What's the proper way to solder an IC to the legs of another IC?

[Chuu]

Some backstory, I have an amplifier that needs to be repaired, and after some troubleshooting with the builder it was discovered that a specific IC (?PC1237 [pdf]) had to be replaced.  It's the 8-pin SIP in the middle of all the voltage measurements in the following picture:



No problem!  I ordered the part, and in the meantime was trying to figure out how to get that daughterboard out . . . and just couldn't figure out how it was attached to the case.  I sent an e-mail to the builder, and his response was that it was not removable, and to simply cut off the legs of the old IC and solder the new IC to the legs.

I've probably spent ~40 hours total soldering so I am still a beginner, and have never had to do something like this.  I couldn't find anything on google about this procedure either.  The biggest fear is that if I apply too much heat to the leg, I ruin the solder joint on the other side of the board which I cannot get to.  I was going to try something like the following, but if anyone has any advice, a better procedure, or knows of a socket specifically designed for this purpose please share!

• Cut off the legs of the old IC
• Tin 8 pieces of extreemly short wire (<1 inch.) on both ends.  Solder to the cut off legs being extreemly generous with flux and removing the iron as soon as the solder liquefies and bridges
• Heat-shrink the ends connected to the PCB
• Put some unshrunk heat-shrink over the wires, solder the new IC to the wires, and heat shrink the legs of the new IC
• Secure the IC to the board (haven't figure out the best way to do this one yet)

[amyk]

I don't believe it's "not removable". It's probably screwed in place after being soldered to some components mounted underneath it. I can see the bottoms of several solder joints along the edges.

[Jwalling]

If I were doing this and the board *really* could not be removed from the unit, I would rock the SIP back and forward a few times - this will eventually break off the pins. Then just tack solder the new part in and you'd be done.

Jay

[grumpydoc]

If I were doing this and the board *really* could not be removed from the unit, I would rock the SIP back and forward a few times - this will eventually break off the pins. Then just tack solder the new part in and you'd be done.

Rocking is likely to berak the pin quite low down so not leave much to solder to.

The board looks to be through hole plated.

I would cut the pins fairly high - even to the extent of cutting through the bottom of the package to leave a good bit of pin to get hold of.  Then heat each pin and remove it from the board with needle nose pliers or fine tweazers followed by cleaning out the holes with solder sucker or wick. Finally drop the new part in and solder from the top of the board.

Much neater and much less likely to fail than tacking onto the old pins.

I don't believe it's "not removable". It's probably screwed in place after being soldered to some components mounted underneath it. I can see the bottoms of several solder joints along the edges.

+1 but if there is a lot of stuff the board is attached to it might just be easier to re-work that 8-pin SIP from the top.

[T3sl4co1l]

It is quite possible to remove something from the top, as long as the leads are accessible.  Bend and break off the existing part, then use a very hot iron to melt each pin in succession, then quickly follow with a solder sucker to extract it.  If the pins are clinched, try pulling them out with pliers before sucking.

Tim

[Ian.M]

Removing the board really doesn't look that bad.  The connections AC1 - AC5 on the left look like they may be transformer tags and should be fairly easy to desolder as long as an iron with an adequate power rating is used.  Use a solder sucker to remove most of the solder then clean up with desoldering braid and additional electronics grade flux.  Alternatively it may be possible to simply unbolt the transformer from the chassis and lift it enough to get access to the underside of the board. 

The leads at the top appear to have enough slack in them for the board to be flipped over to the right.

The two connections at the bottom edge of the board may also need desoldering if they aren't simply a board mounted component so be careful when lifting the board.

As you don't have a lot of experience desoldering, some time spent practising desoldering larger parts from any through hole board you can acquire from whatever scrap electronic device you can find would be helpful so you can avoid damaging any tracks on your amplifier board.

[Chuu]

Thanks a ton for your expertise.  I think I like grumpydoc's suggestion the best and will attempt it when I get the part.  For some reason I didn't even consider that it was fine soldering to the "wrong" side of a through-hole pcb.

[android]

For some reason I didn't even consider that it was fine soldering to the "wrong" side of a through-hole pcb.

...well, it *could* be fine. I've been bitten by a non plated-through hole being used as a via ... so the through-hole component had to be soldered on the top *and* the bottom.

BTW, if you're worried about damaging the new component you might want to solder a SIL socket instead (and just plug the component in afterwards)

[Chuu]

For some reason I didn't even consider that it was fine soldering to the "wrong" side of a through-hole pcb.

...well, it *could* be fine. I've been bitten by a non plated-through hole being used as a via ... so the through-hole component had to be soldered on the top *and* the bottom.

BTW, if you're worried about damaging the new component you might want to solder a SIL socket instead (and just plug the component in afterwards)

Thanks for the tip, I ordered some sockets because I was worried about having to make this repair again.  Thinking about sockets though, that gave me an idea of how to fix if it I really couldn't get to the back -- cut off the legs, use an upside-down socket to attach to the remaining legs, cut a very small protype board (literally 2x8 holes), and solder the IC and the legs of the socket to the board.

[Stephan_T]

I recently bought a cheap ZD-211 desoldering iron which is basically a combination of a solder iron with a piston pump:


http://www.china-zhongdi.com/products.asp?CataID=140&cataupper=&k=&

For small repair jobs, this works pretty fine and much better than my unheated standard desoldering pump.
I paid less than 10€ including postage.

It should be relatively easy to open the solder connections that prevent you from removing the board and get to the right side of the joints of your IC.