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Re: 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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