You asked the following—post-facing with "I am not a metallurgist, and I am
at a loss as to where to find this information."—unfortunately, there is no
easy way to find the information, and some of it may not as yet exist.
> 1. Does the elimination of such a small amount of silver from the alloy
> contribute to any significant increase in the solder's ductility after
> soldering is completed?
> A: It is not so much the reduction of the Ag-content (which by the way on a
general basis leads to reduced creep-fatigue lives under ATC), but the addition
of Ni and Ge that changes the metallurgical structure of the alloy. While
Keith states that SN100C has better ductility than SAC305, I have not seen any
data, and ductility is not as important as is the modulus of elasticity
> 2.Specifically, can you provide data as to exactly what the ductility
> delta is between all three alloys? I would expect a significant
> difference between 63/37 and SN100 or SAC305, due to the percentage of
> A: See above.
> 3. Also, with the understanding that VPS would probably provide better
> wetting, how would it otherwise affect the ductility of the alloy after
> soldering is completed? The profile used is essentially the same.
> A: Typically it is the resulting grain structure that determines properties,
so it is not whether you use VPS or something else, but the cooling rate.
However, please note that the grain structure of solders is unstable and will
coarsen over time, temperature and stress-level enhanced.
> 4. For a given assembly that has inherently high CTE stresses due to
> design issues as Amol's assembly presumably has, are you saying that
> using SN100 and VPS rather than SAC305 and convection reflow will cure
> his problems?
> A: Cannot be determined a priori.
> 5. How do the long-term creep fatigue rates of Sn100 compare with SAC305
> and SN63Pb37?
> A: I have not seen data as yet.
> Werner Engelmaier
Solder Joint Reliability: Parts 1 through 4, July 17/18, Thal, Switzerland
Pb-Free Soldering Processes—Survival, Quality, Reliability, August 18,
Reliability Issues with Lead-Free Soldering Processes, September 22,
Failure Mode and Root Cause Analyses Reliability (Fatigue, Brittle Fracture,
ENIG), September 22, Schaumburg
Solder Joint Reliability: Parts 1 & 4, Oct. 9, Moscow, Russia
Solder Joint Reliability: Parts 1 & 4, Oct. 22, Tallinn, Estonia
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