Electronics > Beginners
exposing double sided boards
Zero999:
--- Quote from: Simon on December 29, 2010, 11:33:08 am ---but what are transparency prices for laser ? I can probably pick up a free inkjet from someone on freegle/freecycle particularly after xmas
--- End quote ---
Tracing paper will definitely work with a laser. I've never tried plastic film but I don't see why it wouldn't work.
mikeselectricstuff:
--- Quote from: Hero999 on December 29, 2010, 02:44:28 pm ---
--- Quote from: Simon on December 29, 2010, 11:33:08 am ---but what are transparency prices for laser ? I can probably pick up a free inkjet from someone on freegle/freecycle particularly after xmas
--- End quote ---
Tracing paper will definitely work with a laser. I've never tried plastic film but I don't see why it wouldn't work.
--- End quote ---
Plastic film tends to soften through the fuser, leaving crinkles when it cools. Toner adhesion and coverage is also often poor. The rough surface of tracing paper gives good adhesion and minimal toner drift, so line density is consistent across each line - I've often seen toner 'bunch up' at the edges of lines printing on plastic.
DJPhil:
--- Quote from: mikeselectricstuff on December 29, 2010, 12:45:31 pm ---
--- Quote from: Simon on December 29, 2010, 11:34:20 am ---
--- Quote from: mikeselectricstuff on December 28, 2010, 11:21:38 pm ---The trick is to line up the 2 sides, then staple it on 3 sides to form an envelope. The key is getting the distance from the edge of the PCB to the staple right - long enough that it doesn't curl away from the PCB surface at the PCB edge, and short enough to minimise slippage. Typically about 5mm. Use small staples - the stapled thickness should be less than the PCB thickness.
You can use tape, but stapling is easier to fix without affecting the alignment.
Protect the top side form light (old style rubber mousemats are good), Turn over carefully - it helps a lot of your exposure box has a flush top to you can slide the board off instead of lifting off.
--- End quote ---
surely with staples the two layers will "rock" from side to side ?
--- End quote ---
Not quite sure what you mean, but here is no lateral shift - depending on PCB size I typically use 1 or 2 staples per side on 3 sides. It is important to use a small stapler to keep the profile low.
--- End quote ---
I believe I understand what Simon is worried about. If you staple two pieces of paper together and attempt to slide them against each other perpendicular to the staple they'll often have a millimeter or more of play due to the torsion on the staple. This could lead to registration problems.
I think it could be mitigated by stapling in a zigzag pattern or at right angles to each other. Clever mixture of the staples so they're not all parallel should do the trick. :)
mikeselectricstuff:
--- Quote from: DJPhil on December 29, 2010, 05:06:35 pm ---
--- Quote from: mikeselectricstuff on December 29, 2010, 12:45:31 pm ---
--- Quote from: Simon on December 29, 2010, 11:34:20 am ---
--- Quote from: mikeselectricstuff on December 28, 2010, 11:21:38 pm ---The trick is to line up the 2 sides, then staple it on 3 sides to form an envelope. The key is getting the distance from the edge of the PCB to the staple right - long enough that it doesn't curl away from the PCB surface at the PCB edge, and short enough to minimise slippage. Typically about 5mm. Use small staples - the stapled thickness should be less than the PCB thickness.
You can use tape, but stapling is easier to fix without affecting the alignment.
Protect the top side form light (old style rubber mousemats are good), Turn over carefully - it helps a lot of your exposure box has a flush top to you can slide the board off instead of lifting off.
--- End quote ---
surely with staples the two layers will "rock" from side to side ?
--- End quote ---
Not quite sure what you mean, but here is no lateral shift - depending on PCB size I typically use 1 or 2 staples per side on 3 sides. It is important to use a small stapler to keep the profile low.
--- End quote ---
I believe I understand what Simon is worried about. If you staple two pieces of paper together and attempt to slide them against each other perpendicular to the staple they'll often have a millimeter or more of play due to the torsion on the staple. This could lead to registration problems.
I think it could be mitigated by stapling in a zigzag pattern or at right angles to each other. Clever mixture of the staples so they're not all parallel should do the trick. :)
--- End quote ---
It doesn't really happen - first the tracing paper has fairly high surface friction, and also the tail ends of the staple pressing on the surface, combined with the rectangular cross-section of the staple wire mean it has a natural preference to spring to the nominal position it was at when stapled. With a single staple there is some potential rotation due to enlarging of the holes, but once you have 2 staples in pretty much any relative orientation, you just don't get any noticeable shift.
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