BGA or TQFP? package soldering advice needed

[Rick]

I am looking at doing a very low cost very small (about 25 units) run of a
design in which I would like to use an atmel arm7 microcontroller, like the
AT91R40008 which includes 256kbytes of 32 bit wide sram in chip (very nice).
This chip comes in a TQFP 100 package which is a piece of cake for me to solder
(I have hand soldered several 208 pin Spartan II devices with 100% success).

On the other hand, the exact same chip is available for $2 more that includes
2Mbytes of 16 bit wide 90ns flash on chip in a 0.8mm 121 ball BGA package. That
2 Meg, which IS needed would cost me at least $20 if I have to use an external
chip, not to mention board space.

I have googled and perused old s.e.d. threads, but I have not really developed a
warm fuzzy feeling that small runs of a 0.8 pitch BGA device can be done with a
high success rate using common cheap technology (hot air guns, toaster ovens,
hot plates, etc.).

How many of you have soldered something like this with simple devices, and what
was your success rate?

Thanks,

Rick

 

[Rick]

Nevermind. I just created the BGA part in my layout program....I don't see any
way to fit that design into the rules for the cheaper board houses 7/7 or 6/6.
Even vias with 10mil finished holes are way too large. Now I am curious how 0.8
or heaven forbid 0.5mm grid BGA pad designs on circuit boards are even done!

TQFP for me!

Rick

 

[red rover]

I have very high success rate with having
boards re-worked for BGAs. The generally
have a hot air gun tool built for this exact purpose.
A square-ish nozzle that goes over the device
and I believe hot air knives that shoot under the
device. Are you against going to a proto shop?

BGA breakouts are not problem either. I could
possibly get you more info. on how we break them
out but I don't think that is necessary. 7/7 and 6/6
seems positively stone-age now. I've seen the cost
of pcbs plummet in the last 3-4 years and there just
doesn't seem to be that many board shops that can't
do much better. The $20 savings on the devices would
more than pay for a any delta in pcb costs by going
to a 4 or 5 mil design.

Steve

 

[qrk]

Nevermind. I just created the BGA part in my layout program....I don't see any
way to fit that design into the rules for the cheaper board houses 7/7 or 6/6.
Even vias with 10mil finished holes are way too large. Now I am curious how 0.8
or heaven forbid 0.5mm grid BGA pad designs on circuit boards are even done!

TQFP for me!

Rick

0.8mm BGAs are unpleasant creatures. Via fanouts we use are 16 mil
pads, 10 mil drill. We routinely use 5/5 rules on these designs. You
need to use a decent board house.

I assume you could do BGA soldering at home. A company that sells
rework equipment suggests spreading a layer of solder paste on a very
flat surface (e.g. glass). You apply solder paste to the balls by
dipping the BGA balls on the solder paste layer. You will need to
experiment with the solder paste thickness. This means you don't need
to put solder paste on the board which requires an infinite amount of
patience or a solder stencil. You then place the part on the board and
use your favorite BGA soldering technique (oven, hot air, IR, ...).
I've never tried it.

Stick with the TQFP and extra cost. I have a rabid hatred for BGAs,
especially 0.5 mm grided devices!

Mark

 

[Martin Riddle]

Laser drilling, state of the art.
Not much more than a standard board.
http://www.protoeng.com/ gave us some nice results.

Cheers