Removing IC with rework: when to lift off?

[komatsu]

When using a hot-air rework station to remove an IC from a PCB - how do you know when do you "lift" the chip off?

i.e. how do you know when the connections have completely melted?

[c4757p]

Apply a constant, gentle pull. It's ready to lift when it lifts. If you don't have an easy way to apply a constant pull, apply a constant, gentle nudge from the side with tweezers or something, and then pull it when it moves.

Emphasis on the "gentle", particularly if the pads are small.

[komatsu]

ok, that's a good tip...do you have to wait for the "crackling" sound?

[c4757p]

...crackling sound?

I seriously hope you mean that you've applied flux and it's boiling.

If yes, no. (Well, it'll happen first anyway.)
If no,

[wraper]

Cannot agree with c4757p, especially for bga. You'd better try to push it gently time to tome and see if it starts moving. Then heat it a 3-10 seconds more, especially larger chips, then remove. If doing constant push all the time it is easy that hand will slip and it is just catastrophic, especially on crowded boards. There will be a mess as solder around particular is melted too.

[komatsu]

no flux applied - is there really need? none of the YouTube videos of ICs being removed show flux being applied?

btw, its a hard drive PCB

Don't worry I am only practicing ( they are redundant PCBs )

[wraper]

I usually apply flux. That make job easier. Especially if you want to reuse the part.

[komatsu]

What type of flux would you use?

[wraper]

I prefer tacky flux. It lasts longer and does not burn out instantly when you are heating the chip.

[c4757p]

Cannot agree with c4757p, especially for bga.

Techniques are definitely a bit different for BGA.

If it's easy to slip and knock things, than you have misinterpreted "gently" by at least an order of magnitude

[wraper]

If it's easy to slip and knock things, than you have misinterpreted "gently" by at least an order of magnitude

When there are other parts at <1mm distance from the part you are pushing, it is risky to put there tweezers by itself. It is not so easy to precisely hold tweezers in one point, especially when producing force, even smallest. It is just very hard to control the force precisely for a prolonged time. Quiet often will happen that what you thought was tiny force, was able to push surrounding parts. Of course not much an issue when desoldering huge SO-8 ICs and 0603 resistors.

[rob77]

doing a knock-knock with tweezers/needle/whatever from side will tell you it's ready if the chip moves a little bit during knocking it from it's side,  it means all pins/balls have the solder melted and it's safe to lift.

a good habit is to cover the PCB in the proximity of the chip with kapton tape - to avoid knocking off passives and other chips (and avoid unnecessary heating of those). it's not funny to solder back knocked off 0402 components - been there, and i'm not lazy  to place the kapton tape any more

[komatsu]

What does the flux do?

[curiosu]

The flux gets under the IC, it helps spreading the heat evenly, it helps with keeping the balls "in one place" and don't spread around due to surface tension and also prevents oxidation.

[Ryano]

What does the flux do?

Same thing in rework as it does in new construction. Help transfer the heat and prevent oxidization. When pulling a part it will reflow sooner and stay wet longer with flux. For hot air pulls I prefer to use a Rosin RMA flux pen as it is thinner then most liquid flux and doesn't cake the board as badly. If you don't have that handy you can wash the board with some IPA and then mix in a little thicker flux and achieve the same result.

+1 for using Kapton tape to mask off surrounding components. This is a life saver when working high density boards.  The tape will help prevent "blow off" of the surrounding parts. I've been in situations where I've had to apply enough heat that the Kapton was singeing, but the underlying components stayed stuck down solid.

Show us what kind of package you are trying to remove and I'll tell you how I would approach it. There are different techniques for different packages.

 

[pickle9000]

I don't know what these are called but they are useful. Basically a bit of spring wire with a handle. They prevent pushing too hard. You do need to bend them to get a decent grab. To use a bit of pressure (just a little bit) in the direction you want to go and the chip will lift as soon as the solder melts.

[komatsu]

thanks for the great replies so far.

What temp AND air flow to use on hot air rework station?

Do you go for Max. Temp and Max. Air Flow and how long 60 seconds?

[helius]

your air flow will be constrained by any small parts like SMD resistors in the area. too much air and you will blow them around. otherwise the more air the better.
temperature should be roughly 30C higher than the solder liquidus to avoid damage
you must move the tool around the area continuously, letting it stay in one place can cause damage

[komatsu]

I was just practicing some more.

Using temperature of 400C ,  it took approx 1min and 15 secs before chip came loose

Not surprisingly chip became extremely HOT. Was 400C overkill? Would this temp damage chip?

[pickle9000]

Stress (on devices and the pcb) can be greatly reduced by using a board preheater. They are worth every penny.

[komatsu]

But is a pre-heater really needed just to remove one IC?

[pickle9000]

But is a pre-heater really needed just to remove one IC?

Needed no, as long as the device is small and the board is not too thick, nor should it have a large ground plane.

If you have a look at the datasheet for a device it will give you soldering information. If you have a new device or one your planning to save check out the datasheet.

Large devices really do need a preheater for removal to reduce component damage. There is also the issue of lifting a pad.

I have seen some amazing work done with a hot air gun, no preheater. I've also seen makeshift preheaters using heating pads, a lamp with a grate on top and so on.

If you have a toaster oven set it at a low temp (150F) warm up a practice board then give it a go. Place the board on top of the oven for the actual removal work. It will keep it warm long enough for you to try it out.

[tautech]

But is a pre-heater really needed just to remove one IC?

No it's not required.

But if you intend to do lots of rework they are valuable.

One thing that has not been mentioned in this thread is lead free solder and the increased temp needed to melt it.
Nearly all commercial manufacture is done with it today.
But this stuff doesn't make rework as simple as it should be.

I personally curse the stuff because of the additional thermal stress everything must suffer, not to mention how easy leaded solder is to use by comparison.

But of course Lead is a noxious element  that we must avoid for our good health's sake.
Never mind it has been part of history for 1000's of years and it's affects well known for most of modern time.

[pickle9000]

- I hate lead free solder.
- I was told the rosin smoke is more harmful than lead but that washing your hands was a good idea so you don't ingest the lead. A fan on the bench is a good idea.
- Rosemetal is a low temp alloy that can be used to help remove chips.
- I really hate lead free solder, really.

Rose metal on ebay, I didn't look hard so I'm sure it can be found with cheaper shipping than Russia.

http://www.ebay.ca/itm/Roses-metal-Rose-metal-Bismuth-Lead-Tin-alloy-220-g-/281570225039?pt=LH_DefaultDomain_0&hash=item418ee4ab8f

[komatsu]

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).

[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.