Radiation imagery chemistry: process – composition – or product th – Imaged product – Nonsilver image
Reexamination Certificate
2001-04-09
2002-07-23
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaged product
Nonsilver image
C430S270100, C430S275100, C430S277100, C430S311000, C430S326000, C430S909000, C430S910000, C430S919000, C430S920000, C430S964000, C216S049000, C427S592000
Reexamination Certificate
active
06423456
ABSTRACT:
This invention relates to electronic parts and to their production using positive working radiation sensitive compositions.
We have developed novel radiation sensitive compositions and in our earlier-filed patent, application PCT/GB97/01117, published on Oct. 30, 1997, we disclose these novel compositions and their use as imagable coatings for lithographic printing form precursors. We later determined that such compositions are suitable as radiation sensitive coatings for printed circuit and other electronic part precursors. However they are not optimal for use as coatings on all electronic part precursors. In particular, they are not optimal for use as coatings on thin, flexible substrates which are the precursors for some electronic parts and they are not optimal for use on substrates required to be coated and imaged on both sides. For such applications we have sought a composition which can better withstand flexure and surface contact, without becoming scratched, cracked, flaked or delaminated. We have now devised a particular class of heat sensitive compositions which are extremely suitable for such applications.
The coatings used in pattern forming methods for electronic parts such as printed circuits are classified into two types: negative working and positive working. After exposure to radiation and development, the coating pattern is used as a screen for forming the patterns onto the underlying electronic elements—for example by etching an underlying copper foil. Due to the high resolution demands and the requirements of high resistance to etching techniques, positive working systems are widely used. In particular, in the main there have been used alkali developable positive working coatings mainly composed of alkali-soluble novolac resins as disclosed in J. C. Streiter, Kodak Microelectronics Seminar Proceedings, 1979, p. 116. The primary active component of such positive working compositions, both in the context of lithographic printing forms and electronic parts, is a naphthoquinonediazide (NQD) derivative.
The types of electronic parts whose manufacture may use a radiation sensitive coating include printed wiring boards (PWBs), thick- and thin-film circuits, comprising passive elements such as resistors, capacitors and inductors; multichip devices (MDCs); integrated circuits (ICs); and active semiconductor devices. The electronic parts may suitably comprise conductors, for example copper board; semiconductors, for example silicon or germanium; and insulators, for example silica as a surface layer with silicon beneath, with the silica being selectively etched away to expose portions of the silicon beneath (a step in the manufacture of e.g. field effect transistors).
A composition for use in the present invention is heat-sensitive in that localised heating of the composition, preferably by suitable radiation, causes an increase in the aqueous developer solubility of the exposed areas.
Therefore according to one aspect of the present invention there is provided a method of making an electronic part, the method comprising the steps of:
a) delivering heat selectively to regions of a precursor of the electronic part, the precursor comprising a surface carrying a coating, the coating comprising a heat-sensitive composition itself comprising an aqueous developer soluble polymeric substance and a compound which reduces the aqueous developer solubility of the polymeric substance (hereinafter called the “reversible insolubilizer compound”) wherein the aqueous developer solubility of the composition is increased by the said delivery of heat; and
b) developing the precursor in a said aqueous developer in order to remove the heat-sensitive composition in regions to which said heat was delivered;
wherein the aqueous developer soluble polymeric substance comprises a polymer of general formula
wherein R
1
represents a hydrogen atom or alkyl group, R
2
represents a hydrogen atom or alkyl group, R
3
represents a hydrogen atom or alkyl group, and R
4
represents an alkyl or hydroxyalkyl group, and wherein the ratio n/m is in the range 10/1 to 1/10.
We have found the method set out above, using a polymer of formula I, to be a very effective one. The precursors we have used in such a method have excellent performance, with good imaging and development qualities and, at the same time, good mechanical properties, for example excellent flexibility, peel resistance, crack resistance and scratch resistance. Heretofore, despite considerable efforts, using other polymeric substances, we did not find it possible to optimise imaging and development qualities whilst maintaining the mechanical properties required of an electronic part precursor, in particular of an electronic part precursor of a thin flexible nature and/or which is coated on both sides. Furthermore the imaging and development qualities are stable over a useful time frame, whereas with some compositions we have tested, we have found that they become considerably more insoluble, in a given developer, as a function of time after coating, to the extent that they are not of practical utility.
The electronic part precursor may, for example, be a precursor for any of the electronic parts set out earlier in this specification. The said surface may thus be a semiconductor in which case the method may involve one or more subsequent doping steps selectively in regions in which the composition has been removed, such doping steps being for example by vapour phase, liquid immersion or by ion implantation methods. It may be an insulator which is etched to reveal a conductive or semiconductor layer below. For example it may be silica etched to reveal silicon. Alternatively it may be a conductive surface on which a wiring pattern is to be formed, for example by etching the printed circuit precursor in an etchant to remove said conductive surface selectively in the said regions. Preferably, when the surface is conductive it is a copper or a copper-rich alloy. Preferably such a surface is supported by an insulating substrate. The insulating substrate is suitably a dimensionally stable plastics board, for example of epoxy resin reinforced by glass fibers. There may be a conductive surface on one or both sides of the insulating substrate.
Whilst the said surface defined herein may be an insulator requiring to be selectively subjected to etching in order to remove portions thereof to reveal an electroactive layer beneath it, preferably the said surface itself is an electroactive layer. By electroactive we mean a conductor, a semiconductor or a material which when doped functions as a semiconductor. Most preferably the said surface is conductive. It may suitably be a metallic sheet of thickness not exceeding 200 &mgr;m, preferably not exceeding 100 &mgr;m, most preferably not exceeding 30 &mgr;m.
When, as is preferred, an insulating substrate is provided, to support a conductive sheet on one or both sides thereof, the total thickness of the part, prior to application of a said coating, including the conductive sheet or sheets, preferably does not exceed 500 &mgr;m, and more preferably does not exceed 300 &mgr;m.
A preferred part has a metal-insulator-metal sandwich structure.
According to a second aspect of the invention there is provided a precursor for an electronic part, which precursor comprises a surface (not being an aluminium surface which has undergone electrograining, anodising and post-anodic treatments) and a coating carried by the said surface, the coating being as defined above with reference to the first aspect.
In order to increase the sensitivity of the heat-sensitive compositions used in the present invention it is beneficial to include an additional component, namely a radiation absorbing compound capable of absorbing incident radiation and converting it to heat, hereinafter called a “radiation absorbing compound”. A radiation absorbing compound is suitably a dye or pigment.
Therefore according to a further aspect of the present invention there is provided a precursor for an electronic part wherein said coating is adapted to prefe
Bennett Peter Andrew Reath
Kitson Anthony Paul
Ray Kevin Barry
Baker & Botts L.L.P.
Kodak Polychrome Graphics LLC
Schilling Richard L.
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