Ultra-large-scale integration of multifunctional high-power-electronic devices place rapidly increasing demands on the heat dissipation capabilities of their high-density packaging that can no longer be accommodated with current thermal management designs and materials. A novel copper thermal via technology is presented that allows the direct formation and integration of large mm-size thermal vias into Printed Circuit Boards (PCBs), ceramic and glass substrates, thus maximizing heat dissipation. Modeling indicates that such a design can achieve a heat transfer coefficient exceeding 3000 W/cm2*K. The novel ActiveCopper material presented here allows for rapid prototyping and the process can be fully integrated into PCB manufacturing. It can be applied via direct dispensing or large area-type stencil printing. The ActiveCopper material exhibits multiple unique features: 1) it comes in a paste form that flows easily allowing for rapid filling of holes of any shape, size and thickness; 2) it sinters to bulk Cu in air at normal reflow temperatures of 200–235°C but can operate at temperatures exceeding 300°C. It can be processed using typical hot-pressing conditions as employed in standard FR4 PCB manufacturing. 3) After fusion, the resulting large via is filled with copper. No other binders are left behind resulting in very high thermal conductivity currently at 364 W/m*K. 4) The material is fully RoHS compliant, safe to handle in air and stored at room temperature. This new materials system enables many new applications and overcomes the limitations of electroplating. One can directly bond and solder to the material; it exhibits high reliability having passed nearly 3500 thermal shock cycles at -55 to +125 °C already.

Large, High Conductivity Direct-Fill Copper Thermal Vias for High Power Devices

Current and next-generation high power devices require a new set of materials with higher electrical and thermal conductivity to efficiently spread and remove increased waste heat. Kuprion's ActiveCopper technology enables the formation of bulk copper joints at typical soldering temperatures, yet the resulting interconnects are stable up to 500°C or more. This technology has been developed for a number of applications including die attach, thermal vias, and a replacement for WCu heat spreaders. Die attach materials can be dispensed, screened, or stenciled like traditional solder pastes followed by a solder-like thermal profile in a reflow oven under an inert atmosphere. Sintering can be achieved with or without pressure. Thermal vias are generated by stenciling an ActiveCopper paste directly into open circuit board cavities up to 4 mm in diameter followed by hot pressing under conditions similar to those used for traditional PCB manufacture. The resulting copper vias have thermal conductivity up to 330 W/mK, are solder compatible with or without further surface finish, and show excellent bonding to electroplated copper on the via sidewalls. Near net shape heat spreaders akin to WCu or AlSiC can also be generated via hot pressing or injection molding. The CTE of vias and spreaders can be tuned by adjusting the formulation of the original paste. ActiveCopper technology enables the design of all-Copper systems that can handle the increased thermal demands of next-generation electronics while avoiding failure modes attributed to intermetallic formation. Copper also presents an advantage over silver-based systems which show increased migration, dendritic growth, and voiding under higher thermal and electrical loads.

Next-generation Packaging Enabled by an Engineered Copper Nanomaterial

This work developed a copper (Cu) coin structure embedded on a printed circuit board (PCB) to dissipate a 12 W peak power out of the device system working at less than 60 °C. The designed Cu coin was based on the manufacturing limitations and allowed the thermal setup to be mounted on the bottom side of the board for automated test equipment (ATE) applications of the device. Thermal simulations through computational fluid dynamics (CFD) were analyzed and presented both for Cu coin and thermal vertical interconnect access (VIA), to quantify the thermal performances and compare the thermal benefits. Size variations on the designed Cu coin were investigated and quantified setting a thermal decay rate per change in dimension. The actual thermal measurement for the fabricated Cu coin design was presented on the experimental results, matching the simulation values and proving the viability of thermal Cu coin.

Marcus Miguel V. Vicedo

Papers

Copper Coin Over Thermal VIA in PCB for Thermal Management of 12W