BGA my balls keep rolling away

[dicky96]

Hi guys
So after best part of a year doing other stuff, I'm back to master this BGA reworking, 2nd time lucky I hope

So I thought the best place to start was with the steps that were giving me problems last time.

With this type of reballing jig and stencils:
https://www.aliexpress.com/item/3303...archweb201603_



What is the best tyoe of flux to use to get the balls to stick to the BGA. Amtech NC559-ASM?

Once I have applied the balls, how do I melt them without them rolling away? Even with my Hot Air (Quick 861DW) on minimum airflow once the flux liquidizes the balls start floating around.

I did try last time using this little hot air preheater I have, and putting a square sheet of metal over the hot air vent then using it like a hot plate to put the BGA on top, but I still had trouble with the balls moving, though it was more successful than the Quick 861.

https://www.aliexpress.com/item/3270...archweb201603_

Is this due vibration from the heater?


Is there some way to do this reliably with what I have or do I need to get something like this?

https://www.aliexpress.com/item/3303...archweb201603_

Cheers

[diif]

There are two types of stencil. Indirect and direct. With direct heat, the balls are held in place with the stencil, hot air is applied and the stencil removed when the balls have melted.
Indirect heat does not use hot air, it uses a hot plate and as there is no airflow the balls melt in place.

Yes so thing like that hot plate, or perhaps something much smaller and cheaper like the LED reflow plates.

[dicky96]

Thanks diif, I remember that now, and the stencils and jig I have are indirect heat yes?

When you say something cheaper you mean something like this?

https://www.aliexpress.com/item/4001...archweb201603_

Or get some direct heat stencils?
https://www.aliexpress.com/item/4000...archweb201603_

https://www.aliexpress.com/item/3291...archweb201603_
Which type are the best/easiest to use or is it a matter one type is better for certain work than others?

[diif]

I was thinking even cheaper, although it might need some finer control with a PID controller/thermocouple. https://www.aliexpress.com/item/33057592999.html I've used my larger 20x20cm hotplate as per your first link when reballing as it was what i had on hand, but it's far larger than it needs to be and i wouldn't buy one solely for reballing.

It's mainly matter of preference I think although when i needed a stencil a year or so ago it was only available in direct heat, with direct heat there is sometimes difficulty of releasing the stencil.

[dicky96]

OK that is cheap - and with the money saved I can grab some direct heat stencils and have a play with them too - see what works best for me

I could attach one of my digital thermometers to that plate and switch it off once it gets hot enough to melt the balls - otherwise I wonder how it would work on my 2000VA Variac?

I saw some videos using solder paste and a plastic spatula with direct heat stencils - I suspect you probably tried that sometime, is that method any good?

[diif]

I've seen the paste and stencil method on Apple SMC and memory chips, it's not something I've tried.

I use one of those cheap hotplates for doing LED replacements, with a cheap thermocouple permanently jammed in, I did fit a PID controller but it didn't work, I should revisit it.

[dicky96]

I did it

I used the indirect heat stencil and jig.

I used the Kada 853B and NC-559-ASM flux applied with a small paint brush

I used the base off an old el cheapo soldering iron stand, with the springy soldering iron holder removed, and it just fitted exactly over the KADA hot air plate with about 2mm spare each side. I used the little indent where the sponge should go as a tray for my BGA.

Even with the KADA on the highest setting, I couldn't get the thermocouple to read over 182C, but I noticed around that point all the balls seemed to have aligned fully on the pads and were looking shiny, so I turned off the heater and left the fan running to cool it down - and found that the BGA was reballed.

Possibly the thermal mass of the soldering iron base was too high for the heater to get it any hotter or maybe it was because the thermocouple was not on the hottest part directly above the hot air. It's possible these are 0.76mm 60:40 lead balls as 183 is the melting point for leaded solder

Anyway - regardless - I had success the first time round... this time round.... LoL. It's not the biggest BGA in the world but I feel pretty good about it.

[stj]

this looks interesting!
https://www.youtube.com/watch?v=o3vK0fikX80

[diif]

Originally Posted by stj

this looks interesting!
https://www.youtube.com/watch?v=o3vK0fikX80

Interesting yes, but at £90 it's not that interesting.

[stj]

lol - i didnt check the price!

[dicky96]

Out of interest (or anyone else trying this) I think the reason that balancing a metal sheet on top of the hot air pre-heater failed when I tried it before (the balls moved and some joined together) was because I used a very thin piece of metal which was the top from some RF section of an old PCB I was stripping down. This was like very thin tin or something.

And I think with such a light piece of metal the vibration from the pre-heater was moving the solder balls. This time I used something fairly hefty, and possibly the pre-heater struggled a little bit with the thermal mass but it definitely worked.

Anyway that's my best guess on it - FWIW

Rich

[stj]

you should use something thick to spread the heat evenly - like 5mm aluminium or even copper if you can scavange something.