Strange SMT reflow issue - Page 1
Forum section: electronics / general

author: Psi
author_rank: Super Contributor
timestamp: May 11, 2017, 10:38:02 am
content: Has anyone seen this before.Basically the flux is trapping solder balls so they can't join up with the main group and it's leaving a mess of balls over the PCB after exiting reflow oven.Solder paste is ChipQuik T4 no clean leaded solder and is applied with metal stencil. (Alignment on pads is perfect when it goes into the oven.Reflow oven is just a dual element toaster oven on variac. In for 4min at 210C approx (from fluke dmm temp probe)i don't think the oven is to blame, ive done boards fine before with the same setup.Any ideas?My thoughts are that A ChipQuik sucks and B ChipQuik sucks.

author: IanJ
author_rank: Unknown
timestamp: May 11, 2017, 10:52:32 am
content: Hi,Good info here:-Tiny Solder Balls After Reflow:-http://www.circuitnet.com/experts/87416.htmlIan.

author: wraper
author_rank: Unknown
timestamp: May 11, 2017, 11:05:01 am
content: Expired or improperly stored solder paste. Generally solder paste is guaranteed to be good for 6 months if stored in refrigerator. Some solder pastes can become unusably bad if stored at room temperature for 1-2 months.

author: Psi
author_rank: Super Contributor
timestamp: May 11, 2017, 11:30:48 am
content: This paste was stored in the fridge since i got it from digikey.

author: Psi
author_rank: Super Contributor
timestamp: May 11, 2017, 11:32:03 am
content: Quote from: IanJ on May 11, 2017, 10:52:32 am"You may have moisture in your solder paste which is causing the solder balls to explode off during reflow. This can happen if the paste is refrigerated and not allowed to get to room temperature before opening causing moisture to condense on the paste."Thanks for thatThat could be it, i grabbed the tub straight from the fridge.

author: DTJ
author_rank: Super Contributor
timestamp: May 11, 2017, 12:01:55 pm
content: I don't use an oven, I use a heated plate & reflow with hot air so it may not apply to your situation.I often get what's shown in your photo and applying more heat for longer generally fixes it.

author: Kjelt
author_rank: Super Contributor
timestamp: May 11, 2017, 12:56:05 pm
content: Quote from: Psi on May 11, 2017, 10:38:02 amYes have you ever heard of a reflow profile ? You are not following the profile specified by the manufacturer so anything can happen.Esp placing a roomtemperature pcb directly in a 210C oven could cause splatter, secondly the phase where you get the flux to activate (120-160C) is absent so your flux might not behave as expected.Finally since the normal reflow profile end temperature is around 230C you might also not get the expected result.You do not follow the industry standard and then you start blaming the solder paste, really ?

author: Jeroen3
author_rank: Super Contributor
timestamp: May 11, 2017, 01:03:57 pm
content: If you get tiny solder balls it's because the flux boils, which is because you're heating too quickly.

author: Psi
author_rank: Super Contributor
timestamp: May 11, 2017, 08:24:48 pm
content: Quote from: Jeroen3 on May 11, 2017, 01:03:57 pmGood point. Will try slowerThanks

author: Psi
author_rank: Super Contributor
timestamp: May 15, 2017, 07:02:58 am
content: Quote from: Kjelt on May 11, 2017, 12:56:05 pmYep. I am.Because ive heard others say chipquik is terrible.Also its worked fine before. Ive not changed my procedure. It just started happening and ive done 100s of board no problem in the past

author: Kjelt
author_rank: Super Contributor
timestamp: May 15, 2017, 07:30:14 am
content: Quote from: Psi on May 15, 2017, 07:02:58 amwhy did you buy it then?QuoteYou did the 100s boards with other paste and it just happened when you used the chipquick paste?Then you know your answer, if you only change one parameter and the outcome changes it is the changed parameter which is the most probable cause.Recheck with the paste you had before.

author: tatus1969
author_rank: Super Contributor
timestamp: May 15, 2017, 07:38:29 am
content: Quote from: Psi on May 11, 2017, 11:32:03 amDid you stir it thoroughly and let it warm up to room temp before applying?Another thing that I noticed: you have vias in the pad region, sucking away solder. That may exaggerate your problem.

author: Psi
author_rank: Super Contributor
timestamp: May 15, 2017, 11:19:55 am
content: Quote from: Kjelt on May 15, 2017, 07:30:14 amI bought it because there isn't much choice for no-clean leaded solder tubs from digikey.na, ive been using this chipquik tub for a while. It's not that new, about half full.Ive been playing around with the paste on PCBs using hot air at varying temps and speeds to see what causes it.Seems i can kinda repeat the effect if i go too hot.Not sure what this means yet. temp probe said oven was 210 which should be totally fine.Quote from: tatus1969 on May 15, 2017, 07:38:29 amNo vias in pads, where are you seeing that?Yeah, i let it get to room temp and also tried to pre-bake the pcbs at 80 for 15min to remove any moisture.Same problem after reflow.

author: Kjelt
author_rank: Super Contributor
timestamp: May 15, 2017, 11:36:57 am
content: Quote from: Psi on May 15, 2017, 11:19:55 amWhich temp you call too hot?Try to place a tempsensor next to the paste to get a better indication of temp and time.You can get temp sensors with usb connection for $60 the pc can record the profile which will give you better calibration of the experiments.I suspect that your pre-heat soak time is too short or the soak temperature too high.