Getting started with BGA reflow and reballing ... - Page 1
Forum section: electronics / beginners

author: axero
author_rank: Regular Contributor
timestamp: June 28, 2014, 11:59:46 am
content: I have an Aoyue Int2703A+ soldering station combined with the Aoyue Int883 pre-heater and I want to reflow and reball the GPU chip on a laptop motherboard. I have read a few guides but there are still some questions that are still unresolved before I continue. I'm new to this and I've never done this before.Quesion 1: What is recommended pre-heater temperature? The melting point of leaded solder is around 180°C and lead-free about 200°C, if I understand it correctly. How can I tell what alloy has been used? The laptop is an Asus, the motherboard was manufactured in 2007, most likely by Foxconn as that brand is mentioned on the motherboard. It has no RoHS or other markings that I can see that could potentially indicate that a lead-free soldering process has been used in the manufacturing.Question 2: When I put the motherboard on the pre-heater, there are components on the back-side (facing the heating elements of the pre-heater), won't the solder melt and make these components fall off the PCB? Or will the surface-tension of the melted solder keep them in place anyway? Is there any measure I can take to prevent components from falling off the PCB?Question 3: Can I put the entire motherboard as it is on the pre-heater or should I use some metal shroud that shields all parts of the motherboard but the surface underneath the GPU? Maybe that can damage the pre-heater? I suppose I could take a few layers of household aluminium foil and cut a square in it...Question 4: Is there a risk that the motherboard will bend because of the heat or is it designed to take the heat? Maybe I should make some kind of pcb jig or fixture that prevents the motherboard from carrying its own weight so it won't bend when the heat softens it? I'm hoping that this won't be necessary.The jig that comes with the pre-heater will only hold the motherboard on its edges.Question 5: Are all components designed to take the heat? I.e. the plastic sockets and connectors, won't they melt from the heat? The caps, isn't there a risk that they will pop? Strangely enough I cannot see any electrolytic caps on the motherboard so perhaps this is not an issue, but what applies in the more general case?

author: wraper
author_rank: Unknown
timestamp: June 28, 2014, 12:27:01 pm
content: No way you can reflow big BGAs with this equipment with acceptable rate of success. You will get 1 working board out of 4 at best. Other will be irreversibly dead (lifted pads, popped PCB) if you will succeed to remove IC at all. Moreover Nvidia BGAs don't handle even smallest overheat, they will pop. Also reball is a hoax in most cases because problem usually hides inside the IC itself (lost connection between die and substrate) and heating just revives it temporarily. Usually 1 week - couple of months. Also need to mention, most nvidia GPUs on ebay, aliexpress and other places made before 2009 are pure crap. They are just dead IC's removed from motherboards but they will work for a short time as described before. Also there are bunch of remarked chips sold. They might be IC's with different memory bus (will work in many cases but with ram divided by 2 for example). May be lower/higher end variation of the same chip, desktop GPU sold as notebook or even more exotic variants.

author: axero
author_rank: Regular Contributor
timestamp: June 28, 2014, 01:19:16 pm
content: So what equipment do you propose to be used then? What temperatures are these GPU chips designed to take? They must be able to take something, otherwise they wouldn't survive manufacturing. And I read a lot of success stories on the tube of fixed Xboxess, Playstations and all sorts of remorseless pieces of laptop motherboards...So I feel like you are exaggerating quite a bit here, I have soldered a lot of things but I have rarely experienced e.g. lifted pads. Still waiting for answers to my questions

author: wraper
author_rank: Unknown
timestamp: June 28, 2014, 01:54:06 pm
content: Problem with such hot air stations is that you can't evenly heat up large area, therefore while you are burning one area, solder is not yet melted in another. Trust me, soldering BGA is completely different from soldering SMT resistor or QFN IC. Board warping also is a serious problem, that's why big preaheaters are needed.There are large IR or hot air stations with big preheaters and tight temperature control for this. For example:http://www.ebay.com/itm/Newest-BGA-ACHI-IR-12000-Dark-Infrared-Rework-BGA-Station-for-Reworking-BGA-/181281761347?pt=LH_DefaultDomain_0&hash=item2a353c2843http://www.ebay.com/itm/Jovy-RE-8500-Infrared-BGA-Rework-Station-for-SMD-BGA-Reflow-Rework-/151320432090?pt=LH_DefaultDomain_0&hash=item233b668ddaBut I can't call them super duper stations. They are in budget range, so not perfect at all. I would say that they are cheapest you can buy to get acceptable results when soldering large BGA's. There are cheaper ones with halogen heat lamp but they are total crap.

