New-Tech Europe Magazine | Q1 2021

3D Power Packaging for Low Power DC/DC converters

Matthew Dauterive, DC/DC Product Manager RECOM

Low power non-isolated DC/DC switching regulators and isolated converters need to be cost-effective, despite ever-increasing demands for better performance and improved power density. Manufacturers have responded over time with many form-factors that leverage low cost manufacturing, often with a minimal component count with transformers and inductors hand-soldered to traditional PCBs. Tominimize the PCB footprint, through-hole SIP versions are often used, though they can complicate the assembly, requiring mixing of wave, or even hand soldering with the reflow process for the other SMT components used on the board. Although millions of this style of through-hole DC/DC converter are sold each year, a long-term goal for RECOM has been to develop versions which can be handled,

placed and soldered like any other modern SMT component, but also with a low profile to match today’s slim-line products. However, the footprint must still remain small to realize the advantages of a module over a discrete design. To achieve this, non-isolated DC/DC switching regulators and isolated converter modules have to utilize the Z direction by integrating 3D assembly techniques. The evolution of low power surface-mount DC/DC packaging The first SMT DC/DCs on the market were simply versions of potted through-hole types with the leads bent into ‘gull-wing’ shapes. These could not withstand a regular reflow soldering profile, so often still required hand assembly. A natural progression was to switch to a

package using an internal leadframe with high melting-point solder joints which was then injection- molded with material that could withstand IR-reflow temperatures. However, lead-free soldering raised peak soldering oven temperatures to over 300°C, causing difficulties with the reliability of internal joints and anyway, the lead-frame plus injection-molding technique only allowed for the inclusion of a few discrete components in the simplest of circuits, any IC being difficult to include. Since then, manufacturers have moved to open-frame converters to avoid any reflow soldering problems, accepting that the internal component solder joints would reflow again, but stay on their substrate. SMT pin terminations have varied from gull-wing to blocks and pillars to solder balls and more recently land grid arrays. This has

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