Colder bonding, microfluidics and technical TIMs to evacuate heat.
Growing thermal challenges, as 3D packaging is turned to and virtual logic continues to evolve, push R barriers
The fundamental physics of having too much heat trapped in too small an area leads to tangible problems, such as customer products that are too hot to hold. However, the loss of strength and reliability is much worse, as overheated DRAMs have to cool and chips are subjected even more to pressure in high-temperature sectors such as automotive.
“In an ideal world, their die would be copper and their substrate would be 100 percent copper,” said Nathan Whitchurch, senior mechanical engineer at Amkor. “But even if I could, I wouldn’t get more functionality because of other restrictive points. in the package. “
Thermal problems and resolution of design and previous packaging in 2. 5D and 3D packages. “Heat dissipation is one of the key issues we want to consider, whether it’s reminiscent of logic, but also logic of logical stacking,” said Yin Chang, senior vice president of sales and marketing at ASE.
As the industry looks for solutions, microfluidics and thermal interface fabrics (TIM) are key development spaces. The first sees progress. The latter brings incremental improvements. To remove heat, liquid coolers can be connected directly to the chips or channels can be incorporated into the chips themselves. On the TIM side, sintered silver epoxy is used.
It is possible that microfluidics will soon move into production. “I bet microfluidics will start to appear beyond hyperexotic places, especially if it starts stacking high-performance logic,” said Rob Aitken, a prominent architect at Synopsys. Do nothing to cool, its stacked logic is limited to heat dissipation from an unmarried die. There is a huge economic push to solve those problems. Given that, and given people’s creativity, I bet he’ll figure it out in a smart way. .
Two years ago, an organization at the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland presented a prototype that brought the refrigerant as close as possible to the heat source. directly on a chip, rather than relying on TIM or links, which makes the ad market nervous due to reliability issues.
The Swiss team overcame demanding situations by creating, in their paco language consistent with, “a monolithically incorporated multichannel microchannel cooling design [in which] heat fluxes exceeding 1. 7 kilowatts per square centimeter can be extracted only 0. 57 watts per square centimeter of pumping power. “2
The article piqued the interest of investors and its concept went from the laboratory to the start-up. Its first author, Remco van Erp, along with EPFL professor Elison Matioli and COO Sam Harrison, co-founded a company called Corintis3, which secured investment from Swiss to create advertising versions of its innovation.
“From a thermal standpoint, the Corinthian technique is a very attractive cooling solution, as the refrigerant can get as close as possible to the location of heat resources and several thermal barriers can be removed in this configuration,” Herman said. Oprins, senior member of the IMEC technical staff. But he cautioned that the adoption of advertising is not a given. of this cooling method. It is well suited for hard programs with very high force densities, such as the force bar structures presented in the article. For CMOS programs, with force densities in diversity of several hundred W/cm², separate cooling blocks with more flexible channel diameters of several hundred μm can only be used.
Imec introduced its own microfluidics prototype 3 years ago. Its press describes the concept as “a microchannel Si heatsink assembled to a high-performance chip to cool it. [Achieves] a low overall thermal resistance of 0. 34 K/W at 0. 28 K/W with a pumping force of less than 2 W. “4
“We have two main types of prototypes,” Oprins explained. One is the silicon microchannel cooler. There, the biggest progression is the joining of chips with low thermal resistance. The moment is direct liquid cooling in the 3D published cooling geometries of the chip in complex shapes.
While imec’s efforts have yet to be commercialized, corporations are already filing designs, according to Oprins.
Describing the origin of the imec prototype, Oprins said: “We leveraged our wafer-to-wafer bonding wisdom to attach the cooler to the chip, with a very low thermal resistance of less than 1mm2-K/W. Therefore, instead of a thermal interface material, melt bond, oxide bond, or steel bonding can be used. The biggest merit for semiconductor processing is that there can be tight tolerances with a very thin line.
Oprins has several problems. ” For the mechanical integrity of your packaging, you need to compensate for the lack of a lid with a reinforcing ring,” he said. “If you make channels that are too small, the voltage drop you want to get your coolant pathway will be too high. It is limited to the extent that it can happen with liquids.
However, he noted that while higher tension is a potential drawback, it is not an obstacle. “The main reasons for slow adoption are reliability issues (leaks), lack of increased maintenance, and formula complexity. “
Fig. 1. Different cooling approaches. Source: Imec
Oprins has classified existing and proposed approaches to liquid cooling into 4 distinct types:
In addition to this work, Sam Sadri, senior process engineer at QP Technologies, recently presented a prototype of an internal refrigerated enclosure. Created with 3D generation, it is composed of ceramic alumina that uses the generation of thick layers for metallization, in which several SiC FETs will be connected.
“Alumina is already an oxide (Al2O3) and copper oxidizes easily, so the two oxides come together, and that’s how this interface is made,” Sadri explained. “This is by far the most economical way to build a force module, with ceramics. There are tactics to further reduce costs. An insulated steel substrate (IMS) looks like any PCB production technology, but uses heavy copper. What I’ve noticed regarding anything that’s more successful than alumina with the same footprint.
