Wiring Substrate Pad Depth Control via Galvanic Etching

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Solution Overview

Problem

The miniaturization of solder bumps on wiring substrates leads to cracking at the interface due to electromigration, causing defective bonding, and existing methods to address this issue, such as varying pad opening areas or using different solder ball diameters, are impractical due to alignment and accuracy requirements.

Innovation Solution

A wiring substrate design with recesses of varying depths and diameters, where metal layers with different ionization tendencies are used to control the etching process, ensuring consistent electrode terminal heights across pads of different sizes, thereby facilitating accurate bonding without the need for high-accuracy alignment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the opening area of the pad is increased to reduce electromigration, then the reliability of the solder bump connection is improved, but the manufacturing precision and alignment accuracy are worsened due to the difficulty of forming pads with different opening areas

Engineering Contradiction:

Improvebonding reliabilityVSAvoidalignment accuracy

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The invention applies local quality by forming pads with different opening areas selectively - only the first pad has a large opening area while the second pad has a small opening area. This is achieved through selective resist removal and etching processes that modify only specific pad regions, allowing localized optimization for high-current paths without affecting other pads.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention changes the opening area parameter of specific pads to control electromigration. By increasing the opening area of the first pad connected to high-current circuits, the current density is reduced, thereby reducing electromigration effects and improving bonding reliability without requiring all pads to have uniformly large dimensions.

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If electrode terminals are formed by mounting solder balls with the same diameter on pads with different opening areas, then the ease of manufacture is improved, but the manufacturing precision is worsened because the electrode terminal heights become inconsistent

Engineering Contradiction:

Improveease of forming electrode terminalsVSAvoidelectrode terminal height consistency

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The invention applies local quality by creating pads with different opening areas - the first pad has a large opening area while the second pad has a small opening area. This selective differentiation allows each pad to be optimized for its specific electrical connection requirements while maintaining a uniform solder ball mounting process.

Inventive Principle:

Principle #3Local quality

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 allows for precise control of pad depths and electrode terminal heights, enhancing bonding reliability and practicality by reducing electromigration effects and eliminating the need for precise alignment during manufacturing.

Implementation Method 1

a first metal layer formed on the third electrode pad and electrically connected to the first electrode pad... wherein a depth of the first recess is larger than that of the second recess

Methodology Applied

Scientific EffectGalvanic effect:

Implementation Method 2

perform etching using an etchant

Methodology Applied

Scientific EffectEtching:

Data Source

PatentUS9084339B2Wiring substrate and method of manufacturing the same

Publication Date: 2015.07.14 SHINKO ELECTRIC IND CO LTD

AI summary

A wiring substrate includes: a wiring substrate body including a first surface and a second surface; a first electrode pad including a first recess therein and formed on the first surface of the wiring substrate body; a second electrode pad including a second recess therein and formed on the first surface of the wiring substrate body; a first solder resist layer on the first surface of the wiring substrate body to cover the first and second electrode pads, the first solder resist layer including a first opening and a second opening whose opening area is larger than that of the first opening; and a first metal layer electrically connected to the first electrode pad and made of a material whose ionization tendency is smaller than that of a material of the first electrode pad. A depth of the first recess is larger than that of the second recess.