3D Power Packaging (3DPP®) Advancements

What is three-dimensional power packaging (3DPP^®)?

Maximizing system performance in practically any market or application space in the electronics world tends to be highly-dependent on the power subsystem, which includes all power supplies, power conversion devices, filters, protection devices, and interconnects (connectors, wires, cables, circuit board traces, or otherwise). Hence the focus and characterization on the size, weight, and power metrics (a.k.a. – SWaP factors, SWaP-C when combined with cost metrics) [1].

One of the best tools in the toolbox of the perpetual pursuit of optimizing SWaP-C is in advanced packaging techniques, particularly in the area of three-dimensional power packaging (3DPP). 3DPP is a new offering of cutting-edge assembly processes allowing for maximum power density and minimal footprints. When applied to surface-mount DC/DC converters, 3DPP enables solutions that combine best-in-class performance with maximum power density and minimal footprints. This results in power products that are significantly smaller than other power conversion modules and still highly efficient without the costly footprint [2].

3DPP technology eliminates the need for an internal printed circuit board (PCB) by mounting intrinsic components directly to a lead frame, thereby reducing the amount of space required by the conversion components within the module. As an order-of-magnitude example, one of the newly available 3DPP switching regulator products – the RPX-1.0 – is only 3 mm x 5 mm x 1.6 mm making it nearly as small as an integrated circuit (IC).

This reduction in size allows engineers and designers to have more streamlined PCB profiles with integrated power conversion without pursuing costly, custom converter design. 3DPP-technology-enabled devices are available in several package types including land grid array (LGA), gull-wing, quad-flat no-leads (QFN), blocks-and-pillars, and solder balls, which can make a world of difference in space-constrained applications.

RECOM provides an excellent overview of the value propositions and latest offerings in this regard [3]. The figure below is an example of the evaluation solutions provided to simplify bench testing and accelerate getting product to market.

Enabling the Miniaturization of DC/DC Converters

To better understand how 3DPP and other advanced packaging techniques drive continuous miniaturization of DC/DC converters, it is prudent to dig a little deeper into various packaging practices along with advancements in component technology.

Combining previously disaggregated components into a single assembly is not a new concept, but the methodologies have advanced greatly over the last couple decades. In power solutions, an integrated module typically referred to a classic, discrete implementation with components tightly-packed on a thin piece of FR-4 (a.k.a. – PCB), then covered with some kind of plastic or metal cap. The caps were mostly for aesthetics to give the illusion of being a single, IC-like assembly though the metal cap could also serve a practical purpose in terms of electromagnetic interference (EMI) and/or thermal mitigation.

Then along came a push for actual process integration of all these disaggregated components into what is now known as heterogeneous integration. A definition of heterogeneous integration from the Institute of Electrical and Electronics Engineers (IEEE) Electronics Packaging Society (EPS) Heterogeneous Integration Roadmap (HIR) is as follows –

“Heterogeneous Integration refers to the integration of separately manufactured components into a higher level assembly that, in the aggregate, provides enhanced functionality and improved operating characteristics.” [4]

The HIR was the culmination of numerous stakeholders, industry leaders, and proceedings from workshops and conferences characterizing the state-of-the-art (SOTA) in this space. While a comprehensive overview of this effort is outside the scope of this blog article, a handful of key drivers specific to power converters/solutions is noteworthy here. Recall the push for optimizing SWaP factors as outlined up at the beginning of this discussion. While the desire to reduce size/weight may be more tangible, the drive for increasing power density and the strategies for accomplishing that goal may be less obvious.

In most switching power topologies (i.e. – those using carefully-controlled switches to modulate power conversion from one voltage to another), the key figure of merit (FOM) driving size is related to the switching frequency of the power converter. In order to avoid outlining a series of equations charting the mathematical relationships between converter design/component calculations and switching frequency, which a simple Google search will yield copious amounts of input on, there a couple rules-of-thumb to consider here. Switching frequency is inversely proportional to the size of energy storage and filter components (i.e. - transformers, inductors, toroids, chokes, bulk/electrolytic caps, safety caps, etc.), which often dominate the overall size/weight of power supply (and even be a primary contributor to whole system size/weight).

Parasitic effects of inductance from longer interconnects and fast current transitions [v(t)=L*di/dt] induced by higher switching frequencies can cause catastrophic voltage spikes (a.k.a. – transients) to a converter’s control scheme and/or power train. Parasitic effects of capacitance from the natural separation of conductors in a system and fast voltage transitions [i(t)=C*dV/dt] induced by higher switching frequencies can cause catastrophic energy storage and circulating currents that can rear their ugly heads in any number of undesirable ways.