The dimensions of the prototype are approximately 4″ x 2 1/2″ x 3/4″ deep. Although thicker than a typical substrate, what makes this oblong design special is that it has channels running all the way, with holes in its shorter sides. “It’s one of the coolest things I’ve ever noticed in effect,” Sadri said. heat? It sends a refrigerant such as bloodless air, nitrogen, coolant, or other bloodless substance through the channels. While it is working, it also cools down.
However, many TIMs turn out to be as effective as their widespread use suggests. “Thermal interface fabrics are adjusting to a significant thermal bottleneck as liquid cooling functionality improves,” Oprins said. “System integrators have many questions about how TIMs can be replaced with larger actuation fabrics and reliability risks. “
The challenge is to note that it has a very high thermal conductivity, while being very flexible and comfortable to adhere to the topology of the other components.
“In general, maximum fabrics that have intelligent conductivity are also very rigid, so not only will they not meet the standards, but they can also increase stresses,” Oprins explained. “You’re looking for a mix that’s hard to find. Therefore, there will be no individual curtains that have those properties. Researchers will have to design one by manufacturing composite materials. There may be compounds. There may also be carbon nanotubes or graphene sheets. There are many advances in this specific area. We start with silicone-based fabrics and eventually end up with metal. -thermal interface fabrics based on, however, there are many reliability problems to solve first.
Given the pressing need for new fabrics, Amkor’s Whitchurch is under pressure for all engineers to respect how important advances in fabric science will be to solving thermal disorders, and that the industry still has a long way to go to find fabrics that can be flexible and reliable. and economic.
“We are exploring many other TIMs, which are no longer polymer-based,” he said. Matrix of a silver alloy between the cap and the matrix. Another example would be softer metallic materials, such as those based on indium. Gallium scares other people because it reacts with aluminum, so we haven’t noticed this kind of environment as much. . A few years ago, we talked about phase replacement hardware, but that turned out to be extinct when other people learned that reliability and other benefits just weren’t there. The other things I’ve noticed, like graphite pads, also provide demanding situations that are too hard to overcome. Single-way graphite is very thermally conductive, but integrating it into a package is a complicated challenge.
To get rid of the force in an upside-down chip pack, Sadri said: “Traditionally, a metallized SiC force FET chip on the back is connected to a heatsink employing welding (e. g. AuSn). Today, sintered silver epoxy has shown higher thermal, so other people use non-pressure sintered epoxy (e. g. , Atrox) or pressurized epoxy (Argomax). (TIM) on the interface. Other inventions use a series of wires on the back of the chip and then place the wires on a plane from floor to the PCB to thermal. Copper-tungsten and copper-molybdenum are other types of heat sinks that others people like the CTE corresponding to silicon, but they are expensive. Copper remains the most productive and very cost-effective thermal interface. »
One technique of choice would absolutely be TIM’s desire, which is one of the motivations for imec paints on microfluidics. said. ” We want to bring it closer to the chip so we can those fabrics. I would say that’s the back line. Either update the fabrics or get rid of them.
However, replacing takes time. ” The industry is very conservative,” Oprins said. “It takes a lot of conviction to move on to something they don’t know. Everything you introduce is very complex. I perceive the reluctance to adopt something new until it has been shown that it has worked and all liability issues have been resolved. However, there are many wonderful ideas out there. We know they still have a lot of work to do and we are looking for new recruits who can help us.
references
When contemplating the warmth in the electronics, designers want to compare the entire case. While applying for a laminate manufacturer and now that I’m back in PCB manufacturing, there are very smart opportunities for FR4 that multilayer structures can be built with. These thermal fabrics can be used in many tactics to beat heat or paints along with heavy coppers, heat sinks or other technologies!
It is transparent how the EDA network is preparing for the demanding situations ahead.
Details on more than $500 billion in new investments through some 50 companies; What is the expansion frenzy, why now and the demanding situations ahead?
113 startups raise $3. 5 billion; batteries, AI, and new architectures are the smartest on the list.
BPD improves performance, but requires wafer bonding, substrate thinning and, in all likelihood, new interconnect metals.
The United States exerts pressure on Japan and the Netherlands; Samsung mass-produces 1TB of V-NAND; ASE innovates in Malaysia; IBM 433-qubit processor.
It is transparent how the EDA network is preparing for the demanding situations ahead.
Advanced etching is the key to nanosheet FETs; Evolutionary trail for long-term nodes.
From the design team’s express to organizational and economic impacts, the shift to traditional silicon is changing things.
Who does what in next-generation chips, and when do they expect to do it?
Are you about to have a major disruption in the EDA industry, along with the emerging era of domain-specific architectures?The academy thinks so.
New memory approaches and demanding situations in CMOS scaling involve radical changes, and massive innovations, in semiconductor designs.
Manufacturing capacity reaches a point large enough to compete with BGA and 2. 5D flip-chips.
Details on more than $500 billion in new investments through some 50 companies; What is the expansion frenzy, why now and the demanding situations ahead?