Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to etching copper and more es-
pecially to new and improved alkaline etchant solutions and pro-
cesses for dissolving copper.
United States Patent 3,505,135 discloses the steady ~tate
etching of copper cladded printed circuit boards utilizing an
ammonium persulfate ~olution having an initial predetermined molar
concentration as etchant. Copper is removed from solution at the
rate in which it is dissolved therein and etching reagent consumed
during the etching proces~ is replaced at an equivalent rate.
United States Patent 3,705,061 relates of a continuous redox pro-
cess for dissolving copper. An alkaline etch solution containing
cupric ions as oxidizer is used to oxidize and thereby dissolve
copper with attendant reduction of the cupric ions to the cuprous
state. A portion of the etch solution is continuously removed
from ~he system, and a source of oxygen and an ammonia based re-
plenishing solution are added to the etch solution to recons~itute
it. The replenishing solution requirements of the system are
determined by continuously monitoring the specific gravity of the
etch solution and the pH with respect to ammonium content. United
States Patent 3,466,208 discloses alkaline ammoniacal chlorite
solutions for dissolving copper and containing one or both of
ammonium chloride and ammonium nitrate in full or partial substi-
tition of ammonium bi~arbonate used ln a prior system. United
States Patent 3,677,950 discloses a chemical etchant solution for
dissolving copper from printed circuit boards and consisting of an
a~ueous ammoniacal solution of a normally acidic oxidizer such as
ammonium persulfate, cupric chloride or cupric sulfate, the solu-
tion having an alkaline pH up to about ll. United States Patent
3,650,957 relates to etching solutions for stripping copper from
substrates and containing a source of cupric ions as an oxidant,
one or more complexing agents for the cupric ions which is capable
of forming a soluble copper (II) complex at solution p~, a source
o~ bromide or chloride ions, and molybdenum, tungsten or vanadium
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9865 ~ ~
ions for retarding attack on tin and tin-lead solder plate, the
solutions havin~ a pH between about 4 and 13. United States Patent
3,650,958 discloses etchant solutions for copper containing a
source of cupric ions, and one or more non-fuming complexing agent~
for the cupric ions, the complexing agent b~3ing capable o forming
a soluble copper (II) complex at ~olution pH. United States Patent
3,650,959 discloses etchant solutions for copper, containing a
source of cupric ions, one or more non-fuming complexing agents
~ for cupric ions which is capable of forming a soluble copper (II~
; 10 complex at solution pH, chloride or bromide ionsl and nitrate ions
in amount sufficient to prevent build-up of a film on the surface
of the copper being etched. United States Patent 3,367,874 per-
tains to acid baths for dissolving nickel, copper, zinc, cobalt or
iron and containing concentrated nitric aaid, and a mixture of
additives capable of providing urea in the bath and capable of
forming sulfamate ions in the bath. United States Patent 3,537,895
discloses cleaning-pickling solutions for removing copper oxides
~` from copper, the solutions being aqueous solutions containing
sulfuric acid, sulfamic acid, or an equivalent acid salt thereof
for dissolving cupric oxide from the surface of a workpiece, hydro-
gen peroxide, and an organic stabilizing compound such as an
organic compound from the class of benzoic, glycolic or propionic
acids, glycerine, ethylene and propylene glycols.
The prior art etchan~ solutions are in general not suit-
able for ekching away copper in the ma~ufacture of additive-type
- printed circui~ boaxds. The reasons for this is the prior art
etchant solutions etch copper at too fast a rate and the etching
rate fluctuates excessively. In additive type prinked circuit
board manufacture a thin copper film is elec~rolessly deposited
over the entire dielectric board from an elec~roless copper plat-
ing solution, as contrasted with the relatively thick copper foil
bonded to the board in subtractive-type printed circuit board
manufackure. In ~electively etching away unwanted copper in addi-
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~0508~5
tive-type printed circuit board manufacture, it i8 important to
etch away the unwanted copper at a rela~ively slow rate to avoid
etching away the entire circuit, which occurls with u~e of the prior
art etchant solutions having the fa3t or high speed etching rate.