The growing use of wide bandgap (WBG) power semiconductors (i.e. – gallium nitride or GaN, silicon carbide or SiC, etc.) in power electronics designs provides the best and worst of both worlds. WBG devices have the ability to offer significant increases in switching frequency along with greater thermal FOMs (enhancing reliability and power density), but may also come with a steep learning curve that complements their improved power density FOMs. While out of the scope of this blog, it should be noted even just the gate driver circuits for WBG devices can be far more complex due to increased switching speeds and transients that are a departure from the design rules for traditional, silicon power semiconductors [5]. An excellent overview and reference to such challenges can be found in our whitepaper "DC/DC Converters for GaN Gate Drivers". Though certainly a deeper topic for a future discussion, it should be noted advancements in high-frequency magnetics materials are a critical enabler for WBG-based solutions and have received focused attention in the last decade due to a research gap in this space (reference some free workshop proceedings at the bottom of this website).

Now that there is a much better understanding of the need for reducing package size, packaging-induced parasitics, and support for the SOTA in semiconductors, the focus can shift to other components that can be beneficial and enabling to heterogeneous integration in 3DPP products. Shrinking the overall power solution also means shrinking the other active (i.e. – ICs, switches) and passive devices (i.e. – resistors, capacitors, inductors, diodes) and bringing them closer together by embedding them in a heterogeneous arrangement. At some point, even the internal package interconnects (i.e. – pins, bumps, pads, etc.) become prohibitive and induce undesired parasitics. There are numerous technologies that allow the embedding of both passive and active devices. While not deep-diving here, it should be noted the utilization of planar magnetics has been hugely enabling. This refers to the transition of a traditional magnetic, with wiring physically wound around a bulky magnetic core, to using PCB traces routed around magnetic core material for a much cleaner, tightly-controlled, yet repeatable and robust magnetic component. [6]

As with any major technology evolution, numerous challenges must also be worked out. Combining many, traditionally disaggregated manufacturing processes requires an adaptive supply chain and learning curve. Subassemblies may require extra process steps, and therefore perhaps trips to different locales, and/or processed may be combined into consolidated operations in which process cannibalization may have learning curves and associated operator training for the newer aspects.

As with any process shift in manufacturing comes the rippling changes both up and down the chain, which can include component/consumable processing, new capital equipment, tighter environmental controls, enhanced quality management system (QMS) oversight, functional testing, inspection/rework, hazardous material handling/disposal, etc.

As the ol’ adage goes, “nothing comes for free.”

Improving Thermal & Power Density FOMs

The reliability, and therefore operating life, of electronics revolves around the system’s ability to regulate the local environmental and component temperatures. While temperature is certainly not the only factor governing quality metrics (i.e. – min/max/derated operating temperature, mean time between failures or MTBF, mean time to failure or MTTF, failures in time or FIT rate, etc.), keeping electronics “thermally happy” is always a good strategy for a robust product life that meets the intended operating parameters and lifetime.

3DPP can introduce some thermal challenges by squeezing stuff in closer together. This can be in the form of radiant heat from adjacent devices affecting its neighbors, though the ability to trap this heat can be reduced by simply removing the empty space in an otherwise larger assembly. After all, air is an excellent insulator (both thermally and electrically). A significant thermal challenge in any system that combines heterogeneous materials can come with trying to balance out different coefficients of thermal expansion (CTE) [7]. This challenge is particularly pronounced in the heterogeneously integrated assemblies described above that yield the biggest challenges of all the previously separate processes, combining metals, ceramics, fiberglass, various inks, glues/adhesives, and other materials in one big sandwich. As if that does not sound challenging enough, this blog will not even dare to broach the impact of these factors in flexible hybrid electronic (FHE) assemblies!

Conversely, 3DPP also (and generally more so) provides opportunities for getting the heat away from the source and transferred to where it can be mitigated quicker and more efficiently. The ability to mitigate external pins and directly attach surface-mount device (SMD) power modules to PCBs is a victory for thermals and quality (e.g. – fewer issues with manually-inserted pins, solder joints, etc.). As the figure below shows, high power density is achieved with a multilayer, internal PCB, which utilizes plugged and blind vias for good thermal conductivity and efficient use of the available space.

Getting the heat out of the package more efficiently also facilitates the ability to spread it out to larger thermal masses (i.e. – system power planes, larger copper pours, adjacent assemblies). From the external side of the package, system-level thermal mitigation (i.e. – heatsinks, convection or forced-air cooling, water-cooled baseplates, thermal interface materials or TIMs, etc.) can also be utilized more effectively.

The Value of 3DPP in Critical Applications

It is difficult to capture all the benefits and enhancements 3DPP can bring to a product line in a short blog. Though many have been tabled here, there are some factors that move the needle for critically-important factors.

It is rare to meet any stakeholder in the world of electronics that has not been impacted by supply chain issues, whether it be assurance of supply, raw material sourcing, counterfeits, tariffs, shipping logistics, or otherwise. As the recent COVID pandemic showed us, even end-consumers now have greater awareness of how all these issues, seemingly so far away, can impact inflation via the cost of the car they buy or the food on the shelves at the grocery store.

