Chipquick TS391AX250 solder paste issues - Page 1
Forum section: electronics / general

author: Mangozac
author_rank: Frequent Contributor
timestamp: July 09, 2020, 09:47:17 pm
content: We've been trying out Chipquick TS391AX250 solder paste while commissioning our new conveyor reflow oven (as part of our new SMT line) but we're having lots of issues with tiny solder balls suspended in the flux residue post reflow. We tried it with our little prototyping batch oven and had the same results. We chose Chipquick because it's supposed to have a very long shelf life and is less fussy about storage (even though we keep it refrigerated).- The paste was purchased from Digikey with a date code of this year- The paste was brought to room temperature and well mixed before use- Paste was applied using a stencil but components were placed by hand, so it was a few hours before entering the oven- The reflow profile has been set as per the solder paste datasheet. It has been confirmed by passing a PCB with fitted thermocouples through the oven- Research indicated that this can be caused by initial temperature ramp being too steep but adjusting this setting did not make any discernible difference- Humidity was around 60% on the day but we've found similar results earlier this week on days with low humidityI've contacted Chipquick but yet to have a response from them so thought I'd check if the knowledgeable people here have any suggestions what might be happening...Thanks!

author: Rat_Patrol
author_rank: Frequent Contributor
timestamp: July 09, 2020, 10:14:25 pm
content: I use the TS391AX50 paste with good results.Things I found out:-It REALLY doesn't like more paste than needed, then it forms solder balls. No big issue when applied with a stencil.-It required a fairly steep profile in my batch oven. I use a Controleo converted toaster oven, and it runs pretty much full power until reflow.From your pics, I would suspect it did not pre-heat long enough and perhaps more likely didn't hold temp during reflow temps long enough, or possibly you need to bump reflow temp a bit. My best guess would be either not long enough dwell time during reflow and/or not high enough relow temp.

author: wraper
author_rank: Unknown
timestamp: July 09, 2020, 10:53:06 pm
content: Quote from: Rat_Patrol on July 09, 2020, 10:14:25 pmNope. If paste is good it will melt OK regardless. If there are small balls around, the paste is a dead trash.

author: SMTech
author_rank: Frequent Contributor
timestamp: July 09, 2020, 10:58:51 pm
content: Solder balls can in theory be caused by water or even flux boiling off if the the humidity is high or the profile very steep but is more easy to cause by just having too much paste, that could be a poor footprint, too thick a stencil, poor gasketing or just a crap stencil in general.However, I'm with Rat_Patrol on this one, I don't think these are what we might call a mid chip solder ball, it just looks uncooked, maybe check that profile with thermocouples again on this or a similar board and overlay that with their sample profile.

author: Mangozac
author_rank: Frequent Contributor
timestamp: July 09, 2020, 11:54:22 pm
content: Thanks guys.We've tried this on two different boards. Stencils are from JLC. Gasketing was good (we inspected on the microscope after pasting). We also tried slowing down the conveyor (extending out the profile) and speeding up (although the profile presented in the datasheet is actually already quite a fast one) but the results were the same.At this stage I'd like to try another paste - what's the recommendedleadedoption that's going to be as forgiving as possible and with a decent stencil life.

author: wraper
author_rank: Unknown
timestamp: July 10, 2020, 12:06:19 am
content: Loctite GC10 is temperature stable but produces quite a lot of nasty deposition in the oven. I like AIM M8 more because it's less nasty and flows better. Not temperature stable but you can store it for 3 months at room temperature.https://aimsolder.com/sites/default/files/m8_solder_paste_tds.pdf

author: Mangozac
author_rank: Frequent Contributor
timestamp: July 10, 2020, 12:24:44 am
content: Thanks but we're fortunate enough to still be able to run leaded solder for 99% of the stuff we do. I'm intending to get some GC10 for the one RoHS board where it's necessary.

author: kylehunter
author_rank: Regular Contributor
timestamp: July 10, 2020, 03:42:35 am
content: Kester EP256HA is our goto leaded paste. Make sure you get the HA version. It's high activity no clean solder. Their standard 256 has wetting issues.