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Constrained Coefficient of Thermal Expansion
(CTE)
A traditional issue when encapsulating a metallic
insert is differential CTE between the plastic and the insert. As the
encapsulant and insert expand and contract at different rates, the stress
level between insert and plastic will change and microcracks can be initiated.
By modifying the encapsulant to match the CTE of the insert (for example
copper, aluminum, or steel), these issues can be mitigated. Ceramic fillers
have proven to be especially effective in certain applications because
the low CTE values achievable tend to be isotropic in nature. In most
plastic systems, CTE rates increase exponentially with temperature. This
change magnifies differentials and accelerates the aforementioned problems.
A benefit of ceramic filler is the relative linearity of CTE with temperature.
By working with combinations of fillers and base
polymers, Encap can tailor a resin to a specific CTE value. Constrained
CTE can be of benefit as follows:
- Improved hermetic sealing due to mitigation of microcracks
(Applications: Lead frames, termination areas, submersible motors)
- Consistent pre-load stress on encapsulated components
- Mitigation of cracking issues during thermal cycling
or thermal shock tests
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