using solder paste out of a tub

[macboy]

got some flux from the radiator building shop at work and mixed it in.

You must use electrical soldering flux. The stuff used for pipes is often acid based and is far too corrosive for electrical work.

[Simon]

oh, I thought flux was acid full stop

[Kjelt]

You gotta be kiddin, i would think it was an april fools joke   

[BrianG61UK]

oh, I thought flux was acid full stop

As I understand it, they are all acidic, but electrical/electronics flux is only slightly acid and only when it's hot.

[tooki]

The paste from a tub is for stencil use, not for syringe use. The lead balls are much bigger and stiffer than paste from a syringe (look under the microscope).

The size of the solder balls has nothing to do with whether it’s a jar or syringe type. The size is given by the screen size (think sifting): T3 is kinda standard. T4 and T5 are progressively smaller. I think there’s T6, too.

For very fine stencils (for tiny pads), you need a finer screen. But you don’t want any finer than necessary, because finer balls oxidize faster (=shorter paste shelf life) and also tend to cause more satellites (little balls of solder after reflowing).

[Infraviolet]

As you mentioend trouble getting the paste to flow, a little tip regarding dispensing, get plastic concial needles rather than metal straight ones. The cone shape is much less prone to jamming up than the long thin region inside a metal needle.

[tooki]

Very true! The conical tips waste more paste (there’s more paste in it when you remove the tip) but indeed make dispensing far easier!

[Kjelt]

Old zombie topic.
Plastick vs metal.
With my multicore pneumatic / vacuum electronic paste dispenser the metal needle gives a 100% reproducable dispense result. The plastick ones differ but tend to post-ooze paste.
Tried many settings longer vacuum post dispense time etc. but the metal needles work te best probably bacause there is less material to retract with the post vacuum.

[Kjelt]

The size of the solder balls has nothing to do with whether it’s a jar or syringe type.

Yes correct if you can get the different varieties.
Remember, this was an 8 year old topic, with for instance Farnell you only had a choice between jar and syringe. That was the difference back then, when I bought a jar it had the larger balls unfit to be dispensed with tiny needles.

[Watth]

What I do to put grease in syringe:
Use a spatula-like thing (I bought tongue depressors, they're cheap and have many uses) to put the grease in a small zip lock bag.
Close the zip-lock bag and cut a small corner of the bag.
Remove the syringe's plunger and press the bag to fill the syringe.