MEMS Die Step-Cut Structure for Bonding Pad Clearance
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Solution Overview
Problem
Existing MEMS die bonding methods face issues with adhesive spread over the ASIC die bonding pad, leading to failed wire bonding due to insufficient clearance, and current solutions involve MEMS size reduction, ASIC size increase, or the use of expensive Die Attach Film (DAF) adhesive.
Innovation Solution
The solution involves reducing the span length of the MEMS die by applying a step cut on its bottom, allowing the adhesive layer to extend to a non-horizontal surface without reaching the top part, thereby improving clearance and preventing adhesive spread onto the ASIC die bonding pad.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If adhesive layer is used to stack MEMS die on ASIC die, then mechanical attachment is achieved, but adhesive spreads over bonding pad causing wire bonding failure
Solution Approach 1:
The MEMS die is divided into two distinct parts: a first part (bonding surface) and a second part (side surface), separated by a step structure. This segmentation allows the adhesive to be confined to the first part while keeping the second part clear for wire bonding operations, thus resolving the conflict between mechanical attachment strength and wire bonding reliability
Solution Approach 2:
A step structure is introduced in the vertical dimension (z-direction) to create different elevation levels on the MEMS die surface. The first part is positioned at a lower elevation than the second part, allowing the adhesive layer to spread horizontally on the first part without reaching the bonding pad area on the second part, thereby preventing wire bonding failure while maintaining strong mechanical attachment
2Reliability
If MEMS die size is reduced to improve clearance, then adhesive spread is prevented, but MEMS functionality is compromised
Solution Approach 1:
The MEMS die is segmented into a first part for adhesive bonding and a second part for wire bonding, allowing the overall die size to remain large enough for MEMS functionality while creating local clearance zones through the step structure that prevent adhesive spread onto bonding pads
Solution Approach 2:
Instead of reducing the MEMS die size in the horizontal plane, the invention uses vertical dimensionality (step structure) to create clearance. This allows the MEMS die to maintain its full size and functionality while the step structure provides the necessary clearance by elevating the bonding pad area above the adhesive spread zone
3Reliability
If expensive Die Attach Film adhesive is used, then adhesive spread is controlled, but manufacturing cost increases
Solution Approach 1:
The step structure segments the MEMS die surface into distinct zones, allowing the use of standard, cost-effective adhesive materials. The geometric confinement provided by the step structure controls adhesive spread physically rather than relying on expensive specialized adhesives, thereby maintaining reliability while reducing manufacturing cost
Data Source
Figure 1
Figure 2a~2b
Figure 3a~3b
AI summary
The disclosure is based on the idea of reducing the span length of a MEMS die which is attached to the top of an ASIC die via an adhesive layer by applying a step cut on the bottom of the MEMS die. This improves the clearance between the MEMS die and bonding pads attached to the top of the ASIC die, thereby preventing failures of electrical connections between the MEMS die and the ASIC die.