Method for removing molding residues in the fabrication of plastic packages for semiconductor devices

Abstract

A method is for removing residue of plastic from metal parts of plastic packages of semiconductor devices, e.g., heat-sinks and terminals. The surfaces to be treated are subjected to pulsed laser radiation. The wavelength is chosen in such a way that residue of plastic in thin films have good transparency to the radiation, and the metal has a high absorption capacity with respect to the radiation. Moreover, the intensity and duration of application of the radiation causes the formation of plasma at the point of impact of the radiation with the surface to be treated.

That which is claimed is:  
     
         1 . Method for removing residues of molding material from metal parts of plastic packages of semiconductor devices, characterized in that at least one surface region of a metal part ( 12 ) covered with residues ( 14 ) of molding material is subjected to pulsed laser radiation, the wavelength of which is chosen in such a way that the molding material, when it forms residues of a thickness less than a predetermined value, is at least partially transparent to the radiation and in that the metal parts are at least partially absorbent in respect of the radiation, the intensity of the radiation and the duration of application of the radiation being chosen in such a way that the radiation causes the formation of plasma at the point of impact with the said surface region.  
     
     
         2 . Method according to    claim 1   , in which the wavelength of the laser radiation is chosen also in such a way that the molding material, when it forms residues ( 14 ) of a thickness equal to or greater than the said predetermined value, is able to absorb the radiation to a large extent, the intensity of the radiation and the duration of application of the radiation being moreover chosen in such a way that the radiation causes a direct attack of the molding material.  
     
     
         3 . Method according to    claim 1    or    2   , in which the laser radiation has a wavelength of between 180 and 700 nm.  
     
     
         4 . Method according to any one of the preceding claims, in which the pulses of the laser radiation have a duration of between 3 and 30 ns.  
     
     
         5 . Method according to any one of the preceding claims, in which the operation of subjecting to laser radiation at least one surface region of a metal part comprises a scanning of the laser radiation over the surface region and the duration of application of the radiation is determined by the number of radiation pulses applied per unit area.  
     
     
         6 . Method according to    claim 5   , in which the scanning motion is synchronized with the emission of the pulses.  
     
     
         7 . Method according to any one of the preceding claims, used in the fabrication of plastic packages with metal parts ( 11 ,  12 ), in which the molding material is an epoxy resin with carbon particles as additive.  
     
     
         8 . Method according to    claim 7   , in which the carbon particles have for the most part dimensions greater than 10 μm and in which the said predetermined value of the thickness of the molding material is around 10 μm.  
     
     
         9 . Method according to any one of the preceding claims, in which the metal parts ( 11 ,  12 ) comprise copper parts.  
     
     
         10 . Method according to any one of the preceding claims, in which the metal parts comprise nickel-plated copper parts.