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Importance of Low Modulus versus High Tensile Strength for Device
Reliability
At first glance, it would seem important to choose the die attach adhesive
with the highest strength. However, adhesives with these very high values are
typically also stiff materials with low elongation that are not able to absorb
stress. This can lead to the generation of very high forces on the electronic
device during heat exposures, thermal cycling or simply after long service
life. These high stresses can result in damage to devices or interconnections
and ultimately in failure of the electronics.
In electronic uses, it is often better to utilize a material with good
intimate adhesion that will maintain its functionality for long times and in a
wide variety of extreme service environments. Silicone die attach adhesives,
with their low modulus (definition rollover, see Appendix) properties after
curing, have been shown to do this very well. The low modulus of the cured
adhesives maintains a low stress environment on the electronic devices that
can significantly enhance the reliability of the part.
Low modulus also brings benefits in vibration dampening or sudden shocks to
the electronics such as those experienced in drop tests. It will also
maintain a low stress environment in board bending tests. Materials with low
modulus can remain more compliant and make the electronic systems less
sensitive to many sources of mechanical shock.
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