Hybrid BGA reflow (oven & hot air): recommended temperatures for two-sided PCB? - Page 1
Forum section: electronics / general

author: touchatout
author_rank: Contributor
timestamp: April 20, 2023, 10:12:18 am
content: The need=======I need to reflow one or more BGA on two-sided circuit boards, mostly SSD and USB flash drives.The goal is that the weld is good enough to bring the storage media back in working condition and extract the data.I don't need the need to last for years, and approximately respecting the temperature profile should be sufficient.Issues identified / Risks=================Additionally to the fact that BGA chips are more tricky to resolder than the ones with pins, I see three trends that increase the risk of things getting worse during the repair attempt:1. Many PCB aretwo-sided, with therisk of accidentally desoldering components on the opposite side.2. Some components like capacitors and resistors gettruly miniaturized, increasing the risk of for them being blown awayby hot air and being lost, or if not lost, hard to put back into place.3.The components tend to become closer one of another. One need the temperature being high enough for reflowing the BGA, but at the same time not burn connectors that may contain plastic parts. (e.g. SATA connector)Practical case==========Let's take the printed circuit represented by the attached photos, coming from a Samsung SSD.Although the NAND memory is on one side only, there are still components on the back side like the capacitors and resistors opposite to the controller, plus a few legged chips.I want to reflow the controller (which is invisible from the BIOS), whilst minimizing the thermal stress on the rest of the PCB, and especially to the NAND memory chip. Although NAND chip can support some heat, including thus for reflow, it is good practice to heat it as little as possible when reflowing something else.Tools at disposal============At my disposal for this relow are the following tools:1. Small kitchen oven, with temperature up to 240 °C (464 °F), from a good brand.2. Hot air rework station Yihua 852D+, with hot air temperature up to 500°C (932 °F), variable air speed and three optional nozzles of misc diameters.3. Small tools, like tweezers large enough to maintain chips into place (if the hands do not shake), high temp resistant adhesive tape.Current process for review==================My process to attempt reflowing the controller of this board is as follow:1. Protect everything apart the controller with polyimide adhesive film (Kapton® / Koptan).The goal is twofold:- protect components from detaching themselves and being blown away- protect the components a little from the hot air from the hot air nozzle2. Further protect the SATA connector with a piece of aluminium foil, taped with polyimide film.3. Put some flux around the controller. The flux will become liquid and seep under the chip when heating, facilitating the reflow.4. Add a single layer of polyimide adhesive tape on the controller, to prevent it to accidentally slide or from being blown away.5. Preheat the board to a temperature that cannot damage the plastic of the SATA connector, nor desolder components, particularly by gravity.6. Take the PCB out of the oven and pulsing hotter air on the controller with the rework station, using the medium diameter nozzle, to melt the solder balls.7. Put the PCB back in the oven and let it cool down slowly.Considerations from past experiences- Plastic parts doesn't risk much under 150°C (302 °F)- Plastic parts like SATA connectors can resist to higher temperature ~180°C (356 °F), likely even more (likely > 210°C).- In convection oven, BGA chips can detach themvelves due to gravity or air flow at relatively low temperatures, that are close to the melting point but can possibly be below it, because the weld starts to become fluid. (For large chips, gluing corners with epoxy could be a solution.)- The alloy and its melting point are not known. We can only guess.First cautious attemptSo, assuming a melting point at 217°C (~443 °F) here are the temperatures that I used in a cautious first attempt.I assume it was not enough for the balls to melt, but at least I avoided damages to the board.1. Oven: temperature gradually increased up to 180°C.Maybe not enough, but ensuring that no component is detached from the back of the printed circuit board.So, I kept the temperature below the melting point of leaded solder (183 °C), even if the welder is extremely likely lead-free.I also wanted to keep some security margin due to the fact I don't know about the precision of the oven thermometer and if it is well calibrated.Although I have read that for a pure oven reflow, the temperature can be in the 230°C - 240°C, I was reluctant doing so.Despite the adhesive tape, my main fear is components to detach on the back side, due to the effect of gravity.Not sure how much surface tension compensate for this.2. Hot air: 235°C - 240°C.I assume that the hot air temperature displayed on the rework station is the one measured within the station and that the temperature of the air going out of the nozzle is lower.For instance, for hot air at 100°C, my impression is that the air comes out at around only 50-60°C.However I wanted to be cautious for the first attempt.In the past, I saved some SSD with pure hot air (without oven).I likely increased the air temperature to some 280°C as displayed on my station, but likely to much lower temperature when going out of the nozzle.I cannot remember if it was two-sided, but it was a small mSATA one ; maybe could I maintain opposite chips slightly pressed between tweezers.Planned aquisitions==============To better control the process, I plan acquiring first a temperature sensor, which will help a lot, and then possibly also a hot plate to limit heat loss when the board is out of the oven.Suggestions?=========I would like to collect some opinions and suggestions about the process.Please, no moral lessons (I know that I know that high end equipment do exist) but constructive proposals. Thanks.If the process considered makes sense, which temperatures would be recommended for the oven and hot air out of the nozzle?Also, is the unique layer of polyimide tape over the controller a good idea or not?Does is prevent too much the heat from reaching the controller?One difficulty that I see with the tape is, is that it is harder to confirm solder ball melting by visual observation (fumes).

