To operate efficiently and ensure reliability, heat must be removed from heat generating power components.
As a result of faster speeds, reduced format, and more devices being populated on Printed Circuit Board, more heat is being generated that must be removed for efficient operation.
The move to sustainable-energy increased the demand for energy management electronics which also create much heat because of the high electrical currents as used on these applications (Power inverters for solar and wind-energy, powertrain electronics for HEV)
Thermal management through various applications aids in directing heat away from heat generating system components. The following are a review of various thermal management approaches, applications and capabilities.
PCB Thermal Management Types
Applications requiring PCB Thermal management
It is important to utilize the best application for your thermal management application. Considerations of cost and how much thermal heat removal required are important. Typical applications for Thermal Management may include:
- Power Applications: Power amplifiers, DC power supplies, Power control systems, RF/MW applications
- Automotive: Motor Control Modules, Electric brake system, Power-train in EV
- High Speed Computing
- Lighting systems: Automotive, Industrial, Consumer
Thermal Conduction in PCBs
Thermal resistance at each level of an electronic system will impact conduction and Heat generated must be transferred to Environment.
Thermal Conduction in PCB
Air Gap Thermal Resistance
The air gap under components generally represents the greatest thermal resistance
- Air has a thermal conductivity approximately 0.025 W/ mK
- Under filling the component can dramatically reduce thermal resistance
PCB Thermal Conductivities
PCB’s are composed of resin, glass and a random distribution of copper that is parallel to the PCB surface. An approximate value for parallel and perpendicular conductivity is:
K II = 27.5 W/mK
K= 0.41 W/mK
Approximations are based on FR4 based laminate and will vary based on actual board construction and specific distribution of copper but they are a good starting point.
Thermal conductivities of common PCB materials
PCB materials Thermal conductivities
PCB Thermal Resistance: Parallel
This example does not take into account the thermal resistance from the IC and perpendicular resistance in the PCB.
PCB Thermal Resistance: Perpendicular
Relatively large thermal resistance in the Z axis since copper layers are separated by high resistance laminate
PCB Thermal Management – Heavy Copper
Thick Cu Outer layers in Printed Circuit Boards
External conductors we can employ Copper-plate & Etch technology
Heavy copper PCB
210um (6Oz) final copper thickness on external layers
Heavy Copper Inner-layers in printed Circuit Board
6 Layer Heavy copper PCB
- Two cores with two 10oz/10oz copper layers based on print and etch process
- To avoid reliability-issues with extreme heavy copper on outer-layers it is recommend to move heavy copper to inner layers
4 Layer Heavy copper PCB
One core with two 410um (12 Oz) copper layers based on print and etch process
PCB Thermal Management – Insulated Metal Substrate (IMS)
Metal Clad PCB Manufacturing Process
Insulated Metal Substrate (IMS) PCB Capabilities
| Al IMS (5052) | Cu IMS | |
| Material | Ventec Bergquist | Ventec Bergquist |
| Layer Count in MP | 1L | 1L |
| Max Panel size | 18” x 24” | 16” x 21” |
| Min dielectric layer thickness | 75um | 75um |
| Max Copper thickness | 3oz | 3oz |
| V-cut | Yes | Yes |
| Routing | Yes | Yes |
| Solder mask | Green, White, Black | Green, White, Black |
Insulated Metal Substrate PCB Case studies:
IMS PCB Example 1
Metal Type: 5052 Al
Dielectric thickness: 100um
Copper Thickness: 3 OZ
Al thickness: 1.9mm
Surface finish: LF-HASL
IMS PCB Example 2
Metal Type: 5052 Al
Dielectric thickness: 75um
Copper thickness: 2 OZ
Al thickness: 1.9mm
Surface finish: LF-HASL
IMS PCB Example 3
Metal Type: 5052 Al
Dielectric thickness: 75um
Copper Thickness: 3 OZ
Al thickness: 1.0 mm
Surface finish: LF-HASL
IMS PCB Example 4
Metal Type: 5052 Al
Dielectric thickness: 100um
Copper Thickness: 3 OZ
Al thickness: 1.0 mm
Surface finish: LF-HASL
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