Additional information
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Revision 4.0
2021-10-11
Recommendations for board assembly of Infineon transistor outline
type packages
Mounting of through-hole devices
Figure 18
Schematic drawing of TO247 package with clip mounting.
4.4
Soldering of THD
THDs are designed for wave soldering and not for reflow soldering. As the number of THDs on each board has
been decreasing in some applications wave soldering, however, becomes less cost effective. The few remaining
THDs (mostly connectors and special components) are soldered with selective or wave soldering, or with the
pin-in-paste technique plus reflow soldering.
TO THD are often mounted on a carrier or submount that has special features which enable it to serve as a good
heat sink. In this case, special processes are needed to attach the component.
Wave soldering and selective soldering of THDs
These processes use a tank holding molten solder. The components are inserted into the PCB and the loaded
PCB is passed across a pumped wave or cascade of solder. The solder wets the exposed metallic areas of the
board (those not protected with solder mask), creating a reliable mechanical and electrical connection.
In the case of TO THD, only the leads that reach through the drilled holes in the PCB are directly in contact with
the hot solder. The body of the package only gets heated by the hot leads. As a result, the package body is
cooler than in case of reflow soldering, and the temperature gradient between leads and body and inside the
package is steeper compared to reflow soldering.
The heat resistance of wave-solderable TO THD is tested according to JESD22-B106 and IEC 60068-2-20
(typically 260°C for 10 s). This gives the maximum acceptable temperature and time for selective/wave
soldering (e.g. for dual wave: max. time in wave 1 + max. time in wave 2 < 10 s) [8][9].
Note:
Immersing the whole TO THD package body into the molten solder is not recommended. This
would result in a temperature shock of the package body, which is not rated for this stress.
There are various types of wave soldering machines available. The basic components and operating principles
of these machines are the same. A standard wave solder machine has three zones: the fluxing zone, the
preheating zone, and the soldering zone. An additional fourth zone, cleaning, may be used depending on the
type of flux applied. Dual-wave soldering is the most commonly used wave soldering method.
The peak temperatures, ramp rates and times depend on the materials used and on the wave soldering
equipment. The first wave has a turbulent flow and therefore guarantees wetting of nearly all shapes of leads
and board pads, but also results in a large number of solder bridges. These solder bridges must then be
removed by the second, laminar wave. When using Pb-free solder alloys, a nitrogen atmosphere is
recommended.
Selective soldering is typically used when only a few THD components have to be mounted. Generally this is
done after the other components are already soldered by reflow soldering. These components must be
protected while undergoing selective soldering. This protection can be achieved either by using special fixtures
