Solder-Metal-Solder Stack for Flip-Chip Electromigration
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Electromigration in solder connections between semiconductor devices leads to failure, particularly in flipchip packages, due to inadequate current handling and solder bridging issues, which existing lead-free SAC alloys like SnAgCu struggle to address effectively.
Innovation Solution
A solder layer stack comprising a copper layer between SnAg solder layers on pillars, allowing copper diffusion to form a SAC-like material, improving electromigration performance and controlling bond line thickness through a modified bump stack profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SnAg solder material is used in solder connections, then the solder provides adequate strength and wettability, but the solder shows poor electromigration performance and inadequate current handling
Solution Approach 1:
The patent applies composite materials by creating a multi-layer solder structure combining SnAg solder layers with a copper layer in between. During reflow processing, copper diffuses into the SnAg solder to form a SAC-like composite material in situ, achieving improved electromigration performance and current handling capacity while maintaining the original solder's strength and wettability properties
Solution Approach 2:
The patent changes the compositional parameters of the solder material by introducing copper into the SnAg solder structure. The copper layer thickness is controlled at 0.5-5.0 micrometers, and during reflow, copper atoms diffuse into the solder to create a gradient composition that optimizes electromigration resistance and current handling while preserving mechanical properties
2Reliability
If a copper layer is added to the solder stack, then electromigration performance improves, but the manufacturing process complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-depositing a copper layer between the SnAg solder layers before final assembly. This preliminary copper layer is then activated during standard reflow processing to diffuse into the solder and form the desired SAC-like composite material, achieving improved electromigration performance without requiring additional specialized processing steps
Solution Approach 2:
The patent employs self-service by utilizing the standard reflow processing already required for soldering to automatically activate the copper diffusion process. The thermal energy from normal soldering operations causes copper atoms to diffuse into the SnAg solder layers, forming the improved composite material in situ without requiring separate treatment steps
3Reliability
If copper is diffused into SnAg solder material, then the solder converts into a SAC-like material with improved EM performance, but the manufacturing precision requirements increase
Solution Approach 1:
The patent controls the copper diffusion process by precisely specifying the copper layer thickness parameters (0.5-5.0 micrometers) and utilizing the standard reflow temperature profile. These parameter controls ensure that copper diffuses adequately into the SnAg solder to form SAC-like material with improved reliability, while the process remains compatible with existing manufacturing capabilities
Solution Approach 2:
The copper diffusion process is self-regulating during standard reflow processing. The thermal energy from normal soldering operations automatically drives copper atoms to diffuse into the SnAg solder layers to the appropriate extent, creating the desired SAC-like composite material without requiring precise external control or additional processing parameters
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
Enhances electromigration resistance and reliability by converting SnAg into a copper-enriched SAC material, reducing solder bridging and improving current handling capacity in semiconductor devices.
Implementation Method 1
heating (reflowing) a SnAg solder material on both sides of a metal comprising layer that including at least primarily copper that diffuses the copper into the adjoining SnAg material
Data Source
AI summary
An electronic device includes a substrate having top side contact pads including metal pillars thereon or a laminate substrate having land pads with the pillars thereon. A solder including layer stack is on the pillars, the solder including layer stack having a bottom solder material layer including in physical contact with a top surface of the pillars, a metal material layer, and a capping solder material layer on the metal material layer. The metal material layer is primarily a copper layer or an intermetallic compound (IMC) layer including copper.