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RE: 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
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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