Exposed-Die MEMS Pressure Sensor Packaging to Reduce Mold Flashing
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Solution Overview
Problem
Existing MEMS packages face challenges in producing small, defect-free devices due to high production costs and low yields, with issues such as mold flashing and die cracking during the molding process, and require protection from external stresses.
Innovation Solution
The use of a lead frame tape as a base layer in MEMS package fabrication, which includes exposing the sensing component to the ambient atmosphere through apertures, reduces material usage and minimizes mold flashing and die cracking by using bonding wires and alternative molding methods like compression or injection molding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional MEMS packages are used to protect internal components and electronic connections, then reliability is improved, but production cost increases and manufacturing precision deteriorates due to mold flashing and die cracking
Solution Approach 1:
The patent applies preliminary action by placing the MEMS die on the lead frame tape before the molding process, with the sensing component exposed to ambient atmosphere through apertures. This pre-arranged configuration allows the molding compound to be applied without causing die cracking or mold flashing, as the die is already securely positioned and the aperture structure is prepared in advance to accommodate the molding process.
Solution Approach 2:
The lead frame tape serves as an intermediary element that holds the MEMS die in place during the molding process. The tape provides a stable substrate that prevents die cracking while allowing the molding compound to flow around the exposed sensing component. This intermediary structure mediates between the need for die protection and the requirement for precise molding without defects.
2Reliability
If molding compound is applied to completely encapsulate bonding wires and semiconductor dice, then protection of electronic connections is improved, but material usage increases and production cost increases
Solution Approach 1:
The patent applies local quality by selectively exposing the sensing component to ambient atmosphere through apertures while still providing molding compound protection for the bonding wires and semiconductor dice. This localized approach allows the sensing area to remain open for atmospheric pressure sensing while the electronic connections are encapsulated for protection, optimizing material usage by not unnecessarily covering the sensing aperture with molding compound.
3Manufacturing precision
If lead frame tape is used as base layer with exposed sensing component, then manufacturing precision is improved by reducing mold flashing and die cracking, but device complexity increases
Solution Approach 1:
The lead frame tape serves multiple functions: it provides mechanical support for the MEMS die, acts as a substrate for the molding process, and creates the aperture structure for sensing component exposure. This multi-functional element simplifies the overall package structure by combining several functions into a single component, thereby reducing device complexity while maintaining manufacturing precision.
Data Source
AI summary
A MEMS pressure sensor packaged with a molding compound. The MEMS pressure sensor features a lead frame, a MEMS semiconductor die, a second semiconductor die, multiple pluralities of bonding wires, and a molding compound. The MEMS semiconductor die has an internal chamber, a sensing component, and apertures. The MEMS semiconductor die and the apertures are exposed to an ambient atmosphere. A method is desired to form a MEMS pressure sensor package that reduces defects caused by mold flashing and die cracking. Fabrication of the MEMS pressure sensor package comprises placing a lead frame on a lead frame tape; placing a MEMS semiconductor die adjacent to the lead frame and on the lead frame tape with the apertures facing the tape and being sealed thereby; attaching a second semiconductor die to the MEMS semiconductor die; attaching pluralities of bonding wires to form electrical connections between the MEMS semiconductor die, the second semiconductor die, and the lead frame; and forming a molding compound.