As density of electrical components at PCBs is increasing,
the problem of conduction off the heat produced by that parts gets
more and more essential. The usual solutions are so called
“
Heat sinks” 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 Heat Sinks 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 causing additional weight and increasing the
volume of the PCB assembly.
What are the technical alternatives to Heat Sinks ?
a) 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.
b) 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.
c) 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 paste – 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.
The advantages of such Heat Sink Paste are as follows :
- 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 .
