chamber or tray 40 with heat insulating walls in which a supply of solder 38 39 is maintained molten by suitable heating means not shown liquid solder is continuously pumped from chamber 40 by a first liquid metal pump 41 to first solder wave station 34 and similarly liquid solder is continuously supplied from tray 40 by a second liquid metal pump 42 to second solder wave station 36 ribbon 16 is drawn from left to right past station 34 in tracks 43 and 44 which terminate just beyond station 34 then the ribbon is drawn past station 36 in tracks 45 and 46 which begin just before station 36 tracks 43 and 44 cause ribbon 16 to twist from a nominal horizontal orientation by about 20 degrees in a first direction track 44 and tape 15 being higher than track 43 and tape 14 on the other hand track 45 is higher than track 46 so that in these tracks tape 14 is higher than tape 15 and the ribbon is twisted to an orientation displaced from the horizontal by about 20 degrees in the opposite direction the gap between tracks 43 44 and tracks 45 46 comprises reverse twisting station 35 tape 14 travels first in track 43 and then in track 45 while tape 15 travels first in track 44 and then in track 46 so that a forty degree twist in ribbon 16 occurs by this arrangement portions 34 a 34 of leads 12 are retinned at station 34 and then portions 34 a 34 of leads 13 are retinned at station 36 as will now be described stations 34 and 36 are similar and only one will be described.