How much protection is an IC socket?

Question

I read that if you try to solder an IC directly to a PCB, the heat from the soldering iron tends to destroy the delicate IC — unless you have elite-level soldering skills. (Hint: I do not have such skills!)

For my current project, my plan was to solder IC sockets to the board, do all of the other soldering work, and then insert the ICs into the sockets once I've put the iron away. Presumably the worst an iron can do to a plastic IC socket is maybe melt it a little bit. It's unlikely to completely (and invisibly) destroy it like an IC.

However... I'm using a matrix board. Almost every single connection requires another hoop of wire, and several of these need to connect pins on opposite sides of the ICs. Having got part way through the project, I'm becomming concerned that once I finish platting the board with its tangle of wire, I might not actually be able to physically insert the ICs for the amount of wire in the way.

The other option is to insert the ICs now, and continue soldering, hoping that the IC sockets will save me. Realistically, how much protection against thermal damage is a socket going to give? I mean, it's designed to make a good electrical connection, so it probably makes a reasonable thermal connection too. On the other hand, maybe it has more thermal mass, or a larger surface to dissapate heat? I don't know.

(The ICs are DIP-14, in case that makes any difference to anything.)

Answer 1

Even for a beginner, damaging ICs from soldering is not something to worry too much about. Especially DIP ICs where you will be applying the soldering iron to pin on the bottom side of the board.

A handful of analog ICs are very succeptible to soldering heat. They don't get destroyed, but their performance can be degraded by even normal heat. Socketing is used when really needed here.

The more common reason to socket is to make ICs field replaceable. If you blow up an IC or it turns out to be defective (which was much more common in the 70s!) you can just pop it out and replace it rather than scrapping the whole board or trying to desolder it. Another reason is for ROM chips that might need to be programmed before inserting, or replaced to do a firmware upgrade. Almost everything now is in-circuit programmable, but that was quite common back in the day.

In any case, if you are set on socketing, there is no problem inserting the ICs as soon as the socket is in place. You aren't going to overheat a part when soldering its neighbor unless you are doing something really crazy.

Answer 2

The other option is to insert the ICs now, and continue soldering, hoping that the IC sockets will save me. Realistically, how much protection against thermal damage is a socket going to give?

Probably not too much, metal has a high thermal conductivity and the pins are thermally connected as well as electrically. The advantage of a socket is you can put the IC in after you install the socket. But lets talk about your soldering skills for a minute.

Most IC's can tolerate a solder profile like this (look it up for your IC's, the manufacture will have it on their website sometimes it is hidden).

Source: http://www.klmicrowave.com/kelfil.php

Rohs solder melts at a temperature of ~188C, that gives you plenty of room to not burn up your IC. Usually I set my iron to 360C (but wait that is too hot!!!), the reason being is the solder is actually not that hot and the iron cools down a bit when it touches the solder. There is also some heat that goes out into the surrounding PCB traces. A thermal camera really helps to see how hot the components actually get, so if you can borrow one of those or a thermocouple to 'see' the temperature, this should mitigate some of your fears.

The last things is use lots of flux, flux also helps keep the temperature down and also helps the solder flow. Watching videos of people soldering on youtube also helps. Its actually probably more time consuming for you to install sockets than to figure out how to solder properly and install IC's (or even have to replace a bad one if you can't get the hang of it).

I mean, it's designed to make a good electrical connection, so it probably makes a reasonable thermal connection too. On the other hand, maybe it has more thermal mass, or a larger surface to dissipate heat? I don't know.

Borrow, rent or buy a thermal camera, you'd be surprised at how heat flows around on a PCB. Traces and other metals conduct heat readily so I don't think a socket is going to help much unless you buy the long machine pinned sockets and stand chips off the board. Sockets also add additional inductance, and resistance and can create some problems.

Answer 3

Normally you'd want to run the wires underneath the board so the sockets are unobstructed on the top. This is pretty common with wire wrapping or point to point soldering.

With DIP ICs it is difficult to damage them from applying excessive heat but not impossible. Don't let the iron dwell for more than a few seconds and if you have to go back and re-work things provide time for the chip to cool down. It can help to practice on an old scrap PCB first.

If you heat up a socket pin too much the plastic frame will melt and the pin will shift out of its normal position. The socket doesn't do much to reduce thermal strain on the chip.

You'll have the same problem where you either assemble the board with empty sockets and can't find space to insert the chips afterward, or you assemble the board with populated sockets and can't find space to pry up and replace a damaged chip. I think if you have wires going over the top of the board you'll be in a difficult place regardless of what you do with the sockets now.

Answer 4

Sockets can be more trouble than they are worth. If you use IC sockets use decent quality (turned pin) ones. The cheap ones tend to oxidise more and don't make great contact in the first place, so can lead to reliability issues. I tend to only use them on prototypes. A properly soldered joint is one of the most reliable forms of connection.

As others have said, it is pretty hard to damage an IC when soldering. They are designed to take some heat, and are less fragile (in this sense) than they appear. And there is no magic about soldering - buy a decent iron, use a tip that is of suitable size, tin it, apply solder and tip to the pin simultaneously until the solder flows on the pin, and you're done. Hint : do the two diagonally opposite pins roughly to hold the chip in place first (laying the board on its back is good if there are no higher components, so the work surface presses the chip against the board), then do all other pins, then do the first two again. (When you have the two opposite pins down, you can reheat one corner while using a finger to push the IC flat to the board if needed.)

The trick with soldering (whether doing cables, chips or whatever) is to get the solder to flow nicely round the joint, remove the iron, and keep the components still as the solder sets. This won't always work out first time, but you can re-touch the joint (adding a bit more solder) or use braid to get the solder off if there is too much. It's not that hard - you will get the hang of it pretty quickly.

(Hint 2 : if you are assembling a complete through-hole board, solder in the components in height order : typically diodes, resisitors, IC,s ... for reasons described above.)