Kody, 

Don't hold your breath for electoplated SAC305, ?and I will explain why.? Electroplating may be considered the mirror image of the operation of a battery.? All forms of plating involve the transfer of electrons to reduce metals, while batteries give up electrons when you put two dissimilar elements together.? 

Plating may be either electroplating (which is what I think you mean) where the source of the electrons is a direct current from a rectifier, or electroless plating using the reaction between two chemicals (oxidation) to give electrons to deposit metals from their ionic state (reduction).? Immersion plating is even more like a battery where one metal dissolves (oxidizes) and another metal in solution deposits as metal (reduction). During fabrication, the exposed copper of a printed?circuit board goes into solution while either silver?or tin?in solution deposit out on spots to be soldered (immersion?silver or immersion tin plating respectively).? 

Plating involves electochemical potentials.? Here is a chart of the potentials of many common elements:

Electromotive Series




Aluminium 

1.67

V



Antimony 

-0.1

V



Arsenic 

-0.3

V



Barium 

2.9

V



Beryllium 

1.7

V



Bismuth 

-0.226

V



Brass 

-0.47

V



Bromine 

-1.06

V



Bronze 

-0.47

V



Cadmium 

0.4

V



Caesium 

3.02

V



Calcium 

2.87

V



Chlorine 

-1.36

V



Chromium 

0.71

V



Cobalt 

0.28

V



Copper 

-0.47

V



Fluorine 

-3.03

V



Gallium 

0.5

V



Gold 

-1.42

V



Hydrogen 

0

V



Indium 

0.336

V



Iodine 

-0.53

V



Iron 

0.44

V



Lanthanum 

2.37

V



Lead 

0.13

V



Lithium 

3.02

V



Magnesium 

2.4

V



Manganese 

1.05

V



Mercury Hg 

-0.85

V



Monel 

-0.47

V



Nickel 

0.25

V



Oxygen 

-0.397

V



Palladium 

-0.83

V



Platinum 

-1.2

V



Polonium 

-0.4

V



Potassium 

2.92

V



Rubidium 

2.99

V



Silicon 

-0.26

V



Silver 

-0.8

V



Sodium 

2.71

V



Stainless Steel 

-0.09

V



Steel 

0.45

V



Strontium 

2.89

V



Sulphur 

0.51

V



Tellurium 

0.827

V



Thallium 

0.33

V



Tin 

0.14

V



Uranium 

1.4

V



Water 

-1.23

V



Zinc 

0.76

V




It is VERY, VERY hard to plate more than one metal at a time from solution, as the lower potential metal will tend to be deposited first as it has the lowest reduction potential.? So, SAC 305 with 96.5 % tin (potential 0.14 Volts), 3.0% silver (potential -0.8 Volts), and 0.5% copper (potential -0.47 volts) would tend to plate out first?tin, then copper, then silver.? Even binary metal plating systems are very hard to control so that the metals plate in uniform ratios across a panel or a?wafer.? Ternary systems require a horrendous balance of chelators, grain refiners, leveling agents, etc to have any chance to trick mother nature and electromotive series.? 

Ahhh, but you say, I plated 63% tin, 37% lead for many years on circuit boards, and reflowed that into fused tin/lead (solder).?? We were all damned lucky that tin potential is 0.14 volts, and lead potential is 0.13 volts - so there is very little tendency to plate preferentially.?? 

Are you trying to bump wafers to replace the "soon to be RoHS eliminated" high lead solder bumps on wafers?? A lot of people are working on that technology for electroplating, but I can't imagine the answer will be "SAC 305 electroplate".?? I think there was a "Gordon Conference" recently held on electrochemistry, and perhaps there were some really innovative papers on substitutes for high lead?presented.? I do not have?the proceedings, but may be abe to get second hand information.? 

Denny Fritz
MacDermid, Inc. 


-----Original Message-----
From: Kody <[log in to unmask]>
To: [log in to unmask]
Sent: Thu, Jul 30, 2009 3:08 pm
Subject: [LF] Plating SAC305



Has there been any success in plating SAC305 by either plating copper
then tin then silver or using a SnAg solution on copper?  More specifically
for wafer bump plating.  Any information would be helpful.

                                        Thanks, Kody



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