Are there any low temperature (60 - 100 degree celsius) soldering pastes?
There are chip removal alloys (lead-free) that melt around 79-91°C. 

As well as being expensive, they're probably brittle and perhaps nasty in other ways. 

Leaded alloys are available that melt at ~58°C, a bit less than what you are asking for. 

As far as I know, those alloys are not available in paste form, however. What the industry calls "Low Temperature Soldering" is more like peak 190°C (lead-free process).