author: SMTech
author_rank: Frequent Contributor
timestamp: April 20, 2023, 11:48:06 am
content: Buy the same mediocre but cheap Chinese BGA rework station as all the shops do that rework Xbox/Playstations in the back room, and deploy your protective tape.Or buy a Seamark one for like $8k or spend the 25-60k for the established commerical offerings, which is clearly overkill for your use case.

author: asmi
author_rank: Super Contributor
timestamp: April 20, 2023, 03:03:21 pm
content: These are relatively small chips, so you should not have any problems de-soldering them even without preheater, through having it will make things easier (and safer). And soldering is even easier as you can replace LF balls with leaded ones before soldering them onto a board. Your biggest problem will be those small components which are close to BGAs.

author: SMTech
author_rank: Frequent Contributor
timestamp: April 20, 2023, 03:58:14 pm
content: Quote from: asmi on April 20, 2023, 03:03:21 pmI could be wrong but from the description the OP appears to be attempting something very similar to ye olde Xbox360 repair. That is assuming the cause of failure is a BGA ball fracture caused by thermal stress and attempting to fix it using a reflow cycle. Clearly thermals are not something manufacturers of 2.5" SATA SSDs are concerned about given the plastic box they shove them in with zero heat dissipation so how effective this is or how lucky @touchaout got with that attempt that worked is maybe a question for another thread.However the example PCB is clearly a ROHS compliant fully SMD processed board including the connector so it handle 250C for short periods. It takes a while with a hot air tool to transfer enough energy into a device, a probe on the board can show your progress pre heating/underside heating helps reduce the work that hand tool needs to do. Small parts that close are always going to be an issue if your heat transfer method is air. IR solves that issue but introduces others, plenty of the cheapy eBay rework stations are IR tho'. There are also threads about models like the T862+ on here with experiences etc. I'd read them.

author: asmi
author_rank: Super Contributor
timestamp: April 20, 2023, 06:11:43 pm
content: Quote from: SMTech on April 20, 2023, 03:58:14 pmHe is talking about SSD and USB flash drives, the largest chips in those are actual flash memory arrays, there is nothing there that's even close to the size of SoC of Xbox360. For larger - and dare I say - more expensive chips I can totally recommend investing into the proper BGA rework machine, but flash chips and RAM are relatively cheap. I wouldn't bother because those machines cost several thousands of $$$ unless I have a reasonable pathway to get a return on such investment.

