Browse Prior Art Database

Improved Lead Structure for Surface Mount Components

IP.com Disclosure Number: IPCOM000061718D
Original Publication Date: 1986-Sep-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Kang, SK: AUTHOR [+2]

Abstract

The reliability of Surface Mount Components (SMCs) is strongly dependent upon the strength of the solder bonds which hold the components Plastic Leaded Chip Carriers (PLCCs), Small Outline Packages (SOPs), etc. to circuit boards. It has been found that larger area components, high I/O count PLCCs for example, may fail because the surface solder bonds fail when the components are subjected to physical stress. The strongest bonds are those for which the solder fillet completely surrounds the I/O lead. The structure described below facilitates the flow of the solder over the entire I/O lead during the solder reflow operation. Elimination of trapped gas is important. Before vapor phase reflow, the circuits are baked with the components in place to drive volatile liquids from the solder paste.

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Improved Lead Structure for Surface Mount Components

The reliability of Surface Mount Components (SMCs) is strongly dependent upon the strength of the solder bonds which hold the components Plastic Leaded Chip Carriers (PLCCs), Small Outline Packages (SOPs), etc. to circuit boards. It has been found that larger area components, high I/O count PLCCs for example, may fail because the surface solder bonds fail when the components are subjected to physical stress. The strongest bonds are those for which the solder fillet completely surrounds the I/O lead. The structure described below facilitates the flow of the solder over the entire I/O lead during the solder reflow operation. Elimination of trapped gas is important. Before vapor phase reflow, the circuits are baked with the components in place to drive volatile liquids from the solder paste. During baking, gases trapped beneath the I/O lead surfaces create voids which may lead to failure of the bond. This new structure provides for an additional route for the gases to escape. The infrared Nd-YAG laser is a rework tool for individual leads for both SMCs and Tape Automated Bonding (TAB) packages. However, the I/O lead surface may absorb the laser radiation and conduct the heat away from the bonding area, keeping the heat from reaching the solder to be reflowed. The lead structure described below provides direct access to the solder for the laser radiation. This improves the rework process. Figs. 1 and 2 are views showing the structure before bonding, and Figs. 3 an...