gEDA-user: fun/easy BGA part

[Andy Peters]

On Dec 15, 2006, at 12:45 PM, DJ Delorie wrote:

> Ok, a s.e.design thread has got me thinking about pan-frying BGAs.
> Now I'm curious.  What's a good BGA to start with?  "Good" is defined
> as:
>
> 1. Inexpensive, cause I'll probably toast a few.
>
> 2. Useful, because it's good to see results.
>
> 3. Easy to design around, because I want to worry about the soldering
>    process, and not burn through a number of chips getting the design
>
> 4. Require a minimum of support components.
>
> 5. Not so complex that lots of tiny vias would be needed.  If I can
>    get by with two rows pulled out on the top with 7/7 rules, and the
>    remaining rows tied to gnd/vcc through one or two big vias, that's
>    acceptable.
>
> Hmmm... BGA challenge anyone?  ;-)

There are various small analog parts that are BGA.

We use a lot of FT256 BGAs here at the day job (Spartan2E FPGAs).  We  
can hand-attach them.  We have a rework kit that includes a paste  
mask for that package, so you line up the mask, squirt some paste,  
then place the chip.  To solder, we put the board in the board-holder  
jig for a hot-air rework tool.  We put a heater block directly under  
the FPGA location, and then flow low-velocity hot air around the chip  
(using a FQP nozzle).  You watch the balls using a stereoscope, and  
you can see when they get soft and melt.  The chip self-aligns on the  
pads.  Works well, but does take some practice.

-a