Apparatus and method providing substantially two-dimensionally uniform irradiation

[0002] The present invention pertains to an apparatus and method providing substantially two-dimensionally uniform irradiation of large areas with a high level of radiation. More particularly, the present invention pertains to an apparatus for and a method of uniformly projecting a high level of radiation onto a large planar target surface so as to uniformly treat the surface.

[0003] Various manufacturing processes include treating a planar surface by irradiating the surface with, for example, ultraviolet light or other radiation. The radiation treatment may be related to curing, purification, disinfection, advanced oxidation or some other procedure. By way of example, manufacturing of printed circuit boards frequently involves forming conductive paths by a photoresist process in which a board treated with a photoresist in a desired pattern is irradiated as a part of a process to remove material from specified areas on the board. Similarly, in some printing processes a printed pattern is cured by irradiating the pattern. Obtaining a high quality, uniform product requires irradiating a two-dimensionally uniform high level of radiation over the entire target area. Otherwise irregularities in the finished product may result.

[0004] Existing devices often expose the central area of the irradiated surface to more radiation than the edge areas of the surface. The areas of high radiation may receive more than the desired level, possibly causing damage, while the areas of low radiation may be undertreated.

[0005] Various techniques have been used in the past to control the uniformity of irradiation of planar target surfaces. By way of example, U.S. Pat. No. 4,010,374 discloses an ultraviolet light processor including a primary light source which exposes a target surface on a work piece to ultraviolet light with the ultraviolet flux incident per unit area of the target surface greater at the central region of the surface than at edges of the surface, and a secondary light source which is positioned in a different plane than the primary light source and which exposes the target surface to ultraviolet light with the ultraviolet flux incident per unit area of the surface greater at the edge areas of the target surface than at the central region. Not only is such an ultraviolet light processor complex and expensive to manufacture and to operate, but also it is difficult to control in a manner that maintains the ultraviolet radiation received at the edge areas of the target surface from the secondary source at substantially the same level as the ultraviolet radiation received at the central area of the target surface from the primary source.

[0006] U.S. Pat. No. 4,276,479 discloses a tunnel type irradiation chamber with a plurality of cylindrical ultraviolet lenses through which an object to be treated is conveyed. Two sets of radiation sources, providing light of two different wavelengths, are within the chamber, providing light in two stages. Not only is this apparatus complex to control, but also it does not provide uniform radiation distribution on the object surface.

[0007] U.S. Pat. No. 4,348,015 shows a radiation projection system including complex lenses in order to provide uniform irradiance. Numerous other systems have been attempted. These generally are complex and expensive, both to construct and to operate. Even so, they generally have difficulty in achieving uniform irradiance, particularly two-dimensionally uniform irradiance.

[0008] The present invention is an apparatus for and a method of providing substantially two-dimensionally uniform irradiation of large areas with a high level of radiation. In accordance with the present invention at least two substantially identical sources of radiation are provided for producing radiation to irradiate a target surface. Each source may include an elongated discharge bulb. Each bulb is arranged within a corresponding elongated elliptical reflecting trough, with the bulb being spaced from the focal axis within the trough. The troughs, with the radiation sources in them, are positioned side by side in a plane substantially parallel to a planar target surface. Preferably, planar reflectors extend from the troughs to the target surface, being pivotally attached to the troughs so as to accommodate various sizes of target surfaces. Preferably also, planar reflectors extend from the interior longitudinal edges of the troughs, the inner reflectors being pivotally attached to the troughs to permit adjustment of the angular position of the inner reflectors so as to optimize the uniformity of the radiation distribution on the target surface. Each of the sources of radiation can be a light source, preferably a source of ultraviolet light such as a microwave electrodeless discharge bulb, an arc discharge bulb, or a fluorescent discharge bulb, for example.

[0009] In a preferred embodiment of the present invention, the positions of the troughs are adjustable in the direction of the minor axes of the ellipses defining the troughs, likewise aiding in optimization of the uniformity of the radiation distribution on the target surface.

