Double Side Molding for RDL Interposer Warpage Control

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Solution Overview

Problem

Wafer level packaging faces challenges with warpage and cracking due to thermal expansion mismatch and thick molding compounds, especially in large-sized wafers with fine-pitch RDL processes, making it difficult to maintain die-to-wafer coupling and increasing the complexity of TSV interposer fabrication.

Innovation Solution

A semiconductor package with double side molding, where a first molding compound covers the semiconductor die and a second molding compound surrounds solder bumps and the vertical sidewall of the RDL interposer, with different compositions to alleviate warpage and prevent cracking, ensuring reliable assembly and reduced warping.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a thick layer of molding compound is used to cover the wafer and dies, then the packaging provides adequate protection, but warpage increases due to CTE mismatch and the packaging thickness increases

Engineering Contradiction:

Improveprotection of diesVSAvoidwafer warpage

Core Design Contradiction:

ReliabilityVSShape

Solution Approach 1:

The molding compound is divided into two separate applications: a first molding compound applied to the front side covering the dies, and a second molding compound applied to the back side covering the solder bumps and sidewalls. This segmentation allows each molding layer to be optimized independently, reducing overall warpage while maintaining protective function.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent changes the parameter of molding compound application by transitioning from a single thick layer to two thinner layers applied on opposite sides. This parameter change reduces the CTE mismatch effect and minimizes wafer warpage while still providing adequate protection for the dies and solder bumps.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If a thick layer of molding compound is used to cover the wafer, then protection is adequate, but the packaging thickness increases

Engineering Contradiction:

Improveprotection of diesVSAvoidpackaging thickness

Core Design Contradiction:

ReliabilityVSLength of stationary object

Solution Approach 1:

The protective function is segmented into two separate molding compound layers applied on opposite sides of the wafer. The first layer protects the front side dies, while the second layer protects the back side solder bumps and sidewalls. This segmentation reduces the overall packaging thickness compared to a single thick layer while maintaining adequate protection.

Inventive Principle:

Principle #1Segmentation

3Ease of manufacture

If conventional single side molding is used, then the process is simpler, but cracking of the RDL interposer occurs due to warpage

Engineering Contradiction:

Improvemolding process simplicityVSAvoidRDL interposer integrity

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The molding process is segmented into two separate steps: first applying molding compound to the front side, then applying a second molding compound to the back side. This segmentation prevents cracking of the RDL interposer by distributing stress evenly, while the process remains relatively simple and can be integrated into existing wafer-level packaging workflows.

Inventive Principle:

Principle #1Segmentation

4Manufacturing precision

If TSV interposer with RDL is used to redistribute I/O pads, then fine-pitch routing is achieved, but warpage prevents successful die-to-wafer assembly

Engineering Contradiction:

ImproveI/O redistribution precisionVSAvoidwafer warpage

Core Design Contradiction:

Manufacturing precisionVSShape

Solution Approach 1:

The patent changes the parameter of molding compound application by using two separate layers on opposite sides instead of one thick layer. This parameter change reduces the CTE mismatch effect and minimizes wafer warpage, enabling successful die-to-wafer assembly while maintaining the fine-pitch I/O redistribution capability of the TSV interposer with RDL.

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

The double side molding approach effectively reduces warpage and prevents cracking of the RDL interposer, enhancing the reliability and assembly precision of wafer level packages by counteracting thermal expansion issues and protecting the vertical sidewall of the RDL interposer.

Implementation Method 1

the thick layer of the molding compound results in increased warping of the packaging due to coefficient of thermal expansion (CTE) mismatch

Methodology Applied

Scientific EffectCoefficient of thermal expansion (CTE) mismatch: Thermal Expansion

Implementation Method 2

the heat generated by the dies must be diffused efficiently through the package structure to ensure the operation the dies

Methodology Applied

Scientific EffectHeat diffusion: Conduction (thermal)

Data Source

PatentUS9613895B1Semiconductor package with double side molding

Publication Date: 2017.04.04 MICRON TECHNOLOGY INC

AI summary

A semiconductor package includes an RDL interposer having a first side, a second side, and a vertical sidewall extending between the first side and the second side; at least one semiconductor die mounted on the first side of the RDL interposer; a first molding compound disposed on the first side covering the at least one semiconductor die; a plurality of solder bumps or solder balls mounted on the second side; and a second molding compound disposed on the second side surrounding the plurality of solder bumps or solder balls and covering the vertical sidewall of the RDL interposer.