Method for fabricating leadless solder for IC packaging

Abstract

A novel method for fabricating leadless solder for IC packaging includes the following steps: A. to prepare a mixture containing Zn, 7-11 wt %; Co, 0.1-0.5 wt %; and Sn for balance; or a mixture containing Zn, 7-11 wt %; Co, 0.1-0.5 wt %; P, 0.005-0.05 wt % and Sn for balance; or a mixture containing Zn, 7-11 wt %; Al, 0.1-0.5 wt %; and Sn for balance; a mixture containing Zn, 7-11 wt %; Al, 0.1-0.5 wt %; P, 0.005-0.05 wt % and Sn for balance; or a mixture containing In, 10-15 wt %; Co, 0.1-0.5 wt % and Sn for balance; B. to place the mixture in a high frequency furnace to be melted together at a temperature lower than 350° C., then take it out of the furnace for a quick freezing and cast it into an ingot in an adequate size; C. to treat the ingot with a homogenization processing at 180-240° C. for 30-240 minutes; D. to draw the homogenized ingot into the form of leadless solder filament or granule.

What is claimed is:  
     
         1 . A method for fabricating leadless solder for IC packaging comprising at least following steps: 
 A. to prepare five metal alloys, a mixture containing Zn, 7-11 wt %, Co, 0.1-0.5 wt %, and Zn for balance, a mixture containing Zn, 7-11 wt %, Co, 0.1-0.5 wt %, P, 0.005-0.05 wt % and Zn for balance, or a mixture containing Zn, 7-11 wt %; Al, 0.1-0.5 wt %, and Zn for balance, or a mixture containing Zn, 7-11 wt %, Al, 0.1-0.5 wt %, P, 0.005-0.05 wt % and Zn for balance, or a mixture containing In, 10-15 wt %, Co, 0.1-0.5 wt %, wt % and Zn for balance;    B. to utilize a high frequency furnace to melt said mixture together at a temperature lower than 350° C., then take it out of the furnace for a quick freezing and cast it into an ingot in an adequate size;    C. to treat said ingot with a homogenization processing at 180-240° C. for 30-240 minutes to present a smooth surface without dents and pits; and    D. to drawn said homogenized ingot into a form of leadless solder filament or granule.    
     
     
         2 . The finished leadless solder as fabricated in accordance with the steps A through D of  claim 1  has the liquidation temperature and solidification temperature ranging from 183° C. to 200° C., making the soldering temperature less than 250° C. to assure highly reliable packaging in IC production.  
     
     
         3 . The finished leadless solder as fabricated in accordance with the steps A through D of  claim 1  has the tensile strength between 5.7-6.2 kgf/mm 2 , greater than 5 kgf/mm 2 , elongation between 33% and 68%, greater than 10% to ensure better solderability.