Self-Aligned Dice Stacking via Reflow Surface Tension
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Solution Overview
Problem
Conventional methods for making stacked packages either result in high defective fractions due to untested die elements before stacking or face alignment issues during the stacking process of tested die elements.
Innovation Solution
A method involving a carrier with platforms, where tested dice are self-aligned through a reflow process, followed by molding compound formation and cutting to create packages, eliminating the need for high-accuracy die attach machines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If die elements are not tested before stacking, then manufacturing process is simpler and faster, but defective fraction increases
Solution Approach 1:
The patent applies preliminary action by testing die elements before stacking them into packages. This ensures that only functional die are selected and placed onto the wafer, thereby reducing the defective fraction in the final stacked packages while maintaining manufacturing efficiency through automated testing and sorting processes
2Reliability
If die elements are cut off and tested individually, then defective fraction decreases, but alignment precision deteriorates due to difficulty in aligning during stacking
Solution Approach 1:
The patent applies segmentation by dividing the wafer into multiple stacked packages, each containing multiple die elements. This allows individual testing and selection of die while maintaining their spatial relationships, thereby achieving both high reliability through testing and good alignment precision through the segmented package structure
Solution Approach 2:
The patent uses an intermediary approach by implementing a automated die attach machine with alignment markers and vision systems. This intermediary system facilitates precise alignment between die elements during stacking, overcoming the alignment difficulties that would otherwise occur when handling individually tested die
3Manufacturing precision
If a die attach machine with high accuracy is used, then placement precision is improved, but equipment cost increases
Solution Approach 1:
The patent applies self-service by designing die elements with built-in alignment markers and features that enable self-alignment during the stacking process. This reduces the reliance on expensive high-precision die attach machines, as the die themselves provide the alignment reference, thereby achieving good placement precision with lower-cost equipment
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 reduces defective fractions and alignment errors, enabling cost-effective, accurate placement of dice with increased yield rates and flexibility in stacking different-sized dice.
Implementation Method 1
the solder layer 11 has surface tension during the reflow process, which makes the dice 2 on the solder layer 11 able to self-align
Data Source
AI summary
A package and the method for making the same, and a stacked package, the method for making the package includes the following steps: (a) providing a carrier having a plurality of platforms; (b) providing a plurality of dice, and disposing the dice on the platforms; (c) performing a reflow process so that the dice are self-aligned on the platforms; (d) forming a molding compound in the gaps between the dice, and (e) performing a cutting process so as to form a plurality of packages. Since the dice are self-aligned on the platforms during the reflow process, a die attach machine with low accuracy can achieve highly accurate placement.