7・63 Let the set $A=\{0,1,2, \cdots, 9\},\left\{B_{1}, B_{2}, \cdots, B_{k}\right\}$ be a family of non-empty subsets of $A$, such that when $i \neq j$, $B_{i} \cap B_{j}$ has at most two elements. Find the maximum value of $k$.