IEC 60191-4:2013 specifies a method for the designation of package outlines and for the classification of forms of package outlines for semiconductor devices and a systematic method for generating universal descriptive designators for semiconductor device packages. The descriptive designator provides a useful communication tool but has no implied control for assuring package interchangeability. This edition includes the following significant technical changes with respect to the previous edition: a) Material code "S" is added to indicate a silicon based package. b) Description of "WL" is added to be used for general use.