Typically PTH components do not get exposed to soldering temperatures. The leads and boards get exposed but the components do not. Regardless of whether or not they are leaded or lead free, the temperature of the leads and the board is based upon the temperature of the wave solder pot.
The Top side preheat temperature should be high enough, for example 200 to 250 F, on the top side of the board, to help the solder flow through the holes, but at those temperatures the components are not exposed to the soldering temperatures of 361F for 63/37 or 419 for the lead-free solders.
Now if the discussion is for surface mount components which are secured to the bottom of the board with an adhesive, the story is somewhat different. That thermal profile must follow the component guidelines from the component suppliers. Basically it is a 2 to 3 Degrees C/second with a thermal shock not to exceed 80 to 100 degrees C.
This profile must be defined and monitored and the solder pot temperature must be adjusted accordingly to properly solder the components. I would not recommend continuously changing the solder pot temperature but varying the conveyor speeds and the preheat section of the board to create this thermal profile.
I hope this answers your question
Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.
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