exxos's Atari, Amiga & retro forum

im about to fit my ide board and was wondering best approach for desoldering the 68000
got desoldering gun ,braid , hot air etc.
is it best to do 1 side then the other or alternate sides to spread the heat
cheers phil

If you've got a proper vacuum desoldering gun then it's pretty easy:

• Place the tip over the pin and wait for 2-3 seconds for the solder to melt right the way through.
• Pull the trigger to start the pump.
• Wiggle the tip around the pin in a circular motion for about 2-3 seconds.
• Remove the tip.

If the solder doesn't come out first time apply some new solder, melting it with the tip, and repeat the above.

Once you've done this to all the pins try wiggling the pins with the tip of a screwdriver, they should all spring freely. Those which don't will still be connected by a bit of solder, repeat the above on that pin.

At this point the CPU should basically fall off the board.

P.S. On my Hakko FR-301 I use the 350C (lowest) temperature setting and it works well.

philbo34 wrote: 14 Oct 2020 09:12 im about to fit my ide board and was wondering best approach for desoldering the 68000
got desoldering gun ,braid , hot air etc.
is it best to do 1 side then the other or alternate sides to spread the heat
cheers phil

My approach is to use good clippers and clip the 68000 legs off and then desolder the legs one at a time. You obviously destroy the 68000 this way but its fast and 68000s are cheap. Zero risk to your board.

Second way is to use the desolder gun as above.

I wouldnt use the hot air for this job except as a gentle preheater.

many thanks gents

Pin 16 and 53 are Ground and could potentially be more problematic due to heat dissipation.

+1 for proper vacuum solder gun. Bought one last year as a Christmas present for myself and wish I had bought one many years earlier. Makes the job so much easier.

Yeah, you may need to keep the desoldering gun on them for about 5 seconds before pulling the trigger.

My personal tip:
If you use the gun on a leg but it doesn't get all the solder, the gun probably won't do it, just re-solder that leg with some fresh solder and try again with the gun - it will definitely work this time.

Sometimes - *especially* with SIP resistors, I re-solder them first and then use the gun.

philbo34 wrote: 14 Oct 2020 09:12 is it best to do 1 side then the other or alternate sides to spread the heat

I've always just gone straight across one side and back on the other and never had any problems. The chip has always survived. The 68000 DIL is a pretty big chip, so I think it can take a lot of heat.

+2 for the de-solder gun, it's been the best tool I ever bought and has saved a lot of time and is generally kind to the PCBs if you use it properly.

I use mine at anywhere between 350C and 450C dependent on solder type, thermal mass (Ground & power planes etc). The sweet spot for STs seems to be about 370-380c and about 3-5 seconds on target before pulling the trigger.

For ground/power planes with a high thermal mass I tend to heat the board gently with hot air (They are quite easy to scorch if you're not careful) and then re-visit the pins that are problematic with the gun.

I have done quite a few successfully with solder wick and an iron(I use Chem-Wick, it's very good and fluxed too) but there is the risk of damaging vias if you use too much heat. Also, if you have any areas that solidify before you remove the wick, it can be possible to pull off vias\traces as you pull the wick away, so be gentle.

As for manual de-solder pumps, I just don't use them anymore because they can jump as you use them and they aren't hugely effective.

One other option I have seen, is a solder blower. It's kind of like the reverse of the de-solder gun, only it blows air through the nozzle to push out the molten solder. I don't imagine it would be great to have molten solder blowing all over the place though!!