Silver Layer Eutectic Bonding for Chip Carrier Reliability
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Solution Overview
Problem
Existing electronic circuit arrangements face challenges in achieving stable, high thermal and electrical conductivity connections between semiconductor chips and chip carriers, particularly due to issues with lead-containing soldering layers causing toxicity and whisker formation, and the limitations of palladium-containing alloys in eutectic bonding.
Innovation Solution
A silver layer is introduced as an adapter between the soldering layer and the bonding layer on the chip contact location for eutectic bonding, using a lead-free soldering layer with a predominantly palladium composition, and a three-layer structure of nickel, palladium, and gold, allowing for high conductivity and avoiding whisker formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead-containing soldering layers are used, then good electrical and thermal conductivity is achieved, but toxicity increases and environmental harm occurs
Solution Approach 1:
A silver layer is introduced as an intermediary between the lead-free soldering layer and the bonding layer. This silver layer enables eutectic bonding while allowing the use of environmentally friendly lead-free soldering materials, thus resolving the contradiction between conductivity requirements and toxicity concerns
Solution Approach 2:
The invention changes the material composition parameters by using a predominantly palladium-containing soldering layer instead of lead-containing materials. This parameter change maintains bonding effectiveness while eliminating toxicity, achieving both good conductivity and environmental safety
2Ease of manufacture
If tin-plated chip carriers are used, then ease of soldering is improved, but whisker formation occurs causing short circuits
Solution Approach 1:
The silver layer acts as a protective intermediary between the tin-plated substrate and the bonding process. This intermediary prevents direct interaction that would cause whisker formation while still allowing effective eutectic bonding to occur, thus eliminating harmful effects while maintaining manufacturing ease
Solution Approach 2:
The invention extracts the problematic tin layer from direct contact with the bonding process by placing the silver layer in between. This separation removes the source of whisker formation while preserving the beneficial soldering properties of the tin-plated substrate
3Reliability
If palladium-containing soldering layers are used to avoid whiskers, then reliability is improved, but eutectic bonding capability is lost
Solution Approach 1:
The bonding interface is segmented into multiple functional layers: a palladium-containing soldering layer for reliability and whisker prevention, and a separate silver layer for eutectic bonding capability. This segmentation allows each layer to perform its specific function optimally without compromise
Solution Approach 2:
The invention creates a composite structure at the bonding interface by combining palladium-containing material for stability with a silver layer for bonding. This composite approach integrates the advantages of both materials, achieving both reliability and eutectic bonding capability
4Reliability
If wire bonding is used to connect chip to carrier, then electrical connections are established, but the chip contact location area is underutilized
Solution Approach 1:
The invention replaces the mechanical wire bonding system with a direct eutectic bonding system using the silver layer. This substitution eliminates the need for wires and enables direct bonding across the entire chip contact location area, maximizing space utilization while maintaining reliable electrical connections
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 solution provides a stable, ecologically safe connection with high thermal and electrical conductivity between the chip and chip carrier, preventing whisker formation and ensuring reliable bonding without environmental harm, while allowing for further processing and soldering onto printed circuit boards.
Implementation Method 1
A silver layer for eutectic bonding with the bonding layer is provided on the soldering layer in the region of the chip contact location
Data Source
AI summary
Electronic circuit arrangement, includes a chip and a chip carrier having a substrate and a chip contact location. At least the chip contact location is provided with a soldering layer. The chip includes a bonding layer. A silver layer for eutectic bonding with the bonding layer is provided on the soldering layer in the region of the chip contact location.