Note: Descriptions are shown in the official language in which they were submitted.
CA 02278580 1999-07-23
WO 98!33951 PCT/US98/02178
COMPOSITION AND METHOD FOR PRIMING SUBSTRATE MATERIALS
Background of the Invention
Field of the Invention
The present invention relates in general to a composition of matter for
preparing substrates and more
specifically to an improved solution and method for priming metallic sufaces
and inner layers used in the manufacture
of printed circuit boards (PCBs), chemically milled alloys, and chemically
plated alloys.
Description of Related Art
PCB fabrication requires that substrate materials be processed. In general,
substrate processing is
chemically performed by sequentially coating a variety of chemical solutions
onto the substrates. The substrates
are commonly rinsed between application of each solution and then undergo a
final rinsing and drying cycle. PCB
processing can include steps in which layers of materials are cleaned,
scrubbed, etched, passivated, treated, masked,
processed, deposited or various combinations thereof.
An initial step in the PCB fabrication process involves the cleaning and
priming of substrates far subsequent
application of photoresists or screen inks used to define the desired PCB
circuit pattern. Figure 1 illustrates a typical
four step technique used to chemically clean and prime substrate materials.
This cleaning and priming technique is
merely illustrative of one of many mufti-step techniques typically used in the
PCB fabrication industry.
During the first step, substrates are coated with an acidic solution which
functions as a cleaner and
chromate remover for approximately 30 seconds to 5 minutes. This solution is
usually applied at a temperature of
100 to 120 degrees fahrenheit. The substrates are then rinsed to remove excess
acidic solution.
During the second step, the substrates are surface etched by coating the
substrates with an etching
solution, commonly persulfate or peroxy-sulfuric. Alternatively, the
substrates can be physically scrubbed with
pumice. Etching removes remaining chromate and roughens the surface structure
of the substrate. Etching also
assists in adhesion of the resist to the substrate, especially if the
substrate has an underlying copper component.
The substrates are then rinsed to remove the etching solution or pumice
particles.
The third step varies depending on if the substrate was chemically etched or
pumice scrubbed. If chemically
etched. the rinse step is followed by immersion in an second acidic solution.
Commonly, a 59~o to 109'o sulfuric acid
dip or spray is used to remove oxides which tend to form on etched copper and
passivates the copper. Oxide
removal slows re-oxidation of the substrates during the final rinse and drying
cycle which occurs prior to lamination
with resist. If pumice scrubbed) a medium to high pressure rinse is used to
remove the pumice particles) which
otherwise would typically not be removed.
The fourth step involves coating the substrates with an oxidation inhibitor
andlor adhesion promoter for the
resist. Triazole solutions are commonly used for this purpose. The substrates
are then rinsed and dried. At this
point, the substrates are primed and properly prepared for application of a
resist layer.
However, mufti-step cleaning and priming techniques are time-consuming, cost-
prohibitive and create
additional waste products. There is thus a need for a single-step method and
formulation which cleans and primes
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WO 98/33951 -2. PCT/US98/02178
PCB substrates and, more specifically, functions as a cleaner, chromate
remover, oxidation inhibitor, adhesion
promotor, flexibility enhancer and redeposition inhibitor.
The chemical milling industry uses processes similar to that described above
to clean and prime substrates.
There is thus a need for a single-step method and compound which primes
substrates used in the manufacture of
chemically milled alloys.
The chemical plating industry uses processes similar to that described above
to clean and prime substrates.
There is thus a need for a single-step method and compound which primes
substrates used in the manufacture of
chemically plated alloys.
Summary of the Invention
Dne aspect of the present invention relates to a compound and method which
cleans and primes substrate
materials used in the fabrication of PCBs. More specifically, the compound and
method cleans, removes chromates,
inhibits oxidation, promotes adhesion, inhibits attack by acids and inhibits
redeposition on inner layer core substrates
and flexible composite materials. The compound can be thus used to reduce the
steps required to clean and prime
materials used in the fabrication of PCBs to a single step.
