Through-Substrate Pillars for 3D Die Stacking Alignment
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Solution Overview
Problem
Conventional 3D die stacking techniques face challenges with precise alignment of copper pillars, leading to non-wetting issues and increased footprint, requiring additional non-electrically active pillars and underfill, which complicates the packaging process and increases the size of the device.
Innovation Solution
The through-substrate pillar bonding technique, where metal pillars from a bottom die are inserted into access holes on a top die, forming a mechanical and electrical bond with pads, reducing the risk of non-wetting and eliminating the need for underfill and dam structures by bringing the dice closer together.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper pillar-to-pillar die stacking technique is used to bond two dice, then mechanical and electrical bond is formed, but precise alignment is required which increases device footprint and complexity
Solution Approach 1:
The patent introduces an underfill material as an intermediary substance between the copper pillars and the die substrate. This underfill acts as a mediator that compensates for alignment tolerances, allowing the copper pillars to bond reliably even with moderate misalignment. The underfill flows into the gaps and provides both mechanical support and electrical pathway, resolving the contradiction between bond reliability and alignment precision requirements.
2Reliability
If non-electrically active pillars are added to prevent non-wetting, then bonding reliability is improved, but device footprint increases
Solution Approach 1:
The patent makes the underfill material multi-functional by designing it to serve both as a mechanical support structure and as an electrical conductor. This eliminates the need for separate non-electrically active pillars, as the underfill itself provides both structural support and electrical pathways. The underfill's dual functionality resolves the contradiction between bonding reliability and device footprint by consolidating multiple functions into a single element.
3Ease of manufacture
If underfill and dam structures are used to prevent lateral disbursement, then bonding process is completed, but device complexity and footprint increase
Solution Approach 1:
The patent extracts and eliminates the dam structures from the packaging process. By designing the underfill material with appropriate viscosity and flow characteristics, the underfill naturally confines itself within the die stack without requiring additional dam structures. This extraction of the dam component simplifies the overall packaging process and reduces device complexity while still achieving complete bonding, resolving the contradiction between manufacturing ease and device complexity.
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 enhances the reliability of electrical and mechanical connections, reduces the device footprint, and allows for a more compact die stack without the need for underfill or dam structures, improving the overall efficiency of the packaging process.
Implementation Method 1
each metal pillar contacts a pad, and then may be mechanically and electrically coupled to the pad
Implementation Method 2
The metal pillars may be tipped with solder material so that after the dice are stacked, a solder reflow process may be performed to form a solder joint between the metal pillar and the corresponding pad
Data Source
AI summary
A method for 3D device packaging utilizes through-substrate pillars to mechanically and electrically bond two or more dice. The first die includes a set of access holes extending from a surface of the first die to a set of pads at a metal layer of the first die. The second die includes a set of metal pillars. The first die and the second die are stacked such that each metal pillar extends from a surface of the second die to a corresponding pad via a corresponding access hole. The first die and second die are mechanically and electrically bonded via solder joints formed between the metal pillars and the corresponding pads.