Hello,
Could I ask you what is your SMD soldering technique?
I'm sorry to be a bit presumptuous, and I'm quite sure that you already know and practice this, but you should not directly use the solder with the SMD pad. The
correct procedure consists in using
a lot of flux on the pads and a bit of solder on the solder pencil tip.
In this scenario, the actual solder size is not relevant.
Personally, I prefer any good quality, recent 60/40 lead with rosin core and a no-clean, tacky, syringe dispensed flux.
Cheers,
Dan