Vacuum soldering with paste

For vacuum soldering with pastes – especially in conduction furnaces – some points have to be considered during process development. The adjustment of the atmospheric pressure and the oxygen concentration results in new degrees of freedom, but also stumbling blocks. This includes for example, the controlled removal of paste residues by vacuum. However, activators of the paste can also lose their effect due to wrong vacuum setting, resulting in poor wetting.

For this reason, we offer special training and process consulting for vacuum soldering with paste.

Possible training and project contents:

  • Development of soldering profiles with conduction ovens
  • Typical faults that arise during soldering and temperature profiling
  • Temperature measurement techniques and sources of errors
  • Influence of previous processes on the paste soldering
  • Material quality check, soldering jigs and fixtures, as well as systems with rapid testing functions
  • Identification of save process windows
  • Transfer of laboratory processes to mass production
  • Introduction of inline measurements and statistical process control
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Solder paste with formic acid or hydrogen

In recent years, some pastes have appeared on the market that contain only solvents instead of resins and acids (e.g. carbon acids). These pastes require formic acid or hydrogen to reduce the surface oxides.

The solder paste with HCOOH support represents a middle ground between preforms and paste soldering. The special features of the formic acid or the reducing gas must be taken into account and the vapor pressure curves of the paste must be known. This ensures that the solvents evaporate before the alloy melts and the acid can reduce the surfaces.


We help you to develop suitable profiles and select the right system technology.

Solderability matrix for different flux types and reducing atmospheres

The following matrix shows the solderability on different metallizations or surfaces for different reducing agents and pastes. HCOOH refers to formic acid vapors and H2 assumes 100% hydrogen. Plasma refers to reduction using argon-hydrogen at room temperature.


Table 1: Solderability matrix for different fluxes and surfaces

Material Flux RMA Flux RA Flux WS Flux WS-H Flux NC HCOOH H2 Plasma
Aluminum x x x x x x x x
Brass ~ ok ~ ok ~ ~ ~ ~
Bronze ~ ok ~ ok ~ ~ ~ ~
Chromium x x x x x x x x
Copper ok ok ok x ok ok ok ok
Steel x ok x ok x x x x
Gold ok ok ok x ok ok ok ok
Nickel ok ok ok x ok ~ ok ok
Platinum ok ok ok x ok x x x
Silver ok ok ok x ok ok ok ok
Titanium x x x x x x x x
Tin ok ok ok x ok ok ok ok
Zinc x ok ok ok x x ~ x
OK = good solderability
x = not solderable
~ = depends on alloy and surface quality

Articles about paste soldering:

Do you have further questions regarding vacuum soldering? Do not hesitate to contact us!