The effects of underfill on the reliability of flip chip solder joints |
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Authors: | Peng Su Sven Rzepka Matt Korhonen C Y Li |
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Institution: | 1. Department of Materials Science and Engineering, Cornell University, 14853, Ithaca, NY, USA 2. Fakult?t Elektrotechnik, Technische Universit?t, Dresden, D-01062, Dresden, Germany
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Abstract: | Thermal fatigue damage of flip chip solder joints is a serious reliability concern, although it usually remains tolerable
with the flip chip connections (of smaller chips) to ceramic boards as practiced by IBM for over a quarter century. However,
the recent trend in microelectronics packaging towards bonding large chips or ceramic modules to organic boards means a larger
differential thermal expansion mismatch between the board and the chip or ceramic module. To reduce the thermal stresses and
strains at solder joints, a polymer underfill is customarily added to fill the cavity between the chip or module and the organic
board. This procedure has typically at least resulted in an increase of the thermal fatigue life by a factor of 10, as compared
to the non-underfilled case. In this contribution, we first discuss the effects of the underfill to reduce solder joint stresses
and strains, as well as underfill effects on fatigue crack propagation based on a finite element analysis. Secondly, we probe
the question of the importance of the effects of underfill defects, particularly that of its delamination from the chip side,
on the effectiveness of the underfill to increase thermal fatigue life. Finally, we review recent experimental evidence from
thermal cycling of actual flip chip modules which appears to support the predictions of our model. |
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Keywords: | Underfill finite element simulation flip-chip solder joints |
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