solderball

Solderballs are small spherical drops of solder used as interconnects in surface-mount electronics, most notably in ball grid array (BGA) and flip-chip packages. They provide the solder joints that connect a die to a printed circuit board or substrate after reflow.

Most solder balls are tin-based alloys. Leaded versions historically used Sn63Pb37, but modern assemblies typically use lead-free compositions such as SAC305 (Sn-3.0Ag-0.5Cu) or other Sn–Ag–Cu variants to meet RoHS requirements. Ball diameters range from about 0.25 to 1.0 millimeter, with common sizes including 0.4, 0.5, and 0.65 mm. The diameter and height are chosen to achieve the correct standoff and joint reliability for the package pitch.

Manufacturing and use: Solder balls can be pre-formed and placed on pads using a ball-attach method or formed in place by depositing solder paste and reflowing. In BGA assembly, solder mask openings and pad metallurgy are prepared, flux is applied, balls are placed, and reflow creates spherical joints due to surface tension. Some processes use ball bonding or stencil-printing to apply paste before reflow.

Quality and standards: Solder balls are produced with tight tolerances on diameter, roundness, and height; inspection checks for voids, misalignment, and ball integrity. Industry standards from IPC govern solder alloy compositions, ball deposition, and inspection, while RoHS and related regulations constrain lead content.