Semiconductor Interconnection Structure Preventing Solder Delamination
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Solution Overview
Problem
Conventional interconnection structures in semiconductor packages form brittle nickel-tin compounds during the reflow process, leading to mechanical strength, lifetime, and fatigue strength issues, resulting in bump cracking and delamination.
Innovation Solution
A metal layer made of gold, silver, lead, or copper is formed between the nickel layer and the solder material, preventing the formation of nickel-tin compounds and replacing them with copper-tin compounds, which have improved hardness and fracture toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a nickel layer is formed directly on the bonding pad and solder material is applied, then the electrical connection is established, but brittle nickel-tin compounds form during reflow causing mechanical strength degradation and bump cracking
Solution Approach 1:
A metal layer made of gold, silver, lead, or copper is introduced as an intermediary between the nickel layer and the solder material. This intermediate metal layer prevents direct contact between nickel and tin during reflow, thereby preventing the formation of brittle nickel-tin intermetallic compounds while maintaining electrical conductivity and mechanical strength.
Solution Approach 2:
The interconnection structure uses a composite multi-layer metallization system consisting of bonding pad, nickel layer, intermediate metal layer (gold, silver, lead, or copper), and solder material. This composite structure combines the advantages of each material: nickel provides oxidation resistance, the intermediate metal prevents brittle compound formation, and solder provides low melting point bonding capability.
2Reliability
If nickel-tin intermetallic compounds are formed during reflow, then electrical connection is achieved, but the compounds are brittle and cause delamination and reduce product lifetime
Solution Approach 1:
The intermediate metal layer (gold, silver, lead, or copper) acts as a barrier that prevents tin from the solder material from diffusing into the nickel layer during reflow. This eliminates the formation of brittle nickel-tin intermetallic compounds at the nickel-solder interface, thereby improving product lifetime and reliability.
Solution Approach 2:
Instead of allowing harmful nickel-tin compound formation, the invention uses the reflow process to form beneficial copper-tin compounds when copper is used as the intermediate layer. These copper-tin intermetallic compounds have improved hardness and fracture toughness compared to nickel-tin compounds, converting a potentially harmful process into a beneficial one.
3Reliability
If a metal layer is added between nickel and solder material, then cracking and delamination are prevented, but the device complexity increases
Solution Approach 1:
A single intermediate metal layer is sufficient to prevent brittle compound formation and improve fatigue strength. While this adds one layer to the structure, it significantly enhances reliability by preventing cracking and delamination, making the added complexity worthwhile for achieving the desired fatigue resistance.
Solution Approach 2:
The intermediate metal layer serves multiple functions simultaneously: it provides electrical conductivity, prevents formation of brittle nickel-tin compounds, acts as a diffusion barrier, and improves mechanical strength and fatigue resistance. This multi-functionality justifies the additional layer by consolidating multiple requirements into a single component.
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 solution effectively prevents solder bump cracking and delamination, enhancing the mechanical strength, lifetime, and fatigue strength of the interconnection structure, thereby improving product reliability and yield.
Implementation Method 1
By forming a metal layer made of one of gold, silver, lead and copper on the nickel layer, the present invention prevents the generation of nickel-tin compounds during a reflow process of the solder material
Implementation Method 2
The solder material 15 is reflowed to form solder bumps. During the reflow process, an intermetallic compound 13′ is formed at interfaces between the nickel layer 13 and the solder bumps
Data Source
AI summary
An interconnection structure for being formed on bonding pads of a substrate in a semiconductor package is provided. The interconnection structure includes a nickel layer formed on each of the bonding pads, a metal layer formed on the nickel layer, and a solder material formed on the metal layer. The metal layer is made of one of gold, silver, lead and copper, and has a thickness in the range of 0.5 to 5 um. As such, when the solder material is reflowed to form solder bumps, no nickel-tin compound is formed between the solder bumps and the metal layer, thereby avoiding cracking or delamination of the solder bumps.