author: axero
author_rank: Regular Contributor
timestamp: June 28, 2014, 03:09:21 pm
content: The Int 883 is big enough to heat an entire full ATX motherboard so I don't think size and power is an issue here. The heating elements of the pre-heater looks pretty good too and they are probably quite capable of distributing the heat evenly. Here's an overview of the 883 and its smaller sibling 863:http://bit.ly/VvTTWtI realize now that the jig can be configured to secure the motherboard so that it won't warp. I bought this unit from a reputable seller that sells equipment that costs more than 6 times as much as the ebay items you linked to.Perhaps there may be an issue with the hot air gun of the re-work station. Perhaps these questions better be asked at bga rework forums, as I seem to get no answer here...

author: wraper
author_rank: Unknown
timestamp: June 28, 2014, 03:52:50 pm
content: Obviously BGA forum would be better place. What I can almost guarantee that you will get dead board if you have not couple of scrap boards to try on them first.Answers:Solder is lead free. Parts won't fall off (except big parts with very small footprints) unless you'll shake the board. You must cover plastic connectors nearby. All board must be heated evenly underneath. If this is Nvidia GPU made in 2007 then just either heat that chip and it will work some more time or you need to get replacement with 2009+ date code (with all problems getting proper one, I wrote about). Name the chip model BTW as some are no way you can get normal replacement. As BGA is almost certainly glued to the board on the sides (must remove most of the glue on board preheated to 110-140oC), you will be unable to catch solder melt moment without controlling the temperature (lifted pads I warned about). That jig is no good, as it will move parts underneath when solder melts, there must be no any objects under the GPU and nearby.

author: axero
author_rank: Regular Contributor
timestamp: June 28, 2014, 08:07:26 pm
content: Ok, but during the reflow process I guess that the pre-heater should bring the temperature up to at least 180°C. Then the top heater should bring it up to at least 220°C for a few minutes during the peak of the reflow process. The pre-heater is programmed to bring the temperature up and down slowly and "soak" the PCB it as they call it.The BGA chip is not that big, it's only 32 by 32 mm and there is a 30 by 30 mm nozzle for the heater gun so the heating will be pretty evenly distributed over the chip on the top side as well.The GPU chip is an nVidia G84-625-A2 sharing the heat-sink with an Intel SLA5U chip. It is a GeForce 9500M GS and it has its own dedicated RAM, i.e. it isn't sharing RAM with the system. The enclosed picture shows these two chips. As can be seen in the picture, it looks like the chips are glued to the PCB in the corners.The system boots normally and I can log in to windows 7 as usual but the screen is black and there is no image output from any of the three ports (LCD 30-pin, VGA out, HDMI out). No BIOS, no ASUS greetings logo, no MS-DOS prompt, no Windows, nothing, the screen is black the entire time.

author: wraper
author_rank: Unknown
timestamp: June 28, 2014, 08:46:09 pm
content: You can heat up GPU a bit, for example to 120-150oC with hot air and try if MB works. If it works ok, 100% GPU fail. So you either need to heat it to higher temperature to prolong it's life to couple of months or if you are very lucky maybe even year. Or change it,no reball, as it is useless and only stressing PCB. Actually it is not so small and it may be difficult to successfully change it and will require higher preheat than with normal equipment. You must try on something else first (at least removing the chip) or you will get a dead board with 95% probability. Verified by a lot of people including myself. Also small thermocouple near to the BGA would be very helpful. Most of the G84-625-A2 sold from China and other places proven to be remarked in most cases, from something that usually won't work. On Russian notebook repair forums repair guys suggest to change it to G84-603-A2 which proven to be usually good, not rebadged.http://www.ebay.com/itm/2012-Brand-New-NVIDIA-G84-603-A2-64Bits-128Mb-BGA-IC-Chipset-graphic-chip-/180896277641?pt=LH_DefaultDomain_0&hash=item2a1e4224892 rules when buying: Date code newer than 2009 and white compound around the die, not black.

