MEMS Package Stress Isolation via Substrate Segmentation

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Solution Overview

Problem

MEMS devices are sensitive to strain-induced performance drift, which becomes more significant as package thickness and form factor are reduced to meet market demands, leading to challenges in managing stress and maintaining sensitivity.

Innovation Solution

A MEMS package configuration with a side-by-side arrangement of MEMS and IC dies on a surface mount substrate, incorporating a trench and openings in the substrate for stress isolation, and an air gap between substrates to reduce stress transfer, along with a controlled molding compound height to expose the MEMS die to the ambient environment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If package thickness is reduced to meet market needs, then form factor is improved, but strain susceptibility increases

Engineering Contradiction:

Improvepackage thicknessVSAvoidstrain susceptibility

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The substrate is segmented by creating trenches and openings that divide it into isolated regions. The MEMS die is placed in a region isolated from the substrate by these trenches and openings, which segment the stress transmission path and prevent strain from reaching the MEMS device while maintaining thin package thickness.

Inventive Principle:

Principle #1Segmentation

2Volume of moving object

If package thickness is reduced to meet market needs, then form factor is improved, but performance drift increases

Engineering Contradiction:

Improvepackage thicknessVSAvoidperformance drift

Core Design Contradiction:

Volume of moving objectVSMeasurement precision

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

3Reliability

If MEMS die is isolated from substrate stress, then strain susceptibility is reduced, but package complexity increases

Engineering Contradiction:

Improvestrain susceptibilityVSAvoidpackage complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The harmful stress transmission path is extracted from the system by removing material from the substrate to create trenches and openings. This extracts the stress isolation function from the substrate structure itself, providing strain protection without adding complex external isolation mechanisms.

Inventive Principle:

Principle #2Taking out (Extraction)

4Adaptability or versatility

If MEMS die is exposed to ambient environment, then sensing capability is improved, but contamination risk increases

Engineering Contradiction:

Improvesensing capabilityVSAvoidcontamination risk

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

A thin encapsulation layer is formed over the MEMS die to provide environmental protection while maintaining exposure to ambient conditions for sensing. This thin film structure allows the MEMS device to sense environmental characteristics while protecting against contamination.

Inventive Principle:

Principle #30Flexible shells and thin films

Data Source

PatentUS9656856B2Method of lower profile MEMS package with stress isolations

Publication Date: 2017.05.23 APPLE INC

AI summary

MEMS packages, modules, and methods of fabrication are described. In an embodiment, a MEMS package includes a MEMS die and an IC die mounted on a front side of a surface mount substrate, and a molding compound encapsulating the IC die and the MEMS die on the front side of the surface mount substrate. In an embodiment, a landing pad arrangement on a back side of the surface mount substrate forms and anchor plane area for bonding the surface mount substrate to a module substrate that is not directly beneath the MEMS die.