Replacing broken pins/legs on a DIP IC package

Question

An absolute beginner at this, so forgive me. Took an intro to EE class last year wherein we learned how to use op amps.

EE store had a bunch of free surplus LM348Ns and 741s that I collected for a potential rudimentary analogue computer project to test out electrical modelling of differential equations, integration, etc. However I had dropped one of them causing a couple of the DIP pins bend quite sharply, and in a haze of unhinged all-or-nothing OCD I tore the rest off down to the small exposed slits of metal where the legs once were, forgive me.

I then used my uni's tinker lab to attempt to solder some wires back on but the blobs of solder wouldn't adhere, probably because I had no flux, and I only ended up damaging the thing further, so I just sanded it down to see what was inside. A very tiny IC die, wow.

I know I got these mass-produced units for free and they're otherwise 60 cents apiece but it would just be nice to know how to repair IC legs for future reference, long before I ever dare to build a synthesizer from a Yamaha YM2151 chip.

Answer 1

Pins tend to break off right at the edge of the IC package which leaves very little metal to solder a wire to. If not enough material is left on the outside of the package you can try to grind the package down to access the internal lead frame.

For DIP parts (and others) the lead frame makes up most of the package space and the chip is relatively small: _{Image from the book "Open Circuits"}

With the right grinding tools you might be able to access the remaining internal lead and solder a wire to it.

Here is a repair example of a broken pin, also applicable to similar DIP packages.

Answer 2

It’s possible but only something to try if there’s no other option. You’ll need to tin the remains of the pin and then solder a short length of tinned wire to it. Without fresh flux a blob of solder will start to oxidise very quickly if reheated, so if the surface isn’t bright and shiny then more flux is needed. Perhaps solder a relatively long wire and then cut it to length, as this will be easier to handle.

Back in the day a popular trick was to keep precious ICs in a dedicated socket and then insert that into another socket on the PCB - that was to avoid damaging the pins on your EPROM or whatever but could serve to protect a repaired pin.

Answer 3

it would just be nice to know how to repair IC legs for future reference

Generally if the pins are broken like that, there might also be breaks inside the die. The bonding could be damaged etc. Or it can seem to work fine then break later on because of strain introduced.

For this reason, during through-hole assembly, the technician is not allowed to bend the legs of a component at the point where it meets the component body. If the legs need to be bent to suit for example a 0.1'' grid, then they have to be bent further down the leg with flat nose pliers.

Summary: in a professional setting you don't repair an IC with damaged legs, you replace it.

As for DIP parts, the general best practice during prototyping/lab board assembly is to never solder them directly to the board, but to use DIP sockets.

Answer 4

If you MUST repair an IC package as described then you already nailed it - flux. A good flux will allow you to perform miracles when it comes to soldering. Otherwise a new IC is always the answer. Using a slightly higher temp solder (e.g. Sn96) might help a little as it's stronger and will take a little more handling stress. I'd recommend OA flux for a cleaner result.