René Raaijmakers
18 March

As a supplier of hybrid-bonding machines, Besi has a rock-solid position in the hardware ecosystem for the artificial intelligence hype. ASMPT is gearing up, however, and now has two orders for its hybrid bonders.

As with all of Besi’s quarterly earnings reports in the past years, analysts last February focused on hybrid bonding, the technology that gave the machine builder an aura as ‘the ASML of the back-end.’ Its apparent untouchability in this area quickly started to evaporate, however, after the recent announcement of rival ASMPT. The back-end market leader – more than twice the size of Besi – has secured two orders for its Lithobolt hybrid bonders. It shows that you always have to look over your shoulders in the back end. It’s a market with a low threshold to technology entry, even for something as magical as hybrid bonding.

Hybrid bonding is an advanced technology that requires high precision and very clean operations. ASMPT is now showing that a lead in this area is a lot less commanding than ASML’s position in EUV for front-end chip manufacturing. Robin Ng is proving this by securing rock-hard orders. The ASMPT CEO says he’ll start delivering hybrid-bonding machines to customers in the second half of this year. He also expects to be able to announce more at the next quarterly earnings report.

According to Ng, ASMPT is ready to deliver machines when mass production of chip system packaging with hybrid bonding really takes off. Asked for more detail, a spokesman for the Singapore company didn’t want to comment on a specific time frame. “We’re confident that we can eventually intercept the high-volume manufacturing ramp with our next-generation hybrid-bonding tools.” Clearly, for Besi, it’s back to basics in the bloody back-end equipment market.

ASMPT Lithobolt
ASMPT secured two orders for its Lithobolt system and expects more this quarter. Credit: ASMPT

Generous lead

ASMPT, like Besi rooted in Arthur del Prado’s ASM International, can’t afford to miss opportunities in advanced packaging. In the back end, it’s important to be able to serve customers with different types of machines that complement each other in packaging chips. The strategy of the major players is to offer a broad portfolio of systems, with which they can fill entire customer factories, so to speak. Ng stated that ASMPT would substantially increase its R&D budget for advanced packaging, including thermal compression bonding, photonics and hybrid bonding.

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Besi may have ASMPT in its rearview mirror, but the Dutch company still has a generous lead in hybrid bonding. While presenting the annual results, CEO Richard Blickman revealed that by 2023, it had won six new customers for these machines in addition to its three existing customers. A total of forty hybrid-bonding systems from Besi are now in the market.

The orders Besi scored in 2023 came from multiple customers, with a mix of first-generation machines with 150-200 nm accuracy and the new “One Plus” generation with 100 nm accuracy, according to Blickman. The latter systems have been with customers for six months, and their qualification has led to additional orders from four chip manufacturers and foundries, said the CEO. “Generation One and One Plus were split fifty-fifty among fourth-quarter orders,” he commented.

Besi also provides thermal compression bonding (TCB) equipment, with which it competes with market leaders ASMPT and Kulicke & Soffa. According to some experts, TCB is a good alternative to hybrid bonding. Like hybrid bonding, it connects bare chips. In the case of TCB, this is done by precisely pressing a pattern of thousands of contact bumps together under pressure and heat.

Top executive Blickman sees customers moving toward hybrid bonding in more advanced applications. “What we hear from customers is that they continue with their installed TCB tools when the bump pitch is above 25 microns.” The current state of the art in TCB is 35 microns, but Kulicke & Soffa thinks 5 microns is eventually achievable.

With the continued desire to miniaturize, both TCB and hybrid bonding must prove themselves in the coming years. Besi has delivered hybrid-bonding systems to customers who are gaining experience with bond-pad pitches smaller than 20 micrometers. Blickman: “The question isn’t whether we’ll get opportunities. We’re getting them.” The main question, according to the Besi top executive, is whether customers will shift to hybrid bonding or to dimensions that can be produced with more accurate TCB machines at the design stage of their systems.

ASMPT and Kulicke & Soffa expect customers to stick with the much cheaper and proven TCB for a while longer. The back end is traditionally very conservative, with a heavy emphasis on cost.

Side by side

Intel and TSMC are lead customers for Besi, but Blickman has especially high hopes for the future in the memory market. “The peak volume in high-bandwidth memory is potentially significantly higher than for logic,” he noted. According to him, that’s because there’s a high probability that manufacturers will deploy hybrid bonding for stacking DRAMs in HBM modules – the high-speed memory modules designed to provide information to GPUs and (AI) processors in data centers.