author: Rigby
author_rank: Super Contributor
timestamp: June 28, 2014, 09:07:25 pm
content: I saw a chap on YouTube reflow an XBox 360 chip with nothing other than a high temp heat gun. One of the ones that puts out air at one temp with one fan speed. DeWalt branded, pretty sure. So, it can be done, though I would not expect success on your first try. He spent a lot of time preheating things and cooling things gradually. In the beginning he had a nonfunctional console and in the end it worked fine.You aren't going to be able to do that on your first go. No one is, not even with the proper gear.The lesson here, and it is a lesson I learned long ago, is to prevent yourself from purchasing design flaws like this one in the first place by simply not buying consumer grade laptops. They are ALL crap in one way or another. Business models are more expensive, yes, but they have much longer lifecycles, and often come with 3-year warranties instead of 90-day warranties.That doesn't fix your issue, I'm afraid, but I am not sure anything will.Sorry about being a Debbie downer.

author: axero
author_rank: Regular Contributor
timestamp: June 28, 2014, 10:07:48 pm
content: I'm in the market for a new laptop. It's not that easy to tell the difference between business grade and consumer grade laptops these days. In the past I used to prefer Lenovo as they made good laptops with generous warranty policies. Today Lenovo is crap just like Acer and MSI and they only offer 1 year limited. Dell used to be good but I heard a lot of bad things about them during the last couple of years. At least Asus provide 2 years of warranty. Laptops such as Hewlett-Packard, Packard-Bell or Fujitsu-Siemens give me the Heebiejeebies. They really feel like something that came with the cereal box, and their driver support with bloatware is nothing short of abysmal.I guess that the only thing we can rely on is the ifixit teardown guides and their repairability scores that they give on different stuff. I wonder what happened to all those sustainable development environment policies and product life-cycle ditto. But I guess that people are busy talking about global warming these daysBut yes, I do want to learn how to reflow and reball properly and if I fail with this, it won't be the end of the world. I understand that there is a risk but of course I want to get all info possible and do what I can to succeed. Although Aoyue may not be in par with more established brands such as Weller, Ersa, Scytle, or whatever Chinese that is popular right now, in terms of quality, I spent quite a bit of money into this equipment. So I couldn't wish anymore than that it will be put into good use.I will try an ordinary reflow without reballing. All plastic details on the heater side will be covered with aluminium foil fastened with kapton tape. I'll make sure that as much of the motherboard surface will be exposed to the pre-heater as possible. I will heat the GPU with the heater gun as well. The pre-heater comes with a termocouple so I guess all I have to do is to make sure that the temperature never exceeds 220°C. I saw on some German info page that it is unsafe to exceed that temperature. I will also mount and secure the motherboard as much as possible in order to prevent warping.

author: Fsck
author_rank: Super Contributor
timestamp: June 28, 2014, 10:27:05 pm
content: Lenovo's pretty good. X, T and W series - new X series are a bit crap now in expansion. Dell Precisions are still excellent. HP zbook, elitebook.not that hard to tell the difference between business and consumer, especially if you go with a workstation type laptop.

author: Rigby
author_rank: Super Contributor
timestamp: June 28, 2014, 10:45:30 pm
content: HP workstation laptops are excellent. Not cheap, though.

