Is solder mask an insulator?

By definition solder mask is not an insulator. The function of a solder mask material is to reduce the amount of solder used during the soldering operation and to prevent shorts from occurring between conductive traces.

Is solder a good thermal conductor?

While there are several physical properties and characteristics of solders that are of interest to the electronics community at large, one of the most significant physical properties to a thermal engineer is thermal conductivity. The solders with just one melting temperature listed are eutectic alloys.

Does solder mask affect impedance?

The solder mask coating can lower the impedance by up to a few ohms (depending on the type and thickness of the solder mask). Accurate calculation of the impedance of the coated microstrip structure requires that the designer supply values for the coating Er and thicknesses around the trace to the impedance calculator.

How do you calculate the thermal conductivity of a PCB?


  1. Find the thickness of the PCB board and the thickness of the copper traces on the board.
  2. Calculate the thermal conductivity parallel to the plane of the board using the formula Kp = 0.8 + 350 (ZCu/Z) where the variable “Kp” represents thermal conductivity parallel to the plane of the board.

Is solder mask necessary?

Not always, but that depends on the design and end-use of the printed circuit board (PCB). Solder mask (also called resist and overcoat) is used to isolate conductive areas of the PCB by covering them with an insulative layer.

Is solder a bad conductor?

Soldering is especially useful for electronics because not only does it create a strong physical connection between metals, but it also creates an excellent conductive path for electric current to flow from one conductor to another. This is because the solder itself is an excellent conductor.

Is all solder conductive?

The electrical conductivity of soft and hard solders is considerably less than that of copper, varying with composition between approximately 9 percent and 13 percent for soft solders and 20 percent and 40 percent for silver solders.

How much power can a PCB dissipate?

a. In order to dissipate 1 watt of power a good rule of thumb is that your board with need to have an area of 15.3 cm² or 2.4 in² per watt dissipated for a 40°C rise in board temperature. If the board is subject to airflow this requirement can be cut in half (7.7 cm² or 1.2 in² per watt).

Why is most PCB green?

It is due to the solder mask, which protects the copper circuits printed on the fibre glass core to prevent short circuits, soldering errors, etc. The colour of the solder mask gives the board its appearance.

What is the point of solder mask?

Solder mask is a thin layer of polymer that is put on a circuit board to protect the copper from oxidation and shorts during operation. It also protects the PCB from environmental influences such as dust and several other contaminants that may lead to shorts in the long run.

Why is solder mask important for thermal resistance?

Heat transfer by radiation is directly proportional to the emissivity coefficient of the material. Secondly, solder mask is so thin that it has virtually no thermal resistance. Therefore, I conclude that putting solder mask over the copper of a PCB heat sink is absolutely critical to maximizing thermal transfer from the PCB.

Why do you need soldermask on copper PCB?

For a larger contact area, thermal resistance drops accordingly. However, soldermask has another very important role. If you use immersion gold, large copper areas without soldermask may result in a thick gold layer, and your PCB fab will be asking who’s gonna pay for the extra gold.

How can I reduce the thermal resistance of my PCB?

Putting solder mask over the surface copper foil REDUCES the thermal resistance of the PCB to still air. Don’t expose the copper! If the board is small, the series θ’s near the IC don’t matter much; but as the PCB gets larger, the θ’s near the IC will mostly determine the total θ of the layout.

What’s the difference between FR4 and PCB thermal resistance?

For 1 cm², 70 °C/W for 63 mils of FR4 vs. 1000 °C/W for the PCB to air. This means that even if you only have copper on one side of the PCB, the other side will dissipate almost as much heat into the air. And an interior layer with a direct metal connection will be almost as effective as a surface layer.