AU612892B2 - Method of selectively directing electromagnetic radiation to a predetermined location on an article - Google Patents

Description

u~.~?~CLYawru~ecfm~nnaol- COMMONWEALTH OF AUSTRALIA PATENT ACT 1952 COMPLETE SPECIFICATION 61

(ORIGINAL)

FOR OFFICE USE

CLASS

INT. CLASS Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority: Related Art-:

C

I tC t NAME OF APPLICANT: ADDRESS OF APPLICANT: KRONE AKTIENGESELLSCHAFT Beeskowdamm 3-11 D-1000 Berlin 37 FEDERAL REPUBLIC OF GERMANY 4 2 0 39 0 1 os s 4t 4 0 1 o oa 0 4 4 oo 4 NAME(S) OF INVENTOR(S 4444,4 ADDRESS FOR SERVICE: DAVIES COLLISON, Patent Attorneys 1 Little Collins Street, Melboarne, 3000.

COMPLETE SPECIFICATION FOR THE INVENTION ENTITLED: "METHOD OF SELECTIVELY DIRECTING ELECTROMAGNETIC RADIATION TO A PREDETERMINED LOCATION ON AN

ARTICLE"

The following statement is a full description of this invention, including the best method of performing it known to us -1la METHOD FOR SELECTIVELY DIRECTING ELECTROMAGNETIC RADIATION TO A PREDETERMINED LOCATION ON AN ARTICLE 4€ SThis invention relates to a method for selectively i directing electromagnetic radiation to a predetermined location on an article.

I There are circumstances under which it is desirable to selectively direct electromagnetic radiation such as light to the surface of an article. In particular, in the manufacture of printed circuit boards, it is usual to clad the printed circuit board with a copper coating which is then covered with a layer of ultraviolet light-sensitive material.

Desired portions of the layer of ultraviolet light-sensitive material are exposed to ultraviolet light from a suitable source to change the h- characteristics of the material where the light is incident thereon. After exposure, the board is treated with an appropriate solvent to wash away part of the ultraviolet sensitive material, particularly from areas which have been either subjected to ultraviolet light or not so subjected during the described exposure step, whereby to remove that part of the layer which either has or has not been subjected to the ultraviolet light. This removal is usually effected by chemical etching. Generally, since the boards are flat, no difficulty arises in selectively providing a suitable pattern of lighting on the surface, to define the areas of the underlying copper which are to be removed or retained as the case may be. In particular, it is customary to provide a suitable mask in the form of, say, a black and white transparency embodying the desired pattern of lighting usually defining desired circuit board tracks) and this may be juxtaposed over the circuit board and illuminated, or may be projected by photographic projection techniques onto the board.

The above technology is well known and, as indicated, provides satisfactory results with the essentially two dimensional circuit board configurations presently in common use.

rca More recently, however, there is an emergent technology which utilises printed circuit boards, commonly called "injection moulded circuit boardr",which circuit boards have complex three dimensional surface shapes. With these, it is difficult to form desired circuit tracks by selective illumination in the etching process.

U I i rr

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-3- Broadly, in a first aspect, the invention provides a method for selectively directing electromagnetic radiation to a predetermined location on an article, such as a printed circuit board, wherein the electromagnetic radiation is passed into a tool in the form of a body of material substantially tranwparent to said electromagnetic radiation, the surface of which body is altered, over a first portion thereof which is positioned adjacent said location on the article, as compared to an adjacent second portion of the surface of the body, whereby to cause the electromagnetic radiation passed into the body to be selectively emitted from said first portion, for incidence on said article at said location, the electromagnetic radiation being passed into the tool in a way such that the angle of incidence of the electromagnetic radiation with respect to the first and second portions of the surface of the body is greater than a critical angle necessary for total internal reflection of said electromagnetic radiation at said first and second portions of the surface.

In particular embodiments of the invention, the body is formed with a roughened surface at said first portion.

The second portion may, for example, be opaque to prevent emergence of the electromagnetic radiation and/or may be smooth or polished and arranged in such a fashion that the electromagnetic radiation entering into the body is totally internally reflected thereat.

According to a second aspect of the present invention, there is provided a method of forming an electrically conductive region on a circuit board by a process 25 of exposing a selected portion of a first layer of electromagnetic radiation sensitive material of the board to electromagnetic radiation to alter physical characteristics thereof at the exposed portion, subsequently removing either the exposed or a non-exposed portion of the first layer and subjecting the board to a process whereby a copper layer below the first layer is removed at the removed portion of the first layer and is left present below the non-removed portion of the first layer to form the electrically conductive region, characterised in that the selective ap.,ication of light Ct 44 91D42,vrsspc.05krnc.13 r_~ -4is effected by a method according to the first aspect of the present invention.

