Abstract:
A stainless steel plate establishes a mask plate for a laser trimming tray. The plate has several openings through which laser light can be directed onto semiconductor chips borne by the tray. The plate is supported on pneumatic pistons which can raise the plate to allow a tray to be disposed underneath, and then the plate is lowered and pressed against the tray, with the weight of the plate flattening and straightening the tray to promote precise laser cuts of the chips on the tray.

Description:
TECHNICAL FIELD 
     The present invention relates generally to cutting circuit components on a microprocessor chip using laser trimming principles. 
     BACKGROUND OF THE INVENTION 
     A laser trimming handler is used to convey what are to become microprocessor chips across the path of a laser, which cuts predetermined circuit components into the chips. Several chips can be loaded onto a tray, with the tray then being placed at an input loading station and conveyed through the laser cutting chamber. The tray is extracted and unloaded at an output station. 
     It is to be appreciated that as microprocessor chips are made with ever-smaller circuit components, the above-described laser cutting process must make ever-finer cuts. The present invention has made the critical observation that the trays in which the microprocessor chips are borne through the cutting chamber are frequently reused, and that over the course of their lifetime can become bent and warped. The deformation of the trays is not noticeable to the human eye and consequently can remain undetected. Unfortunately, even a minute deformation of a tray can alter the cutting depth of the laser sufficiently to cause improper component formation. Accordingly, the present invention has provided the below-disclosed solutions to one or more of the above-noted problems. 
     BRIEF SUMMARY OF THE INVENTION 
     A device for promoting precise laser cuts in a laser trimming apparatus is disclosed. The laser trimming apparatus can include a conveyor system that moves trays into and out of a laser cutting chamber, with each tray holding plural semiconductor devices. The device of the present invention includes a rigid hard plate that preferably is made of steel and that is formed with at least one opening through which laser light can be directed. A lift system is engaged with the plate for moving the plate between a raised position, wherein the plate is distanced from a tray such that the tray can be moved beneath the plate, and a lowered position, wherein the plate contacts the tray to flatten the tray. The preferred plate is located within the cutting chamber. 
     In a preferred embodiment, at least one bottom edge of the plate is formed with a chamfer for aligning the plate with the tray. More preferably, the bottom edge includes two chamfers and a distance is defined between the chamfers. The distance is marginally larger than a length of an edge of the tray. 
     In another aspect, a method for undertaking a laser cut of at least one semiconductor device includes disposing the semiconductor device on a tray, and conveying the tray into a cutting chamber of a laser trimming apparatus. The method also includes lowering a plate onto the tray to flatten the tray. The plate defines at least one opening. Accordingly, a laser can be directed through the opening onto the semiconductor device to cut a component into the device. Then, the tray is conveyed out of the cutting chamber. 
     In still another aspect, an assembly for laser trimming includes a tray configured to hold semiconductor devices, and a laser cutting chamber is also included. A conveyor system conveys the tray into and out of the cutting chamber. A lift system selectively presses a plate against the tray to flatten the tray and thereby facilitate precise cutting. 
     Other features of the present invention are disclosed or apparent in the section entitled DETAILED DESCRIPTION OF THE INVENTION. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a schematic view of the present mask plate in an exploded relationship with a laser trimming apparatus; 
     FIG. 2 is a perspective view of the present mask plate; 
     FIG. 3 is a detail of the chamfer as indicated by the circle  3 — 3  in FIG. 2; 
     FIG. 4 is a perspective view of the mask plate in the raised position; and 
     FIG. 5 is a perspective view of the mask plate in the lowered position. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring initially to FIG. 1, a mask plate is shown, generally designated  10 , in operative relationship with a laser trimming apparatus  12  that includes a conveyor system which moves trays  14  holding plural semiconductor devices  16 , e.g., microprocessor chips, into and out of a laser cutting chamber  18 . As discussed in further detail below, the plate  10  preferably is reciprocatingly mounted inside the cutting station  18 . 
