C&H Technology PowIRtab Mounting Guidelines User Manual

Page 3

Application Note

Another solution is a laminated busbar, as supplied by the
Rogers Mektron Busbar Division. Here a single busbar is
stamped to the step height of the package & an isolating
laminate & second busbar added. The PowIRtab

packages can then be bolted (or rivetted) down to this
strip to form a single assembly, with two large single
outputs. A typical example is shown below in Figure 4.

Plain washer

Sprung washer

Busbar connection to lead

Figure 3

Figure 4

3.5 Leadforming

In some applications, forming or bending the lead to an
angle of 90 degrees is desirable (Figure 5). This could
facilitate connection to a PCB situated above the package.
The minimum recommended distance of the bend point
from the plastic body is 2.50mm (0.098ins). This will
produce a leadform as shown in Figure 5.

This particular leadform is offered as an option direct
from IR, under the designated leadform option LF-68.The
form occurs at the lower edge of the stress relief slots in
the lead. The vertical height of the lead, measured from the
underside of the unformed section of lead is typically

16.6mm (0.653ins). The stress relief slots, as well as
making the leadforming operation simpler, help to reduce
the stresses imposed on the plastic body caused by

differential expansion at higher operating temperatures.
During the leadforming operation, it is very important that
the area of lead between the plastic & the bend is securely
clamped, to ensure that the plastic is not cracked by this
operation.

Care must also be taken not flex or bend the lead over
sharp angles repeatedly. If the lead is bent through 30
degrees & back again more than twice, it will be
considerably weakened & liable to breakage.

Another type of leadform under development is a
PowIRtab

with the lead shortened to form 3 short leads,

as shown below in Figure 6. The use of this outline would
allow a lower profile insertion of the package into PCBs
than that of the standard outline.

PowIRtab with 90
degree leadform

Figure 5

PCB insertion
pins

Tab (Header)

Shortened lead

Figure 6

This lead option would work well in applications where
greater power than a T0-247 is required, but the designer
wishes to retain the basic mechanical structure & PCB. A
good example would be that of an OR-ing application with
a higher output current.