09 – Heatsink PCBs

Heatsink PCBs are understood as PCBs that are able to dissipate high surface temperatures. Generally, these temperatures are caused by power semiconductors (transistors, thyristors, diodes and LEDs) as well as resistors. The following methods are suitable to dissipate the heat:
• The use of heat transfer compounds
• Higher copper thicknesses
• Heat dissipation using a metal core
• Heat dissipation using a metal heat-conducting plate

09.1 – Heat transfer compound (single-component paste)

The heat transfer compound is applied in a similar way to the silkscreen using a screen-printing procedure. The thickness of this layer is approx. 100 – 150 μm.

09.2 – Higher copper thicknesses

In case of thick-copper boards, the heat is absorbed and dissipated directly by the copper. Here, the copper thicknesses are at least 105 μm, 210 μm or 400 μm. The disadvantage of this technology, however, is that fine conductor structures can only be achieved with much effort and therefore the production is thus costly.

09.3 – Heat dissipation using a metal core

In case of metal or metal-core PCBs, a solid aluminium or copper sheet is used instead of standard base material.

Structure with metal core: see figure on the right
A copper foil is laminated onto a metal core using a prepreg.
This variant is mainly utilized in combination with special SMD-LEDs. These LEDs are extremely bright and thus achieve very high temperatures, which have to be dissipated through the PCB. Heat dissipation by heat sinks directly on the components is not possible.

The metal core is therefore a fixed component of the PCB. These PCBs can also be produced double-sided by the use of throughplating. To this end, prepregs are applied to both sides, and resin flux insulates the drill holes to prevent short-circuits on the PCB.

09.4 – Heat dissipation using a metal heat-conducting plate

In this case, the PCBs undergo the standard production process. The PCB is finally press-moulded to the metal heat-conducting plate using a prepreg.

Standard single-sided structure: see figure on the right
However, this version is controversial, as the heat dissipation is not optimal. The heat must first penetrate the base material before it can be dissipated. Should you decide on this version, we recommend selecting the thinnest possible FR4.

Possible solutions

• PCBs made from metal core material
• Alternatively, self-press-moulded base material
• Double-sided through-plated PCBs (aluminium-core PCBs)
• Standard production, single-sided PCBs with subsequent press-moulding with aluminium
• PCBs with heat-transfer compound

Technical information

Metal core PCBs
Finished laminated aluminium base material from various manufacturers, with special prepregs (thermal conductivity from 1 W/mK)

Alternative design
Self press-moulded aluminum base material with "no-flow"-prepreg 0,1 mm and copper foil in various thicknesses

Single-sided PCBs using standard technology
FR4 carrier with single-sided copper is press-moulded to the aluminium using prepreg 0,2 mm. The thickness of the aluminium is approximately
1,2 – 1,6 mm

Heat-transfer compound
Single-component heat sink paste, HSP 2741, black, made by the Peters company, using screen-printing procedure

Thick copper PCBs
Only possible to 210 μm. At this thickness, problems may occur with the solder resist varnish (flank coverage, dependent on layout). In this case, the gaps are filled with paste. Min. width and gaps of tracks: 1,0 mm