Sacrificial Metallic Layer for Solder Bump Formation

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Solution Overview

Problem

The increasing density of electronic devices poses challenges in packaging microelectronic substrates, requiring robust and reliable interconnection systems, and existing solder bump technologies are limited by high costs, complexity, and potential damage to substrates during processing.

Innovation Solution

A method involving the formation of a sacrificial metallic layer on microelectronic substrates, which acts as a barrier to prevent unwanted reactions and protects the substrate during photoresist removal, allowing for efficient and selective etching and alloying with solder, thereby forming robust solder bumps suitable for fine pitch architectures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If conventional solder bump technology is used, then interconnection is achieved, but the process is expensive and complex

Engineering Contradiction:

Improvemanufacturing cost and process complexityVSAvoidinterconnection reliability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

A sacrificial metallic layer is introduced as an intermediary between the photoresist and the substrate. This layer protects the substrate from chemical damage during photoresist removal while enabling reliable solder bump formation, thus maintaining interconnection reliability while simplifying the manufacturing process

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The sacrificial metallic layer is deposited on the substrate before applying the photoresist layer. This preliminary action ensures that the substrate is protected in advance during subsequent chemical processing steps, eliminating the need for complex protective measures during manufacturing

Inventive Principle:

Principle #10Preliminary action

2Ease of manufacture

If photoresist removal is performed directly on substrate, then photoresist is removed, but substrate is damaged by chemical composition

Engineering Contradiction:

Improvephotoresist removal efficiencyVSAvoidsubstrate damage from chemical composition

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The sacrificial metallic layer serves as a protective intermediary between the chemical composition used for photoresist removal and the substrate. The chemical composition removes the photoresist without directly contacting or damaging the substrate, as the metallic layer absorbs the chemical attack

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The sacrificial metallic layer is intentionally designed to be consumed or removed during the process. It performs its protective function temporarily during photoresist removal and can be selectively etched away afterward, sacrificing itself to protect the valuable substrate

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Productivity

If smaller solder bumps are formed for high density packaging, then packaging density increases, but manufacturing precision requirements increase

Engineering Contradiction:

Improvepackaging densityVSAvoidsolder bump formation precision

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The sacrificial metallic layer enables precise control of solder bump dimensions by serving as a defined etch stop and barrier. The layer's thickness and composition can be precisely controlled during deposition, ensuring consistent and accurate solder bump formation even at small sizes required for high-density packaging

Inventive Principle:

Principle #35Parameter changes

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 enables the formation of smaller, less expensive, and more robust semiconductor package configurations by preventing damage to the substrate and allowing for the efficient removal of photoresist and metallic layers, while also alloying with solder to enhance bump composition, resulting in high-performance interconnections.

Implementation Method 1

The metallic layer may function as a barrier layer and eliminate unwanted reactions between a dry film (photoresist) layer and a solder resist layer during solder deposition

Methodology Applied

Scientific EffectBarrier layer protection:

Implementation Method 2

the metallic layer protects the solder resist layer and underlying substrate from chemical compositions used to strip the dry film

Methodology Applied

Scientific EffectChemical protection:

Implementation Method 3

portions of the metallic film can be alloyed with the as-deposited solder composition

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 4

the exposed portions of the metallic layer at least partially diffuse into the solder

Methodology Applied

Scientific EffectAlloying:

Implementation Method 5

After removal of the dry film, the metallic layer can be selectively etched, thus avoiding damage to, and delamination of, the solder resist

Methodology Applied

Scientific EffectSelective etching:

Data Source

PatentUS10535592B2Method for forming solder bumps using sacrificial layer

Publication Date: 2020.01.14 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A barrier layer is formed over electrically conductive contact pads on a substrate such as a wafer. A photoresist layer is applied over the barrier layer, and openings in the photoresist layer are filled with solder to form solder bumps. The barrier layer may be removed from within the openings prior to filling the openings with solder. The process is applicable to fine pitch architectures and chip size packaging substrates. The photoresist layer and portions of the barrier layer outside of the openings are removed following solder fill.