MEMS Contact Pads on Cap Substrate for Wafer-Level Testing
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Solution Overview
Problem
The existing methods for accessing and testing MEMS signals are inefficient and costly, especially when an ASIC is bonded to a MEMS wafer level, as they require complex evaluation electronics and additional circuits, making it difficult to identify and characterize MEMS components before wafer bonding, and are not adaptable for new tests during development or series production.
Innovation Solution
The solution involves a micromechanical device with a MEMS substrate and a cap substrate that enclose cavities, where contact pads are situated on the cap substrate and connected to the MEMS structure via strip conductors, allowing for electrical characterization without measuring pads on the MEMS substrate, and enabling direct electrical connections between the MEMS and cap substrates, which can be established beyond chip boundaries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an ASIC is bonded to a MEMS wafer level, then the MEMS signal can be conducted onto the cap and processed by the ASIC, but direct access to the MEMS signals is no longer possible and complex evaluation electronics are required
Solution Approach 1:
The contact pads are moved from the traditional planar position on the MEMS substrate to the vertical dimension on the cap substrate surface. This dimensional transition allows electrical access to MEMS signals while the ASIC is bonded to the wafer, avoiding the need for complex evaluation electronics and enabling direct testing through the cap substrate surface.
Solution Approach 2:
The cap substrate serves as an intermediary element that provides access to MEMS signals. By placing contact pads on the cap substrate surface, the invention creates an intermediate access point that allows electrical connection to MEMS structures without requiring direct access to the MEMS substrate or complex evaluation electronics.
2Ease of operation
If measuring pads are provided on the MEMS substrate, then direct electrical access to MEMS signals is possible, but the chip size increases and fewer chips can be produced per wafer
Solution Approach 1:
The electrical access function is segmented from the MEMS substrate and transferred to the cap substrate. This segmentation allows the MEMS substrate to be optimized for sensor functionality with minimal area, while the cap substrate provides the necessary electrical access points, thereby reducing the overall chip area and increasing yield per wafer.
Solution Approach 2:
The contact pads are relocated from the horizontal plane of the MEMS substrate to the vertical surface of the cap substrate. This dimensional relocation eliminates the area occupation of measuring pads on the MEMS substrate, reducing chip size and increasing the number of producible chips per wafer while maintaining ease of electrical access.
3Reliability
If additional circuits are included in the ASIC for MEMS signal testing, then MEMS components can be characterized, but the ASIC complexity increases and additional functions must be kept available in each ASIC
Solution Approach 1:
The testing and characterization functions are extracted from the ASIC and relocated to external evaluation equipment. By providing contact pads on the cap substrate surface, the invention enables direct electrical access to MEMS signals, allowing comprehensive testing using simpler external equipment rather than embedding complex testing circuits within each ASIC.
Solution Approach 2:
Instead of implementing complex testing circuits in each ASIC, the invention uses the cap substrate contact pads to create a simplified interface that replicates the functionality of having direct MEMS access. This allows external evaluation equipment to perform all necessary testing without requiring auxiliary functions within the ASIC itself.
Data Source
AI summary
A micromechanical device that includes a MEMS substrate and a cap substrate that enclose at least one first cavity, with at least one contact pad that is situated outside the first cavity. A MEMS structure is situated in the first cavity and connected to the contact pad with the aid of a strip conductor, the strip conductor extending at least partially in the MEMS substrate. The contact pad is situated at a surface of the cap substrate.