Flip-Chip Copper Bump Joint Structure for Crack Resistance
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Solution Overview
Problem
Lead-free solder bumps used in flip-chip bonding are prone to cracking due to coefficient of thermal expansion mismatches and the rigidity of copper bumps, leading to unreliable solder joints with low electro-migration resistance and a narrow process window for mass production.
Innovation Solution
A novel integrated circuit structure featuring a copper bump with a nickel-containing barrier layer and a lead-free solder region that connects the copper bump to a bond pad, with a specific ratio of dimensions and vertical distance to reduce stress and crack formation, enhancing crack resistance and electro-migration resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If lead-free solder materials (SnAg, SnAgCu) are used to replace lead-containing solders, then environmental safety is improved, but the solder joints become too brittle and crack resistance deteriorates
Solution Approach 1:
The patent changes the physical parameters of the solder joint structure by increasing the vertical distance between the bond pad and copper bump to greater than 30 μm, and optimizing the dimensional ratio between copper bump and solder resist opening to greater than 1. These parameter changes reduce stress concentration and improve crack resistance of lead-free solder joints
Solution Approach 2:
The patent employs a composite material structure consisting of copper bump, nickel-containing barrier layer, and lead-free solder material. This composite structure combines the advantages of each material while mitigating their individual disadvantages, particularly improving the crack resistance of lead-free solder joints through the nickel barrier layer and optimized geometry
2Ease of manufacture
If conventional flip-chip bonding is used with standard dimensions, then manufacturing simplicity is maintained, but the process window for mass production is too narrow and reliability is poor
Solution Approach 1:
The patent specifies optimized dimensional parameters: vertical distance between bond pad and copper bump greater than 30 μm, and ratio of copper bump dimension to solder resist opening dimension greater than 1. These parameter changes expand the process window for mass production while maintaining manufacturing feasibility and significantly improving reliability test pass rates
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 proposed structure significantly reduces crack lengths in solder joints, achieving reliable bonding and expanding the process window for mass production by effectively managing stress through optimized dimensions and material combinations.
Implementation Method 1
a nickel-containing barrier layer over and adjoining the copper bump
Implementation Method 2
a solder region electrically connects the copper bump to the bond pad
Implementation Method 3
A ratio of the first dimension to the second dimension is greater than about 1. Further, a vertical distance between the bond pad and the copper bump being greater than about 30 μm
Data Source
AI summary
An integrated circuit structure includes a first work piece and a second work piece. The first work piece includes a copper bump at a main surface of the first work piece and having a first dimension; and a nickel-containing barrier layer over and adjoining the copper bump. The second work piece is bonded to the first work piece and includes a bond pad at a main surface of the second work piece; and a solder mask at the main surface of the second work piece and having a solder resist opening with a second dimension exposing a portion of the bond pad. A ratio of the first dimension to the second dimension is greater than about 1. Further, a solder region electrically connects the copper bump to the bond pad, with a vertical distance between the bond pad and the copper bump being greater than about 30 μm.