Removing IC with rework: when to lift off?

[pickle9000]

Lead-free components are not liked on this thread I see!

When doing the real thing (i.e. not a redundant PCB), is 400C too hot a setting on a hot-air rework station to remove a chip?  Will I damage the chip? (it contains adaptive firmware data which  must be subsequently transferred onto another PCB).

With hot air the distance, angle, flow rate all change the actual temp on the part. If you have a bead type (small mass) temp probe place it beside the device and check. Also there is nothing wrong with using the hot air to heat around the perimeter of the device. This will raise the temp of the pcb itself (like a preheater). I often use that temp setting (400) but take that with a grain of salt, my methods will not be the same as yours.

[tautech]

Lead-free components are not liked on this thread I see!

Not conponents at all, just lead free solder. I'm with pickle9000 and hate the stuff too. 

Hot air use is a little daunting at first, you'll be scared of hurting something, get some old PCB's and experiment, you'll get the hang of it. 

[Shock]

This video covers most of what you need to know when removing and installing ICs but practice first on things like old computer motherboards. BGA and through hole are different techniques. There are plenty of videos showing removing and reworking all sorts of components.

You can always substitute tools but they are generally inferior to proper tools and technique.

Preheating prevents warping and less damage to pads and rather than attacking the board with heat you can take your time and then with control hit the melt point and remove the component without disturbing other components.

A hot air rework station and preheating pad can be subbed for a hair dryer or hot air torch (watch out for flammable IPA). In certain situations you can also cut the IC or use low temp soldering alternatives like CHIP QUIK as an alternative to hot air, but it's risky unless your technique is perfect.

There is no substitute however for fresh flux or fresh flux and solder and cleaning with IPA. Dry oxidized joints generally need a bit more heat. Adding this to your process makes things so much easier and a much tidier job overall, especially when using solder wick.

[rob77]

Lead-free components are not liked on this thread I see!

When doing the real thing (i.e. not a redundant PCB), is 400C too hot a setting on a hot-air rework station to remove a chip?  Will I damage the chip? (it contains adaptive firmware data which  must be subsequently transferred onto another PCB).

400C is way too much !  set your hot ait to 280-300 for the beginning and once you're practised enough you will find the 260-280C as an accurate temperature.
leadfree solder melts at approx 217C (actually depends on the alloy and might be anywhere in the 200-220 range). the exta 40C (when working with 260C air) is needed to overcome the temperature drop "mid air" while the air gets from the nozzle to the board.

and you must be patient it takes some time to heat up evenly the board and the chip with hot air at correct tremperature ! i know with 400C the chip reflows in few seconds, but you wan't to rework/fix something not to kill it and btw... i think the 400C explains the cracking sound you mentioned earlier

[Howardlong]

Be aware that if the board is multilayer with large power planes, it'll take significantly more time to warm up enough to remove the device. Removing a device from a simple two layer board is much quicker.

[rob77]

This video covers most of what you need to know when removing and installing ICs but practice first on things like old computer motherboards. BGA and through hole are different techniques. There are plenty of videos showing removing and reworking all sorts of components.

You can always substitute tools but they are generally inferior to proper tools and technique.

Preheating prevents warping and less damage to pads and rather than attacking the board with heat you can take your time and then with control hit the melt point and remove the component without disturbing other components.

A hot air rework station and preheating pad can be subbed for a hair dryer or hot air torch (watch out for flammable IPA). In certain situations you can also cut the IC or use low temp soldering alternatives like CHIP QUIK as an alternative to hot air, but it's risky unless your technique is perfect.

There is no substitute however for fresh flux or fresh flux and solder and cleaning with IPA. Dry oxidized joints generally need a bit more heat. Adding this to your process makes things so much easier and a much tidier job overall, especially when using solder wick.

that guy in the video..... well....
why would someone bother with masking and preheat during removal of the chip and then let the board cool off , remove the masking and then introduce a yet another  thermal shock to clean the pads ? and actually clean the pads with iron and solder wick without masking ? cleaning the pads with iron and wick is the most risky part when considering knocking off some small components with the iron...

better  way is to keep the board on pre-heat (120-150C preheat is enough) and keep the masking on while cleaning the pads and soldering the new chip. it introduces less thermal shocks and it's faster (btw... faster is a "must" when doing repairs - keep the cost low).