     As shown, one preferred but non-limiting conveyor system includes a handler  19  supporting an input station  20  into which the trays  14  are disposed, an output station  22  from which the trays  14  are extracted, and a conveyor belt  24  running therebetween. A laser beam from a laser system  28  can propagate through one or more rectangular openings  30  in the plate  10  inside the cutting chamber  18  to cut circuit components into the semiconductor devices  16 . 
     The details of the mask plate  10  can be seen in reference to FIGS. 2 and 3. In the presently preferred embodiment, the plate  10  is made of a rigid hard material, preferably steel. 
     It is formed with plural openings  30  that are generally rectangular in the embodiment shown but that can be other suitable shapes. Plural lift system holes  32  are formed around the edges of the plate  10  to engage the plate  10  with the lift system described further below. 
     As envisioned by the present invention, to help align the plate  10  with a tray  14 , at least one bottom edge  34  is formed with at least one chamfer  36  and preferably with two chamfers  36 ,  38 . If desired, the edge opposite the bottom edge  34  can also be formed with chamfers. In any case, the distance “d” between the chamfers  36 ,  38  is approximately equal to (marginally larger than) the length “1” (FIG. 1) of a side of a tray  14  that is juxtaposed with the bottom edge  34 . With this cooperation of structure, as the plate  10  is lowered on to the tray  14  as set forth further below, the side of the tray is closely received between the chamfers  36 ,  38 , with the chamfers being configured to guide the plate  10  onto the tray  14  in alignment therewith. 
     More specifically, as shown best in FIG. 3, the chamfer  38  is somewhat convex, rather than defining a right angle joint between orthogonal surfaces. With this structure, the tray  14  can ride along a chamfer surface  40  of the chamfer  38  until its mates flush with a receiving portion  42  of the bottom edge  34 . It will be appreciated that the length of the receiving portion  42  is equal to the length “1” of the side of the tray  14 . It is to be understood that the chamfer  36  is configured identically to the chamfer  38 . 
     As discussed above, the plate  10  is disposed in the cutting chamber  18 . In one preferred embodiment, as shown in FIGS. 4 and 5 the plate  10  is engaged with a lift system  44 . The lift system  44  moves the plate  10  up as indicated by the arrow  45  to a raised position shown in FIG. 4, wherein the plate  10  is distanced from the tray  14  such that the tray  14  can be moved beneath the plate as indicated by the arrow  46 . The lift system  44  also moves the plate  10  downwardly as indicated by the arrow  48  to a lowered position shown in FIG. 5, wherein the plate  10  contacts the tray  14  to flatten the tray  14 . 
     A preferred non-limiting lift system  44  can include opposed pistons  50  that reciprocate inside respective pneumatic cylinders  52  (only one piston-and-cylinder shown in FIGS.  4  and  5 ). The pistons  50  can be engaged with the plate  10  by respective fasteners that extend through intermediate lift system holes  32   a  in the plate  10 . Also, if desired cylindrical rod guides  54  can slide within respective lateral lift system holes  32   b  in the plate  10  to guide the plate  10  as it moves up and down. If desired, the entire lift system  44  can be engaged with the conveyor such that in a less preferred embodiment the plate  10  need not remain disposed inside the cutting chamber, but rather can move along the conveyor with a tray  14 . 
     In any case, the weight of the plate  10  and the force of the piston-and-cylinder lift system  44  when the plate  10  is in the lowered position press the plate  10  against the tray  14 . This flattens the tray  14  in case any warping and/or bending or other deformation of the tray  14  might have occurred, thereby facilitating precise cutting of components on the semiconductor devices  16 . 
     While the particular TRAY MASK PLATE FOR LASER-TRIMMING APPARATUS as herein shown and described in detail is fully capable of attaining the above-described objects of the invention, it is to be understood that it is the presently preferred embodiment of the present invention and is thus representative of the subject matter which is broadly contemplated by the present invention, that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more”. All structural and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for”.