Problem with solder paste - Page 1
Forum section: electronics / general

author: PartialDischarge
author_rank: Super Contributor
timestamp: June 08, 2022, 01:18:45 pm
content: I'm trying this solder paste Sn96,5Ag3Cu0,5 (https://www.tme.eu/Document/a020b649db9c39a3f9343be8bbeacb50/TDS%20Easy%20Print%20ang.pdf) and it is not melting using a curve with 235ºC peak.Parts of the board just remain with the paste as a dry grey powder after reflow.To be honest it has not been stored in a cool place, so should I add no-clean flux to it until I get a less viscous paste?

author: 48X24X48X
author_rank: Frequent Contributor
timestamp: June 08, 2022, 03:02:30 pm
content: At around 217 Degree Celsius, you should see the paste become fluid. If it doesn't, what you measure is not the board temperature and probably is the air temperature? 245 Degree Celsius is the recommended peak temperature for SAC305 paste.

author: PartialDischarge
author_rank: Super Contributor
timestamp: June 08, 2022, 03:49:01 pm
content: I'm pretty sure its not the temperature. I've gone as high as 245+ and still does not melt, I'm talking about turning the board brown. There may be an error but it can't be that high. I've had to add liquid flux that includes rosin to the board for the solder to melt. I believe this paste is "dry" and has lost some of whatever it had that made it melt

author: Siwastaja
author_rank: Super Contributor
timestamp: June 08, 2022, 04:02:34 pm
content: If it does not melt at all, then temperature is low. There is no other possibility. Flux can go bad (causing the solder to flow poorly, forming balls, etc.), but the metals do not magically turn into other metals, their melting points won't change.Obviously, tin does not know about temperature elsewhere. Tin melts when the temperature of the tin itself exceeds its melting point. For this to happen, if you use air as heat transfer medium, air temperature must be significantly higher because air has poor thermal capacity (i.e., the only way to make it store enough energy is to increase delta T), and air-to-solder paste interface can only transfer so much heat, air being poor thermal conductor; again, all you have to facilitate thermal conduction is enough temperature difference.So where are you measuring the temperature?Depending on the oven, required air temperature for lead-free solder paste can be anything from 300 degC to over 400 degC.Consider using leaded solder. It is exempt from RoHS for prototyping, repair etc. Leaded solder gives you over 30degC more margin for error which is only good for beginner. I only use leaded for prototypes, and let the manufacturing figure out optimum process for lead-free solder (something which took the industryyearsto learn).

author: wraper
author_rank: Unknown
timestamp: June 08, 2022, 04:04:09 pm
content: I bought the same paste from TME a few years ago. It was well within its shelf life but it was just as bad as yours. My main suspicion was that TME does not store it properly in refrigerator and paste is very sensitive to storage temperature.QuoteIt will not help once paste is bad.

author: wraper
author_rank: Unknown
timestamp: June 08, 2022, 04:10:16 pm
content: Quote from: Siwastaja on June 08, 2022, 04:02:34 pmMetals oxidize or experience other chemical reactions. The main problem with solder pastes is preserving fine metal powder from chemical reactions. Once it oxidized, it will not melt like a normal solder.

author: PartialDischarge
author_rank: Super Contributor
timestamp: June 08, 2022, 05:07:59 pm
content: The temp set by the oven is fine, just measured it with a themocouple at the tray base and it can't ve more than 5º apart.There is something wrong with this paste.. anyway I'll buy some other from mouser or digikey and try again. Any suggestions?

author: mon2
author_rank: Frequent Contributor
timestamp: June 08, 2022, 07:27:54 pm
content: Consider the LOCTITE GC-10 No clean paste. We use it for production and love the stuff. I understand that there are some lower temp pastes out there but we have been using GC-10 for the past few years with success. Can store @ room temps as well. We do use our solder paste mixer which mixes the paste to become more fluid for a nice print.You can buy it from this contact or some local in your region:Quote

author: PartialDischarge
author_rank: Super Contributor
timestamp: June 08, 2022, 07:39:14 pm
content: I noticed Chip Quick also has this one which does not require fridge:https://www.mouser.es/datasheet/2/73/TS991SNL35T4-2511339.pdf

author: Mangozac
author_rank: Frequent Contributor
timestamp: June 09, 2022, 02:18:48 am
content: You need to buy the paste from somewhere nearby who will ship it either in a cold pack or at least overnight. Even though most modern pastes don't need refrigeration, getting baked in the back of a truck during transit is still highly detrimental.

author: jmelson
author_rank: Super Contributor
timestamp: June 09, 2022, 03:48:31 pm
content: Quote from: mon2 on June 08, 2022, 07:27:54 pmYes, I have had great luck with this. it lasts a long time, wets the pads very well, and almost eliminates the little solder balls that appeared after reflow with other solders. Fantastic stuff!Jon

author: PartialDischarge
author_rank: Super Contributor
timestamp: June 13, 2022, 12:00:26 pm
content: Just received this paste from digikey (https://www.sra-shops.com/pub/media/docs/srasolder/datasheet/tds-sslfnc-t3.pdf) and it works, used the same curve as before, 235º, but actually I did peek inside thetray at 220º and it was already melted.So something very wrong from the paste I got from TME.

author: kvide
author_rank: Newbie
timestamp: April 06, 2025, 10:57:48 am
content: Quote from: PartialDischarge on June 13, 2022, 12:00:26 pmI was about to order solder paste, but realized that TME has withdrawn all their solder paste offerings. Any idea why? Quality issues, dangerous goods/logistics issues, something else?The Polish manufacturer seems still up and running though:https://termopasty.com/en/

author: jayx
author_rank: Regular Contributor
timestamp: April 06, 2025, 08:08:05 pm
content: Seems to be available if you select shipping to Poland, I've also checked Germany, but if select UK it says "This product is not available for sale in your country."

author: jpanhalt
author_rank: Super Contributor
timestamp: April 06, 2025, 09:36:13 pm
content: I picked up a new T-962 reflow oven cheap a few years ago. Aside for the usual modifications, the first thing I did was calibrate the TC's. They were way off. I've had no problems since. Have you calibrated the TC's? I am not saying within 0.1°C accuracy, I mean within a degree or two?

author: Rat_Patrol
author_rank: Frequent Contributor
timestamp: April 06, 2025, 10:05:54 pm
content: You may want to try a different brand of solder paste. I've had great success with ChipQuick

author: PartialDischarge
author_rank: Super Contributor
timestamp: April 07, 2025, 06:15:30 am
content: People this is an old thread. Temp of the oven was fine, that paste was bad somehow, now I'm using Chipquik with some kind of flux that does not evaporate and very happy with it.