Reflowing my first BGA: Tips needed - Page 1
Forum section: electronics / general

author: lawrence11
author_rank: Frequent Contributor
timestamp: September 17, 2019, 06:25:49 pm
content: So I have my controleo3 all ready, its been "learned", the profile program has been tested.I am reflowing on 1 chip ATM due to them being the only leadfree BGA of the gang, a 216 bga .8mm with no balls in the middle.Should I risk aligning manually? Or should I contatc somebody with an xray to help? Is manually best I can good enough?Should I put some flux on the pcb copper pads of the bga?This my fluxhttps://www.amazon.com/Solder-Welding-Electronic-Soldering-Lead-free/dp/B076M49M63/ref=sr_1_47?keywords=solder+flux&qid=1568731253&s=gateway&sr=8-47

author: cgroen
author_rank: Unknown
timestamp: September 17, 2019, 06:33:50 pm
content: Quote from: lawrence11 on September 17, 2019, 06:25:49 pmI have done many BGA's on the "kitchen table" until now. Not one single has failed, everyone worked the first time!The pictures below is of a 0.65 CPU (RT1064), I used a stencil, leaded paste and a hotplate. Works perfect. Alignment is a non-issue, I align it (with a vacuum pen) reasonably well, the surface tension pulls the device to the correct place when reflowing

author: lawrence11
author_rank: Frequent Contributor
timestamp: September 17, 2019, 06:36:10 pm
content: thanks, my chip is lead free, I didnt put any solder paste on the pads, my only solder paste is leaded.do I need solder paste or flux on the copper pads?

author: cgroen
author_rank: Unknown
timestamp: September 17, 2019, 06:41:14 pm
content: Quote from: lawrence11 on September 17, 2019, 06:36:10 pmI have always used (only) solder paste on the pads (copper), and I have seen several recommending that. It has so far worked 100% for me

author: lawrence11
author_rank: Frequent Contributor
timestamp: September 17, 2019, 06:47:10 pm
content: But dont the bga already have soldr balls?

author: lawrence11
author_rank: Frequent Contributor
timestamp: September 17, 2019, 06:59:03 pm
content: can I mix leaded paste and non leaded balls?

author: Berni
author_rank: Super Contributor
timestamp: September 17, 2019, 07:27:56 pm
content: First of all don't duplicate your treads over the forum, and try to edit your previous post when you have something to add rather than adding a replyNo problem in mixing it, just use lead where ever possible because it makes things easier. The flux you want is usually the more liquid stuff in a syringe. Its possible to reflow a BGA onto a board by tinning the pads while making sure the bump you leave on each one is the same size, rub a small amount of flux over the board, place the chip as precisely aligned as you can. Heat it with a hot air gun until it moves over a bit as the surface tension centers it, gently tap it down with tweezers to make sure its down properly and let it cool back down. Done. I did that for 0.5mm BGA chips before and had it work, but does take a little bit of practice and some magnification to make sure its centered well enough.My preferred method of doing it is what user "cgroen" said. Buy a paste mask for the PCB (They are pretty cheap from china), lay it on the board, squeegee some qood quality leaded paste across to print it onto the board. Carefully place the BGA in its location since you don't want to move it around too much or the paste will get messed up underneath. Then finally put it trough a reflow soldering oven (But a hot plate is fine too once you 'dial in' your manual temperature profile).Once you are done you can peek under the chip by looking from the side. When you did it right you can see nice round balls that are squashed down to about half there height by the weight of the chip, they should not be dragged off to the left or right too much as that shows the chip is not aligned all that well. If there is enugh room around the chip you can even shine a light trough the space between the balls from the other side to check there are no bridges. A multimeter on diode test can be used to check for any pins that did not connect properly (To fix that you can sometimes just heat it up using a hot air station and tap the top of the chip gently)

author: lawrence11
author_rank: Frequent Contributor
timestamp: September 17, 2019, 07:36:36 pm
content: And if I just rub some flux on the pads and put in the oven?I have a controleo3.I have a stencil, but I cut off the bga section with a razor blade as I thought the chip was going to get in my way when I wanted to apply paste for the other components and I read we shouldnt mix.What I have is a tiny bga stencil, barely bigger than the holes.

