Selective Soldering under Nitrogen  [ Return towards  Applications  ]

In many cases where only a few connectors are used and board real estate is crucial, the use of special wave soldering process - selective soldering - may be advantageous. Selective soldering is the equivalent of performing a wave soldering process with a mask – a somewhat tricky process. It allows to have SMDs on both sides of the printed circuit board hence and a few PTH connectors that are required for their mechanical strength. Selective soldering is now gaining rapid adoption in the electronics manufacturing industry.

There are a few types of selective soldering methods. Equipment can be manual, in-line and robotized to adapt to modern PCB assembly lines requirements. Some equipment use laser diodes while the vast majority uses a mini-wave of molten solder. Similarly to wave soldering systems, the mini-waves are subject to creating dross. However, due to the nature and precision of the wave, a dross-free mini-wave is essential to a high-yield process. The need for nitrogen is therefore essential in mini-wave soldering. In addition, the inert atmosphere improves wetting while increasing surface tension, which results in higher quality joints. The flow of nitrogen is normally very low at 100 scfh and its low cost is easily offset by the gained benefits.

Rework of PCBs with Hot Nitrogen

Every efforts are made to eliminate defects in PCB assembly. However, due to process variations and the complexity of soldering, defects are always present in PCB assembly. Because of the hi-cost of PCBs and components, it is generally advantageous to correct or rework these small defects.

Rework is typically performed with the help of rework station. These are generally manually operated and use hot gas to melt, move, and resolder the defective joints. The hot gas jets provide localized heat to only the portion of a substrate you wish to rework – without damaging nearby components.

These rework stations can either use compressed air as a hot gas or nitrogen. Hot gas rework using nitrogen has proven to be very effective. It allows the pulling of components more easily while increasing wettability and the appearance of the joints they are newly creating. The rework process is a precise and sensitive process, using nitrogen helps increase the quality and yield of this process. The required flows of nitrogen are generally very low so adding this feature is cost-effective.

If your rework equipment is not configured for nitrogen, a slight equipment modification might be required. Please contact us for more information.