VanguardLH wrote:
"daytripper" wrote:
On Sat, 24 Nov 2012 23:58:33 -0600, VanguardLH wrote:
[...]
The mobo maker could just make a plastic frame to hold the chip in place
(both for position along with affixing to the mobo via spring clip) and
the user would use a soldering iron with a tip designed for the BGA grid
pattern. The user would buy the mobo they want, the CPU they want, and
then do a one-time solder of the CPU onto the mobo.
[...]
That's some funny stuff right there.
Unless you're serious, of course...
Cheers!
I was serious. You do know what "ball" means in BGA, right? It's a
ball of solder. So why can't the chip, even a CPU, come prepped with
the balls of solder on its pads, the mobo come with balls of solder on
its grid and using feedthroughs so the solder is reached from the
backside of the board, and all you have to do is keep the chip pressed
against the grid, keep it aligned, heat up the solder gun with a
matching grid tip, and just melt all the solder to weld the chip to the
grid?
You've never applied new solder to the underside of a PCB so it heats
the solder on the other side through a feedthrough to use solder wick on
the other side when you cannot otherwise reach the other side with a
soldering iron? Heat travels.
Of course, we're talking about DIY'ers that know how to solder and that
it flows towards the heat source and what level of heat to apply and not
the boobs that barely know how to push down the level for a ZIF socket.
Not having sockets doesn't mean you can't DIY. It means the DIY'er will
need better skills than pushing stuff into a socket or slot.
You at least want to solder all the balls at the same time.
There is a magic alignment effect, where the wetted contacts
tend to "pull" the chip into alignment, such that the chip
rotates to the grid of contacts underneath. You want the
solder to fill the pads properly, which is going to
happen if all the balls melt at the same time
and the chip settles into place.
If you were a home user, and desperate for adventure,
you could try a toaster oven. That's the closest thing
to IR reflow you can arrange for real cheap. Some people
used the toaster oven method, to fix Nvidia GPU solder joints.
But I would still put this idea in the "repugnant" category.
You have absolutely no control of the temperature profile
that way, and the toaster oven is going to be heating all sorts
of stuff you don't want heated (think "burned plastic").
At the factory, they use an XRay machine to verify BGA soldering.
On a processor, 2/3rds of the balls could be VCC and GND, and
they wouldn't be candidates for boundary scan verification. An
XRay, can uncover balls damaged by the "popcorn" problem
for example. And more than one XRay is taken. By holding
the XRay machine on an angle, you can photograph the balls
from either side. No home user would be able to verify
the solder job was completed properly. You wouldn't want
to burn some power connections, because too many VCC or
GND pins were open circuit.
http://upload.wikimedia.org/wikipedi...joint_xray.jpg
(Voids caused by excessive moisture level on the solder balls.)
http://glenbrook.webworksnow3.com/bl...3/bga_fig4.gif
With care, I'm told you can get defectivity down to around
1 ball in 100,000. That means, if you solder down a hundred
chips each having 1000 balls underneath, one of the chips
will have a single bad solder joint. It would take a little
effort and expense though, to get that good at it. The
results of home users doing such soldering, isn't going to be
that good.
Paul