Old Vs. New Packages

Two packaging technologies are making microchips smaller and more durable.

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Over the years, the semiconductor industry has witnessed a parade of packaging innovations, such as system-in-package, semiconductor embedded in substrate, and fan-out wafer-level packaging.

Two interesting packaging innovations are now being used in the process of miniaturizing microchips and electronics. One is a new concept that combines two tried-and-true technologies. The other is a decades-old technique that is being used in new ways.

Keeping dirt, humidity, air, even atmospheric pressure away from electronics is what hermetic packaging and sealing processes have done almost since the age of dinosaurs–for more than 75 years, predating the transistor and the integrated circuit. The process of hermetic packaging and sealing puts an impenetrable layer around electronics that keeps air (gas) and water vapor away from electronic parts, making them air- and water-tight, thus protecting them from corrosion and other environmental hazards.

New developments in hermetic packaging and sealing are now making faster, lighter, and smaller electronics possible.

Any technology that helps cram in more components without sacrificing functions is also welcome to handset manufacturers. Another technology front in the quest for greater miniaturization is the substrate-like printed circuit board, or SLP. It represents a cross between a flexible substrate and a rigid board.

The SLP shows up only in smartphones now, but it may be used in IoT devices and eventually AI applications, augmented and virtual reality devices, and automobiles. One of the big advantages is the flexibility of not having to choose between a PCB or substrates.

Substrate-like PCBs
Substrate-like PCBs were employed in assembling the iPhone 8 models and the iPhone X, according to Yole Développement, which describes the technology as “a clash of two worlds,” PCBs and substrates. SLP could prove to be an alternative to modified semi-additive processes, also known as mSAP, according to Yole.

“Advanced substrates must answer demands on both the scaling and functional roadmaps,” writes Emilie Jolivet, a technology and market analyst at Yole. “The transition from the subtractive to the mSAP process and from PCB to substrate-like PCB is under way in high-end smartphones, driven by Apple and its iPhone 8/iPhone X. Other high-end smartphone suppliers, such as Samsung and Huawei, are expected to join in the near future.”

SLP will have to contend with other technologies, namely package substrate vs. no substrate with fan-out platforms, along with through-silicon via packaging vs. TSV-less packaging.

Yole forecasts the SLP market will increase from $1.9 billion in 2016 to $2.24 billion by 2023.

“The 28 selected PCB/substrate manufacturers are all believed to have mSAP technology, and some of them can manufacture SLP,” said Yole’s Vivienne Hsu. “Driven by high-end smartphone demand, certain players appear to have high capital expenditures. Meanwhile, some large players show steady revenue in their PCB/substrate business.”

Seung Wook Yoon, director of group technology strategy for the JCET Group, the parent company of STATS ChipPAC, describes SLP as “a game changer for the industry.”

SLP could mean that outsourced semiconductor assembly and test (OSAT) customers won’t have to choose between PCBs or substrates for their products. He expects Samsung to follow Apple’s example.

Fan-out wafer-level packaging is for high-end application processors going into premium products, the flagship smartphone models for handset vendors, according to Yoon. SLP is meant for the motherboard of phones, reducing the space needed for such assemblies. Ball grid arrays or flip-chip packages are more typically used for fine-pitch slots in a phone, he noted. Wafer-level packages offer even finer pitches.

He likened SLP to chip-on-board packaging.

Printed circuit boards are progressing to the point where they can offer integration in addition to interconnection, according to Yole. Yoon echoed that observation. “This is mainly for the integration,” he says.

While the first noteworthy implementation of SLP is in mobile phones, such advanced semiconductor packaging could also find applications in 5G wireless communications, artificial intelligence, augmented and virtual reality, automotive electronics, and Internet of Things devices.

When it comes to advanced packaging, system-in-package technology and modules are other leading space-saving innovations, Yoon notes. “The cost may be higher,” he says.

He sees SLP possibly being used in IoT devices, in addition to mobile phones. Reducing the cost and the size remain the prime considerations.

Hermetic packaging and sealing
Hermetic packaging and sealing, meanwhile, is already ubiquitous. It is used in automotive electronics, aerospace and aviation systems, optical communication components and system for fiber-optic data telecommunications, sensor manufacturing, and other industrial applications. The airbag igniter in automobiles is one example of hermetic packaging.

“It’s hard to pinpoint just one overarching trend,” said Robert Hettler, head of R&D for optoelectronics at SCHOTT Electronic Packaging, a unit of SCHOTT North America and Germany’s SCHOTT AG. “However, there are a number of trends within various markets and applications.”

Higher precision is one of them. The world’s ever-growing hunger for data and faster transmission rates has increased demand for higher-performance chips.

“Faster chips need reliable, high-performance hermetically sealed packaging to achieve ever-faster data rates. The so-called ‘last mile’ to the customer, which covers fiber transmission lines to the home, would be unachievable without a new generation of high-performance, high-precision hermetic packages,” says Hettler. “SCHOTT recently introduced 50G hermetic transistor outline can packages, which can pave the way for much-needed bandwidth increases on datacom networks. 50G transistor outline (TO) technology will also enable faster data transmission to wireless cell towers, providing a technology that will be used to deploy 5G cellular networks, an improvement that will deliver speeds exponentially faster than current 4G infrastructure.”

He also cites the variety in materials used for hermetic packaging and sealing.