author: wraper
author_rank: Unknown
timestamp: June 28, 2014, 10:52:55 pm
content: Good video how to do:

author: axero
author_rank: Regular Contributor
timestamp: June 29, 2014, 10:51:28 pm
content: I'm actually considering finding a replacement chip then since the defect may rather be within the chip as stated. I can't really see how the substrate would come off the die. Maybe the wire bondings lose contact with the substrate if they aren't properly welded to the die.The video is interesting and it is nice that the author put some effort into making it in good quality. There are some things that the video doesn't explain however; he didn't reveal the reflow temperature profile and it didn't show how he protected the components on the back side of the PCB, nor did it show what measures he took to monitor the temperatures during the reflow process, i.e. the thermocouplers. But I did notice some interesting things; the motherboard didn't seem to be fixed in a jig during the reflow process as discussed above. Also, although he did cover the plastic CPU slot near the chip during the reflow process, he didn't cover the plastic pin connector, which is even closer to the GPU than the CPU slot.Edit: I actually watched this video from the same guy:Edit2: I have watched some more clips from the same guy, although I don't understand his language I noticed that he uses a fixture to support the motherboards on the back. A also noticed some "cheap" equipment in the background of the clip. Maybe he uses them for smaller PCBs such as the WLAN module. (Which is also broken on this laptop). I'll watch some more...Edit3: I see now that the termocoupler is set on the motherboard near the chip to be soldered. He claims the peak temperature when soldering a BGA Radeon HD3200 chip to be about 220°C. So I guess that 180-190°C with the pre-heater will do and then I bring the temp up to 220°C for a few minutes with the top heater.

author: wraper
author_rank: Unknown
timestamp: June 29, 2014, 11:11:09 pm
content: There are very small balls between die and substrate called bumps. Fault is that contact is lost between die and substrate because of cracked or delaminated bumps.It is hard to suggest temperature because controlling it introduces serious error. As board don't ideally transfer temperature to thermocouple(s) and shows lower temperature that actually is (if using IR). If using hot air, it might be even opposite as thermocouple might be closer to the nozzle. Therefore you should find right temperature for your equipment trying on the scrap boards. But you should heat up to approximately 230oC real temperature, not measured.

author: axero
author_rank: Regular Contributor
timestamp: June 29, 2014, 11:34:50 pm
content: Ah, now I understand the problem. That's why one guy insisted on fixing the thermocoupler against the PCB with some kapton tape. Perhaps I should simulate the reflow process on a scrap board a few times before commencing the real deal.I didn't know that the little glassy chip on top of the BGA assembly is called "die". That's not what that word usually means. I found the info here:http://www.anandtech.com/show/2682. A more in-depth article is found herehttp://semiaccurate.com/2010/07/12/nvidia-backpedals-gf100gtx480-underfill/Now I understand the whole deal with faulty 2007 chips, that fabrication error did not only affect the XBox/PS3. Maybe it is possible to reball and reflow the "die", but that glue doesn't look like something that would come off easily. It looks like some kind of epoxy to me. If nVidia struggles get the underfill to work it would be an even more daunting undertaking for a single individual like myself.I found thistraining manual. So I guess that more sophisticated reflow equipment use a thermal vision camera to monitor the temperature and heat distribution of the BGA. No wonder the advanced equipment is so expensive!

author: wraper
author_rank: Unknown
timestamp: June 30, 2014, 12:55:47 am
content: Don't know anyone in the world to success with reballing the die. Those bumps are so microscopic and there is so many of them that it is almost impossible to do. Moreover it is very difficult to remove die undamaged.

author: axero
author_rank: Regular Contributor
timestamp: June 30, 2014, 08:41:32 pm
content: When searching for BGA reflow/reballing guides, most guides applies to toasters, hot plates and all sorts of kitchen equipment not intended for this purpose so they aren't that useful to me, but I found this guide that appears to be praised by the moderators of this BGA forum:http://www.bgamods.com/forum/viewtopic.php?f=51&t=191I read it before but it didn't answer my questions. The stand that holds the top heater is interesting. I wonder where to get such a stand with clamp, they are ridiculously expensive on eBay. The preheater has a hole for screwing a stand on. Maybe I can build something myself. Either I can buy a cheap metal rod, lathe and thread one end so I can screw it onto the preheater. Or I build something squary out of aluminium that looks like those stands for the top heaters found on more expensive BGA rework stations. There must be some kind of alu profile kits where one can build such things oneself. I have seen tons of these things, both in research labs and out in the manufacturing industry. I just don't know what they are called. Suggestions are appreciated.As I browsed around the BGA mod forums I found a few very interesting posts:Quote from: code0102stinks@bgamods.comQuote from: fj12_rider@bgamods.comAlso the eBay seller of that replacement GPU chip recommended to bake the chip in 100-150°C for 24 hours before soldering it on the board. I'll continue browsing around in the bgamods forums...

