Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Patent
1993-10-14
1996-09-10
Lesmes, George F.
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
430325, 43027014, 430 5, 427375, 4273884, G03C 500
Patent
active
055544878
DESCRIPTION:
BRIEF SUMMARY
This invention is concerned with improvements in and relating to the formation of patterned resist masks in the manufacture of printed circuit boards and like electronic circuitry.
The use of resists in the manufacture of printed circuits is well established and such resists are used, for example, as etch resists, plating resists and solder resists. One common manner in which photoresists are employed comprises a so-called "photoimaging" technique. In such a technique, a layer of the resist upon an appropriate substrate is imagewise exposed to radiation through a patterned mask whereby portions of the resist exposed to radiation are cured (polymerised) and portions not so exposed remained uncured. The layer of resist, after exposure, is then "developed", i.e. by removing uncured (unexposed) portions of the resist by washing with an appropriate solvent. In order to obtain good resolution and definition in the exposure stage, it is most desirable that the patterned mask be placed in actual physical contact with the layers of resist.
A layer of resist may be formed upon a substrate by laminating a dry film resist to the substrate or by coating a solution of the resist onto the substrate and allowing it to dry by the evaporation of volatile solvent or diluent. The use of mechanical liquid coating techniques (such as curtain coating, dip coating, etc.) for applying a resist is generally more flexible and economic than is a laminating process. However the use of a solution of the resist material generally limits such a process to the use of appropriate organic solvents for dissolution of the resinous components of the photoresists and, nowadays, processes which make it possible to use aqueous solvents are often preferable.
It has now been found, in accordance with the present invention, that an acceptable patterned cured resist layer may be obtained by mechanically applying, in the first instance, a suspension or dispersion of a solid powdered resist material in a liquid carrier, to a substrate, subsequently removing the liquid carrier and then photoimaging the resultant layer of photoresist material.
According to the invention, therefore, there is provided a process for the formation of a patterned cured resist upon a substrate which comprises the steps of: resist material in a liquid carrier to the substrate; reflowing, under the action of heat, the powdered solid to give a coherent film on the substrate; mask whereby portions of the layer exposed to radiation are cured; and portions thereof with an appropriate solvent.
The process of the invention is applicable to the formation of various patterned resist layers upon printed circuit boards, or like electronic circuits, during the course of their manufacture, for example etch resists, plating resists and solder resists, particularly the latter.
The basic material used in the process of the invention comprises a suspension of powdered solid photoresist material in a liquid carrier. The liquid carrier may be an organic solvent and/or water. In general, it is preferred to employ water as carrier, for environmental and safety reasons. In general terms, the suspension used in accordance with the invention will comprise from 20 to 80% by weight of powdered solid resist, preferably from 20 to 50% by weight thereof; the balance being formed by the liquid carrier. As will be appreciated it is generally desirable to maintain as high a level of powdered solid material in the suspension as possible so as to reduce the amount of energy necessary to remove the liquid by evaporation but, at the same time, consideration has to be given to question of applicability of the suspension as a whole. In this latter connection, any suitable mechanical process may be used to form a layer of the suspension upon the substrate, e.g. spray coating, dip coating, roller coating, curtain coating etc.
The powdered solid material suitably has a particle size of from 0.1 to 15 microns, preferably 0.5 to 8 microns.
The basic components of the photoresist material will generally be: material capa
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Ivory Nicholas E.
Jeffries Michael
Palmer Robert J.
Thatcher Wrenford J.
Coates Brothers PLC
Lesmes George F.
Weiner Laura
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