[0010] These and other aspects and advantages of the present invention are more apparent from the following detailed description and claims, particularly when considered in conjunction with the accompanying drawings. In the drawings:

[0011] FIG. 1 is a rear perspective view of a first embodiment of an apparatus for providing substantially two-dimensionally uniform irradiation of a planar target surface in accordance with the present invention;

[0012] FIG. 2 is a top plan view of the apparatus of FIG. 1;

[0013] FIG. 3 is a schematic sectional view of the apparatus of FIG. 1 and is taken along line 3—3 in FIG. 1;

[0014] FIG. 4 is a front elevation view of the apparatus of FIG. 1;

[0015] FIG. 5 is a rear perspective view of a second embodiment of an apparatus for providing substantially two-dimensionally uniform irradiation of a planar target surface in accordance with the present invention;

[0016] FIG. 6 is a schematic sectional view of the apparatus of FIG. 5 and is taken along the line 6—6 in FIG. 5;

[0017] FIG. 7 is a front elevation view of the apparatus of FIG. 5;

[0018] FIGS. 8 and 9 are graphs illustrating the operation of the apparatus of FIG. 1;

[0019] FIGS. 10 through 17 are graphs illustrating the operation of the apparatus of FIG. 5 with the radiation sources at various positions;

[0020] FIG. 18 is a rear perspective view of an apparatus for irradiating a planar target surface, this apparatus having a single radiation source;

[0021] FIG. 19 is a schematic sectional view of the apparatus of FIG. 18 and is taken along line 19—19 in FIG. 18;

[0022] FIG. 20 is a front elevation view of the apparatus of FIG. 18; and

[0023] FIGS. 21 and 22 are graphs illustrating the operation of the apparatus of FIG. 18.

[0024] In the following description of the present invention, reference is made to the accompanying drawings which form a part hereof and in which are shown by way of illustration various embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized, and that structural and functional modifications may be made without departing from the scope of the present invention.

[0025] FIGS. 1-4 depict a first embodiment of an irradiation apparatus 30 in accordance with the present invention. Apparatus 30 includes a first radiation source 32 and a substantially identical second radiation source 34, each of which is depicted as an elongated discharge bulb. By way of example, in a low power irradiation apparatus in accordance with the present invention, each radiation source 32, 34 might be a six-inch long, 2400-watt ultraviolet lamp, while in a higher power apparatus each source might be a 10 inch long, 6-kilowatt ultraviolet lamp. Radiation source 32 is positioned within an elongated elliptical reflecting trough 36, while radiation source 34 is positioned within a substantially identical trough 38. Each trough 36, 38 preferably is substantially one half of an ellipse, although each trough could be less or more than one half an ellipse if desired.

[0026] Radiation sources 32 and 34 irradiate a relatively large planar target surface 40. The longitudinal axes of radiation sources 32 and 34 define a plane which is substantially parallel to planar target surface 40. The ellipse of first trough 36 has a first focal point within the trough. The locus of the first focal point along the length of trough 36 thus defines a first focal axis 42 of the trough. The ellipse of first trough 36 has a second focal point outside the trough, the locus of which defines a second focal axis 44. Similarly, the ellipse of second trough 38 has a first focal point within the trough, the locus of which defines a first focal axis 46 of trough 38. Further, the ellipse of second trough 38 has a second focal point outside the trough, the locus of which defines a second focal axis 48. Each radiation source 32, 34 is spaced from the corresponding first focal axis 42, 46 at positions that result in optimum two-dimensional uniformity of the radiation distribution on target surface 40. By way of example, this might be a position toward target surface 40 by about ten percent of the focal length of the trough.

[0027] Preferably, each radiation source 32, 34 is mounted within its respective reflecting trough 36, 38 by an adjustable mount 37, 39 permitting adjustment of the position of each radiation source relative to the first focal axis of its respective elliptical reflecting trough, so as to optimize the uniformity of the radiation distribution on target surface 40. While FIG. 3 depicts radiation sources 32 and 34 positioned between focal axes 42 and 46 and target 40, the radiation sources could be on the side of the focal axes that is further from the target surface if such positions result in optimum uniformity of the radiation reaching the target surface. Preferably, each radiation source 32, 34 is on the major axis of the ellipse of its respective trough 36, 38.

