Composite solder balls metallised on the surface and calibrated for the assembly of electronic boards

A method for manufacturing composite solder balls metallized on a surface and calibrated, of diameter Df, said composite solder balls comprising:

• a core consisting of a spherical support particle of diameter D0, made of expanded polystyrene (EPS) and having an intergranular porosity of at least 50%, and
• a shell that covers said support particle and is formed by a plurality of metallic surface layers, comprising a copper coating of thickness Ecu, at least one nickel layer of thickness ENi, and a gold top coat of thickness EAU, said method comprising:
• providing support particles, followed by:
• granulometric sorting of the support particles consisting of physical and/or mechanical separation of the support particles having a diameter D0 such that D0=Df−2*(ENi+Ecu+EAu), wherein D0 is between 200 μm and 1000 μm;
• activating treatment of the support particles thus selected to obtain activated support particles;
• metallizing said activated support particles by means of autocatalytic chemical deposition of one or more layers of copper, and repeating metallizing until a copper coating of thickness Ecu of copper of between 15 and 30 μm to obtain copper-coated support particles;
• metallizing the copper-coated support particles by means of autocatalytic chemical deposition of at least one layer of nickel alloyed with phosphorous NiP having a mass percentage of from 7 to 10% phosphorous with respect to the total weight of said layer of NiP, performing until a thickness ENi of the layer of chemical nickel of between 4 μm and 7 μm is obtained, to obtain support particles coated with chemical nickel;
• metallizing the support particles coated in chemical nickel consisting of depositing gold by means of a method of galvanic displacement implemented by immersion in an aqueous solution containing gold ions, to obtain composite solder balls metallized and coated on the surface with a gold top coat of a thickness EAU of between 0.05 μm and 0.12 μm;
• and
• granulometric sorting the metallized particles in order to sort and select composite solder balls metallized on the surface and have a diameter Df, at a tolerance of +/−5%.