in addition, eutectic solder or Pb rich solder can also exhibit self  
healing effect at elevated temperature (85 - 105 C) during power on/ 
off cycle for assembly intended to operated at temperature >70 C  
environment (add 25 C for heating by power on).  if you select alloy  
chemistry correctly, you can get good grain refinement during PWA  
usage (power on/off) and release stress.... can't remember which  
paper (may be never made it to conference...:-)...I love Pb alloy  
solder... (add bit of Cd even better) - leadfree solder just extended  
the EU Jap engineers life, with all the lead paint, still around  
(harmful), no longer use leaded gas (good), with all those use extra  
energy to reflow the leadfree at higher temp, it is not sure cost  
benefit at all... still need to be convinced.
jk
On Nov 16, 2017, at 1:37 PM, Stadem, Richard D wrote:

> SAC 305 breaks almost immediately due to its much lower modulus of  
> elasticity. HOWEVER, Kester's K100LD has properties very similar to  
> Sn63 and has excellent SOLDER JOINT creep life before fracturing  
> under stress. So there can be a major difference in creep  
> properties amongst just different lead-free solder alloys.  With  
> respect to the wire elongation testing only, but not the finished  
> solder joint, the flux content will also affect the time to  
> fracture when hanging weights on a wire. Within an alloy type the  
> creep factor can vary widely depending on the very minor doping  
> used. For example, K100DL has less than .1% of a doping material,  
> yet it is extremely different than a standard SN100, and even more  
> different than a 2% or 3% silver SAC alloy.
> Even Sn60 is very different from a Sn63 with regard to the creep  
> characteristics.
> It takes very little to change the creep characteristics of  
> finished solder joints, but fortunately not so much that it becomes  
> a huge issue.
> But it can under the right conditions, so it should be considered.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Julie Silk
> Sent: Thursday, November 16, 2017 11:39 AM
> To: [log in to unmask]
> Subject: Re: [TN] Question on Loading Solder Joints
>
> Test SnPb vs SAC and you'll see a difference.  My colleague back in  
> the days when we were still in denial about the transition to Pb- 
> free did a similar test attaching the wires to his wall and using  
> paper clamps on the end (not much weight).  They didn't break, but  
> kept elongating, to different lengths.  Now, if a heavier weight  
> was used, which would break first?  How much weight to break each?