  The theory of signature invariants of links in rational homology spheres is
applied to covering links of homology boundary links. From patterns and Seifert
matrices of homology boundary links, an explicit formula is derived to compute
signature invariants of their covering links. Using the formula, we produce
fused boundary links that are positive mutants of ribbon links but are not
concordant to boundary links. We also show that for any finite collection of
patterns, there are homology boundary links that are not concordant to any
homology boundary links admitting a pattern in the collection.
