An arrangement for laser bonding

Abstract: An arrangement for providing improved efficiency in laser bonding is disclosed. In particular, at least one piece part 12 in the arrangement is formed to include means for concentrating a beam of radiation at a predetermined attachment location (or several locations). The concentrating means may be in the form of an aperture, such as a conical or parabolic opening, which will concentrate the radiation to the area of interest. Alternatively, if the piece part is transparent to the wavelength of the radiation, the concentrating means may be in the form of a lens or grating formed on the surface of the piece part.

Description: The present invention relates to arrangements for laser bonding. Laser bonding has been successfully utilized in a number of applications to provide joining of piece parts. See, for example, U.S. patent 4,990,741 entitled "Method of Laser Welding" and issued to R.J. Moores et al, on February 5, 1991. As disclosed, first and second metallic components may be joined along a weld path, with the beam focused by a low turbulent flow of an inert shielding gas along a portion of the path. In most applications, the material used to form the piece part (plastic or metal, for example) is opaque to the optical radiation and the radiation must therefore impinge the material from the side of the point of contact. This limitation is considered to further complicate and increase the cost of laser welding systems. Thus, a need remains in the art for increasing the utility of laser sources in various bonding applications. U.S. Patent 4,320,281 describes a laser bonding technique whereby conductive (metal) leads 12 are bonded to pretinned ends of a thin film capacitor 10. A dimple 20 is formed in the leads 12 resulting in an indentation 21 and a protrusion 22. The latter is placed in contact with end 11 and a pulsed laser beam is directed into indentation 21. The beam is absorbed in the opaque metal and generates heat, which by conduction, causes the tinned end to reflow in the vicinity of protrusion 22 and to form a bond therebetween. JP-A-57160590 describes a laser bonding arrangement in accordance with the preamble of claim 1. According to the present invention there is provided an arrangement as defined in claim 1. The need remaining in the prior art is addressed by the present invention which relates to laser bonding and, more particularly, to a scheme for improving the efficiency of laser bonding. In accordance with the present invention, at least one piece part is formed to include predefined features which concentrate the optical radiation toward predetermined locations which are to be joined. An advantage of the concentrating features is that the piece part itself may be formed of a material which is opaque to the wavelength of optical radiation. In an embodiment, a first piece part is be formed of a transparent material and include concentrating means, for example, an integral lens, to concentrate the radiation at the predetermined location. For an embodiment where both piece parts are transparent, an absorbing material (such as an epoxy) may be used at the interface between piece parts to absorb the radiation and become heated. Alternatively, a first piece part may be formed to including diffraction means for concentrating the radiation near the location where the piece parts are to be joined. Other and further embodiments and advantages of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings. Brief Description of the Drawing Referring now to the drawings, where like reference numerals represent like parts in several views: FIG. 1 illustrates an exemplary arrangement utilizing concentrated laser bonding; FIG. 2 illustrates an alternative arrangement utilizing concentrated laser bonding; FIGs. 3 and 4 illustrate alternative aperture geometries which may be utilized: FIGs. 5-7 illustrate alternative embodiments of the present invention utilizing at least one transparent piece part and alternative concentrating means; FIG. 8 illustrates an embodiment utilizing aperture geometries capable of forming a plurality of laser bonds within each aperture; and Fig 9 illustrates an embodiment of the present invention FIG. 10 illustrates an exemplary piece part including a number of differing aperture geometries suitable for use in providing bonding. It should be noted that the embodiments described with reference to figures 1-4, 8 and 10 do not fall within the scope of the invention as defined in the appended claims. FIG. 1 illustrates an exemplary arrangement 10 for providing concentrated laser joining (which may be referred to hereinafter as "laser welding", but may also include laser tacking or bonding). Arrangement 10 includes a first piece part 12 and a second piece part 14, where both piece parts may comprise a material which is opaque to optical radiation, for example, plastic or stainless steel. It is to be assumed that the piece parts are to be attached at locations A and B as shown in FIG. 1. Piece part 14 is formed to include a pair of concentrating apertures 16 and 18. Concentrated optical radiation impinges upon piece part 14, as shown, entering apertures 16 and 18. In particular, the radiation is in the form of a plurality of collimated beams which enter apertures 16 and 18 (the geometry, number and location of the apertures being arbitrary and will be discussed in greater detail below; attachment will occur at any predetermined number of sites). The radiation entering apertures 16 and 18 is illustrated as being continuously concentrated toward terminations 20 and 22 of apertures 16 and 18, respectively. In general, as long as the sidewalls of apertures 16 and 18 taper inward, a sufficient amount of radiation impinging the sidewalls will be re-directed back into the apertures and continue its propagation toward terminations 20,22. It is to be noted that terminations 20,22 do not necessarily have to be coincident with end surface 24 of piece part 14. As along as terminations 20,22 are substantially near surface 24, sufficient heating will occur such that laser welding at locations A and B is achieved. An alternative arrangement 30 which may utilize laser welding is illustrated in FIG. 2. A first member 32 is joined to a second member 34 at location 36, as shown. Here, aperture 38 is formed at the sidewall of second member 34, where sidewall 39 of aperture 38 is angled so as to direct radiation upward. First member 32 may also have an angled sidewall (not shown). Various other aperture geometries, including those illustrated in FIGs. 3 and 4, are possible. FIG. 3 illustrates a piece part 40 including a concentrating aperture 42 for providing laser welding . As shown, aperture 42 includes inwardly curving sidewalls 44,46 which serve to direct the laser radiation toward weld site 48. In this particular embodiment, aperture 42 terminates within piece part 40 at a location separated from weld site 48. However, as mentioned above, the concentrating of the laser radiation at the terminations has been found to provide sufficient heating (as indicated by the dotted lines) to form a weld at site 48. Thus, the process used to actually form apertures need not be precisely controlled, and the formation of apertures at least near the depth of the weld site will usually be sufficient. FIG. 4 illustrates another piece part including an aperture terminating at a position displaced from the weld site. In particular, piece part 50 includes a concentrating aperture 52, in this case with concave curving sidewalls 54,56. Weld site 58 is also illustrated in FIG. 4 as being separated from the location of the termination of aperture 52. It is to be understood that various other apertures may be successfully used, to provide concentrated laser welding. In general, virtually any geometry capable of directing energy toward desired locations may be used. FIG. 5 illustrates an embodiment 60 where the re-direction of the optical radiation is provided by refraction. In particular, a first member 62 is to be attached to a second member 64 at location 66. In this case, second member 64 must be sufficiently transparent to the wavelength of the impinging radiation. As shown, second member 64 comprises a lensed surface 68 which functions to concentrate the collimated beam of radiation toward weld site 66. If second member 64 comprises a plastic material, lens 68 may be formed during a molding operation. Alternatively, if second member 64 comprises a silicon substrate, lens 68 may be etched. In any case, the shape of surface 68 is not critical, as long as a sufficient amount of radiation is concentrated relatively near to the desired weld site 66. Another embodiment which also utilizes a transparent concentrating member is illustrated in FIG. 6. As shown, arrangement 70 includes a first member 72 and a second member 74, where second member 74 is sufficiently transparent to the wavelength of the impinging radiation. Second member 74 includes a concentrating region 76, shaped as illustrated in FIG. 6, to direct the radiation toward weld site 78. In particular, concentrating region 76 is formed so as to provide for reflection of the radiation, since an air gap is illustrated as surrounding region 76. FIG. 7 illustrates yet another embodiment of the present invention which may be utilized with a transparent concentrating member. In particular, arrangement 80 includes a first member 82 and a second member 84, where second member 84 is sufficiently transparent to the wavelength of the impinging radiation. Second member 84 includes a diffraction grating 86 formed on the surface thereof. In one embodiment, the diffraction grating may comprise a zone plate. As is well-known in the art, a diffraction grating may be formed so as to result in concentrating the impinging radiation at a desired location, in this case at predetermined weld site 88. As mentioned above, a concentrating aperture may be formed to include a parabolic-type opening such that a pair of laser welds are simultaneously formed within a single aperture. FIG. 8 illustrates, in a three-dimensional view, an exemplary arrangement 90 wherein a first piece part 92 is to be joined to a second piece part 94. Second piece part 94 includes an aperture 96 with a pair of parabolic-shaped walls in opening 98 and 100, as shown. Therefore, an incoming collimated beam will be directed to the location of parabolic aperture 96, the focal lines being along 102 and 104 in this embodiment. Therefore, a pair of linear laser welds will be formed within a single aperture. FIG. 9 illustrates an embodiment 120 for providing linear laser welds. In this arrangement, a first piece part 122 is to be laser welded to a second piece part 124, where piece part 124 is sufficiently transparent to the wavelength of the optical radiation used to perform the welding operation. Sidewalls 126 of piece part 124 are formed, as shown, to comprise parabolic shapes so as to focus the incoming collimated radiation along lines 130 and 132. As mentioned above, various aperture geometries are suitable for providing laser bonding, as long as the aperture provides sufficient concentration of the radiation near the bond location. FIG. 10 illustrates an exemplary piece part 140 including a plurality of various apertures which may be utilized as discussed above. In contrast the embodiments discussed above, the apertures of piece part 140 are shown as terminating in geometries other than a point or straight line. In particular, a set of four apertures 142 are illustrated as terminating in arcs, which may provide for bonding around the periphery of a circular piece part, for example. As with the arrangements discussed above, the apertures are formed to include sidewalls which provide for concentration of the laser radiation along the apex. Aperture 144 is illustrated as terminating in a cross-shaped apex, another suitable form. In general, any desired geometry may be used to provide the desired results. It is to be understood that there exist may other arrangements suitable for providing concentrated laser attachment in accordance with the present invention. The various embodiments as discussed above are exemplary only, and for the purposes of explanation not limitation. Further, as mentioned above, the concentrating features may be utilized with various types of laser-based bonding procedures, including, but not limited to, welding, soldering or tacking

