Rationale for Chisel tips over Conical
Chisel tips have a little flat area on either side which assists in conducting heat from the central copper core of the tip to the joint, via a thin iron plating. Even on the fine chisel tips, the tip is two-dimensional, rather than just a point, to assist driving heat into the joint. Conicals have only one point mostly in contact with the joint (picture the side of a cone), with the parts further away having to conduct the heat through the solder between the tip and joint parts.
Conicals are also geometrically challenged. Consider that the tips are typically a copper core (very good thermal conductivity) with an iron plated coating, for extended tip life, but with much less thermal conductivity.
Looking at the image you can see that the very tip, just due to geometry of the cones, has a long distance between the last pointy bit of copper (compromised for heat flow anyway) and the actual tip. Longer distance equates to slower heat transfer. The pointier the tip, the worse this effect is. More will probably go out the sides to the joint than from the very tip.
Thermal conductivity of
iron is nearly five times worse than copper.
Solder is nearly eight time worse than copper. So you need the copper, and as much of it, next to the joint to make a good joint in a short time.
The other effect that kicks in is that the joints take longer to flow, so the operator turns the iron temperature up to compensate for lack of heat flow. Tip life suffers and results in more profit for the parts suppliers.
If you are going to solder some 0.4mm pitch IC legs one at a time (that's the hard way) then a conical might get you out of trouble. The chisels are always a nicer tip to use, IMHO.
. This is because the tip life generally a little less, and the heat transfer a little slower due to a couple of geometry effects.
