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November 27, 2006

Wave soldering lead-free components

We are using components which are lead-free and tin-lead in printed circuit board assembly. Please help me understand the proper wave soldering temperature, for soldering, using lead/tin solder for lead-free components? What is the correct hand soldering temperature setting for such boards?

Veerendra Kumar Sing

Experts Comments

Tin and silver finishes have been widely used for both surface mount and through hole components for many years due to their slow oxidisation characteristics and therefore long shelf life. So the simple answer is that you can use the same pot and solder iron temps that have always been used.

When the molten solder from a Sn/Pb pot comes in contact with the higher melting point lead free metals on the components they will melt and dissolve. The pot temp used will be around 245 - 255 for Sn/Pb which is higher than the 232 temp of the highest metal finish (pure tin) and will cause localised melting. Also the solder dissolves the surface of the component much in the same way as it would the copper finish on an osp board, The copper melts in excess of 1000 degrees but still solders well most of the time.

The whole solder process relies on metal dissolution and chemical bonding to work not melting.

Solder Irons remain the same for the same reason and also because they are at about 380 centigrade. Again this is plenty of heat to melt a lead free alloy. What we have found in Europe is that even with lead free wire that you can keep the same temperature but reduce the diameter of the wire to the next available size down. This ensures that there is no increased risk of temp damage to the components around where the hand solder process is taking place and the soldering speed is the same.

Doug Dixon
Global Marketing Director
Henkel Electronics
Mr. Dixon has been in the electronics field for over twenty years and is the Global Marketing Director with the electronics group of Henkel. Prior to joining Henkel, he worked for Raytheon, Camalot Systems, and Universal Instruments.
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