Wafer Level Packaging Edge Bonding Reliability
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Solution Overview
Problem
The wafer level packaging method often experiences un-bonded issues at edge areas of bonded wafers, leading to reduced yield due to gaps between the wafers during the bonding process.
Innovation Solution
A method involving sequential grinding and trimming processes to reduce wafer thickness, including chemical mechanical polishing, where the first grinding process removes the upper chamfered edge, followed by a trimming process to remove the lower chamfered edge, and a second grinding process to further reduce thickness, ensuring bonding before trimming to maintain edge conditions and prevent chipping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wafer bonding is performed before thickness reduction, then bonding reliability is improved, but edge chipping risk increases during subsequent grinding
Solution Approach 1:
The thickness reduction process is segmented into multiple stages: first reducing thickness to an intermediate value, then performing bonding, and finally reducing to the target thickness. This segmentation allows bonding to occur at an intermediate thickness where the wafer is thick enough to resist chipping but thin enough to achieve the final specification, thereby resolving the contradiction between bonding reliability and chipping risk.
Solution Approach 2:
A preliminary thickness reduction is performed before bonding to create an intermediate thickness state. This preliminary action prepares the wafer for bonding while maintaining sufficient thickness to prevent edge chipping during the bonding process, thus resolving the contradiction between achieving reliable bonding and preventing edge damage.
2Object-affected harmful factors
If wafer thickness is reduced before bonding, then edge chipping is prevented, but bonding reliability deteriorates due to insufficient thickness
Solution Approach 1:
The thickness reduction is divided into two segments: a first reduction to intermediate thickness performed before bonding to prevent chipping, and a second reduction to final thickness performed after bonding. This segmentation allows each process to occur under optimal thickness conditions, resolving the contradiction between chipping prevention and bonding reliability.
Solution Approach 2:
A preliminary thickness reduction is performed before bonding to establish an intermediate thickness that prevents edge chipping while maintaining sufficient structural integrity for reliable bonding. The final thickness reduction is then performed after bonding when the bonded structure provides additional support.
3Manufacturing precision
If multiple grinding processes are performed, then thickness precision is improved, but production time increases
Solution Approach 1:
The grinding process is segmented into two distinct stages: a first grinding process that removes a first thickness amount to achieve intermediate thickness, and a second grinding process that removes a second thickness amount to achieve final thickness. This segmentation allows each grinding operation to be optimized for its specific thickness reduction requirement, improving overall precision while managing production time through efficient process sequencing.
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 effectively avoids un-bonded problems at the edge areas, enhances yield, protects devices during thinning, and is suitable for hybrid bonding, preventing both un-bonded and chipping issues.
Implementation Method 1
The first grinding process and the second grinding process may respectively include a chemical mechanical polishing process
Data Source
AI summary
A wafer level packaging method includes the following steps. A first wafer is bonded over a second wafer. A first grinding process on the first wafer is performed, to remove an upper chamfered edge of the first wafer and reduce a thickness of the first wafer. A trimming process is performed on the first wafer, to remove a lower chamfered edge of the first wafer to form a trimmed first wafer. A second grinding process is performed on the trimmed first wafer, to reduce a thickness of the trimmed first wafer.