Copper Pillar Bumps with Trapezoidal Base for IC Thermal Stress Reduction
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Solution Overview
Problem
Current semiconductor technologies face challenges with thermal stresses and reliability issues in finer pitch integrated circuits due to solder bumps, which can lead to bridging, non-uniform bump heights, and mechanical deformation, especially with the transition to lead-free solder materials and decreasing terminal pitches.
Innovation Solution
The use of copper pillar bumps with a trapezoidal or wider base shape, where the base portion is wider than the upper portion, reduces thermal stresses by maintaining the pillar's shape during reflow and providing a larger underbump metallization area, thereby enhancing thermal performance and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder bumps are used for connections, then electrical connectivity is achieved, but thermal stresses and reliability issues occur due to melting and deformation during reflow
Solution Approach 1:
The patent changes the material parameter from solder to copper, which has a higher melting point and does not deform during reflow processing. This parameter change eliminates the shape instability and reliability issues associated with solder bumps while maintaining electrical connectivity functionality
Solution Approach 2:
The patent replaces the disposable solder material that deforms and melts with a permanent copper pillar structure that maintains its shape indefinitely through reflow processes, effectively using a more durable material to replace a temporary bonding material
2Productivity
If terminal pitch is decreased to increase density, then more connections per area are achieved, but bridging between adjacent bumps occurs
Solution Approach 1:
The patent changes the physical parameters of the connection structure by using copper pillars with controlled height and diameter ratios, which maintain structural integrity at finer pitches where solder bumps would bridge due to their deformable nature
3Stress or pressure
If pillar height is increased to reduce stress, then thermal stress distribution improves, but mechanical strength decreases
Solution Approach 1:
The patent optimizes the geometric parameters of the copper pillar, specifically the height-to-diameter ratio, to achieve an optimal balance where sufficient height provides stress distribution while the cylindrical geometry and material properties maintain mechanical strength
Solution Approach 2:
The patent uses a cylindrical pillar geometry with curved surfaces that provides optimal stress distribution compared to angular shapes, while the continuous curved structure maintains mechanical integrity and resistance to fracture
4Ease of manufacture
If conventional columnar pillars are used, then manufacturing is simplified, but thermal stresses concentrate on various layers causing delamination
Solution Approach 1:
The patent modifies the geometric parameters of the pillar by optimizing the height-to-diameter ratio to a specific range that simultaneously achieves stress distribution benefits while remaining compatible with standard semiconductor manufacturing processes
Data Source
AI summary
Apparatus and methods for providing solder pillar bumps. Pillar bump connections are formed on input/output terminals for integrated circuits by forming a pillar of conductive material using plating of a conductive material over terminals of an integrated circuit. A base portion of the pillar bump has a greater width than an upper portion. A cross-section of the base portion of the pillar bump may make a trapezoidal, rectangular, or sloping shape. Solder material may be formed on the top surface of the pillar. The resulting solder pillar bumps form fine pitch package solder connections that are more reliable than those of the prior art.