Elephantech Has Developed SAphire™ B: A Low-Resistance Copper Nanopaste for Inter-Board Connections in High-Layer-Count PCBs Achieves High Reliability Through Low-Temperature Sintering in Ambient Atmosphere

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Inter-Board Connection Demands in the AI Era

The rise of generative AI is driving demand for high-performance computing systems capable of transmitting massive volumes of data at high-speed while providing large, stable power supply. As a result, PCB designs for AI infrastructure, semiconductor inspection equipment, and probe cards are incorporating increasingly high layer counts to enable greater signal densities and power delivery requirements.

As the number of layers in advanced multilayer PCBs continue to grow, single-board manufacturing becomes more challenging, accelerating a pivot toward modular approaches (e.g., N-layer + N-layer and N-layer + M-layer architectures), in which relatively lower-layer-count modules are fabricated separately and then connected to form an ultra-high-layer-count assembly.

Existing Technologies and Challenges

Both inter-board and inter-layer connections in ultra-high-layer-count PCBs are conventionally formed with conductive filler pastes consisting of metal particles dispersed in a resin matrix. Despite their long-lasting track record in electronics manufacturing, these materials are limited in demanding applications due to the relatively high resistance of their composite.

To address the intensifying performance requirements of advanced multilayer PCBs, low-resistance interconnect materials have attracted growing interest, including Transient Liquid Phase Sintering (TLPS) materials, silver sintering materials, and copper sintering materials. Among these, copper sintering materials are regarded as the most promising solution with resistance levels comparable to silver alternatives and lower than TLPS materials, while providing dramatically lower material costs than silver. However, copper sintering materials also present great technical challenge in realizing practical low-temperature sintering.

Comparison of inconnect materials options

SAphire™ B Overview

Elephantech has developed SAphire™ B, a copper sintering material for inter-board connections based on the self-assembling copper nanoparticle technology platform behind the SAphire™ product family. The material expands the series’ application beyond die-attach and TGV into advanced PCB interconnects.

Through hot-press processing at 220 °C and 1 MPa in ambient atmosphere, SAphire™ B achieves a volume resistivity of 15 μΩ·cm.

SAphire™ B Specifications

Reliability Testing

SAphire™ B has maintained stable electrical performance throughout testing of 1,000 thermal cycles. Specifically, a 36-via daisy-chain sample was subjected to thermal cycling between −55 °C and 125 °C for 1,000 cycles, with resistance variation remaining below 1 %.

Samples for reliability testing were fabricated in the process shown below: SAphire™ B was applied to vias formed in prepreg layers, then during hot pressing, the material sinters simultaneously with prepreg curing, forming electrical interconnects between PCB modules in a single integrated process.

Inter-Board Connect Process Using SAphire™ B

Resistance Variation at 125 °C During Thermal Shock Testing.

Interconnect integrity maintained after reliability testing

Outlook

SAphire™ B is now available for evaluation with PCB manufacturers in Japan and overseas. Elephantech will work closely with customers to optimize implementation methods to meet specific requirements for PCB layouts, materials, and manufacturing conditions.

Going forward, the company will continue to expand reliability testing data and validate consistency for mass production. Elephantech aims to address the growing needs for low-resistance, reliable interconnects in high-layer-count and high-density PCBs, remaining committed to advancing semiconductor packaging in the AI era through its proprietary nanomaterials technologies.