Already well known as a key enabler of system-in-packages (SiPs), IPDs enable the assembly of increasingly complete and autonomous systems with the integration of diverse electronic functions such as sensors, RF transceivers, MEMS, power amplifiers, power management units, and digital processors.

“The categories and applications for IPD will continue to evolve, especially as TSVs become available to provide vertical interconnections within the IPD, then new applications like silicon interposers will become increasingly significant to the market. Many providers think of silicon interposers as a way to provide for a new package substrate with a higher routing density. The fact that some capacitors can be integrated into silicon interposers will only make it more powerful, where the capacitor is even closer to the IC within the package. The ‘decoupling loop,’ which is the distance from the capacitor to the to-be-decoupled IC, will be considerably reduced and the decoupling’s effect will be much greater to resolve power integrity issues—especially with high-frequency digital applications.”

Many players in the IPD market

There are a lot of players involved in the IPD market. It was one of the things that surprised Yole analysts during their research for the IPD report. It’s not a large market, yet there are many players. “Everyone seems to find IPD very promising and want to make sure they’re ready to take an active role in the market,” says Yannou. “There’s a wide variety of IPD manufacturers—some are IDMs, IC makers, while others are OSATs. There are a few traditional discrete passive component suppliers, and even a few IPD-dedicated companies. The ESD/EMI submarket is already a mature one, so there are very established players in that area.”

When Yole compiled a world map of the IPD players for its report, they were also surprised to find that Europe leads the way in terms of IPD manufacturers and users. According to Yannou, it appears that 50% of IPD players are in Europe, followed by 25% in the U.S., and 25% in Asia.

What applications are driving the IPD market?

The IPD market is being driven primarily by RF or wireless packages and applications including, but not limited to, cell phones, WiFi, GPS, WiMAX, and WiBro, notes Seung Wook Yoon, deputy director of technology marketing at STATS ChipPAC (www.statschippac.com; Singapore). “In particular, applications and products in the emerging RF CMOS market that require a low cost, smaller size, and high performance are driving things,” he adds. “Other promising market applications include ESD/EMI protection, mixed-signal applications, MEMS, and miniaturized microsystem applications.”

Handheld multimedia applications such as smartphones are the key drivers, as seen by Amkor Technology (www.amkor.com; Chandler, Ariz.) at this point. “They demand high levels of integration in small form factors in high volumes that promise to drive IPD cost down for adoption in other applications where silicon/package integration can provide cost and performance benefits,” explains Lee Smith, vice president of product marketing at Amkor.

ASE (U.S.) Inc.’s (www.aseusa.com; Santa Clara, Calif.) John Hunt, director of engineering, and Andy Tseng, director of technical marketing, are also seeing the IPD market being driven increasingly by RF modules. “As SiP integration becomes mainstream, more and more passive devices that were originally in chip and PCB are being integrated into the package—offering clear benefits such as size reduction and performance improvement,” Hunt elaborates.

Challenges

There are some cost issues associated with IPDs, however, which has slowed their adoption. In many cases, IPDs are still more expensive than discrete passive devices. Yannou believes that the value proposition for IPDs needs to be based on smaller size and thickness advantages, better electrical performance, as well as thermal and reliability performance to compete with the mainstream passive industry.

Since it’s not a standardized industry yet, there are some manufacturing challenges in terms of setting up the supply chain. Yannou points out that there aren’t standard IPD devices—most of it is custom design. When a customer wants an IPD they work on the design with the IPD supplier, it’s not off-the-shelf, so it can occasionally be problematic to find someone to design it.

Other manufacturing challenges include materials and process standardization, library component development, correlation between design and IPD performance, and integration of TSV IPD, according to Yoon.

And Smith points out that higher capacitor density at a lower manufacturing cost is critical. WLP lines require increased R, L, C density with improved defect density/yields.

The bottom line, according to Hunt and Tseng, is that cost is the biggest challenge currently facing IPD manufacturing.

IPD-dedicated technologies

It’s still difficult to define “dedicated” IPD technologies, however Hunt says the industry is becoming increasingly aware that IPD has higher Q value and performance compared to system-on-chip (SoC)—and it’s easily integrated and provides strong cost benefits.

Wafer-level chip-scale packaging (WLCSP) and wafer supply for die stacking with mixed-signal ICs are the primary packaging technologies used with IPDs, says Smith.

“IPDs can be made by integrating the silicon, glass, GaAs, and attaching to laminate substrates,” Yoon says. “IPDs made on silicon substrates have shown performance, as well as cost advantages. IPD is already being dedicated to SoC for RF applications and the trend will continue and expand to fan-out WLP where the IPD can be integrated into the layers built on the reconstituted wafer or panel. IPDs embedded into substrates could also emerge as a dedicated technology.” The drivers are, as always, cost and size.

Influence of WLP/TSV technology platforms

TSV technology should help IPD technologies become “real” alternatives for packaging—not only for integration of passive devices, but also for packaging.

“When you look at the main packaging platforms today, the organic substrates are already 3D, they have through-vias,” explains Yannou. “The same is true for ceramic substrates like LTCC or HTCC. But even if they are a good fit for IPD and routing horizontally, they don’t have the vertical interconnection feature only achieved with TSVs. Thanks to TSVs, the value proposition of IPDs will be greatly reinforced. We can expect more IPDs within RF SiPs, and also imagine stacking any kind of IC on top of an IPD within a wafer-level package type of configuration. TSVs will likely be a key enabler for silicon interposers with embedded decoupling capacitors. That’s key for the successful takeoff of IPD technology.”

Discrete passive components are still primarily used in electronic packages and products, but thin-film IPDs can provide significant advantages and be extended to use in WLP and TSV packaging technology moving forward, creating high-performance RF/wireless packaging solutions,” Yoon says. “In addition, TSV IPD interposers can add value to advanced logic solutions and help translate the interconnect pitch of advanced fab nodes to lower-cost laminate substrates, cost effectively. The advantages are electrical performance, less power consumption, and lower cost in smaller form factors,” he adds.

IPDs are fabricated in both mature IC fabrication lines and new WLP/bumping lines, notes Smith. However, the integration of active circuits like diodes requires IC fabrication processes. “Deep trench capacitors are in use for high-capacity density IPD requirements that use the DRIE and thin-film process technologies required in TSV fabrication,” he elaborates. “True TSV interconnects may be too costly and design-limited for IPD requirements until IPD-to-IC interconnect standards are in place.”

Hunt and Tseng believe thin-film IPDs will be integrated into multiple platforms—focusing on providing strong size, cost, and functionality benefits.

Future roles for IPDs

In the future, Yoon expects to see IPDs find applications in low-noise amplifiers and power amplifiers that need to work with multiple frequencies with higher performance driven by 3G and WCDMA adoption in wireless communication. He points out that IPDs can be packaged as side-by-side with other active ICs in one package, stacked IPD solutions (wire bond or flip chip), integration of IPD in fan-out WLP, IPD integration in MEMS, IPD embedding in laminate substrate and IPD is used as the package substrate.

3D packaging and 3D IC technologies will also help expand the applications for IPDs into high-performance requirements where IPDs are integrated in silicon substrates that provide an interposer between ICs, Smith says.

The many possible future uses for IPDs includes modules, RF, power amplifiers, etc., according to Hunt and Tseng.


Timing for IPDs

We should begin seeing interposers without anything embedded, just TSV, with the routing on the front side and the back, become available by some suppliers as early as 2010. But when it comes to integrating the TSV with components, Yannou thinks that’s another technical challenge that should take another two years—putting us at 2012.