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Embedded Packaging Comes of Age
December 31, 1969 |Estimated reading time: 6 minutes
By Risto Tuominen, Imbera Electronics
The market emphasis on improved and growing functionality within smaller spaces in the electronics applications arena is straining existing semiconductor and system-in-package (SiP) packaging technologies. The need to increase the level of miniaturization while improving electrical and thermal performance and still maintaining a competitive manufacturing cost level sets an immediate challenge for system product innovation for both product designers and package engineers. This trend is clearly visible in telecom/handheld electronics applications, which can be seen as one of the major driving forces in today's electronics industry.
The evolution of electronics manufacturing from thru-hole technologies to today's sophisticated surface mount technologies included a tremendous amount of innovation and enabled the industry to improve packaging efficiency in a cost-effective way. During the past decade, a great deal of development has been completed in the area of 3D packaging where components or component packages are vertically mounted or stacked on each other. This has enabled improvement in packaging space efficiency on the board, but has sacrificed cost to sophisticated manufacturing processes. Today's volume packaging technologies provide robust and cost-effective manufacturing solutions, but, at the same time, the possibility to further improve capabilities is becoming more challenging. The electronics industry is constantly in search of new and revolutionary manufacturing technologies that would meet demands from high-end electronics applications and provide the next evolution of electronics manufacturing.
Several novel technology approaches are being developed to increase product miniaturization and performance. During recent years, component embedding inside PCB motherboards and substrates has generated attention and is seen as one of the most promising future technology solutions. Today, many of the technologies are under development or are used in limited volume production. For any technology to gain wide industry acceptance it needs to fulfill several demanding criteria, such as providing significant size and performance improvement compared to existing manufacturing solutions and showing an extended life potential. The process must be robust and provide consistent high yield levels early in any product production. The technology should be accessible easily for the customers without significant change in their supply chain, product structure, or design flow. A strong and credible value chain will support technology ramp-up and high-volume manufacturing. Also, the technology needs to be accessible through multiple service providers. For widespread adoption, the technology must be cost-competitive and provide further cost reduction once it has been used in high volume and the process has reached maturity.
Unless the technology can meet all these criteria, it is challenging, if not impossible, to gain wide acceptance in the electronics industry.
Integrated Module Board (IMB) TechnologyIMB technologies allow users to embed discrete components inside an organic, low-cost PCB motherboard or substrate. The current generation of this technology provides a flexible platform for multiple component types from low- to mid-range I/O-count components. Essentially, this technology fuses component packages with substrates or PCBs. The manufacturing process combines numerous separate production phases into a single process, enhancing overall efficiency and offering a range of new capabilities.
IMB technology originated in the Helsinki University of Technology in the late 1990s. The technology's feasibility and reliability was evaluated through functional and nonfunctional programs. In 2002, technology transfer brought the integrated module concept into the electronics manufacturing supply chain.* After initial technology development, it was used for commercial product prototyping and small-volume manufacturing. The next phase of integration into the electronics manufacturing process involves a multi-based volume supply chain to support high-volume manufacturing ramp-up.
The IMB manufacturing process (Figure 1) begins with a copper foil pre-treatment process where all the necessary alignment marks and microvias are manufactured into the foil. This is followed by nonconductive paste (NCP) printing and component alignment with a chip shooter line or flip chip bonder. The alignment method is selected based on the component interconnection pitch and related alignment accuracy requirement. Once the component is attached to the foil and the NCP cured, the component and pre-manufactured microvia alignment are fixed and no movement occurs between the host copper foil and its attached embedded component. This manufacturing method enables component-to-microvia alignment accuracy and provides a high interconnection yield. After the component attachment, a PCB core layer is build around the embedded components using standard PCB pre-preg materials such as FR-4, high-Tg FR-4, or BT epoxy. The pre-pregs are aligned and pressed with heat, vacuum, and pressure.
The PCB core must be designed to provide a minimal stress structure for a planar substrate with no warpage. Also, the cavity around the components must be filled completely with the epoxy to ensure that no voiding or delamination occur around the embedded component. At this phase, the IMB core layer structure resembles a standard PCB core with a copper layer on both surfaces. Thus, the IMB core patterning can be manufactured with existing standard PCB build-up technologies. Depending on the product and component complexity, and the I/O count, several build-up layers can be manufactured to enable sufficient routing capability. A subtractive or semi-additive PCB patterning process is possible, based upon the conductor line and space requirement of the product.
Throughout this manufacturing flow, standard high-volume processes, materials, and equipment are used. This enables robust and high-yielding manufacturing process, a wide supply base with existing solutions, and infrastructure to support volume ramp-up with an associated competitive manufacturing cost level. The IMB process was proven in standard testing specifications in telecom motherboard and semiconductor packaging.
ApplicationsIMB technology provides a flexible and robust platform for various component types. The technology does not have a thickness requirement and can be used with standard discrete passive, IPD, Si, and GaAs components. The embedded core typically is less than 250-µm thick with component thicknesses from 50 to 150 µm. To fabricate a reliable IMB interconnection, the component needs to have minimum of 3-µm copper or gold bump.
The objective of embedding a component inside the substrate can vary significantly from application to application. Common drivers to embed are further product miniaturization, surface space savings, shortened conductor length with improved electrical performance, and improved thermal performance. Freedom in a module design enables the integration of a Faraday's Cage (EMI shield), short conductor length between embedded and surface mounted component, full array of solder lands on back side of the package (as in package-on-package PoP) and localized thermal via structures to cool down the system efficiently.Figure 2. Sample package types that can be embedded with IMB processes
While the technology suits any sector of the electronics market, in the near term the main focus is technology adoption in consumer electronics applications, particularly mobile devices. Product complexity can vary significantly depending on the embedded component type and the required PCB structure. Some options include typical SiP-type of modules with multiple components, system-in-board motherboards, and single IC packages such as iQFN and iBGA packages (Figure 2). Product categories are described in more detail in Table 1.
Conclusion Component embedding technologies provide a necessary third plane a robust and cost-effective way to improve product performance and miniaturization. Several technologies have been developed over the years for embedding components, though few have gained wide market acceptance due to technology limitation, a high total cost of ownership, and a nonexistent supply base.
The IMB concept meets the demanding criteria of providing reliable, high-yielding technology improvement without sacrificing the total cost of ownership. Also, the technology offers a flexible platform that can be used for wide variety of components and applications. The next step in technology rollout will include a high-volume supply of the process, with dedicated embedded systems manufacturing operation.
* IMB technology was transferred to Imbera Electronics, where a third-generation of the IMB process was developed in 2004.
Risto Tuominen, CTO, Imbera Electronics, may be contacted at www.imbera.fi.