pcb布线安规要求：
更详细全面的请参考http://wenku.baidu.com/link?url=iCFkNkpPJaxzN83krI2Oa4R97hmclCgBYX8opCGf9DF_vOmvlb7UI1JZPZ1GierAoy-7lS8oaFLOXAcaWhRryVb1LLXE_qjRzpn-579IJK3
