IC forces <260°C solder temperature; socket needed?

Question

For a school project, we are using LN324-N OP-amps packed in a DIP.

Specifications can be found here.

We need to solder these to a PCB, but section 6.1 of the datasheet says:

Lead Temperature (Soldering, 10 seconds) - min N/A, max 260°C Soldering Information - Dual-In-Line Package - Soldering(10 seconds) - max 260°C

I take it that we can't solder at > 260°C without an IC socket.

I noticed that people rarely solder at < 300°C (I wasn't able to find out why - the only pages that show up when I google "low temp solder disadvantages" or similar are related to other commercial products.)

So the question is:

0. Am I right about how we can't solder at > 260°C, or am I missing something?
1. Do we need a socket, or can we just solder at 250°C without a socket?
2. Will there be significant consequences of soldering at such a low temperature?

Answer 1

I have never ever destroyed an IC due to soldering heat, and I usually run my tip setpoint at 400-450°C (for small tips) or hotair even at 500°C. These figures would also vary a lot from iron to iron depending on how good is the thermal contact from the temperature sensor to the tip surface.

It is important to realize that these temperature are never seen by the parts being soldered. The solder only even starts to wet the part at 220°C, so when the solder is not yet flowing onto the part, it means the part is still colder than 220°C, despite the high numbers that your solder equipment might display.

This is in contrast to soldering in a convection oven. This heats very slowly and homogeneously, so you can set the oven setpoint much closer to the desired soldering temperature.

Answer 2

The school probably made this requirements so that beginners at soldering do not damage the components. You normally don't heat something up for as long as 10 seconds.

RoHS solder wets at around 220 °C and leaded around 180 °C. Leaded solder is strongly recommended for beginners and fine as long as the device isn't going to end up on the market/in public.

Professional soldering is typically done at 350 °C and around one second per joint, but beginners will have a hard time with that.

It is therefore common to set the solder station temperature at 250 °C for beginners, assuming leaded solder. That way you have more time and can take it slow, heating the component for many seconds while waiting for the solder to wet, without damaging anything.

If you set the iron to 250 °C, you don't have to worry much about damaging the IC. It might however be a good idea to use sockets regardless, in case you mess something up. It's always convenient to be able to replace and reuse the IC. Personally I always use sockets whenever I make lab boards with DIP parts.

General solder advise for DIP parts/common through-hole would be to use a flat solder tip, 2–3 mm wide. Heat the via a bit before moving the tip up to the component pin, then at the same time nudge the pin with solder from the other side. Assuming a plated-through via, ensure to apply enough solder so that the joint wets at both sides. There should be no air gaps. Use "no clean" flux, like for example a flux pen, in case you mess up and need to redo a joint. You can also apply flux in advance, especially if you suspect oxidation on the board surface.

Answer 3

Use Pb-free solder (SnAgCu) with the built in flux ("rosin core"). This is the standard thing you find everywhere. IMO skip the Pb solder.

Use clean tip with undamaged plating on at least one side of it. (thus, no abrasive cleaning). Don't use a smaller tip than you need.

Use the phase changes of the solder (1st melting, then changing from hydrophobic to hydrophilic as it wicks) to visually reckon temperature of the component lead and pad. You want to set the iron slightly above this temp, and make contact for a couple of seconds - more with larger objects, less with smaller. For standard Pb-free solder, start at 275-300C (own experience) and adjust from there to make up for differences in the iron and tip. Anything over 350C will IME accelerate the aging of the tip, so I wouldn't do that for too long.

The idea is you need enough excess heat to make up for the heat pulled away by the component and pcb itself, which varies quite a bit. Excess heat can mean either bigger tip or higher temperature. For tiny parts, just one touch can be enough. If not: touch a small bead of solder to the iron, then hold it against component lead or pad to pre-heat it for a couple seconds (this is where experience will develop), then if necessary touch it again with the solder wire to add enough solder material to make the joint and possibly deliver some fresh flux. The second part is more for larger stuff, if you spent several tens of seconds puttering around with something difficult.

DIP's should be very easy, unless there's no thermal relief on a pad connected to a copper plane. In that case, do some combination of higher temp, localized pre-heat as described above, or in extreme cases, actual pre-heat with a dedicated device.