Shrinkage-free soldering of pastes and preforms

The Nexus is specially designed for flux-free vacuum soldering of pastes and preforms. Here, the Nexus works with temperatures of up to 450°C. These high temperatures are necessary in order to ensure that the materials, which are usually highly dissimilar are fused securely. The reduced pressure helps, among other things, to minimise oxidation on the components and on the solder itself. The heat is transferred both via thermal conduction and optionally by radiation too with the Nexus. Individually adjustable heating and cooking gradients ensure flexible processing and make short process times possible. In accordance with the respective customer requirements, different process gases maybe used. Flux-free operation with up to 100% nitrogen, forming gas (95/5), formic acid or up to 5% hydrogen is therefore possible. Should soldering paste containing soldering flux be used, the process gas is cleaned efficiently via the residue management system. Its compact dimensions and high level of user-friendliness mean that the Nexus system is particularly suitable for use in small-scale and medium-scale production, as well as in laboratories.

Heating/cooling plate

The heating or cooling gradient can be predefined based on predetermined parameters. The gradients can be pre-set as required. Within these specification limits, the temperature is adjusted automatically by the Nexus so that these limit values are not exceeded. This eliminates the possibility of a malfunction of the assembly to be soldered. The heating output has been designed for a uniform heating process when fully loaded with high-mass assemblies meaning that short cycle times are also no problem. Sensor components determine and verify the temperatures recorded on the goods carrier support. A heating rate of max. 150K/min and a cooling rate of max. 180K/min (relating to the cooling plate) is possible here. .

Vacuum

The vacuum ensures oxide-free processes, as well as improved wetting and thus better filling of soldered joints. In addition, it drastically reduces the voids in soldered joints and enables processes such as plasma cleaning and atmosphere exchange for advanced packaging. A controlled gas sampling system from the process chamber via a vacuum pump prevents overpressure during controlled flushing via a separate proportional valve for feeding into the process chamber; thus each pressure level can be set as required using a software programme. The vacuum pump to control the chamber pressure of 0–1000mbar also keeps the pressure level constant.

Formic acid bubbler

To achieve a stable, reliable, flux-free soldering process, the inert carrier gas (N2) is enriched with formic acid (HCOOH) and transferred into the process chamber. The formic acid bubbler has a level control to ensure the saturation level remains consistent (saturation level of the N2 gas depends on the level in the formic acid bubbler). In order to ensure that the “saturation” of the carrier gas with formic acid remains constant, the parameters are kept constant while the liquid formic acid is flowing through. These include the flow velocity, flow rate, temperature and the filling capacity of the formic acid tank (bubbler). Thanks to the control engineering that is in use, the nitrogen flow rate can be monitored easily and reliably.