Stress Relief Layer for Microelectronic Packaging Crack Prevention
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Solution Overview
Problem
Microelectronic devices experience cracking and stress issues in passivation layers and interlayer dielectric materials during packaging, particularly due to undercuts and thermal expansion mismatches, leading to potential device failure and limitations in using low-k ILD materials.
Innovation Solution
The implementation of conformal layers and sidewall structures around bumps, which reduce stress and prevent cracking by encapsulating undercuts and providing load sharing, and the use of lead-free solders like tin, silver, or indium for flip-chip attachments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If barrier metal layer etch is performed in the presence of bump, then electrical connection is achieved, but undercut is formed causing cracking in passivation layer and ILD
Solution Approach 1:
A stress relief layer is introduced as an intermediary component between the bump and the passivation layer/ILD. This stress relief layer absorbs and redistributes the stress concentrated at the undercut region, preventing crack propagation while maintaining the electrical connection function. The stress relief layer acts as a mediator that decouples the stress transfer path from the critical dielectric layers.
Solution Approach 2:
The stress relief layer is formed prior to subsequent processing steps to preemptively address the undercut issue. By establishing this protective layer before cracks can initiate or propagate, the structure is pre-conditioned to resist the harmful effects of the undercut geometry formed during barrier metal etching.
2Reliability
If low-k ILD materials are used, then signal integrity is improved, but susceptibility to cracking increases
Solution Approach 1:
The stress relief layer serves as a protective intermediary between the low-k ILD material and the stress-generating bump structure. This intermediary layer has mechanical properties that are more compatible with the low-k material, providing stress buffering that allows the use of low-k ILD for signal integrity without suffering from the material's inherent brittleness and crack susceptibility.
3Reliability
If bump corners are present near passivation layer, then electrical connection is achieved, but stress and cracking are induced in passivation layer and ILD
Solution Approach 1:
The stress relief layer is positioned between the bump corners and the passivation layer to intercept and redistribute the stress concentration that would otherwise be transferred to the passivation layer and ILD. This intermediary structure maintains the electrical connection provided by the bump while eliminating the harmful stress concentration effect.
4Reliability
If thermal expansion mismatch exists between die and substrate, then packaging is achieved, but additional stress and cracking opportunity are created
Solution Approach 1:
The stress relief layer acts as a thermal and mechanical buffer between the die and substrate, accommodating the thermal expansion mismatch. This intermediary layer has properties that allow it to absorb differential thermal expansion stresses, preventing these stresses from concentrating in the passivation layer and ILD where they would cause cracking.
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
This approach effectively limits or eliminates cracking and reduces stress on passivation layers and interlayer dielectrics, enhancing the reliability of microelectronic devices and enabling the use of lead-free materials for packaging substrates.
Implementation Method 1
conformal layers and sidewall structures around bumps, which reduce stress and prevent cracking by encapsulating undercuts and providing load sharing
Implementation Method 2
use of lead-free solders like tin, silver, or indium for flip-chip attachments
Data Source
AI summary
Some embodiments of the present invention include apparatuses and methods relating to processing and packaging microelectronic devices that reduce stresses on and limit or eliminate crack propagation in the devices.