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
2001-06-21
2004-02-03
Baxter, Janet (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
C430S281100, C430S311000, C430S315000, C430S319000, C430S322000, C430S324000, C430S325000, C430S328000, C430S330000, C430S331000
Reexamination Certificate
active
06686122
ABSTRACT:
The present invention relates to a process for the production of a resist coating, and to the use of this process for the production of a primary resist coating, a solder-stop resist coating or for the sequential build-up of multilayer circuit boards.
Resist coatings are an essential tool in the production of modern circuit boards. Inter alia, a distinction is made here between so-called primary resists and solder-stop resists.
Primary resists are imagewise-structured coatings on a substrate which are intended to protect certain parts of the substrate for a temporary period against the effect of a certain treatment to which the substrate is subjected, for example when a copper-laminated laminate as substrate is to be subjected to an etch treatment, in which the copper is to be removed from certain areas of the laminate. After completion of this treatment, the primary resists are generally removed completely from the substrate again. The imagewise structuring of the primary resist coating is generally produced by imagewise exposure of a continuous layer of a resist material on the substrate, which chemically modifies the resist material at the irradiated points. With the aid of suitable developers, either the irradiated or the unirradiated areas of the resist coating can then be dissolved and the underlying substrate uncovered. In the case of certain resist types, for example chemically reinforced resists, it is necessary to subject the imagewise-exposed resist coating, before development, to extended heating in order to achieve adequate differentiation of the solubilities of irradiated and non-irradiated material in the developer.
Solder-stop resists, which cover virtually the entire surface of a ready-structured and assembled circuit board, with the exception of the areas at which contact of the printed circuit with a solder material during subsequent treatment of the circuit board with the solder material is desired, are generally not removed after completion of this treatment. The solder-stop resist remains on the circuit board as a protective coating, inter alia against environmental influences and for electrical insulation of the individual conductor tracks of the printed circuit from one another. In addition to a photocurable component system, which, as in the case of the primary resists, is employed for structuring the resist coating by imagewise exposure, if desired heating of the resist coating, and development, solder-stop resists frequently also comprise a purely thermally curable component system, which is only cured with the aid of heat after the structuring of the coating, and which improves the protective properties of the coating.
Owing to their good electrical insulation properties, solder-stop resist compositions are also used, in particular, in the sequential build-up of multilayer circuit boards. In this case, a first printed circuit is coated with a photoresist coating as insulation layer. This is structured by imagewise exposure, if desired heating of the resist coating, and development in such a way that holes are produced in the insulation layer at the points at which electrical connections of the first printing circuit to a further printed circuit applied to the insulation layer are later necessary. The structured resist layer is then, if necessary, thermally cured. The holes in the insulating resist layer are rendered electrically conductive, for example by copper plating, and the second printed circuit is then built up on the insulation layer in a known manner. The outlined procedure is, if desired, repeated one or more times to give multilayer circuit boards.
Whereas “non-thermal” process steps, for example photostructuring, in photoresist applications as mentioned above generally proceed relatively quickly, for example within a few seconds, thermal treatment steps require a significantly greater amount of time. These thermal treatment steps include, for example, predrying of the resist coating on the substrate, i.e. removal of a solvent, which frequently serves as carrier for application of the resist compositions to the substrate, and which generally requires from 20 to 30 minutes in conventional fan-assisted ovens. A similar amount of time may be necessary for the above-mentioned interim heating of the irradiated resist coating before development. In general, however, thermal final curing of solder-stop resist coatings is very particularly time-consuming, generally requiring treatment of the coating at temperatures in the region of about 150° C. for one hour or even longer. Although assembly-line plants, as generally usual today in circuit-board technology, are able to conceal the time needed for the thermal treatment steps in circuit board production, they require, however, very large ovens for this purpose and/or complex plants for transporting the assembly-line product into the ovens in order to ensure that the boards remain in the oven for a sufficiently long time at a given assembly line speed in order to complete the thermal treatment.
EP-A-0 115 354, Example 1, has already described the final curing of a ready-structured solder-stop mask coating by means of infrared radiation, but precise details of the wavelengths of the infrared radiation used are not given. From the information on the speed at which the coated circuit boards are moved past the infrared radiation source, it is evident that the final curing of a conventional circuit board takes at least six minutes or longer.
The present invention is based on the surprising knowledge that conventional resist compositions absorb radiation in the near infrared range particularly well owing to the polar components present in them, during which the compositions heat up sufficiently that the above-mentioned thermal treatment steps can be carried out within a few seconds, typically within from 1 to 60 seconds and often in less than 10 seconds. Also surprisingly, no technical disadvantages occur here, for example solvent inclusions during predrying or increased brittleness during the thermal curing. In addition, a significantly better degree of curing is generally achieved on use of near infrared radiation for the final curing of solder-stop resist layers.
The invention therefore relates to a process for the production of a resist coating, in which
(a) a substrate is coated with a resist composition which comprises at least one component which absorbs radiation in the near infrared region with warming of the coating; and
(b) the resist composition or a composition derived therefrom and obtained during the process is subjected at least once during the process to thermal treatment with the aid of radiation in the near infrared region.
In this application, the term radiation in the near infrared region is taken to mean, in particular, radiation having a wavelength of from about 760 to 1400 nm. Heating systems based on this radiation have been known for some time and are marketed commercially by, for example, Research Inc., US, or INDUSTRIESERVIS, DE, but have hitherto not been employed in resist technology and in the production of electrical circuit boards. The radiation employed according to the invention preferably essentially comprises radiation having a wavelength of from 760 to 999 nm.
The emitters for the near infrared radiation are preferably installed in such a way that they irradiate the entire width of the conveyor belt passed beneath, on which the substrates provided with the resist coating, for example the circuit boards, are moved forwards. It may be necessary to install a plurality of emitters alongside one another. The separation between the emitters and the belt and the power with which the emitters are operated are preferably optimized as a function of further process parameters, inter alia the specific resist composition, the thickness of the resist layer to be thermally treated, and the most suitable temperature for the desired thermal reaction, which is possible for the person skilled in the art using a few simple experiments.
There are no specific restrictions for the type of
Baxter Janet
Levato Tiffany A.
Neuman Kristin H.
Proskauer Rose LLP
Vantico Inc.
LandOfFree
Production of photoresist coatings does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Production of photoresist coatings, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Production of photoresist coatings will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3277200