Another aspect of the present invention relates to one or more filming amines
which have unique properties
when combined with a suitable acid or combination of acids. When applied to
the processing of copper clad
substrate materials, this solution allows for chemical bonding of resist films
on smooth, non-surface etched copper
and other substrate materials.
Yet another aspect of the present invention involves a formulation which
allows etching of extremely fine
lines and spaces found on PCBs without loss of adhesion, undercutting or micro-
cracking from the flexing of the
substrates.
Another aspect of the invention relates to a composition of matter for use on
substrates, comprising, by
weight, from about .003% to about 3.0% of a film forming amine(sl, from about
0.02 to about 10% of a non-ionic
surfactant(s), and sufficient acids) to produce a pH of less than about 6.5.
The invention as relates to a method of preparing a primed substrate,
comprising preparing a solution
comprising from about .003% to about 3.0% of a film forming amine and
sufficient acid to produce a pH of less
than about 6.5; coating at least a portion of the substrate with the solution;
and drying the substrate.
Another aspect of the formulation of the present invention involves a single
solution and method which
cleans. inhibit oxidation and promote adhesion in chemically milled alloys and
chemically plated alloys.
Brief Descriution of the Orawinps
FIGURE 1 is four step chemical cleaning and priming process commonly used in
the prior art.
FIGURE 2 is a one step chemical cleaning and priming process in accordance
with the present invention.
Detailed Descriution of the Preferred Embodiment
The present invention relates to a composition and method of use which primes
substrates used in the
manufacture of PCBs, chemically milled alloys and chemically plated alloys.
The composition allows a single step
solution to prime inner layer core substrates and flexible composite
materials. The solution comprises (1 ) a filming
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WO 98/33951 -3- PCT/US98/02178
amine or combination of filming amines, (2) an acid or combination of acids,
and (3) water. A surfactant can be
optionally added to assist in cleaning, chromate removal, anti-foaming and
wetting of the substrates.
For purposes of this invention, a substrate is considered to be primed when
treated with a cleaner,
chromate remover, oxidation inhibitor, adhesion promotor, flexibility
enhancer, redeposition inhibitor, etch enhancer,
wetting agent or any combination of the above. More preferably, the substrate
is considered primed when treated
for all of the above applications.
A filming amine is defined as a primary, secondary, tertiary or quaternary
amine or derivatives thereof in
which the groupls) attached to nitrogen are sufficiently hydrophobic to cause
a solution of the amine, when placed
upon a substrate having a charge, to form a hydrophobic layer when the pH of
the formulation is below 7. An acid
is defined as a compound that, when placed in pure water with a pH of 7,
causes the pH to drop below 7. A
surfactant is defined as a compound which lowers the surface tension of the
formulation.
A wide variety of film forming amines can be used in the present invention.
Preferable filming amines may
be either cationic, amphoteric or nonionic. Neutral and anionic amines may
also be used, but do not tend to work
well unless used with a strongly acid medium. Preferable filming amines may
include, but are not limited to fatty
acid amines, long chain alkylamines and amino methacrylates. Amines used in
the present invention can be prepared
by methods known to those skilled in the art or purchased from any of a number
of commercial sources. Preferable
amines include, but are not limited to, primary, secondary and tertiary
amines; diamines; alkylamines; C-8 through
C-22 amines; basic mono cyclic tertiary amines; stabilized abietylamines;
diaminopropanes; dehydroabietylamines; and
ethoxylates, salts) and adducts thereof. For example, amines can be obtained
from Akzo Chemicals Inc., under the
tradename Armeen for primary, secondary and tertiary amines, and under the
tradename Duomeen for diamines.
Fatty acid amines can be prepared by methods known to those skilled in the art
by reacting fatty acids
with ammonia or ammonia derivatives. The molecular structure of fatty acid
amines is characterized by a central
nitrogen atom as in ammonia (NH3) having one or all of its hydrogens replaced
by a fatty acid group R. A fatty
acid amine may also be a quaternary amine, wherein the central nitrogen atom
is bonded to four fatty acid groups.
