Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
1999-04-29
2001-03-27
Hamilton, Cynthia (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C522S095000, C430S277100
Reexamination Certificate
active
06207347
ABSTRACT:
The present invention is directed to negative-acting photoimageable compositions such as those used as photoresists in the art of printed circuitry. The photoimageable composition contains, as a portion of its photoimageable component, a urethane biuret oligomer.
BACKGROUND OF THE INVENTION
This invention is directed to negative-acting photoimageable compositions which are developable in alkaline aqueous solutions. The invention is particularly applicable to primary photoimaging resists, but is applicable, as well, to compositions that are hardenable so as to form solder masks and the like.
A variety of such photoimageable compositions are described. Essential compositions of the type to which the present invention is directed are A) a binder polymer; B) photopolymerizable &agr;,&bgr;-ethylenically unsaturated compound(s), and C) a photoinitiator chemical system. The binder polymer A) has sufficient acid functionality, generally carboxylic acid functionality, that the binder polymer is soluble in alkaline aqueous solution and thereby renders the photoimageable composition developable in alkaline aqueous solutions. The photopolymerizeable compound(s) B) are monomers and/or short chain oligomers, a substantial portion of which have multiple &agr;,&bgr;-ethylenic unsaturated functionality.
The photoinitiator chemical system C) includes chemicals which generate free radicals upon exposure to actinic radiation. These free radicals propagate the polymerization of the &agr;,&bgr;-ethylenic unsaturated moieties of the photopolymerizeable compounds B). Herein, the photoinitiator system C) is deemed to include not only chemical compounds which generate free radicals, but catalysts or sensitizers which promote the free-radical initiated polymerization of the &agr;,&bgr;-ethylenic unsaturated moieties of the photopolymerizeable compounds B).
Circuit boards almost invariably have through-holes to connect circuitry on opposite faces of the board. With holes becoming larger on circuit boards, higher tenting strength is becoming increasingly important; thus greater flexibility of photoimageable compositions is required.
Improved flexibility also contributes to an improved cross hatch adhesion which allows for better compatibility with automated polyester removal systems. If the photoresist is brittle, these polyester removal systems will cause chipping of the photoresist and subsequently, circuit line defects.
By replacing a portion of conventional photo reactive monomers (like ethoxylated trimethylolpropane triacrylate) with an isocyanuric, urethane-based oligomer, a significant improvement to tenting strength and flexibility was observed. However, even though the flexibility was noticeably better, the fine line adhesion was not improved and the oligomer was shown to be a major source of developing scumming.
Improved fine line adhesion and lower developer scum has been demonstrated when the isocyanuric oligomer is comprised of the product of a polyethoxymonomethacrylate and the isocyanurate trimer of hexamethylene diisocyanate, as described, for example, in European Patent Application EP 0 738927 A2 and Japanese Patent Document JP 08-2868372. The use of the product of a polyalkoxymonomethacrylate in UV-curable photoresists enhances the performance of such compositions over those made with urethane compounds based on the isocyanurate trimer of hexamethylene diisocyanate. Present day commercial requirements include further improvements to both fine line adhesion and developer scumming.
Herein, urethane biuret oligomers are incorporated as at least a portion of the photopolymerizeable component B). The urethane biuret oligomers are found to minimize the developer scum. Along with improving the developer scum problem, it has been found that urethane biuret oligomers improve the fine line adhesion of the photoresist.
SUMMARY OF THE INVENTION
The present invention is directed to a negative-acting photoimageable composition comprises A) between about 30 and about 80 wt %, based on total weight of A) plus B) of an organic polymeric binder having sufficient acid functionality to render the photoimageable composition developable in alkaline aqueous solution, B) between about 20 and about 70 wt % based on total weight of A) plus B) of addition-polymerizeable, non-gaseous &agr;,&bgr;-ethylenically unsaturated compounds capable of forming a polymer by free-radical initiated chain-propagating addition polymerization, and C) between about 0.1 and about 20 wt % relative to total weight of A) plus B) of an organic, radiation-sensitive free-radical generating chemical system activatable by actinic radiation to initiate chain-propagating addition polymerization of the addition-polymerizeable material. In accordance with the invention, component B) comprises between about 1 and about 70 wt %, based on total weight of A) plus B) of a biuret urethane oligomer having the general formula:
R—CO—NH—Z—N—(CO—NH—Z—NH—CO—R)
2
where the R's are the same or different and have the general formula:
—A
m
—[—CO—NH—Z—NH—CO—]
s
—A
p
—O—CO—CY=CH
2
,
where m=6-20, p=0-20, s=0-1;
the A's are the same or different and are selected from the group consisting of;
—[O—CHY—CHY—]—,
where the Ys are the same or different and are selected from the group consisting of H, CH
3
, or C
2
H
5
,
—[O—(CH
2
)
3-4
—]—,
—[—O—(CH
2
)
3-5
—CO—]—
and mixtures thereof; and
Z is a divalent alkyl, cycloalkyl, aromatic, or alkylaromatic hydrocarbon moiety.
In the formula above, it is important that m equal at least 6 to obtain the requisite flexibility of the photoimageable composition. U.S. Pat. No. 4,019,972 describes photoimageable compositions containing similar photopolymerizable compounds. However, in the examples of this patent, in the corresponding compounds, m=1. This patent further explicitly teaches in Column 5, lines 9-14, that it is disadvantageous for m to be 5 or greater. Contrary to the teaching of U.S. Pat. No. 4,019,972, it is found that improved flexibility is increased without loss of adhesion to the copper substrate. If m is not equal to at least 6, more brittle compositions result.
Where it is stated above that the A's are the same or different, it is meant that the A's may be the same or different in any one oligomer molecule or may be the same or different within any one R group. If the A's are different within any one R group, the different A's may be randomly distributed or the different A's may be in blocks.
In the general formulae above, simple examples of Z include hexamethylene, phenylene, and cyclohexylene, although more complex divalent hydrocarbon moieties are also suitable. The choice of Z is generally not considered to be particularly critical, the selection generally depending upon the commercial availability of suitable precursors.
DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS
Herein, unless otherwise noted, all percentages are weight percentages. Component A) (the binder polymer) and Component B) (the photoimageable compounds) which are herein considered to equal 100 wt %, and other components, including the components of the photoinitiator chemical system, being based on total weight of A) plus B).
The invention is directed to photoimageable compositions which are developable in alkaline aqueous solution and which therefore have substantial acid functionality. Such photoimageable compositions typically have a binder A) having acid functionality, typically an acid number of at least about 80, preferably at least about 100 and more preferably about 150 or more, up to about 250. The acid functionality is typically carboxylic acid functionality, but may also include, for example, sulfonic acid functionality or phosphoric acid functionality. Binder polymers for photoimageable compositions typically have weight average molecular weights between about 20,000 and about 200,000, preferably at least about 80,000.
The polymers are typically derived from a mixture of acid functional monomers and non-acid funct
Lundy Daniel L.
Negandhi Nitin J.
Hamilton Cynthia
Nichigo-Morton Co. Ltd.
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