Power Overlay Metallization for Copper Wirebond Reliability
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Solution Overview
Problem
Current power device packaging structures face challenges with copper wirebonding due to material mismatch and increased stress, leading to unreliable connections and potential device damage, especially when dealing with dissimilar metallization materials and the need for efficient current distribution.
Innovation Solution
A power overlay (POL) structure with a dielectric layer and metallization layer having metal interconnects through vias, allowing copper wirebonds to be directly coupled to the metallization layer, which acts as a stress buffer and provides parallel current paths for efficient energy transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If copper wirebonds are used to connect directly to aluminum contact pads, then electrical resistance is reduced and efficiency is improved, but reliable electrical connections cannot be formed due to material mismatch
Solution Approach 1:
A metallization layer is introduced as an intermediary between the copper wirebond and the aluminum contact pad. This metallization layer is deposited over the aluminum pad and provides a compatible bonding surface for copper wirebonds, enabling both low resistance and reliable connection simultaneously
2Reliability
If copper wirebonds are used to connect directly to copper metallization, then material compatibility is improved, but device stress increases and potential damage occurs due to higher bonding energy requirements
Solution Approach 1:
The metallization layer is applied locally only where wirebond connections are needed, rather than converting the entire contact pad structure to copper. This localized approach allows copper-compatible bonding where needed while preserving the original aluminum structure elsewhere, reducing overall device stress
3Adaptability or versatility
If multiple power devices from different manufacturers are integrated into a single module, then device selection flexibility is improved, but wirebonding difficulty increases due to dissimilar metallization materials
Solution Approach 1:
The metallization layer serves multiple functions: it provides a universal bonding surface that is compatible with copper wirebonds regardless of the underlying contact pad material (aluminum or copper), enabling standardized wirebonding processes across devices from different manufacturers with different metallization schemes
4Device complexity
If current flows directly from contact pads to wirebonds, then interconnect path is simplified, but current distribution efficiency decreases due to lack of parallel paths
Solution Approach 1:
The metallization layer is segmented into multiple conductive regions that extend from the contact pads to the wirebond bonds. These segments create multiple parallel current paths, allowing current to be distributed more efficiently across the interconnect structure while reducing overall resistance and energy loss
Data Source
AI summary
A power overlay (POL) structure includes a power device having at least one upper contact pad disposed on an upper surface of the power device, and a POL interconnect layer having a dielectric layer coupled to the upper surface of the power device and a metallization layer having metal interconnects extending through vias formed through the dielectric layer and electrically coupled to the at least one upper contact pad of the power device. The POL structure also includes at least one copper wirebond directly coupled to the metallization layer.