Solder paste - Page 1
Forum section: electronics / beginners

author: rob.manderson
author_rank: Regular Contributor
timestamp: December 20, 2017, 01:07:36 am
content: Now this might sound like a silly question but...What are the symptoms when one's solder paste is out of date? I was out in the garage an hour ago and had to pour what seemed like an awful lot of heat from the hot air gun to get the stuff to melt. I've been using the same hot air gun for about a year now and used the same syringe of paste about a month ago and it behaved normally then. It's not particularly cold out there in the garage (this is Phoenix after all) so I'm wondering if it's the paste or the hot air gun.

author: wraper
author_rank: Unknown
timestamp: December 20, 2017, 01:15:10 am
content: When paste is really bad, it just wont melt at all and will stay as a grey gunk. When paste goes bad it starts forming small balls around instead of all of it ending in a single solder joint. As of what you are experiencing, it sounds like PCB has higher thermal mass compared to what you used earlier. Or there is something wrong with your hot air. Solder paste melting temperature does not change over time.

author: james_s
author_rank: Super Contributor
timestamp: December 20, 2017, 01:40:18 am
content: My experience is that it gets more viscous and doesn't like to stick to the pads. I usually mix a bit of liquid flux into expired solder paste and it works fine then for hobby use.

author: wraper
author_rank: Unknown
timestamp: December 20, 2017, 01:57:23 am
content: Quote from: james_s on December 20, 2017, 01:40:18 amThat's just drying out. Also some pastes tend to loose liquid in remaining paste when applied through the stencil. Liquid migrates into the paste which is left on the board. Or in case of syringe, liquid is squeezed out and remaining paste becomes drier as you use it. Because of this, I no longer use one otherwise excellent paste.

author: rob.manderson
author_rank: Regular Contributor
timestamp: December 20, 2017, 03:11:11 am
content: Quote from: wraper on December 20, 2017, 01:15:10 amThis description does sound like what happened. I've ordered a new hot air gun and new paste so we'll see what happens.

author: nanofrog
author_rank: Super Contributor
timestamp: December 20, 2017, 04:56:11 am
content: Quote from: wraper on December 20, 2017, 01:57:23 amWould you provide details regarding the paste you're no longer using?FWIW, Kester's EP256 is specified at 1.5hrs working time after application, andCML Supplyrepacks it into hobbyist/small repair shop friendly sizes.Quote from: rob.manderson on December 20, 2017, 03:11:11 amDo you have a DMM with a temperature function and an appropriate type of thermocouple for it?It'd be quick and easy to check your existing hot air gun (set temp v. actual temp). Could be as simple as calibrating your unit.

author: wraper
author_rank: Unknown
timestamp: December 20, 2017, 08:57:00 am
content: Quote from: nanofrog on December 20, 2017, 04:56:11 amWarton metals P2010, it's temperature stable solder paste.https://www.rapidonline.com/warton-metals-microprint-p2010-sac305-88-0-25-45-no-clean-solder-paste-547774I now use GC-10 instead which also is temperature stable but don't have this issue.

author: Teledog
author_rank: Regular Contributor
timestamp: December 21, 2017, 09:07:52 pm
content: Sounds like the solvent has dried out.Is there an expiry date on it?I still use expired stuff if it hasn't solidifiedAlso keep my bottles within a sealed glass jar in the fridge (don't tell the GF!)& let it warm up an hour or so before using.You can sometimes add IPA & mix it around a bit..but sometimes it's just too chunky..time to trash it..(uh, safely, of course & all the usual enviro blabber)

author: rob.manderson
author_rank: Regular Contributor
timestamp: December 21, 2017, 10:33:14 pm
content: Well it turns out it *was* the hot air gun. The new one arrived today (from Amazon) and the solder paste is now behaving itself. However, I've had that syringe for a bit over a year so methinks it's time to replace that as well.I'm also thinking maybe it's time to get a thermocouple - I do have the HP3456A to connect it to!

author: nanofrog
author_rank: Super Contributor
timestamp: December 22, 2017, 12:17:17 am
content: Quote from: rob.manderson on December 21, 2017, 10:33:14 pmHere's a couple of products that will work for you.Adapterto fit the binding posts.K Type thermocouple(K Type = most common version, and has the widest temp range).Rather inexpensive too.Hope this helps.

author: rob.manderson
author_rank: Regular Contributor
timestamp: December 22, 2017, 01:09:43 am
content: Ordered!