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Posted on 05 May 2019

Real Life Innovation with Practical Applications

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The story of Danfoss Bond Buffer

Back in 2010, the market was buzzing with anticipation following the release of a seminal white paper describing the future potential of copper wire bonding. At Danfoss Silicon Power, we were excited by the prospect of a new generation of semiconductors, where a protective layer of copper was added to the chip allowing the use of superior copper wires.

By Siegbert Haumann, Danfoss Silicon Power

Back in 2010, the market was buzzing with anticipation following the release of a seminal white paper describing the future potential of copper wire bonding. At Danfoss Silicon Power, we were excited by the prospect of a new generation of semiconductors, where a protective layer of copper was added to the chip allowing the use of superior copper wires. The implications were enormous. The more we looked into the technology the more we realized that this could be a real game changer for the industry. We anxiously waited for the first semiconductors to enter the broader market.

A protective layer of copper was added to the chip allowing the use of superior copper wires

While we waited, our engineers and technicians began their own series of trials – experimenting with different solutions, where adding protective copper layer to the die allowed the use of more efficient copper wires. It turned out to be harder than it appeared - the delayed presence of the new promised solution on the market suddenly made sense.

We realized that any front-end wafer-based solution would probably be limited in its application (thin wafers) - and only be mastered by a select number of suppliers of power semiconductors.

It was therefore unlikely that it would solve the challenges we saw looming in the market: Cost competitive solutions allowing the use of ever smaller chip sizes and an increased demand for longer lasting modules that are more durable against power and temperature cycling – especially in the automotive and renewable energy sectors.

Innovation is more than a word

At Danfoss Silicon Power, there’s a tendency to remain focused on at a challenge until a solution is found. The word “innovative” is sometimes overused in our industry, but with all modesty, the work that went on behind closed doors at our research lab in Flensburg, in cooperation with University of Applied Science (Fachhochschule Kiel, Germany) , between 2011 and 2013 genuinely broke new ground in power module thinking.

By 2012 we were confident that we’d found a solution. We called it the Danfoss Bond Buffer (DBB). Developed to fulfill ambitious power module lifecycle requirements of the automobile and renewable energy markets, our new solution went beyond what could be achieved with today’s bonding and joining technologies.

In many industrial and automotive applications, reliability and longevity of components is critical. Traditional solutions suffer from limited reliability due to solder fatigue and failing aluminium wire bonds.

By using unique silver sintering techniques rather than traditional soldering - and using copper instead of aluminum wires, along with the new Danfoss Bond Buffer technology, we created modules with outstanding reliability and significant performance. The design of the DBB was dimensioned for the thermo-mechanical optimum to reduce the mechanical stress due to CTE mismatch.

The innovative combination of the copper bond buffer, copper wire and sintered joints lead to a much longer lifetime and/or higher current density. Other significant advantages include additional thermal capacity, better short circuit performance and lower forward voltages. (For more information attend the oral session at PCIM 2014, Tuesday 20th May at 15.00h, where the paper “Influence of Danfoss Bond Buffer and Cu-Wire bonds on the Electrical Switching Behaviour of IGBTs” will be presented by Dipl.-Ing (FH) Guido Mannmeusel, Danfoss Silicon Power) As the copper layer has a large cross-sectional area, which increases the vertical current flow, the DBB provides a uniform current density distribution in the semiconductor. Due to the improved vertical current flow, there is no longer a need to place a stitch bond on the semiconductor.

Due to the improved vertical current flow, there is no longer a need to place a stitch bond on the semiconductor

The results are convincing. DBB technology offers unmatched reliability – at least ten times higher than previously seen, plus extreme lifetime, increased power density and cycle capability. Test revealed better reliability up to 15 times better compared with state of the art power modules – and to a power of 60 times compared to industry standards. And to top it all, it’s applicable to pretty much any power semiconductor available.

By using DBB technology you can achieve 30% roughly longer life, lower cost improved reliability depending on your product needs.

Ideal for tomorrow’s automotive applications

The market is growing for hybrid electric vehicles (HEVs) and producers are hungry for competitive advantages. But the HEV market is still immature, and customer motives are different to those in the regular automotive sector. Legislation is driving OEMs to lower the CO2 impact of their entire fleet. Higher-end manufacturers simply cannot meet these new requirements, as they have no smaller, economy models in their portfolio. The only way they can conform to new legislation is by offering some of their fleet as hybrid standards.

In addition, early adopters, driven by a desire to minimize their environmental impact, are willing to pay for their conscience. The truth is though, that the cost add-on for the electrification won’t pay back for 5 to 8 years. These consumers account for a mere 3-4% of market. Most automotive consumers still perform a basic ROI analysis on their new car purchase and expect payback in 2 to 3 years.

As a consequence, manufacturers want to dramatically lower the cost for the electrification of a vehicle – and get the ROI down to 2 years. If they can achieve this, then their products viability is drastically increased, attracting a broad market and with that, drive economies of scale.

Danfoss Bond Buffer technology solves these problems by allowing the use of higher temperatures and use of less silicon area for comparable power output

In the automotive industry, extreme power cycling requirements are hard on traditional aluminum wire solutions. The typical solution is derating the power module by adding additional silicon area. But silicon and vehicle space are expensive - so using less silicon while maintaining reliability is the key. Danfoss Bond Buffer technology solves these problems by allowing the use of higher temperatures and use of less silicon area for comparable power output.

Increased reliability for the wind industry

A wind turbine has an average lifetime of 20-30 years. Wind turbines have extremely tough power cycle issues especially on the generator side of the inverter, but failure is not an option. Downtime is expensive and maintenance and repairs - especially in offshore parks and remote regions - can be complicated and costly. Reliability is the key issue at every level. A DBB solution can offer longer life of up to 30% or a solution with less silicon.

With the combination of the improved thermal efficiency offered by Danfoss’ ShowerPower® cooling technology and DBB technology you get the perfect solution for using less modules in a given stack. This is especially crucial for turbines, where weight and size are physically limited. In a typical example - with around 24 chips in a module - with a 3 MW turbine, the magnitude of savings in this hypothetical case could mean a reduction of one in five stacks.

For reliable lifts and hoist applications

Lift and hoist applications also have extreme requirements for power cycles and long lifetime. Safety here is obviously paramount. In a normal hotel lift, for example, regular starting and stopping precisely at every floor means excessive driving around zero frequency - which is extremely tough on traditional aluminum bonds. For safety reasons, manufacturers are obliged to de-rate the module to ensure the lifetime or number of power cycles required. The impact is cost. A DBB solution limits the silicon required, while still maintaining life time and critical safety requirements demanded. critical safety requirements demanded.

Danfoss Silicon Power

Danfoss Silicon Power is the expert in design and manufacturing of power modules and stacks individually designed to meet application requirements. In addition to customer-specific solutions, we design, manufacture and market a wide selection of plug-in compatible power modules.

Globally, we cover an extensive range of business areas such as consumer appliances, industrial controls and automotive, as well as medical equipment and renewable energy applications. Based in Germany, we are supplier to some of the world’s leading companies.

For more information please contact: Siegbert Haumann; siegbert.haumann@danfoss.com

 

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