Why solder balls squeeze out?

[short_toground]

Been using 365c with air speed of 3. Too high?

[orx]

clear situation , too high temperature .. lowers to 320 for reflow and increases the speed of the air. FEW SECONDS.......

[short_toground]

Originally Posted by orx

clear situation , too high temperature .. lowers to 320 for reflow and increases the speed of the air. FEW SECONDS.......

What's good air speed to use? Is 320c good temperature for reballing too?

[orx]

for reballing depend where you reball ..example , U2 5s (no danger zone ) i use 345 air to level 4..anyway is important which rework station you have .
Flux is very important for all work process ..quality flux and quality tin solder paste help you.

[short_toground]

What size nozzle do you recommend? I'm confused temperature difference for removing chips that have underfill

[orx]

small / medium depend work area.

[short_toground]

What's best, high temp with low air speed or lower temp with higher airflow?

[Kradziej]

You are trying to heat IC with uderfill, balls will always squeeze out from uderfill when expanding under high temp. Just lift it with sharp, very thin tool and clear glue, don't bother about balls running all around the board.

[short_toground]

Originally Posted by Kradziej

You are trying to heat IC with uderfill, balls will always squeeze out from uderfill when expanding under high temp. Just lift it with sharp, very thin tool and clear glue, don't bother about balls running all around the board.

So you can't simply "reflow" a chip that has underfill? It needs to be removed because solder balls always squeeze out?

[Kradziej]

Originally Posted by short_toground

So you can't simply "reflow" a chip that has underfill? It needs to be removed because solder balls always squeeze out?

Unfortunately yes. Underfill encloses solder balls and restricts their ability to expand properly, so they make little cracks in underfill and molten solder bursts out shorting to neighbor pins.
Its possible to heat it up a little to only melt surfaces of solder balls but what temperature and how long exactly there is not straight answer, boundary between overheating and proper reheating is very thin, in practice I never had long standing success with such method.

[Tretiakova]

@kradziej: what temp on air do you use for reflow on TouchIC (Cumulus and Meson) chips?

Senior Research & Development Tech - L3

[Kradziej]

Originally Posted by Tretiakova

@kradziej: what temp on air do you use for reflow on TouchIC (Cumulus and Meson) chips?

It always depends on what type of hot gun you are using, for me its quick 861 and I use 380/120(max airflow) with possibly small nozzle and a lot of caption tape around to prevent cpu from overheating .
With high airflow you can see when solder balls melted so you have better control over whole process.

[alfyguy]

I think either airflow or temp is too high