Sunday, March 15, 2009

Panel plating copperclad substrates proceeds as follows:

  • Calculate the total plating time.

An acid copper plating bath based on the Lea Ronal PCM+ additive system deposits 0.0011" (1.10 mils, 28 microns, 0.81 oz) of high ductility copper in 1 hour at 20 ASF(Amps per Square Foot). Plating up "one ounce" of copper (i.e. plating 1 oz. of copper onto 1 square foot of board) is equivalent to plating a thickness of 0.0013" (1.3 mils or 34 microns).

Example: If you are starting with "half ounce" copperclad and want to plate up to a finished thickness of "one ounce", you will need to add .65 mils (0.00065"). The total plating time at 20 ASF will be:

[0.65 mils / (1.1 mils/hr.)] x 60 min./hr. = 35.5 minutes = TC

  • Calculate the required plating current.

Convert the total area of the substrate being plated into square feet (remember both sides!) and multiply the result by 20.

Example: If you are plating a 12" by 9", double-sided board, you will need:

[(12" x 9" x 2 sides)/144] x 20 = 30 Amps = C

  • Carefully inspect the substrate for deep scratches and nicks that might impair the quality of the finished circuit.
  • Format the drilling stack to minimize burr formation during drilling.
  • Drill the through-holes and mounting holes, and mill/router any slot or cavity that is to be plated.
  • Activate the hole-walls.
  • While the ink is curing, take a few minutes to analyze the electrolyte. If you have a hull cell, this is a good time to run a test to insure that the organic components of the bath (which are very difficult to test directly) are in balance and present in the proper concentrations.
  • After activation and curing, both sides of the substrate should be thoroughly cleaned to remove any trace of conductive ink from both surfaces. Any ink that is not removed will almost certainly show up in the worst possible place so take your time cleaning the board and make a good job of it!
  • An abrasive pad (e.g. Scotchbrite® pad) can be used to remove ink that proves to be too stubborn for conventional cleaning, but be careful. You must be certain that you do not break the electrical contact between the conductive ink on the inside of the holes and the copper foil on the surface of the board or the holes in question will not plate properly.
  • Rinse the board thoroughly in deionized water before proceeding.
  • Dip the board into a 10% solution of sulfuric acid to minimize the introduction of contaminants into the copper plating tank.
  • Attach the cathode clip to the board, making certain that both copper surfaces have good electrical contact to the negative terminal of the plating power supply.
  • Turn the power supply on.

Note: The power supply should be adjusted so that, at its lowest setting, it establishes an electrical potential of about 0.25 Vdc when the board is first lowered into the bath. This will help prevent the formation of a low adhesion "electroless" copper layer that might lead to trace peeling and cracking during soldering.

  • Lower the board into the plating tank halfway between the two anode banks until the top edge is at least 1" below the surface of the electrolyte.
  • Swish the board gently back and forth to drive any trapped air bubbles out of the through holes.
  • Turn on the air compressor and adjust the air flow until a uniform blanket of agitation roils the top of the bath on both sides of the board. You only need about 2 CFM (Cubic Feet per Minute) of air flow per square foot of bath surface.
  • Slowly ramp up the current (take about 20 sec.) to the value C calculated above.
  • Plate the board for ½ the total time (TC) calculated above.
  • Turn the current down and flip the board top to bottom and left to right. This will help minimize any plating non-uniformity that results from asymmetric, inconstant plating conditions.
  • Reconnect the cathode clip and lower the board back into the bath.
  • Plate the board for ½TC.
  • Remove the board from the bath and thoroughly rinse in the rinse tank to remove most of the electrolyte. Rinse the board under running tap water to remove the rest.

Note: If no outside contamination is introduced, the water in the primary rinse tank can be added back into the plating bath to make up for drag out and evaporative losses. This is crucial to reducing the effluent from this process to near zero.

  • Blow dry.
  • The plated board is now ready for further processing.

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