Nanoparticle Paste Sintering for Low-Temperature Chip Joining
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Solution Overview
Problem
Conventional semiconductor chip joining methods using gold or nickel/gold coatings are undesirable due to their detrimental effects on semiconductor structures, and lead-free soldering processes at high temperatures result in brittle intermetallics and thermal stress, leading to solder joint failure and thermal budget consumption.
Innovation Solution
A method involving the sintering of a nanoparticle paste with very small diameter nanoparticles, such as silver, gold, or copper, in a reducing gaseous environment at lower temperatures (100-200°C) to connect lead-free solder bumps or coatings on semiconductor chips to copper or non-gold coated substrate bond pads without the need for flux or gold coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead-free soldering is performed at high temperatures, then solder joints can be formed, but brittle intermetallics form and thermal stress increases leading to solder joint failure
Solution Approach 1:
The patent changes the temperature parameter from conventional high-temperature soldering (200-300°C) to low-temperature sintering (100-200°C). This parameter change enables the formation of strong solder joints without creating brittle intermetallics and excessive thermal stress, thereby improving solder joint reliability while reducing temperature
Solution Approach 2:
The patent uses a composite nanoparticle paste containing metal nanoparticles (silver, gold, or copper) dispersed in an organic vehicle. This composite material enables low-temperature sintering to form strong bonds between lead-free solder bumps and substrate pads, resolving the contradiction between joint strength and temperature by combining nanoparticle benefits with organic binder properties
2Reliability
If conventional high-temperature soldering is used, then chip joining can be achieved, but thermal budget is consumed and chip life is reduced
Solution Approach 1:
The patent reduces the temperature parameter from 200-300°C to 100-200°C, enabling chip joining to be performed at lower temperatures that consume less of the chip's thermal budget. This extends the chip's operational life and allows for additional processing steps without exceeding thermal limits, while still achieving reliable joints
3Reliability
If gold or nickel/gold coatings are used for chip joining, then reliable connections can be formed, but detrimental effects on semiconductor structures occur
Solution Approach 1:
The patent extracts and eliminates the harmful gold and nickel/gold coating layers from the chip joining process. By using nanoparticle paste that can bond directly to copper substrate pads without requiring these toxic coatings, the invention removes the source of harmful effects on semiconductor structures while maintaining connection reliability through the nanoparticle sintering mechanism
Solution Approach 2:
The patent replaces expensive and harmful gold/nickel-gold coatings with a cost-effective nanoparticle paste formulation. The organic vehicle in the paste decomposes during low-temperature sintering, leaving only the metal nanoparticles that form the bond, eliminating the need for persistent harmful coating layers
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 approach reduces thermal stress, preserves the semiconductor chip's thermal budget, improves chip life and performance, and produces less brittle intermetallics, enhancing solder joint fatigue life while allowing chip joining to various substrates without gold or nickel/gold coatings.
Implementation Method 1
sintering, in a reducing gaseous environment, the nanoparticle paste to connect each of the one or more solder contacts on the semiconductor chip to a semiconductor substrate bond pad
Data Source
AI summary
An approach to provide a method of joining a semiconductor chip to a semiconductor substrate, the approach includes depositing a nanoparticle paste and aligning each of one or more solder contacts on a semiconductor chip to a substrate bond pad. The approach includes sintering, in a reducing gaseous environment, the nanoparticle paste to connect the semiconductor chip to a semiconductor substrate bond pad.