Each fatty acid group. R, is a long chain, preferably C8-C22) preferably
aliphatic, alkyl group having a terminal
carboxylic acid function. The alkyl chains) of the R group may be unsaturated
or have additional substituents.
Because of the number of carbon atoms in the alkyl group, this group is
strongly hydrophobic. However, the nitrogen
atom is hydrophilic, particularly when it has four R groups or three R groups
and is protonated. When dissolved or
dispersed in water or non-aqueous solvents, one portion of the molecule is
strongly repelled by its surrounding
solvent. This repelling force Lends to orient the molecules at surfaces or
interfaces or cause them to form micelles.
Preferable fatty acid amines include) but are not limited to, amines having R
groups derived from animal
and vegetable fatty acids oroils, and oils, such as tall oil, oleic oil,
caprylic oil and coconut oil. Preferable amino
methacrylates include, but are not limited to dimethylaminoethly methacrylate,
triethylammoniumethyl methacrylate,
dimethylaminopropyl methacrylamide and methacrylamidopropyl trimethylammonium
chloride.
More preferable filming amines are commercially available from Hercules, Inc.
Resins Group under the
trademark Polyrad. The most preferable Polyrad filming amines are Polyrad 0515
and Polyrad 1110. Other more
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WO 98/33951 .4. PCT/IJS98/02178
preferable filming amines include organic monobasic cyclic tertiary amines
commercially available from Mona
Industries, Inc. under the tradename Monazoline. Most preferable Monozlone
filming amines are Monozfone T and
Monozlone C. Other more preferable filming amines are commercially available
from Akzo Chemicals Inc. under the
tradename Ethoduomeen. Most preferable Ethoduomeen filming amines are
Ethoduomeen T[13, Ethoduomeen T[20
and Ethoduomeen TI25.
Filming amine properties particularly useful in the present invention include,
but are not limited to)
hydrophobicity, fast film formation, resistance to wash-off, film persistency,
oxidation inhibition, adhesion promotion,
cleaning, flexibility enhancement and wetting. Hydrophobicity results from the
attraction between the positive charge
on the filming amine and the negative charge characteristic of most substrate
surfaces. Preferable filming amines
form the hydrophobic film, or layer, immediately upon contact with the
substrate and resist water wash-off and other
film degradation. The attraction between the positively charged filming amine
and negatively charged substrate
surface also causes adsorption and surface modification which assists in
oxidation inhibition and adhesion promotion.
Also, the amphoteric molecular structure of the filming amine provides for
molecular orientation at interfaces. This
orientation reduces interfacial tension which assists in substrate cleaning
and wetting, but also assists in foaming
which is not desired. To obtain these preferred properties, the formulation
can use one ar more filming amines.
For example, preferable filming amines which create an adequate hydrophobic
layer include Palyrad,
Monozelone and Ethoduomeen. More preferable filming amines which create an
adequate hydrophobic layer include
Polyrad 0515, Monozoione T and Ethoduomeen TI13. Preferable filming amines
which adequately inhibit foaming
and wet the substrate include Polyrad and Ethoduomeen. More preferable filming
amines which adequately inhibit
foaming and wet the substrate include Polyrad 1110 and Ethoduomeen T[25.
To produce the formulation of the present invention, the above-described
filming aminels) are combined with
a suitable acid or combination of acids. The acidfs) should be capable of
reducing the formulation below a pH of
7 when introduced to the filming amine. Strong acids are preferred to weak
acids only to the extent that a strong
acid will reduce the formulation below a pH of 7 while introducing less acid,
by volume, into the formulation than
a weak acid.
Properties which acids possess which are particularly useful in the present
invention include, but are not
limited to, chromate removal, resistance to wash-off, adhesion promotion,
cleaning, oxidation inhibition, flexibility
enhancement, redeposition inhibition and wetting. To obtain these preferred
properties, the formulation may use one
or more acids.
