Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2000-06-02
2003-04-22
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S320000, C430S326000, C430S330000, C430S331000, C430S270100, C430S277100, C430S905000, C430S910000, C430S909000, C430S945000, C430S944000
Reexamination Certificate
active
06551763
ABSTRACT:
BACKGROUND OF THE INVENTION
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. The compositions disclosed therein comprise a polymeric resin and a compound which we called a “reversible insolubilizer compound”. The polymeric resin alone is relatively soluble in aqueous developers, but is rendered substantially less soluble in them by the presence of a reversible insolubilizer compound, in the compositions. However, on delivery of heat to the compositions the compositions become more readily soluble in aqueous developers. Hence, if heat is delivered in a pattern to the compositions, the pattern may be revealed by development in an appropriate aqueous developer.
We later determined that such compositions are suitable as radiation sensitive coatings for printed circuit and other electronic part precursors.
Up to now most commercial positive working printing plate compositions have contained naphthoquinodiazide (NQD) moieties as a “reversible insolubilizer compound”, such compositions being imaged using UV radiation.
We have now devised compositions which are useful at least for forming patterns on electronic part precursors, and which, to our surprise, do not require any said “reversible insolubilizer compound”. These compositions are able to record an image effectively, by means of heat, when freshly coated, but not, we believe, reliably thereafter. Therefore they are suitable for use as imagable compositions on electronic part precursors, where it is an industry practice for a single manufacturer to both apply an imagable composition to a precursor and to image the precursor, within a relatively short time frame.
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 electromagnetic 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 but without any said “reversible solubilizer 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.
The electronic part may, for example, be 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 fibres. There may be a conductive surface on one or both sides of the insulating substrate.
While 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, 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”, but which does not also function as a reversible insolubilizer 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 preferentially absorb radiation and convert said radiation to heat.
In one embodiment of the present invention there is provided a heat-sensitive positive working precursor for an electronic part wherein the said coating includes an additional layer disposed beneath the heat-sensitive composition; wherein the additional layer comprises a radiation absorbing compound.
Preferably the aqueous developer solubility of the composition is not increased by incident UV radiation. When we state that the aqueous developer solubility of the composition is not increased by incident UV radiation we mean that it is not substantially increased (that is, by an amount which would mean that UV safelighting conditions would have to be employed) over a time span applicable to the manufacturing process involved—which in the case of electronic part manufacture means over a time span of up to 2 hours, preferably up to 6 hours, most preferably up to 24 hours. Insubstantial increases in solubility due to incident UV radiation, arising from ambient light, for example arising from daylight or ordinary white lights such as fluorescent strip lights, over such periods, may be tolerated within the scope of this invention.
Preferably the aqueous developer soluble polymeric substance is applied directly to the surface of the electronic part precursor, and is preferably used “fresh” that is, it is imaged, by the patternwise delivery of heat, within 14 days, preferably within 7 days, most preferably with
Bayes Stuart
Bennett Peter Andrew Reath
Kitson Anthony Paul
McCullough Christopher David
Ray Kevin Barry
Baxter Janet
Faegre & Benson LLP
Kodak Polychrome Graphics LLC
Lee Sin J.
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