The current state of the art is generation three, HBM3. In the fourth generation, HBM4, the number of stacked DRAM chips will possibly increase to sixteen. Possibly, because SK Hynix, Samsung and Micron each follow their own approach and make their own system choices for the HBM modules. In any case, the interconnect density is increasing, so the likelihood of manufacturers switching to hybrid bonding for this is also increasing.

Until now, Besi counted only Micron among its customers, but it recently added a Korean memory chip manufacturer to the list. Blickman says his company and Applied Materials are currently conducting initial experiments with these customers at their test center in Singapore. He doesn’t expect the memory market to deploy hybrid bonding for first-generation HBM4; he believes generation two is more likely.

Blickman says the volume in HBM is potentially significantly greater than for logic once the hybrid-bonding market matures. “A ratio of one to four, one to six, it could even be more than that,” he told analysts at the announcement of the annual results.

It remains to be seen, however, whether Besi will play a major role in stacking DRAM memories in the HBM market. For NAND, manufacturers already use wafer-on-wafer hybrid bonding processes to connect entire wafers. That’s where EV Group already serves a significant market. EVG is also ASMPT’s partner for hybrid bonding.

EV Group testing
Just as Besi and Applied Materials act as partners, with the former taking care of component placement and the latter preparing the chips and wafers, ASMPT and EV Group are also working together. Credit: EV Group

In wafer-to-wafer, stacks of chips are only separated after wafer bonding. Such a process is more precise than die-to-wafer (in which Besi plays a role) where cut and cleaned chips are individually placed on a wafer. Hybrid bonding may play a role in placing DRAM stacks on a substrate or other chip if it helps to increase yield.

Investing in technology like hybrid bonding isn’t obvious in back-end semicon, as illustrated by the choices made by Kulicke & Soffa. This American company – second in the back end – is putting all its cards on TCB for now. It’s working with the University of Los Angeles to get the pitch of chip interconnects down from 35 microns – the current practice – to below 5 micrometers. Hybrid bonding achieves 10 microns in die-to-wafer processes. “We have a hybrid-bonding program, but we expect the market to be limited in the short term,” says Joe Elgindy, senior director of finance at K&S.

Eventually, many packaging technologies will be used side by side. Hybrid bonding won’t replace TCB; they’ll complement each other. Right now, system developers such as Apple, AMD, Nvidia and Intel are looking into both. It remains to be seen in what proportion foundries and logic and memory manufacturers will adopt the two interconnect options. That could also vary quite a bit from customer to customer. For example, AMD already uses hybrid bonding in its microprocessors, while Nvidia settles for TCB. Both technologies are still being developed. Hybrid bonding is a serious option if the pitch drops below 25 micrometers, but it’s more expensive.

Photonics

Current numbers show the health of different chip market segments to vary quite a bit. The AI hardware segment is steady, while the rest of the markets – computers, automotive and cell phones – are still failing. The results from ASMPT, Kulicke & Soffa and Besi reflect that.

The figures also show that Besi’s focus on the high-end is paying off. While the overall performance of its rivals remained flat year on year, Besi’s sales rebounded somewhat at the end of 2023 due to orders for its advanced-packaging machines. This has resulted in a 30-percent rise in the last quarter compared to the previous three months.

Besides hybrid bonding, the increase is fueled by higher deliveries of packaging systems for devices that are currently in high demand for data centers and AI. In Besi’s case, these are assembly machines for so-called 2.5D applications and equipment for connecting chips and photonic components. Besi also shipped its first flip-chip system for 2.5D assembly in the HBM market.

Machines for connecting optical components to chips remain somewhat underexposed in all the excitement about Besi’s position in hybrid bonding. However, this part of the company’s advanced-packaging portfolio is beginning to grow in importance.

In data centers, where heat management and energy conservation are hot topics, the need for optical communication is increasing. Not only because of the need for higher speeds but also because of increasing heat issues. With the introduction of fiber optics, it’s crucial to connect semiconductors and glass. This requires machines for assembling and positioning components such as lasers, photodiodes and transceivers with glass fibers.

In the photonic interconnect segment, Besi has strong competition from ASMPT, Kulicke & Soffa and small vendors. However, the Dutch company seems to benefit from its position in hybrid bonding here. Indeed, in addition to automotive, its photonics equipment is focused on putting together devices for data centers. Having a hybrid-bonding foot in the door there also gives it an edge in talks about providing photonic assembly systems.

Besi hasn’t responded to inquiries from Bits&Chips and High-Tech Systems Magazine. Main picture credit: Kulicke & Soffa