PCB Heat Sink Assembly for Partial Discharge Suppression
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Solution Overview
Problem
The presence of air pockets in thermal interface materials between printed circuit boards and heat sinks leads to a significant risk of partial discharges due to the lower permittivity and dielectric strength of air, which degrades insulation properties and reduces the service life of the circuit board.
Innovation Solution
The lowest metal layer of the printed circuit board is set at the same potential as the heat sink, acting as a shield, with the electrically insulating layer between it and the adjacent metal layer providing insulation, thereby minimizing the potential difference and reducing the risk of partial discharges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the thermal interface material is used to cool the printed circuit board, then thermal connection is improved, but air pockets in the material create a risk of partial discharges due to lower permittivity and dielectric strength
Solution Approach 1:
The patent applies equipotentiality by connecting the lowest metal layer of the printed circuit board to the heat sink potential through a short-circuit path. This creates an equipotential region between the lowest metal layer and the heat sink, eliminating the potential difference that would otherwise exist across the thermal interface material. By doing so, the harmful electric field is removed from the thermal interface material region, preventing partial discharges while maintaining effective thermal connection.
2Reliability
If the electrically insulating layer is made thicker to prevent partial discharges, then insulation reliability is improved, but thermal connection to the heat sink deteriorates
Solution Approach 1:
The patent resolves this contradiction by creating an equipotential connection between the lowest metal layer and the heat sink. This eliminates the need to increase the thickness of electrically insulating layers because the potential difference is removed from the thermal interface region. The shortest possible distance can be used while maintaining both insulation reliability and thermal connection efficiency.
3Reliability
If the carrier board is arranged at a distance from the heat sink to reduce partial discharge risk, then insulation reliability is improved, but thermal connection and space efficiency deteriorate
Solution Approach 1:
The patent applies equipotentiality by establishing a short-circuit path between the lowest metal layer and the heat sink. This creates an equipotential region that allows the carrier board to be placed as close as possible to the heat sink without risking partial discharges. The potential difference is eliminated through the equipotential connection, enabling minimal spacing while maintaining both insulation reliability and optimal thermal connection.
4Reliability
If the lowest metal layer is connected to the heat sink potential, then partial discharge risk is reduced, but the electric field between metal layers concentrates in the printed circuit board
Solution Approach 1:
The patent applies parameter changes by modifying the electrical potential parameter of the lowest metal layer, connecting it to the heat sink potential. This changes the distribution of electric field stress, concentrating it within the printed circuit board's internal insulation layers where it can be managed, rather than allowing it to extend into the thermal interface material where partial discharges would occur. The parameter change in potential distribution resolves the contradiction between reliability and field stress management.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances insulation properties and service life by preventing partial discharges and allows for effective thermal connection and cooling without the need for stringent thermal interface material requirements.
Implementation Method 1
the electrically insulating layer (for example, FR4 material) between the lowest metal layer and the metal layer adjoining it serves as the only insulating layer for insulating the carrier board from the heat sink
Implementation Method 2
a thermal interface material, which may be arranged between the carrier board and the heat sink
Data Source
AI summary
A printed circuit board assembly includes a printed circuit board with an upper face, a lower face, multiple metal layers, and multiple electrically insulating layers. The printed circuit board assembly additionally includes a metal heat sink on which the lower face of the printed circuit board lies at least in some regions, wherein the metal heat sink has a heat sink potential. The bottom metal layer of the printed circuit board is set to the heat sink potential while the other metal layers of the printed circuit board have an electric potential which deviates therefrom.