Microchip Blocking Apparatus Prevents Metal Seal Migration
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Solution Overview
Problem
The use of metal bonds in microchip fabrication often results in liquid metal oozing onto interconnect pads, causing short circuits and significant yield loss due to the rapid liquefaction of metal alloys at their eutectic point, leading to increased fabrication costs.
Innovation Solution
A blocking apparatus, such as trenches or protrusions, is positioned between the interconnects and the metal seal to prevent the migrating metal from contacting the interconnects, using surface tension or containment to trap excess metal and prevent electrical connection, allowing the metal seal to cool and form a secure bond without short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal bonds are used to bond cap die to base die, then hermeticity and bond strength are improved, but liquid metal oozes onto interconnect pads causing short circuits and yield loss
Solution Approach 1:
The patent divides the bonding interface into distinct functional zones: an outer metal seal ring for hermetic bonding and an inner isolation trench for electrical isolation. This segmentation allows the metal seal to provide hermeticity while the isolation trench prevents liquid metal from reaching interconnect pads, thereby resolving the contradiction between reliability and manufacturing precision.
Solution Approach 2:
The patent introduces an intermediary structure (isolation trench or blocking apparatus) between the metal seal and the interconnect pads. This intermediary acts as a barrier that stops liquid metal migration while allowing the metal seal to maintain hermeticity, thus preventing short circuits without compromising bond strength.
2Reliability
If glass seal is used to bond cap die to base die, then hermeticity is achieved, but seal footprint increases die size
Solution Approach 1:
The patent changes the material parameter from glass to metal for the seal, enabling hermetic bonding with a smaller footprint. Metal bonds can achieve comparable hermeticity to glass seals but with reduced width, thereby decreasing the overall die size while maintaining reliability.
3Strength
If metal is heated to melting point and pressure applied for bonding, then bond strength is improved, but liquid metal migrates and contacts interconnect
Solution Approach 1:
The patent applies preliminary anti-action by pre-configuring isolation trenches or blocking apparatuses before the bonding process. These structures are designed to counteract and contain the harmful effect of liquid metal migration that occurs during heating and pressing, thereby preventing short circuits while allowing strong bonding.
Solution Approach 2:
The patent converts the harmful effect of liquid metal migration into a beneficial containment process. The isolation trench captures the migrating liquid metal, preventing it from reaching interconnect pads. The harmful migration is thus redirected into a controlled zone where it cools and solidifies without causing damage.
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
The blocking apparatus effectively reduces yield loss and fabrication costs by preventing metal from reaching the interconnects, maintaining the integrity and performance of the microchip, while allowing the use of a variety of metal alloys for bonding.
Implementation Method 1
the rapid liquefaction of metal alloys at their eutectic point
Implementation Method 2
liquid metal oozing onto interconnect pads
Implementation Method 3
using surface tension or containment to trap excess metal
Data Source
AI summary
A microchip has a base die with a conductive interconnect and an isolation trench around at least a portion of the conductive interconnect, and a cap die secured to the base die. A seal, formed from a metal material, is positioned between the base die and the cap die to secure them together. The microchip also has a blocking apparatus, between the isolation trench and the metal seal, that at least in part prevents the metal material from contacting the interconnect.