author: SiliconWizard
author_rank: Super Contributor
timestamp: September 17, 2019, 07:55:41 pm
content: Added thought: obviously the approach would be slightly different depending on whether you're going to reflow the whole board at once, or just the BGA chip, manually (with hot air for instance).In the former case, adding solder paste is kinda obvious, since you're going to use a stencil anyway (unless you're nuts). Masking the BGA pads, or rubbing off the solder paste afterwards, to replace it with flux, would not make much sense. Besides, in an oven, the BGA on just flux (especially if the flux is too liquid) might "surf" over the pads before reflowing, and thus get misaligned. If you control that manually with hot air or infrared, you can always help the chip properly align.For manual assembly, I have only done low pin (ball) count parts, but flux was enough, the balls are indeed solder balls that can reflow. I've heard people manually reflowing pretty large BGAs with flux only with success.

author: lawrence11
author_rank: Frequent Contributor
timestamp: September 17, 2019, 08:04:01 pm
content: Some people say to tin them instead or I should just add solder paste ? For sure now, only flux will risk sliding, I dont like tjhis option while its easy.Would like to see a video of people tinning bga pads, what tips they use etc...I hav a good soldering iron hakko fx-888 and some various tips I bought, some leaded kester solder, I soldered before but never in a such a small fashion you know..Problem: I never really soldered these types of things, My hakko is still in the box, I m noobie. But I want to get better, Im ready.I even got my magnifier helmet type thing 3.5x with a LED.I have a stencil, but I cut off the bga section with a razor blade as I thought the chip was going to get in my way when I wanted to apply paste for the other components and I read we shouldnt mix.What I have is a tiny bga stencil, barely bigger than the holes. Yeah... Its complicated...Please help me get through this

author: SiliconWizard
author_rank: Super Contributor
timestamp: September 17, 2019, 08:35:56 pm
content: For manual reflowing, to keep the BGA from sliding, many use kapton tape on at least two sides as guides.You can watch this, from Pace (they should kinda know what they are talking about):

author: lawrence11
author_rank: Frequent Contributor
timestamp: September 17, 2019, 09:37:34 pm
content: Kapton tape has been ordered through amazon

author: Berni
author_rank: Super Contributor
timestamp: September 18, 2019, 05:20:28 am
content: To tin the pads i just put flux on the board and drag a soldering iron across all of them with plenty of solder on the tip. Flux is a big help there since it makes the solder flow a lot better so you get a more even amount of solder on each pad. Most of the reason for doing this is to make sure that once the board reflows there is a molten pool of solder sitting on each pad that grabs onto the BGA ball and becomes one.But tinning is not strictly needed. If the surface of the pads is in good condition you can get away with only flux. You want the pads to have no significant oxidation on them and no other dirt (like finger grease or old flux). This makes sure the flux you use has an easy job of keeping things clean enough for solder to stick. Especially since you must use very little flux for this. My method is to apply it and then very gently wipe it off with a cloth, leaving behind a thin layer of it. Usually more flux the better, but here having too much flux causes it to boil under the BGA when being heated up, when the underside of the chip is nothing but flux the gas has nowhere to go so it builds pressure and lifts the whole chip up, making it dance and jump around, screwing up the alignment.There are many ways of doing this as you found out, the best one is using solder paste when placing all of the other components and reflowing the whole thing in one go. The other methods mentioned tend to take a bit of skill and practice to be reasonably reliable on big high pin count BGAs, but are still fairly easy on small ones like 3x3 or 4x4 pins.You are quite likely to mess something up the first time, so practice a bit by soldering 1 or 2 spare chips on a blank board to get the hang of it before going for the board you already soldered everything on and don't want to mess up.

author: cgroen
author_rank: Unknown
timestamp: September 18, 2019, 07:16:26 am
content: Quote from: SiliconWizard on September 17, 2019, 08:35:56 pmThey might know what they are doing, the idea with the kapton is nice (if you have the room on the (real) board for that, but the mocking around with the tweezers on the chip is something I would never do (and never had any reason to do)....

author: SiliconWizard
author_rank: Super Contributor
timestamp: September 18, 2019, 02:09:50 pm
content: Quote from: cgroen on September 18, 2019, 07:16:26 amThis is actually quite common to do this when hand-assembling to check that the part has reflowed (for BGAs and QFNs). You obviously have to be gentle and not push this too far.

