Method for increased dimensional accuracy of 3-D object creation

Abstract

A stereolithographic (STL) apparatus for forming structures such as semiconductor die packages which uses a laser beam focused to a generally annular “spot” having an annulus of enhanced laser power surrounding a central “hole” of reduced (or no) laser power. The structures are formed of a stack of light-polymerized photopolymer layers. Scanning of a beam having power concentrated in the annulus enables simultaneous production of a self-supporting structure having at least semisolid, smooth lateral outer polymer walls and an upper hardened polymer skin extending over liquid polymer still lying between the walls. The structure may be subjected to heat or broad source light of suitable wavelength after removal from the STL apparatus to accelerate complete polymerization of the structure to a solid state.

What is claimed is:  
     
         1 . A method of forming a three dimensional structure, comprising: 
 providing an electromagnetic radiation-curable, liquid material;    generating a beam of electromagnetic radiation having a beam cross section with an outer portion of relatively greater power density than an inner portion of the beam cross section;    directing the beam of electromagnetic radiation across a surface of the electromagnetic radiation-curable, liquid material; and    curing a portion of the electromagnetic radiation-curable, liquid material with the beam of electromagnetic radiation to form an at least partially solidified three dimensional structure.    
     
     
         2 . The method of  claim 1 , wherein forming an at least partially solidified three dimensional structure comprises forming a three dimensional structure having an at least partially solidified outer surface retaining a volume of the electromagnetic radiation-curable, liquid material.  
     
     
         3 . The method of  claim 1 , further comprising curing the volume of the electromagnetic radiation-curable, liquid material retained within the at least partially solidified outer surface of the three dimensional structure.  
     
     
         4 . The method of  claim 3 , wherein curing the volume of the electromagnetic radiation-curable, liquid material comprises exposing the three dimensional structure to a broad source of electromagnetic radiation.  
     
     
         5 . The method of  claim 3 , wherein curing the volume of the electromagnetic radiation-curable, liquid material comprises heating the three dimensional structure.  
     
     
         6 . The method of  claim 1 , wherein curing a portion of the electromagnetic radiation-curable, liquid material with the beam of electromagnetic radiation comprises: 
 curing a first portion of the electromagnetic radiation-curable, liquid material to form a first layer of at least partially solidified material; and    curing at least one additional portion of the electromagnetic radiation-curable, liquid material at a location superimposed over the first layer of at least partially solidified material to form at least one additional layer of at least partially solidified material adhered to the first layer of at least partially solidified material.    
     
     
         7 . The method of  claim 6 , further comprising forming at least one of the layers of partially solidified material to have a thickness between about 0.0001 inches to about 0.03 inches.  
     
     
         8 . The method of  claim 7 , further comprising forming at least one of the layers of partially solidified material to have a thickness between about 0.001 inches to about 0.02 inches.  
     
     
         9 . The method of  claim 1 , wherein forming an at least partially solidified three dimensional structure comprises forming a protective structure to at least partially surround a semiconductor die.  
     
     
         10 . The method of  claim 9 , further comprising forming the protective structure to at least partially surround a semiconductor die mounted on one of a lead frame and a carrier substrate.  
     
     
         11 . The method of  claim 9 , wherein forming a protective structure to at least partially surround a semiconductor die comprises directing the beam of electromagnetic radiation around a periphery of the semiconductor die in a series of passes to form side-walls comprising serially cured, superimposed layers of at least partially solidified material.  
     
     
         12 . The method of  claim 9 , wherein forming a protective structure to at least partially surround a semiconductor die further comprises directing the beam of electromagnetic radiation over an upper surface of the semiconductor die to form a cover layer of at least partially solidified material adhered to the side-walls and covering at least a portion of the upper surface of the semiconductor die.  
     
     
         13 . The method of  claim 12 , wherein forming the side-walls further comprises forming the side-walls to a height substantially contiguous with the upper surface of the semiconductor die.  
     
     
         14 . The method of  claim 12 , wherein forming the side-walls further comprises: 
 forming the side-walls to a height above the upper surface of the semiconductor die; and    forming the cover layer to retain a volume of the electromagnetic radiation-curable, liquid material in a space bounded by the side-walls above the upper surface of the semiconductor die.    
     
     
         15 . The method of  claim 14 , further comprising curing the volume of the electromagnetic radiation-curable, liquid material retained within the space bounded by the side-walls above the upper surface of the semiconductor die.  
     
     
         16 . The method of  claim 15 , wherein curing the volume of the electromagnetic radiation-curable, liquid material comprises exposing the protective structure to a broad source of electromagnetic radiation.  
     
     
         17 . The method of  claim 15 , wherein curing the volume of the electromagnetic radiation-curable, liquid material comprises heating the protective structure.  
     
     
         18 . The method of  claim 11 , wherein forming the side-walls further comprises: 
 directing the beam of electromagnetic radiation around the periphery of the semiconductor die in a first series of passes to form an internal side-wall boundary of at least partially solidified material; and    directing the beam of electromagnetic radiation around the periphery of the semiconductor die in a second series of passes to form an external side-wall boundary of at least partially solidified material.    
     
     
         19 . The method of  claim 18 , further comprising: 
 forming the internal and external side-wall boundaries in a spaced relationship to surround a volume of electromagnetic radiation-curable, liquid material between the internal and external side-wall boundaries; and    curing the volume of electromagnetic radiation-curable, liquid material to form a unitary side-wall structure.    
     
     
         20 . The method of  claim 1 , further comprising generating the beam cross section with the power density of the inner portion of the beam cross section being less than about 60% of the power density of the outer portion of the beam cross section.