Soldering paste - syringe or cup? Which is better? Which lasts longer? - Page 1
Forum section: electronics / beginners

author: dusan
author_rank: Regular Contributor
timestamp: January 13, 2023, 09:37:09 am
content: I'm buying my first SMD soldering paste and there are two options. In a small cup or in a syringe. I don't expect I'll be using it much, I only need few parts every couple of months. Which is better? Which lasts liquid longer?

author: bidrohini
author_rank: Regular Contributor
timestamp: January 13, 2023, 09:50:39 am
content: As far as I know, the difference is in the amount of flux they contain. Not in longevity. No matter if the paste is in syringe or cup, the manufacturer will mention the expiry date. You must see that before buying. Here is a thread with many good answers:https://www.eevblog.com/forum/beginners/using-solder-paste-out-of-a-tub/

author: Infraviolet
author_rank: Super Contributor
timestamp: January 15, 2023, 12:47:02 am
content: Syringe vs cup probably depends on how you'll use it. If you have a pasting needle setup to squirt small blobs then buying in a syringe that can link up to your dispenser system saves you having to transfer the paste to a syringe from whatever you bought it in. If you apply it via a wiper and stencil then a cup might be easier, but this will always be more wasteful of the paste.

author: Psi
author_rank: Super Contributor
timestamp: January 15, 2023, 01:15:21 am
content: Tubs are messy, you can end up with solder paste everywhere that youneedto clean up because you don't want to accidently leave a mess on your workbench and then touch it days later and end up eating it accidently.

author: twospoons
author_rank: Frequent Contributor
timestamp: January 15, 2023, 10:51:48 pm
content: Go for the syringe. Less mess, easier to dispense. Also keep it in the fridge when not in use.

author: Faranight
author_rank: Unknown
timestamp: January 16, 2023, 12:10:03 pm
content: Definitely get a syringe, and while you're at it, also get a dispenser, if you can.I got one like this from aliexpress and it works wonders.https://sigaris-electronics.eu/2020/09/manual-dispenser-for-soldering-pastes/

author: JustMeHere
author_rank: Frequent Contributor
timestamp: January 16, 2023, 01:25:02 pm
content: I've had a syringe that has lasted for years. I always use flux, and I don't know how much it's helping; however, the paste still wets well. I don't even do a good job of keeping it in the refrigerator.

author: wraper
author_rank: Unknown
timestamp: January 16, 2023, 01:36:43 pm
content: If you mean a paste which contains solder, then depends on how you use it. If you need to apply it to some pads, get a syringe. If you use stencil, certainly get a jar since you usually get about 3x more paste for the same price. Paste supplied in syringes is the same as the stuff available in jars. Also you can fill a syringe yourself, just avoid using syringes with rubber plunger and use fully plastic. Also avoid creating air bubbles since it will make application much messier. Cheap pastes from China are OK but they often cheat on actual quantity.If you mean tacky/paste flux, get a syringe. Decent stuff is almost non-existent is small jars and you don't need 500g for something like $70. Also don't buy garbage Amtech knockoffs from China.

author: donlisms
author_rank: Frequent Contributor
timestamp: January 16, 2023, 04:26:59 pm
content: I have the impression that the expiration is when the solvents in the flux dry out, or something like that. If that's true, then it seems all you'd have to do is reconstitute it, and that would be easier in a cup than in a syringe.Much speculation, here! I can't remember where I heard about the expiration, and my paste is not dried out yet!

author: wraper
author_rank: Unknown
timestamp: January 17, 2023, 08:06:13 am
content: Quote from: donlisms on January 16, 2023, 04:26:59 pmNo, solder pastes particles experience chemical reaction and will no longer melt properly. As it starts to go bad there will be small solder balls appearing around the pads. Then eventually there will be unmelted sludge after reflow.As of fluxes, they become less active and do not remove oxidation from metal as well and may have some other unwanted effects. Overall fluxes usually can be used many years after expiry date, unlike solder pastes.