Browse Prior Art Database

Circuit Board Stand-Off to Reduce Thermal Fatigue

IP.com Disclosure Number: IPCOM000034462D
Original Publication Date: 1989-Feb-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Meeks, S: AUTHOR [+3]

Abstract

Height of a solder joint (the distance from the board surface to the component) is critical to the thermal cycle fatigue lifetime of the solder connection. This fatigue is caused by difference in thermal expansion between the printed circuit board material and the components mounted on the board by means of solder joints. The differences in the thermal coefficients of expansion are greater for components mounted on injection molded thermoplastic cards than for the same component mounted on FR-4 boards. This significantly decreases the solder joint lifetime due to thermal cycling (power on-off cycles) on injection molded boards versus conventional boards. The figure shows a platform or stand-off molded in a thermoplastic card to control such fatigue.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 71% of the total text.

Page 1 of 2

Circuit Board Stand-Off to Reduce Thermal Fatigue

Height of a solder joint (the distance from the board surface to the component) is critical to the thermal cycle fatigue lifetime of the solder connection. This fatigue is caused by difference in thermal expansion between the printed circuit board material and the components mounted on the board by means of solder joints. The differences in the thermal coefficients of expansion are greater for components mounted on injection molded thermoplastic cards than for the same component mounted on FR-4 boards. This significantly decreases the solder joint lifetime due to thermal cycling (power on-off cycles) on injection molded boards versus conventional boards.

The figure shows a platform or stand-off molded in a thermoplastic card to control such fatigue. The stand-off increases the solder joint height of components on an injection molded card, thus increasing the fatigue lifetime of the joint. Small stand-offs are molded into the card to increase the height of the joint. The nominal shear strain on a solder joint is given by the equation where q =

Shear strain WV = Difference in thermal coefficient of expansion

between the component and substrate

WT = Difference in temperature of component and

substrate between power "on and off" conditions

DNP = Distance between the center of the component and

the relevant solder joint (Distance to Neutral

Point)

H = Stand-off height of the component This indicates that a taller solde...