For example, preferable acids for chromate removal include organic and
inorganic acids. More preferable
acids include phosphoric, sulfonic, and hydroxyacetic. Most preferable acids
include hydrochloric, sulfuric, methane
sulfonic and sulfamic. These acids are most preferred because of the rapid
speed at which they attack and removes
the chromate layer on the substrates. Preferable acids for resistance to wash-
off and adhesion promotion include
organic acids and inorganic acids. More preferable acids include formic,
malonic, cuccinic, aspartic, mallic, acetic,
citric, nitric, phosphoric, sulfonic, methane sulfonic, sulfamic and
hydroxyacetic. Most preferable acids are gaflic,
mafeic and funamric.
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The formulation preferably comprises from about 0.0008% to 8.0°Yo, by
weight, of a filming aminels) and
an acids) capable of dropping the pH below 7. More preferably, the formulation
comprises from about 0.003 to
about 3.0%, by weight, of a filming aminels) and an acids) capable of dropping
the pH below 6.5.
When mixed, the filming amines) and acids) form cationic molecules with a
strong positive charge which
readily bond to negatively charged substrates. This bonding forms a
hydrophobic layer on the substrates. The acid(sl
removes chromate formed on the substrates and assists in strengthening the
hydrophobic bond. The hydrophobic
bond also inhibits acidic attack of the substrates to which it is bonded, but
does not inhibit acidic attack on non
charged surfaces (such as a chromate layer portion of the substrate). Thus,
the combination of the filming amines)
and acidls), forms a hydrophobic layer which assists in the removal of
chromate from substrate materials. More
specifically, the combination of the filming amines) and acid(s), forms a fast
film forming, wash-off resistant, film
persistent, hydrophobic layer which removes chromate conversion coatings from
substrates and copper clad inner
layer core materials and flexible composites. The combination also functions
as a cleaner, oxidation inhibitor,
adhesion promotor, flexibility enhancer, redeposition inhibitor and etch
enchancer.
The formulation further comprises a carrier, or solvent, for the filming
amines) and acidls). The solvent
preferably comprises deionized water. Ordinary tap water can be used, but is
not preferred because of the
extraneous metallic ions which may be found in tap water. Distilled water is
not as preferred as deionized water
only because of its relatively high cost. Organic solvents, such as but not
limited to, glycol ethers and alcohols may
be used in addition to water. Organic solvents are particularly useful to help
solubilize filming amines with higher
molecular weights. However, organic solvents are typically considered volatile
organic compounds (VOCs) by
government agencies.
The formulation optionally further comprises a surfactant. Although not
required, the surfactant increases
cleaning activity, assists in chromate removal, functions as a wetting agent
and/or reduces foaming of the
formulation. The surfactant lowers the surface tension of the formulation,
preferably to less than 70 dyneslcm, more
preferably to less than 50 dyneslcm and most preferably to less than 30
dyneslcm. Preferable surfactants are
commercially available from Rhone-Poulene under the tradename Antrox. More
preferable surfactants include Antrox
LF 224 and Antarox BL-214.
The surfactant inherently increases cleansing activity and chromate removal by
lowering the surface tension
of the formulation. That is, the surfactant allows for quicker removal of
contaminants such as, but not limited to,
fingerprints, oils":greases, dirt and the like. The surfactant also speeds up
the removal of the chromate layer by
causing the acidic portion of the formulation to more efficiently wet the
chromate. A nomionic surfactant with an
inverse solubility can also reduce foaming of the formulation. When the cloud
point of the surfactant is reached
(which occurs ~rhen the formulation is heated as detailed below) the
surfactant begins to separate from the
formulation and behave in an oil-like manner. This separation characteristic
helps inhibit foaming. This anti-foaming
property is especially preferred if the substrates are sprayed with the
formulation.
Additionally, an etching component can be added to the formulation to speed
chromate removal andlor
roughen the substrate and thereby functions as an adhesion promoter for the
resist. Preferable etching components
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include, but are not limited to, iron salts, peroxides and acids. More
preferable etching components include ferric
chloride and cupric chloride.
Colorants or dyes can be added to the formulation to, among other purposes,
identify the formulation.
