Electroless plating solution

An electroless plating solution containing a metal ion source having a parent phase that contains Sn and a Sn-Cu alloy, and an intermetallic compound crystal that contains Sn, Cu, Cr, Al and Ni, dispersed in the parent phase,

• the parent phase in the metal ion source having a composition represented by:
• Cu:
• 5 to 0.02% by mass;
• Cr:
• 0.001 to 18% by mass;
• Al:
• 3 to 0.02% by mass;
• Ni:
• 1 to 0.02% by mass;
• and
• the balance of Sn,
• the intermetallic compound crystal having a composition represented by:
• Cu:
• 5 to 50% by mass;
• Cr:
• 0.001 to 18% by mass;
• Al:
• 0.1 to 20% by mass;
• Ni:
• 0.1 to 6.5% by mass;
• and
• the balance of Sn,
• and proportion of the intermetallic compound crystal being 20 to 60% by mass.