Mold Compound Extract Testing for Wire Bond Corrosion

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Solution Overview

Problem

Semiconductor die encapsulation materials, such as mold compounds, can be corrosive to metals like Copper and Aluminum used in wire bonds, leading to impaired electrical and mechanical performance and reduced reliability of integrated circuit devices.

Innovation Solution

A method to evaluate the suitability of encapsulation materials by exposing unencapsulated substrate/die assemblies to a mold compound extract, measuring the bond shear strength of wire bonds before and after immersion, and comparing the results to determine if the material adversely affects the bond strength.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a mold compound is used to encapsulate a semiconductor die for protection, then the die is protected from environmental contaminants, but the mold compound may be corrosive to metal wire bonds (Copper and Aluminum), impairing their electrical and mechanical performance

Engineering Contradiction:

Improveprotection of semiconductor dieVSAvoidcorrosion of wire bonds

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent extracts the harmful corrosive components from the mold compound by creating a mold compound extract through solvent extraction. This allows the test to identify corrosive properties without exposing the actual device to the full mold compound, thereby protecting the device while still detecting the harmful effect.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces a mold compound extract as an intermediary substance that mediates between the mold compound and the wire bonds. The extract contains the corrosive components in a controlled manner, allowing testing of corrosivity without direct exposure of the device to the complete mold compound system.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If wire bonds are used to provide electrical interconnections in the packaged device, then electrical connectivity is achieved, but the wire bonds are susceptible to corrosion by the mold compound, reducing their operational lifetime

Engineering Contradiction:

Improveelectrical connectivityVSAvoidoperational lifetime of wire bonds

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The patent performs preliminary testing of the mold compound's corrosive properties on wire bonds before final device packaging. By conducting compatibility tests in advance using the extract, potential corrosion issues are identified and addressed before the actual device is packaged, preventing future failures.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent establishes a feedback mechanism where the results of wire bond strength measurements after extract exposure are used to evaluate mold compound compatibility. This feedback information guides the selection or modification of mold compounds to ensure long-term wire bond reliability.

Inventive Principle:

Principle #23Feedback

3Reliability

If compatibility testing of mold compound with wire bonds is performed, then corrosive effects are identified, but the testing process requires immersion in extract and measurement of bond shear strength, adding complexity to the evaluation process

Engineering Contradiction:

Improveidentification of corrosive effectsVSAvoidtesting process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent creates a simplified copy of the mold compound in the form of an extract that captures the essential corrosive properties. This copy allows testing without requiring the complete complex mold compound system, thereby simplifying the testing process while maintaining the ability to identify corrosive effects.

Inventive Principle:

Principle #26Copying

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 method effectively identifies whether a mold compound corrodes wire bonds, allowing for the selection of non-corrosive encapsulation materials that maintain the mechanical strength of wire bonds, thereby enhancing the reliability and operational lifetime of integrated circuit devices.

Implementation Method 1

A particular mold compound may be excessively corrosive to materials used to fabricate the integrated circuit device. Corrosion can impair the electrical and mechanical performance of an integrated circuit device

Methodology Applied

Scientific EffectCorrosion: Crevice Corrosion

Implementation Method 2

a mechanical strength of a wire bond included at the substrate/die assembly can be evaluated after exposing an unencapsulated substrate/die assembly to a mold compound extract

Methodology Applied

Scientific EffectShear stress measurement: Shear Stress

Data Source

PatentUS8955388B2Mold compound compatibility test system and methods thereof

Publication Date: 2015.02.17 NXP USA INC

AI summary

A technique for testing the compatibility of an encapsulation material and a wire bond included at an unencapsulated assembly. The technique includes immersing the assembly in an encapsulating compound extract. The assembly includes a semiconductor die and a bonding wire affixed to a metalized pad of the semiconductor die by the wire bond. After the immersing, a mechanical strength of the wire bond is determined.