Solder mask, a protective layer on printed circuit boards (PCBs), exhibits specific thermal properties, primarily its thermal conductivity, which impacts how heat dissipates through the board.
Key Thermal Properties of Solder Mask
The thermal properties of solder mask are crucial for understanding its role in PCB thermal management. Based on typical specifications, these properties include:
- Thermal Conductivity: This is a measure of how well a material conducts heat. A lower value indicates poorer heat conduction (acting as an insulator), while a higher value indicates better heat conduction.
- Thickness: The thickness of the solder mask layer also affects thermal performance. A thicker layer presents more resistance to heat flow for a given conductivity.
According to the provided reference:
- Typical solder mask has a thermal conductivity of 0.2 W/m.K.
- Typical solder mask thickness ranges from 20 to 25 µm.
This thermal conductivity value (0.2 W/m.K) is relatively low compared to materials like copper (around 400 W/m.K) or FR-4 PCB substrate (around 0.3-0.6 W/m.K), indicating that solder mask acts more as a thermal insulator than a conductor.
Understanding Thermal Resistance
Thermal resistance is another important thermal property derived from conductivity and geometry (thickness and area). It quantifies how effectively a material resists heat flow. A higher thermal resistance means heat flow is more impeded.
The provided reference gives a specific example illustrating this:
- A 1 cm² area of solder mask with a typical thickness (20-25 µm) and a thermal conductivity of 0.2 W/m.K will have a thermal resistance of 1°C/W.
This means that if 1 Watt of heat power flows through this 1 cm² area of solder mask, there would be a temperature difference of 1°C across its thickness. This value helps engineers understand the thermal bottleneck presented by the solder mask layer, especially when components dissipate heat through the top surface of the board covered by the mask.
Summary of Typical Thermal Values
Here is a brief summary of typical thermal values for solder mask as cited:
| Property | Typical Value | Unit | Notes |
|---|---|---|---|
| Thermal Conductivity | 0.2 | W/m.K | Indicates insulation |
| Thickness | 20-25 | µm | Influences resistance |
| Thermal Resistance | 1°C/W for 1 cm² area | °C/W | Example derived from above |
These properties highlight that solder mask serves primarily as a protective layer and electrical insulator, not as a significant path for heat dissipation on a PCB. Its low thermal conductivity means heat generated under the solder mask must primarily spread laterally through the copper planes and substrate or be dissipated through other means like convection or radiation from the surface.
