I have been following the recent thread relating to temperature stickers and
contacted the supplier of Templaq mentioned by John Crawford. Templaq is
geared for assembly rework and is not available in a temperature setting to
suite my requirements. 

My question is this:
Does anyone know of a temperature-indicating ink which might be screened or
otherwise applied to boards during manufacture and whose purpose is to
"ballpark" the highest temperatures seen during assembly, or to indicate
that the board has exceeded a known temperature during assembly?