Browse Prior Art Database

LOW MECHANICAL STRESS LEADFRAME

IP.com Disclosure Number: IPCOM000005562D
Original Publication Date: 1985-Oct-01
Included in the Prior Art Database: 2001-Oct-16
Document File: 3 page(s) / 129K

Publishing Venue

Motorola

Related People

Paul R. Theobald: AUTHOR [+2]

Abstract

Transfer molding of thermosetting epoxy compounds is a commonly used method to encapsulate integrated circuit devices which have been attached and connected to a dual-in-line multiple lead metal frame, thereby pro- viding mechanical protection and electrical insulation among separate components within the packages unit. Dur- ing the high temperature molding process, chemical curing of the epoxy compound and thermal contraction differences between the molded plastic body and the metal leadframe result in residual compressive stresses within the metal structure which are greater than the critical load required to cause buckling in the delicate leadframe members, An improved leadframe is described which substantially provides control of the residual metal stresses for dimensional stability of the critical structural members.

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MOTOROLA Technical Developments Volume 5 October 1985

LOW MECHANICAL STRESS LEADFRAME

by Paul R. Theobald and Victor M. Torres

ABSTRACT

   Transfer molding of thermosetting epoxy compounds is a commonly used method to encapsulate integrated circuit devices which have been attached and connected to a dual-in-line multiple lead metal frame, thereby pro- viding mechanical protection and electrical insulation among separate components within the packages unit. Dur- ing the high temperature molding process, chemical curing of the epoxy compound and thermal contraction differences between the molded plastic body and the metal leadframe result in residual compressive stresses within the metal structure which are greater than the critical load required to cause buckling in the delicate leadframe members, An improved leadframe is described which substantially provides control of the residual metal stresses for dimensional stability of the critical structural members.

DESCRIPTION

   A typical metal leadframe structure for molded plastic dual-in-line integrated circuit packages is shown in Fig- ure 1. Characteristic features requiring critical mechanical stability include tool positioning datum holes 10 used for package assembly, a semiconductor die attach pad 12, and semiconductor wire bonding posts 14. Structural members connecting these critical position features to the main frame body include a molding compound dam bar 16 and a die attach pad tie bar 18.

   Problems associated with this typical structure as a result of molding process residual stresses result from the contraction of the dam bars 16 causing distortion of the datum holes 10 to the extent that the holes do not fit tooling pins for lead forming operations. Also, contraction of the tie bar 18 causes bar 18 to buckle resulting in tilting the die attach pad 12 and wire bonding posts to the e...