“On a material level, there has been an increase in demand for the use of non-magnetic materials, like titanium and niobium, which are interesting materials for a number of high-reliability applications. Glass-titanium compounds are especially well-suited for use in the areas of aviation, aerospace, oil and gas, and medical technology — if non-magnetic yet lightweight housings are needed. Alternatively, nickel-copper alloys are ideally suited for chemically aggressive environments due to its acid and alkali resistance,” Hettler says. “In medical electronics, the trend toward implantable devices is also leading to an increase in demand for the use of biocompatible materials like titanium and tantalum. Here, the development of highly reliable, yet more and more miniaturized hermetic packaging is of the essence. The development of glass-to-aluminum sealing technology now enables the manufacture of hermetic feedthroughs made with aluminum. This material is highly interesting for applications in which there is a need for lightweight materials or where aluminum is typically used for the casing, such as supercapacitors, electric double-layer capacitors, and lithium-ion batteries. Newly developed aluminum lid systems with hermetic glass-to-aluminum sealed feedthroughs support higher or longer-lasting performance of capacitors and batteries.”

Miniaturization in modern-day electronics is a priority, and hermetic packaging and sealing can address that need.

“Miniaturization in hermetic glass-to-metal and ceramic-to-metal sealed packages is a main point of focus,” he says. “Increasing application demands, particularly for smaller and smaller form-factor components, have made miniaturization a key topic in product innovation. A particularly relevant example can be found in the fiber-optic arena as TO packages for high-speed data transmission have been reduced in size for new, cutting-edge applications: in the development and transition from TO56 to TO38 packages, the footprint shrank by nearly 33%. Besides miniaturization of hermetic glass-to-metal and ceramic-to-metal packaging, full-ceramic multilayer housings and substrates experience increased interest. Multilayer ceramics support the growing trend towards miniaturization, cater for enhanced complexity requirements but also offer excellent thermal management properties: The multilayer design enables the production of miniature 3D interconnect solutions, paving the way for high-density input/output capability in small-form-factor hermetic packages for both feedthroughs and multilayer ceramic circuit board substrates. Superior thermal conductivity of high-temperature co-fired ceramics and temperature resistance beyond 300 degrees Celsius (572 degrees F) make HTCC substrates a perfect fit for high-power applications.”

How is hermetic packaging and sealing being used today?

“The most popular uses for hermetic seals vary widely across many different areas,” Hettler says. “Some of the most notable uses include fiber optics and high-speed data transfer, automotive safety systems and other components, and pressure sensor feedthroughs and packaging applications. In the defense, aviation, and aerospace industries, hermetic housings and connectors are often used to protect reliability-critical control and instrumentation electronics.”

Microelectromechanical system devices are one area where hermetic packaging and sealing are required, not just a technology that’s good to have in certain applications.

MEMS are sensitive and fragile components that are often placed in harsh environments, or in places in which replacement is expensive and inconvenient. Hermetic packaging and sealing provides reliable protection that can help prolongate the lifetime of these devices,” he says. “For example, SCHOTT HermeS glass wafer substrates with hermetically sealed solid metal through-glass vias enable miniaturized yet highly reliable and robust 3D wafer-level chip-scale packaging. The fine-pitched vias allow the reliable conduction of electrical signals and power into and out of the MEMS device. The use of glass wafers in hermetic packaging has increased rapidly in recent years. The core reasons are the superior properties glass offers as a packaging material in particular, including its biocompatibility, the excellent transparency to radio frequencies and the transparency to visible light, which enables a wide range of optical applications. TGV technology enable long-term, reliable and extremely rugged packaging of industrial sensors, RF MEMS, and medical electronics.”

Conclusion
Achieving ever-advancing miniaturization in microchips and electronics can call for a variety of new packaging technologies. Then again, tried-and-true approaches, such as hermetic packaging and sealing, can also fill the bill.



2 comments

Michael Mingliang Liu says:

Hermetically sealed packages are usually MSL-1 graded and therefore rather costly to qualify and mass produce; especially at larger package sizes.

Moreover, at microwave frequencies, expensive add-on’s such as gold-plated and/or glass pass-through pins are often warranted around the package, due to signal-integrity requirements.

For a less stringent MSL grade (e.g. MSL-2a or MSL-3) at a relatively lower manufacturing cost than that of a hermetic seal’s, the OSAT may consider applying B-stage epoxy, which is a system where the reaction between resin and curing agent is, by design, made incomplete.

Due to this incompleteness, the system is kept in a partially cured stage (i.e., B-stage), until when the time comes for the system to be reheated at elevated temperatures. That is, the reaction between resin and curing agent is “revived” and made complete. As a result, the system fully cures.

With key feature-benefits such as the ability to precisely control both bond line thickness and placement location of the adhesive material, and the flexibility of implementing “pick-and-place” instead of dispensing operations in a real-time production environment, a B-stage epoxy system can be tailored to sealing various lids made of LCP, ceramic, metal or glass, to ceramic, metal, or even organic substrates, all the while maintaining a high moisture vapor resistance, along with a helium leak-free sealing performance (a.k.a. a near-hermetic sealing).

In a nutshell, a B-staged epoxy is a solid form of uncured epoxy. This intentional staging of deposit-then-cure processes can significantly enhance the logistic flexibility for the OSAT (either through timing of process steps or handling of assembly materials; at multiple stations or facilities), with an ultimate goal of maximizing production (packaging) yield and promoting efficiency for a near-hermetic seal.

HRH Prince Sven Olaf Kamphuis says:

we don’t care about ‘smaller and more components on the chip’. nobody ever asked for 3.3v or lower smd stuff. some manufacturers just made that up on their own. we just want 5 volt dip stuff in mil spec ceramic packages rated -40 to +125C operating temperature, running a parallel bus, like before. it’s stable, it works for centuries, and it ends up in metal cases that are at least half a cubic meter big anyway, so who cares about ‘size’ or ‘weight’. we don’t even actually care about ‘price’. stuff should be designed to last -forever-. not merely held together by some traces on the outside layer of the pcb.

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