Flip Chip Alignment Mark Exposure via Laser Ablation

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Solution Overview

Problem

In semiconductor chip fabrication, the use of optically opaque wafer level underfill coatings obscures alignment marks, hindering the processing and attachment of solder bumps, leading to potential damage and reliability issues during packaging.

Innovation Solution

A method involving laser ablation to selectively remove portions of the optically opaque coating, exposing the alignment marks and allowing for their detection and cleaning, thereby enabling precise alignment and attachment processes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an optically opaque wafer level underfill coating is applied to protect the attachment surface, then the protective benefit is improved, but the alignment marks become obscured making detection difficult

Engineering Contradiction:

Improveprotective benefitVSAvoidalignment mark detection

Core Design Contradiction:

ReliabilityVSDifficulty of detecting and measuring

Solution Approach 1:

The coating is selectively removed from specific regions (alignment mark areas) while maintaining coverage in other areas. This segmentation allows alignment marks to be visible for detection while the majority of the coating remains intact to provide protective benefits against damage and contamination.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The coating properties are made non-uniform by creating local variations: opaque protective coating in most areas versus transparent or removed coating in alignment mark areas. This local quality differentiation enables simultaneous achievement of protection and detectability.

Inventive Principle:

Principle #3Local quality

2Measurement precision

If the optically opaque coating is completely removed to expose alignment marks, then alignment accuracy is improved, but the protective benefits are lost and damage risk increases

Engineering Contradiction:

Improvealignment accuracyVSAvoidprotective benefit

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

Instead of complete removal, the coating is segmented such that only specific portions covering alignment marks are removed or made transparent. The remaining coating continues to provide protective benefits while the segmented exposed areas enable precise alignment detection.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Rather than completely removing the coating (excessive action), only the necessary minimum portions are removed or made transparent just enough to expose alignment marks. This partial action achieves alignment accuracy while minimizing loss of protective benefits.

Inventive Principle:

Principle #16Partial or excessive action

3Difficulty of detecting and measuring

If additional processing steps are added to expose alignment marks, then alignment detection is improved, but manufacturing complexity and costs increase

Engineering Contradiction:

Improvealignment mark detectionVSAvoidprocessing steps

Core Design Contradiction:

Difficulty of detecting and measuringVSDevice complexity

Solution Approach 1:

The coating is pre-configured with transparent or removed portions at designated alignment mark locations before the attachment process. This preliminary action eliminates the need for additional complex processing steps during manufacturing, as alignment marks are already exposed and ready for detection.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The problematic opaque coating material is extracted or removed only from the critical alignment mark regions. This extraction simplifies the overall process by eliminating the need for additional complex steps to expose alignment marks, while maintaining coating integrity elsewhere.

Inventive Principle:

Principle #2Taking out (Extraction)

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 enhances the reliability of semiconductor device packaging by reducing damage to passivation layers, improving alignment accuracy, and maintaining the protective benefits of the wafer level underfill coating, while minimizing additional processing steps and costs.

Implementation Method 1

A portion of the coating material overlying an attachment alignment mark can be selected and removed, such as by using laser ablation

Methodology Applied

Scientific EffectLaser ablation: Laser Ablation

Data Source

PatentUS9824925B2Flip chip alignment mark exposing method enabling wafer level underfill

Publication Date: 2017.11.21 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

Alignment marks on a semiconductor device surface are exposed and exposed surfaces cleaned after an obscuring coating is applied over the surface and marks. The surface can be an attachment surface of the device and can include C4 solder bumps of a flip-chip type device and the coating can include a wafer level underfill coating that is substantially optically opaque. Laser ablation, such as with a UV laser, can remove the coating while minimizing heat transfer to the device.