Preventing Misshaped Solder Balls via Planarization

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Thick pad semiconductor dies face issues with solder leakage and oblong solder ball formation due to downward-inclined discontinuities, leading to yield loss and incorrect C4 contact geometry during manufacturing.

Innovation Solution

The method involves addressing downward-inclined discontinuities by adding dummy shapes, using CMP to planarize the passivation surface, applying a halftone mask for controlled light exposure, or employing an etch-back process to relocate and control discontinuities, ensuring proper adhesion of the photoresist layer and preventing solder leakage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If thicker metal lines are used to meet inductance and current carrying requirements, then the cross-sectional area of the lines is sufficient, but the size of out of plane conditions (topography) increases

Engineering Contradiction:

Improvecross-sectional area of metal linesVSAvoidtopography (out of plane conditions)

Core Design Contradiction:

Quantity of substanceVSShape

Solution Approach 1:

The patent applies planarization processes (such as CMP or spin-on-glass) before applying the photoresist layer and forming solder balls. This preliminary flattening of the topography ensures that the photoresist can be applied uniformly and that solder balls will form with correct geometry, preventing the topography from causing manufacturing defects later in the process

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces additional processing steps in the temporal dimension (multiple planarization steps, intermediate photoresist applications) to compensate for the three-dimensional topography issues caused by thick metal lines. By breaking down the complex 3D topography problem into a series of 2D planarization operations, the process achieves acceptable flatness for subsequent manufacturing steps

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Area of stationary object

If photoresist layer is applied over downward-inclined discontinuities, then the surface coverage is achieved, but solder leakage occurs and solder balls become misshaped

Engineering Contradiction:

Improvephotoresist surface coverageVSAvoidsolder ball geometry

Core Design Contradiction:

Area of stationary objectVSManufacturing precision

Solution Approach 1:

The patent performs planarization of the topography before applying the photoresist layer. By flattening the surface in advance, the photoresist can be applied uniformly without bridging over discontinuities, preventing solder leakage and ensuring correct solder ball formation

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent divides the photoresist application into multiple stages with intermediate planarization steps. The first photoresist layer is applied, then planarization is performed, followed by a second photoresist layer. This segmentation allows each layer to be applied on a flatter surface, preventing the photoresist from bridging over discontinuities and causing solder defects

Inventive Principle:

Principle #1Segmentation

3Shape

If multiple planarization steps are performed to flatten the surface, then the topography is reduced, but the manufacturing process complexity increases

Engineering Contradiction:

Improvesurface flatnessVSAvoidmanufacturing process complexity

Core Design Contradiction:

ShapeVSDevice complexity

Solution Approach 1:

The patent applies planarization processes more extensively than the minimum required, performing multiple planarization steps to ensure complete elimination of topography issues. This excessive action guarantees that all discontinuities are removed, preventing solder defects, even though it increases process complexity

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The patent divides the planarization process into multiple separate steps interspersed with other manufacturing operations. Rather than performing all planarization at once, the process is segmented into first and second planarization steps, allowing other processes to occur in between and reducing the complexity of any single planarization operation

Inventive Principle:

Principle #1Segmentation

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

These approaches effectively prevent solder leakage and maintain spherical solder ball geometry, reducing yield loss and ensuring correct C4 contact formation, thereby improving manufacturing efficiency and quality.

Implementation Method 1

Chemical-mechanical-polishing (CMP) is one currently conventional planarization process which planarizes surfaces with a combination of chemical reactions and mechanical forces

Methodology Applied

Scientific EffectChemical-mechanical polishing:

Implementation Method 2

ensuring proper adhesion of the photoresist layer

Methodology Applied

Scientific EffectAdhesion: Adhesive

Data Source

PatentUS9331037B2Preventing misshaped solder balls

Publication Date: 2016.05.03 MARVELL ASIA PTE LTD

AI summary

“Thick line dies” that, during manufacture, avoid locating an upstanding edge of a photoresist layer (for example, the edge of a dry film photoresist layer) on top of a “discontinuity.” In this way solder does not flow into the mechanical interface between the photoresist layer and the layer under the photoresist layer in the vicinity of an upstanding edge of the photoresist layer.