Wikipedia has a long list of solder alloys :
https://en.wikipedia.org/wiki/Solder_alloysYou can see in the description what addition of various percentages of Silver or Copper do to the solder.
Euctetic formulations should be better most of the time ... for example 63/37 is better than 60/40, but 60/40 is more user friendly, more bad soldering iron friendly (stays liquid / soft for longer time, stays liquid within a wider range)
ex
Sn63Pb37 183[19] Pb Yes Sn63, ASTM63A, ASTM63B. Common in electronics; exceptional tinning and wetting properties, also good for stainless steel. One of the most common solders. Low cost and good bonding properties. Used in both SMT and through-hole electronics. Rapidly dissolves gold and silver, not recommended for those.[8] Sn60Pb40 is slightly cheaper and is often used instead for cost reasons, as the melting point difference is insignificant in practice. On slow cooling gives slightly brighter joints than Sn60Pb40.[17]
Sn62Pb37Cu1 183[18] Pb Yes Similar to Sn63Pb37. Copper content increases hardness of the alloy and inhibits dissolution of soldering iron tips and part leads in molten solder.
Sn62Pb36Ag2 179[5] Pb Yes Sn62. Common in electronics. The strongest tin-lead solder. Appearance identical to Sn60Pb40 or Sn63Pb37. Crystals of Ag3Sn may be seen growing from the solder. Extended heat treatment leads to formation of crystals of binary alloys. Silver content decreases solubility of silver, making the alloy suitable for soldering silver-metallized surfaces, e.g. SMD capacitors and other silver-metallized ceramics.[15][17][22] Not recommended for gold.[8] General-purpose.
Sn60Pb40 183 190[5] 188[6] Pb Near Sn60, ASTM60A, ASTM60B. Common in electronics, most popular leaded alloy for dipping. Low cost and good bonding properties. Used in both SMT and through-hole electronics. Rapidly dissolves gold and silver, not recommended for those.[8] Slightly cheaper than Sn63Pb37, often used instead for cost reasons as the melting point difference is insignificant in practice. On slow cooling gives slightly duller joints than Sn63Pb37.