Hi Akira-san,
We have an application note on "SMT assembly for Leadless Package" that includes our recommendations on the land pattern, the stencil openings, the reflow temp profile for various LP and LC packages. I hope this AN will be a helpful reference to resolve your reflow issue. Below is the link to this app note,
http://www.hittite.com/content/documents/smt_assembly_for_leadless_packages.pdf
Best Regards,
MN