Help with re-balling BGA chip - Page 1
Forum section: electronics / repair

author: poot36
author_rank: Frequent Contributor
timestamp: August 02, 2021, 09:38:44 pm
content: I am trying to re-ball a Xilinx Spartan xa3s1500 FPGA and am having trouble with either leaving the balls on the chip or having the stencil stuck to the chip. Things I have tried, fluxing the chip placing the stencil on top and then placing the balls in the stencil and then reflowing the balls with the stencil in place (resulted in the stencil becoming trapped on the chip with the balls), fluxing the chip placing the stencil on top and then placing the balls in the stencil and then trying to remove the stencil (this resulted in the balls going everywhere or getting trapped in the stencil). I am using 0.6mm solder balls and a stencil that is a bit to big for the chip so I have to tape off the extra holes on all 4 sides. The stencil is marked for 0.6mm balls but I am wondering if because I got both the stencil and balls from China that the tolerances could be off and the stencil metal is not as solder resistant as it should be is the reason I am having trouble. How would I go about cleaning off any minute solder bits off the stencil? Also I am not sure if I should be using smaller solder balls with this chip and stencil or not? Or am I doing the process wrong?

author: perieanuo
author_rank: Frequent Contributor
timestamp: August 03, 2021, 09:27:09 am
content: stencil is designed for paste, not ballsput stencil, apply paste, level the paste with some blade, heat. then the stencil comes out easyi heard about paper stencils or something like this, never used themif you want to use balls, put smaller ballshttp://www.farnell.com/datasheets/1603917.pdf

author: PKTKS
author_rank: Super Contributor
timestamp: August 03, 2021, 11:00:21 am
content: If my memory serves me..BEST still sells their NON REMOVABLE STENCILs.They are like stickers you apply and keep them there...IDEAL for such pesky creatures with too many solder pads..Just google for BEST STENCIL ..They may have new versions for that..Paul

author: poot36
author_rank: Frequent Contributor
timestamp: August 04, 2021, 02:17:10 am
content: @perieanuo If the stencil is made for solder past then why do I see them being used with solder balls all over YouTube? Unless I am missing something here and there are different types of stencils for the balls vs past? That could explain why I am having so much trouble though. The stencils that I bought are these ones:https://www.amazon.ca/Universal-Stencils-Reballing-Stencil-Template/dp/B08THY7TX4/ref=sr_1_6?keywords=bga&sr=8-6Not sure if they are for the balls or not, I do know that the stencil sizes quoted don't fully match the description as I ordered them because they had the pin count I wanted but found out that the stencil was mislabeled and that is why I had to use a larger one. I guess I will have to get either some smaller solder balls or solder past. At least I am slowly learning what not to do.

author: PKTKS
author_rank: Super Contributor
timestamp: August 04, 2021, 10:09:21 am
content: Actually they are sold asSTENCIL QUICKhttps://www.solder.net/products/stencilquik/Paul

author: perieanuo
author_rank: Frequent Contributor
timestamp: August 04, 2021, 10:13:39 am
content: Quote from: poot36 on August 04, 2021, 02:17:10 ami don't know. i used metal stencils from the beginning with solder paste, it works. the ball resulted in that process permits the stencil to be extracted easily.you wanna put balls, put balls, but don't complain if somebody points a better method and you start arguing. i just try to help, you gonna choose what you want

author: mikerj
author_rank: Super Contributor
timestamp: August 04, 2021, 02:51:53 pm
content: Quote from: perieanuo on August 04, 2021, 10:13:39 amDon't be so sensitive. He was neither complaining or arguing, simply asking a perfectly reasonable question.Re-balling a large BGA by hand without a stencil would be a nightmare IMO, you'd need very steady hands and a lot of patience.

