IGBT Modules - Technologies, Driver and Application (Second Edition) - page 100

Fig. 2.26
Plug connectors for IGBTmodules Press-in technology
The pressing in of contacts falls into the category of cold or contact welding technology
and represents a conditionally separable connection. Cold welding has been used in a
wide variety of applications for many years, mainly in low signal connections. It has only
recently been extended, as a press-in technology, to high current connections in PCB.
Press-in contacts are used instead of screw connections, for example, and now also for
control and load connections in IGBTmodules.
The principle of coldwelding, which has been around since the 1940s, works as follows:
Metallic contacts of the samematerial that are to be bonded together electrically do not
have a 100% smooth surface
).When the two contacts touch each other, the
current is transported via only a few direct contact points. The application of force,
bringing with it a certain deformation, increases the effective surface of the contact
). An additional, secondary, effect of the high force is that it removes
existing oxidation by friction and/or the fritting effect (chapte
and creates a gas-
proof connection at the contact points which is not susceptible to external
contamination, e.g. by salt water or oxidising gases. The actual connection at the
contact points is created by free electrons in the atomic lattice of the metals, which
spreads beyond the contact point to create cross-linking. Initially, the connection is
weaker than in a coherent atomic lattice. After a few hours, however, the connection is
strengthened as a stable lattice forms in and beyond the contact zone. This can be
checkedmetrologically by comparing the press-out pressures required directly after the
press-inprocesswith a contact that has had time to builda complete connection.
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