author: cgroen
author_rank: Unknown
timestamp: September 18, 2019, 02:25:40 pm
content: Quote from: SiliconWizard on September 18, 2019, 02:09:50 pmYes, I realize that for hotair this might be needed, however, I think he overdid it a littleAnyway, benefit of hotplate (I use a ReflowR fromhttp://www.reflowr.com/) is that the timing is perfect every time, so no need to push things around (although I can see the problem for hotair work!)

author: lawrence11
author_rank: Frequent Contributor
timestamp: September 18, 2019, 02:42:53 pm
content: I Thank you all, the method I have chosen to try will be...I'll tin the pads, I dont see how a layer of tin will cause unequal surface to affect things...I'll put some kapton tape, by using a caliper/magnifier I have measure approx the side of the chip before the forst layer of balls, I ill just install the tape slightly further, or equal.I'll put the board in he oven, I'll push the chip in, lead-free profile, press start.Eventually I will think of a better process, I think just going lead free everywhere would have been simplest.

author: SiliconWizard
author_rank: Super Contributor
timestamp: September 18, 2019, 02:59:24 pm
content: Quote from: cgroen on September 18, 2019, 02:25:40 pmAgreed, but this was probably just for illustration purposes.Quote from: cgroen on September 18, 2019, 02:25:40 pmAgreed again, but again, hot air work allows to selectively reflow one part. A hotplate, not so much...(That said, a hotplate can still be used to heat the board to prepare it for hot air reflow - just don't heat it to full reflow temperature...)There are alternatives to hot air for selective reflow, such as IR rework stations. Expensive though.

author: lawrence11
author_rank: Frequent Contributor
timestamp: September 18, 2019, 03:30:07 pm
content: Nevermind hotplate.I have controleo3, the BEST bang for the buck.I can do it all now, soon, right after my first BGA I'll be hyper flexible with this.This whole experiment is just to make a few prototypes, then, I'll be busy with other things, for a while.This whole PCB/Manufacturing thing has really slowed me down, ALOT! Hope to get this over with soon, I'm getting bored of manufacturing.After that, I'll upgrade all this hobby stuff.BTW, wich is the absolute best bang for buck in terms of used scopes? I had identified my best new bang for buck as the new siglenthttps://siglentna.com/digital-oscilloscopes/sds2000x-e/sds 2352X-E.It sucks tho, I really wish the pattern was true for 300$ more a 4 channel of this sortAll there is out there are these old pieces of 500mhz crap tektronix/agilent that could bust and waste my budget/time.

author: SiliconWizard
author_rank: Super Contributor
timestamp: September 18, 2019, 03:45:08 pm
content: Quote from: lawrence11 on September 18, 2019, 03:30:07 pmIf you don't mind the extra weight and volume (and often power draw and noise), many of the older digital Tektronix/Agilent/HP/Lecroy.... scopes are fantastic stuff. I'm of course talking about the digital scopes, not the very old analog scopes, which may appeal to some but can't be compared with a modern digital scope.Many of those older ones are actually MUCH more capable than a recent, low-end one.You can find 500MHz/2GS/s or over for a few hundred bucks, and they are definitely NOT crap. You just need to make sure they are fully functioning before buying (or that you'll know how to repair them).

author: Berni
author_rank: Super Contributor
timestamp: September 18, 2019, 04:32:20 pm
content: Quote from: lawrence11 on September 18, 2019, 02:42:53 pmThe problem is that if you tin the pads really unequally (leaving a larger bump of solder on some pads and smaller bump on others) then the chip will sit kinda wonky and wobble about once placed on top. Once it reflows this results in more solder on some pads and less on some so it could cause a ball to grow bigger and potentialy short to the next one or a ball not pressing down on the pad enough to properly flow together.Having tined pads does have one advantage tho that it lets you "feel" the correctly centered location. The chip will want to "fall off" the round tined pads so by moving it about you can sense that the chip wants to fall in between the pads, so you nudge it back and forth until you find the peak of the bump where the chip starts trying to "fall off" in the oposite direction. But hopeful you have your BGA package outline marked on the PCB well enough so that you can use it for centering. Most cheep chinese PCB fabs will offset the silkscreen layer too much for the smaller chips, or when repairing a existing board there might be no outline at all (since the pick and place machine knows where to put it anyway). Its best to mark the corners of your chip on the soldermask or copper layers because those are made to better precision in the chinese fabs.

author: lawrence11
author_rank: Frequent Contributor
timestamp: September 18, 2019, 07:37:09 pm
content: Quote from: SiliconWizard on September 18, 2019, 03:45:08 pmWich of these models if the absolute best?tds5000, tds3000, tds7000I know lecroy and infiniium are poopie...

