WLCSP Packaging with Support Ring for Ultra-Thin Wafer Handling
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Solution Overview
Problem
Conventional WLCSP technologies face challenges in handling and protecting ultra-thin wafers due to lack of mechanical support, making it difficult to separate individual chip packages from the wafer without damaging them, especially when the front surface is covered with molding compound, which obscures the scribe line.
Innovation Solution
A method involving the deposition of a first packaging layer on the wafer's front surface, grinding to expose metal bumps, forming cutting grooves aligned with the scribe line, thinning the wafer from the back surface with a support ring to prevent cracking, and cutting through the packaging layers to separate individual chips, ensuring mechanical strength and clear scribe line visibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the wafer is thinned to reduce substrate resistance and Rdson, then the electrical performance is improved, but the mechanical strength deteriorates making it difficult to handle and separate individual chips
Solution Approach 1:
A support ring is formed around the periphery of the wafer before thinning to provide mechanical strength. This preliminary structural reinforcement allows the wafer to be thinned to the desired thickness for electrical performance while the support ring prevents cracking and handles during subsequent processing and chip separation
Solution Approach 2:
The support ring is positioned at the periphery of the wafer, separating the functional chip area from the support structure. This segmentation allows the central region to be thinned for optimal electrical performance while the peripheral support ring maintains mechanical integrity during handling and chip separation
2Strength
If molding compound is applied to the front surface to enhance mechanical support, then the mechanical strength is improved, but the scribe line becomes obscured making it difficult to cut along the scribe line
Solution Approach 1:
Cutting grooves are formed on the front surface of the wafer before applying the molding compound. These grooves are positioned to expose the scribe line, creating a visible guide for subsequent cutting operations. The molding compound is then applied over the front surface, providing mechanical support while the pre-formed cutting grooves maintain scribe line visibility
Solution Approach 2:
The cutting grooves act as an intermediary structure between the molding compound and the scribe line. They provide a physical guide that penetrates through the molding compound layer, allowing the scribe line to remain visible and accessible for cutting operations despite the presence of the molding compound
3Length of moving object
If the wafer is thinned to ultra-thin dimensions, then the chip thickness is reduced for advanced packaging, but the difficulty of handling and separating individual chips increases due to lack of mechanical protection
Solution Approach 1:
The support ring is formed around the wafer periphery before thinning operations. This preliminary reinforcement enables the wafer to be thinned to ultra-thin dimensions while maintaining sufficient mechanical strength for handling. The support ring remains after thinning, providing ongoing mechanical protection during chip separation and packaging operations
Solution Approach 2:
The support ring provides beforehand cushioning and mechanical protection to the ultra-thin wafer. It acts as a protective structure that prevents cracking and damage during handling and separation processes, enabling ultra-thin chips to be manufactured and processed without compromising mechanical integrity
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 effectively enhances the mechanical strength of ultra-thin wafers, allows precise separation of chip packages without cracking, and maintains the integrity of the scribe line for accurate cutting, enabling the production of ultra-thin chips suitable for power devices.
Implementation Method 1
depositing a packaging layer to cover the front surface of the wafer
Implementation Method 2
grinding to expose the metal bumps
Implementation Method 3
thinning the wafer from its back surface with a support ring to prevent cracking
Data Source
AI summary
A WLCSP method comprises: depositing a metal bump on bonding pads of chips; forming a first packaging layer at front surface of wafer to cover metal bumps while forming an un-covered ring at the edge of wafer to expose the ends of each scribe line located between two adjacent chips; thinning first packaging layer to expose metal bumps; forming a groove on front surface of first packaging layer along each scribe line by cutting along a straight line extended by two ends of scribe line exposed on front surface of un-covered ring; grinding back surface of wafer to form a recessed space and a support ring at the edge of the wafer; depositing a metal layer at bottom surface of wafer in recessed space; cutting off the edge portion of wafer; and separating individual chips from wafer by cutting through first packaging layer, the wafer and metal layer along groove.