Claims: A laser bonding arrangement including a first piece part (e.g., 62,72,82) and a second piece part (e.g., 64,74,84) wherein the first piece part is to be laser bonded to the second piece part in at least one predetermined attachment site (e.g., 66,78,88), and at least one piece part includes a structural feature (e.g., 68,76,86) for concentrating radiation from the laser toward said at least one attachment site, said structural feature including a transparent pathway which causes the concentrated radiation to impinge on said attachment site, CHARACTERIZED IN THAT said structural feature transparent pathway either comprises a shaped surface (e.g., 68) of at least one transparent piece part at a location capable of providing concentration of the laser radiation at the at least one attachment site, or comprises a region (e.g., 76) within the transparent piece part which is tapered so as to provide internal reflection sufficient to concentrate the laser radiation toward the at least one attachement site, or comprises a diffraction grating (e.g., 86) formed on the surface of the at least one transparent piece part. An arrangement as defined in claim 1, wherein the feature comprises a lens. An arrangement as defined in claim 1, wherein the diffraction grating comprises a zone plate. An arrangement as defined in claim 1 wherein said at least one attachment site comprises either essentially a point, or a line segment, or comprises an arc, or comprises a predefined geometry.

Inventors: BERGMANN ERNEST EISENHARDT, BERGMANN, ERNEST EISENHARDT
Applicants: AT & T CORP, AT&T CORP.
Application year: 1993
Main classification: B23K26
IPC codes: B29C65, C09J11, B23K26, C09J201