According to a third aspect of the invention, there is provided a printed circuit board when produced by a method according to either one of the first or second aspects of the present invention.

According to a fourth aspect of the present invention, there is provided a tool for selectively directing radiation onto a selected area of a non-planar surface, the tool i having a body portion which comprises radiation input and output ports, radiation i 10 guiding surfaces for guiding radiation input at the input port at an angle of incidence with respect to the guiding surfaces greater than or equal to a critical angle necessary ii for total internal reflection of said radiation at said guiding surfaces, in a direction generally towards said output port, said radiation output port comprising selected i surface modification of the body portion of the tool such that radiation guided by the guiding surfaces is output from the tool in a pattern corresponding to said selected area of the non-planar surface.

The invention is further described by way of example only with reference to the accompanying drawings in which: 910423,vrspc.005,krone.1,4 Figures 1 and 2 are diagrams illustrating the phenomenom of total internal reflection; Figure 3 is a perspective view of a tool useful in practising the invention; and Figure 4 is a fragmentary perspective diagram of portion of a moulded printed circuit board with which the tool of figure 3 is useful.

Referring firstly to figures 1 and 2, a ray 10 of light travelling within a body 12 of optically "transparent material is shown as being incident at an angle on a surface 12a of the body. If, as shown in figure 1, the surface 12a is smooth, the light ray will, if incident at a relativel-y small angle, be totally internally reflected within the body at the 'corresponding angle as shown. On the other hand, if the surface of 12a is rough, as shown in figure 2, the ray 10 will not be totally internally reflected when incident at the angle but will be refracted at the surface 12a to pass outwardly from "tthe sulrface 12a.

Figure 3 shows a tool 20 in the form of a rectangular prismatic body of optically transparent material, such as glass. The tool is designed for directing light selectively to the surface of a cavity 22 formed in the surface 24 of an article in the form of an injection moulded printed circuit board 44.

Cavity 22 is of rectangular cross section corresponding to the cross section of the tool The cavity presents four side wall surfaces 22a, 22b, -s22c and 22d. For the purposes of the present 1- ~"E~a 1 example, it is supposed that it is desired to irradiate all of the surfaces 22a, 22b, 22c and 22d, save for a strip-like region 22e on the surface 22d and a circular region 22f on the surface 22a.

By the present invention, light, from a light source such as an ultraviolet light source is directed lengthwise into the tool 20, at the upper end as shown in figure 3 to a lower end as shown in figure 3, the lower end being neatly accommodated within the cavity 22 whereby lower portions of the side surfaces of the tool 20 are closely adjacent to respective ones of the surfaces 22a, 22b, 22c and 22d of cavity 22. Over the major part of its outer surface, the o tool 20 ha' a smooth surface which is however optically opaque insofar as light transmission exteriorly of the tool is concerned, due to internal reflection of the light from source 40 which is directed lengthwise into the tool. The four side surfaces 20a, 20b, 20c and 20d are, however, over lower portions thereof which are adjacent the surfaces 22a, 22b, 22c, 22d respectively of the cavity 22 when the tool is positioned in cavity 22, treated in a manner effective to provide light transmission as required to the surfaces 22a, 22b, 22c and 22d. In particular, surface 20a which is brought adjacent surface 22a in use of the tool, has a roughened portion 26 at the centre of which is provided an opaque circular portion 28, which portion is in use of the tool to be brought adjacent a corresponding region 22f of surface 22a of cavity 22. The lower portions of the surfaces 20c and are roughened where these are to be adjacent surfaces 22c, 22b in use of tool 20. Similarly, the ~~lru- u. ~l lower part 30 of surface 2 where this is to be adjacent surface 22d of cavity 22, is roughened over a portion 30, save for a strip-like portion 32 which is to be positioned against the correspondingly shaped region 22e of surface 22d.

In use, then, with the tool 20 inserted into the cavity 22 as described, ultraviolet light from the light source 40 is directed lengthwise of the tool and, due to the roughening of the portions 26 and and lower portions of the surfaces 20c, 20b light is caused to be emitted from the tool over those portions and to be incident upon the surfaces 22a, t 22b, 22c and 22d. Light is, however, blocked from e reaching the region 22f because of the opaqueness of the portion 28 on the tool 20 and is similarly blocked from reaching region 22e by virtue of the opaqueness of the portion 32.

By the above, the surface of the circuit board 44 may, at the cavity 22,be formed with a suitable ultraviolet sensitive substance coated thereon, over an underlying copper coating whereby, on exposure to light at the surfaces 22a, 22b, 22c and 22d as described, to leave the regions 22f and 22e such as not to have light exposed thereon. Thus, in a subsequen.: etching step the portions of the surfaces 22a, 22b, 22c and 22d to which light was directed may be etched away leaving underlying copper only at the regions 22e and 22f. These regions may, for example, comprise electrical contacts associated with the circuit board 44.