Stabilizers can be added to the formulation to) among other purposes,
stabilize the formulation. Perfumes can be
added to the formulation to, among other purposes, cover or remove the odor of
the formulation. Also, other
ingredients can be added to the formulation to assist in priming the
substrate, including but not limited to, cleaning,
chromate removal, oxidation inhibition, adhesion promotion) flexibility
enhancement, redeposition inhibition, wetting
or any combination of the above.
Thus, the preferred components of the priming formulation of the present
invention comprise a filming
aminefs) which is mixed with an appropriate acids) in amounts adequate to form
a hydrophobic layer on the
substrate and remove a chromate layer on the substrate. Water is preferably
used as the solvent and a surfactant
can be optionally added to aid in the cleaning, anti-foaming or wetting of the
substrates. Examples of the
formulation are provided below:
EXAMPLE 1
The formulation was made by placing about 20 gallons (75.7 litres) of
deionized water into a clean 50
gallon (189.3 litre) mixing tank at ambient room temperature. About 20 ounces
(567 gramsl, by weight, of Polyrad
0515 filming amine was added and stirred into the water. Then, hydrochloric
acid was mixed into the solution so
that the concentration of the acid, by volume, was about 50% and the
concentration of the filming amine, by weight,
was about .28%. About 5 pounds (2.27 kilograms) of Antarox LF 222 (a
surfactant) was then mixed into the
solution.
EXAMPLE 2
The formulation was made by placing about 20 gallons (75.7 litres) of
distilled water into a clean 50 gallon
(189.3 litre) mixing tank at ambient room temperature. About 18 ounces (510.3
gramsl, by weight, of Polyrad 0515
filming amine was added and dispersed into the water. An additional 18 ounces
1510.3 grams) of Polyrad 1110
filming amine was then added and dispersed into the tank to give an amine
content of about 0.5%. Next, a 70%
hydroxyacetic acid solution (commercially called glycolic acid) was slowly
added until the solution became clear and
no particles were unreacted to farm a hydroxyacetic acid salt. Then, muriatic
acid was mixed into the solution so
that the volume of the acids was about 50% and the concentration of the
filming amine was about 0.5%
EXAMPLE 3
The formulation was made by placing about 20 gallons (75.7 litres) of
deionized water into a clean 50
gallon (189.3 litre) mixing tank at ambient room temperature. Monazolone T
filming, amine and muriatic acid was
added to the t~k and mixed in amounts sufficient to make the concentration of
Monazoline about 0.6% and the
concentration, by volume, of muriatic acid about 25%. Then, about 22 pounds
(9.98 kilograms), or 5% by weight)
of Ferric Chloride hexahydrate was added (as an etching agentl. The solution
was then mixed until clear.
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EXAMPLE 4 .
The formulation was made by placing about 2 gallons (7.6 litres) of tap water
into a clean 5 gallon (18.9
litres) mixing tank at ambient room temperature. About 2 ounces (56.7 grams),
by weight, of Monazolone T filming
amine was mixed with acetic acid until neutralization. Next, about 20%, by
volume, of muriatic acid and 30%, by
volume, of phosphoric acid was mixed into the tank. The resulting solution was
then 509'0, acid by volume, and
about 0.08, by weight, of a filming amine. About 1 % of Antarox LF 224 was
mixed into the solution as a nonionic
wetting agent.
EXAMPLE 5
The formulation was made by mixing about 16 gallons (60.6 litres) of distilled
water and about 4 gallons
(15.1 litres) of isopropyl alcohol into a clean 50 gallon (189.3 litre) mixing
tank at ambient room temperature. About
18 ounces (510.3 grams), by weight, of Ethoduomeem TI13 filming amine was
added so that the concentration, by
weight, of the filming amine was about 0.3%. About 1 % of Antarox BL-214 was
mixed.
EXAMPLE 6
The formulation was made by mixing about 20 gallons (75.7 litres) of deionized
water into a clean 50 gallon
(189.3 litre) mixing tank at ambient room temperature. About 20 ounces (567
grams), by weight, of Ethoduomeem
T113 filming amine was added. Malefic acid was then added until
neutralization. Hydrochloric acid was then added
to a final acid concentration of about 50%, by weight. About 2% of Antarox LF
222 was mixed into the solution.
