Elongated Bump Structures for Flip Chip Interconnects
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Solution Overview
Problem
Conventional circular copper pillar bumps in flip chip technology face limitations due to increased size, mechanical stress, and electrical current density, which hinder device miniaturization and lead to issues like dielectric layer delamination and electromigration.
Innovation Solution
The use of elongated bump structures with a conductive pillar and under-bump metallurgy layer, which provide a tighter pitch and reduced mechanical stress, allowing for more reliable connections and improved thermal expansion matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If circular copper pillar bumps are used, then fixed stand-off is provided independent of bonding wire pitch, but significant size is added to the interconnect structure limiting pitch dimension
Solution Approach 1:
The patent changes the geometric parameters of the bump structure from circular to elongated rectangular shape. This parameter change allows the bump to provide fixed stand-off while occupying less area, specifically reducing the pitch dimension requirement and enabling tighter interconnect spacing in the package structure.
Solution Approach 2:
The invention transitions from a circular bump (isotropic in two dimensions) to an elongated rectangular bump (anisotropic in two dimensions). This dimensional reconfiguration allows the bump to extend primarily in one direction (providing stand-off) while being compact in the perpendicular direction (reducing pitch dimension), effectively utilizing dimensional orientation to resolve the contradiction.
2Reliability
If circular copper pillar bumps are used, then connection is provided between chip and external circuitry, but mechanical stress is created due to mismatched thermal expansion
Solution Approach 1:
The patent changes the geometric parameters of the bump structure from circular to elongated rectangular shape. This parameter change allows the bump to provide fixed stand-off while occupying less area, specifically reducing the pitch dimension requirement and enabling tighter interconnect spacing in the package structure.
Solution Approach 2:
The invention transitions from a circular bump (isotropic in two dimensions) to an elongated rectangular bump (anisotropic in two dimensions). This dimensional reconfiguration allows the bump to extend primarily in one direction (providing stand-off) while being compact in the perpendicular direction (reducing pitch dimension), effectively utilizing dimensional orientation to resolve the contradiction.
3Reliability
If circular copper pillar bumps are used, then electrical connection is provided, but large electrical current density contributes to electromigration and electric stress
Solution Approach 1:
The patent changes the geometric parameters of the bump structure from circular to elongated rectangular shape. This parameter change allows the bump to provide fixed stand-off while occupying less area, specifically reducing the pitch dimension requirement and enabling tighter interconnect spacing in the package structure.
Solution Approach 2:
The invention transitions from a circular bump (isotropic in two dimensions) to an elongated rectangular bump (anisotropic in two dimensions). This dimensional reconfiguration allows the bump to extend primarily in one direction (providing stand-off) while being compact in the perpendicular direction (reducing pitch dimension), effectively utilizing dimensional orientation to resolve the contradiction.
Data Source
AI summary
A package structure includes a chip attached to a substrate. The chip includes a bump structure including a conductive pillar having a length (L) measured along a long axis of the conductive pillar and a width (W) measured along a short axis of the conductive pillar. The substrate includes a pad region and a mask layer overlying the pad region, wherein the mask layer has an opening exposing a portion of the pad region. The chip is attached to the substrate to form an interconnection between the conductive pillar and the pad region. The opening has a first dimension (d1) measured along the long axis and a second dimension (d2) measured along the short axis. In an embodiment, L is greater than d1, and W is less than d2.