Backside Connector Package Structure for LPDDR Routing Reliability
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Solution Overview
Problem
Existing semiconductor packages face issues such as inability to support commodity LPDDR DRAM due to ball map and routing capability limitations, backside joint pad damage from copper dendrite formation, and environmental contamination leading to electrical failures, particularly in packages with backside redistribution layers.
Innovation Solution
A package design featuring a backside connector with a tapered portion and underbump metallization to enhance polymer adhesion, eliminating the need for laser drilling and reducing contamination risks, while using electrochemical plating for copper RDL step coverage and optimizing polymer and RDL thickness for stress relaxation and warpage control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If backside redistribution layers are used to support LPDDR DRAM, then routing capability is improved, but copper dendrite formation causes backside joint pad damage
Solution Approach 1:
The patent extracts the problematic backside joint pad structure from the package design. By eliminating the backside joint pad entirely and using only frontside connections, the invention removes the source of copper dendrite formation while maintaining LPDDR DRAM support through alternative routing paths on the frontside.
Solution Approach 2:
The patent converts the limitation of no backside connections into a benefit by designing all connections to occur on the frontside. This eliminates copper dendrite issues while the encapsulant material is selected specifically to provide mechanical support in the absence of backside reinforcement, turning a structural weakness into a reliability strength.
2Manufacturing precision
If laser drilling is used to create openings in polymer layers, then manufacturing precision is improved, but environmental contamination leads to electrical failures
Solution Approach 1:
The patent replaces the mechanical laser drilling process with a chemical etching process. The etching process uses chemical solutions to create openings in the polymer layers, eliminating the high-energy laser process that can introduce contamination. This chemical approach maintains sufficient precision while avoiding the harmful effects of laser-induced contamination.
3Reliability
If backside enhancement layers are added to prevent damage, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent extracts and removes the backside enhancement layer from the package structure. By eliminating this additional layer entirely and accepting the frontside-only connection architecture, the invention reduces device complexity while maintaining reliability through the alternative design approach that avoids the root cause of damage.
Solution Approach 2:
The encapsulant material is designed to serve multiple functions: it provides electrical insulation, mechanical support for the semiconductor die, and structural reinforcement in the absence of backside connections or enhancement layers. This multi-functionality eliminates the need for separate backside enhancement layers.
4Manufacturing precision
If copper RDL step coverage is enhanced through electrochemical plating, then manufacturing precision is improved, but production time increases
Solution Approach 1:
The patent optimizes the electrochemical plating parameters including current density, plating time, and electrolyte composition to achieve adequate step coverage in reduced time. By carefully controlling these parameters, the invention maintains sufficient copper coverage on RDL steps without requiring excessively long plating cycles, thus balancing precision with productivity.
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
The solution effectively supports LPDDR DRAM, reduces the risk of backside joint pad damage and environmental contamination, and improves reliability by eliminating the need for laser drilling and backside enhancement layers, while providing tunable warpage control and reduced cycle time.
Implementation Method 1
using electrochemical plating for copper RDL step coverage
Implementation Method 2
optimizing polymer and RDL thickness for stress relaxation and warpage control
Data Source
AI summary
A package includes a frontside redistribution layer (RDL) structure, a semiconductor die on the frontside RDL structure, and a backside RDL structure on the semiconductor die including a first RDL, and a backside connector extending from a distal side of the first RDL and including a tapered portion having a width that decreases in a direction away from the first RDL, wherein the tapered portion includes a contact surface at an end of the tapered portion. A method of forming the package may include forming the backside redistribution layer (RDL) structure, attaching a semiconductor die to the backside RDL structure, forming an encapsulation layer around the semiconductor die on the backside RDL structure, and forming a frontside RDL structure on the semiconductor die and the encapsulation layer.