[0028] Trough 36 terminates in an outer or first longitudinal edge 50 and an inner or second longitudinal edge 52. Similarly, trough 38 terminates in outer or first longitudinal edge 54 and inner or second longitudinal edge 56. A top reflector 58 extends from outer longitudinal edge 50 of first trough 36 to an end edge 51 which extends along the top edge of planar target surface 40. In like manner, a bottom reflector 60 extends from outer longitudinal edge 54 of second trough 38 to an end edge 53 which extends along the bottom edge of planar target surface 40. A first side reflector 62 extends from the first transverse edges 61, 63 of troughs 36 and 38 to an end edge 55 which extends along a first side edge of target surface 40. A second side reflector 64 extends from the second transverse edges 65, 67 of troughs 36 and 38 to an end edge 57 which extends along the second side edge of target surface 40. Preferably, reflectors 58-64 are pivotally connected to troughs 36 and 38 to permit accommodation of various sizes of target surfaces. The edges of the top and bottom reflectors 58, 60 and the side reflectors 62, 64 may be joined by flexible, rolled, or telescoping reflective material, if desired, to accommodate such pivoting. Preferably, also, the space between second longitudinal edges 52 and 56 of first trough 36 and second trough 38 is closed by a further reflector 66.

[0029] A first inner reflector 68 extends from inner or second longitudinal edge 52 of first trough 36, while a second inner reflector 70 extends from the inner or second edge 56 of second trough 38. Reflectors 68 and 70 might extend to or beyond the respective second focal axes 44 and 48, as desired, to obtain optimum uniformity of the radiation distribution on target surface 40. First inner reflector 68 might extend substantially parallel with bottom reflector 60, while second inner reflector 70 might extend substantially parallel with top reflector 58. However, preferably inner reflectors 68 and 70 are pivotally connected to inner longitudinal edges 52 and 56 to permit angular adjustment of the reflectors relative to the troughs so as to further optimize the uniformity of the radiation distribution on planar target surface 40.

[0030] Preferably, troughs 36 and 38 and their radiation sources 32 and 34 are movable in the direction of the minor axes of the troughs, permitting adjustment of the spacing between the two troughs, and thus between the two radiation sources 32 and 34, so as to permit further optimization of the uniformity of the radiation distribution on target surface 40. By way of example, first trough 36 may be mounted within a first housing 72 and second trough 38 mounted within a similar second housing 74. Housings 72 and 74 are adjustably mounted on supports 76, permitting movement of the troughs and radiation sources. Although in FIGS. 1-4 troughs 36 and 38, together with elongated discharge bulbs 32 and 34, are depicted as having their longitudinal axes extending horizontally, the axes could extend vertically or at an angle, if desired.

[0031] FIGS. 5, 6, and 7 depict a second embodiment of an apparatus for providing substantially two-dimensionally uniform irradiation of a planar target surface in accordance with the present invention. FIGS. 5, 6, and 7 are respectively a rear perspective view, a schematic sectional view and a front elevational view of apparatus 80. The top plan view of apparatus 80 is substantially the same as FIG. 2. Apparatus 80 of FIGS. 5-7 differs from apparatus 30 of FIGS. 1-4 by having three radiation sources 82, 84, 86 mounted within respective elongated elliptical reflecting troughs 88, 90, 92. Radiation from sources 82, 84, 86 is directed toward a planar target surface 94. Apparatus 80 includes top and bottom reflectors 96 and 98, which extend from the first or outer longitudinal edges of troughs 88 and 92 to the top and bottom edges of target surface 94, and first and second side reflectors 100 and 102, which extend from the first and second transverse edges of troughs 88, 90, and 92 to the first and second side edges of target surface 94.

[0032] A first inner reflector 104 is mounted on the second or inner longitudinal edge of trough 88. A second inner reflector 106 is mounted on the first longitudinal edge of trough 84, while a third inner reflector 108 is mounted on the second longitudinal edge of trough 84. A fourth inner reflector 110 is mounted on the second or inner longitudinal edge of trough 92.

