencies and secure with tape across one end so that they can open and close like a book. tape this sandwich on the on the opposite side bottom transparency side to the glass frame. Put the PC board onto the opened transparency and tape it's corners to the bottom transparency. Fold over the transparency top, be certain that the moires are perfectly aligned. I use a loupe to check, then tape the other corners to the bottom glass. I now put the top glass on the entire conglomeration and secure with wing nuts. I used to expose each side at a time but now do both simultaneously.
I should explain that I made my exposure frame and exposure setup from materials lying about the house. If you are going to expose in an open frame as I do in the basement, block most sunlight. It's not necessary to go crazy and have the room totally dark.

You can not do thru hole plating at home without the addition of expensive equipment. you need to remember to solder the lead to both sides of the board, or in the case of radial components mounted on the top with the ground plane on top, design the board with a hole near the bottom of one lead that clears the footprint of the component then bend the lead and pass it from bottom to top and solder the top. If the leads are small an extender trace on the bottom that clears the footprint of the component can be soldered from bottom to top using a cut off lead from other components. I always keep a supply of various thickness scrap copper leads for this purpose.
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