Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Removal of imaged layers
Reexamination Certificate
1998-12-04
2001-06-19
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Removal of imaged layers
C430S325000, C430S331000, C430S493000
Reexamination Certificate
active
06248506
ABSTRACT:
The present invention is directed to alkaline aqueous development solutions such as are used to develop photoresists.
BACKGROUND OF THE INVENTION
In the process of manufacturing printed circuit boards, UV curable photoresist are used. The exposed portion of the photoresist becomes insoluble in developer solution (dilute alkaline solution) and forms a protective barrier to other processing chemicals (for example, etching and plating solutions). The unexposed portion of the photoresist needs to rinse freely from the circuit board with a mild alkaline solution (for example, 1% sodium carbonate, monohydrate in water). The development occurs because the polymer in the photoresist contains acid functionality. These acid groups within the organic polymer matrix are neutralized in alkaline solution forming a water miscible organic salt. As the photoresist builds up in solution (called developer loading), insoluble organic materials begin to form in the developing tank, eventually forming a water insoluble scum or residue. The presence of anti-foam additives (conventionally added to developing solutions to minimize foaming) greatly increases the tendency for scum to form. As the level of scum builds, chances increase for an inadvertent redeposit of these water insoluble residues onto the developed circuit board. These redeposited residues cause a retardation of the etching solution (etching chemistries have difficulty penetrating any organic residues). Where the etch is retarded, circuit shorts form causing a defective circuit board. In addition to increasing the potential for defective circuit boards, this residue also makes it difficult to clean equipment increasing maintenance time.
Accordingly, it is a primary object of the present invention to provide developing solutions in which the build-up of scum and residue is reduced.
SUMMARY OF THE INVENTION
In accordance with the invention, alkaline aqueous developing solutions, containing between about 0.1 and about 3.0 wt % of a base, are improved by the addition of
A) between about 0.05 and about 1.0 wt % of a first surfactant or surfactant mixture, the first surfactant(s) having the general formula:
R—O—(AO)
n
—H (I)
where AO are alkylene oxide units selected from ethylene oxide units (CH
2
—CH
2
—O) and propylene oxide units (CH(CH
3
)—CH
2
—O) or (CH
2
—CH(CH
3
)—O) and mixtures of ethylene and propylene oxide units, either in the mixture of molecules, where R is a hydrophobic group, typically a hydrocarbon group, n is between about 8 and about 200, preferably between about 15 and about 40, and
B) as a second surfactant, between about 0.05 and about 1.0 wt % of an organic salt, the weight ratio of A) to B) being between about 1:5 and about 5:1, preferably in the range of 1:1, said organic salt having the formula:
where
R is an alkyl or aryl group, preferably phenyl,
A is selected from carboxyl, sulfonyl, phosphonyl and mixtures thereof, preferably sulfonyl,
M is a charge-balancing cation, and
n is between 1 and about 200, preferably between 2 and about 100.
The developing solution may also contain an anti-foam agent, e.g., at between about 0.01 and about 1.0 wt %.
DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS
Aqueous developing solutions to which the present invention generally applies are well known for developing photoresist compositions, both primary photoresists and photoresists which are intended to form hard permanent layers, such as are suitable for solder masks. Examples of such photoresists and the alkaline aqueous development solutions are found, for example, in U.S. Pat. Nos. 5,576,145, 5,609,991, 5,393,643, and 5,364,736, the teachings of each of which are incorporated herein by reference.
The photoresist compositions vary in composition, but typically such photoresist compositions comprise A) between about 20 and about 80 wt % of a binder polymer having an acid number between about 40 and about 250, B) between about 15 and about 50 wt % of &agr;,&bgr;-ethylenically unsaturated compounds, typically monomers and short-chain oligomers, and C) between about 0.1 and about 25 wt % of a photoinitiator or photoinitiator chemical system, these weight percentages being based on total weight of A) plus B) plus C).
Typically, the alkaline aqueous solution is a solution of sodium carbonate, e.g., 1% sodium carbonate monohydrate. However, other bases, such as NaOH, KOH, triethanolamine, potassium carbonate etc. may be used to provide the alkalinity necessary for developing photoresists of this type. The alkalinity of the developing solution forms salts with the acid functionality of the binder polymer, typically carboxylic acid functionality, rendering the binder polymer miscible in the alkaline aqueous solution. Thus, photoresists of this type are applied as a layer to a substrate, exposed to patterned actinic radiation, and developed in alkaline aqueous solution which washes away non-exposed, un-polymerized portions of the photoresist layer.
Alkoxylated emulsifiers A) in accordance with the invention, in particular an emulsifier with a tristyrylphenol hydrophobe proved effective, by itself in reducing oily residues. However, large amounts of sinking residues were present. By adding an organic salt B), such as a phenolic sulfonyl salt, to the mixture, the solid residues were eliminated. By itself, a phenolic, sulfonyl salt did not reduce the floating scum. Therefore, this combined synergistic mixture of emulsifiers A) and B) is useful for elimination of all photoresist residues. A weight ratio of A) to B) of about 1:1 appears to be optimal.
In the preferred alkoxylated emulsifier (R of formula (I)), the hydrophobe is tristyrylphenol. Such emulsifiers are sold as Soprophor® BSU and Soprophor® S/40-P having the chemical formula
for Soprophor® BSU, n=16; for Soprophor® s/40-P, n=40.
A suitable organic salt is a phenolic sulfonyl salt which is sold as Newkalgen® TX-C and has the formula:
(n is not specified specified by the manufacturer but is believed to be in the range of 2 to 100).
The cation may be any suitable charge-balancing cation, such as potassium, lithium, ammonium, magnesium, calcium, cesium, etc.
The alkaline aqueous solution may also contain an anti-foam agent, such as that sold as Antifoam 80 by Morton International.
The invention will now be described in greater detail by way of specific example.
REFERENCES:
patent: 4329422 (1982-05-01), Langlais
patent: 4370406 (1983-01-01), Jones
patent: 5122438 (1992-06-01), Nogami
patent: 5364736 (1994-11-01), Eramo, Jr. et al.
patent: 5393643 (1995-02-01), Lundy et al.
patent: 5576145 (1996-11-01), Keil et al.
patent: 5609991 (1997-03-01), Briguglio et al.
patent: 5922522 (1999-07-01), Barr
patent: 6063550 (2000-05-01), Lundy
Ser. No. 09/069,517, filed Apr. 29, 1998, Robert Barr and Daniel E. Lundy.
Ser. No. 09/069,518, filed Apr. 29, 1998, Robert Barr and Daniel E. Lundy.
Barr Robert
Lundy Daniel E.
Barreca Nicole
Huff Mark F.
Nichigo-Morton
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