Furthermore, use of the prior art etchant solutions having the fast
etching rate for etching copper in additive-type circuit board
manufacture results in undesirable undercutting o~ ~he circuit
lines.
One object of the invention is ~o provide new and im-
proved etchant solution for dissolving copper.
Another ob]ect is to provide new etchant solution~ e~-
pecially adapted for use in selectively~etching away copper in
additive-type printed circuit board manufacture.
A further object is to provide new etchant soIutions
characterized by etching copper at a desired controlled ~low rate.
A further object is to provide new etchant solution~
capable of etching away unwanted copper in the preparation o~
additive-type printed circuit boards without any substantial
,:
, undercutting of the circuit lines or pattern.
; 20 Still another object is to provide a new and improved
process for dissolving or etching away copper.
Additi~nal objects and advantages will be readily
apparent as the invention is hereinafter described in more detail.
The aforementioned objects and advantages are attained
in accordance with the present invention by an alkaline etchant
solution comprising essentially sulfamate ions for accelerating
appreciably the etching or dissolving of the copper, cupric ion~
as an oxidant for the copper, and ammoniu~ ions for maintaining ;~
the solution pH on the alkaline æide of p~ 7.
The etchant solutions of this invention i~ characterized
by the highly desirable property that its ~tripping rate for
stripping or etching copper can be either increased or decrea-~ed
(although still faster than in the ab3ence of the sulfamate ion~)
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at any given copper content of the solution merel~ by var~ing the
sulfamate ion concentration of ~he solution. Thu~ at any given
copper concentration of the solution, the rate of stripping or
dissolving copper can be increased merely by increasing the con-
centration of sulfamate ions in the solution, or the stripping
rate for copper can be lowered ~imply by having a lower concentra-
tion of sulfamate ions ,n the solution albeit still an appreciably
faster stripping rate than in the absence of the sulfamate ions.
The cupric ions are supplied in the etchant solutions
of this invention by cupric carbonate or cupric ammonium sulfate
~Cu-(NH~)2(S04)2). Only these two cupric salts of the plurality of -
~copper salts tested resulted in the desired slow rate o etching
the copper by the etc~ant solution.
Cupric chloride, cupric nitrate or cupric acetate were
~ound to be unsatis~actory in the etchant solutions due to re~ult-
ing in the etchant solution etching away the copper at an undesir-
able fast rate, which was attributed to the anion of these cupric
salts. Cupric sulfate was also found to be unsatisfactory in the
etchant ~olution due to forming a slu~ge in the etching machine
after only a limited tlme, and resulting in clogging of the spray
nozzles of the machine.
The sulamate ion are supplied in the etchant 301utions
; o thi~ invention by any suitable source of sulfamate ion. Exem-
plary of the sulfamate ion source is sulfamic acid, ammonium
sulfamate, and an alkali metal sulfamate, e.g. sodium or potassium
suLfamate.
Any suitable source of ammonium ion i9 utilizable in
the e~hant solutlons herein. As exemplary, ammonium hydroxide,
ammonlum sulfamate, ammonium chloride, ammonium ni~ra~e, ammonium
phospha~e, ammonium carbonate, ammonium citrate, and NH3 ga~ which
forms in situ in the etchant solution NH4+ ions are utili~able.
The sulfamate ions (calculated as OSOaN~) are present
in the etchant solutions of this invention in an effect:Lve amount,
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which is sufficient to accelera~e appreciably ~he etching or dis-
solving of the copper. The sulfamate ion~ may be present in the
etchant solutions herein in an effective amount of at leas~ 0.2
mole per liter. The amount of sulfamate ions utili~ed in tha
etchant solutions herein should be insufficient to result in a~
uncontrollable, fast etching rate, and a fast etching rate which
results in significant undercutting of the circuit lines or pattern
in the preparation of additive-~ype printed circuit boards.
The cupric ions may be present in the etchant 301utions
herein in an amount (calculated as Cu~ of 0.2 mole per liter to ~ -
saturation.
