WLCSP Packaging with Grooved Molding for Thin Wafer Support
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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 for mechanical strength, and cutting through the packaging layers to separate individual chips, ensuring the scribe line remains accessible.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the wafer is thinned to reduce substrate resistance, then Rdson is reduced, but the wafer becomes difficult to handle and treat due to lack of mechanical protection
Solution Approach 1:
A molding compound layer is deposited on the front surface of the wafer before thinning the wafer. This preliminary protective layer provides mechanical support during the thinning process and subsequent handling, preventing the ultra-thin wafer from cracking or warping while allowing the wafer to be thinned to the desired thickness for low Rdson
Solution Approach 2:
The molding compound acts as an intermediary protective layer between the external environment and the ultra-thin wafer. It provides mechanical protection and support, enabling the wafer to maintain its structural integrity during handling and processing despite being thinned to reduce substrate resistance
2Strength
If the front surface of the wafer is packaged with molding compound to enhance mechanical support, then the wafer is protected from cracking, but the scribe line is covered making it difficult to cut the wafer
Solution Approach 1:
The molding compound layer is segmented by forming cutting grooves that expose the scribe line. This segmentation allows the protective molding compound to cover most of the wafer surface for mechanical support, while localized removal through cutting grooves provides access to the scribe line for precise cutting operations
Solution Approach 2:
The molding compound coverage is made non-uniform by creating cutting grooves at specific locations. The scribe line area is locally modified to be exposed or accessible, while the rest of the wafer surface maintains the protective molding compound layer. This local quality change enables both protection and cutting accessibility
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 enables the successful separation of ultra-thin chip packages with enhanced mechanical strength and protection, reducing the risk of cracking and warping, while maintaining the integrity of the scribe line for precise cutting.
Implementation Method 1
a packaging material is deposited to form a first packaging layer covering the front surface of the wafer
Implementation Method 2
The first packaging layer and the wafer are ground to thin the first packaging layer and expose the metal bumps
Implementation Method 3
the wafer is thinned to reduce the substrate resistance, thus Rdson is reduced
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.