Most solders will work but your choice is based on your heat source. My oxy-mapp torch has unlimited heat but if you use a std propane torch the lowest melting temp solders are preferred but that means higher si content and carries a higher price
The smaller 1mm 650deg can be "ringed" around the flange. then it will run and fillet the join very well with plain Mapp gas.
www.cupalloys.co.uk/medium-temp-silver-solder/index.asp
ps - there is a small brazing hearth in "Franks stuff" if you're interested.