In mission-critical applications, the process consolidation organically brought on by the use of 3DPP technologies can help to mitigate a lot of the risks and headaches listed above, where there is a lot less margin for error. Not only does the incorporation of more processes into a single manufacturing operation force groups like Procurement, Enterprise Resource Planning (ERP), and Quality/Component Engineering to sharpen their pencils, but it also forces more collaboration and thinking beyond the first order to ensure collaborative success. These points can really come through in catastrophic situations (i.e. – acts of God, political unrest, etc.) when the business continuity plan (BCP) must be set in motion to transfer operations between factories (perhaps even countries) as fast as possible.

With consolidation of processes and supply chain management also comes a reduction in overhead and logistical costs. The tighter control and automation applied to the assembly and manufacture of components (especially magnetics) leads to improved product reliability, WHILE applying economies of scale, which is a great recipe for driving SWaP optimization and year-over-year (YoY) cost reduction.

Medical equipment (and similar use cases with high isolation/safety requirements) are an example of a critical application in which 3DPP can add a lot of value. Safety-certified, medical-grade isolation is required to different degrees as classified by levels of means of operator protection (MOOP) & means of patient protection (MOPP) [8].

An example of a DC/DC converter that achieves a high level of medical-grade isolation combining all the 3DPP benefits described here is the recently released R05CT05S from RECOM. This is an economical, 0.5W part with 5V nominal input and selectable outputs of 3.3V or 5V, alternatively 3.7V or 5.4V, to provide head voltages for low-drop-out regulators (LDOs). The converter is in a compact 10.3mm x 7.7mm SMD package just 2.65mm high for space-constrained applications.

The product’s highlight specification for medical applications is its 2 x MOPP / 250VAC continuous rating according to IEC/EN 60601-1 with 5kVac test voltage. It also has just 3.5pF coupling capacitance, for negligible leakage current in 250VAC / 50Hz applications. In non-medical applications the ratings are even more impressive – reinforced isolation at 800 VAC working voltage according to EN 62368-1. Operating temperature is up to 140 °C with derating and the part features enable, sync and trim functions along with an undervoltage lockout. [9]

It should be noted these value propositions can also be extended to non-critical systems that still require low-power isolation for applications like external communication ports such as with a Controller Area Network (CAN-bus), Universal Serial Bus (USB), or Power over Ethernet (PoE), which are ubiquitous in automotive, computing, and consumer application spaces.

Conclusion

Packaging may not always be the first thing that comes to mind when considering the future of electronics roadmaps, but as this blog has reviewed, there are numerous and significant performance and quality factors tied directly to packaging.

3DPP and heterogeneous integration are yielding evolutionary improvements in packaging and therefore nearly all the top priorities when it comes to optimizing SWaP-C at the power solution and overall system levels.

Want to test out 3DPP-enhanced solutions to see the difference it can make in a design? Feel free to contact RECOM (info@recom-power.com) to get your hands on these products and start accelerating SWaP-C improvements on your product roadmaps today!

References

[1] “Power Supply Design for maximum Performance,” RECOM Blog, Oct 21, 2022, https://recom-power.com/rec-n-power-supply-design-for-maximum-performance-229.html (accessed January 23, 2023).

[2] “Introducing RECOM 3D Power Packaging® (3DPP),” RECOM Blog, Feb 26, 2021, https://recom-power.com/rec-n-introducing-recom-3d-power-packaging-(3dpp)-145.html (accessed January 23, 2023).

[3] 3D Power Packaging® for Low Power DC/DC converters, https://recom-power.com/3dpp.html (accessed January 23, 2023).

[4] “Heterogeneous Integration Roadmap,” IEEE Electronics Packaging Society, updated 8 Feb 2017, https://eps.ieee.org/technology/heterogeneous-integration-roadmap.html (accessed January 23, 2023).

[5]“DC/DC for GaN,” RECOM Blog, Sep 16, 2022, https://recom-power.com/rec-n-dc!sdc-for-gan-225.html (accessed January 23, 2023).

[6] PSMA Packaging Committee, “3D Power Packaging With Focus on Embedded Passive Component and Substrate Technologies,” PSMA 3D Power Packaging Phase III, Power Sources Manufacturers Association (PSMA), February 2018.

[7] Wikipedia contributors, "Coefficient of thermal expansion," Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/wiki/Thermal_expansion#Coefficient_of_thermal_expansion (accessed January 23, 2023).

[8] Wikipedia contributors, "Means Of Protection (MOP)," Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/wiki/Electrical_safety_testing#Means_of_Patient_Protection_(MOPP) (accessed January 23, 2023).

[9] “Advanced power packaging enables medical isolation in DC/DC converters,” RECOM Blog, Mar 12, 2021, https://recom-power.com/rec-n-advanced-power-packaging-enables-medical-isolation-in-dc!sdc-converters-144.html (accessed January 23, 2023).