@dicky96: Hope you didn't buy any of those T-xxx machines? (Sorry, didn't see this thread before).
Read this first maybe, hope it can help you a bit:
Hot Air (HA) vs IR, some thoughts on it.
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This is about BGA rework MACHINES, not HA guns.
They might be ok for small pcbs/chips, forget them for serious BGA rework.
This article is a compilation of my thoughts/experiences and chats/posts with/from others about BGA rework.
I'm nt a scientiest, no scientific research or explication for it, but did a lot of testing.
Might be a bit messy to read, as much is copy/paste from old and newer posts and questions answered by me.
Comments between *** are thaughts/experiences added later instead of rewriting article, to keep it as complete as possible.
Hot air is better controllable, faster profiles possible.
*** What's meant here I think is going faster with HA is a bit lesse of a risk for some components compared to IR.
After modding my machine, think my machine can go even faster compared to HA, physically I mean, not that it's wise to do.
You also have to follow some standards/profiles to prevent components getting fried ***
HA Needs different nozzles for different sizes of chips.
With HA You need to create a profile per chip/board/nozzle, while doing that you use a "control" TC *(ThermoCouple) to check the result.
(The "control TC" only controls the temp at that point, no feedback to the controls of the machine).
Once it's working and tuned, you use that profile for that specific board.
In theory, no need for the "control" TC anymore (athough it's never a bad idea to check in case it goes wrong).
The profile is controlled with the TCs in the hot air heads.
And one for the IR preheather offcourse.
Also consider a 3 zone uses IR for preaheat and top and bottom HA for the profile.
Depending PCB mass, profile/preheat, heat can still be drawn awy from PCB BGA zone.
Where a 2 zone machine, like IR and some HA, heats up bottom more evenly.
This also means the whole bottom get's a higher temp, where on a 3 zone temps outside bga zones can be lower = lesser stress for the components.
With IR you can rework all sizes of chips without nozzles.
IR profiles usually are longer, as at start it heats up slower.
You should in fact take into account your "real" profile only starts once preheat reaches 60-80C.
*** Also depends on the used controls and heaters like short medium or low wave and fast or slow heating elements.
Might apply to 3 Zone HA (Hot Air) machines too if they use slow ir preheaters that needs to warm up first. ***
A big different compared with hot air is IR rework stations use a closed loop system with active feedback to the controller.
With a 2 zone IR you have 2 controls, 1 for the the preheater (bottom) and 1 for the top heater.
Mostly the bottom heater only preheates the pcb to a set temp controlled by a TC and keeps it at that setting, no profile.
The TC measures the temp, reports back to controller, until settings are reached.
The top heater uses a programmable ramp/set/dwel controller to run the profile. Same principle, TC reports back.
The profile for the BGA is controlled by the TC in real time by real pcb temps on top of the PCB close to the BGA.
This means, depending controller and using some functions correctly, with IR You might even need only a few profiles
for all boards, say for thin/thick, low/hig mass.
No need for a nozzle helps too.
(Remeber, with HA the controller controls the air, heating it up, which results to a certain temp on the pcb/bga for only
that specific board and nozzle as the "control TC" doesn't report anything back to this process to adjust air temps.)
IR is harder to control and shouldn't be used the same as HA.
*** Most of the time temp only has to go up untill solder liquidus, so not really a problem.
But with wrong settings or profile, you might get overshoot and there is also the mas of the elements.
HA is "active", air flowing over element prevent this more probably.
For me, it's not a problem, can control it pretty fine, will post some pics later ***
I wrote about this in the past. *** (Conptrol with IR) ***
It was about using radiation more instead of usig the element's heat, giving more convection heat.
If you understand that, it can become very useful.
Using radiation (element further above object) instead of convection (heat of the element if to close to object) can give you much better control.
However, it has a steeper learning curve and you will destroy a few more chips in the beginning probably.
*** In fact, 2 zone IR is more straight forward compared to 3 zone HA, for both learning might cost you, but some chips are more sensitive for IR.
Like the old PS3 RSX BGAs, IR gives a slightly more risc for solder bleeding. BUT... this can just al wel happen with HA.
It all depends on your profiles. See also comment below ***
As said, with IR you can rework all sizes of chips without nozzles.
Or larger areas in 1 go, can be handy too.
Like say you want to take off (small) components from a pcb for later use.
Put it on your IR, fire it up.
Once solder is melting, take off what you need.
Starting top first.
But don't forget heating a specific are to long can destroy components in that area too.
Done a certain area? Move the heater or pcb, start picking the next components.
If you want to take off trough hole, once all on top is removed, set your bottom heater to higher temps so bottom solder melts.
And you can take of elcos, sockets or whatever in a jiff.
It can rework plastics without problems, was a big + years ago.
Most plastics used now are suited for lead free temps, so mostly not a problem with HA either anymore.
Once you mastered IR, it can do a pretty good job.
But as said before, might have to be a bit more carefull on some chips.
Especially on first gen xbox 360 (popcorn), PS3 RSX = solderbleeding etc.
This might have been a problem of the transition from lead to lead free, recent chips seem to be able to stand more now.
You can influence these problems by using e.g. kapton on reflective parts, or reflecting tape to protect sensitive components from higher temps.
Or adjusting your profiles or using it manually, it does everything hot air can do.
I also think, but that is my opinion, can be wrong on this, beeing a bit more carefull and slower results often in "better" reflows.
With this I mean all balls, from middle to outside, fully liquidus.
Not saying HA can't, as said, might be wrong, and as I don't have hot air can't speak from experience.
But it looks like reflow returns are higher on HA then on IR, also reported from someone switching from IR to HA.
But he prefers his HA machine as it never gives him problems and he only places new chips.
When starting BGA rework myself, hot air was to expensive.
IR machines are much easier to fabricate.
That's probably why they were offered much cheaper and bought more, only for the price.
If cheaper, I would've gone for hot air probably myself.
Do I regret now I got an IR machine?
ABSOLUTELY NOT!
Love my IR machine, but it's modded heavily.
If I would buy one now would I go for HA?
Dunno, for the same money, I would probably build my own IR machine using quality components only.
Again, don't have a hot air BGA rework machine myself.
It's my experience with IR and what I collected by reading, reading posts, chatting, voice communication etc with people and their experiences about/with HA.
Also helped a friend with a HA machine (Shutle Star)to get his profiles right.
He had probs in the beginning too with solder bleeding sometimes, rarely popcorning.
However, once his profiles were tweaked he never had that problem anymore.
Only want to say when one starts with this, even with hot air, you can/probably will destroy some chips setting up your profiles.
But it does seem to have lesser probs with HA.
With IR however, even if your profile works without problems mostly, it can still happen suddenly.
Why, who knows? Condition of the chip? Has it been raped before maybe? etc...
*** Popcorn is moisture related.
Drying/baking PCBs/BGAs/Components should prevent most of popcorning/delamination.
You should get an oven (DIY works ok) for this as soon as you start BGA rework.
Most reballers wil tell you "no need to bake, I never do it, never had problems" wich might be true.
But say you get something with a 1000$+ FPGA on it, would you risk to popcorn it if baking it for a few hours might prevent this? ***
Here some profile graphs using my IR setup:
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