author: wraper
author_rank: Unknown
timestamp: June 30, 2014, 09:04:50 pm
content: Popcorn because of the moisture, higher temperature and god only knows what Chinese guy have done to it while reballing. What I can say is that reballed chips from China popcorn much easier than old chip on the pcb (without any previous baking), Baking is a very good thing if you have where to bake them at 100ofor 24 hours. It is a lot of electricity and time to bake just one IC. So I usually have done poor man's baking on ~120-130oC temperature for 1.5-2 hours. Making stand just for one off don't have a lot of sense. Also as your nozzle is much smaller than the IC, you must move it to evenly heat the chip and PCB around it. Otherwise it will be fried in the center while solder still not melted on the corners.

author: axero
author_rank: Regular Contributor
timestamp: July 03, 2014, 02:08:54 pm
content: So you are saying that the replacement chip you recommended is not legit? I thought that the replacement chip is a new spare-part re-manufacture and not pulled from a prior system.It seems that choice of cleaning detergent may also pose a risk factor to popcorning. They recommended pure methyl ethyl ketone (MEK - also known as butanone) and isopropyl alcohol (IPA). Apparently methyl ethanol is not as good, but some recommended pure acetone and what they call thinners. The meaning of 'thinner' may vary depending on where you live.But if this is such a sensitive task, then why not slap an LGA socket onto the motherboard after the chip is removed? Balling and mounting an LGA chip as a BGA is a bit difficult because surface mounted components are usually found in the center of the pad side of the chip. But a BGA chip on the other hand ...I wonder if I can ruin someone's movie night by baking his popcorns in the oven

author: wraper
author_rank: Unknown
timestamp: July 03, 2014, 02:48:45 pm
content: What I recommend is legit in terms it will work. Likely it will be a factory reject at best. Like it had missing balls which were added later with some man in China. Or removed from new MB which didn't pass QC. Or just removed from faulty MB. There are ways to get new BGAs, like if you are Samsung authorized service center. So Samsung sends you a new Nvidia GPU. Even if you can find a really new part, it will cost you like a whole motherboard if not more.Find LGA socket that corresponds particular BGA IC and fits to the motherboard and do not melt while overheating. Then order special version of BGA chip with gold plated pads. Then make a special version of heatsink that will fit on top of this miracle. Do not forget to drill mounting holes for the LGA socket in the motherboard first.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 03, 2014, 04:20:24 pm
content: I'm not an expert in BGA reflow, but I have repaired macbook pros, macbook airs, white iMacs and aluminium iMacs, all with these nvidia chips that develop cracked solder joints, a few dozen Macs in total, with this simple "recipe" I was given:1.- If you have air conditioning, turn it off. If you've got a fan, turn it off too. And close the windows. You don't want any currents of air where you do this.2.- Put the pcb over the preheater set at exactly 120 degrees celsius and leave it there for at least 10-15 minutes before continuing. Check again: we don't want any air currents over the pcb/preheater cooling the pcb.3.- The idea is that a preheated pcb only needs a bit more heat over the nvidia chip to melt its ballsWe are going to leave the preheater on during the entire process.4.- Proper timing and a bit of hot air does the rest: The "recipe" I got said blow hot air (*) @ 300 degrees celsius during 3 minutes no more as close as you can (I do it at about 5mm) without ever touching the chip, all over the nvidia chip and nothing else. You can do zig-zags, go in circles, whatever, but keep it moving over the nvidia chip and only over the nvidia chip. You will feel the hot, but no, don't turn on the AC or the fan yet or you will ruin the experiment.5.- After 3 minutes turn off everything, the gun and the preheater, and let it cool alone. Now you can turn the AC back on :-)6.- The first time I did it I had no faith at all. But that was two years ago and that Mac and all that have come after it are still working fine.(*) I use a chinese gun like this in EEVblog #167 - Atten 858D, with the medium sized noozle (I think it's 12mm).

