Dear Hans,
Micropelt thin-film thermoelectric coolers are supplied and handled as "chip"
component.
That looks somehow similar to chip (SMD) components, like inductors, resistors, NTC's or photonic components like LED's or laser diodes.
Our customers do assembly our TECs in their package of choice (like TO-46,
TO-39, TO-56, TOSA or any other common in photonics or sensor markets) via their assembly lines with standard wire-bonding.
Micropelt TECs cannot be soldered via standard solder equipment, like any
engineer is having is his lab to solder passive and active components on his
PCB.
The mentioned leads in the datasheet are the '+' and the '-' of the TEC. A TEC is current controlled, and can in principle be controlled with current in both directions. The direction of the current determines which side will get "cold" and "hot".
Does this answer your question ?
Best regards,
Wladimir Punt