Carrier Substrate Cushion Layer for Thermal Stress Relief
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Solution Overview
Problem
Stress-sensitive chip devices, such as sensors with movable parts, face thermal stress issues due to mismatched expansion coefficients between the chip and substrate, leading to device damage and inaccurate measurements, as existing stress-reducing methods are not compatible with sensitive structures and cause plastic deformation in solder connections.
Innovation Solution
A carrier substrate with a multilayer structure featuring an organic cushion layer and conductive elongated parts that compensate for thermal expansion differences, allowing for stress relief without compromising process-sensitive structures, and enabling the use of stress-sensitive devices like MEMS microphones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dielectric polymer layer is applied over the contact surface of a chip device to reduce stress, then thermal stress is reduced, but process-sensitive structures and membranes of sensor devices cannot withstand the deposition and structuring steps
Solution Approach 1:
The patent introduces an intermediary carrier substrate with a cushion layer between the stress-sensitive sensor chip and the rigid substrate. This intermediary structure absorbs thermal stress through its elastic properties while being compatible with sensitive sensor structures, avoiding direct exposure to harsh deposition and structuring processes.
Solution Approach 2:
The patent changes the mechanical parameters of the mounting structure by using a cushion layer with specific elastic properties (E-modulus between 0.1-10 GPa) and optimized thickness (10-100 μm). This parameter optimization allows stress absorption while maintaining compatibility with sensor fabrication processes.
2Ease of manufacture
If solder materials with moderate melting point (180°C to 230°C) are used, then ease of assembly is improved, but mismatch dependent stress leads to plastic deformation of the solder connection
Solution Approach 1:
The patent applies beforehand cushioning by placing an elastic cushion layer between the solder connection and the rigid substrate. This cushion layer pre-absorbs thermal expansion stresses before they can cause plastic deformation of the solder joints, protecting the connection strength while allowing use of low-melting-point solder materials.
3Reliability
If thermal expansion coefficients are matched between chip and substrate, then thermal stress is minimized, but manufacturer is restricted to using materials not optimized for desired function
Solution Approach 1:
The carrier substrate acts as a mediator that decouples the thermal expansion mismatch problem from the sensor chip. The cushion layer with intermediate mechanical properties absorbs expansion differences, allowing the sensor chip to use optimized materials (like silicon with specific thermal expansion characteristics) without being constrained by substrate material choices.
4Ease of operation
If the sensitive membrane is exposed to stress, then device functionality is maintained, but sensor characteristic parameters vary with stress leading to measurement deviation
Solution Approach 1:
The elastic cushion layer serves as a stress-isolating intermediary that prevents rigid substrate stresses from transmitting to the sensor membrane. This isolation maintains membrane functionality while ensuring measurement accuracy by eliminating stress-induced parameter variations.
Solution Approach 2:
The patent applies local quality by creating a localized elastic cushioning zone directly beneath the sensor chip mounting area. This localized approach provides stress relief exactly where needed (at the chip-substrate interface) without affecting the overall structural integrity or requiring modification of the sensitive membrane itself.
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 solution effectively reduces thermal stress across temperature variations, maintaining sensor accuracy and preventing device damage by using a low E-modulus cushion layer and strategically structured conductive elongated parts, ensuring reliable operation and precise measurements.
Implementation Method 1
Due to the elastic properties of the polymer layer that is usually made from BCB, PI or PBO the stress can be reduced down to a certain amount
Implementation Method 2
When mounting a stress sensitive chip on a substrate having a different coefficient of expansion every temperature variation causes tension in the chip
Data Source
AI summary
A carrier substrate and a method for making a carrier substrate are disclosed. In an embodiment a carrier substrate includes a substrate body having a multilayer structure, electrical connection pads on a top surface of the substrate body, an organic cushion layer on the top surface of the substrate body, electrically conductive elongated parts arranged on top of the cushion layer, wherein each conductive elongated part is contacted to a respective electric connection pad and a solder pad located at an end of each elongated part distant from the respective connection pad.