BGA's are killing my project

Oliver Betz <OBetz@despammed.com> wrote:
> Joerg wrote:
>
> [desolder TQGP]
>
>>> microcontroller when I zapped it during ESD tests. All I need is a
>>> matching funnel (wording?) and hot air to remove the IC and a
>>> soldering iron with a hoof shaped tip and a magnifier to solder the
>>> new one. Well, some solder wick could be necessary.
>>
>>It's usually called nozzle. As you said, you can buy square nozzles for 
>
> thanks, nozzle is the word I didn't remember. We have one with a
> spring loaded vacuum cup, so the TQFP is lifted automatically as soon
> as the solder is molten. Really easy to use and not very expensive.

Slightly remedial question, perhaps, but I've never used BGA devices, and
we're only just moving from hand assembly to automated for our stuff:

How does the solder melt in BGA placement?  Does the board have to be
heated sufficiently to melt it, or the chip, or both?  I can't see
how either could be done without damaging stuff - delaminating the
board or buggering the IC, but I guess it is done millions of times
around the world every day so someone's obviously figured it out ;-P

-- 
Nobby Anderson

> ...
>
> How does the solder melt in BGA placement?

In temperature controlled oven.

>  Does the board have to be
> heated sufficiently to melt it, or the chip, or both?

Both, I guess.  Sometimes, it helps to direct some hot air under the
chip, but not too much to blow the solder balls away.  Designing BGA
re-oven is an art by itself.

In article <1160950400.342759.271290@e3g2000cwe.googlegroups.com>,
 "linnix" <me@linnix.info-for.us> wrote:

> > ...
> >
> > How does the solder melt in BGA placement?
> 
> In temperature controlled oven.
> 
> >  Does the board have to be
> > heated sufficiently to melt it, or the chip, or both?
> 
> Both, I guess.  Sometimes, it helps to direct some hot air under the
> chip, but not too much to blow the solder balls away.  Designing BGA
> re-oven is an art by itself.
> 

The "solder balls" on a BGA so not melt. They are made of a solder with 
a higher melting temperature than 60/40 solder. 

The solder pads on the board have dabs of solder on them. The BGA is 
placed on these blobs and has to align more or less perfectly. The whole 
thing is run though a temperature profile which will melt the dabs of 
solder but not the balls on the BGA. The temp ramps up, stays a while 
and then ramps down. The BGA then self aligns itself with the solder 
pads as it floats on the molten solder.

You really have to control the temperature carefully. Otherwise if the 
balls melt, bah bye!

Al

Al wrote:
> In article <1160950400.342759.271290@e3g2000cwe.googlegroups.com>,
>  "linnix" <me@linnix.info-for.us> wrote:
>
> > > ...
> > >
> > > How does the solder melt in BGA placement?
> >
> > In temperature controlled oven.
> >
> > >  Does the board have to be
> > > heated sufficiently to melt it, or the chip, or both?
> >
> > Both, I guess.  Sometimes, it helps to direct some hot air under the
> > chip, but not too much to blow the solder balls away.  Designing BGA
> > re-oven is an art by itself.
> >
>
> The "solder balls" on a BGA so not melt. They are made of a solder with
> a higher melting temperature than 60/40 solder.

It depends on the BGA.  One BGA I worked with contains just regular
solder, so much solder that you can't have additional solder on the
board.  They do melt to form a flat contact surface.

> One BGA I worked with contains just regular
> solder, so much solder that you can't have additional solder on the
> board.  They do melt to form a flat contact surface.

The BGAs I have worked with - and those I have only considered - are
all meant to be soldered like this, i.e. all balls do get liquid during
reflow.
This also does the final placement adjustment (surface tension), or,
well, misplacement (I once had that... :-). I have posted some
experience
about vias inside the pads, they can be looked up, I guess.

 To those without experience and avoiding the BGAs fearing trouble:
not really such a pain, I have had more soldering issues with 0.5mm
spaced
TQFPs than with 256 or 352 balled 1.27 mm pitch BGAs. I have not
done 0.8mm BGAs yet, though, not to speak about 0.5mm ones.

 For prototyping you can use just about any kitchen oven
provided you are armed with an IR thermometer to monitor the
temperature.
I have done it dozens of times. If the 220 C are reached within 5-6
minutes
(mostly due to IR from the top), things should be fine. Be careful when
taking the board out of the oven, everything is still liquid. I use a
wooden
plate to which I fix the preassembled board; once I lightly hit the
plate
in an obstacle while taking it out and oh boy what a mess of
slid BGAs, TSSOPs and stuff I had! Took a complete reflow and
remake of all balls...

Dimiter

------------------------------------------------------
Dimiter Popoff               Transgalactic Instruments

http://www.tgi-sci.com
------------------------------------------------------


linnix wrote:
> Al wrote:
> > In article <1160950400.342759.271290@e3g2000cwe.googlegroups.com>,
> >  "linnix" <me@linnix.info-for.us> wrote:
> >
> > > > ...
> > > >
> > > > How does the solder melt in BGA placement?
> > >
> > > In temperature controlled oven.
> > >
> > > >  Does the board have to be
> > > > heated sufficiently to melt it, or the chip, or both?
> > >
> > > Both, I guess.  Sometimes, it helps to direct some hot air under the
> > > chip, but not too much to blow the solder balls away.  Designing BGA
> > > re-oven is an art by itself.
> > >
> >
> > The "solder balls" on a BGA so not melt. They are made of a solder with
> > a higher melting temperature than 60/40 solder.
>
> It depends on the BGA.  One BGA I worked with contains just regular
> solder, so much solder that you can't have additional solder on the
> board.  They do melt to form a flat contact surface.