The ready-to-use e~chant solutions o$ this invention will
u~ually contain the constituents in amounts wI~hin the following
proportion ranges: ;
Sulfamate ions (calculated as OS02N~
from about 0.3 to 1.0 mole per li~er
Cupric ions (calculated ~g Cu)--
from about 0.3 to 1.0 mole per liter
Ammonium ions (calculated a~ NH4)--
sufficient to maintain pH in the range
of about 8 to about 12.
The etchant solutions herein are u~ually supplied as
a concentrate which is adapted to be mixed together with an aqueaus
liquid, such as waterl to ~orm the ready-to-use etchànt ~olution.
A source of ammonium ion may also be mixed together with the con-
centrate solution and water. The concentrate solutio~s are u~ually
aqueous solutions containing cupric ions, sulfamate ions and
ammonium ions. The etchant concentrate ~olution~ of course contain
a les~er amvunt of water than do the ready to-use etchant solution~
The concentrate solution is mixed togethex with water by the usqr
to form the ready-to-use etchant solution typically in a volume
ratio of concentrate solution to water of about 1:3 respectively.
The etchant concentrate solutlons will usually contain
the ~onstituents in amounts within the following proporti.on ranges:
... . .
SulEamate ions (calculated a~ OSO2NH )--
from about 0.3 to 3.0 moles per l~ter
Cupric ions ~calculated as Cu)--
from about 0.3 to 3.0 moles per liter
Ammonium ions ~calculated as NH4)--
from about 1 to 18 moles per liter
The kemperature of the etchant solutions herein during
the dissolution or etching of the copper can be room temp~ra~ure
or elevated temperatures up to about 135F. The etching rate in- ;
creaqes with increasing solution tempera~ure. ~emperatures of
the etchant solution much above 135F. should be avoided, due to
expelling ammonia at Ruch higher temperatures.
The ionic copper concentration of the etchant solution
during the etohing process can be determined by any suitable means
; or method. Thus the determination of the ionic copper aoncentra-
tion, such as the cupric ion concentration can be effected by
batch or manual means or method or by continuou or automatlc means
or method. One suitable means and method for the oontinuous deter-
mination of the ionic copper concentration of the et~hant solution
is that disclosed and claimed in United States Patent 3,70$/061 and
involvlng sensing the specific gravity of the solution, to generate
a signal when the concentration of i~nic copper reaches a predeter-
mined maximum. Exemplary of a batch or manual means and method for
determining the ionlc copper concentration is titration.
When required, the sulfamate ions are replenished in
,. ~
the etchant solutions herein. The replenishment of the sulfamate
ionic in the solution is conveniently effected by adding a re-
plenisher solution containing the sulfama~e ions, ammonium ions
and water to the etchant solution. The replenisher solution i5
,: ,
exemplified by an aqueous solution of the ollowing compo~ition:
Sulfamlc acid.............. ~....... 290 g/l
;~ Ammonium hydroxide......... O....... S00 g/l
H2o... ~............. q......... ~........ to 1 liter
)
The designation "g/l" herein means grams per liter. ;The addition
6-
~0~0~6S
of this replenisher concentrate al~o serves to maintal~ the pH o~
the solution within the desired alkaline pH range due to the
ammonium ion~
- The followlng example~ of ready-to-use et~hant ~olutlon~
of this inven~ion for dl~solving copper are illu~tratlv~ only:
: EXAMPLE I
Sulfamic acid (calculated a~ sulfamate,
i-e- OSO2NH2)~ ~---......... 0.3 mole/liter
Cuprlc carbonate ~calculated as
Cu),........................ 0.3 mole/lltor
- ~mmonium hydroxid~............. sufficient to malntai~
p~ in th2 range of about ~i
; 11-12 -~ -
H2O............................ to 1 liter ~ :
- EXAMP~E~
Sulfamic aaid (calaulated as sulfamat~, ;
i-e- OSO2NH2) -----......... 0,5 mole/liter
, Cupric carbonate (calculated a3
CU)D~ O~6 mole/liter
A~unonium hydroxide............ ~ufflcien~ to maintain -
; pH in the range of about
; 11-12
H~O.............. ,................................. to 1 liter
EXAMPLE III
Sulfamia acid ~calculated a~ sul~amate,
2N~2) .. ~ ...... ~ ......................... 1. 0 mole/liter
Cupric carbonate ~calculated as
Cu)............. ........ .... ....................... l.0 mole/liter
Ammonium hydroxide............. 3ufficient ~o maintain
p~ in the range of about
11-12
. H2O............................ to 1 liter
EXAMPL~ IV
:; Sulfamic a~id ~calcula~ed a~ ~ul~mata, i.e.
