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In this pad structure, increase of the resistance in the via opening due to high resistivity intermetallic, which may form as a result of the solder reaction with the pad, is minimized or eliminated.
English (United States)
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Low Resistance Solder Via Pad Structure
In this pad structure, increase of the resistance in the via opening due to
high resistivity intermetallic, which may form as a result of the solder reaction
with the pad, is minimized or eliminated.
The pad 10 supported on the top passivation layer 12 and making contact to
an underlying metallurgy layer 14 through via opening 16 is part of the metallurgy
system of device 18. The pad 10 consists of a thin chromium layer 20 supported
on layer 12 and making contact to metallurgy stripe 14, a phased chromium-
copper layer 22, a relatively thick copper layer 24, a phased chromium-copper
barrier layer 26, and an overlying solderable layer 28.
The thickness of copper layer 24 is approximately the thickness of the top
passivation layer 12. By making the copper layer 24 thick, any intermetallic
compound formed between the solderable layer and the ultimate solder ball (not
shown) is formed over the entire surface of the pad and will therefore not unduly
raise the overall resistance of the pad. If the layer 24 were very thin, the
intermetallic so formed would be located largely within the via 16 and materially
increase the resistance of the pad, particularly when the area of the via is very
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