Problems Using Solder Paste to Re-ball???

[reessi]

I have been trying to re-ball some chips on some phones with stencils and some solder paste. It was cheap paste from China, not sure if thats the problem or my technique.

I've watched lots of youtube videos and seams to work easily for people.

I hold the stencil down over the chip with the tweezers, apply paste and wipe excess off with tissue or a blade. I check under the Micrsocope.

Then on my digital hot air I set lowest setting of 1 litre of air out of 120!!

Tried temps around 350 to 400, previously tried higher air.

The problem is everytime without fail the paste jumps out and balls up all over making a right old mess! Leaving empty holes, some with massive sticking out balls etc etc. Its like its alive!

I tried leaving the paste out to harden as recommended by someone doing videos in vietnam, this improved it, made it stiffer but still some popped out.

Any ideas please what I'm doing wrong?

Cheers.

[stj]

Re: Problems Using Solder Paste to Re-ball???

too much flux probably

[reessi]

Re: Problems Using Solder Paste to Re-ball???

So that means I need to buy a different paste right?

What have you used?

Cheers.

[petehall347]

Re: Problems Using Solder Paste to Re-ball???

can you post pics are better a video ?

[reessi]

Re: Problems Using Solder Paste to Re-ball???

I'll try in the morning, not got a camera on the microsope though! Cheers.

[Seagorman]

Re: Problems Using Solder Paste to Re-ball???

reessi, i'd try changing your flux for a high quality flux such as Amtech BGA NC-559, its not cheap but will save you a lot of time/hassle by doing so, i dont do phone repairs but i've found this flux works really well on Laptop/PC Motherboard repairs, its tacky and holds even very small components nicely in place, i got mine on ebay, theres a lot of fake stuff about so you'll probably need to do a good search, i cannot even vouch what i got is genuine but i suspect it is, really happy with it. I think your hot air settings are OK, I usually operate at around 380 degrees, works well for me, occasionally need to ramp it up slightly depending on the size of the component though

[stj]

Re: Problems Using Solder Paste to Re-ball???

try starting at a lower temperature to dry out some of the flux instead of it boiling and throwing the solder everywhere.

[reessi]

Re: Problems Using Solder Paste to Re-ball???

Hi, Seagorman thanks for the advice but I was talking about solder paste where it has solder in the flux as a mix not just flux. I have been using kingbo for all other soldering without any problems so far. Like you said aloto of fakes thats why I didn't buy amtech as was un-sure.

As for the solder paste with the stencils I will try a lower temperature like stj said as that seams like what is actually happening. I will report back tomorrow.

Cheers.

[reessi]

Re: Problems Using Solder Paste to Re-ball???

Also I couldn't get a photo as promised as my camera wouldn't focus that close in!

[diif]

Re: Problems Using Solder Paste to Re-ball???

insatint is the genuine UK seller on eBay. The difference between genuine Amtech and Kingbo is massive.

[Seagorman]

Re: Problems Using Solder Paste to Re-ball???

sry reessi, my mistake, lol, thought you were talking about flux

[reessi]

Re: Problems Using Solder Paste to Re-ball???

For anybody else looking, for perfect reballs - I use 200c and 60 litre airflow (half on my station) and come in slow until you've practiced and gauged it!

I use the cheapest China Leaded Solder Paste. When it arrives its a bit watery with the Flux which when heated can cause the balls to pop out. Store the Paste tube with tip down and after a week the Lead has moved to bottom moving alot of Flux to top so drying it out - Much better.

Even so practice and bring the air in slow, its normal for the paste to rise above a little and then shrinks when it melts back into the holes.

Stop heating as soon as shrank or they spew out and you have to do again.

Good Luck.