author: touchatout
author_rank: Contributor
timestamp: April 20, 2023, 06:30:51 pm
content: Quote@asmi: Thank you, but don't wantreballing(replacing balls) but simplyreflowing(re-melting existing balls), to make sure they are no cracks within them, and that they are also properly tied to the chip and to the board.I am aware that reballing is prefereable to reflowing if the weld is to last. I would also prefer leaded solder balls for this task.But reballing also means more risks, and more time spent. A weld that last is not what I aim at.The goal here is — at least initially — is to attempt restoring the working state of the circuit to allow data being copied elsewhere.It does not prevent a later reballing if reflow does not suffice.Quote@SMTech: Your understood right. Sometimes, balls can also be detached from the chip.Quote@SMTech: Thank you. Yes, I also think so.Good to know that the connector can also 250°C if not during too long time.My main fear remains accidentally desoldering components on the back side. The tape limit the risk of loosing them.Quote@SMTech: Absolutely. Hence the oven to preheat the board.But I fear even more loosing the small components on the back side when the board is hot.Quote@SMTech:Yes, a probe on the board, or even on the controller, is something that I'm strongly considering.Is there some that you would recommend?Reducing the need of hand tools reduces stress and is much appreciated. I have only two hands and no assistant.Quote@SMTech: I agree, but by covering everything with polyimid adhesive tape, there should not be any air flow (or very little) below the tape. Not sure if polyimid insulates a lot themally, but it is thin, so it should be ok. I also plan to use medium to low air flow speed and to blow it vertically. The diameter of the medium nozzle is 8 mm. Seems a good compromise between blowing enough air and precision. I move the nozzle from one corner to another of the chip.

author: touchatout
author_rank: Contributor
timestamp: April 20, 2023, 06:39:24 pm
content: Quote@asmi: Yes, but SMTech just wanted to point out that I am currently considering a reflowing (re-melt) process, and not a reballing.Quote@asmi: The purpose here is not restoring the SSD for its intrinsic value (they are relatively cheap nowadays). But for data recovery.I know that my original thread is quite long, but I think everything is in it.QuoteTotally agree. I progressively enhance my equipement and methods. Investment in more expensive equipement is worth when you have enough volume.Else, I try keeping on a budget, but taking precautions to do the job professionally.

author: janoc
author_rank: Super Contributor
timestamp: April 20, 2023, 08:20:27 pm
content: Quote from: touchatout on April 20, 2023, 06:39:24 pmAnd are you actually sure the problem is cracked solder joints?Given that an SSD or USB drive doesn't see high temperatures and large temperature swings (unlike a CPU) and the ICs are relatively small (again, compared to a CPU), I think you are going to be closer to making the device completely unrepairable by accidentally moving other components or scorching the board, ruining any chances of data recovery in the process, rather than fixing it by using this bullshit "repair technique".Reflowing works only if the solder joints are the problem. Which is actually very rarely the case. If the drive fails it is usually because either the controller dies or because one of the flash chips dies, not because of cracked solder. Re-melting the solder balls would do exactly nothing there.