author: axero
author_rank: Regular Contributor
timestamp: July 03, 2014, 05:28:43 pm
content: Well, I just figured that this Chinese guy may have managed to find a way to coax out a few spare chips from the manufacturer, presumably by posing as a licensed nVidia service company or found an excess supply or something. Maybe he knows a friend of a friend who pulled some strings, Corleone style ...The LGA conversion thing shouldn't be that impossible, and no new holes would need to be drilled. A slightly increased distance between motherboard and heatsink would prompt the need for taller screws, and some kind of thermally conductive shim or spacer for the Intel chip (unless that is converted to LGA to boot) but that's it.I'm not sure why I should set the pre-heater at 120°C, it must be safer to heat it to 180°C, the lead-free solder needs to be melted so the temperature must be brought up to 220°C for that to happen.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 03, 2014, 05:46:19 pm
content: Quote from: axero on July 03, 2014, 05:28:43 pmA friend of mine did it @ 180 celsius and he's still trying to put back all the smd caps and resistors that fell onto the preheater, from underneath the nvidia chip :-)

author: axero
author_rank: Regular Contributor
timestamp: July 03, 2014, 09:41:44 pm
content: And you are sure that 1) the thermocouple was properly calibrated and 2) firmly attached to the top side of the PCB while he was slowly bringing the temperature up to 180°C?

author: wraper
author_rank: Unknown
timestamp: July 03, 2014, 10:28:40 pm
content: They won't fall unless are mechanically moved with something or board is shaken hardly.

author: cpt.charlie
author_rank: Contributor
timestamp: July 04, 2014, 04:36:14 pm
content: Normally you need to preheat the entire board at 150-170ºc maximum, 120º is too low.

author: kripton2035
author_rank: Super Contributor
timestamp: July 14, 2014, 07:24:15 pm
content: Quote from: GeorgeOfTheJungle on July 03, 2014, 04:20:24 pmI did almost exactly as you tell us here ... and I revived 2 macbookpros that where lying around for 2 years ...many thanks.I used a yihua 853AA recently boughtput the bottom plate at 200°C (that make around 150° on the board)put the top gun at 300°Clet the bottom heat the logic board for ten minutesthen run the gun at 7 air speed for 3 minuteslet it all cool downvery good recipe ! thanks again.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 15, 2014, 10:40:57 am
content: Quote from: kripton2035 on July 14, 2014, 07:24:15 pmWoohoo !

author: axero
author_rank: Regular Contributor
timestamp: August 06, 2014, 03:41:03 pm
content: I just had a practice session after an old broken motherboard with a built-in GPU was donated to me.I noted that the temperature sensors of the preheater give off somewhat different temp'ture readings compared to my multimeter. Since the multimeter showed the highest readings I regulated the temperature against that just to be safe. Funny though is that while the thermocouple (of my multimeter) can measure all temperatures, the materials around the thermocouple cannot take the heat. They melted and burned at higher temperatures. I figure that a good temperature sensor to monitor the heating is a must as the thermocouples of the preheater cannot be relied on. I tried sticking the thermocouples with kapton tape but alas the tape unsticks from the board as the heat builds up, so I had to manually readjust the thermocouples during the preheating process. Perhaps the kapton tape uses a bad quality adhesive, the tape itself can take the heat without problems though. I also noted that it is considerably hotter near the top heater than on any other spot of the board,even though it is not turned on. I think that's a good thing to keep in mind.To assess the collateral damage from the practice session, surprisingly little damage was caused by the reflow processes. There were no "popcorning", nor were there any lifted pads during the process and I successfully removed the BGA chip without a hitch.There were a few mistakes I did though. Firstly, I didn't get proper measures of the temperature because I measured too far away from the chip. As I moved the thermocouple of the multimeter close to the chip underneath the top heater I realized that the temperature was over 240°C. Some small surface mounted chips came loose in the process, including one on the chip itself. I take it that it must be the high temperature that caused it. A good note to take is to watch for surface mounted components that might come off from the chip if one doesn't lift the chip carefully. No biggie I guess.Secondly, there was some board warping, but that's because of a stupid mistake I did with the rig. The warping is very small which is great considering the weight of the components the board had to take during the process. The warping is not likely to interfere with the refitting of the BGA chip. The lesson here is to make sure that the board is properly rigged, especially when heavier components rest on it.Before I started the practice session with the motherboard I removed all electrolytic caps just to be sure I won't be bothered with popping caps during the process. Pretty much all of the other components could take the heat with a few exceptions. All PCI/AGP slots are unaffected, so are the D-sub connectors, mini-DIN, USB/RJ45 and 3.5 mm telejack housings, and the internal floppy/IDE connectors as well as the plastic CPU socket and adjacent DIMM slots. The ATX power connectors show a light brown discoloration near where they touch the motherboard but seem otherwise unaffected. The plastic holder for the CPU-cooler otoh has partly melted from the heat, but not to such a degree that it likely would interfere with the operation. But a lesson learned here is that it should be removed before preheating the motherboard.I did get a lifted pad from the GPU chip, but not when lifting the chip from the motherboard. I was a little careless when removing the solder from the chip. I used a copper wick and accidentally pulled a pad with the wick. So be careful with the wick when cleaning the pads is a lesson to be learned here.For ventilation I improvised and used a chassis fan together with some active-carbon filter for kitchen fans. I put it all in a small cardboard box where I carved a hole for the fan on one side and carved out almost the entire wall on the opposite side for the carbon filter. It isn't perfect as some of the smoke comes through anyway, but I guess that it is better than nothing.