[0033] Preferably reflectors 96-102 are pivotally mounted to troughs 88-92 so as to accommodate target surfaces of different sizes. Preferably, also, reflectors 104-110 are pivotally mounted to the troughs to allow angular adjustment of the inner reflectors relative to the troughs so as to permit further optimization of the uniformity of the radiation distribution on target surface 94.

[0034] Radiation source 84 and its trough 90 are positioned substantially centrally of target surface 94 in the direction transverse to the longitudinal axis of the reflecting trough. Troughs 88 and 92 and their radiation sources 82 and 86 are preferably movable in the direction of the minor axes of the troughs, for example by being mounted within housings 112 and 114, respectively, with these housings adjustably mounted on supports 116. This permits further optimization of the uniformity of the radiation of target surface 94.

[0035] Preferably, the space between trough 88 and trough 90 and the space between trough 90 and trough 92 are closed by further reflectors 118, which might telescope to accommodate movement of troughs 88 and 92 as housings 112 and 114 move along supports 116.

[0036] The use of three radiation sources in respective troughs improves the uniformity of the radiation distribution on target 94. The uniformity can be further optimized by adjustment of the distance of the radiation sources from the elliptical axes of the respective troughs, the positions of troughs 88 and 92 and radiation sources 82 and 86, and the adjustment of the angular positions of inner reflectors 104-110.

[0037] Although in FIGS. 5-7 the longitudinal axes of radiation sources 82-86 and of troughs 88-92 are depicted as extending horizontally, they could extend vertically or at an angle, if desired.

[0038] The following examples, based on computer simulations, indicate the advantages of the present invention.

[0039] An apparatus in accordance with FIGS. 1-4 was simulated. The apparatus 30 includes first and second elongated irradiation sources 32 and 34, each of which is a ten inch, six-kilowatt tubular microwave powered ultraviolet discharge bulb. Each source 32, 34 is in an associated elongated elliptical reflecting trough 36, 38. Each trough is one-half of an ellipse having a major axis of approximately six inches and a minor axis of approximately four and one-fourth inches. Each radiation source 32, 34 is positioned on the major axis of the ellipse of its respective trough approximately 0.1 inch from its respective first focal axis 42, 46, which is a position found to provide optimum uniformity of radiation distribution on target surface 40. Target surface 40 is a 24 inch by 24 inch photosensitive film located approximately 24 inches from edges 50-56 of troughs 36 and 38. Reflectors 68 and 70 are pivoted to further optimize the uniformity of the radiation distribution. FIG. 8 depicts the horizontal or X direction distribution of the radiation reaching target 40, while FIG. 9 depicts the vertical or Y direction distribution. The X and Y directions are shown in FIG. 4. As can be seen from FIGS. 8 and 9, the distribution of the radiation is substantially uniform.

[0040] An apparatus having three radiation sources in three associated troughs, as depicted in FIGS. 5-7, was simulated. Each radiation source 82, 84, 86 is a ten inch, six-kilowatt tubular microwave powered ultraviolet discharge bulb. Each bulb 82, 84, 86 is in an associated elongated elliptical reflecting trough 88, 90, 92, the ellipse of which had a major axis of approximately six inches and a minor axis of approximately four and one-fourth inches. Troughs 88 and 92, together with their radiation sources 82 and 86, are positioned at locations approximately two-thirds of the distance from the center of trough 90 toward top reflector 96 and bottom reflector 98, respectively. Each radiation source is positioned on the major axis of its associated trough at a location found to provide optimum uniformity to the radiation distribution on target surface 94. Reflectors 104-110 are pivoted so as to further optimize the uniformity of the radiation distribution on target surface 94. The target surface is a photosensitive film which extends 24 inches in the X direction and 48 inches in the Y direction and is positioned approximately 24 inches from troughs 88-92. The X and Y directions are shown in FIG. 7. FIG. 10 depicts the horizontal or X direction distribution of the radiation reaching target surface 94, while FIG. 11 depicts the vertical or Y direction distribution. As can be seen from FIGS. 10 and 11, the radiation distribution on target surface 94 is substantially uniform.

