Additional information
14 of 31
Revision 4.0
2021-10-11
Recommendations for board assembly of Infineon transistor outline
type packages
Mounting of surface-mount devices
The solder alloy particles are dispersed in a blend of liquid flux and chemical additives (approx. 50% by volume
or 10% by weight), forming a creamy paste. The flux and chemical solvents have various functions such as
adjusting the viscosity of the paste for stencil printing or removing contaminants and oxides on the surface.
The solder paste solvents have to evaporate during reflow soldering, while residues of the flux will remain on
the joint. The capacity of the flux additive for removing oxides is given by its activation level, which also affects
the potential need for removing the flux residuals after the assembly. For leadless packages in which the solder
joint is formed mainly on the package bottom side, a “no clean” paste is recommended to avoid subsequent
cleaning steps underneath the package. Small gaps make cleaning highly difficult if not impossible. Certain
precautions have to be taken if any kinds of flux residues remain on the board prior to any kind of coating. For
power packages, leakage currents and the potential for shorting below components have to be considered
when choosing the specific flux type (e.g. halide-free vs. zero halides).
Generally, solder paste is sensitive to age, temperature, and humidity. Please follow the handling
recommendations of the paste manufacturer.
3.3
Component placement of SMD
The pick-up nozzle should be chosen according to the package size. The nozzle should be slightly smaller than
the package mold body.
For TO SMD packages, most of the time the nozzle position needs to be in the center of the mold body and not
in the center of the overall package outline. That is due to the fact that TO SMD packages typically are single-
end leaded.
Although the self-alignment effect due to the surface tension of the liquid solder will support the formation of
reliable solder joints, the components have to be placed accurately depending on their geometry. An
automated pick-and-place machine is recommended to obtain reliable solder joints.
Component placement accuracies of +/-50 µm and less are obtained with modern automatic component
placement machines using vision systems. With these systems, both the PCB and the components are optically
measured and the components are placed on the PCB at their programmed positions. The fiducials on the PCB
are located either on the edge of the PCB for the entire PCB, or at additional individual mounting positions
(local fiducials). These fiducials are detected by a vision system immediately prior to the mounting process.
For further information about component placement, please refer to the
General Recommendations for Board
Assembly of Infineon Packages
document that is available on the Infineon web page [1]. Please also feel free to
contact your local sales, application, or quality engineer.
3.4
Reflow soldering
For PCB assembly of the TO SMD packages, the widely used method of reflow soldering in a forced convection
oven is recommended. Soldering in a nitrogen atmosphere can generally improve the solder joint quality but is
not necessary to create a reliable joint.
Typical most PCB assemblies contain various package types and sizes. The the reflow settings have to match
the allowed profile range of all the components and materials. Components with large thermal masses do not
heat up at the same speed as lightweight components. In addition, the position and the surrounding of the
component on the PCB, as well as the PCB thickness, can influence the solder joint temperature significantly. It
is therefore recommended to measure the temperatures at critical positions by thermocouples.
Power packages where leakage currents and shorting below the component have to be considered should be
soldered with decreased flux spreading. Therefore, it is recommended to optimize the reflow profile in such a
way that excessive flux or solder spattering is avoided. The soldering profile should be in accordance with the
recommendations of the solder paste manufacturer to achieve optimal solder joint quality.