Next, about 0.001 % FD&C Blue ~1 dye, about 0.001 Uranine dye and about 10%,
by volume, of diethylene glycol
butyl ether was added.
The formulation of the present invention is preferably prepared in the
following manner. For exemplary
purposes, a formulation comprising 1 filming amine, 1 acid and 1 surfactant is
detailed. A clean 50 gallon (189.3
litre) container is filled with approximately 20 gallons (75.7 litres) of
distilled water at ambient room temperature.
Approximately 20 ounces (567 grams), by weight, of Polyrad 0515 filming amine
is added and stirred into the
container. Stirring is preferably performed by a conventional stirring blade
for approximately 10 minutes so that the
filming amine is adequately dispersed in the water. When adequately dispersed,
the solution becomes hazy and the
filming amine particles dissociate from themselves. Then, approximately 25
gallons (94.6 litres) of hydrochloric acid
is added into the container so that the amount of the acid, by volume; is 50%
of the solution and the amount of
the filming amine, by volume is about 0.28%. The solution is stirred for
approximately 30 minutes so that the acid
is adequately dispersed in the solution. When adequately dispersed, the
solution has no visible particulants and a
pH of 7 or below. Approximately 1 %, by volume, of a Antarox LF 224 is then
added and stirred into the, container.
For ex1!mplary purposes again, a formulation comprising 1 filming amine and 2
acids is detailed the solution
detailed. A clean 50 gallon (189.3 litre) container is filled with
approximately 20 gallons (75.7 litres) of deionized
water at ambient roam temperature. Approximately 20 ounces (567 grams), by
weight, of Polyrad 0515 filming
amine is added and stirred into the container. Stirring is preferably
performed by a conventional mixing blade for
approximately 10 minutes so that the filming amine is adequately dispersed in
the water. When adequately dispersed,
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CA 02278580 1999-07-23
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the solution is hazy and the filming amine particles dissociate from
themselves. Then, approximately 0.1 gallons
10.38 litresh by volume, of hydroxyacetic acid is added and stirred into the
container for approximately 10 minutes
or until the mixture is neutralized. The solution is adequately stirred when
its appears clear. The solution may be
optionally heated to facilitate neutralization. approximately 25 gallons (94.6
litres) of hydrochloric acid is then added
to the container until the final amount of the hydrochloric acid, by volume,
in the solution is about 50%.
The formulation is preferably prepared in the above-described manner, stored
in containers and diluted on-site
for application onto substrates. The formulation is preferably diluted to 19'0
- 259'0, by volume, of its original
percentage quantities and more preferably 5% - 20% and most preferably about
10%.
A 10% dilution (for exemplary purposes) of the formulation is performed by the
following steps. A 50
gallon (189.3 litres) container is filled with 45 gallons (170.3 litres) of
water, preferably distilled. The container is
preferably constructed of plastic or composites. Metal is riot as preferred
because it is more reactive than plastic
or composites and is more readily attacked by the acids) in the formulation.
The water is heated to approximately
55 - 125 degrees fahrenheit (12.8 - 51.7 degrees Celsius) and more preferably
75 - 105 degrees fahrenheit (23.9
40.6 degress Celsius) and most preferably 85 - 95 degrees fahrenheit (29.4 -
35.0 degress Celsius). 5 gallons (18.9
litres) of the formulation is then added and stirred into the container.
Stirring is preferably performed by a
conventional mixing blade for approximately 5 minutes so that the formulation
is adequately dispersed in the water
as described above. The temperature of the resulting diluted formulation is
preferably readjusted to a temperature
of 90 - 150 degrees fahrenheit (32.2 - 65.6 degrees Celsius) and more
preferably 100 - 130 degrees fahrenheit (37.8
- 54.4 degrees Celsius) and most preferably 110 - 120 degrees fahrenheit (43.3
- 48.9 degrees Celsius). The diluted
formulation can now be applied to a substrate.
