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Browse Prior Art Database

Improved Lead Frame Structure for Surface-Mounting Package

IP.com Disclosure Number: IPCOM000062371D
Original Publication Date: 1986-Nov-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Kang, SK: AUTHOR

Abstract

Solder wicking along leads of surface mount packages during reflow is recognized as an important problem leading to improper fillet formation, weak joint strength and, thereby, short fatigue life. This seems more serious with plastic leaded chip carrier (PLCC)-type packages having J-leads than with other types of packages, such as small outline IC and flatpack. Solder wicking is also concerned in case of rework, where solder application and the reflow process are less controllable. Solutions presented here are based on an idea of retaining solder at surface-mounted pads by various surface treatments of lead frames. The drawing shows an exemplary PLCC package having lead beams with narrow strips of surface-treated area (hatched portions) to prevent solder wicking along leads during reflow or rework.

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Improved Lead Frame Structure for Surface-Mounting Package

Solder wicking along leads of surface mount packages during reflow is recognized as an important problem leading to improper fillet formation, weak joint strength and, thereby, short fatigue life. This seems more serious with plastic leaded chip carrier (PLCC)-type packages having J-leads than with other types of packages, such as small outline IC and flatpack. Solder wicking is also concerned in case of rework, where solder application and the reflow process are less controllable. Solutions presented here are based on an idea of retaining solder at surface-mounted pads by various surface treatments of lead frames. The drawing shows an exemplary PLCC package having lead beams with narrow strips of surface-treated area (hatched portions) to prevent solder wicking along leads during reflow or rework. Several surface- treatment schemes, which can be incorporated in a manufacturing process of lead frames for surface mount packages, are as follows: 1) Spot evaporation of thin metallic films, such as Al, Ti or Cr layer, onto lead frames, as shown in the drawing. 2) Coating or spraying high temperature-resistant polymeric materials, such as polyimide, onto lead frames, as shown in the drawing. 3) Local oxidation of lead frames by dipping into chemicals. 4) Forming layers of oxide, carbides or nitrides selectively by either plasma or laser treatment. 5) Electrochemical reaction to produce oxides locally to lead f...