Copper Layer Solder Bump Interconnect Reliability
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Solution Overview
Problem
Conventional Pb-free solder bump alloys, such as Sn/Ag/Cu, face reliability issues due to mechanically weak regions formed during assembly and thermal expansion, with excessive Cu incorporation leading to reliability problems and limited control over Cu concentration in intermetallic compounds.
Innovation Solution
A copper-containing layer is formed on the solder bump or bump pad before reflow, which is partially consumed by the solder melt to form a ternary Sn/Ag/Cu alloy and an intermetallic compound region, enhancing mechanical and electrical reliability by controlling Cu concentration and reducing fracture risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Pb-free solder bump alloys (Sn/Ag/Cu) are used to replace traditional Pb/Sn alloys, then compliance with RoHS legislation is achieved, but mechanically weak regions form during assembly and thermal expansion causing reliability issues
Solution Approach 1:
The patent changes the chemical composition parameters of the solder alloy by adding copper (0.1-5.0 wt%) to the Sn/Ag base alloy. This parameter modification transforms the mechanical properties of the solder joint, eliminating weak regions and improving fracture resistance while maintaining RoHS compliance.
Solution Approach 2:
The invention creates a composite solder material system consisting of Sn-Ag-Cu alloy with controlled intermetallic compound formation. The multi-phase composite structure (e.g., Cu6Sn5 + Ni3Sn4 intermetallics in Sn-Ag matrix) provides enhanced mechanical strength and reliability compared to simple Pb-free alloys.
2Strength
If copper is added to form Sn/Ag/Cu alloy, then solder joint strength is improved, but excessive Cu incorporation leads to reliability problems and limited control over Cu concentration in intermetallic compounds
Solution Approach 1:
The patent implements feedback control through controlled Cu diffusion during reflow processing. By managing the reflow temperature profile and Cu source availability, the process self-regulates the Cu concentration in the final solder joint, preventing excessive Cu incorporation while achieving optimal strength.
Solution Approach 2:
The invention precisely controls the Cu concentration parameter within specific ranges (0.1-5.0 wt% in solder, 0.5-5.0 μm intermetallic layer thickness). This parameter optimization balances strength enhancement with reliability maintenance, avoiding the harmful effects of excessive copper.
3Manufacturing precision
If a copper-containing layer is formed on the solder bump or bump pad before reflow, then Cu concentration in the solder joint is controlled, but additional manufacturing steps are required
Solution Approach 1:
The patent applies preliminary action by depositing a copper-containing layer (0.5-5.0 μm) on the bump pad or solder bump before the reflow process. This pre-positioned copper source enables controlled Cu diffusion into the solder during reflow, achieving precise Cu concentration control without requiring complex in-process monitoring.
Solution Approach 2:
The copper-containing layer serves as an intermediary Cu source between the external environment and the solder joint. This intermediate layer controls the rate and amount of Cu diffusion into the solder during reflow, enabling precise compositional control while simplifying the overall manufacturing process.
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 method improves the mechanical and electrical reliability of solder joints, reducing bump failure incidence and extending the operating lifetime of electronic devices by forming a Cu/Sn intermetallic compound region that suppresses the growth of brittle Ni/Sn intermetallic compounds.
Implementation Method 1
partially consumed by the solder melt to form a ternary Sn/Ag/Cu alloy
Implementation Method 2
forming a Cu/Sn intermetallic compound region that suppresses the growth of brittle Ni/Sn intermetallic compounds
Data Source
AI summary
A method of forming an electronic device provides an electronic device substrate having a solder bump pad located thereover. A nickel-containing layer is located over the solder bump pad. A copper-containing layer is formed on the nickel-containing layer prior to subjecting the electronic device to a reflow process.