  In this article, we decrease the degree of the polynomials on the boundary of
the weak functions and modify the definition of the weak laplacian which are
introduced in \cite{BiharmonicSFWG} to use the SFWG method for the biharmonic
equation. Then we propose the relevant numerical format and obtain the optimal
order of error estimates in $H^2$ and $L^2$ norms. Finally, we confirm the
estimates using numerical experiments.
