(all Settings of parameters are subject to customized processing procedures )

 

General:

Flexible and flex- rigid boards of Polyimide are

hygroscopic, i.e. even under normal ambient

conditions they absorb humidity from the air. E.g., a

dry Polyimide foil already reaches its degree of humidity

saturation within a few hours.

During the soldering process, the absorbed humidity

can vaporise explosively, leading to delamination,

blisters, rupture effects etc.

The risk of delamination rises exponentially with

the soldering temperature !

 

Target:

 

  • Drying to reduce humidity in laminates before soldering process
  • Prevention of delaminating by thermal stress after moisture consumption

 

Methods:

  • Drying by application of convection respective in vacuum drying ovens
  • Parameters are depending on: type of laminates, soldering surface, layer count, time span up to start of soldering, Layout (areas of copper; size, amount, …)

 

Recommendation for parameters:

  • Drying in convection-, circulating air oven or in vacuum oven, drying not piled up

 

Drying: Material  Parameters  Time span before soldering

  • FR4 (Tg 135°C)  120°C; ≥ 120 min  Max. 24 h
  • FR4 (Tg > 135°C)  130 – 150°C; ≥ 120 min  Max. 8 h
  • Rigid-Flex, Flex,  130 – 150°C; ≥ 120 min  Max. 8 h
  • rigid ML > 6 layers  130 – 150°C; ≥ 120 min  Max. 8 h

 

  • Vacuum drying at 50 mbar permits decrease of temperature by 20 K and the reduction of time by 60 minutes
  • Vacuum drying is highly recommended for sensitive surfaces (i.e. electroless tin)