Wafer Coating and Plasma Dicing for WL-CSP Yield

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Solution Overview

Problem

The challenge in manufacturing wafer-level chip size packages (WL-CSPs) is the difficulty in coating the front surface of wafers with bumps using a spin coater, as the resin flow can be blocked by bumps, leading to incomplete coverage and reduced yield during plasma etching.

Innovation Solution

A method involving holding the wafer with the front surface downward and pressing it against a fluid curable resin to ensure uniform coating, followed by curing and using a laser beam to remove the resin film along the streets, allowing for effective plasma etching to divide the wafer into individual device chips.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a spin coater is used to coat the front surface of the wafer with resin material, then the resin material can be spread by centrifugal force, but the flow of resin material is blocked by the bumps, resulting in incomplete coating coverage

Engineering Contradiction:

Improvecoating processVSAvoidcoating coverage

Core Design Contradiction:

Ease of operationVSManufacturing precision

Solution Approach 1:

The wafer is inverted and held with the front surface facing downward toward the resin material. This inversion allows the resin material to contact the front surface from below, enabling it to flow into and coat the areas around the bumps that would be blocked during conventional spin coating.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The invention uses a mold that replicates the bump structure on the wafer's front surface. By pressing the resin-coated mold against the wafer, the resin is transferred and coated uniformly around the bumps, achieving complete coverage that cannot be obtained by direct spin coating.

Inventive Principle:

Principle #26Copying

2Productivity

If the wafer is cut by a cutting blade, then the wafer can be divided into device chips, but chipping and cracks are formed on the front surface, lowering flexural strength and quality

Engineering Contradiction:

Improvewafer divisionVSAvoiddevice chip quality

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The mechanical cutting process is replaced with plasma etching. The resin film serves as a mask during plasma etching, allowing precise division of the wafer into device chips along the streets without mechanical contact, thereby preventing chipping and cracks on the front surface.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Productivity

If plasma etching is applied to divide the wafer, then device chips can be manufactured, but complete coating of the front surface including gaps between bumps is difficult to achieve

Engineering Contradiction:

Improvedevice chip manufacturingVSAvoidresin film coating completeness

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

By inverting the wafer and contacting the front surface with resin material from below, the resin can naturally flow into and coat the gaps between bumps, achieving complete coverage necessary for effective plasma etching masks.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

A mold with a surface replicating the bump structure is used as an intermediary. The resin is first coated on the mold surface, then transferred to the wafer by pressing, ensuring uniform and complete coating coverage including areas around the bumps.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 ensures complete and uniform coating of the wafer surface, including gaps between bumps, improving yield and preventing chipping or cracking during the plasma etching process, thereby enhancing the quality of WL-CSPs.

Implementation Method 1

a curing step of curing the curable resin to form a resin film

Methodology Applied

Scientific EffectPhotopolymerisation: Photopolymerisation

Implementation Method 2

a laser beam applying step of applying a laser beam having such a wavelength as to be absorbed by the resin film to the resin film along each street, to thereby remove the resin film on each street

Methodology Applied

Scientific EffectLaser ablation: Laser Ablation

Implementation Method 3

a dividing step of supplying a gas plasma to the workpiece to divide the workpiece along each street into individual device chips with the resin film as a mask

Methodology Applied

Scientific EffectPlasma etching: Plasma

Data Source

PatentUS11355359B2Workpiece processing method

Publication Date: 2022.06.07 DISCO CORP

AI summary

A workpiece processing method includes a holding step of holding a workpiece with a front surface of the workpiece directed downward so as to face an upper surface side of a base supplied with a fluid curable resin, a coating step of moving the workpiece downward to press the workpiece against the curable resin, thereby coating the whole of the front surface of the workpiece with the curable resin such that the curable resin enters gaps between bumps and the front surface and the bumps are embedded in the curable resin, a curing step of curing the curable resin to form a resin film, a laser beam applying step of removing the resin film on each street, and a dividing step of supplying a gas plasma to the workpiece to divide the workpiece along each street into individual device chips with the resin film as a mask.