By use of arrangements as above described, tools of i I~ -L -8different form to the described prism may be utilised, such as configured as desired in. order to permit selective application of light to various cavities or other complexly formed regions of the surface of the circuit board 44.

While, in the described embodiment, reference is made to the use of a source of ultra-violet radiation, the invention may be practised, where appropriate, by using other sources of electromagnetic radiation, particularly where the sensitive coating of the circuit board is sensitive to radiation from such other sources.

Generally, in the described method use will make use of sources of electromagnetic radiation of optical or near optical wave lengths.

The described construction has been advanced merely by way of explanation and many modifications and variations may be made thereto without departing from the spirit and scope of the invention.

In the following claims, angles of incidence of radiation upon a surface are defined in the conventional sense with respect to a vector normal to the surface. Thus an angle of incidence of zero is normal to the surface.

S.i 910423,vrsspcfO5,kroe.1,8 mL-- j

Claims (11)

1. A method for selectively directing electromagnetic radiation to a predetermined location on an article, wherein the electromagnetic radiation is passed into a tool in the form of a body of material substantially transparent to said electromagnetic radiation, the surface of which body is altered, over a first portion thereof which is positioned adjacent said location on the article, as compared to an adjacent second portion of the surface of the body, whereby to cause the electromagnetic radiation passed into the body to be selectively emitted from said first portion, for incidence on said article at said location, the electromagnetic radiation being passed into the tool in a way such that the angle of incidence of the electromagnetic radiation with respect to the first and second portions of the surface of the body is greater than a critical angle aecessary for total internal reflection of said electromagnetic radiation at said first and second portions of the surface.

2. A method as claimed in claim 1 wherein the body is formed with a roughened surface at said first portion.

3. A method as claimed in claim 1 or claim 2 wherein the second portion is opaque to prevent emergence of the electromagnetic radiation and/or is smooth or polished and arranged in such a fashion that the electromagnetic radiation entering into the body is totally internally reflected thereat.

4. A method of forming an electrically conductive region on a circuit board by a process of exposing a selected portion of a first layer of electromagnetic radiation sensitive material of the 91423,vrsspe.OOS,kone.,9 board to electromagnetic radiation to alter physical characteristics thereof at the exposed portion, subsequently removing either the exposed or a non-exposed portion of the first layer and subjecting the board to a process whereby a copper layer below the first layer is removed at the removed portion of the first layer and is left present below the non-removed portion of the first layer to form the electrically conductive region, characterised in that the selective application of light is effected by the method claimed in any one of claims 1 to 3. A method as claimed in claim 4, wherein said region is positioned on a surface of a cavity formed in said circuit board, said body having a portion of complementary cross-section to the cavity and being inserted thereinto so that portions of the side surfaces of the body are positioned adjacent corresponding surfaces of the cavity prior to said directing of said electromagnetic radiation.

6. A method as claimed in any preceding claim wherein said electromagnetic radiation comprises light of optical or near optical wave length.

7. A method as claimed in claim 6 wherein said light is ultraviolet light.

8. A printed circuit board when produced by the method claimed in claim 4 or claim -11-

9. A tool for selectively directing radiation onto a selected area of a non-planar surface, the tool having a body portion which comprises radiation input and output ports, radiation guiding surfaces for guiding radiation input at the input port at an angle of incidence with respect to the guiding surfaces greater than or equal to a critical angle necessary for total internal reflection of said radiation at said guiding surfaces, in a direction generally towards said output port, said radiation output port comprising selected surface modification of the body portion of the tool such that radiation guided by the guiding surfaces is output from the tool in a pattern corresponding to said selected area of the non-planar surface. A tool according to claim 9 wherein the radiation output port comprises a smooth external surface of the body portion of the tool, arranged at an angle to Sradiation guided by the guiding surfaces which is greater than or equal to the angle 15 of total internal reflection of the radiation at the external surface, said surface i i modification comprising selective roughening of the surface of the body portion of the *i tool at the output port so as to correspond to said pattern such that total internal reflection of radiation guided by the guiding surfaces is prevented where the surface has been roughened, said radiation thus being output at the output port in the pattern corresponding to said selected areas of the non-planar surface.

11. A method of selectively directing radiation to a predetermined location on an i article substantially as hereinbefore described with 9023,vtsmpc.005,kranc.lll.1 w- I i i-i ili ea; reference to the accompanying drawings.

12. Apparatus for selectively directing radiation to a predetermined location on an article substantially as hereinbefore described with reference to the accompanying drawings.

13. A tool for selectively directing radiation onto selected areas of a non-planar surface, substantially as hereinbefore described with reference to the accompanying drawings. DATED this 1st day of September, 1989. KRONE AKTIENGESELLSCHAFT S By its Patent Attorneys DAVIES COLLISON n