Troubles Hand Soldering - Page 1
Forum section: electronics / projects

author: Thewafflication
author_rank: Contributor
timestamp: August 01, 2018, 09:14:37 am
content: I am working on a project, and want to use this part: LMT70A (https://www.mouser.com/ProductDetail/595-LMT70AYFQR)It is a 2x2 bga. It is about the size of 2 0402 resistors next to each other. I am trying to hand solder this part onto my own evaluation module.I have already destroyed 4 of these parts, and 2 of my 3 osh park boards.Does anyone know of a cheaper part in a similar package I could use to practice with. (So far I have only been able to get 3 of the 4 balls to wet, without bridging. I am using a hot air pen to reflow the solder, and a healthy amount of flux. Spent 4 hours Sunday night trying to get this to go...

author: Thewafflication
author_rank: Contributor
timestamp: August 01, 2018, 09:18:12 am
content: Here is my homespun evaluation module. The tiny footprint on the back is the BGA footprint. The front side has 3 0603 hand soldering footprints.I have already decided to use an alternative part, which uses a much friendlier SOT package. I my pride is mostly hurt because I couldn't solder this package.Any help is appreciated.

author: nanofrog
author_rank: Super Contributor
timestamp: August 01, 2018, 09:51:31 am
content: A few questions....How have you tried to solder it?Oven? Skillet? Hot air? ...Solder & flux? Paste (brand used)?And have you preheated the board prior to trying to solder this particular package?I ask, as details matter.

author: Kalvin
author_rank: Super Contributor
timestamp: August 01, 2018, 09:58:43 am
content: Check this out:You need a steady hand, a breakout board (or direct wiring to PCB) and some thin enameled wire. 2x2 BGA should not be *that* hard.

author: Thewafflication
author_rank: Contributor
timestamp: August 01, 2018, 10:07:28 am
content: Quote from: nanofrog on August 01, 2018, 09:51:31 amI have a hot air pen (Quick 861DW)Flux AMTECH NC-559-V2-TFSolder Paste AMTECH SynTech 63/37 25-45 umCurrent ProcessPreheat Temp 190C Air 85L/min Time 30 secApply Flux and componentHeat Temp 270C Air 25L/min Time 10 secSolder Temp 350C Air 30L/min Time 5 secThe pen is held above the board about 4.5 cm. I move the pen to heat the whole board.I was last using a 6mm tip.This process has successfully soldered 3/4 balls. 3 times thus far. (I have reused parts as much as possible.) I also have had better luck with out the solder paste. I have had issues with bridging when I add paste. (I am using 4 balls off an iphone repair stencil that happen to match up.)

author: Kjelt
author_rank: Super Contributor
timestamp: August 01, 2018, 11:36:41 am
content: Did you apply extra flux in addition to the paste because I would not do that.The paste is literally tinballs in flux, too much flux and during the wetting stage of the reflowprocess the balls are swimming everywhere causing bridging.Second if you have bridges you probably could have used too much paste. Add paste so that max 60% of the pad is covered, not more and it should not be too thick/high either.I never did this challenging part but my guess would be to go more moderate on the paste, no extra flux, clean the pads before thoroughly with IPA before applying the paste and follow the standard reflow process as much as possible , eg reheat the paste for 45 seconds at 160 degrees where a lot of flux is already starting to evaporate than continue to 230 degrees.

author: KL27x
author_rank: Super Contributor
timestamp: August 01, 2018, 08:19:01 pm
content: QuoteI would try to reflow it with downward pressure. Put a dab of flux over the chip. Put your tweezers on top of the chip and heat it up again under magnification until your flux melts and you can see the part. When you see the IC move, let go and remove the heat. It is pretty hard (as in freak occurrence) to end up with a bridge/short by doing this. I've never seen it happen, but I have never done anything this small.Yeah, when the part smooshes, you might very briefly bridge some or all of the pads. This shouldn't be a big deal. The pads should be too tiny to hold those bridges in presence of flux.

author: t1d
author_rank: Super Contributor
timestamp: August 01, 2018, 09:36:00 pm
content: Quote from: KL27x on August 01, 2018, 08:19:01 pmThis is a known method for setting some types of IC. You can find videos, of the process, on YouTube, for better understanding.Additionally, you might want to try the iron, or skillet, methods, as the heat comes from underneath, leaving you access, to manipulate the IC, from the top, during reflow. Again, see YouTube

author: nanofrog
author_rank: Super Contributor
timestamp: August 02, 2018, 12:15:36 am
content: Quote from: Thewafflication on August 01, 2018, 10:07:28 amYou might want to tin the pads with an iron first, flux them, and then use the hot air to reflow the chip. Surface tension will line it up, and you won't get bridges.Too many issues trying to use paste on BGA without a stencil IME.

