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Re: BGA soldering



Hi All,
On this one, if it is a space application, all flux needs to be removed,
other wise in a vacuum in space. the flux will migrate and plate it's self
out on all surfaces. The problem with a BGA is being able to clean
underneath it after soldering. No Clean flux is perhaps a solution but it
has sputtering problems, which requires a well controlled 5 stage oven for
soldering.
The adjusting process requires several sacrificial boards to adjust the
temperatures for the thermal mass of the board VS the surface area and
emissive index of the circuit board. X-ray is done to confirm the solder has
flowed on all contact points
The suggestion of a leaded package is a good one. We are currently in the
middle of a change over to lead free to meet European requirements. This
will also lead to a new learning curve after the new fluxes. I doubt that
there is much failure data on a 10 year life span of these parts.
We know what to expect out of beam welded, leaded components ,RMA 37/63
solder, and Tri-Clor-Ethylene cleaning agent. All the other techniques have
left us with defective product, crazy cleaning procedures, and expensive
product.
Sort of an enviromental dark age for technoloigy! Insted of making closed
loop cleaners we outlawed cleaning agents. All of the discarded circuit
boards in San Diego County over a year add up to less than the lead in 3
automobile batteries. How many of those do you see on the road side? If some
defect in the new process causes a failure in three years, we all get to go
out and buy new replacements. Good for business!

Art, KC6UQH
---- Original Message -----
From: <alan_bloom@agilent.com>
To: <kc6uqh@cox.net>; <ssbrockw@swbell.net>; <amsat-bb@amsat.org>
Sent: Wednesday, January 12, 2005 11:05 AM
Subject: RE: [amsat-bb] BGA soldering


> This is an area I know something about since solder was one of my
categories back when I was a Materials Engineer at Hewlett Packard.
>
> Most of the water-soluble fluxes must be washed off after use since they
use a corrosive flux.  Since they are watrer-soluble that's not hard to do.
The rosin-based fluxes generally do not need to be washed off since the acid
is encased in the flux where it doesn't do any harm.  In fact, it is
generally best NOT to try to remove rosin flux because if you don't do a
very good job all you accomplish is to release the ionic contaminants and
spread them around.
>
> The best rosin-based flux for this kind of application is the RMA type.
RMA stands for "Rosin, Mildly Activated".  Mildly activated means the flux
is not highly corrosive.  I believe most solder pastes intended for
electronics work use that kind of flux.
>
> Alan Bloom N1AL
>
>
> > -----Original Message-----
> > From: owner-AMSAT-BB@amsat.org [mailto:owner-AMSAT-BB@amsat.org]On
> > Behalf Of KC6UQH
> > Sent: Tuesday, January 11, 2005 7:07 PM
> > To: Steve KA5YFC; amsat-bb@amsat.org
> > Subject: Re: [amsat-bb] BGA soldering
> >
> >
> > Howard,
> > One comment no clean flux needs a higher temperature to deactivate,
water
> > soluble flux need a high pressure washer at over 140 F and you need room
to
> > get the water underneath. You should contact the solder manufacture on
the
> > use of the flux and some fluxes have a short life time. Organic fluxes
no
> > neutralized will cause early failure, corrosion and high leakage
currents.
> >
> > Art, KC6UQH
> > ----- Original Message -----
> > From: "Steve KA5YFC" <ssbrockw@swbell.net>
> > To: <amsat-bb@amsat.org>
> > Sent: Tuesday, January 11, 2005 4:07 PM
> > Subject: RE: [amsat-bb] BGA soldering
> >
> >
> > > Howard,
> > >
> > > In a previous life, I had to work on and rework some BGA devices. We
> > > found that a hot air soldering station, the kind with an arm that
comes
> > > out over the work area, worked very well for BGAs. The technique that
> > > was used was to make sure the board area was clean of any excess
solder
> > > from previous devices and then apply a small amount of a solder paste
to
> > > each pad. This solder was meant to melt at a given temperature (below
> > > the damage point of the BGA). To get an indication of when the device
> > > was approaching the solder melting point, a small drop of the same
paste
> > > was placed on the top opposite corners of the BGA. When they melted
the
> > > part was approaching the correct temperature. Shortly after these
> > > indicator dots melt, the device will be soldered to the board.
> > > Typically, the device will tend to self-center to the pads on the
board
> > > because of the wetting action of the solder to the balls on the bottom
> > > of the array (if it was placed within reason to begin with). This
seemed
> > > to work very well during prototyping operations and during rework
operations.
> > >
> > > A source of parts to try this out on would be any of the hundreds of
> > > cell phones that your friends have laying around after upgrading. Most
> > > of these will have at least one BGA device and maybe several depending
> > > on the manufacturer and the vintage.
> > >
> > > You may be able to get enough heat by using a hot air gun used to
shrink
> > > the covering on model airplanes or one of the types used to peel paint
> > > off houses. You will have to try and find one that has enough heat but
> > > not too much. Our commercial rework station had a thermostat to
control
> > > the temperature. Try to direct the air flow directly on the BGA and
not
> > > on the surrounding components as they will of course have the solder
> > > melted on them too.
> > >
> > > I think that this is a valuable point no matter which method you are
> > > going to use. After soldering the device, allow it to cool for a
little
> > > while. Moving it while the part and board are still hot will probably
> > > cause the BGA device to shift and then you will have to start over.
With
> > > an oven, the whole board and all the components will be hot, not just
> > > the area that the air was on using the hot air method.
> > >
> > > BGA devices are not impossible to work with, they just take a little
> > > more care, patients and practice.
> > >
> > > 73,
> > > Steve
> > > KA5YFC
> ----
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