Wafer Level Package Solder Joint Structure with Hemispherical Reflow

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Solution Overview

Problem

The high manufacturing cost of wafer-level package structures due to the multiple photo resists and seed layers required in the formation of Under-Bump Metallurgy (UBM) and Post-Passivation Interconnect (PPI) lines and pads, which increases the complexity and expense of the process.

Innovation Solution

A method involving the formation of intermediate solder joints using conductive balls that reflow into a hemispherical shape with a flat side bonded to PPI pads, followed by a molding compound application and plasma etching to create a solder joint with a distinct top and bottom portion, where the top portion has a larger height and smooth transition, enhancing bonding reliability and mechanical strength.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If multiple photo resists and seed layers are used to form UBM and PPI lines and pads, then the manufacturing precision and reliability of solder joints are improved, but the manufacturing cost and process complexity increase

Engineering Contradiction:

Improvesolder joint reliabilityVSAvoidprocess complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent combines the formation of UBM and PPI lines and pads into a single photo resist layer and single seed layer process, eliminating the need for multiple separate photo resist and seed layer layers. This merging reduces process complexity while maintaining the functional requirements for solder joint reliability through the integrated metallization structure.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The single photo resist layer and single seed layer are designed to serve multiple functions: defining both UBM and PPI patterns, providing electrical connectivity, and enabling subsequent solder joint formation. This multi-functional design reduces the number of process steps while achieving the same reliability outcomes.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Manufacturing precision

Engineering Contradiction:

Improvesolder joint precisionVSAvoidmanufacturing cost

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

By merging multiple photo resist and seed layer formations into single integrated layers, the patent reduces material consumption, process steps, and manufacturing time, thereby lowering overall manufacturing costs while preserving the precision needed for accurate solder joint formation.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The integrated photo resist and seed layer design allows for standardized patterning processes to be applied uniformly across the wafer, enabling efficient mass production with consistent precision outcomes without requiring multiple specialized process steps for each layer.

Inventive Principle:

Principle #26Copying

3Strength

If conductive balls are reflowed into intermediate solder joints with hemispherical shape, then the bonding surface area and mechanical strength are increased, but the manufacturing process complexity increases

Engineering Contradiction:

Improvebonding strengthVSAvoidmanufacturing process complexity

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The patent utilizes the phase transition of conductive balls from solid to liquid state during reflow processing, allowing them to naturally form hemispherical shapes with optimized bonding surfaces. This self-organizing phase change process achieves enhanced bonding strength without requiring complex external shaping mechanisms.

Inventive Principle:

Principle #36Phase transitions

Solution Approach 2:

The conductive balls self-form the desired hemispherical geometry through controlled reflow, utilizing surface tension and material flow properties to automatically create the optimal bonding shape without additional processing steps or external intervention, thereby reducing manufacturing complexity.

Inventive Principle:

Principle #25Self-service

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 reduces manufacturing costs by simplifying the process, increases the surface area for bonding, and improves the reliability of solder joints, with a Weibull prediction of 63% failure rate greater than 1000 cycles in thermal cycling simulations.

Implementation Method 1

heating the partially fabricated semiconductor chip to reflow the conductive balls into intermediate solder joints

Methodology Applied

Scientific EffectReflow: Melting

Implementation Method 2

followed by a molding compound application and plasma etching to create a solder joint with a distinct top and bottom portion

Methodology Applied

Scientific EffectPlasma etching: Plasma

Data Source

PatentUS9761551B2Solder joint structure for ball grid array in wafer level package

Publication Date: 2017.09.12 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A semiconductor device package and a method for forming the same using an improved solder joint structure are disclosure. The package includes solder joints having a thinner bottom portion than a top portion. The bottom portion is surrounded by a molding compound and the top portion is not surrounded by a molding compound. The method includes depositing and forming a liquid molding compound around an intermediate solder joint using release film, and then etching the molding compound to a reduced height. The resulting solder joint has no waist at the interface of the molding compound and the solder joint. The molding compound has a greater roughness after the etch, greater than about 3 microns, than the molding compound as formed.