author: KL27x
author_rank: Super Contributor
timestamp: August 02, 2018, 01:39:43 am
content: ^That's how I would do it. I think OP has found this to work better, already. He appears to have continued problem with the tiny part tilting and not connecting on 1 of the pads. And just to state the obvious. Damn, that part is tiny.

author: Ian.M
author_rank: Super Contributor
timestamp: August 02, 2018, 02:26:42 am
content: I think the problem is, without precision control of the amount of paste, and with any lateral temperature gradient across the part, one ball is bound to reflow first, and it then rocks on the as yet unmelted diagonal and surface tension lifts the opposite corner's ball off the pad before it reflows. If there is a well controlled amount of paste, the lifting can be controlled so that the opposite ball + the paste as it reflows remain in contact.Another major problem would be if one of the pads has much higher thermal mass i.e. goes direct to a power plane or heavy trace without necking down to the same width as the other traces to it. Tying T_ON directly to Vdd under the chip would be problematic for that reason as the ball without an external track would reflow slightly after the one next to the track, forcing it to rock.@nanofrog & KL27x,I think you are on the right track for manual soldering with your suggestions if you combine them: pre-tin the pads, flux, then place it and reflow pressing down slightly to ensure all the balls make contact, and only releasing it to let it float into alignment once you are certain its at reflow temperature.

author: OM222O
author_rank: Frequent Contributor
timestamp: August 02, 2018, 07:30:08 am
content: you don't need to use paste at all, you don't even need to re ball the chip if you screwed something up. I've never done hot air rework myself, but I have used a butane torch and was successful to do BGA soldering (After making sure of the chip alignment, I placed the entire PCB into a pan and heated it with the torch from the bottom)You're using a 4 pin chip so it should be fairly easy to just pre-heat the board (then put the hot air away), add some flux, place the chip with a pair of tweezers, let go of the the chip,push (in a scratching motion) the top side of the chip with your tweezers to make sure it's aligned correctly,heat till the solder balls melt, the chip should "snap into place" if your air pressure is not pushing it away too hard (if it is, hold the nozzle further back), then press on top of the chip with your tweezers and hold it place (don't worry about forming bridges, but make sure you're not moving it around, just pushing it down), put the hot air aside and wait for things to cool. after the solder joint has solidified, you can remove the tweezers. if you had issues with alignment or bridges (check with multi meter on PCB pads), you can add some flux around the chip, and heat it gently to melt the solder balls, then remove the hot air quickly(no need to use tweezers or anything this time). This should work perfectly fine, but in case you screwed something up:use hot air to remove the chip ( DO NOT RE BALL WITH PASTE). use some flux and solder wick to clean up the pads, then add small amounts of lead solder (using a traditional iron) to the pads on the PCB, effectively forming small balls on the pads (try to make them around the same size), then place the chip with tweezers, make sure it's aligned, repeat the procedure I described before (i.e. force on top with tweezers while holding down, reflow with just heat and flux if you had bridges).You can watch louis rossman on youtube if you have difficulty understanding what I wrote, he uses the exact same procedure and he can easily solder BGA chips on a mac book. Best of luck.

author: PlainName
author_rank: Super Contributor
timestamp: August 02, 2018, 01:52:34 pm
content: The problem of 3 of 4 balls working sounds like a solder quantity issue: there is uneven quantity on the pads, so three pads are holding the chip higher than the gap on the fourth can be filled.This is why you have solder balls - there is an exact amount (and consistent) amount on each pad so the chip sits level and in contact all around. But working with solder balls is a right pain and I never got it to work successfully. What I do instead is:1. Stick the chip upside down on your work surface (I use blutack to hold it).2. Flood the pads with flux. Gels are good but whatever you usually work with.3. Solder each pad with slightly excessive solder. What you're aiming for is just too much so the excess sticks to the iron from surface tension.4. Leaving some excess on the iron, go back around just wiping the pads with it. The idea here is to completely fill the pads with as much solder as they'll take but no more - the extra stays on the iron.5. Voila - each pad (assuming they are all the same shape/area) now has the same amount of solder on 'em.6. Make sure your board is tinned bu otherwise clean of solder - use a wick to clean it if necessary.7. Add flux to the board, position the chip, apply hot air evenly until the flux gets ejected as the chip is pulled down by the solder melting.Might take a couple of goes to get the hang, but once you've done it it's a piece of cake.