Desoldering and soldering SOJ Rams?

[Stoog]

Hey

I need to replace some SOJ package rams and was wondering if anyone had any tips on doing this? I got a scrap pcb here with some SOJ CPUs fitted and was playing around with it tonight but can't seem to get it off without either over heating the chip or damaging a pad or 2

Ive done most SMD stuff before but SOJ i can't see how to remove and solder back on easy

Whats a good temp setting for my rework station to work correctly and what size nozzle do people recommend? i am using the smallest one i have which is 3 mm

Cheers

 

[channelmanic]

If the part is to be salvaged I use a Pace ThermoTweeze iron with the long blade tips. Load up each side with extra solder, add flux, then use the iron like a pair of tweezers to melt the solder and lift the chip off.

If it's not to be salvaged I use a cheap hot air Ayoue system to pull the chip off. The problem with hot air is that it takes a lot of it to melt the solder and you'll expose the chip to too much for too long.

Chip bodies have moisture in them and the manufacturers keep them in sealed state until they are installed and soldered. When stored they have moisture tattlers in the package. If they show too much exposure the parts get baked to drive out the moisture or they get replaced in inventory. For home you can pre-bake the boards in an oven to help drive out the moisture to keep from popcorning the chip. I'd rather just use a hot iron like the ThermoTweeze to pull the chip.

For putting them down I use a hot iron and liquid flux. You MUST make sure the pads are clean of solder and the chip legs are clean of excess solder and all in a level plane before soldering it to the board.

 

[Alpha-tron]

On side note, if your using the hot air method. Let the pcb cool down do not not go rushing to remove the flux with flux remover. Sudden temperture drops and the flux remover on a hot chip can cause interesting problems.

Here is another method. You can try.

There is low temp solder called chip quik.
It is basically solder that take a bit of time to harden.
Your basically flowing low temp solder around the ic chip.
There should be YouTube videos and other how to do website out there.

http://www.instructables.com/id/Easy-SMT-IC-removal/

 

[Whippersnapper]

I don't have a rework station so I use ChipQuik (http://www.chipquik.com)

It's like solder but it's an alloy with a very low melting point. The idea is to 'contaminate' the existing solder to reduce the amount of heat required to flow the solder and remove the part.

This stuff could really help on tricky pieces even if you have a proper rework station. Works a treat. Just be sure to clean the PCB well and remove all the old solder before soldering a new part on.