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LPKF System - "EasyContac" very expensive "kit" @ $450!
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Eyelets - inexpensive, difficult to use, not 100% reliable
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Soldered Wire - amateur look, not pretty & time consuming
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Conductive Silver - a new technique!
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Conductive Epoxy - another new technique!
James Mitchell submitted a working technique for making very reliable plated-thru holes. His procedure is shown below. We're also working on a variation on his theme using the "conductive silver" technique to plate the holes using a non-photographic mask. This technique when perfected will hopefully solve two problems... having a solder mask and plated-thru holes together!
We've been thinking and experimenting with good success by making a combination solder mask and "via" artwork print on a color printer using solid yellow and green tones (which is actually yellow and cyan). The mask is fused to the copper surface not unlike the circuit image originally done with black toner and the GreenTRF film. When it's just toner, the image will withstand high reflow temperatures whereas toner overcoated with GreenTRF foil will not becuase it's plastic.
The idea is very similar to James's technique below with a few twists. Liquid conductive silver from CircuitWriter would then be applied to each via from each side using a toothpick then lightly blown out to form a coated, conductive hole. We'll keep you abreast of the progress in this area as it developes.
The following technique for making "Plated-Thru Holes" was
submitted to us by James Mitchell (jhmitchell@sympatico.ca)
Introduction:
- After many years of trial and error (i.e. conductive inks, plating tanks, soldering wires between layers), I developed this inexpensive method for ‘plating the holes on my double-sided prototype printed circuit boards. By adding a few simple steps to your board drilling process you too can connect the top and bottom sides of your prototype printed circuit board.
Materials:
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Avery Laminating Sheets (73603)
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Permatex ‘Quick Grid’ (Rear Window Defogger Repair Kit (auto parts supply store)
Equipment:
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Shop Vac
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PCB Drilling Method
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Oven (a toaster ovens work well)
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Small squeegee
Procedure:
- After both sides of your prototype printed circuit board are etched, I use Pulsar’s toner transfer method follow these steps to ‘plate’ the holes in your circuit board.
- Fully clean the printed circuit board surfaces utilizing water and a scotch-brite pad until to you have a bright copper reflection. Dry the printed circuit board with paper towels or a hair dryer while handling the board by the edges assuring not to leave any finger-prints.
- Cut two sheets of the Avery Laminating Sheets to size to fully cover your printed circuit board. Remove the laminating sheet backing and apply to the board surface assuring not to wrinkle the sheet. Use a hard plastic straight edge (old ruler) to apply pressure to the laminating sheet and remove all air bubbles.
- Use your normal method to drill all of the holes. A 10K plus RPM drill works best and provides the cleanest holes.
- Use paper towel to wipe off all drilling dust from the laminate.
- Hold the board at a 30° degree angle over a flat surface covered by paper towel. Pour a small amount of the Permatex Quick Grid on the board at the lower portion making a small pool of the liquid. Using the squeegee pull the liquid up over the holes in the board until they are completely covered. (hold the board up to light to verify full coverage) Using your shop vac, run it quickly over the opposite side of the board until the holes are now open. Now flip the board and repeat the process, this will ensure the inside of the holes are fully covered by the Permatex.
- Remove the laminate slowly by pulling it from one corner. It should come off in one piece.
- Place the board in the oven at 150°F for approximately 1 hour.
The ‘plating’ process is now done and all of the holes should be connected top to bottom.
Note:
I have utilized this process with SMT boards where I place the components with solder paste and heat the board to 450°F to reflow the paste, even multiple times, and the plating has stayed intact. JHM