Semiconductor Package Sidewall Protection via Backside Molding

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Solution Overview

Problem

Wafer Level Chip Scale Packages (WLCSPs) face challenges with die chipping or cracking during handling and assembly due to insufficient sidewall protection and inefficiencies in existing molding compound formation methods, such as the front side mold and fan out approaches.

Innovation Solution

A semiconductor package design featuring a redistribution layer on the die surface with exposed areas for molding compound application, providing protection on sidewalls and edges, and a method involving backgrinding and mechanical separation to form packages with controlled molding compound thickness for enhanced die protection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If molding compound is formed on the active side of the wafer using front side mold approach, then die protection is provided, but solder bumps require additional cleaning of mold residue and manufacturing efficiency decreases

Engineering Contradiction:

Improvedie protectionVSAvoidmanufacturing efficiency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent inverts the conventional front-side molding approach by forming molding compound on the backside of the wafer instead. This allows the molding compound to wrap around and protect the sidewalls of the die without contacting the solder bumps on the active side, thereby eliminating the need for cleaning operations while maintaining die protection.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent transitions from two-dimensional planar protection (molding compound on top of die) to three-dimensional sidewall protection by having the molding compound extend vertically along the sidewalls of the die. This dimensional change provides comprehensive protection against chipping and cracking while avoiding interference with solder bumps.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Ease of manufacture

If half cut is performed between successive die with constraints on kerf width and scribe lane width, then wafer separation is achieved, but sidewall protection is insufficient leading to increased die cracking risk

Engineering Contradiction:

Improvewafer separationVSAvoidsidewall protection

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent performs preliminary action by forming the molding compound on the backside of the wafer before separating the die through half-cut or scribe-and-break methods. The molding compound is formed to extend over the edges of the die, creating a protective framework that remains intact during subsequent separation processes, thereby providing sidewall protection despite the constraints of narrow kerf and scribe lane widths.

Inventive Principle:

Principle #10Preliminary action

3Productivity

If fan out approach is used to form molding compound from backside of die, then mold residue cleaning is eliminated, but wafer cracking and breakage increase requiring multiple warpage adjustment steps

Engineering Contradiction:

Improveprocess simplificationVSAvoidwafer stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent applies local quality by forming the molding compound selectively on the backside of the wafer in a controlled manner. The molding compound is applied to specific regions where it provides structural support and protection without causing excessive stress or warpage that would lead to cracking. This localized approach maintains wafer stability while eliminating the need for mold residue cleaning.

Inventive Principle:

Principle #3Local quality

4Reliability

If molding compound thickness is increased to improve die protection, then chipping and cracking resistance increases, but manufacturing complexity and cost increase

Engineering Contradiction:

Improvechipping and cracking resistanceVSAvoidmolding compound thickness control

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies partial action by forming the molding compound to a sufficient thickness that provides adequate protection against chipping and cracking, but not excessively thick that would create manufacturing difficulties. The molding compound extends just enough to cover the sidewalls and provide protection, optimizing the balance between protection and manufacturability.

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS11562937B2Semiconductor package with protected sidewall and method of forming the same

Publication Date: 2023.01.24 STMICROELECTRONICS PTE LTD

AI summary

A semiconductor package having a die with a sidewall protected by molding compound, and methods of forming the same are disclosed. The package includes a die with a first surface opposite a second surface and sidewalls extending between the first and second surfaces. A redistribution layer is formed on the first surface of each die. An area of the first surface of the die is greater than an area of the redistribution layer, such that a portion of the first surface of the die is exposed. When molding compound is formed over the die and the redistribution layer to form a semiconductor package, the molding compound is on the first surface of the die between an outer edge of the redistribution layer and an outer edge of the first surface. The molding compound is also on the sidewalls of the die, which provides protection against chipping or cracking during transport.