Copper–Tin Reactions in Thin-Film Samples
On a silicon chip, thin-film under-bump metallization (UBM) is needed to join the solder bump to the Al or Cu wiring on the chip and also to control the size of the solder bump. This is because the oxide on a free Al surface prevents the wetting of molten solder. On the other hand, Cu reacts extremely fast with molten solder, therefore the Cu thin-film wiring cannot be wetted by molten solder.
KeywordsSolder Joint Solder Bump Molten Solder Kirkendall Void Eutectic SnPb
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