TDK's Guide to Electrically Conductive Adhesives (3): How does epoxy differ from solder during manufacturing?
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A. The general process for mounting components with conductive epoxy is similar to solder mounting. The following table displays the differences.

Process Epoxy Solder
1 Disperse glue Disperse solder
2 Place component Place component
3 Cure Heat/Reflow
4 Cool (if heated cure) Cool
Table 1 : Epoxy and solder mounting processes.

The curing durations for epoxies are significantly longer than the heating and cooling times for solders, and care must be taken to make sure they are maintained at the proper temperature during curing, or the epoxy may not fully cure.

Conductive epoxies can be made in one or two part systems. One part systems have the advantage of not needing to mix the resins to form the final epoxy. They often have high curing temperatures (150°C), and often need to be refrigerated until used.

Two part epoxies have the advantage of being able to cure at lower temperatures (often room temperature) than single compound epoxies, plus they do not need to be refrigerated. These compounds need to be used immediately after mixing, and can be ruined by an improper mixing ratio of the curing agent.

Special care must be taken when placing the conductive epoxy. In the case of solder, excessive solder can be moved back to the landing point when heated because of the surface tension of the solder. However, epoxies cure without moving, and this can create shorts and silver migration issues (which could eventually result in a short).

Figure 1: Excessive solder and glue placement.

Figure 2: Short risk from excessive glue.

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