Ideas & Solutions
As density of electrical components at PCBs is increasing, the problem of conduction of the heat produced by the components gets more and more essential. The usual solutions are so called “Heatsinks” which are cooling elements made of metal (aluminium or copper) which are to be mounted at spots on the PCB from which the heat need to be leaded away. The disadvantages of these Heatsinks are obvious :
- additional mounting work;
- precious space at PCB is kept away by Heat Sinks;
- as these are electricity conduction metals, a proper insulation from PCB layers is necessary to avoid shorts;
- heat sinks cause additional weight and increase the volume of the PCB assembly.
- metal core PCBs (basic material is an aluminium or copper alloy itself – these metals have the higher specific heat conductivity (HC): copper – 400 W / mK, aluminium – 200 W / mK compared to epoxy glass fibre, the PCB basic material which has only about 0.4 W/mK HC. Disadvantages: expensive in material and workmanship, only 1and max. 2 Layer PCB possible.
- thick copper foils as “Thermo – Layers” … these are available at thickness up to 400 micron. They can be used in Multilayer PCB constructions as inner layers or even outer layers (with inner signal layers and isolated vias through the Thermo – Layer. Disadvantage : complicate construction and higher costs.
- a new elegant solution is the “Heat Sink Paste” (also called“ Printed Heat Sink”) which is offer by a German producer of PCB– chemicals Lackwerke Peters GmbH + Co KG, Germany. The processing of that Heat Sink Paste is by screen printing directly to PCB through a screen like a solder paste stencil and curing afterwards. The HC of the pastex – it consists of solid particles based in an epoxy resin - is by 2 W/mK – as via hole of the PCB are partly filled, additionally head dissipation is achieved.
- easy application by screen printing and usual drying methods;
- high definition for design of variable structures and layer thickness;
- heat is dissipated from source of its generation, possibility to fill heat vias with the paste;
- economical process compared with alternatives;
- continuous heat resistant to 155° C;
- electrical isolator itself (no insulation necessary);
- no volume shrinking, good mechanical, chemical and solder bath resistance;
- flame class V0 as per UL.