C&H Technology PowIRtab Mounting Guidelines - Manual

PowIRtab Mounting Guidelines
by Paul Westmarland & Pamela Dugdale
1.0 Introduction
The PowIRtab TM package has been designed to fill the
gap in the market between the TO-247, more expensive
metal case devices & non-isolated power modules. It is
the natural replacement for metal case outlines such as
DO-4 & DO-5, but it is also suitable for new innovative
solutions, thanks to a package outline that combines low
profile, excellent die to footprint ratio & sturdy
connectivity. It utilises a large lead for high current
connection, carrying both a mounting hole & PCB
insertion pins. The body is compatible with a T0-218
outline, with an exposed heatsink & non-isolated mounting
hole.
It is anticipated that the devices would find typical
applications in busbar assemblies or finned heatsinks,
reducing component count & cost of ownership.
2.0 Scope
This application note covers the various fixment methods
that are possible with this device, & the associated thermal
properties resulting from their use:
a) Optimum mounting torque.
b) Type of fixings.
c) Effect of torque on thermal resistance (‘wet’ & ‘dry’).
d) Effect of pressure on contact thermal resistance (‘wet’
& ‘dry’).
3.0 Mechanical Considerations
3.1 Type of Fixings
The PowIRtab TM possesses mounting holes in the tab &
lead for electrically connecting the device to heatsinks or
busbars. The lead also carries PCB insertion pins so that
the lead end may be soldered into a board.
Tab (Header)
Lead
PCB insertion
pins
Stress relief slots
Figure 1
3.2 Tab Connection
Using the mounting hole in the tab allows a designer to
attach the PowIRtab
TM to a heatsink. The tab of a
PowIRtab TM acts as one of the terminals. There is no
common additional lead, so the mounting hole contact
must be very good, with the heatsink forming part of the
circuit. For the best results the surface of the heatsink must
AN-1010