Wafer-Level Semiconductor Die Attachment Self-Alignment
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Solution Overview
Problem
Conventional semiconductor die attachment methods require high precision alignment, leading to increased placement time and reduced process throughput, especially when dealing with multiple dies on a pre-singulated wafer, which results in low efficiency and high costs for optoelectronic packaging.
Innovation Solution
A wafer-level semiconductor die attachment method where semiconductor dies are initially placed with temporary solder layer contact and then reflowed to align and permanently attach to sub-mounts, utilizing self-alignment restoring forces to achieve high precision without the need for high initial placement accuracy, allowing for simultaneous attachment of multiple dies across the wafer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If optical microscopy alignment method with high magnification is used to achieve high placement accuracy, then alignment precision is improved, but placement time increases and process throughput decreases
Solution Approach 1:
The patent employs self-alignment features (fiducial marks) that automatically guide die placement without requiring high-precision optical alignment. The mating features on the die and sub-mount self-correct positioning errors during solder reflow, enabling accurate attachment even with initial placement tolerances of 50-100 micrometers, thus eliminating the need for time-consuming high-magnification optical alignment while maintaining high final placement accuracy
Solution Approach 2:
The patent changes the placement accuracy parameter from requiring high precision (single-digit micrometers) to accepting lower precision (50-100 micrometers) during initial placement. The self-alignment mechanism then compensates for this relaxed initial tolerance, allowing faster placement speeds and higher throughput while achieving the same final alignment accuracy through the combination of fiducial mark guidance and solder reflow self-correction
2Object-affected harmful factors
If eutectic soldering is performed on singulated sub-mounts to avoid flux contamination, then optical facet cleanliness is improved, but process time increases due to sequential processing
Solution Approach 1:
The patent merges multiple singulated sub-mounts onto a single carrier wafer, allowing simultaneous eutectic solder reflow processing of multiple dies in parallel. This wafer-level processing approach maintains fluxless soldering benefits (no optical facet contamination) while achieving high throughput by processing 16-64 dies simultaneously on one wafer, eliminating the sequential bottleneck of individual sub-mount processing
Solution Approach 2:
The carrier wafer serves multiple functions: it holds multiple singulated sub-mounts, provides a unified reflow processing platform, and enables parallel attachment of multiple dies. This multi-functional approach allows the system to achieve both clean fluxless soldering and high-volume production by processing entire wafer arrays simultaneously rather than individual components
3Manufacturing precision
If multiple semiconductor dies are attached individually to sub-mounts using conventional methods, then alignment accuracy is maintained, but placement time for each die increases the total process time
Solution Approach 1:
The patent performs preliminary actions by pre-forming fiducial marks and mating features on both the carrier wafer and individual dies during fabrication. These pre-established alignment features enable rapid automated placement without requiring time-consuming real-time optical alignment for each die, as the fiducial marks provide built-in guidance that simplifies the placement process while maintaining accuracy
Solution Approach 2:
The patent replaces the mechanical/optical alignment system (requiring high-magnification microscopes and manual adjustment) with a self-aligning system based on pre-formed fiducial marks and mating features. The alignment is achieved through geometric matching of these features rather than optical measurement, eliminating the time-consuming optical alignment step while preserving placement accuracy through the self-correcting solder reflow process
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 significantly reduces placement time and improves process throughput by enabling high alignment accuracy through die and sub-mount mating features, resulting in a 72% time savings compared to conventional methods and enhancing the efficiency and cost-effectiveness of optoelectronic packaging.
Implementation Method 1
The first portion of the solder layer that is in contact with the die pad of the first semiconductor die is heated to temporarily hold the first semiconductor die at the initial placement position
Implementation Method 2
Due to reflowing of the pre-singulated wafer, the first semiconductor die slides from the initial placement position to a final placement position
Data Source
AI summary
A wafer-level semiconductor die attachment method includes placing a semiconductor die of a plurality of semiconductor dies at an initial placement position to overlap a sub-mount pad on a sub-mount of a pre-singulated wafer. A die pad of the semiconductor die comes in contact with a solder layer deposited over the sub-mount pad. The semiconductor die and the sub-mount include a plurality of die and sub-mount mating features, respectively. The solder layer is heated locally to temporarily hold the semiconductor die at the initial placement position. The pre-singulated wafer is reflowed, when each semiconductor die is temporarily held at the corresponding initial placement position. During reflow, each semiconductor die slides from the initial placement position and a contact is established between the corresponding plurality of die and sub-mount mating features. Thereby, each semiconductor die is permanently attached to the corresponding sub-mount.