Does BGA already have solder on it?

[alank2]

Hi everyone,

Does BGA already have solder on it?  I've just a very small amount of toaster oven soldering and I wonder what is different about BGA.  An avr tiny84a says it comes in a UFBGA.  Curiously how do you reflow these?  Do you use solder paste?  Does the balls sticking off the ic melt?  Do they not melt?

Thanks,

Alan

[T3sl4co1l]

Yes, they come with balls, which are nothing more than the specified type of solder.  Yes, you still want to use paste.  The reason is, the balls remain firm, like balloons of solder, and may not stick to the surface; whereas the paste is finely divided, and wets and connects to surfaces very effectively.  So the paste is able to wet both the pad and the ball, and stick them together.  When everything is settled, the balls are slightly larger (the paste coalesces into the balls), and the joint is made.

Can't say I recommend ultra-fine pitch parts for the amateur, of course!  You'll have a hard enough time lining them up to the fine footprint, heck... you'll have a hard enough time getting the boards made with that precision!  Not something you're likely to get successful from Seeed Studio.  Though I think OSHPark or better would be fine?

Tim

[rx8pilot]

Hand placing and toaster oven reflow of BGA packages sounds about as fun as a sharp stick in the eye.

The hardest part is very accurate placement of paste - both position and volume. VERY unlikely to hand apply paste and not have 20 pins bridged. You cannot see a solder bridge without X-ray machine.

[Paul Moir]

It also comes in SOIC and even DIP, not to mention a few other packages.  Do you really need that density?

[janekm]

Actually, for hand-soldering and rework, it is better not to use paste with BGA parts (since as rx8pilot the likelihood of shorts is far too high, if you don't have an x-y positioning jig of some sort to place the part). I have seen this method specifically endorsed for rework in the datasheets of some BGA parts.
A good "tacky flux" is essential though, but can just be spread over all the pads (a thin layer though, bubbling flux is not helpful either!).

[alank2]

I'm just wanting to learn about bga, I'll stick to tqfp unless I want to try to make some extremely small for example as a one off, etc.  So janekm you are saying don't use any paste just a thin layer of flux and place?  Interesting.

[krenzo]

I solder BGA FPGAs by rubbing a flux pen over the pads, putting the chip down and lining it up visually, and then putting it in a toaster oven.  When the solder balls melt, the chip gets pulled to the proper position on the pads.

[wraper]

In PCB production, small amount of solder paste is applied. For DIY or repair just use a tacky flux. However there are also not too common micro BGA ICs where balls are made not of solder but actually metal coated polymer. For those you cannot just use the flux as some amount of solder is needed too.

[rob77]

definitely flux only if reworking BGA... and forget bigger BGA chips unless you have a IR  BGA rework gear. with hot air you can do smaller BGAs only. aligning is actually not a big deal, it's not worse than aligning a QFN.

[marshallh]

Reflowing BGA is stupidly simple, don't let all the naysayers discourage you. Reballing is more difficult. It only gets fiddly aligning the packages with <0.5mm pitches.
Still easier IMO than placing packages like QFN, or DRQFN.

See the link in my signature.

[alank2]

What exactly is reballing?  WHY would reballing NEED to be done?  I'm not talking about rework, but firstwork...

[rob77]

What exactly is reballing?  WHY would reballing NEED to be done?  I'm not talking about rework, but firstwork...

reballinig => cleaning up all the solder and place new solder balls to the bga chip. it has to be done every time the BGA is removed from the PCB. for example a misplaced BGA during the "first work" needs to be reballed in order to place it correctly.

[alank2]

marshallh that is a very nice bga doc, thanks!

[Zero999]

In PCB production, small amount of solder paste is applied. For DIY or repair just use a tacky flux. However there are also not too common micro BGA ICs where balls are made not of solder but actually metal coated polymer. For those you cannot just use the flux as some amount of solder is needed too.

Would it work if you tinned the PCB well, then covered it in a layer of sticky flux before placing?

[rob77]

In PCB production, small amount of solder paste is applied. For DIY or repair just use a tacky flux. However there are also not too common micro BGA ICs where balls are made not of solder but actually metal coated polymer. For those you cannot just use the flux as some amount of solder is needed too.

Would it work if you tinned the PCB well, then covered it in a layer of sticky flux before placing?

if you will clean the pads with solder wick, then you can tin them - and actually that's the case when reworking BGAs - the PCB pads are tinned
you need to clean the pads to make sure the surface is perfect flat, otherwise the BGA chip might skid or develop shorts due to extra solder on some pads.