To create cultural awareness and boost intercultural communication successfully, you will have to prepare the tools before PBL groups are formed. Proactivity is preferable to interventions. 

In practice, students should have either 2 hours or 2 days of one-hour meetings each, before the groups are formed where they undertake an awareness exercise and exercises that require the most attention, respectively.

In a STEM learning environment, it does not make sense to interrupt the study activities to introduce a tool unless there is a problem in the group.  

Nevertheless, the teacher has to observe and take note of intercultural challenges that emerge, as well as identify tools that can solve the problem. 

The value of aiding the students in their intercultural communication journey transcends their studies. They will be able to reap the benefits later, in their working life.