02NH~ ) ~ D ~ O ~ 5 mole/lit~r :~
Cupric carbonate tcalculated a
Cu)....... ~........................................ 0.3 mole/liter
~mmonium hydxoxide................................. sufi~ient to mainta~n
pH in ~he range o~ about :~
`~ 40 11-12 ~:
: H2O....... O................................... to 1 lit~r
.
~(~8~;S
The following examples of etchant concentrate solutions
o~ this invention, which are adapted to be mixed togcther with
water to form the ready-to-usc concentrate solutions, are illu~
~ra~ive only.
EXAMPLE V
Sulfamic acid (calculated as sulfamate, i.a.
O2NH2) -- -~ ............. 0.6 mole/liter
Cupric carbonate (calculated as
Cu~......................... 0.~ mola/liter
Ammonium hydroxide........ ...... 300 g/l
H2O............................ to 1 liter
This aqueous concentrate solution is mixed together wi~h wat~r in
the volume ratio of 1:1 re~pectively to form the ready-to-use
etchant solution. Ammonium hydroxide is also added to adjust the
pH of the resulting solution to within the pH range of about 11 ~o :;
12.
E~AMPLE VI
Sulfamic acid (calculated as sulfamate,
i.e. OSO~NH2).......... 0.6 mole/liter
Cupric carbonate (calculated as
Cu)..... ~................................. 0.8 mole/liter
Ammonium hydroxide........................ 300 g/l
H2O....................................... to 1 liker
This a~ueous concentrate solution is mixed together with wate~ in
the volume ratio o 1:1 respectively to form the ready-to-u~e
etchant solution. Ammonium hydroxide is also added to adjust the
pH of the resulting solution to within ths pH range of about:ll to
.l2.
EXAMPhE VII
Sulfamic acid ~calculated as sulfamate,
OSO2NH2) o ---~ 0.9 mole/liter
Cupric carbonate (calculated as
Cu~.. O........ O.......... .......... O.g mole/liter
Ammonium hydroxide....... .......... 500 g~l
H2O............................... to 1 liter
This concentrate solution is mixed together with water ln the
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volume ratio of 1-3 respectively to form the ready-to-use etchant
solution. Ammonium hydroxide is al90 added to the solution mixture
to adjust the pH of the resulting solution to within the pH range
of about 11 to 12.
EXAMPLE VIII
Sulfamic acid (calculated as sulfamate, i.e.
OS02NH2).................... 3.0 moles/liter
Cupric carbonate (calculated as
Cu)................ 0........ O.~ moles/liter
Ammonium hydroxide.... ,........ 500 g/l
H20....................... ..... to make 1 liter
This aqueous concentrate solution is mixed together with water in
the volume ratio of 1:3 respectively to form the ready-to-u~e ~-
etchant solution. Ammonium hydroxide is also added to adjust the
p~ of the resulting solution to withln the pH range of about 11 to
12.
The following tests were carried out:
The sulfamate ion concentration was varied by varying
the sulfamic acid concentration in a plurality of solutions each
initially containing 3 oz./gal. cupric ions (calculated as Cu) and
NH40H suficient to adjust the pH to 11. The etchant solutions
were each at a temperature of 75~C., and the solutions were used
to etch copper ~rom ABS panels. The copper was immersed in the
solutions in separate beakers. The following results were o~tain- ;
edo
TABLE I
Etching Rate
Sulfamic Acid Minutes to Etch 25
Concentratlon Micro-inches of Cu
0.1 M No etching (blackened Cu)
0.3 M 5.0
0.5 M 3.5
1.0 M 2.5
2.0 M 2.0
The test results of Table I show that at a sulfamic acid concen-
tration of 0.3 moles, the fastest etching rate occurred, and that
at progressivaly higher sulfamic concentrations up to 2.0 mole ,
_g_ .
