The overall goal of thermal management on the bare board and in the assembly is to conduct heat from the heat-generating components to an external heatsink. Improved heat exchange results in a better mean time between failures (MTBF) and, in some cases, will be a decisive factor in meeting the design specifications of a given product. MCPCB Technology
A simple way to manage heat is to switch from FR4, the standard material used in multilayer PCBs, to dielectric materials with different thermal conductivity bonded to a solid metal core film (MCPCB). This will significantly improve a PCB's thermal performance. MCPCB works by using a thermally conductive pre-impregnation between the copper conduction layers, which draws heat energy toward the metal core and away from the components. MCPB technology can be implemented as a single layer on a metal base or as a multi-layer on the top and bottom sides of the metal base.
Below you can see a 2-layer MCPCB structure showing the heat transfer from the surface-mounted component through heat buildup to the metal base. This can achieve a thermal conductivity of up to 12 W/mK, but currently, this solution does not offer a significant improvement. To achieve higher thermal conductivity, we recommend a different technology, such as using a copper component.
Copper-based PCBs, a growing technology
In this article, we want to delve into the technology of copper PCB components. Heat exchange occurs at a higher rate when using materials with high thermal conductivity. Copper is highly conductive, offering 400 W/mK and above, as are other materials like diamond, which can be up to five times more conductive than copper. But
who would want to use diamonds in their PCBs? Copper is one of the best ways to manage heat while maintaining both electrical and thermal conductivity.
What's known as a PCB "copper coin" is simply a piece of copper typically placed beneath components that require cooling. This copper piece can provide twice the cooling capacity of a via array. And, instead of using thermally conductive materials, the copper piece provides direct contact between the heat-generating component's support and the heatsink. Copper's thermal conductivity is, on average, 30 to 200 times better than any dielectric pre-impregnation available.
Copper heat sink technology is best suited when a small or specific number of PCB components generate most of the heat. The copper heat sink provides the best solution for localized heat dissipation on a PCB, regardless of the number of layers or the PCB material. This concept involves press-fitting a copper heat sink into a pre-cut recess in the board, directly beneath an identified hotspot. This allows heat to be transferred directly to a heatsink through the PCB stack. This process bypasses the PCB material stack that has traditionally caused heat dissipation bottlenecks.
The copper piece is embedded in the PCB and can be incorporated in various shapes and configurations. The configuration chosen by the engineer will reflect the trade-off between routing, power plane requirements, and the proximity of the copper piece to the component requiring cooling.
Figures 1 and 2 show a solid copper piece spanning layers 1 through 4, which acts as an assembly support and provides the best heat exchange channel for a hot component.
In other cases, if the support size is too small and routing under a hot support must be considered, the copper piece can also be inserted only up to a specific layer and not
through the entire PCB. Figures 3 and 4 show the implementation of a copper piece located between layers L4 and L2 that does not make contact with layer L1.
Copper coin
Piece of copper
Figure 5 shows a copper T-shaped part. The T-shape exemplifies how to utilize the excellent properties of copper part types where either the heat-generating support or the heat sink has different surface areas—for example, a small support and a large heat sink, or vice versa.
Another example of its use is when there are limitations on the minimum dimensions of the
copper part. Using a T-shape allows us to keep the overall dimensions of the copper part within the minimum limits while still creating contact with a support that is smaller than the minimum size requirement for the copper part. T-shaped parts offer excellent trade-offs in terms of performance and footprint because the shape provides flexibility regarding the space the part occupies.
Although this technology is relatively new, we have seen considerable success when the PCB is optimally designed for it. With each additional foreign object, registers and tolerances become a major concern, and the required process increases. The copper part represents the pinnacle of heat exchange that can be efficiently applied at the board level without components. Whether you are working on the design of an MCPCB or a copper part, we recommend collaborating with your PCB supplier, especially when dealing with such new technologies.
Article provided by NCAB Group Iberia
