Re: gEDA-user: OT: soldering QFN packages with exposed bottom pad?

[joe tarantino <joeft@xxxxxxxxxxxxx>]

   If the balls haven't been deformed, the surface tension of the solder
   does help the part align.  It's interesting to see the part get pulled
   into position as the solder melts.
   I've seen a switcher chip (can't remember the p/n at the moment) that
   has on the order of 80 balls, most of which are ground.  Both for
   current and heat sinking.  It's a small part, but is able to get rid
   of whatever heat it needs to as it is switching about 30W @ ~ 400 kHz
   as I recall.
   Joe T

   On Tue, Apr 28, 2009 at 12:58 PM, John Griessen
   <[1]john@xxxxxxxxxxxxxx> wrote:

   I'm going to look into methods of dealing with BGAs in prototypes

     since Bob's tech says they're less trouble after a learning curve.

   I've heard and can imagine the way they pull themselves to alignment
   by surface tension between the grid of chip balls and the grid of
   lands on the pcb.

     Do BGAs use zones of balls to dissipate heat?
     John

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References

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