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Voids or bubbles may be found in C4 solder balls under certain processing conditions. This process application includes:
English (United States)
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Page 1 of 2
Void Free Pb-Sn Solder
Voids or bubbles may be found in C4 solder balls under certain processing
conditions. This process application includes:
1) The Balling Step wherein solder is heated above its melting point to
homogenize and reflow the solder.
2) The Chip Joining Step wherein chips are placed in position over pads and
reflowed to effect electrical and mechanical joint to the substrate.
Referring to Fig. 1, the voids are usually found in and around the etched hole
1 that forms the interconnection from an A1 line 2 buried between SiO(2) layers
3, 4 and solder ball 5 of Pb-Sn alloy.
This article discloses a process whereby voids observed in C4 balls or other
solder systems are removed. Heating is first carried out in a vacuum to above
the melting temperature of the solder balls, where some voids are eliminated but
additional voids are created. Then, the newly created voids are eliminated by
allowing a reducing gas (e.g., deoxygenized forming gas) to enter the vacuum
chamber until atmospheric pressure is reached. The solder balls are then cooled
to freeze the void-free solder. A temperature cycle for use with Pb-Sn solder is
shown in Fig. 2.
Page 2 of 2
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