A acrylate copolymer obtained by copolymerization of a monomer mixture containing a monomer of the general formula ,wherein R1 is a hydrogen atom or methyl, R2 is a linear or branched alkylene group having 1 to 8 carbon atoms and Y is a single bond or an oxygen atom, a monomer copolymerizable with the monomer and a crosslinking monomer. The single-sided lid flash memory card may be formed from a semiconductor package having two or more tapered, stepped or otherwise shaped edges capable of securing a single-sided lid thereon. And, the auxiliary urging force by the auxiliary urging mechanism when the trunnion shaft is located at the neutral position is weaker than the auxiliary urging force by the auxiliary urging mechanism when the trunnion shaft is located at the operational position.