author: touchatout
author_rank: Contributor
timestamp: April 21, 2023, 04:12:44 pm
content: Hi janoc, and thank you for your contribution.Here are some explanations about my decision attempting a reflow of the controller.QuoteI am sure of nothing until hardware comes back to life.I consider a repair attempt, in this case to attempt a controller reflow, basing on several criteria:Security of dataResults from premilinary testsPast experienceRisksDifficulty of the diagnosisDifficulty and cost of alternative data recovery methodsThe existence of alternative if the attempt failsIn consideration of the mentioned case:1. Security of dataIs preserved. The temperature within the oven can be supported without problem by the NAND chip.2. Results from preliminary testsThecontroller is not detected in BIOS. When the PCB and controller are both ok, the controller is usually detected but cannot read the data (no media detected).This puts me on the track that the problem can be due to the controller.It is not certainty, but plausibility.The wholeboard is in good optical condition(no burn components), tracks from the SATA connector were doubled with tin.Welds of several components were re-melt with some additional leaded tin solder.Voltages on the pins at the rear of the SATA connector were checked.So, the controller is one of the possible culprits.If so, either the controller is badly solered, or it is dead.In the second case, controller replacement (reballing) will still be possible in later time.3. Past experienceQuoteIn the past, I saved a mSATA SSD by reflowing its chips with hot air.I admit that solder cracks or bad solder joins are rare, but they still do exist.4. RisksQuoteThe components won't desolder themselves in the oven if the temperature in the oven remains limited.180°C in the oven shouldn't be a problem. I think even more (how much) if not too hot and too long (~2 minutes),knowing that the melting point of unleaded solder is usually around 217°C and 235°C-245°C are necessary for the reflow peak.The main risk that I see are the components on the back side, right under the controller, during the temperature peak provided by the hot air nozzle.I want to avoid them to fall.But in case they drop, the polyimide tape is here to collect them and they are not too small. One idea could be to paint them with different colors and take a picture. To know which one goes where and be able to put them back into place if necessary.I am a careful and meticulous person.This is why I am asking advice.Even with budget equipement is is possible to do things right, when knowing where the risks are, and taking appropriate mesures to master the process.Equipement matters, but knowledge and experience are to my opinion even more important.QuoteCertainly not. I have nine years experience in electronic repairs using the iron and eight years with hot air (although doing it on a casual basis).Although each case is unique and there is still to learn, I know by experience quite well how do PCB and components do react to heat.QuoteDefinitely not.The NAND chip itself will be heated much less than would be necessary to unsolder it.There will remain many possibilities for a data recovery : reballing, controller replacement, donor SSD with NAND chip transfer, direct reading from the NAND chip with a hardware/software complex like Rusolut, Flash Extractor, PC-3000 Flash, PCB board repair.But those require more workmanship, skills, and equipement.5. Difficulty of the diagnosisDiagnosing a board with small components by probing it is not that easy.Sometimes a "blind repair", based on a simplified diagnosis and intuition can give good results and is worth attempting, as long as risks are kept under control.QuoteAttempting things, with caution, is part of the diagnosis.I do not pretend they will do fix things directly. Sometimes it directly fix them, sometimes not.But whichever the result, this brings data helping to find where the problem is or was located.There is always a part of risk, which must be kept under control.Even if doing direct NAND chip reading, there is some risk desoldering the chip.Heating the controller is less risky than heating the NAND chip. The data are in the NAND, not in the controller.6. Difficulty and cost of alternative data recovery methodsAs mentioned, other data recovery methods will still remain possible.But the require much more workmanship and/or equipement and are (much) more expensive.So, the controller reflow is to my opinion the first relatively easy thing to attempt in this case.The other methods can be tried sucessively in later time.7. The existence of alternative if the attempt failsWould a failure be irreversible?No.Do alternative remains if the reflow attempt fails?Yes. There are several ones for this case, that can be attempted successively.I give a chance to simple methods first, and to difficult ones after.QuoteOf course.But if controller dies, it will have to be replaced (reballing of a new controller). So, in this case, it makes sense attempting a reflow first.There is a unique flash chip here. If the will reflow of the controller first. Then, the flash chip. If it does not suffice, chip off and reballing (on same board or new one of the same model) and if still does not suffice, chip off again and direct reading of the NAND remains possible (although such recovery is much more complicated.)

author: PCBprototyping
author_rank: Contributor
timestamp: April 21, 2023, 06:02:11 pm
content: I repaired around 10 PC graphic cards and machine controller boards with BGAs using the following method(100% success rate):- protect the whole board with aluminum foil for cooking. You need to make rolls of aluminum and put them below the cover layer of aluminum. that way, you get a good insulation and THT components won't melt. Be generous with aluminum rolls!- make a window, where BGA to be resoldered is- add a heavy metal object like nut or copper block to put some weight to the BGA during reflow- extend the reflow time as it will take more time to heat up the copper block and all the aluminum foil- weight will press the balls during reflow and board should be ok, if BGA is not faulty. I even used this method to prove to EMS supplier that they supplied poorly soldered board and the reason BGAs occasionally stopped to work is because of their process, not faulty chips.- use a convection reflow oven, the oven you have is most probably without fan, fan is necessary. Maybe even infrared oven would work, if your block is not to shinny.- 240°C is too low for convection oven in my experience as temperature above the board will be lower and below the solder melt temperature. 260°C will be appropriate temperature(PCB temperature will be lower, you won't damage the component).You can also use the aluminum foil and reflow oven method to desolder the BGAs or ICs in general. Just protect the board with aluminum, make a window for the component, flip over the board, reflow it, open the drawer right after reflow, hit the board with your finger and component will fall off the board.If you want to repair the boards more proffesional way, check out this channel:https://www.youtube.com/@NorthridgeFix/videos