Hot air soldering - balls - Page 1
Forum section: electronics / beginners

author: JonPyro
author_rank: Regular Contributor
timestamp: August 29, 2019, 09:55:16 pm
content: Hi All,I have done my first hot air soldering this afternoon after ordering a pro board and stencil from JLC. I am using chipquick solder paste (lead free, you cannot buy leaded within the EU as retail anymore).I warmed the board up for about 20 seconds at 100 degrees (lowest my hot air gun can go) and the board was about 30mm away using fairly large nozzle, about 9mm nozzle. Then upped to 160 degrees to fully melt with air speed about 80%.From a visual inspection it looked quite good, until i looked with an eye glass. Between my pads are loads of very tiny solder balls, all hanging out on the solder mask. I have tried to get a photo but I don't have a microscope of macro lens so I tried to shoot through my magnifier, you can see the edge of the pad lined with balls but this continues across with ever smaller balls.Could anyone suggest how to stop this from happening?I have tried spending more time a lower temperature and the opposite, high temperature and soldering as quickly as possible - these didin't work. I have also tried to replicate the oven profile of the paste with limited success and that doesn't seem to help either. could this be too much airflow? not enough airflow?My solder paste was warm as i had left it out the fridge for about 5 hours.

author: GreyWoolfe
author_rank: Unknown
timestamp: August 30, 2019, 01:26:16 am
content: That very well might be due to the high air pressure you used. I was soldering a few 0605 and 0402 passives and I had my Quick 957DW turned down to between 1 and 2. Very little air movement was necessary. I started out higher but started to blow components a little.

author: worsthorse
author_rank: Super Contributor
timestamp: August 30, 2019, 03:10:03 am
content: Based on the splatter and the look of the solder joints, too much air pressure combined with too much movement. Check the size of the nozzle attachment, turn down the blower, don't try to do too large an area at once. Think about how a simple reflow oven works... no air movement at all, just heat.

author: JonPyro
author_rank: Regular Contributor
timestamp: August 30, 2019, 05:55:58 pm
content: Ok so I tried turning down the air speed to 10% And raises the temperature slowly over about 4 mins inline with the datasheet for the paste making allowances for loss of temperature.However, my result still has solder balls lining the pads

author: TheHolyHorse
author_rank: Regular Contributor
timestamp: August 30, 2019, 06:11:13 pm
content: I'm no expert so I could be far off here but isn't 160 degrees way to low. Like it wouldn't even melt leaded solder.

author: worsthorse
author_rank: Super Contributor
timestamp: August 30, 2019, 06:20:03 pm
content: The good news? You are getting closer to getting it right.The photo is a little fuzzy but the solder joints look more like they should. So if you have the temperature right and not too much air flow, then some other questions: did you clean the board before soldering? do you have a proper flux? have you tried a different solder paste? are you using too much solder paste?For simple SMD soldering like this, preheating the board, complicated temperature profiles and such are just confusing the issue.edit: Here's a pretty good tutorial video for you. The second half demonstrates the "no solder mask" method...

author: KL27x
author_rank: Super Contributor
timestamp: August 30, 2019, 10:42:28 pm
content: This is probably down to the paste. The solder balls occur because the flux spatters as it heats up, and it flings little bits of paste around. When that paste reflows and dries out with nothing to attach to, it forms little solder balls.Blueskull recommends GC10 paste. I'd give that a try. He does a lot of this sort of thing, and the boards he makes look like they could go into a cell phone.

author: JonPyro
author_rank: Regular Contributor
timestamp: August 30, 2019, 11:13:13 pm
content: I haven't cleaned the boards actually, maybe I should IPA them first.I am using a stencil to get the correct amount and position of paste.I am not using any flux, I assumed the paste would contain the correct amount of flux?Intresting the video shows really quick 400 degree heat. My paste should melt at 138 and reflow at 165 according to the datasheet. I was assuming the balls were developing because the flux was not burnt off before the solder flowed, so slow build heat was better than going full out on it. Annoyingly he doesn't show a close up his joints so it's not possible to tell if he has mini balls.Gc paste is out of my budget as you can only buy it in large syringes or tubs here. It would be far cheaper to hand solder.I deliberately bought chipquik paste as I thought being a brand it would be reliable than some dirty eBay buy.Oh well, I will carry on experimenting tomorrow in the hope of finding the sweet spot.....i am running out of boards to solder lol.

author: KL27x
author_rank: Super Contributor
timestamp: August 31, 2019, 12:06:12 am
content: Yeah, the paste has the flux in it. A lot of pastes tend to splatter. The solder bits aren't as well suspended in the emulsion, and they will trap solvent vapors enough to cause little mini explosions.If the cost of GC10 paste is more than the money it saves, then you probably shouldn't even be bothering with paste and stencils.IMO, unless you have a PnP machine (and you are doing a job big enough to bother setting it up), using solder paste is just playing with a toy that wastes more time than it saves. Even hot air flowing QFN's with a center pad, regular solder is faster than messing with paste, IME. (This doesn't stop EE bloggers from making videos showing how cool it is to solder with paste for no reason.)

author: JustMeHere
author_rank: Frequent Contributor
timestamp: August 31, 2019, 03:20:44 am
content: If you put solder on the mask and heat it, balls will form. Brush them away. I usually work with lead solder at 240 C. I wash my boards in 90% IPA and use an old toothbrush. Should I use a static free brush, maybe; but the IPA should help with the static.Solder balls on the mask are expected. If they are on the pads, then I would question if enough heat was applied.On real small pins, I still usually have to do some cleanup with my iron. Globbing some flux can also help clean up the pins.I apply the solder with a syringe and a smallish blunt needle. Some people just draw a line across the pins with the syringe.Based on your photo, you could use a bit more paste.

author: Bud
author_rank: Super Contributor
timestamp: August 31, 2019, 04:12:30 am
content: Quote from: KL27x on August 30, 2019, 10:42:28 pmI second that, seems the paste issue to me. Try a different paste.

author: JonPyro
author_rank: Regular Contributor
timestamp: August 31, 2019, 02:30:09 pm
content: Ok some more experiments below, board cleaned before.20190831_151716.jpg was lots of heat20190831_151756.jpg is of the stencil paste20190831_151825.jpg is at 138 degrees for about a minute (datasheet says the paste melts at 138.)20190831_152633.jpg￼ was high heat then cleaned with IPA and stiff brush.None of them really successfully. Lots of balls and this is without the chipset to have to clean around. While the last one cleans up ok I don't think i could achieve it that clean once a small chipset was sitting there.Are my expectations too high for this?EDIT: with a brutal brushing the boards do clean up...

author: rs20
author_rank: Super Contributor
timestamp: August 31, 2019, 03:14:52 pm
content: Could you please provide a link to this solder paste's datasheet? Lead free solder generally has a higher melting point than leaded solder paste, not something as low as 138. Makes me wonder what paste you've actually got there.

author: JonPyro
author_rank: Regular Contributor
timestamp: August 31, 2019, 03:21:18 pm
content: Sure, attached.

author: Illusionist
author_rank: Regular Contributor
timestamp: August 31, 2019, 06:21:44 pm
content: It'll have a high level of bismuth in it, similar to the stuff they sell for reworking boards.