author: lawrence11
author_rank: Frequent Contributor
timestamp: September 18, 2019, 07:39:34 pm
content: good stuff good stuff berni...I was thinking the same... So paste if better than?I think I can find the sweet spot with kapton limits?

author: Berni
author_rank: Super Contributor
timestamp: September 19, 2019, 12:40:46 pm
content: Just do your BGA in whatever way you find best for your situation, there is no single best solution for all cases. But for newly assembled boards its best to use paste and reflow solder the whole board with the BGA included.In terms of scope choice it depends a lot on what you want from a scope. The setup i am happy with is a Agilent MSO6000 and a DSO9000H infiniium. The smaller 6000 scope is good for quick poking around with its high waveform update rate, easy setup and fast boot time(<10 sec). The big 9000 scope is for more serious work where quick setup is not as important. It has 20GS/s, 4GHz, 1000Mpts...etc Its still new enough to run the latest infiniium software (Same software as the current flagship scopes that go to 110GHz) so you get tons of features.But yeah id be careful with the old infiniium scopes that run win 98 and such. They really lack in some important specs and can be a pain to maintain. Can be useful if you need the bandwith, but suck as a general purpose scope.

author: NorthGuy
author_rank: Super Contributor
timestamp: September 20, 2019, 02:16:48 pm
content: Don't add the paste. BGA has enough solder in the balls. If you try to calculate how much solder you add with the paste compared to what you already have in the balls - this is practically nothing. But you do add a risk of shorting something when the paste get spread around as you're trying to manually align the BGA.Don't tin. You don't really need extra solder. But, when you place BGA, you don't want your BGA to slide down from the tinned ares into the valleys where it can attach to wrong places.It is not very likely that you short something under BGA even if you add paste or tin the pads, but these actions add to your risks without providing any benefits.Simply apply ample amount of tucky non-clean flux, place and heat. But don't add too much - you don't want bubbles under the BGA as they may lift it and misplace it. This is easy to correct if you use a heat gun, but not in the oven.

author: ale500
author_rank: Frequent Contributor
timestamp: September 25, 2019, 03:49:35 am
content: I have a couple of questions:And how about the surface finish of the PCB ? Is HASL workable ? or you always need immersion gold ?When you talk about "large" and "small" BGAs, what is "large" 256 PINs ? or something like 131 ?

author: asmi
author_rank: Super Contributor
timestamp: September 26, 2019, 12:13:52 am
content: Quote from: ale500 on September 25, 2019, 03:49:35 amI successfully reflowed 24 ball BGAs on HASL, but never tried anything better. I work with FPGAs which cost a lot of money, so no point in saving few bucks by choosing HASL over flat options (OSP, ENIG or immersion silver).

author: luiHS
author_rank: Frequent Contributor
timestamp: October 01, 2019, 12:38:37 am
content: Quote from: cgroen on September 17, 2019, 06:33:50 pmInteresting, I work with RT1020 but its LQFP, also SDRAM but in TSOP.I want some day start to test BGA chips.I have some questions:1.- For BGA always at least 4 layers for PCB ?2.- Do you always need to apply solder paste on the PCB pads for BGA chips or BGA tin balls are enough?I don't understand why you have to put solder paste on the BGA pads, if the BGA already has tin balls (I suppose). It only occurs to me that with the solder paste the chip is fixed to the board and will not move.I have a Pick and Place machine, and although the positioning can be quite accurate, I suppose that if there is no solder paste in the BGA pads, it will move through the vibrations of the machine and will be poorly positioned.

author: NorthGuy
author_rank: Super Contributor
timestamp: October 01, 2019, 01:53:57 am
content: Quote from: luiHS on October 01, 2019, 12:38:37 amIf you have stencil and PnP machine already, it is silly to apply flux to BGA pads when you can simply apply solder paste at no cost or effort since you already do this for the rest of the board.

author: SiliconWizard
author_rank: Super Contributor
timestamp: October 01, 2019, 01:06:49 pm
content: Quote from: ale500 on September 25, 2019, 03:49:35 amNever tried it on HASL finish, but it should be doable for the larger pitches. I probably wouldn't try it for fine-pitch BGAs (such as 0.4mm or even 0.5mm). Not saying that it won't work...HASL is often even more of a problem for QFNs than BGAs.