Hybrid Device Package CTE Matching for Thermal Stress Reduction
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Solution Overview
Problem
Hybrid device packages face thermal stress issues due to mismatched coefficients of thermal expansion (CTEs) between components, leading to bowing and channel cracking, which degrades detector performance in optical sensors.
Innovation Solution
A hybrid device package design where the CTE of the balanced composite structure (BCS) and baseplate are matched, reducing thermal stress on the detector array IC by compressing the ROIC, and incorporating an alumina ceramic baseplate with an integrated electrical interface board to minimize CTE mismatches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the CTE of the BCS is matched to the detector to reduce thermal stress on the detector, then detector stress is reduced, but the ROIC experiences increased thermal stress and bowing
Solution Approach 1:
The patent changes the CTE matching parameter from detector-matched to baseplate-matched. By designing the BCS with a CTE matched to the alumina baseplate rather than the detector, the system achieves a different stress distribution pattern that eliminates channel cracking while maintaining acceptable detector stress levels through the compliance of the thin detector layer.
Solution Approach 2:
The patent applies different CTE matching strategies to different components: the BCS is CTE-matched to the baseplate structure, while the thin detector layer is allowed to have residual stress that does not cause cracking. This localized quality approach recognizes that the detector's thinness provides stress relief.
2Ease of manufacture
If the CTE of the electrical interface board is different from the baseplate, then the board can be made from standard materials, but thermal mismatch causes bowing or relative motion between board and baseplate
Solution Approach 1:
The patent extracts the electrical interface board from the rigid structural assembly. By making the board removable and not rigidly bonded to the baseplate, the design allows the board to have a different CTE without causing assembly bowing or stress. The board can be attached and detached independently, eliminating the thermal mismatch problem.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design reduces thermal deformation and stress below the threshold for channel cracking, maintaining a flat detector array and improving performance by eliminating bowing and channel cracking, while potentially reducing the package's parts count.
Implementation Method 1
the CTE of the 'stack' that includes the BCS and the first IC is approximately equal to that of the baseplate, thereby reducing the thermal stress to which the at least one additional IC is subjected when cooled to its operating temperature
Implementation Method 2
the CTE of a BCS is designed to match that of an alumina baseplate, which compresses the ROIC less than a BCS that is CTE-matched to the detector
Data Source
AI summary
A hybrid device package comprising a baseplate, a balanced composite structure (BCS) on the baseplate, a first IC on the BCS, and at least one additional IC physically coupled to the first IC. The coefficient of thermal expansion (CTE) for the stack formed from the BCS and the first IC is arranged to be approximately equal to that of the baseplate, thereby reducing the thermal stress to which the at least one additional IC is subjected when cooled to its operating temperature which might otherwise result in physical damage to the IC. The baseplate is preferably an alumina ceramic baseplate. In one embodiment, the first IC is a readout IC (ROIC), the at least one additional IC is a detector array IC which is on the ROIC, and the hybrid device package is a focal plane array (FPA).