Dear Mr. Hertlein:
I might be able to assist, in general terms, with some of your questions. Absolute
data on cost and performance of acid vs. alkaline etching, depends upon your location,
type of process equipment and method of control, and method of oxidation (acid etching
only).
1. The cost to etch 1 kg of Cu utilizing cupric chloride varies based upon the
oxidizer used to replenish the system and the acid normality at which the system is
maintained. The three oxidizers most commonly used are chlorine gas, sodium chlorate,
and hydrogen peroxide; chlorine gas generally being the least expensive and hydrogen
peroxide the most expensive (in terms of chemical costs only). Depending upon the HCl
normality desired, the acid costs can account for 15-50% of the operating cost (again
in terms of chemical costs only).
With this in mind, it is possible to calculate the quantity of reactants required to
etch 1 kg of Cu. Inserting your chemical costs, an estimate of the total cost may be
obtained using the information below.
CHLORINE GAS: Cu + Cl(2) ---> CuCl(2), hence
at 1.0 N acid concentration
- 0.54 kg of Cl(2) gas x cost/kg of Cl(2) gas = ?
- 0.70 L of HCl, 31% x cost/L of HCl, 31% = ?
----
total/Kg
at 3.0 N acid concentration
- 0.54 kg of Cl(2) gas x cost/kg of Cl(2) gas = ?
- 2.1 L of HCl, 31% x cost/L of HCl, 31% = ?
----
total/Kg
HYDROGEN PEROXIDE: Cu + H(2)O(2) + 2HCl ---> CuCl(2) +2HOH,
hence:
- 0.9 L of H(2)O(2), 50% x cost/L of HOOH, 50% = ?
- 2.8 L of HCl, 31% x cost/L of HCl, 31% = ?
----
total/Kg
NOTE: The above calculation assumes no excess HCl, 31% in the working bath. Typically
the HCl N is maintained between 1 -3 N requiring additional acid. Use the cost to
maintain excess acid concentration calculated in the chlorine gas method to determine
actual operating costs.
SODIUM CHLORATE METHOD:
Cu + (1/3)NaClO(3) + 2HCl ---> CuCl(2) + HOH + (1/3)NaCl, hence
- 0.418 Kg NaClO(3) x cost/Kg of NaClO(3) = ?
- 2.8 L of HCl, 31% x cost/L of HCl, 31% = ?
----
total/Kg
NOTE: The above calculation assumes no excess HCl, 31% in the working bath.
2. The cost to etch 1Kg of Cu utilizing alkaline etchant is dependent upon formulation
of "replenisher" employed. It is recommended you contact a supplier of alkaline
etchant to determine the volume of product required to etch one Kg of Cu.
Treatment costs of the spent etchant vary depending upon copper concentration; and for
cupric chloride, the concentration of free acid and/or sodium. In general, the higher
the copper concentration the lower the treatment cost and conversely the higher the
acid and/or sodium concentration the higher the treatment cost.
3. Comparing the performance (in terms of speed and undercut (undercut in terms of
line width uniformity or "edge factor) of alkaline vs. acid etching is also somewhat
complicated. It is believed the etching performance of both acid and alkaline systems
is dependent as much upon the equipment as the chemistry.
Equipment variables that are important are nozzle type (fan or cone) and nozzle
density, spray pressure, spray pattern (oscillating or fixed), volume per minute
manifold capacity, horizontal or vertical processing, and method of control. My
opinion, albeit based upon limited experience, is:
1. Horizontal processing is preferable to vertical;
2. 90 degree impact of etch solution on the board improves "edge factor";
3. Oscillating spray is preferable, particularly if the entire manifold
oscillates whereby solution impact is maintained at 90 degrees relative
to the panel (versus individual "sweep" spray bar oscillation");
4. The more nozzles the better, with fan preferable to cone; and
5. The higher the manifold flow the better.
Additionally, and limited strictly to cupric chloride etching:
6. The lower the acid concentration the better the "edge factor";
7. The higher the acid concentration the better the speed; and
8. The higher the cupric chloride concentration the better the speed.
Regarding methods of continuous control for acid etching, I am aware of
ORP/Conductivity and "transmittance" (see http://www.oxfordvue.com).
As seems inevitable with most processes in our industry, a balance must be achieved
between cost, speed, and performance, as dictated by the type of product being
produced. Regarding questions 4. - 7., it is recommended you contact recycling
facilities directly.
If you have additional questions, please feel free to contact me.
Regards,
Ted Stern
(612-479-6525)
Walter G Hertlein wrote:
> I am doing a technology survey which needs comparison data between the two
> etch processes used in PWB fabrication: acidic vs. alkaline. I would very
> much appreciate to receive data on following items -- please indicate type
> of product range, throughput and etch speed, type of etch resist and energy
> cost --
>
> 1. chemical cost of etching 1 kg copper by cupric chloride and treatment
> costs of spent etchant
> 2. chemical cost of etching 1 kg copper by alkaline etchant and treatment
> costs of spent etchant.
> 3. quality difference between alkaline and acidic copper etching in terms of
> defect density / production yields, line width uniformity, undercut, etch
> profiles,
> 4. relevant cost for the of waste water treatment plant which are
> attributable to the etch process (only patterning not any microetch or metal
> deposition process) in absolute figures and in percentage of total waste
> water treatment installation costs.
> 5. transport cost for spent etchants; conditions of the supplier / recycler
> for the etchant "lease".
> 6. total cost of ownership for etching 1 kg copper by cupric chloride
> 7. total cost of ownership for etching 1 kg copper by alkaline etchant.
>
> Thanks.
>
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