Taking the collaboration to the next level: What triggers Pharma to bring equity in biotech companies?

Pharma is one of the main partners a biotech company can find to accelerate its innovation, and the collaboration can take many forms to align with respective needs, roadmap and pipeline, context and resources. One of the ways an R&D collaboration can be furthered for pharma companies is to take one more step and bring equity into the equation. What makes pharma choose to add capital investment? When is it relevant for them to do so? What are the components of such a deal, the steps towards it, the implications and challenges?