MEMS Package with Exposed Conductive Pillars and CTE-Matched Molding
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Solution Overview
Problem
The existing MEMS package structures using Quad Flat No-leads (QFN) technique face limitations in miniaturization due to wire bonding, which results in high resistance and potential damage from thermal expansion mismatches between molding compounds and MEMS dies.
Innovation Solution
A semiconductor package device with a MEMS die, conductive pillars, and a package body that exposes the top surface of the conductive pillars, along with a binding layer and redistribution layer, to reduce size and resistance, and match thermal expansion coefficients with the MEMS die.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wire bonding technique is used to connect MEMS die to lead frame, then electrical connection is achieved, but the package size cannot be miniaturized and resistance is relatively high
Solution Approach 1:
The patent extracts and eliminates the bonding wire from the conventional QFN package structure. Instead of using wire bonding to connect the MEMS die to the lead frame, the invention directly integrates the MEMS die onto the lead frame substrate, removing the intermediate wire connection and its associated loop height, thereby enabling miniaturization and reducing resistance.
Solution Approach 2:
The patent transitions from a three-dimensional wire bonding approach (with loop height) to a planar integration approach where the MEMS die is directly mounted on the lead frame substrate. This dimensional change eliminates the vertical loop structure and reduces the overall package footprint.
2Stability of the object's composition
If molding compound with CTE close to lead frame is selected, then lead frame compatibility is improved, but CTE mismatch with MEMS die occurs causing potential damage
Solution Approach 1:
The patent applies local quality by using different molding compounds for different regions of the package. Specifically, a first molding compound with CTE matching the lead frame is used for the lead frame area, while a second molding compound with CTE matching the MEMS die is used for the MEMS die area. This localized material selection ensures both lead frame compatibility and MEMS die protection during thermal cycling.
Solution Approach 2:
The patent employs composite materials by combining two different molding compounds in a single package structure. Each molding compound is selected for its specific CTE properties to match different components (lead frame and MEMS die), creating a composite packaging solution that addresses the thermal expansion mismatch problem through material composition rather than a single uniform material.
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
This configuration enables reduced size and improved electrical performance while preventing thermal damage to the MEMS die by minimizing resistance and matching thermal expansion coefficients.
Implementation Method 1
the package body is made of a material having a glass transition temperature greater than a temperature at which to form the binding layer
Data Source
AI summary
A micro-electromechanical systems (MEMS) package structure includes: (1) a circuit layer; (2) a MEMS die with an active surface, wherein the active surface faces the circuit layer; (3) a conductive pillar adjacent to the MEMS die; and (4) a package body encapsulating the MEMS die and the conductive pillar, and exposing a top surface of the conductive pillar.