Copper Pillar Sidewall Protection via Conformal Passivation
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Solution Overview
Problem
Conventional semiconductor packaging methods face reliability issues due to solder wetting on copper pillar sidewalls, leading to void formation and non-uniform intermetallic compounds, which degrade the quality of bonded joints and reduce their reliability under stress tests.
Innovation Solution
A method involving the formation of a conformal passivation layer on copper pillar sidewalls using a nonwettable polymer, such as parylene, which is selectively etched to leave only the sidewalls covered, preventing solder wetting and ensuring uniform solder joints through an anisotropic etching process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If no passivation layer is formed on copper pillar sidewalls, then the manufacturing process is simple, but solder wetting occurs on sidewalls causing void formation and non-uniform intermetallic compounds
Solution Approach 1:
A conformal passivation layer is deposited on the copper pillar sidewalls before the soldering process to prevent solder wetting. This preliminary protective action ensures that when solder is applied, it only contacts the intended surfaces (top of the pillar and substrate pad) rather than wetting the sidewalls, thereby preventing void formation and ensuring uniform intermetallic compound formation.
Solution Approach 2:
The conformal passivation layer acts as an intermediary barrier between the solder and the copper pillar sidewalls. This intermediate layer prevents direct contact between solder and copper sidewalls, eliminating the harmful wetting effect while allowing the soldering process to proceed normally on the intended surfaces.
2Manufacturing precision
If a conformal passivation layer is formed on copper pillar sidewalls, then solder wetting is prevented and joint uniformity improves, but the manufacturing process complexity increases
Solution Approach 1:
The conformal passivation layer is deposited in advance using standard semiconductor fabrication techniques (such as CVD or PVD) before soldering. This preliminary step ensures precise coverage of the sidewalls with uniform thickness, which directly controls the subsequent soldering process to produce uniform joints without requiring complex real-time adjustments during soldering.
3Reliability
If solder wetting occurs on copper pillar sidewalls, then the process is simple without passivation, but void formation degrades joint quality
Solution Approach 1:
The conformal passivation layer serves as a mediator that blocks solder from wetting the copper sidewalls. This intermediate barrier allows the manufacturing process to remain relatively simple while eliminating the harmful effect of sidewall wetting that causes void formation, thereby improving joint reliability without significantly complicating the overall manufacturing flow.
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 copper pillar connections by preventing solder wetting on sidewalls, resulting in more reliable and durable bonded joints that perform better under temperature cycling and high-temperature storage conditions.
Implementation Method 1
forming a conformal passivation layer on at least the sidewall of the metal post
Implementation Method 2
Horizontal portions of the conformal passivation layer may be removed utilizing an anisotropic etch
Data Source
AI summary
Methods for copper pillar protection may include forming a metal post over a contact on a semiconductor die, where the metal post comprises a sidewall. A metal cap may be formed on the metal post and may be wider than the width of the metal post. A solder bump may be formed on the metal cap, and a conformal passivation layer may be formed on at least the sidewall of the metal post. The metal cap may be rounded shaped or rectangular shaped in cross-section. The metal post and the metal cap may comprise copper. The metal cap may comprise a copper layer and a nickel layer. The seed metal layer may comprise one or more of titanium, tungsten, and copper. The conformal passivation layer may comprise a nonwettable polymer. Horizontal portions of the conformal passivation layer may be removed utilizing an anisotropic etch such as a plasma etch.