Lead-Free Solder Ball

Abstract

A lead-free solder ball is provided which suppresses interfacial peeling in a bonding interface of a solder ball, fusion defects which develop between the solder ball and solder paste, and which can be used both with Ni electrodes plated with Au or the like and Cu electrodes having a water-soluble preflux applied atop Cu. The lead-free solder ball for electrodes of BGAs or CSPs consists of 1.6-2.9 mass % of Ag, 0.7-0.8 mass % of Cu, 0.05-0.08 mass % of Ni, and a remainder of Sn. It has excellent resistance to thermal fatigue and to drop impacts regardless of the type of electrodes of a printed circuit board to which it is bonded, which are Cu electrodes or Ni electrodes having Au plating or Au/Pd plating as surface treatment.

The invention claimed is: 
     
         1 . A method of forming a solder joint, comprising:
 placing a solder ball having an alloy composition on an electrode provided on a module substrate for a BGA or a CSP;   heating the solder ball to form a solder bump on the electrode;   preparing a printed circuit board by applying a solder paste onto an electrode provided on the printed circuit board;   mounting the module substrate onto the printed circuit board by contacting the solder bump with the solder paste, wherein the solder bump is facing downwards with respect to the printed circuit board during the mounting step; and   heating the solder bump and the solder paste to solder the solder bump to the electrode of the printed circuit board,   wherein the alloy composition of the solder ball consists of:
 1.6-2.9 mass % of Ag; 
 0.7-0.8 mass % of Cu; 
 0.05-0.08 mass % of Ni; 
 optionally at least one element selected from Fe, Co, and Pt in a total amount of 0.003-0.1 mass % or optionally at least one element selected from Bi, In, Sb, P, and Ge in a total amount of 0.003-0.1 mass %; and 
 a remainder of Sn. 
   
     
     
         2 . The method of forming a solder joint as set forth in  claim 1 , wherein the electrode of the module substrate is selected from the group consisting of: an electrolytic Ni/Au electrode, an electroless Ni/Pd/Au electrode, and a Cu—OSP electrode. 
     
     
         3 . The method of forming a solder joint as set forth in  claim 1 , wherein the electrode of the module substrate is an electrolytic Ni/Au electrode. 
     
     
         4 . The method of forming a solder joint as set forth in  claim 1 , wherein the electrode of the module substrate is an electroless Ni/Pd/Au electrode. 
     
     
         5 . The method of forming a solder joint as set forth in  claim 1 , wherein the electrode of the module substrate is a Cu—OSP electrode. 
     
     
         6 . The method of forming a solder joint as set forth in  claim 1 , wherein the solder ball has a diameter of at least 0.1 mm. 
     
     
         7 . The method of forming a solder joint as set forth in  claim 1 , wherein the solder ball has a diameter of at least 0.3 mm. 
     
     
         8 . The method of forming a solder joint as set forth in  claim 1 , wherein the solder ball has a diameter of at least 0.5 mm. 
     
     
         9 . The method of forming a solder joint as set forth in  claim 1 , further comprising applying a flux to the electrode of the BGA or CSP prior to placing the solder ball on the electrode. 
     
     
         10 . The method of forming a solder joint as set forth in  claim 1 , wherein a reflow furnace is used to solder the solder bump to the electrode of the printed circuit board. 
     
     
         11 . The method of forming a solder joint as set forth in  claim 1 , wherein the alloy composition of the solder ball consists of:
 1.9-2.3 mass % of Ag;   0.7-0.8 mass % of Cu;   0.05-0.08 mass % of Ni; and   a remainder of Sn.   
     
     
         12 . The method of forming a solder joint as set forth in  claim 1 , wherein the alloy composition of the solder ball consists of:
 1.6-2.9 mass % of Ag;   0.7-0.8 mass % of Cu;   0.05-0.08 mass % of Ni;   at least one element selected from Fe, Co, and Pt in a total amount of 0.003-0.1 mass %; and   a remainder of Sn.   
     
     
         13 . The method of forming a solder joint as set forth in  claim 1 , wherein the alloy composition of the solder ball consists of:
 1.6-2.9 mass % of Ag;   0.7-0.8 mass % of Cu;   0.05-0.08 mass % of Ni;   at least one element selected from Bi, In, Sb, P, and Ge in a total amount of 0.003-0.1 mass %; and   a remainder of Sn.   
     
     
         14 . A method of mounting a module substrate for a BGA or a CSP to a printed circuit board, comprising:
 placing a solder ball having an alloy composition on each of a plurality of electrodes provided on the module substrate for the BGA or CSP;   heating the solder balls to form a solder bump on each of the electrodes;   preparing the printed circuit board by applying a solder paste onto each of a plurality of electrodes provided on the printed circuit board;   mounting the module substrate onto the printed circuit board by contacting the solder bumps with the solder paste, wherein the solder bumps are facing downwards with respect to the printed circuit board during the mounting step; and   heating the solder bumps and the solder paste to solder the solder bumps to the electrodes of the printed circuit board,   wherein the alloy composition of the solder ball consists of:
 1.6-2.9 mass % of Ag; 
 0.7-0.8 mass % of Cu; 
 0.05-0.08 mass % of Ni; 
 optionally at least one element selected from Fe, Co, and Pt in a total amount of 0.003-0.1 mass % or optionally at least one element selected from Bi, In, Sb, P, and Ge in a total amount of 0.003-0.1 mass %; and 
 a remainder of Sn. 
   
     
     
         15 . An electronic part comprising a module substrate for a BGA or a CSP mounted on a printed circuit board, wherein the module substrate is mounted on the printed circuit board through one or more solder joints formed according to the method of  claim 1 .