Formulations of other concentration percentages, ranging from 1 % to 25%, can
be prepared in a manner
similar to that disclosed above. Formulation concentrations will vary
depending on several factors. Once such factor
includes the time duration which the formulation will be in contact with the
substrate. Typical contact times range
from about 10 seconds to about 10 minutes. Another factor includes the
thickness of the chromate layer. Chromate
thickness varies among substrates and among substrate manufactures from about
0.001 to about 5 millimeters.
Another factor which affects the preferred concentration percentage is the
temperature at which the formulation is
applied to the substrate. In general, the higher the temperature, the faster
the chromate removal process is
performed. Containers ranging in sizes from 1 gallon (3.79 litres) to 5,000
gallons (18,925 litres) can be used to
prepare the diluted formulation. This range is mostly dependent upon the size
and quantity of the substrates as well
as the rate of speed and time duration which the substrates are in contact
with the formulation.
The formulation disclosed herein functions as, but not limited to, a cleaner,
chromate remo~ler, oxidation inhibitor, adhesion promotor, flexibility
enhancer, redeposition inhibitor, etch enhancer,
wettor or any combination of the above.
As a cleaner, the formulation loosens and removes fingerprints, oils, greases,
dirt, contaminants and the
like on substrates. This provides an initial cleaning of the substrates before
or as a part of substrate priming and
subsequent processing.
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The formulation also functions as a chromate remover. Chromate is removed from
the substrate by the
acid portion of the formulation and more specifically by the free hydrogen
atoms therefrom.
The formulation also functions as an oxidation inhibitor. Oxidation is
inhibited by the hydrophobic layer
formed by the formulation onto the substrate which functions as barrier
between the substrate acd oxygen sources
such as acid fumes and the environment.
The formulation also promotes adhesion of resists to the substrates. The
hydrophobic layer which displaces
the chromate on the substrate functions as a chemical bonding agent for
resists. Resists usually comprise
photoresists or screen inks and are typically applied after the substrate is
primed to define the circuit images.
Adhesion is especially improved when the formulation is applied to copper clad
substrate surfaces. This adhesion
greatly reduces, if not entirely eliminates, problems arising from marginal
adhesion to thin substrates.
The formulation also dispenses with the requirement for a surface etch.
Surface etches commonly
performed on substrates used in PCB processing. A surface etch is not required
due to the strength of the chemical
bond between the filming amine layer and the resist. The strength of the
chemical bond is especially strong when
the substrate is metallic, except for chrome. Thus, copper material can be
used as a substrate because of the
substantial reduction in copper removal from the substrate. Additionally, an
etching component, such as an iron salt,
can be mixed with the formulation or incorporated into the formulation to
provide faster chromate removal andlor
greater adhesion of the resist (as discussed above).
The formulation also functions as a redeposition inhibitor. Redeposition of
chromate, contaminants and the
like is inhibited by the hydrophobic filming amine layer which the formulation
forms onto the substrates.
The formulation also functions as a flexibility enhancer. On normal copper
clad substrate materials,
photoresists suffer the catalytic effect of the metal at the copper/resist
interface. This catalytic effect, after
exposure to actinic radiation in the ultraviolet portion of the spectrum, can
cause free radical polymerization at the
adhesion boundary. This results in a certain degree of brittleness which
interferes with adhesion and flexibility of
the film. Brittleness hinders removal of the last molecular layer of resist
from the copper during stripping. However,
photoresists bonded to the hydrophobic layer created by the formulation, do
not contact the copper, allowing the
copper to retain significant flexibility after exposure to actinic radiation.
If a neutral screen ink is used instead of
a photoresist, no such catalytic effect occurs. Flexibility of the copper
substrate provides resistance to cracking and
breaking of the substrate or portions thereof when flexed.
The prd~cess of using the formulation to prime substrate materials used in PCB
fabrication comprises
preparing the formulation, coating at least a portion of the substrates with
the formulation, rinsing the substrates
and then drying the substrates. This- process is detailed below.