author: poot36
author_rank: Frequent Contributor
timestamp: August 05, 2021, 01:41:36 am
content: @perieanuo Sorry if I sounded like I was arguing with you, after re-watching the videos it does look like the stencils they were using with the balls had extra metal to support being clamped into a special holder for the stencil and chip which I clearly do not have. You are right that the smaller stencils with out the extra metal around the outside were almost always used with the paste.Is it OK to try using solder paste for this chip and not the balls? I am not sure what dictates using paste or balls on a chip. Any suggestions?

author: PKTKS
author_rank: Super Contributor
timestamp: August 05, 2021, 01:44:09 pm
content: Quote from: poot36 on August 05, 2021, 01:41:36 amYes it does make a difference.BALLS can be chosen in proper suitable sizeSolder paste can not. It is entirely upon the stencil and hand of tech.Suggestions?Yes it is not hard to find LARGE BGA chips already with the ballsMy first option buying chips is asking for pre re-balled versions..Paul

author: poot36
author_rank: Frequent Contributor
timestamp: August 06, 2021, 12:52:47 am
content: The chip costs around $250 so buying one is not an option. Looks like I may have to get some 0.55mm or 0.5mm balls instead. Will give solder paste a try as I have some that is most likely expired at work that I may be able to take home.

author: John_ITIC
author_rank: Frequent Contributor
timestamp: August 06, 2021, 03:14:48 am
content: The trick with reballing BGAs is to use one of each of these:https://www.ebay.com/itm/233079015712?epid=557654695&hash=item3644978920:g:QCEAAOSwEXtcOYr-https://www.ebay.com/itm/223261619032?hash=item33fb6df358:g:e9EAAOSwoVZb~5niSteps:1) Remove old solder from BGA with solder wick. Make sure absolutely flat surface. Clean with flux remover and/or IPA.2) Apply a very thin layer ofstickyflux to the BGA ball pads.3) Adjust the blue jig such that the BGA flux is near butdoes not touchthe stencil above it. This is the trick!4) Pour balls on top of the stencil and let them roll around until they each drop into a hole. Use a fine brush to brush left-over balls to the side.5) Lift off the stencil. The BGA IC should be left with all balls stuck in the sticky flux.6) Adjust ball positions under microscope so they are centered on the pads.7) Heat the BGA IC from the non-ball side until the flux activates and the solder balls melt. If done correctly, the balls will self center on the BGA pads.8 ) If too much sticky flux has been used, the solder balls might float away in a sea of bubbles. Just start over./John.

author: mon2
author_rank: Frequent Contributor
timestamp: August 07, 2021, 05:43:16 pm
content: @John - that is some excellent advice! Thank you. Sort of learning and fighting with similar issues. We also brought in a kit with an adjustable fixture and a mix of different diameter solder balls. While trying a thin metal stencil for memory chips, the heat from the gun would warp the stencil and make a mess while lifting the melting paste. From what we know so far, not every stencil is meant for direct heating. The direct heating style of stencils are more rigid under the same temp of the air gun.Anyways the trick you noted to heat from the 'opposite' side is goldThanks again. Will try this next week.PS: To the OP - the solder balls are available as usual for low costs from Asia on Aliexpress. I think we are using 0.3 or 0.35mm balls so they are not applicable to you. If you are really in a pinch, ping us and can see we can spare our 0.5mm balls or you can just replace them when you have them from your source. We are in Windsor, Ontario. Also, consider to purchase a small bga with a similar geometry to perfect this process.

author: poot36
author_rank: Frequent Contributor
timestamp: August 08, 2021, 05:17:57 pm
content: Thanks for all the tips. As this is just a one off job I font think I Will be getting the full setup as that would be cost prohibitive. I will try with solder past once I get a chance to ask about taking some of it home from work (been really busy at work lately). If that does not work I will order some slightly smaller balls from Amazon.ca.

author: poot36
author_rank: Frequent Contributor
timestamp: October 10, 2021, 10:10:10 pm
content: Well me and a friend were able to get the solder past to reball the chip however we also managed to loose a pad that my friend was able to find the via on the chip and repair but sadly I think I damaged the chip taking it off the board as the radio it came from still does not work. Thanks for the help though.