Solder Coating Ball Reflow for Consistent Bump Height
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Solution Overview
Problem
The existing packaging methods using copper bumps formed through plating and lithography technologies suffer from low interface stability between solder and electroless Cu, leading to processing instability and deteriorated connection reliability due to height deviations between solder and copper bumps.
Innovation Solution
A packaging method involving the use of solder coating balls, where a plurality of pads and circuit patterns are formed on a substrate, followed by mounting a solder coating ball, performing a reflow process to modify its pattern, and delaminating a dry film pattern to create a solder pattern for chip mounting, ensuring consistent height and improved connection reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper bumps are formed through plating and lithography technologies, then connection resistance is reduced, but interface stability between solder and electroless Cu deteriorates
Solution Approach 1:
The patent introduces a nickel (Ni) barrier layer as an intermediary between the copper (Cu) pad and the solder bump. This Ni layer prevents direct contact between Cu and solder, eliminating the interface stability problem while maintaining low connection resistance through the Cu-Ni-Solder metallurgical structure.
Solution Approach 2:
The patent employs a composite metallurgical structure consisting of Cu pad, Ni barrier layer, and solder bump. This multi-material composite approach combines the advantages of each material: Cu for low resistance, Ni for stability and barrier properties, and solder for reliable joining.
2Ease of manufacture
If plating thickness deviation occurs during copper plating, then manufacturing cost is reduced, but height deviation between solder and copper bump increases
Solution Approach 1:
The patent changes the critical parameter from copper plating thickness control to nickel barrier layer thickness control. Since the Ni layer thickness has less impact on final bump height and can be more easily controlled, this parameter substitution resolves the manufacturing precision issue while maintaining ease of manufacture.
Solution Approach 2:
The Ni barrier layer acts as a thickness-buffer intermediary, decoupling the final bump height from the Cu plating thickness variations. Even if Cu plating thickness varies, the consistent Ni layer thickness ensures uniform overall bump height.
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 method enhances connection reliability and reduces manufacturing costs by forming consistent solder patterns between the chip and substrate, addressing the instability issues of copper bump packaging methods.
Implementation Method 1
the solder coating film is melted and accumulated according to the reflow process to be adhered to the pad
Data Source
AI summary
A packaging method comprises steps of forming a plurality of pads and another circuit pattern on a substrate, forming a second dry film pattern including opening exposing the pad, mounting a solder coating ball in the opening of the second dry film pattern, performing a reflow process on the solder coating ball in order to allow the solder coating ball to have a modified pattern, delaminating the second dry film pattern, and forming a solder pattern including the modified pattern of the solder coating ball in a solder to mount a chip on the substrate using the solder pattern.