Low-melting-temperatue tin and plating process

Abstract

In the low-lead-content plating process of the present invention, tens to hundreds ppms of lead, thallium and iron ions, which are much lower than the international “non-lead” standard, are added into a pure tin plating liquid to change the crystal phase orientation during infrared-ray reflow, thereby reducing the melting point of the plated layer.

What is claimed is:  
     
         1 . A low-lead-content plating process, comprising: 
 providing an anode;    providing a cathode; and    providing a plating bath containing a plating liquid, wherein the plating liquid includes a pure tin plating liquid, iron ions, thallium ions and lead ions, with the concentrations of lead ions of 2.5 to 10,000 mg/l, thallium ions of 1 to 550 mg/l, and iron ions of 1 to 550 mg/l.    
     
     
         2 . The process of  claim 1 , wherein the plating liquid further comprising 
 a brightener;    a methane sulfoante solution; and    a deioned water;    wherein the concentration of the brightener is in the range of 50 to 250 mg/l, and the concentration of the methane sulfonate solution is in the range of 80 to 250 mg/l.    
     
     
         3 . The process of  claim 1 , wherein the plating process is combined with a barrel plating, the rack plating, a PCB plating, a strip-to-strip plating or a reel-to-reel plating.  
     
     
         4 . The process of the  claim 3 , wherein the plating process is combined with the barrel plating, the rack plating, the PCB plating, the strip-to-strip plating or the reel-to-reel plating by using a barrel plater, a rack plater, a PCB plater, a strip-to-strip plater or a reel-to-reel plater.  
     
     
         5 . A final plated layer with low lead content, comprising: 
 tin as the majority component in weight;    lead of 25 to 100,000 ppm in weight;    thallium of 10 to 5,500 ppm in weight; and    iron of 10 to 5,500 ppm in weight.    
     
     
         6 . The final plated layer of  claim 5 , wherein the final plated layer has a melting point of 183 to 232° C.  
     
     
         7 . The final plated layer of  claim 5 , wherein the lead has 25 to 50,000 atoms per cube meter of the composition.  
     
     
         8 . The final plated layer of  claim 5 , wherein the thallium has 10 to 2,500 atoms per cube meter of the composition.  
     
     
         9 . The final plated layer of  claim 5 , wherein the iron has 10 to 2,500 atoms per cube meter of the composition.