FPGAs Get A Performance/Reliability Lift From The Bumps

Recent trends in high-density interconnects have led to the use of copper pillar solder bumps for packaging processes because they provide a fixed stand-off that is independent of pitch


According to Altera it will be the first company to use fine-pitch copper, bump-based packaging technology for commercial purposes. The technology, patented by the Taiwan Semiconductor Manufacturing Company (TSMC), will be deployed in Altera’s 20-nm Arria 10 FPGAs and SoCs.

What makes this fine-pitch version of copper bumping better than the standard stuff? Predictably, Altera says it provides superior quality and reliability. If so, how?

There are some well-documented, practical, and essential design elements relating to high-performance FPGAs. Recent trends in high-density interconnects have led to the use of copper pillar solder bumps (CPBs) for packaging processes because they provide a fixed stand-off that is independent of pitch. This is important, as most high-end products are under-filled and a smaller standoff may cause problems in getting the under-fill adhesive to adequately flow under the die.

Numerous specific benefits are possible with fine-pitch flip-chip manufacturing with copper pillar bumps. They include low-cost, enhanced electro-migration performance, availability of fully developed finite element models to optimize chip package interactions, and their lead-free makeup.

Not only does this technology create the very high bump counts needed for high-performance FPGAs, it also improves bump joint fatigue life and lowers stress on the ELK (Extra Low-K) layers.

Not surprisingly, TSMC’s technology is expected bring higher quality and greater reliability to Arria 10 devices over standard copper bumping solutions because of the fine-pitch design element.

Coolly Efficient

Copper pillar solder bumps, also called thermal bumps, maintain thermoelectric properties that can create a voltage when each side exhibits a different temperature. That brings the design advantage of cooling: Thermoelectric cooling occurs when a current passes through the bump. The bump pulls heat from one side of the device and transfers it to the other; the direction of heating and cooling is determined by the direction of current flow.

A further advantage of TSMC’s fine-pitch copper-bump-based packaging is its scalability, which suits products with large die size and small bump pitch. It includes a design-for-manufacturing/design-for-reliability (DFM/DFR) implementation that can adjust package design and structure for wider assembly process windows. According to TSMC, its technology has demonstrated better than 99.8% production-level assembly yields.

TSMC says it will manufacture 8.0 million wafers this year, including production from three advanced 12-inch facilities, four 8-inch fabs, and one 6-inch fab.

Another First

In another announcement, Altera also claims to have changed the game when it comes to FPGA floating-point DSP performance. The firm says it’s the first programmable logic company to integrate hardened IEEE 754-compliant, floating-point operators in an FPGA. These DSP blocks are integrated in Altera’s 20-nm Arria 10 FPGAs and SoCs.

Design-wise this becomes an important advance because integrated hardened floating-point DSP blocks, combined with an advanced high-level tool flow, enable computationally intensive applications. The DSP blocks are based on a variable precision DSP architecture, which eliminates nearly all of the logic usage required for existing FPGA floating-point computations. 

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Paul Whytock

Paul Whytock is European Editor for Penton Media's Electronics Division. From his base in London, England, he covers press conferences and industry events throughout the EU for Penton...
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