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)