Think & Tinker, Ltd.
P.O. Box 1606, Palmer Lake, CO 80133
Tel: (719) 488-9640, Fax: (866) 453-8473
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||Acid Copper Electroplating
Cu Plating Baths and Consumables
- Can I use copper sulfate that is in powder form? I'm not so sure how to mix it, since the guide I have only deals with liquid copper sulfate.
Copper sulfate "powder" is actually made up of very fine
crystals. The recipes on the web contain instructions for mixing acid copper plating
solutions using both liquid copper sulfate (CuSO4) and crystalline copper
sulfate pentahydrate (CuSO4•5H2O). Go to: Acid Copper
Plating Solution .
Specifically, you want 10 to 12 oz of copper sulfate crystals per gallon
of plating solution. To make up a single gallon of acid copper electrolyte, add:
- 25 oz (weight) or 1.6 cups (volume) 98% sulfuric acid to 3 quarts (12
cups) of COLD deionized. The solution will heat up VERY rapidly as you add the acid so be
- Heat the solution to 60C (140F) and slowly stir in 10 oz. of copper
sulfate flakes. Stir until ALL of the crystals are dissolved.
- Add 0.63 cc of 35% HCl (hydrochloric acid) and 19 cc of Copper Gleam
- You have added a little less copper sulfate than you actually need
but the anodes, when they activate, will quickly make up the difference.
If you are planning to use the crystalline form, be sure that you
specify "snowflake crystal", "plating grade" or "high
purity" copper sulfate pentahydrate. The industrial or agricultural grades may
contain impurities (e.g. iron and chloride) that will be detrimental to the proper
functioning of your bath.
- When I am going to pattern
plate my circuit anyway, why do I first have to panel plate the board just after holewall
To insure that all of the through-holes in your finished board are
completely covered with a uniform layer of copper, it is essential that the conductive ink
layer deposited during activation
be as conductive as possible to optimize deposition and adhesion. Exposing the conductive
ink to the developing solution can result in a "surface poisoning" of the
exposed conductive particles, making it very difficult to plate.
- How do I determine the
total surface area of exposed copper when I am pattern plating?
Hopefully, your CAM software will give you the total combined surface
area of all your circuit elements (on both sides of the board). All you will have to do is
add in any surrounding copper that is not covered with plating resist. If your CAM
software does not provide this critical datum, throw it away and pick up a package that
does. Stop by the vendor's web site to thoroughly flame them on your way to the dumpster.
- How do I account for
the area of the holewalls when I am pattern plating?
When determining the area that you are pattern plating, only use the
area that is exposed on the SURFACE of the board (e.g. traces and pads). This is a very
good first order approximation since the contribution of the walls of the through-holes to
the total surface area is somewhat masked by "electrostatic" effects at the rim
of each hole.
- What will the effect be
if I reduce or increase the plating current to a value other than that calculated using
Generally speaking, reducing the plating current to about 10 ASF
increases the "throwing power" of the plating bath making it easier to plate
inside of the through-holes. A good practice is to plate a freshly activated board at
reduced current for 10 to 15 minutes. During this time all of the hole walls should become
completely covered with a shiny layer of electrolytic copper. After all of the holes are
covered, you can boost the current up to 20 ASF to continue building up the bulk copper on
The effect of increasing the current above the calculated value is
somewhat less predictable. The electrolyte recipe in the web site has been tested at
current densities up to 40 ASF with acceptable plating up to 30 ASF. At plating current
densities above 20 ASF, there was an accelerated consumption of the organic additives as
well as an increase in the production of organic contaminants.
- Why are some of the
through-holes in my board not plating? Some are partially covered with copper while others
do not seem to have been plated at all.
- Before assuming that the problem is with your system, please
Pay close attention to the section that describes holding your board up
to the light to make sure that ALL of the holes are filled after you spread out the ink.
- Also read: Acid Copper Plating
Remember to swish the board back and forth a few times to remove any air
bubbles that might be trapped in the holes.
- Other problems that result in poor throwing power:
High copper - low acid - Other than poor conductive inking technique and trapped air bubbles, this is
the primary cause of poor or inconsistent plating of activated through-holes. You need to
check your bath to insure that the ingredients have been mixed in the correct proportions.