~ ~ . . . .
~ L~5086~
that etching of ~he copper occurred but at a progressively slower
rate~
The temperature of a plurality of solutions was varied
to determine the effects on the rate o~ etching copper~ A plural-
ity of separate solutions were made up init:Lally containing 3 oz./-
gal. Cu metal as CuCO3-Cu(OH)2, 0.3 M sulfamic acid and 150 g/l
NH40H. Each solution had a p~ of 11. The ~opper wa~ immer~ed in
the solutions in separate beakers in carrying out the tests. The
following results were obtained.
TABLE II
Temperature Etching Rate
of Minutes to Etch 25
Solution Micro-inches Q~ Cu
70F 5 0
80F. 4.25
90F. 3,75
100F. 3~75
lZ0F.
140F. ~oss of NH40H
20 The test results of Table II show that the best etching rate occur-
red at room temperature or 70F., and that satisfactory e~ching `
rates were attained at elevated temperatures above 70F. The te~t
results of Table II also show tha~ a temperature of 140F. resulted
in loss of ~H40H from the etchant bath, which was undesirable.
A plurality of etchant solutions containing different
concentrations of cupric ions and sulfamic acid ~s set ~orth in th~
,I table of test results which ~ollows and also NH40H in amount suffi-
cient to adjust the pH of each solution to about 11.0, were utiliz-
;:
ed to etch copper from glas~-epoxy printed circuit boards in a con
ventional etching machine. The etchan~ solutions were each at a
temperature of 75F. during the spray application to the copper in
the etching machine. The following results were obtained, with
the results being given hereafter in terms of the micro-inche~ of
copper etched per minute: ;
. ~ . --10--
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Sulfamic Acid
Content ofCu Metal Content of Etchant Solution
Etchant Solution(oz. Cu/~al of Etchant Solution)
3 4 5 6 7 9
0.3 M 100 110 115 120 115 lQ0
0.5 M 145 160 170 165 160 1~'5
0.7 M 170 190 230 220 205 140
1.0 M 200 4S0 600 650 600 1~l0
Cupric carbonate is the preerred source of cupric ions.
Sulfamic acid and ammonium sulfamat:e are the preferred
source of sulfamate ion.
Ammonium hydroxide is the preferred source of ammonium
ions.
The p~ o the etchant solutions is preferably in the
pH range of ab~ut 11 to about 12.
Preferably the ready-to-use etchant solutions herein
contain the following constituents in amounts within the proportion
ranges hereafter cet forth:
Sulfamate ions (calculated as
OS02NH2)--from ahout 0~3 to 1.0 mole per liter
Cupric ions (calculated as Cu3--
from about 0.3 to 1.0 mole per liter
Ammonium ions (calculated a (NH )--
sufficient to maintain pH in ~he range of
about 11 to about 12
Especially preferred ready-to-use copper etchant solu-
tions o~ this invention contain the ~ollowing constituents in
amounts within the proportion ranges hereafter sek forth:
Sulfamic acid.............. ~.......... 0.3 molar to 1.0 molar
Cupric ions (calculated as Cu).. 22.5 to 67.5 g/1
Ammonium hydroxide.............. l50 to 180 g/l
Such solution has a pH in the range of about 11 to about 12.
The etchant solution is preferably at a temperature
in the range of about 70F. to about 135F. during the etching.
Although the etchant solutions of thi~ invention are
eminently adapted fox selectively etching copper in khe produc-
tion of additive-type printed circuit boards, these et:chan~ solu-
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l~S~ ;5
solution~ are al~o utilizable in ~he preparation of ~ubtractive~ ;
type printed circuit board~ or for ~bher copper etchlng or dis-
~olving purposes.
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