Conductive Solder Bump with Buffer Layer Support for Flip-Chip Reliability
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Solution Overview
Problem
Flip-chip packaging technologies face device failures due to cracks between semiconductor chips and solder bumps caused by thermal stress and external forces, resulting from differences in thermal expansion coefficients and applied forces during bonding.
Innovation Solution
A semiconductor device design featuring a conductive solder bump with a stick or protrusion supported by a buffer layer, where the solder bump is connected to a bonding pad through a first recess and supported by a stick in a second recess, with a metal barrier layer to distribute external forces and reduce stress concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solder bump is used for electrically connecting a PCB substrate with a semiconductor chip, then electrical connection is achieved, but the solder bump is susceptible to damages caused by thermal stress and external force
Solution Approach 1:
The solder bump structure is segmented into multiple functional zones: a bonding pad contact region, a stick protrusion for mechanical support, and a rounded bump portion. This segmentation allows each region to perform its specific function - the stick provides structural support while the rounded portion maintains electrical connection, preventing stress concentration at any single point.
Solution Approach 2:
The stick protrusion is designed beforehand to absorb and distribute external forces and thermal stress before they can reach the bonding interface between the solder bump and bonding pad. This pre-cushioning mechanism prevents crack formation by dissipating stress through the stick structure and insulating layers.
2Reliability
If the solder bump is directly bonded to the bonding pad, then electrical connection is established, but cracks may occur between the semiconductor chip and the solder bump due to thermal stress
Solution Approach 1:
Multiple intermediary layers are introduced between the solder bump and bonding pad: a stick protrusion made of stress-resistant material, and insulating layers surrounding the stick. These intermediaries act as mediators that decouple the thermal expansion differences between the PCB substrate and semiconductor chip, preventing direct stress transmission to the bonding interface.
Solution Approach 2:
The connection structure uses composite material design with the stick protrusion made of a material having different mechanical properties than the solder bump material. This composite structure combines the electrical conductivity of the solder with the mechanical strength and stress resistance of the stick material, creating a hybrid structure that resists thermal stress.
3Strength
If a stick is added to support the solder bump, then mechanical strength is improved, but device complexity increases
Solution Approach 1:
The stick protrusion and insulating layers are merged into a single integrated structure that serves both mechanical support and electrical insulation functions simultaneously. This merging eliminates the need for separate support components, reducing overall device complexity while maintaining structural strength.
Solution Approach 2:
The stick protrusion structure performs multiple functions: it provides mechanical support to prevent bump collapse, acts as a stress-absorbing element against thermal expansion, and serves as an electrical insulator when combined with the insulating layers. This multi-functionality reduces the need for additional components.
Data Source
AI summary
In one embodiment, a semiconductor device includes a semiconductor substrate and a bonding pad disposed thereon. The semiconductor device also includes a passivation layer, a buffer layer, and an insulating layer sequentially stacked on the semiconductor substrate. According to one aspect, a first recess is defined within the passivation layer, the buffer layer, and the insulating layer to expose at least a region of the bonding pad and a second recess is defined within the insulating layer to expose at least a region of the buffer layer and spaced apart from the first recess such that a portion of the insulating layer is interposed therebetween. Further, the semiconductor device includes a conductive solder bump disposed within the first and second recesses. The conductive solder bump may be connected to the bonding pad in the first recess and supported by the buffer layer through a protrusion of the conductive solder bump extending into the second recess.