[rob77]

Be aware that if the board is multilayer with large power planes, it'll take significantly more time to warm up enough to remove the device. Removing a device from a simple two layer board is much quicker.

for those multilayer boards (e.g. PC main board) you would definitely need a higher power pre-heat. you can replace the correct (and preferred) pre-heat plate (like the on in the video earlier in this thread) with a paint stripper hot air gun set to LOWEST temperature setting and blowing from a bigger distance - check with a thermocouple in the air stream at what distance you get  130-150C - and that will be your safe distance for preheating with the paint stripper hot air gun

[Shock]

that guy in the video..... well....
why would someone bother with masking and preheat during removal of the chip and then let the board cool off , remove the masking and then introduce a yet another  thermal shock to clean the pads ? and actually clean the pads with iron and solder wick without masking ? cleaning the pads with iron and wick is the most risky part when considering knocking off some small components with the iron...

better  way is to keep the board on pre-heat (120-150C preheat is enough) and keep the masking on while cleaning the pads and soldering the new chip. it introduces less thermal shocks and it's faster (btw... faster is a "must" when doing repairs - keep the cost low).

One of the mysteries of the internet.

[komatsu]

Thanks for all the replies so far guys.

This new temp. setting is not working at all.

I changed the nozzle on the rework station to a thinner one for a more focused air flow AND dropped the temp. down to 300C and spent 20 minutes
doing a backwards and forwards motion...it only got up to 120C (measured using infrared thermometer)

What am I doing wrong?

[komatsu]

I changed the nozzle back to a larger one and have discovered the hot-air-rework-desolder forumula!

300C for 60 Seconds
followed by
400C for 20 to 25 seconds

Then the chips slice off nice and smoothly.

Using a smaller nozzle ( which I assumed would give a more focused channel of air)  proved to be a complete joke and
the extra 20 seconds at 400C proved essential.

Now doing just like the guyz on You Tube!

A big thanks to all the contributors to this thread.

 

[ion]

Thanks for all the replies so far guys.

This new temp. setting is not working at all.

I changed the nozzle on the rework station to a thinner one for a more focused air flow AND dropped the temp. down to 300C and spent 20 minutes
doing a backwards and forwards motion...it only got up to 120C (measured using infrared thermometer)

What am I doing wrong?

Distance?  If you keep the nozzle 5 - 10mm above the chip you shouldn't need to go above 320C, 300C will be fine for most parts.

First time I used hot air I couldn't get the solder to melt below 400C either, turns out I was keeping the nozzle too far away.

[komatsu]

ion, thanks for the tip re: nozzle height. I will keep it in mind. 

One more thing. How does the IC "stick onto" the PCB which you are transferring to?

[tautech]

ion, thanks for the tip re: nozzle height. I will keep it in mind. 

One more thing. How does the IC "stick onto" the PCB which you are transferring to?

For re-work(essentially what you are doing)  in 2 normal ways:
For hand soldering, solder down 1 or 2 corner pins ensuring the rest are correctly located, then individually solder or drag solder the rest.

For reflow or hot air the solder paste will hold it in position.

[komatsu]

I changed the nozzle back to a larger one and have discovered the hot-air-rework-desolder forumula!

300C for 60 Seconds
followed by
400C for 20 to 25 seconds

Then the chips slice off nice and smoothly.

I have to eat my words here.

I tried this on one more PCB....and 15 minutes later that chip is still not coming off ( even though the board and IC is the same type of previous ones). I eventually had to stop because I noticed that surrounding components were becoming loose but not the chip I want.

Can anyone explain this?

This hot-air rework lark is really beginning to look like hot-air!

[tautech]

Can anyone explain this?

Quite possibly the other right PITA for rework......GLUE.

Sometimes used on bigger components prior to reflow.

[komatsu]

tautech, no sign of any glue...

[tautech]

tautech, no sign of any glue...

Usually a dot of thermo-setting epoxy under the IC.
Get it hot again, enough to loosen surrounding parts and gently pry it off.
Big tip & lots of air.
The donor PCB doesn't matter right?

[richcj10]

suction pen...when it is ready it will pop off.