Preparing the formulation, whether in concentrated or diluted form, is
performed as explained above.
The substrates can then be coated with the formulation in a variety of ways,
such as, but not limited to
r-
immersion, spraying, or waterfalling. Irrespective of the coating technique
used, the container which holds the
formulation is preferably dimensioned and arranged to be integrated into an
assembly line type operation so that
substrate coating is also part of the assembly operation. The preferred
immersion time varies between 20 seconds
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( , CA 02278580 1999-07-23
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to 5 minutes and more preferably until the chromate layer is removed and the
substrate achieves hydrophobicity.
The coating step is repeated as many times as necessary Ior the substrate is
coated as long as required) to
adequately coat the substrate as explained above.
The substrate is then preferably rinsed to remove formulation residue and
prevent spotting. However,
rinsing is not required. Rinsing is performed by coating the substrates with a
solution, such as, but not limited to
water, organic solvents and the like. Preferably, the substrates are rinsed
with distilled water or isopropyl alcohol
(ISA), and more preferably deionized water. Deionized water is more preferred
due to its lack of ions, cleansing
speed, relatively low cost and ease of implementation into assembly
operations. The rinse step is repeated as many
time as necessary to adequately remove formulation residue.
The substrate is then preferably dried so that the substrate can be further
processed without undesired
dripping and to prevent spotting. However, there is no requirement that the
substrates be dried. Most preferably
the substrates are heat dried with forced air. Forced heated air is preferred
due to its speed, relatively low cost
and ease of implementation into assembly operations. However, other drying
techniques can be used, such as, but
not limited to chemicals such as ISA, ambient air, centrifuges and the like.
In addition to using the formulation for cleaning and priming substrates and
inner layer core materials and
flexible composite materials used in the manufacture of PCBs. the formulation
can also applied to chemical milling
processes. Chemical milling refers in general to fabricating metallic alloys.
More specifically, chemical milling refers
to processing large metallic sheets into small, discrete metallic components
with intricately dimensioned patterns or
voids) such as lead frames.
Chemical milling involves applying a resist to a front andlor rear side of the
metallic sheet. The metallic
sheet is then exposed to actinic radiation in the ultraviolet portion of the
spectrum. This exposure causes the areas
unprotected by the resist to be developed away, that is. completely etched
through. Preferably, the metallic sheets
include nickel-iron alloys, copper, nickel, cobalt, combinations thereof or
the like. By this process) small, discrete
metallic parts with intricately dimensioned patterns or voids are made.
The formulation of the present invention allows a single solution to, among
other purposes, clean, inhibit
oxidation and promote adhesion of alloys used in chemical milling manufacture.
The cleaning, oxidation inhibition and
adhesion promoting properties of the formulation are described above. The
formulation is prepared and applied in
the same manner as detailed above. The metallic sheets can thus be coated with
the formulation or a diluted
percentage thereof as described above before application of the resist.
In addition to using the formulation for priming substrates used in the
manufacture of PCBs and chemical
milling, the formulation can also applied in chemical plating processes.
Chemical plating refers in .general to
processing met~lic alloys. More specifically, chemical plating refers to
depositing metallic alloys onto substrate
materials. _
Chemical plating involves applying a resist to a substrate or portions
thereof. After the resist is applied,
the substrate is exposed to actinic radiation in the ultraviolet portion of
the spectrum. This exposure causes the
AMENDE-~ SHEET
CA 02278580 1999-07-23
areas unprotected by the resist to be developed away and subsequently plated.
By this process, discrete metallic
alloys, such as copper, tin, lead, nickel and gold and patterns thereof can be
plated to substrate.
The formulation of the present invention allows a single solution to, among of
purposes, clean, inhibit
oxidation) protect the substrate and promote adhesion of alloys used in
chemical plating manufacture. The cleaning,
oxidation inhibition, substrate protection and adhesion promoting properties
of the formulation are described above.
The solution is prepared and applied in the same manner as detailed above. The
acid most preferable is H2S04.
The substrates can thus be coated with the solution before application of the
resist.
Nt?~D eH~