author: axero
author_rank: Regular Contributor
timestamp: August 07, 2014, 10:28:34 am
content: I figured that an update to what I did yesterday is in order.The preheater was set to regulate the temperature against the thermocouple set on the bottom side of the PCB (the side facing the preheater). It appears to use some kind of a PID controller, it most certainly behaves as one when adjusting the temps. I find the PID controller a little quirky to handle, especially when making small temperature adjustments. Perhaps it gets a little confused when it also has to handle other constraints such as a maximum temperature increasing slope of 3°C per second. But with a little voodoo there was no problem coaxing the preheater to yield desired temperatures. It certainly has the power for it and the heating element uses long-wave IR.The thermocouples of the preheater turned out to be pretty good once they were properly mounted with kapton tape. Making them stick onto the PCB was no easy task, but once I managed, they worked great. I found it to work at best when burying the top probe under some kapton tape right next to the chip to be lifted from the PCB, and the bottom probe somewhere in the middle.I noticed that there was a 50°C difference between the top temperature and bottom temperature. That means that if I wanted to yield 180°C on the topside, I had to set the bottom temp to about 230°C.To prevent accidental removal of nearby surface mounted chips, I covered the area around the BGA chip on the topside with some aluminium tape. It also turned out to give good protection against solder that splashed out from the sides of the BGA when I pressed it onto the PCB with the vacuum pickup tool. No components fell off from the back side of the board.To conclude, I had the following issues:• Lifted pads, not when lifting the chip during reflow butwhen cleaningthe pads from solder, these pads are extremely fragile.• Reballing, the jig I use for reballing is impossible to use• Smoke and fumes, my improvised ventilation solution is not enough

author: jetwolfk2
author_rank: Contributor
timestamp: September 20, 2014, 03:18:33 am
content: i think your preheater is fine, however your use of the hot air nozzle unit does not provide enough power or consistent and even heating for a huge chipif you are having such a big difference in temperature i think you might need to preheat the board longerhave you considered getting a real bga rework machine

author: axero
author_rank: Regular Contributor
timestamp: October 04, 2014, 07:53:20 pm
content: Quote from: jetwolfk2 on September 20, 2014, 03:18:33 amThe temperature difference I mentioned above iswithoutthe top heater. First I brought the topside temp up to 180°C, then while the preheater maintained a constant temperature I topped the temperature up to 220°C with the top heater as instructed on BGA rework support sites.EDIT: RoHS 5/6 compliant hardware use leaded solder and RoHS 6/6 compliant hardware use lead-free solder.

author: jetwolfk2
author_rank: Contributor
timestamp: October 11, 2014, 12:32:10 am
content: It might be that the pcb has a lot of copper in various areas of the board and it needs to be preheated longer in order to saturate the pcb thoroughly