Re: BGA prototyping (was Advice neede: Atmel or Philips ARM)

Peter,

I've seen complicated prototyping solutions abound but do you have any
sure-fire tips for a wannabe BGA prototyper?

my first BGA board 5 years ago had 6 layers, all BGAs were 1.27
pitched.
Two signal layers - and slightly split power and ground planes - is all
it took, the board was as dense as they get, 3 BGA chips, SDRAM on both
sides etc., 3 signal traces between the pads.
I did reflow this boad innumerable times (I'd say 20 to 40 times..),
eventually
I got it to work, and it failed after 3-4 months (lost connections, the
layers
had begun to detach from one another etc, quite a nightmare). After
that,
the second board took just a single reflow and worked.
All equipment it takes for prototyping is a kitchen oven and an
infrared
thermometer to control the temperature.
Contrary on what is widespread and practiced, it is quite allright to
have
a via in the middle of every BGA pad (talking 1.27 pitch BGA), 0.3 or
0.2 mm drilled. This gives you access to all signals while testing,
although it costs an extra operation - you _must_ reflow the BGA
chips once belly (balls) up with some flux so there are no "cold"
balls,
otherwise they (the cold balls) get detached during reflow and flow
down the via ... I have had this at the beginning, 2-3 balls per BGA
seems to be the case (I guess this has been responsible for 1 or two
of the many initial reflows I did until I figured out the medicine).
Once you reflow the BGA with a decent amount of flux, things
get quite stable.
Under the score, be prepared for a reasonably tough fight until you
get
everything fine, but as long as the BGAs are 1.27 (I'd speculate 1mm
as well), it is doable, nothing which should stop you.
Ah yes, beware too much flux under the BGA - it can float away
and get soldered with an "offset"... I have had this as well.
Placing the BGA is difficult and you will have to
spend all the time it takes to make sure it is properly positioned, I
use
the flux to have the BGAs lightly stuck to their positions.
Hope this helps somewhat...

Dimiter

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Dimiter Popoff Transgalactic Instruments

http://www.tgi-sci.com
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Peter Jakacki wrote:
All of my prototypes are simple double-sided PCBs which are are both
cheap and fast to produce. I fear that BGA will force me to go to 6 or 8
layer thereby increasing the cost and turnaround time for protos. Plus
if I stuff the mounting of the chip, unless it is done precisely, I can
add the cost of rework and new chips or new pcb onto that as well.

I've seen complicated prototyping solutions abound but do you have any
sure-fire tips for a wannabe BGA prototyper?

*Peter*

pbreed@xxxxxxxxxxxxx wrote:
We have been doing Coldfire BGA's for about 5 years now.

I will never go back to fine pitch.

The ball to Ball spacing is much wider than the lead to lead spacing in tqfp etc...

We have far fewer production problems with BGA.

Our rewok guy can do BGA's just as fast as fine pitch.( With the proper tools)


The BIG downside to BGA is that if you make a schematic or PCB design error
they are almost impossible to rework.

On prototypes we biring anything that is at all doubful out to a zero ohm jumper resistor.

.

Relevant Pages

  • Re: BGA-272 and double side PCB
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