Capillary Underfill Funnel for Compact Die Stacking
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Solution Overview
Problem
Conventional capillary underfill (CUF) technology is limited by finite dispensing dot size and placement accuracy, requiring a significant 'keep-out zone' (KOZ) between top and bottom die edges, which restricts the tight spacing of dies in 3D die stacking due to the need for standard dispense dot size and equipment alignment accuracy, leading to reduced run rates and increased costs for equipment upgrades.
Innovation Solution
The creation of an underfill material funnel on or within the dies to control the spread of CUF material, allowing it to flow effectively between the top and bottom die edges using capillary forces, thereby reducing the required KOZ without the need for a standard dispense 'tongue' and enabling tight die-to-die spacing using standard CUF process and equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If standard dispense dot size and placement accuracy are used, then CUF technology can be implemented, but a large KOZ (500 um) is required which prevents tight die spacing
Solution Approach 1:
The underfill material application is segmented into multiple discrete dispense dots arranged in a pattern. Instead of requiring a single large dispense area, the underfill is delivered through multiple smaller dots that collectively fill the gap between dies, enabling tight spacing while maintaining standard dispense capabilities
Solution Approach 2:
The invention transitions from a single-plane dispense approach to a multi-dimensional dispense pattern. Multiple dispense dots are positioned at different locations (edges and corners) of the underfill region, creating a distributed application pattern that reduces the required KOZ while ensuring complete underfill coverage
2Quantity of substance
If dispense dot size is reduced and alignment accuracy is improved, then KOZ can be reduced, but run rate decreases significantly and equipment upgrade is costly
Solution Approach 1:
The invention applies underfill material at multiple discrete locations (partial action) rather than requiring continuous material flow. Multiple dispense dots are placed at strategic positions around the die edges, providing sufficient underfill coverage without requiring excessive material or precision, thereby maintaining high run rates with standard equipment
Solution Approach 2:
The multiple dispense dots act as intermediaries between the dispensing equipment and the underfill gap. Instead of requiring direct precise placement of material into tight gaps, the dots serve as intermediate deposition points that allow capillary action to distribute the material evenly, reducing the need for high alignment accuracy
3Area of stationary object
If multiple top dies with narrow die to die spacing are used, then space utilization is improved, but underfill protection becomes difficult due to KOZ limitations
Solution Approach 1:
The underfill protection approach is segmented into multiple dispense locations around each die. Instead of requiring a continuous underfill layer from a single source, the underfill is applied at multiple discrete points along die edges and corners, ensuring reliable protection even in narrow spacing configurations
Solution Approach 2:
The invention extends the underfill application from a single-dimensional linear approach to a two-dimensional distributed pattern. Multiple dispense dots are positioned at various locations including edges and corners of the underfill region, creating comprehensive coverage that protects solder joints reliably while accommodating narrow die spacing
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 allows for very tight top die-to-die spacing and small top die edge to bottom die edge distances in 3D die stacking packages, optimizing space usage on the substrate and reducing costs by maintaining standard dispense dot size and alignment accuracy while achieving dense die packing.
Implementation Method 1
capillary underfill material... to control the spread of CUF material, allowing it to flow effectively between the top and bottom die edges using capillary forces
Data Source
AI summary
An electronic package assembly is disclosed. A substrate can have an upper surface area. A first active die can have an upper surface area and a bottom surface, the bottom surface operably coupled to the substrate. A second active die can have an upper surface area and a bottom surface, the bottom surface operably coupled to the substrate. A capillary underfill material can at least partially encapsulate the bottom surface of the first active die and the second active die and extend upwardly upon inside side surfaces of the first and second active dies. A combined area of the upper surface area of the first active die and an upper surface area of the second active die is at least about 90% of the upper surface area of the substrate.