Applying Epoxy flux using a dipping process is similar to the dipping process with conventional PoP flux, with the exception of the flux coverage of the component bump. With conventional PoP flux or PoP paste, 50 - 60% coverage of the package bump is recommended.
Epoxy flux is intended to fill as much of the area under the component as possible, so a deeper dip depth and/or a longer dip time is needed. Typically, the dip depth should be set between 90 and 100% to maximize the coverage of the bumps and in between the bumps, similar to the image. Too little epoxy flux can result in non-wetting and reduced drop test reliability. Too much epoxy flux can cause the component to float during the reflow process, and the solder joints may not be formed properly, if at all.
The dipping process is not as easy as it sounds. Time should be given before running production to optimize for each of the specific components that will be dipped.
Dipping Process Trouble Shooting:
- Component Electrical Continuity Errors:
- Too much epoxy flux - Reduce the dip depth and/or decrease dwell the time in the flux reservoir to reduce the epoxy flux deposition.
- Too Little epoxy flux - Increase the dip depth and/or increase the dwell time in the flux reservoir to increase the epoxy flux deposition.
- Component stuck in epoxy flux reservoir:
- Use a larger nozzle that will allow more vacuum area on the component surface.
- Use a softer rubber nozzle that will allow for a tighter gasket between the nozzle and the component.
- Reduce dwell time in the flux reservoir.
- Reduce epoxy flux dip depth.
- Pick & Place vision error
- The vision may need to be changed from looking at the individual component bumps to looking at the four sides of the component or the four corners of the component.
- The inspection lighting intensity, color, or angle may need to be altered.
If you have any questions, please feel free to contact me at any time.
* This post is part of the Understanding Epoxy Flux: The Need and the Process series.