Saturday, January 18, 2014

PCB fab - Toner transfer method



I finally perfected the toner transfer method for fabbing my own printed circuit boards.  David Kelley of Ideo says "Fail often to succeed sooner."  Let's just say that the video above was not my first attempt at this process...



I recently picked up a used HP laserjet 5000. The main paper tray feed is broken, but the single feed tray works fine.  This is perfect for printing toner transfers!  You can find them on amazon for around $200, here.



With the printer set to use maximum toner density, I printed a sheet of fabkit arduino boards (plans from MIT here) for practice using this method of making an etch resist for a pcb.  I use toner transfer paper by Pulsar, here.



In the past I've attempted to use a clothes iron to apply heat to the transfer paper, but decided to pick up a cheap laminator to hopefully simplify the process.  This one works like a charm, as long as I run the board through several times.







I found that folding a bit of the paper over the edge of the copper clad board helps hold it in place as it goes through the laminator.




As SOON as the board runs through the laminator, toss it in some room temperature water (as shown in the video at the beginning of this post.)  In the past I've waited too long before putting it in the water, and it doesn't release properly.




Next I add a layer of green TRF foil.  This will adhere to the transferred toner and strengthen the resist against the acid.  Again, I fold a bit over the edge of the board.



And run that through the laminator...



I peeled the TRF foil away, and voil√†! The resist is complete.  Time to etch...



For that, I do what printmakers call the "Edinburgh Etch."  A mixture of ferric chloride, citric acid, and water will etch the unprotected copper away from my board.



I add some adhesive-backed craft foam so the board will float in the acid...







Normally I use an agitator to keep the acid moving around, but I'm currently in the process of upgrading mine.  In that case, I make sure to have the copper side of the board facing down, so that the copper will fall away from the board as it etches.



The board after the etch...




Resist removed with acetone, board trimmed on my bandsaw & beltsander.



My arduino SMD components...



And after (painfully) soldering the tiny components, the board is finished!  Next step would be flashing the atmega chip, but I'll save that for another post.



3 comments:

  1. I'll teach you how to solder smd parts if you teac5 me how to do this. Very cool!

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  2. i'm coming over and we're making art.

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