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Fine lines in high yield (part LXXVIII) problems with residual, excess copper in print/etch and tent/etch processes (Part A). (Tech talk).
The list of potential causes for excess copper seems endless (see Ref. 1), and for most defects it is impossible to assign a single most likely cause. However, some excess copper defects are quite characteristic and unique in nature and appearance so that troubleshooting is often successful. These are the defects to be discussed here. This column is the first of several on the subject, and deals with excess copper caused by organic contaminants other than photoresist.
Terminology
"Excess copper" in print/etch and tent/etch processes is referred to in many terms, depending on the size, shape, nature of the defect caused by excess copper, or regional vernacular:
* "Short": Excess copper bridging two or more conductors Excess copper in clearance holes of power/ground planes may also be referred to as short. More correctly, it is a potential short, shorting out a ground plane after through-hole metallization.
* "Copperspurs": usually excess copper widening a circuit trace, leading to space violations, or violating circuit trace-width uniformity specs.
* "Extraneous or spurious copper": usually copper specks on clear areas away from circuit traces.
* "Copper splashes": irregular copper specks in the shape of splashed paint.
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