First you will need to determine if this is a design related bridging issue or a process related defect.
For design related defects consider the following. This can include, but is not limited too:
- Connector pitch to tight,
- Connector leads too long off bottom of assembly
- Bridge is caused by the use of a selective soldering pallet
- Connector positions in various directions on the assembly.
This is just to name a few.
If you have "design related" issues that are the root cause of the defect, your choices are somewhat limited as to what you can do to eliminate them. You can consider some technologies in the market that include de-bridging hot airknives or selective de-bridging tools.
If running with a lead free alloy the window of operation on these tools is reduced, so make sure you visit a supplier and test this first. You can also consider solder thieves, These are open land traces or so called drainage pads that are placed onto the assembly at the trailing edge of a connector.
The design provides a drainage point to pull the solder from the connectors to a open plated land. Note, these work best with connectors parallel to the conveyor rails.
If not a design related issue, here are some choices
- Run the connectors parallel to the conveyor direction.
- Use a smooth exit transition from the primary wave with a small amount of back flow.
- Run the immersion depth in the primary wave shallow to the boards bottom surface.
- And of coarse your standard process requirements for the flux manufactures and preheat profile.