A high acid level can dramatically improve throwing power. Generally speaking, it is safe
to operate a bath with an excess of acid (max. 15% by volume) so adding more is often a
quick fix. Brightener stability is not affected by increasing the sulfuric acid content.
Exceeding 15%, however, might cause dissolved copper to begin to precipitated out of
solution in the form of tiny suspended crystals that can roughen the board during plating.
Brightener shortage - Assuming that your bath is new and that you followed the mixing procedures
accurately, this is not your problem. In an older bath, however (or a new one that has
seen lots of use) brightener level can fall if the bath is not properly maintained. See: Hull Cell for a
concise treatment on how to determine the level of brightener function in your bath.
- Why are my plated boards
coming out rough, like copper plated sandpaper?
Deposit roughness can result from a number of sources. To wit:
- Anode type - Phosphorized copper (0.04 - 0.08% phosphorous by assay) sheathed with
polypropylene or Dynel bags or packaged in machined Porex® tubes is ideal.
OFHC copper, copper plumbing pipe, or copper wire is not sufficiently pure to avoid the
presence of copper particles in the plating solution.
- Anode bags or tubes - check for holes or breaks in the bottom seal by filling with
water and allowing to drain. Watch closely to see of water pours out of any one area.
- Solution clarity - It is always a good idea to continuously filter a plating bath
at the 1 to 5 micron level. If you use your bath infrequently, and are very careful
to maintain the chemistry and not allow foreign materials to enter the solution, you can
often get by for a while without filtering. Sooner or later, however, you are going to
have to provide some means of removing the particulate contamination that inevitably
begins to accumulate.
- High chloride - Above 125 ppm chloride ion content, there is a tendency to
produce roughness and duller deposits. Letting the bath stay idle with the sparger running
overnight is usually enough to drop the chloride content significantly. Hull cell testing
or chemical analysis should always be used to determine when the proper chloride level is
- Low brightener - In extreme cases, low brightener can contribute to surface
roughness. Hull cell testing should always be used to determine the amount of brightener
to be added.
- Why is my plated
copper coming out dull? Does it matter?
From a practical point of view, dull copper will conduct
heat and electricity just as well as bright, shiny copper. The problem is that, a change
from bright to dull plating can indicate that some form of contamination has entered your
solution. Some types of contamination will not materially affect the performance of the
plating solution. Others will lead to severe deterioration of both the operation of the
bath as well as the quality of the deposited copper. Some common causes include:
- Brightener shortage - Use a Hull Cell to determine whether your bath is
low on brightener. Excess brightener (up to 3 normal strength) is not harmful and can be
beneficial in the presence of organic contaminants in holding stress levels at a minimum.
- Low chloride - Less than 20 ppm chloride can result in dull deposits. Analyze the bath and restore the chloride content to its optimum level.
- Organic contamination - Dull deposits, possibly accompanied by step plating around the
through-holes, are occasionally the result of the build up of organic contaminants in the
electrolyte. For best results the entire volume of the bath should be oxidized with
stabilized hydrogen peroxide
followed by carbon treatment using an approved activated carbon filter.
- Why should I add copper
electroplating capability to my PCB shop?
The short answer to this question is that you would add
copper electroplating if you wanted to fabricate printed circuits with plated
through-holes. Electroplating is cheaper, faster, and far more reliable
than using mechanical rivets (a.k.a. eyelets) to achieve front to back connectivity. If you are thinking about adding multilayer capability later on, copper electroplating
will be essential.
Copper plating is also very handy if you do not have a way
to create negative artwork. Using positive artwork and pattern plating
with copper (for surface build and through-hole plating) and tin/lead (as an
etch resist), you can actually make boards superior to those made using
conventional "print and etch".
- How many boards can I plate with a
standard charge of anode material?
Assuming that you will be starting with "half
ounce" copper clad (0.00065", 17 micron foil on both sides of the
substrate), and plating up the thickness to "1 ounce" (0.0013", 35 micron foil) you can expect to plate about 290 square feet
of double- sided copperclad in the 11 gallon system (12 lb of nuggets) and
about 750 square feet in the 22 gallon system (32 lb of nuggets).
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