[0041] The simulated apparatus of Example 2 is adjusted by moving troughs 88 and 92 approximately one-fourth inch outward (i.e. toward top and bottom reflecting surfaces 96 and 98, respectively), as compared with the position of Example 2. Radiation sources 82, 84, and 86 are positioned within the troughs, and inner reflectors on 104-110 are pivoted so as to provide optimum uniformity to the radiation distribution on target surface 94. FIGS. 12 and 13 depict respectively the X direction radiation distribution and the Y direction radiation distribution. As can be seen, the radiation distribution is substantially uniform.

[0042] The simulated apparatus of Example 2 is adjusted by moving troughs 88 and 92 approximately one-half inch toward top reflector 96 and bottom reflector 98, respectively, as compared with the positions of Example 2. Again the radiation sources are positioned within the troughs, and the inner reflectors are pivoted to provide optimum uniformity to the radiation distribution on target surface 94. FIGS. 14 and 15 depict, respectively, the X direction distribution and the Y direction distribution. Again, it can be seen that the distribution is substantially uniform.

[0043] The apparatus of Example 2 is adjusted by moving troughs 88 and 92 approximately one-half inch inward from the positions of Example 2 (i.e. one half inch further from top reflector 96 and bottom reflector 98, respectively). The radiation sources are positioned within the troughs and the inner reflectors are pivoted to provide optimum uniformity to the radiation distribution on target surface 94. FIGS. 16 and 17 depict, respectively, the X direction radiation distribution and the Y direction radiation distribution on target surface 94. Once more it can be seen that the distribution is substantially uniform.

[0044] To show the improved performance of apparatus in accordance with the present invention, a comparative apparatus 130 having a single radiation source in a single trough, as depicted in FIGS. 18-20, was simulated. FIGS. 18-20 are respectively a perspective view, a schematic sectional view, and a front elevational view of apparatus 130. The top plan view is substantially the same as FIG. 2. Apparatus 130 includes an elongated radiation source 132 positioned within an elongated elliptical reflecting trough 134. A top reflector 136 extends from one longitudinal edge of trough 134 to a top edge of a target surface 138. Target surface 138 is a 24 inch by 24 inch photosensitive film positioned 24 inches from trough 134. A bottom reflector 140 extends from the second longitudinal edge of trough 134 to a bottom edge of target surface 138. First and second side reflectors 142 and 144 extend from the sides of trough 134 to the sides of target surface 138.

[0045] Radiation source 132 is a ten inch, six-kilowatt ultraviolet electrodeless discharge bulb. Trough 134 is one-half of an ellipse having a major axis of approximately six inches and minor axis of approximately four and one-fourth inches. Radiation source 132 is positioned on the major axis at the location found to provide optimum achievable uniformity of the radiation distribution on target surface 138FIG. 21 depicts the horizontal or X direction distribution of the radiation reaching target surface 138, while FIG. 22 depicts the vertical or Y direction distribution. The X and Y directions are shown in FIG. 20. While the X direction distribution is somewhat uniform, the Y direction distribution is clearly non-uniform. Both the apparatus of FIGS. 1-4 and the apparatus of FIGS. 5-7 provide improved two-dimensional uniformity of radiation distribution on a planar target surface, compared with the apparatus of FIGS. 18-20.

[0046] From Examples 2-5 and FIGS. 10-17, it can be seen that a positive shift moving troughs 88 and 92 and radiation sources 82 and 86 closer to top and bottom reflectors 96 and 98, raises the middle part and lowers the edges of the Y direction radiation distribution, while a negative shift, moving troughs 88 and 92 and radiation sources 82 and 86 further from top and bottom reflectors 82 and 86 raises the edges of the Y direction radiation distribution. Thus, by appropriate adjustment, the uniformity of the radiation distribution can be improved.

[0047] It can thus be seen that the present invention is an apparatus and method providing uniform irradiation of large areas with a high level of radiation. Although the present invention has been described with reference to preferred embodiments, various rearrangements, alterations, and substitutions might be made, and still the result would be within the scope of the invention.